Partial Hydrodeoxygenation of a Heavy Bio-Based Oil Fraction (A Technical Feasibility Study)

Partial hydrodeoxygenation of a heavy bio-based oil fraction (A technical feasibility study)

AKSHAY MENON

Master of Science in Chemical Engineering for Energy and Environment Date: November 1, 2020 Supervisor: Efthymios Kantarelis (KTH), Elena Minchak (Nynas AB) Examiner: Lars J. Pettersson (KTH Royal Institute of Technology) School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH)

iii

Abstract

This report is intended to provide the reader with an extensive background information on hydrodeoxygenation (HDO) of Tall Oil Pitch (TOP), combined with results from chemical property analyses of the same. Firstly, the importance of hydrogenation and oxygen removal for a biomass-based feed material is highlighted. The chemical nature of TOP in general is described and the target for the research work is identiﬁed. It is decided to evaluate the possibility of TOP as a prospective material for achieving partial oxygen removal. The eﬀect of catalysis on HDO behavior is assessed, and subsequently, conventional commercial catalysts are selected.

Chemical analyses of the feed mixture provided data on various properties, which can then be correlated to the products from hydrogenation. Kinematic viscosity of TOP is determined, followed by acid number and saponiﬁcation number tests to evaluate the free acid and total acid contents respectively. Reasoning for any deviations are highlighted and suggestions are provided to control deviation in process parameters. GC/MS analysis of the tall oil sample is also conducted to understand the presence of oxygen-containing species. Carbon residue and ash tests revealed the coking and ash forming tendency of the samples. In addition, XRF spectroscopy results indicated the metal presence in the TOP sample.

Experimental trials are carried out to sulphide the catalysts prior to use in hydrogenation experiments. Catalyst sulphidation procedure is also outlined. Furthermore, the lab-scale reactor is tested for hydrogenation to determine challenges that normally arise during high-pressure working conditions. In addition to discussion of challenges regarding batch hydrogenations and sulﬁdations, proposals on future work in this domain is outlined, along with suggestions on an experimental pathway forward. iv

Acknowledgements

First and foremost, I thank Lars J. Pettersson (examiner for the thesis work) and Efthymios Kantarelis (supervisor at KTH) for the guidance I received, throughout the period of my master thesis. Your support has been a constant driving factor for me, to move forward with the work on a daily-basis. I also take this opportunity to acknowledge the eﬀorts taken by Elena Minchak (supervisor at Nynas AB) to share the knowledge and provide constant feedback on the literature part of this report.

Every experimental work is incomplete without the necessary raw material and the facility for conducting research activities. I express my gratitude to Nynas AB for arranging and supplying the raw materials, which include tall oil pitch and sulphided catalysts. The help from the company in terms of conducting the XRF analysis in-house, was also pivotal to the experimental part of the research work. I am also thankful to KTH Royal Institute of Technology for allocating space inside the high pressure laboratory and for providing me the high pressure reactor setup.

Most often, one cannot achieve a certain objective or target without external support. I was fortunate to receive enough support throughout the course of this master thesis work. Firstly, I thank Björn Harrysson (Chief scientist at Nynas AB) for reaching out and providing expert advice on relevant topics. I had the liberty to seek guidance directly, especially during ongoing critical laboratory work. Secondly, I am ever grateful to all the doctoral and post-doctoral students working at the department of process technology at KTH, for their moral support and encouragement. Finally, I acknowledge all my colleagues in the department, for creating an atmosphere of motivation and encouragement. v

Terminology • HYD: Hydrogenation • HYDH: Hydrogenation-Dehydration • AB: Aktiebolag • • ASTM: American Society for Testing LGO: Light Gas Oil and Materials • LPG: Liqueﬁed Petroleum Gas

• CCS: Carbon Capture and Storage • NSP: Nynas Specialty Products

• CSTR: Continuously Stirred Tank Reactor • TBPS: Tertiary-Butyl Polysulﬁde • CTO: Crude Tall Oil • TDO: Tautomerization-Deoxygenation • DC: Decarboxylation • TLO: Tall Light Oil • DDO: Direct Deoxygenation • TOFA: Tall Oil Fatty Acids • DMDS: Dimethyl Disulphide • TOP: Tall Oil Pitch • DO: Deoxygenation • TOR: Tall Oil Rosin • DoE: Design of Experiments • XRF: X-Ray Fluorescence • DOF: Degree of Freedom

• DME: Demethylation

• DTO: Distilled Tall Oil

• GC: Gas Chromatography

• GC-MS: Gas Chromatography Mass Spectrometry

• GHG: Green House Gas

• HDM: Hydrodemetallization

• HDN: Hydrodenitrogenation

• HDO: Hydrodeoxygenation

• HDS: Hydrodesulphurization

• HGO: Heavy Gas Oil

• HR: High Resolution Contents

1 Introduction 1 1.1 Background ...... 1 1.2 Oil reﬁnery vs Bio-reﬁnery ...... 2

2 Hydrotreatment 5 2.1 What is hydrotreatment? ...... 5 2.2 Dynamics of hydrotreatment ...... 6 2.2.1 Reaction behaviour ...... 6 2.3 HDO thermodynamics ...... 9 2.4 Catalysis ...... 10 2.4.1 Undesired characteristics ...... 11

3 Hydrodeoxygenation of Tall Oil Fraction 13 3.1 Understanding tall oils ...... 13 3.1.1 Justiﬁcation for selection of TOP feed ...... 16 3.1.2 Estimate for TOP; Oleic acid hydrotreatment ...... 17 3.1.3 Expected catalytic behaviour for HDO of TOP ...... 17 3.2 HDO of abietic acid model compound ...... 18

4 Materials and Methods 20 4.1 General Description ...... 21 4.2 Analysis parameters ...... 22 4.2.1 Viscosity ...... 22 4.2.2 Acid number ...... 24 4.2.3 Saponiﬁcation number ...... 26 4.2.4 GC/MS analysis ...... 29 4.2.5 Carbon residue content ...... 31 4.2.6 Ash content ...... 34 4.2.7 Metal content ...... 37 4.3 Hydrogenation experiments ...... 39

vi Contents vii

4.3.1 Basic reactor information ...... 39 4.3.2 Reactor startup ...... 40 4.3.3 Blank hydrogenation experiment ...... 42 4.3.4 Trial on catalyst sulphidation ...... 44 4.3.5 Hydrogenation test 1 ...... 47 4.3.6 Hydrogenation test 2 ...... 53

5 Proposal for future work 57 5.1 Hydrodeoxygenation experiments ...... 57 5.2 Characterisation and analysis of results ...... 59

6 Conclusion 60

1 Introduction

1.1 Background

The discovery of crude oil in the 19th century was an important step in the rapid industrialization and economic boom. However, the concerns from an environmental perspective arising out of carbon emissions and greenhouse gas (GHG) effect, has taken a toll on the use of fossil-based oil sources. In the recent years, countries and organizations aim for a partial or complete replacement of crude oil with renewable sources, to achieve goals of carbon neutrality [1]. Subsequently, biomass was considered as a suitable alternative to crude oil, due to its abundance in nature and lower quantities of sulphur, nitrogen and other heavy metals, unlike crude oil [2]. The major difference is that oils from biomass contains a higher fraction of oxygen, in the range of 35 - 50 wt %, as compared to oils from fossil sources. Bio-based oils are comprised of approximately 400 different oxygenated hydrocarbon species; acids, aldehydes, ketones, alcohols, esters, phenols, furans, carbohydrates etc. Some undesired properties like immiscibility with hydrocarbon mixtures, thermal and chemical instability, oxidation, high density and corrosiveness affected the performance of oils extracted from biomass. One of the reasons behind the poor performance of bio-based oils are linked to the higher oxygen content [1].

1 2 Introduction

Hydrodeoxygenation (HDO) reactions facilitate oxygen removal from the bio-based feed containing one or several oxygen functionalities. Catalytic HDO is performed under relatively high temperature and high hydrogen pressure on a heterogeneous catalyst to aid removal of oxygen [3]. Oxygen is eliminated as water and complete hydrogenation of larger molecules leads to cracking of molecular bonds, producing lower boiling hydrocarbon mixtures, which is often the preferred result for fuel reﬁners/producers. [4]. However, it is an undesired result for this work, since the aim here is to hydrogenate the biomass, without leading to cracking reactions. Thus, the preferred end result would be to retain long-chain hydrocarbon mixtures and to also eliminate oxygen partially, to be able to evaluate the physical and chemical properties of the end product.

1.2 Oil reﬁnery vs Bio-reﬁnery

Crude-oil refining processes comprise of both physical and chemical separation of products, in which hydrogenation (HYD) is conducted to upgrade the quality of crude-oil feedstock. The oxygen content is less than 2 wt% in crude-oil, unlike bio-based oils which may contain as much as 50 wt% [5]. Upon comparison of the general chemical classification, hydrogenation of aromatics generate a higher exotherm than that of its aliphatic counterparts. An approximate value can be -200 kJ/mol at 400 ◦C[6]. Moreover, most of the oil refineries target the production of vehicle fuels, and hence, obtaining lighter fractions become a priority. Literature suggests that most HDO reactions were conducted on a NiMo catalyst at high temperature (400 ◦C) and pressure (137 atm) conditions [7]. A typical crude-oil based refinery outline is presented in Figure 1.1. 1.2. Oil refinery vs Bio-refinery 3

Figure 1.1: Product fractions obtained from a conventional reﬁnery infrastructure [8] Legend: CDU = Crude Distillation Unit, ATF = Aviation Turbine Fuel

In a bio-refinery setup, biomass is upgraded to value added products. The major difference of a bio-refinery when compared to that of an oil-refinery lies in its utilization of bio-based feedstock. Such sources of energy aim for sustainable use of natural resource, along with an attractive policy of upgrading low-quality ligno-cellulosic matter into products suitable for the global market. Figure 1.2 depicts a bio-refinery targeting upgrading of crude tall oil.

Figure 1.2: Use of Crude Tall Oil (CTO) from Kraft pulp mill to produce diﬀerent oil fractions along with production of heat for district heating grid [9] 4 Introduction

From figure 1.2, it is seen that the biomass may not be directly used to create an end-product in a bio-refinery. Woody biomass is primarily used in Kraft pulp mills to produce paper products and Crude Tall Oil (CTO) is a by-product of the same. Successful industrial symbiosis utilizes the products from one industry as the feed to another. In this example from Sunpine AB (biorefinery located in Piteå, Sweden), CTO delivered to the company is used to produce chemicals for industrial use along with district heating. Hence, interconnected industries like this reduce wastage through by-product streams and enable generation of more value added products to the global market.

