Hydrodeoxygenation of Lignin Model Compounds Over a Copper Chromite

Home , Vanillyl alcohol

Applied Catalysis A: General 447–448 (2012) 144–150

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Applied Catalysis A: General

jo urnal homepage: www.elsevier.com/locate/apcata

Hydrodeoxygenation of lignin model compounds over a copper

chromite catalyst

∗

Keenan L. Deutsch, Brent H. Shanks

Department of Chemical & Biological Engineering, Iowa State University, Ames, IA 50011, USA

a r t i c l e i n f o a b s t r a c t

Article history: The hydrodeoxygenation of benzyl alcohol, phenol, anisole, o-cresol, catechol, guaiacol, and vanillyl alco-

◦

Received 19 April 2012

hol were carried out from 150 to 275 C at 50 bar H2 with a CuCr2O4·CuO catalyst in a decalin solvent.

Received in revised form 5 September 2012

The hydroxymethyl group of benzyl alcohol was found to be highly reactive towards hydrogenolysis

Accepted 13 September 2012

to form toluene. Demethoxylation of anisole to form benzene was found to be the primary reaction

Available online 8 October 2012

pathway in contrast to demethylation and transalkylation reactions, which are more prevalent for con-

ventional hydrotreating catalysts. The hydroxyl group of phenol strongly activated the aromatic ring

Keywords:

towards hydrogenation forming cyclohexanol which was subsequently dehydrated and hydrogenated

Hydrogenolysis

Hydrodeoxygenation to form cyclohexane. Reaction networks of increasing complexity were devised for the major functional

Bio-oil upgrading

Copper chromite

1. Introduction liquid product from fast pyrolysis [6]. The lignin-derived compo-

nents of biomass are commonly used as model compounds for

The utilization of biomass to produce fuels and chemicals is a HDO because they possess the aromaticity that is important to

topic of increasing importance as petroleum prices rise and reserves maintain to minimize hydrogen consumption [2]. Furthermore,

diminish. Numerous technologies are under investigation to utilize phenolic compounds contain several oxygen functionalities includ-

the various components of biomass: cellulose, hemicellulose and ing hydroxyl groups bound to aromatic and aliphatic carbons and

lignin. A key challenge in the chemical and thermal conversion of methoxy groups that all have different HDO reaction pathways and

biomass is the reduction of oxygen content to produce fuels and susceptibilities [7].

chemicals that are compatible with conventional petroleum-based Numerous HDO studies have investigated the use of conven-

products. Hydrodeoxygenation (HDO) is a promising upgrading tional hydrotreating catalysts consisting of sulphided NiMo–Al2O3

technology that has gained considerable attention in recent years or CoMo–Al2O3 for bio-oil upgrading [8–32]. Both catalysts have

due to the high oxygen content of biomass derived feedstocks, shown to be effective at HDO, where NiMo–Al2O3 favors hydro-

especially in the context of pyrolysis oil upgrading [1–5]. Of partic- genated products and CoMo–Al2O3 favors aromatic products.

ular importance is the minimization of hydrogen consumption by However, there are several concerns with using sulphided cata-

developing catalysts that can perform HDO while minimizing the lysts in HDO such as the loss of the sulphided phase over the

hydrogenation of unsaturated phenolic and furanic species that are course of processing and the introduction of sulphur into the prod-

common in biorenewable feedstocks. uct stream [11,13,15,21,30,33,34]. Some researchers have proposed

Conventional hydrotreating processes have focused primarily co-feeding H2S to maintain the sulphided phase; however, H2S

on hydrodesulphurization (HDS) and hydrodenitrogenation (HDN) competitively adsorbs with oxygenated compounds and dispropor-

because oxygen content in crude oil is very low and does not tionally decreases the selectivity towards hydrogenolysis, which

pose the same environment issues as burning S- or N-containing lowers the production of aromatics. Coking has also been shown

fuels [1]. Many studies of HDO have focused on the phenolic com- to be a signiﬁcant issue with the conventional hydrotreating cat-

ponents of bio-oil which represent a considerable portion of the alysts, which has been attributed to the acidity of the support

[11,16,17,27,35,36].

Alternatives to the sulphided molybdenum hydrotreating cata-

lysts have been investigated in more recent years [33–46]. Noble

∗

metals have shown high activities in HDO; however, aromatic sat-

Corresponding author. Tel.: +1 515 294 1895; fax: +1 515 294 1269.

E-mail address: [email protected] (B.H. Shanks). uration is observed unless high temperatures and atmospheric

K.L. Deutsch, B.H. Shanks / Applied Catalysis A: General 447–448 (2012) 144–150 145

standard of ethanol and identiﬁed and quantiﬁed using an Agilent

GC–MS/FID equipped with a HP-5MS column. The HP-5MS col-

umn was unable to separate benzene and cyclohexane; therefore,

these two compounds were quantiﬁed by m/z values of 78 and 84

respectively.

The catalysts were recovered after reaction and dried for 24 h at

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100 C prior to analysis of coking with a Perkin Elmer Simultaneous

Thermal Analyzer (STA 6000). This analysis consisted of 5–15 mg

of dried catalyst undergoing a catalyst oxidation step followed by

a coke oxidation step under 20 mL/min of air ﬂow. A temperature

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ramp from 50 to 250 C at 10 C/min followed by a 120 min dwell

was used to completely dry and oxidize the bulk of the copper cata-

lysts, which can form passivated oxide layers on the outside of the

catalyst upon exposure to an air atmosphere. Following this step

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was a ramp from 250 to 700 C at 5 C/min in which the observed

Fig. 1. Primary reactants used for HDO (a) benzyl alcohol, (b) phenol, (c) anisole, (d)

o-cresol, (e) catechol, (f) guaiacol, (g) 2-methoxy-4-methylphenol and (h) vanillyl weight loss was attributed to the oxidation of coke. All mass bal-

alcohol. ances could be closed within 95% of the total carbon fed to the

system.

pressures are used to favor aromatic over saturated products.