The issue concerning higher oxygen content in products derived from biomass, is still a topic of research [1]. As mentioned in section 1.1, bio-based oils exhibit a higher oxygen content, appearing in the form of different oxygenated species. Maintaining suitable process conditions for oxygen removal is still a widely researched topic. The calorific value of bio-based oils can sometimes be smaller in magnitude, when compared to that of crude oils. This indicates difficulty in its direct use as a burner fuel. Hence, the other attractive policy would be to consider upgrading of the oil, to suit specific end-user applications [10].

One of the other major challenges in the case of a biorefinery lies in its use of low-cost feedstock (biomass) and subjecting it to a high-cost process (material and energy intensive), to produce value added products that can replace traditional crude oil based industry. Theses processes are energy intensive mainly because of the feed, which has a higher water content and a lower energy density. Therefore, extensive conditions are needed to produce a product suitable to act as a replacement for conventional fuels/chemicals. According to a common definition mentioned in [11], a bio-refinery must ideally produce at least one high value chemical/material and one energy product, apart from electricity and heat generation. In recent developments, the option of integrating a bio-refinery with existing chemical plants are also evaluated. Bio-based oil can be produced locally and then transported to a centralized chemical plant for upgrading to liquid fuel/chemical [12]. 2 Hydrotreatment

2.1 What is hydrotreatment?

The term ’biomass hydrotreatment’ refers to the process where the bio-based feed material is exposed to hydrogen gas, to remove undesired chemical impurities from the feed mixture. The major reaction occurring as a result of hydroprocessing a bio-based feed material is hydrodeoxygenation. Typical oxygen functionalities found in bio-based feed include carboxylic, hydroxyl, carbonyl, etheric groups etc. HDO induces a lowering of acid functionalities in the feed. It also initiates reduction, cracking and even bond-cleavage in case of extreme reaction conditions. Other equally important reactions (occurring in conventional refineries) involving hydrogen gas are Hydrodesulphurization (HDS), Hydrodenitrogenation (HDN) and Hydrodemetallization (HDM), even though the effects of Hydrogenation (HYD) is less prominent in feeds derived from fossil-sources. However, for the case where bio-based sources are used, the importance of conducting HYD increases. E. Furimsky, 2000 [13] suggests that the complex nature associated with HDO kinetics is partly due to the self-inhibiting nature of oxygen-containing species. Moreover, previous research conducted in this domain employed high hydrogen pressure and temperature for fuel-grade hydrocarbon production, and thus a multi-stage process was employed for complete HDO. The scope of present research is different in terms of desired end-product and it is believed that mild-HDO poses higher challenges than complete HDO reactions. This is partly because of the need to control reaction conditions in a such a way, as to not produce light hydrocarbon mixtures. Conventionally used commercial catalysts for hydrotreatment are NiMo, CoMo or NiW [14].

5 6 Hydrotreatment

2.2 Dynamics of hydrotreatment

2.2.1 Reaction behaviour It is worth mentioning two diﬀerent reaction behaviours in this context; namely hydrogenolysis and hydrodeoxygenation. Hydrogenolysis involves cleavage of carbon-carbon or carbon-heteroatom bonds by reaction with hydrogen. On the other hand, HDO involves the reaction of reactant species with hydrogen, where oxygen is removed from the reactant [15]. Figure 2.1 provides an idea of the same.

Figure 2.1: Illustration of diﬀerence between pathways (redrawn from [16])

The present study is targeted for partial HDO, which imply that partial removal of oxygen from the reactant would be of primary interest, unlike complete HDO which removes all available O-containing species with or without saturation of aromatic rings. The higher oxygen content in oils derived from biomass are spread out based on the functional groups and its reactivity at a particular temperature. Table 2.1 gives an overview of the same, which suggests the role of reactor temperature in removing particular oxygenated species. 2.2. Dynamics of hydrotreatment 7

Table 2.1: Reactivity of oxygen containing functional groups (adapted from [17])

Functional groups Isoreactivity temperature (◦C) Ketone 200 Aliphatic alcohols 260 Carboxylic acids 283 Phenols 350

As described by the author, isoreactivity denotes the temperature for which conversion becomes similar to that achieved by a sulphided CoMo/Al2O3 catalyst. The ability to remove functional groups would also depend on the molecular structure. For example, a higher energy is required to break aromatic bonds than aliphatic bonds with the same features. Some typical bond dissociation energies are depicted in Table 2.2.

Table 2.2: Bond dissociation energy (adapted from [18] and [13])

Chemical Bond Energy (kJ/mol) Long C-C 309 Aliphatic C-C 344 Aliphatic C-OH 385 Aliphatic C-OR 339 Aromatic C-OR 422 Aromatic C-OH 468 Biphenyl C-C 476

Table 2.2 provides an indication that several bonds are broken before O elimination from aromatic ring. For aromatic species, HDO proceeds through hydrogenolysis of aromatic C-O bond or through ring hydrogenation followed by de-oxygenation producing cyclohexanes [19]. Thus, a higher hydrogen pressure is unsuitable for present work, as it may lead to excessive aromatic C-O cleavage and ultimately cracking. It is also known that, if a chain-reaction occurs primarily through free-radical mechanism, the observed activation energies could be below the individual bond dissociation energies [18]. Therefore, a hydrogen-abstraction mechanism (Y – H + Z −−→ Y + Z – H) of the reaction could lower the dissociation energy, ultimately leading to cracking reactions, producing shorter carbon-chains. 8 Hydrotreatment

Considering a phenolic species as a model compound upon which reaction pathways are studied, it was stated that the species underwent three HDO routes namely; (a) direct deoxygenation (b) hydrogenation-dehydration and (c) tautomerization-deoxygenation [20]. Routes (a) and (b) are most commonly observed during HDO reactions. This is illustrated in the ﬁgure 2.2.

Figure 2.2: Hydrodeoxygenation routes followed by a phenolic lignin species (redrawn from [20]) [21]

Path (a) induces C-O bond cleavage via hydrogenolysis without intermediary steps for hydrogenation. If the eﬀect of catalyst formulations are neglected, then this path is favoured under low pressure and high temperature during hydrogenation. The opposite is the case with path (b), where a high pressure and low temperature act in its favour [22]. It is also stated by the authors that path (a) consumes less hydrogen and does not hydrogenate the benzene rings to aid oxygen removal [23]. This also implies that path (a) can presumably cause complete deoxygenation. 2.3. HDO thermodynamics 9

2.3 HDO thermodynamics

The inﬂuence of hydrogen pressure on carbon-ring saturation, is given by the following ◦ formula adapted from [13]. Here, Kp denotes the equilibrium constant at 350 C. P,Pp and PR represents H2 gas pressure, product and reactant pressures respectively, α denotes the conversion and m is the number of moles of hydrogen.

α α log Kp = log (1-α ) – m · logP; where (1-α ) = Pp /PR

In the case where aromatic ring is hydrogenated to cycloalkane and aromatic C-O bond is converted to aliphatic C-O bond, hydrogen pressure is an important factor determining the equilibria of reaction. The above equation particularly highlights this behavior at 350 ◦C[13]. If similar thermodynamical correlations are generated, it would be beneﬁcial in determining the reaction progress at diﬀerent stages of deoxygenation.

Bio-oil hydrotreatment A general bio-oil HDO reaction can be written as [24]:

CH1.4O0.4 + 0.7 H2 −−→ CH2 + 0.4 H2O; (2.1) ΔG = -2.4 MJ/kg CH2 refers to an undeﬁned hydrocarbon species

It is estimated that exothermic heat of reaction could be more or less depending on the type of bio-oil used. A relatively high content of heavy molecular weight species can generate a higher exotherm. Therefore, hydrogen addition to the reactor during hydrogenation will have to be conducted batch-wise, to control the reaction exotherm and to provide suﬃcient pressure for the reactions to progress to completion. 10 Hydrotreatment

2.4 Catalysis

Transition metal catalysts are traditionally used for hydrotreatment and one important candidate in this ﬁeld is NiMo/Al2O3 catalytic system. NiMo and CoMo catalysts on alumina supports are sulphided to create MoS2 phase, which is active for initiating hydrogenation reactions. In the case of NiMo catalyst, Ni acts as the promoter and MoS2 contributes to the active sites. One challenge for using this catalyst is that Ni can act as an electron donor and Mo as an electron acceptor. This weakens the molecular bond of MoS2 and thus the active sulphided phase of the catalyst can undergo rapid oxidation or even leaching in the presence of a hydrotreatment feed [25]. The acidic nature of alumina support is also a cause of concern, since the lewis acid sites could result in coking, ultimately leading to catalyst deactivation [26].

A bifunctional catalyst like NiMo contains an acid and a metal functionality. This kind of catalytic systems are employed, where the activity of metal functionality for deoxygenation is low, implying that, acid part contributes to increasing the activity of the metal part. A general understanding would be that C=C and C=O bonds would be hydrogenated by the metal part, while hydrocracking would be achieved by the acid part of the catalyst. The suggestion here is that bifunctional catalysts, if used with extreme reaction conditions, can lead to hydrocracking of feed material [27][28].

Catalyst systems were investigated for hydrotreating bio-oils, to conclude that even though coking and corrosion was observed, Pd/C catalyst was the better alternative for ◦ mild-HDO conducted at 250 C and 100 bar H2 pressure [29]. The present research work should also maintain a similar temperature and probably a lower pressure leading to mild-HDO. J. Wildschut et al., 2009 studied bio-oil derived from fast-pyrolysis process for HDO in a batch autoclave, and some of the signiﬁcant results are mentioned in table 2.3.

Table 2.3: Catalysts employed in bio-oil hydrodeoxygenation (adapted from [29])

Catalyst T(◦C) Pressure (bar) Oil Yield (wt%) Batch Time (h)

NiMo/Al2O3 250 100 30 4 Pd/C 250 100 43 4 Pt/C 250 100 58 4 Pt/C 350 200 27 4 2.4. Catalysis 11

Table 2.3 offers a motivation to select Pt/C catalyst owing to the relatively higher oil yield, but it compromises on the efficiency of oxygen removal. Furthermore, these results may not be entirely applicable to the present work since the composition can vary among different bio-based oils. The use of a commercial catalyst like NiMo/Al2O3 would provide easy scalability and would be an economical option compared to other noble-metal based catalytic systems.

Justiﬁcation for catalysts selection ◦ J. Wildschut et al., 2009 [29] mentions using 250 C, 100 bar H2 pressure and 4 h batch time for Ru-based catalyst as mentioned before. Another factor to note is that both Ru and Ni metals on Al2O3 support show similar ﬁnal oxygen content in pyrolysis oil subjected to mild-HDO. Furthermore, NiMo system has a higher product oil yield than Ru-based system.

In the same work by the author, it is given that Pd/C would be the best option to choose considering the end goal of lower oxygen content and higher oil yield. However, the higher cost of Pd/C catalysts compared to the commercially used NiMo, limits its extent of use [30]. These factors justify the selection of NiMo/Al2O3 catalyst for conducting mild-HDO reactions.

2.4.1 Undesired characteristics 1. Higher temperatures and hydrogen pressures can lead to extensive hydrogenation at molecular level and bond dissociation might occur relative to the respective dissociation energy, as mentioned in 2.2. This tends to produce fuel-grade hydrocarbons of short chain length and methyl-interlinks found in resin acids, unsaponiﬁable fractions of bio-based oil may break-open. For example, literature suggests that cracking was conducted on a feed of depitched crude tall oil mixed ◦ with atmospheric gas oil at 5.5 MPa H2 pressure at 370 C on NiW and NiMo catalysts [31]. 12 Hydrotreatment

2. Bio-oils contain lower amounts of sulphur and nitrogen than crude oils, but comes with a disadvantage of having more oxygen. HDO reactions demand a higher H2 supply and produce H2O as the major side-product. On the other hand, deoxygenation through decarboxylation (yielding CO2) or decarbonylation (yielding CO) has a lower H2 demand, but with the expense of a lower carbon eﬃciency [32]. Hence, an ideal catalyst system for partial HDO would have a lower activity to not lead to saturation of hydrocarbons, also producing less coke. A mild-HDO was conducted on bio-oil/pyrolysis oil to determine that a yield of only 30 - 50 wt% was obtained for the partially deoxygenated liquid mixture. The side products were gases, water and coke [33]. 3 Hydrodeoxygenation of Tall Oil Fraction

3.1 Understanding tall oils

Tall-Oil is one of the prospective starting material for use as a bio-based feedstock. Further discussions in this chapter refer to the use of tall-oil, or more speciﬁcally, product fractions obtained from Crude Tall Oil (CTO). It is important to understand the nature and source of CTO in a process industry. CTO is a by-product from the Kraft pulp mills employed for manufacturing paper and related products. Tall-oil comprises of non-lignin, non-cellulosic fraction of pine trees and is usually subjected to steam/vacuum distillation for basic upgrading. It is estimated that 1 ton CTO normally produces 350 kg rosin acids (TOR) along with 300 kg of fatty acids (TOFA), 350 kg of Distilled Tall Oil (DTO), heads and Tall Oil Pitch (TOP) [34][35]. The term "depitching" essentially implies that the pitch (TOP) is removed from the product mixture. The authors mention that depitching is carried out either in the Kraft mill or in the bio-reﬁnery [36]. In the case of Sunpine plant in northern Sweden, depitching is a part of the process and TOP is the heavy product fraction obtained [9].

13 14 Hydrodeoxygenation of Tall Oil Fraction

Experimental works were conducted to determine the composition of various fractions emanating from the column. These include TOP, TOR (Tall Oil Rosin), TLO (Tall Light Oil), DTO (Distilled Tall Oil) and TOFA (Tall Oil Fatty Acid) (refer figure 3.2)[37]. In the subsequent work by the same author, GC-HRMS was used to analyze the fractions. It was suggested that nearly 60% of the components in the TOP were of high-molecular weight, and particularly, about half of them were acidic in nature. The low molecular weight resin acids were mostly abietic and dehydroabietic acids. Moreover, the unsaponifiable fraction contained fatty and diterpene alcohols along with sterols and de-hydrated sterols [38]. The results from analysis indicated that TOP typically comprises of approximately 48% free acids, 24% esterified acids and 28% unsaponifiables. A closer look at the free acids denotes a split of 10.6% resin acids. Figure 3.1 (top) depicts the structure of the main compounds found in free acids. The analysis of chemical species in TOP also indicates that oleic acid and β-sitosterol are the dominant species in the category of esterified acids and unsaponifiables respectively [38], as seen in figure 3.1 (bottom).

Figure 3.1: Illustration of major acid species in tall oil pitch (adapted from PubChem [39])

The variation of TAN in the feed as well as in the product fractions are indicated in Figure 3.2. It is seen that the top products contain signiﬁcant amounts of residual oxygen. TOFA is commonly used for vehicle-fuel production and TOP holds a comparatively lower TAN value, which invokes interest from a hydrogenation point of view. 3.1. Understanding tall oils 15

Figure 3.2: Depiction of Total Acid Number (TAN) variation with respect to diﬀerent fractions in crude tall oil distillation process (data from [37])

Some important terms regarding tall oils fractions are mentioned below:

• Neutrals refer to the non-acidic components, namely alcohol, ester, aldehyde etc.

• Unsaponiﬁables refer to the components which are unable to form soaps

• Pitch is the tower bottom consisting of heavy-neutrals, leftover fatty and resin acids 16 Hydrodeoxygenation of Tall Oil Fraction

3.1.1 Justiﬁcation for selection of TOP feed The main reason for choosing Tall Oil Pitch (TOP) over fast pyrolysis bio-oil from pine/forest residue is because the TAN value for the former is normally seen to be lower than that for the latter [37][40]. A comparison of diﬀerences in composition are available in Tables 3.1 and 3.2.

Table 3.1: Composition of bio-oil derived from wood pyrolysis (adapted from [41])

Group Content (wt%) Water 30 Lignin 30 Aldehydes 20 Carboxylic acids 15 Phenols, Furfurals, Alcohols, Ketones 5

Table 3.2: Composition of Tall Oil Pitch from Finnish biomass (adapted from [37])

Group Content (wt%) Free acids 48 Esteriﬁed acids 24 Unsaponiﬁables 28

Due to a lower TAN value for TOP and a higher fraction of heavy molecular weight components, it is decided to base the entire research work on conducting mild-HDO reaction on TOP sample. Furthermore, study on TOP enables better utilization of a product, which otherwise is used mainly as a boiler fuel after upgrading with lighter tall oil fractions [42]. Further chapters in the report revolve around the use of TOP as the reactant species for hydrogenation experiments. 3.1. Understanding tall oils 17

3.1.2 Estimate for TOP; Oleic acid hydrotreatment De-oxygenation of oleic acid (dominant species in esteriﬁed acids of TOP) may follow decarbonylation or decarboxylation pathway at the mild-HDO temperature of 300 ◦C[43].

Oleic acid decarbonylation:

C18H34O2 −−→ CO + H2O + C17H32; (3.1)

ΔG = -17 kJ/mol

Oleic acid decarboxylation:

C18H34O2 −−→ CO2 + C17H34; (3.2)

ΔG = -83.5 kJ/mol

From this estimation, it could be inferred that oleic acid species present within TOP could produce diﬀerent levels of isotherm, based on its deoxygenation path. This in turn, provides a correlation between oleic acid content and reactor dynamics during hydrogenation reactions.

3.1.3 Expected catalytic behaviour for HDO of TOP 1. Catalysts with alumina supports exhibited instability in environments containing higher levels of water, like that of bio-oil. The occurrence of this phenomena for the present study, depends on water content in the TOP sample used.

2. Some amount of solids are also expected as a reaction product, when alumina supports are used. This indicates that further challenges are encountered, if solids are to be used downstream to avoid product loss [29].

3. Sulphur in the feed is expected to be leached-oﬀ during the hydrotreatment, which indicates the need for using fresh batch of sulphided catalyst at the start of each successive experimental run [44]. 18 Hydrodeoxygenation of Tall Oil Fraction

3.2 HDO of abietic acid model compound

Rosin acids are the major components obtained from tall oils, apart from fatty acids. Abietic acid, which forms the biggest chunk of rosin acids, contain a tri-cyclic ring structure having conjugated double-bonds and carboxylic acid functional group [34].

It is important to note that composition of the mixture present in gas phase (reaction product) would depend on the equilibrium-limited Water Gas Shift (WGS) reaction [34]. The pressure does not have any eﬀect on this reaction (Le Chatelier principle), however, signiﬁcant levels of conversion is achieved at temperatures above and around 300 ◦C for a Pd/Al2O3 catalyst [45]. This indication can be used in the present study to suggest that, carbon monoxide in the product gas mixture can preferably react with water in the aquous phase, to produce hydrogen and carbon dioxide. The hydrogen produced can participate in the further HYD reactions again as a reactant, while the harmful carbon monoxide is converted to a less-toxic substance. This is an interesting result from a reaction point-of-view. but the actual occurance of the phenomena needs to be studied during the analysis phase of the work.

Information regarding catalyst sulphidation is mentioned in detail by the authors H. Ojagh et al., 2019. The NiMo/Al2O3 catalyst was prepared with 5 wt% Ni and 15 wt% ◦ Mo, then sulphided by DMDS at 20 bar H2 pressure, 350 C for 4 hours. Here, DMDS was expected to undergo a reaction with hydrogen producing H2S gas, which would act as a sulphiding agent for the catalyst. DMDS was also added in the later stages to preserve the sulphidity. Also, dodecane was selected and used as a solvent to limit the exothermic heat generated as a result of breaking chemical-bonds [46]. The authors use an autoclave while maintaining a catalyst/reactant ratio of 1:4.5 at 320 ◦C, 54 bar at a stirring rate of 1000 rpm. Some parameters in this study can match the reactor conditions employed in this research.

Other relevant conclusions for this study would be to identify the extent of conversion for abietic acid species. H. Ojagh et al., 2011 mentions that the concentration of abietic acid decreases fast in the ﬁrst few minutes of hydrotreating, ultimately converting to deoxygenated products after 40 minutes. Hence, a suitable end-result would be to set a batch-time more than 40 minutes to preferably convert abietic acid to partially deoxygenated species [46]. 3.2. HDO of abietic acid model compound 19

Figure 3.3: Conversion of abietic acid into product components (redrawn from [46]) Legend: DO = Deoxygenation, DC = Decarboxylation, HYD = Hydrogenation

Figure 3.3 depicts the conversion pathway studied in the referenced article. However, the aim here would be to control the reaction conditions to obtain partially deoxygenated species, rather than products (P1, P2 and P3) which underwent complete HDO. However, the challenging part would be to experimentally achieve this. A. Bernas et al., 2012 investigated the eﬀect of 10 wt% Pd/C system at 80 ◦C, 10 bar with catalyst/reactant ratio of 1:10. The results suggested that hydrogenation dominated and HDO was absent. Hence, there is a possibility that a kinetics-controlled reaction is in place at lower temperatures, which also depends heavily on reactor pressure [47].