Considering the challenges associated with pyrolysis oil and the 3. Results

desired scale of the technologies, a base metal catalyst may be an

appropriate alternative to conventional hydrotreating catalysts and 3.1. HDO of mono-functional phenolics

noble metal catalysts [5]. Copper mixed metal oxide catalysts are

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interesting materials for HDO because they tend to have weak acid- The HDO of phenol was performed at 200–250 C and the

ity, high hydrogenolysis activity, and low hydrogenation tendency resulting reaction proﬁles can be seen in Fig. 2. The reaction

for furanic compounds [47–51]. of phenol resulted in the hydrogenation to cyclohexanol as the

An important aspect of catalyst research is developing an under- major product. Minor products included benzene, cyclohexene

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standing of the reaction network in complex systems such as and cyclohexane. Benzene was not observed at 200 C, whereas

the HDO of diverse mono-functional and multi-functional phe- it was observed in a 1:10 and 1:20 ratio to cyclohexane at 225

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nolic species. The current work investigated the HDO of benzyl and 250 C, respectively. Cyclohexene was found at a maxima

alcohol, phenol, anisole, o-cresol, catechol, guaiacol, 2-methoxy-4- concentration of less than 1 mM during each run. Cyclohexanol

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methylphenol, and vanillyl alcohol with a copper chromite catalyst was also reacted under HDO conditions between 225 and 275 C

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from 150 to 275 C at 50 bar H2 in a decalin solvent. The primary and the evolution of cyclohexene and cyclohexane showed the

reactants used are shown in Fig. 1. Benzene, toluene, cyclohexanol, same trends as observed in the HDO of phenol. Benzene was

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∼

and methanol were also subjected to HDO conditions to understand detected at a concentration of 0.3 mM by the end of the 275 C

the stability of the primary products at high conversions. A reac- run but was not detected at any other sampling point of the reac-

tion network for copper was developed which can be contrasted to tions.

those of conventional hydrotreating catalysts (S–CoMo–Al2O3 and The product distribution of the HDO of anisole can be seen in

S–NiMo–Al2O3) and noble metal catalysts [8,42]. Fig. 3. Anisole was considerably less reactive than phenol and after

20 h of reaction had conversions of 20, 52, and 88 mol% at 225, 250,

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and 275 C, respectively. The major products included benzene,

2. Materials and methods

cyclohexane, cyclohexanol and methoxycyclohexane. Methanol

was not observed by GC. The selectivity towards benzene decreased

The following compounds were used in reaction studies or to

from 46% to 30 mol% with increasing the reaction temperature from

calibrate the mass spectrometer and ﬂame ionization detector of

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225 to 275 C.

the gas chromatograph (GC–MS/FID): phenol (Sigma 99%), anisole

As seen in Fig. 4, the reactivity of benzene was examined under

(Acros 99%), benzyl alcohol (Fisher), guaiacol (Acros 99+%), catechol

the same HDO conditions. These data demonstrated that the hydro-

(Acros 99+%), o-cresol (Acros 99%), 2-methoxy-4-methylphenol

genation of benzene contributed to the loss of selectivity towards

(Acros 99%), vanillyl alcohol (Acros 99%), benzene (EMD Chem),

benzene under these conditions. Methanol was also subjected to

toluene (Fisher ACS), cyclohexane (Fisher ACS), cyclohexanol

the same HDO conditions and was observed only in trace amounts

(Fisher reagent grade), methanol (Fisher ACS), xylenes (Fisher ACS),

at any sampling period. This result was likely caused by the vapor

methylcyclohexane (Acros 99%) and decalin (Acros 98%). The cop-

pressure exceeding the reaction pressure as methanol approached

per chromite catalyst (Acros) was used as received. The catalyst

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and became supercritical at 240 C.

contained a stoichiometric amount of CuCr2O4 and CuO. The as

2 The HDO of benzyl alcohol occurred the most readily of the

received surface area was 10.3 m /g. The physical and chemical

compounds studied. The reaction proﬁles, shown in Fig. 5, exhibit

properties of this reduced catalyst have been previously reported

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[51]. 100 mol% conversion after 20 h at 150 C. Further increasing the

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reaction temperature to 175 and 200 C achieved complete con-

Reactions were carried out in 75 mL Parr autoclave reactors

version in 5 and 2 h, respectively. In separate experiments, the

with 50 mL of reaction solution at 100 mM reactant concentra-

hydrogenation of toluene to methylcyclohexane was found to

tion, 100 mg catalyst, 50 bar H2 (UHP/Zero Linweld), 500 rpm (this

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reach 8 mol% conversion after 20 h at 225 C. Therefore, the hydro-

stirring rate was found to be outside the external mass trans-

genation of toluene to methylcyclohexane was likely negligible at

fer limited region for the reaction through examining a range

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150–175 C and may have occurred to a very minor extent at 200 C.

of stirring rates below 500 rpm), sampling at 0, 2, 5, 9, and

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The hydrogenation of toluene occurred at approximately 60% of the

20 h, and temperatures ranging from 150 to 275 C depending

rate of benzene hydrogenation.

on the reactant. Liquid samples were prepared with an external Download English Version: https://daneshyari.com/en/article/40629

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