Predicted results from HDO of abietic acid A preliminary conclusion obtained from this section would be to preferably conduct complete HDO on abietic acid components, provided other factors support this concept. This would give some room for other unconverted-oxygenated species in the reaction mixture. The predicted end-result would be that a partial HDO of TOP is still achieved. This agrees with the result that a rapid conversion was noted, even when Pd/C was used as the catalyst system for HDO studies [47]. The test reveals that a temperature close to 300 ◦C could ideally deoxygenate the entire mixture. Thus, the feature of high conversion may not be a catalytic property, but more related to the kinetics of the chemical species. 4 Materials and Methods

The TOP feed was provided by the courtesy of Sunpine AB, Sweden and the catalysts were sourced from Nynas reﬁnery in Nynäshamn, Sweden. The sample of commercial catalysts are unsulphided and needs to be sulphided prior to use, with DMDS preferrably being used as the sulphiding agent. An autoclave is used for conducting the experimental runs (shown in ﬁg.4.1). The experimental conditions to be used are projections derived from the existing literature, and a Design of Experiment (DoE) procedure is to be formulated as well. Detailed explanation of hydrogenation studies are mentioned in the subsequent chapters of the report. Characterization of feed as well as the product will be managed using the resources available at research departments belonging to both KTH and Nynas.

20 4.1. General Description 21

Figure 4.1: Preliminary laboratory reactor setup 4.1 General Description

As suggested by C. Miao et al., 2016 [48], it is expected that the products from hydrotreatment will occur in three diﬀerent phases, namely organic phase (comprising of heavy long-chain hydrocarbon mixture), aqueous phase (comprising of water which is the reaction product) and gas phase (consisting of unreacted hydrogen, carbon monoxide, carbon dioxide etc.). Therefore, it is critical to make a list of experimental tests that can reveal changes in properties before and after the mild-HDO reaction.

The gas and the organic-liquid fraction from the reactor are analyzed using a GC and GC-MS respectively. The amount of water produced in the reaction is an indication of oxygen removal, and this can be correlated to the acid number obtained from analyses of samples before and after hydrotreatment. As for the tall oil pitch, its appearance is of a black paste at room temperature. Literature suggests a viscosity of approximately 200 mPas at 100 ◦C with an acid value of 50 mg KOH/g oil and a stability of 6 months at 25 ◦C[49]. The softening point can be closer to 20 ◦C[50]. 22 Materials and Methods

4.2 Analysis parameters

4.2.1 Viscosity Viscosity of liquid TOP is used as a parameter to understand flow properties under a specified temperature [51]. Kinematic viscosity is measured using a Cannon-Fenske reverse flow capillary viscometer. Calculation of viscosity before and after hydrogenation, provides an indirect correlation of the chemical nature of mixture. This is turn indicates the strength of intermolecular forces and bond stability. It is also expected that a higher degree of bond-saturation post hydrogenation, could lead to an increase in kinematic viscosity of the sample, when compared to a sample prior to hydrogenation at the same temperature.

Kinematic viscosity measurement Experimental design was structured according to ASTM D445 (residual fuel oil and opaque liquids category) [52]. Silicone oil was used as the heat transfer medium in a stirred-heating bath and was maintained at a constant temperature of 102 ◦C. Furthermore, a small quantity of TOP sample was heated and stirred at 102 ◦C. Figure 4.2 illustrates the upward travel of liquid meniscus from point 1 to 2.

Figure 4.2: Viscosity measurement using Cannon-Fenske reverse ﬂow viscometer 4.2. Analysis parameters 23

The standard experimental procedure was followed, and the preheated viscometer was charged with TOP before insertion into oil bath. The time taken for the liquid meniscus to travel between 2 markings around bulb 1 of viscometer was noted. The time was multiplied with the viscometer constant to arrive at a ﬁnal kinematic viscosity value.

Dynamic viscosity was not calculated from the kinematic viscosity value, due to the large deviations/errors arising out of density measurement. One major challenge in density measurement was that sample had to be constantly stirred with the help of a magnetic stirrer to ensure eﬀective heat transfer, and thus a good temperature measurement. However, there was no setup to isolate the sample from surrounding air, and this enabled the dissolution of atmospheric air into the liquid sample. Hence, the measured weight at a particular temperature, would include the weight of air also, which is diﬃcult to quantify. This was the reason for not conducting a density measurement, that can give a dynamic viscosity value, in addition to kinematic viscosity. Factor of viscosity for bulb 1 of viscometer (between points 1 and 2) and that for bulb 2 of viscometer (between points 2 and 3) are 0.258 mm2/s2 and 0.2046 mm2/s2 respectively.

Time taken for the meniscus to traverse from mark 1 to 2 = 1938 seconds Kinematic viscosity (1) = 0.258 mm2/s2 · 1938 s = 500 mm2/s = 500 cSt

The viscosity test was repeated to check for consistency in measurement. The result show a deviation from the previously measured value. The test was repeated to yield consecutive values as mentioned below:

Time taken for the meniscus to traverse from mark 2 to 3 = 547 seconds Kinematic viscosity (2) = 0.2046 mm2/s2 · 547 s = 111.91 mm2/s = 112 cSt

The reason for the large deviation was investigated and found. It was observed that during test(1), improper immersion of viscometer in the heating medium caused certain parts of viscometer to cool down, subsequently reducing the ﬂow velocity of liquid inside the capillary tubes. Hence, it took a longer time for the liquid meniscus to traverse from point 1 to 2.

The error was negated in test (2), where complete immersion of essential viscometer parts into the heating medium was ensured. A larger ﬂow velocity was observed along with a shorter ﬂow time. This was the reason behind a lower kinematic viscosity value for test(2). Therefore, a value of 112 cSt is chosen with a tolerance band of ±0.36%[52]. 24 Materials and Methods

4.2.2 Acid number Acid number is an important parameter for determining the presence of acidic species in a tall oil sample. Acid number of TOP sample before and after HDO reactions help determine the extent of oxygen removal. ASTM D465 standard is used to determine the total free acid number of tall oil pitch [53]. It is believed that HDO may remove oxygen from acid groups and hence, acid number of hydrotreated product could be lower than the starting material.

Determination of total free acids Internal indicator titration conducted with ASTM D465 (Acid number of pine chemical products including tall oil and other related products) was effective in determining acid number of TOP with some minor modifications in standards, since the dark colored nature of analyte inhibited observation of color change. This observation is seen in figure 4.3.

Figure 4.3: Dark-colored nature of TOP analyte used in titration

Some trials were conducted to determine the dissolution of TOP in toluene. It was observed that when toluene was used, the sample solution needed to be exposed to mild-heat to achieve complete dissolution of TOP in toluene. The solution then had to return to room temperature before titration was conducted. On the other hand, when toluene was replaced with a similar quantity of dichloromethane, TOP was readily soluble and the need for heating could be neglected. The absence of heating may reduce errors, since one experimental degree of freedom is removed. Hence, it was decided to progress with 25 mL of dichloromethane as one of the solvents. 2-propanol was employed as the other solvent according to the standard and no change was made in this case. 0.5 N KOH solution and phenolphthalein indicator was freshly made before the start of experiment. 4.2. Analysis parameters 25

Another issue encountered was the dark nature of the solution, which inhibited the observation of color change at the end of titration. It was observed that when a smaller sample was taken and when a more diluted solution was used, detection of color change was then possible. For this purpose, the solution was diluted to 0.3 % (w/v) using repeated and measured additions of 2-propanol and dichloromethane to 300 mL. Then 100 mL of resultant solution was used as the analyte. The titration was repeated to yield consecutive values. The difference in color of samples noted before and after dilution is shown in figure 4.4. The end-point of titration was observed by a permanent pink color induced to the solution (refer figure 4.5).

Figure 4.4: Analyte without dilution (left) and with dilution (right)

Figure 4.5: Observed end-point of titration 26 Materials and Methods

Amount of TOP used initially = 1 g Amount of TOP present after dilution = 0.3 g / 100 mL solution End-point from blank titration = 0 mL Amount of KOH titrant consumed during titration = 0.6 mL Normality of KOH solution = 0.5 N

(0.6 – 0) mL · 0.5 N · 56.1 g/mol Acid number of TOP = 0.3 g sample = 50 mg KOH / g sample

4.2.3 Saponification number Similar to acid number analysis, saponification number also provides an estimate on the presence of acidic groups in the sample. However, saponification number indicates the total acid content (free and combined acids) unlike that for acid number, which reports only the free acid content. This value is also used as a correlation for acid number determined earlier. The experiments are conducted in accordance with ASTM D464 [54].

Determination of total free and combined acids Experimental procedure mentioned in the ASTM standard was strictly followed without any modifications. One minor deviation from the procedure is that TOP was not directly transferred into the Erlenmeyer flask, instead the measured quantity of TOP was dissolved in 10 mL of 1:1 mixture of 2-propanol and toluene. The solution was then slightly heated to dissolve the sample and then transferred to the titration flask. Also, a smaller sample size was used to facilitate detection of color change at the end of titration. The end-point of titration was noted by the color change of solution, which shifts from a dark-brown (or reddish-brown after addition of phenolphthalein indicator) to pale-yellow color upon neutralization by the acid.

It is mentioned in the ASTM standard that unsaponiﬁable material including inorganic and organic acids, increase the saponiﬁcation number [54]. The blank titration value was noted to be larger than sample titration value. This might be because of the presence of acidic species in the sample, which then require less amount of acid titrant to be added to neutralize solution. On the other hand, the absence of any acidic species in the blank titration, increases the amount of acid titrant consumed. Figure 4.6 also depicts the color of analyte before and after titration.

Amount of TOP sample = 0.3 g End-point from blank titration = 42 mL Amount of 0.5 N HCl titrant consumed during titration = 41 mL 4.2. Analysis parameters 27

Figure 4.6: Experimental setup (left) and observed end-point of titration (right)

(42-41) mL · 0.5 N · 56.1 g/mol Saponiﬁcation number (1) of TOP = = 0.3 g sample = 93 mg KOH / g TOP

Subsequently, another measurement was conducted with 0.33 g of TOP sample to measure an end-point at 42.5 mL. The blank titration yields a value of 43.5 mL for this case. (43.5 – 42.5) mL · 0.5 N · 56.1 g/mol Saponiﬁcation number (2) of TOP = = 0.33 g sample = 85 mg KOH / g TOP

Quantiﬁcation of deviation Standard deviation Based on the two experiments, a standard deviation of 4 was obtained, There is a high chance that the higher standard deviation (higher spread of data points) are caused primarily due to the reaction condition, namely the temperature. It is estimated from the above observation that providing a strict control of the analyte temperature, might reduce the standard deviation. 28 Materials and Methods

Degree of Freedom (DOF) analysis The unknowns for this particular experiment can be termed as:

1. Blank titration value

2. Sample titration value

3. Mass of sample used

4. Temperature of the analyte solution maintained prior to titration

5. Degree of mixing achieved for the analyte

6. Concentrations of the solutions prepared (alkali solution of 0.5 N KOH in ethanol and acid solution of 0.5 N HCl)

Total number of unknown parameters = 6

Given/known parameters based on assumptions are given below:

1. Standard preparation procedures as per ASTM standard are followed and hence, variation in concentration for the prepared solutions are ignored.

2. Blank titration value is correct, based on concentrations of prepared solutions

3. Sample titration value is correct, based on concentrations of prepared solutions

4. Analyte is well mixed and a constant stirrer speed is maintained

5. Sample losses in transfer to the Erlenmeyer ﬂask is ignored, since the sample is pre-dissolved in 10 mL 1:1 mixture of 2-propanol and toluene. The solution is then poured directly into the ﬂask.

Total number of known parameters = 5

DOF = (ΣUnknown – Σknown) parameters = 6-5 = 1

Reiterating the same point as mentioned before, a strict control of analyte temperature can decrease the deviation in measured saponiﬁcation number values. 4.2. Analysis parameters 29

4.2.4 GC/MS analysis The results from this analytical measurement act as a supporting argument for acid number and saponiﬁcation number values. The total oxygen content is determined through the peak area method, where it can potentially indicate the approximate degree of oxygen removal during hydrogenation. Figure 4.7 illustrates the chromatogram from the analysis of TOP feed used for hydrogenation.

Figure 4.7: GC/MS chromatogram for tall oil pitch. A wide spectrum of components can be seen, which indicate the presence of various types of oxygenated and non-oxygenated species in the sample (source: KTH labs)

A sample of TOP in dichloromethane was prepared and analyzed in GC-MSD system. For this purpose, Agilent 7890B GC system coupled to Agilent 5977A MSD was employed. Some selected entries from the analysis result indicate the presence of:

• Non-oxygenated species: toluene, benzene, nitrogen containing species (pyridine, acridine, 3-Piperidinamine, Quinoline), decane, butane

• Oxygenated species: sulphur containing species (carbamothioic acid, S-phenyl ester, Acetamide, Lycopodine), nitrogen containing species (4-(p-Methoxyphenyl)-pyridine), Tridecanol, Formic acid, Phenylacetic acid, Cycloprop[7,8]ergost-22-en-3-one 30 Materials and Methods

The selected range of components in the oxygenated species list contain acids, esters, alcohols, saturated as well as aromatic species. The peak area with unit (Ab*s) is provided by the equipment. Using the peak area as the factor, the degree of deoxygenation could be found. The species which undergo deoxygenation gives a lower peak area, and is thus correlated with the results prior to hydrogenation. The GC/MS analysis then serves as the second layer of conﬁrmation for acid number observed after hydrogenation.

The presence of oxygenated species and its distribution as a function of residence time (minutes) is interesting to note. The majority of oxygenated compounds are detected after a residence time of 85 minutes. It is understood from figure 4.7 that distinctive and well-defined peaks are not observed throughout the spectrum. This indicates that the analysed TOP contains a wide range of compounds. However, the GC/MS analysis still qualifies to be used as a method of identification of oxygenated species. The reason is that even though the chromatogram fails to provide a clear understanding of the components, the area under the curve for these detected species could be used, to identify the degree of deoxygenation after each experimental run. 4.2. Analysis parameters 31

4.2.5 Carbon residue content The test conducted as per ASTM D4530 determines the relative coke formation in the sample [55]. This test can be used as a comparison between hydrotreated and non-hydrotreated TOP. For example, based on available literature, a trend can be predicted in such a way that hydrotreated product would form less carbon residues than the initial sample. This behavior is correlated to the degree of unsaturation present in the oil sample. Hence, the greater unsaturation in tall oil pitch could most likely produce more carbon residues than its hydrotreated counterpart [56]. This value however includes non-volatile components such as ash. Thermogravimetric (TG) analysis is used as an alternative to the muﬄe furnace method determined in the standard.

Test for carbon residue content The alumina ceramic crucibles to be used in the experiment were subjected to prior cleaning by using acetone as the cleaning solvent, and then later heated in a calcination oven to burn-oﬀ any unwanted residues or coke deposits which can aﬀect the readings.

Cleaned crucibles were taken from the oven and TG was started, and later proceeding on to creating the base-line correction curve. This represents a blank experiment and conditions similar to the actual experiment were maintained. Constant N2 gas flow was supplied at 30 mL/min with a constant heating rate of 5 ◦C/min, to create an inert atmosphere that prevented oil combustion above its pre-determined flash point. Further on, the sample was subjected to analysis. The viscous TOP sample was transferred into the crucible with utmost care, making sure that sample touched the bottom part of the crucible (location of sample temperature measurement). Checks were performed to confirm that sample did not stick onto the sides of the crucible and losses in transfer of sample from petri dish to crucible was also minimized. 520 mg of sample was weighed initially, out of which 416.52 mg was transferred into the crucible. Hence, the transfer losses can be (520-416.52) mg accounted to 520 mg · 100 = 19.9 %. The test was conducted for a sample mass of 416.52 mg. The oil sample transferred to the crucible is depicted in figure 4.8.

For the thermogravimetric analysis of TOP sample, the instrument measured a mass of 416.52 mg before the start of experiment. The same crucible used for measuring base-line correction was used for the sample test also, to arrive at the below mentioned result:

Residual mass (mg) 14.22 mg Carbon residue (1) = Initial mass of sample used (mg) · 100 = 416.52 mg · 100 = 3.414 % 32 Materials and Methods

Figure 4.8: Transferred TOP sample inside cleaned and pre-heated crucible

After the experiment was conducted, the crucible was kept overnight in the calcination oven. Heating was conducted for 1.5 hours at 900 ◦C to ensure complete burning of carbon residue crusts formed inside the crucible (refer ﬁgure 4.9).

Figure 4.9: Crusts of carbon residues found inside crucible subjected to test (1)

Carbon residue test was repeated with slightly different experimental conditions to determine any changes in final reported values. A constant heating rate of 3 ◦C/min was maintained, as opposed to the 5 ◦C/min fixed for the previous case. Figure 4.10 shows the carbon residues formed in the crucible.

Residual mass (mg) 6.89 mg Carbon residue (2) = Initial mass of sample used (mg) · 100 = 239.057 mg · 100 = 2.882 % 4.2. Analysis parameters 33

Figure 4.10: Crusts of carbon residues found inside crucible for test (2)

The test was carried out again to check for repeatability. Similar conditions were maintained as test (2), except for the fact that the ﬂow rate of protective gas (N2) was increased from 30 mL/min to 150 mL/min. This was done to ensure that the previous test had no errors in terms of gas condensation on the sides of crucible, which can increase the weight of measured carbon residues. The results mentioned below, indicate that no such eﬀects were observed for test (2) and that similar results were obtained. Standard deviation between test (2) and test (3) revealed a short spread of data points, with a value of 0.02. Figure 4.11 illustrate the TG analysis curves obtained, from which the residual mass was calculated.

Residual mass (mg) 5.42 mg Carbon residue (3) = Initial mass of sample used (mg) · 100 = 190.55 mg · 100 = 2.844 %

Figure 4.11: Thermogravimetric analysis result from carbon residue test 34 Materials and Methods

4.2.6 Ash content The ash content is subtracted from the carbon residue value obtained previously. The test was conducted as per ASTM D482 [57]. The alkali content and sulphur contributes to the value and needs to be identiﬁed and quantiﬁed.

Test for ash content Thermogravimetric analysis for measurement of ash content proceeded similar to the carbon residue testing, except for change in process conditions. The dynamic test was conducted in the presence of air, which aids combustion of oil sample, ultimately producing ash. A temperature higher than carbon residue testing was also maintained. Crucible pre-cleaning and heating was also repeated for this measurement. Ash residues formed inside the crucible is seen in figure 4.12. In this case, the sample was heated to a final temperature of 775 ◦C at a constant heating rate of 5 ◦C/min. Finally, an isothermal stage was added to the program to hold the temperature constant at 775 ◦C for 25 min. The flow of air was kept at 150 mL/min throughout the measurement period.

Figure 4.12: Crusts of ash residues found inside crucible subjected to experiment

Residual mass (mass of ash) = 5.91 mg Initial sample mass = 389.75 mg Residual mass (mg) 5.91 mg Ash content (1) = Initial mass of sample used (mg) · 100 = 389.75 mg · 100 = 1.516 %

Non-volatiles in the sample = 3.414 – 1.516 % = 1.898 % 4.2. Analysis parameters 35

The ash test was repeated with new process conditions. In this case, the sample was heated to a final temperature of 775 ◦C at a constant heating rate of 3 ◦C/min. Finally, an isothermal stage was added to the program to hold the temperature constant at 775 ◦C for 30 min. The flow of air was kept at 170 mL/min throughout the measurement period. The lower quantity of residual sample, as compared to the previous experiment can be observed from figure 4.13.

Figure 4.13: Small quantity of ash residues found inside crucible subjected to experiment

Residual mass (mass of ash) = 0.52 mg Initial sample mass = 240.94 mg

Residual mass (mg) 0.52 mg Ash content (2) = Initial mass of sample used (mg) · 100 = 240.94 mg · 100 = 0.216 %

Non-volatiles in the sample = carbon residue content – ash content = 2.882 – 0.216 % = 2.666 % 36 Materials and Methods

Reasoning for deviation There was a large deviation in ash content values for both experiments. One plausible reason can be that, a longer experiment duration enabled the sample to completely burn and produce the right quantity of ash. Proceeding with this logic, it is understood that the residence time for ash test (1) was 2.58 hours, whereas, it was 4.3 hours for ash test (2). Hence, a higher residence time for test (2) coupled with the 20 mL/min increase in air ﬂow rate would have provided adequate conditions for ash formation. Furthermore, in support to this argument, TOP suppplier (Sunpine, Sweden) MSDS indicated an ash content of < 0.2 wt%. The measured value of ash content (2) 0.216 wt% is deemed to be close to the this value. Figure 4.14 illustrates the TG curve obtained as a result of ash test, from which the value of 0.216 % was derived.

The ash test was repeated with an increased ﬂow of protection gas (N2) similar to section 4.2.5 to check for repeatability and to check for errors in measurement. The isothermal time at 775 ◦C was increased from 30 min to 40 min to ensure complete burning of sample to produce ash. The result indicates a similar value to ash test (2) with a standard deviation of 0.005.

Residual mass (mg) 0.49 mg Ash content (3) = Initial mass of sample used (mg) · 100 = 215.744 mg · 100 = 0.227 %

Non-volatiles in the sample = carbon residue content – ash content = 2.882 – 0.227 % = 2.655 %

Figure 4.14: Thermogravimetric analysis result from ash test 4.2. Analysis parameters 37

4.2.7 Metal content Metal content in the TOP sample is determined using the XRF analytical technique. The various metal contents help identify the major ash forming constituents without analysing the ash at a later stage. A patent for utilizing tall oil pitch [58] mentions the presence of K, Ca, Fe, As etc in tall oil. The metals presence may also act as catalyst poison and aﬀect pour point.

Table 4.1: : XRF analysis of tall oil pitch sample (source: courtesy of Nynas)

Metal content Content (ppm) Si 268 P 70 S 3402 K 172 Ca 30 HC 99606

As represented in table 4.1, the highest metal concentration belongs to that of sulphur, primarily originating from white liquor used in the Kraft pulping process [59]. The term ’HC’ refers to undeﬁned hydrocarbon species.

Correlation of results One of the possible interpretations of the analysis, is to ﬁnd the respective fractions of diﬀerent ash forming constituents, using results from the XRF analysis. In table 4.3, metal content is directly taken from table 4.1 and the metal fraction is calculated by dividing the molecular weight of metal with corresponding molecular weight of the compound.

Table 4.2: : Fractions of various ash forming constituents in tall oil pitch [39]

Constituent Metal Content (ppm) (a) Molecular weight (g/mol) Metal fraction (b)

SiO2 268 60 28 / 60 P2O5 70 142 (31*2) / 142 SO 3402 48 32 / 48 K2O 172 94 (39*2) / 94 CaO 30 56 40 / 56 38 Materials and Methods

Table 4.3: : Calculated ash content [39]

Constituent Ash content (ppm) (a / b) Ash content (%)

SiO2 574.3 0.057 P2O5 160.32 0.016 K2O 207.3 0.02 CaO 42 0.004 Total 983.92 0.09

It is suggested that P2O5 is a representative ash forming constituent. In reality, other oxides of these species might be present and isolating them to find the ash content can induce errors in the calculation, since the XRF analysis does not differentiate between different oxides of the same metal [60]. Therefore, the known/observed value of ash content from section 4.2.6 is extracted and compared with the calculated value from XRF analysis.

Diﬀerence in observed and calculated ash content: Ash content (observed) – Ash content (calculated) = 0.21 % – 0.09 % = 0.12 %

The calculated result does not include the ash obtained from the sulphur component. It is expected that sulphur oxides exist mostly in the gaseous phase, and does not contribute to the observed ash content from TG analysis. The diﬀerence in calculated and observed values may also be induced by other oxides of phosphorus present in the sample, apart from P2O5. 4.3. Hydrogenation experiments 39

4.3 Hydrogenation experiments

4.3.1 Basic reactor information The reactor employed for conducting hydrogenation experiment is a batch reactor. The reactor is pressurized using hydrogen gas to the desired pressure, ranging between 20 - 50 bars. Argon gas is used as the inert substance for purging the reactor prior and post hydrogenation experiments. It is also used during the leak-test procedure. Figure 4.15 illustrates the batch reactor and its auxiliary setup.

Figure 4.15: Process ﬂow diagram for the lab-scale hydrogenation reactor

The autoclave was filled with glass beads to ensure good heat transfer from the heating blanket and also to act as a support to the reaction vessel. The heating blanket can be lifted into position with the help of a hydraulic arm. The gas outlets are connected to a gas exhaust located on top of the reactor. Valve V2 acts as a safety valve for the inlet gas line. In addition to this, hydrogen flow is controlled using a volume flow controller with a maximum flow rate of 100 mL/min. An electronic controller attached to the flow valve controls the opening of the valve. The three-way valve ensures no cross flow occurs between hydrogen and argon simultaneously to the reactor. 40 Materials and Methods

4.3.2 Reactor startup This subsection intends to describe some tests conducted before the start of actual hydrogenation reactions. These pre-tests are vital to fully understand the dynamics of the reactor, identify defects in gas lines and other mechanical parts. The reaction vessel which holds the sample during the reaction, has a maximum capacity of 250 mL. Therefore, a desired sample size need to be selected. Other practical factors of importance such as liquid level above/below impeller, mixing characteristics in the reaction vessel as well as stirrer speed, need to be decided before the start of hydrogenation experiments.

It is understood that the mixing cannot be viewed during operation, since the entire system is closed. Henceforth, a tracer can be added to liquid water inside the reaction vessel, which colors the walls and impeller during reactor operation. For this purpose, 150 mL of water was taken in the reaction vessel and catalyst basket was placed at the bottom without any catalyst to mimic original working conditions. A few drops of tracer was added, autoclave bolted into place and allowed ﬂow of argon gas. A leak test was performed and then the reactor was pressurized to 20 bars with the same gas. The impeller was started and a speed of 200 RPM was maintained. The reactor was kept in operation for a short duration of 15 minutes and then later de-pressurized and opened. Figure 4.16 shows the opened autoclave after the run-time.

Figure 4.16: Autoclave after the run-time, with the added tracer to 150 mL of water. Leakage of tracer can be seen in the glass beads placed below the reaction vessel (right) 4.3. Hydrogenation experiments 41

Analysing figure 4.16 for the spread of liquid, it can be seen that although the impeller completely submerged, some amount of liquid had leaked through the gap between the reaction vessel and autoclave. Hence, some color was induced on the glass beads at the bottom of the vessel. There can be multiple factors responsible for the seepage of liquid. One can be that the liquid level was high enough to cause excess agitation and thus the seepage. Secondly, the pressure reduction procedure might not have been gradual and liquid boil-off could have occured, as seen from the froth on the liquid surface. Finally, a higher stirrer speed could also be a factor to consider. Therefore, another tracer study was conducted with 100 mL and 120 mL (including error of ± 0.1 mL) of liquid. Preliminary observation showed that 100 mL was not satisfactory enough to wet the entire impeller. This might cause liquid splash during normal operation. A liquid level of 120 mL (excluding a catalyst basket volume of approximately 15 mL) was sufficient to submerge the entire impeller and also caused no seepage of liquid into the glass-beads. Furthermore, stirrer speed was kept constant at 220 RPM. Figure 4.17 indicates the above mentioned scenario.

Figure 4.17: Opened autoclave after run-time, containing 120 mL of water. There was no leakage of tracer to the glass beads 42 Materials and Methods

4.3.3 Blank hydrogenation experiment It was decided to conduct a blank experiment without the presence of catalyst, to determine any eﬀects of catalyst basket on products obtained after hydrogenation. The catalyst basket is made from steel gauze and inﬂuence of iron on hydrogenation activity (if any) needs to be evaluated.

One of the challenges involved in every experiment is measuring and transferring the required quantity of TOP into the reaction vessel. It is known that 120 mL feed should be constantly used, however, measuring volume for a viscous feed becomes diﬃcult due to many reasons. Graduated cylinders can be used for this purpose with an error of ± 0.1 mL, but taking out the contents from a cylinder becomes diﬃcult due to the viscous nature of sample. Furthermore, this method introduces large errors in the form of transfer losses. Therefore, the alternate method of density measurement was used.

Calculated density of TOP at 25 ◦C = 1113.5 kg/m3 Reference density Calculated density of water at 25 ◦C = 979.5 kg/m3 Actual density of water at 25 ◦C = 997.05 kg/m3[61]

3 Error in measurement = (997.05 – 979.5) kg/m · 100 = 1.76 % 997.05 kg/m3

There exists only a small error in measurement for the reference species, namely water density. Hence, the density value of 1113.5 kg/m3 can be accepted for subsequent experiments. Figure 4.18 indicate the interior conﬁguration of reaction vessel prior to the start of blank hydrogenation experiment. Based on observation, the dimension of a single sheet of catalyst basket was selected to be 6 cm x 4 cm. Two sheets in total, of the speciﬁed dimension was taken and its sides secured, to create the basket.

Weight of TOP required for a volume of 120 mL at 25 ◦C = 1113.5 kg · (120 · 10 – 6) m3 = 133.62 g m3 4.3. Hydrogenation experiments 43

Figure 4.18: Representational image of catalyst basket, prior to catalyst ﬁlling (left) and reaction vessel containing required amount of TOP sample, poured over catalyst basket (right)

Experimental procedure 1. The sample was poured over catalyst basket and reaction vessel was placed in the autoclave. The autoclave was tightened onto the support and heating jacket was locked into position.

2. The reactor was ﬂushed and then pressurized with argon gas to a pressure of 30 barg. A higher pressure than the experimental conditions were maintained, to ensure safety, even if deviations from process parameters occurred.

3. A leak check was conducted to conclude that no leaks were present. The reactor was then purged and pressurized with hydrogen gas to a pressure of 20 barg.

4. Heating sequence was started and a constant stirring rate was maintained. Reactor pressure was monitored at regular intervals and an isothermal stage of 0.5 hours was followed, upon reaching the target temperature of 250 ◦C.

5. After the reaction time, the heating was switched-oﬀ, the heating jacket lowered and the reactor was allowed to cool non-sequentially. Furthermore, the autoclave was depressurized very slowly and then ﬂushed with argon gas before opening to reveal the contents.

It was observed that even though the heater was set to follow a ramp rate of 20 ◦C/min, the eﬀective heating as received by the sample was only 0.28 ◦C/min. This is essentially due to the large chunk of metal mass that needs to be heated and its associated heat transfer resistance that comes into play. The heat supplied by the heating jacket needs to spread across the surface of the autoclave, before reaching the reaction vessel placed inside it. 44 Materials and Methods

Hence, it was decided to double the rate of heating in the further tests, to 40 ◦C/min ramp rate, which allows for a shorter experimental duration. However, the heating rate could not be increased further, due to issues with melting of the heating-coil at higher ramp rate sequences.

4.3.4 Trial on catalyst sulphidation Catalyst as received, occurs in its inactive form. Hence, it was decided to sulphide the catalyst to increase its activity for hydrogenation reaction. For this purpose, NiMo catalyst received from Nynas was used as the raw material and some pre-determined steps were followed during experimentation:

1. NiMo catalysts in their oxide form supported on alumina extrudates are dried at a temperature of 150 ◦C at a slow heating-rate to remove water trapped inside pores of catalyst.

2. The dried catalysts are taken, secured inside a catalyst basket and placed inside the reaction vessel. Furthermore, required amount (120 mL based on reactor conﬁguration) of D10 and T9 are added into the reaction vessel in 1:1 ratio. T9 is a hydrotreated product of D10 distillate. Both liquid mediums are obtained from Nynas reﬁnery.

3. The required amount of sulphiding agent (DMDS) is calculated and added into the reaction vessel, atop the liquid medium and the catalyst basket.

4. The reactor is then sealed, pressure and leak tested with argon gas upto 50 barg. Further on, hydrogen gas is introduced at a constant ﬂow rate of 100 mL/min to a pressure of 30 barg.

5. The stirrer is set to a constant speed. Heating is started and a ramp rate of 1.7 ◦C/min is maintained, to reach a target of 250 ◦C. Thereafter, an isothermal stage was maintained at 250 ◦C for 2 hours. The online article [62] mentions the end of isothermal stage as ’H2 breakthrough point’, the reason being that a signiﬁcant amount of hydrogen sulphide gas is formed at this stage of sulphiding process.

6. At the end of 2 hours isothermal heating step, the temperature is again raised to 345 ◦C at 0.8 ◦C/min ramp rate.

7. Subsequent isothermal stage has a duration of 1 hour. The heater is switched-oﬀ and the reactor is left to cool.

8. The catalyst basket is then supposed to be taken out to recover the sulphided catalyst. 4.3. Hydrogenation experiments 45

The major reactions expected during catalyst sulphiding [62] are mentioned below:

NiO2 + H2S + H2 −−→ NiS + H2O (4.14)

MoO3 + 2 H2S + H2 −−→ MoS2 + 3 H2O (4.15)

Equations 4.14 and 4.15 imply that the catalyst undergoes reaction with the produced hydrogen sulphide with excess hydrogen, to create the sulphided form of catalyst surfaces. Hydrogen sulphide gas is formed as a reaction product of the added sulphiding agent with hydrogen. In this present work, DMDS (Dimethyl Disulphide) was used as the sulphiding agent and this particular compound was selected based on a number of factors, namely [62]:

1. DMDS contains 68 wt% sulphur compared to TBPS (Tertiary-Butyl Polysulﬁde) which contains 54 wt% sulphur. TBPS is another widely used sulphiding agent. Higher sulphur content eases sulphur removal and H2S formation. 2. DMDS breaks down in a two-step process, thus reducing reactor exotherm during sulphiding. It is absolutely important to limit reaction exotherm, since an increase in temperature is mostly accompanied by increase in vapor pressure, which leads to an increase in total reactor pressure. Decomposition reactions [63] for DMDS are given below:

CH3–S–S–CH3 + H2 −−→ CH3SH + H2 −−→ CH3–S–CH3 + H2S (4.16)

CH3–S–S–CH3 + H2 −−→ CH3SH + H2 −−→ CH4 + H2S (4.17)

From ﬁgure 4.19 depicted below, it was observed that the unsulphided catalyst sample had issues with non-uniform extrudate shape and colours. After expert opinion from Nynas, it was concluded that the sample might contain mixed NiMo and CoMo catalyst, thus contributing to the green colour in the former and dark-blue colour in the latter. It was also inferred that NiMo catalyst ought to appear in shades of green, unlike the reddish colour oberved from the picture. Therefore, sulphided catalysts were provided by the courtesy of Nynas, and hence, catalyst sulphidation step was omitted in the research work. 46 Materials and Methods

Figure 4.19: Unsulphided catalyst sample. Diﬀerences in catalyst extrudate shapes can be noted, apart from its non-uniform colour.

The experimental observation from following the sulphidation procedure indicated a trend of constantly increasing pressure. The catalyst sulphiding procedure was followed, as mentioned above, however the sulphiding stage could not be completed. The primary reason is that of rapidly increasing pressure with increase of temperature. Upon comparison of catalyst sulphidation procedure from literature, it was found that most models were based on the use of a flow reactor [64][65][66]. Hence, the conclusion from the failure of catalyst sulphidation step is that, this process should ideally be conducted in a flow reactor, unlike the batch reactor setup that was currently used. The constant flow of gaseous phase reactants and achieving a more precise reactant flow control contribute to the advantages of having a flow reactor. 4.3. Hydrogenation experiments 47

4.3.5 Hydrogenation test 1 The ﬁrst hydrogenation test was conducted at lower-end of temperature range at 200 ◦C and a signiﬁcantly higher pressure of 33 bars hydrogen. Reactant/catalyst ratio was maintained at 10:1 with 120 mL of feed for 12 mL of sulphided catalyst. The poured density of sulphided catalyst was determined by Nynas to be 1130 kg/m3 and the density of TOP at room temperature was already determined to be 1113.5 kg/m3 (refer section 4.3.3). From this information, equivalent amount of catalyst and TOP needed was calculated as 13.56 g and 133.62 g respectively.

Figure 4.20: Prepared catalyst basket (left) and liquid sample poured over catalyst basket, ready to be placed inside the autoclave (right)

Figure 4.20 depicts the catalyst basket used and the liquid TOP sample. It is to be noted that the catalyst basket illustrated in ﬁgure 4.18 looks diﬀerent from the catalyst basket used for the present experiment. The reasoning behind the use of a smaller mesh size, lies in the particle size of sulphided catalyst. The particles were sieved to conclude that particle size was approximately 0.85 mm. The sulphided catalysts were secured inside the basket and stapled on the outer sides to prevent its loss into the reactant liquid.

During the blank hydrogenation test, it was observed that the heating rate was too small, which increased the total experimental duration by a large factor. Hence, it was decided to double the heating ramp rate to 40 ◦C/min to enable faster heating of the sample. The experimental procedure followed for the test, along with observations are outlined as follows: 48 Materials and Methods

1. The reaction vessel containing catalyst and reactant liquid was secured in place and a ﬂow of argon gas was allowed. The reactor was pressurized to 40 bars and leak tested. Furthermore, reactor was purged two times with argon gas, to completely remove traces of air. The heater was then hydraulically lifted into position.

2. Hydrogen gas was allowed inside the reactor through the ﬂow control valve at a rate of 100 mL/min and subsequently purged two times. This ensures that argon atmosphere inside autoclave is fully replaced with hydrogen gas.

3. The reactor was pressurized to 7 bars hydrogen pressure and then the heating was switched ON. It was calculated that an average heating rate of 0.77 ◦C/min was received by the sample when a heating ramp rate of 40 ◦C/min was given by the user.

4. The rise in reactor pressure with subsequent increase in reactor temperature, is illustrated using the figure shown below. A conclusion from figure 4.21 (top), is that a constant increase in pressure was noted, as the reactor was heated. Reduction in vapor pressure due to consumption of hydrogen for hydrogenation was not observed. Considering a linear trend of data points, the change in pressure with temperature (ΔP/ΔT) was 0.145 bar/◦C. This implies that a larger increase of pressure was noted, when compared to similar variation in temperature. This observation is also justified from figure 4.21 (bottom), which show the change in pressure ratio and temperature ratio with increasing sample temperature. 4.3. Hydrogenation experiments 49

Figure 4.21: Reactor behavior observed during hydrogenation experiment 1. For the T ratio vs P ratio plot, a temperature of 60 ◦C and its corresponding reactor pressure of 11 bars were taken as a reference for calculation

5. Upon reaching the ﬁnal temperature of 200 ◦C, an isothermal stage was added. For this purpose, adjustments were done to the controller to maintain the sample temperature very close to 200 ◦C and to avoid temperature overshoots. This was performed in order to rule out any reactions occurring at temperatures above 200 ◦C. The stirrer was switched ON, and a constant speed of rotation was set at 200 RPM. Thereafter, an isothermal batch-time of 0.5 hours was maintained.

6. Upon completion of the desired batch-time, the stirrer was switched OFF and the heater was hydraulically lowered on to the ground-level, away from the autoclave. The reactor was made to cool down to ambient air in an un-sequenced manner. The cooling stage approximately lasted for 5 hours. 50 Materials and Methods

7. When the reactor was cooled-down and the sample temperature was 25 ◦C, gas sampling bag was connected to the reactor gas outlet port and a low ﬂow rate was kept during depressurization. It is to be understood that the reactor temperature of 33 bars at 200 ◦C reduced to 5 bars at 25 ◦C. This in turn means that approximately, 1 litres of gas volume was collected in the sampling bags.

8. The reactor after complete de-pressurization, was unbolted from its place to reveal the product sample (refer ﬁgure 4.22).

Figure 4.22: Hydrogenated product from the reactor. Some amount of froth was observed on the top, primarily occurring as a result of agitation by the impeller blades and due to gases bubbled through the liquid 4.3. Hydrogenation experiments 51

Thermogravimetric analysis A carbon residue test was conducted on the hydrotreated sample twice to yield the results as mentioned below:

Residual mass (mg) 5.19 mg Carbon residue (1) = Initial mass of sample used (mg) · 100 = 176.603 mg · 100 = 2.93 %

Residual mass (mg) 4.82 mg Carbon residue (2) = Initial mass of sample used (mg) · 100 = 177.33 mg · 100 = 2.72 %

The standard deviation between the two readings amount to only 0.105. This justiﬁes the selection of carbon residue content as 2.93 %. The interesting observation is that the TOP feed prior to hydrogenation had a carbon residue value of 2.84 %. This possibly suggests the absence of hydrogenation and subsequent removal of oxygen. The extracted TG analysis curve is shown in ﬁgure 4.23.

Figure 4.23: Thermogravimetric analysis conducted to determine carbon residue content for hydrogenation test 1 52 Materials and Methods

Acid number test Acid number test was conducted similar to that of the feed mixture. The titration was repeated until consecutive values were obtained, which accounted to:

(0.7 – 0) mL · 0.5 N · 56.1 g/mol Acid number of TOP = 0.3 g sample = 65 mg KOH / g sample

Acid number for the feed sample was determined to be 50 mg KOH/g sample (refer section 4.2.2). It is not clear at this stage, as to what might have caused an increase in free acid functionality of the sample after hydrogenation. However, this agrees with the result from carbon residue content, where no signiﬁcant change was observed in the values.

Gas Chromatographic analysis As mentioned before in this section, product gases were sampled from the reactor after cooling down the autoclave to room temperature. The gases were then collected in a sampling bag and admitted to GC analysis. Gases were sampled into the column and the average value from the diﬀerent runs are taken as the measured value.

Table 4.4: Gas chromatographic analysis indicating fractions of various gaseous components, present in the reactor outlet stream

Component Content (%)

CO2 0.714 CO 0.001 CH4 0.577 C2H6 0.015 C2H4 0.003 H2 34.253 N2 7.338 Ar 55.2 Total 98.1

Table 4.4 provides some insights into the gas composition. The higher amount of CO2 with respect to CO show signs of a decarboxylation pathway of reaction. However, no water was found (as a separated layer) in the product mixture and thus, the absence of eﬀective HDO can be seen. Presence of ethane and ethylene (C2 hydrocarbons) are associated to the cracking reactions that occurred. Loss of organic carbon is observed in the form of methane also, which contributes to a lower liquid yield. 4.3. Hydrogenation experiments 53

Nitrogen might have been introduced during gas flow to the GC gas sampling port, or during the collection of gas in the gas sampling bag. Argon was used as the inert species for leak-testing and purging. The continued presence of argon in product gas, is due to the improper evacuation/purging of reactor with hydrogen before the start of the experiment. There is also a significant quantity of hydrogen present in the gas phase, which could be because of the ineffective equilibrium that was established. A lower hydrogen pressure at the start of heating stage, could have impacted the shift of reactants to product, thereby inhibiting hydrogenation reaction.

4.3.6 Hydrogenation test 2 It was concluded from the previous hydrogenation test, that improper purging could have been the reason behind partial evacuation of argon gas prior to start of experiment. Hence, it was decided to take necessary corrective action for the current experiment.

The reactor was initially leak-tested with argon. Here, it was observed that the reactor was leaking from two major locations; (1) Through the base of the thread (totally 6 in number), which secures the autoclave to the top ﬂange and (2) Throughout the circumference of the major ﬂanges. Argon was purged out to investigate the source of the leaks in detail.

Leak 1 The gas from inside of the reaction vessel was pushed out, which ultimately was flowing from the base of the thread upwards and out from the top flange. There are several reasons predicted behind this occurrence. Primarily, the sealing-ring outside the reaction vessel was unable to contain the gas. Secondly, the threads could have been damaged, which then creates minor voids through which the gas can flow.

Fixing Leak 1 It was decided to use silicone paste to provide a barrier to flow of gas. For this purpose, a required amount of paste was applied on to the sides of the thread and further on, the leak test was repeated. It was seen that the leaks from the top flange disappeared, which imply that the silicone sealant is effective. However, leak (2) was still present. It was deemed critical, to evaluate the sealing-ring at this point. 54 Materials and Methods

Leak 2 The ’sealing-ring’ mentioned here refers to the soft-metal ring positioned outside the reaction vessel. The major purpose of this ring is to create a tight gas seal, when the reactor vessel is placed inside the autoclave. A tight gas seal is necessary to contain the gas inside the reactor vessel, especially during operation at higher pressures. Any defects to this sealing-ring inhibits a proper gas seal and hence, the gas escapes to the outer periphery of the reactor to cause leaks (1) and (2).

Figure 4.24: The sealing-ring is seen inside the red boundary, outside of which, gas presence induces leak in the system

Figure 4.24 depicts the major reason predicted for leak (2). This behavior was further confirmed by tightening the threads and applying a higher torque, however, leaks were still observed. This indicates a damaged sealing-ring outside the reactor vessel or effects due to the presence of indentations on the inner surface of top flange. 4.3. Hydrogenation experiments 55

Figure 4.25 depicts the permanent change in color, appearance, texture induced to the inner flange surface after the hydrogenation test. It is seen that the surface near the sealing-ring has been affected. The exact reason behind the improper gas seal is unknown at this point. One can also see multiple points of dark coloration in the figure. It is highly possible to assume that during the test gas leaks occurred, which escaped the reactor through multiple locations, ultimately creating this dark color. Chemical solvents like 2-propanol and dichloromethane were used to clean these marks, but was unsuccessful in doing so.

Figure 4.25: A comparison of the inner ﬂange surface before (left) and after (right) conducting hydrogenation tests

A summary of figure 4.25 indicates that the viscous tall oil pitch has had an effect on the reactor surface finish. This could have occurred sometime during the high temperature, pressure operation. The start of gas leaks during the test, could have forced some gaseous products to leak out, causing color changes even at the top of the flange. Hence, a suitable conclusion for this case is to try and replace the soft metal sealing-ring outside the reaction vessel. This may ensure an effective gas-seal. However, this is a prediction and should not be taken as the final solution to this observed issue. 56 Materials and Methods

Conclusion from leak test Replacing the sealing-ring might solve the problem of gas leak, occurring through the flanges as well as through the threads. Finding a suitable solvent/treating method to clean the persisting stains on the flanges could be useful. It is known that any hard metal parts should not come in direct contact or scratch the inner flange surface. The reasoning is that, metal can produce permanent marks/scratch on the surface of flange, which can serve as a channel for gas leaks later on. Thus, care should be taken to only apply chemical solvents to remove the coloration. It was also observed that there were some existing marks on the flange surface before the start of experiments. It could have been induced during prior use of equipment. It is highly unlikely that these marks are the source of the gas leak, since they are not very prominently seen on the autoclave surface. Hence, purchasing a replacement for the sealing-ring can be considered to be the next step in preparing the reactor for running hydrogenation tests. 5 Proposal for future work

5.1 Hydrodeoxygenation experiments

After the existing leaks are ﬁxed and reactor found suitable to conduct hydrogenation experiments, the following design of experiments methodology can be followed. The aim of this experimental design is to generate necessary data points as a function of three variables, namely temperature, pressure and batch time. If time allows, one can also consider reactant : catalyst ratio as a variable to further understand the system in detail. For the immediate scenario, variables and their range of variation (ﬁxed after discussion with expert advisory from Nynas and KTH) are mentioned below.

Table 5.1: Reaction parameter limits to be followed, during the design of experiments

Variable Temperature (◦C) Pressure (barg) Batch time (h) Lower limit 250 20 0.5 Upper limit 325 50 2

Table 5.1 mentions the upper and lower limits of parameter values that could be maintained during the experimental phase. The default value of reactant : catalyst is maintained at 10 : 1. The batch time and temperature values further depend on this ratio and should be investigated in detail, after conducting the complete set of experimental runs. Table 5.2 further elaborates on the design of experiments model for hydrogenation.

57 58 Proposal for future work

Table 5.2: List of experiments to be conducted, to generate critical data points

Run No. Temperature (◦C) Pressure (barg) Batch time (h) Run 1 250 20 0.5 Run 2 250 50 0.5 Run 3 325 20 0.5 Run 4 325 50 0.5 Run 5 300 35 0.5 Run 6 250 20 1 Run 7 325 50 1 Run 8 300 35 1

The list of experiments mentioned in table 5.2 is not the complete set, and only includes the most critical ones. A complete experimental set for the limits defined in table 5.1 is practically challenging. Thus, the experimental design suggested here could be conducted to generate sufficient data that can evaluate the future possibility of scale-up of this process into an existing refinery.

Estimated time for hydrogenation runs It is also important to mention an estimated time for carrying out the experimental design. During the failed hydrogenation tests, it was noted that one test would take 2 complete working days (8 hours * 2 days = 16 hours) for completion. After the reactant is placed in the reaction vessel and mechanically tightened, it takes approximately 3 hours to carry out the leak test and hydrogen purges. Furthermore, the limitations with the heating coil only allows for a slow heating rate. Hence, it takes a complete day for leak, purge test, hydrogenation and cooling the reactor. The subsequent day is then spent for product gas collection, product transfer out from reaction vessel and cleaning of the reactor parts. The second day could also be utilized to load the next TOP feed for conducting an experiment the following day. This implies that during the 5 working days in a week, 2 runs on average could be performed. Therefore, it ideally takes 1 month for completing the experimental part of work, provided no other physical challenges arise during this period. 5.2. Characterisation and analysis of results 59

5.2 Characterisation and analysis of results

Determining basic properties of product fractions act as the next step in the process. For example, GC/MS, TG and acid number analyses ought to be conducted for each of the product fractions, to arrive at meaningful conclusions regarding the hydrodeoxygenation behavior of TOP.

Estimated time for analyses of products If a fast-paced work is carried out, an entire set of analyses could be ﬁnished in a working week or in 7 days. Going by this deﬁnition, it would take a month or more in conducting analyses for all samples from the runs.

Estimated time remaining for completion of research work Time taken for experiments + time taken for analyses = 2 months or more 6 Conclusion

An experimental feasibility study was conducted, to evaluate the potential of practically implementing hydrodeoxygenation reactions in lab-scale. The primary objective ﬁxed before the start of the research was to carry out partial-hydrogenation of high molecular weight bio-based oil feed material and derive enough data-points to identify its oxygen removal eﬃciency. However, due to time constraints, this target could not be achieved. An extensive study of the practical factors involved in hydrogenation is thus presented. The present work focused on collecting valuable information available from existing literature regarding HDO of TOP, and subsequently, experimentally collecting a range of chemical properties of this mixture.

Viscosity of the tall oil pitch was tested, to determine that the material is highly viscous in nature, with a kinematic viscosity of 112 cSt. Acid number (measure of free acid content) and saponiﬁcation number (measure of free and combined acid contents) are determined to be 50 mg KOH/g TOP and 85 - 93 KOH/g TOP respectively. Reasoning for deviations in values and strategies to eﬀectively reduce deviations are also included in the explanations. GC/MS analysis is also conducted to understand the presence of oxygen-containing species in the sample. In order to evaluate the coking and ash forming tendency of the species, carbon residue and ash tests are carried out. Carbon residue content constituted 2.88 % of the sample and ash content constituted 0.21 % of the sample. Furthermore, metal presence in TOP sample is analyzed using XRF spectroscopy. The results indicate a higher presence of sulphur species along with considerable amounts of Si, K, Ca etc.

60 61

In conclusion, this thesis work elaborates on the chemical analyses procedure and practical challenges associated with conducting laboratory sulphidation and hydrogenation reactions. A reader of this report could potentially extract the information to conduct and gather data on partial-HDO in laboratory-scale. To aid this purpose, a proposal for future work is also described, by explaining the experimental pathway to be followed. Bibliography

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