Experimental Evaluation of Hydrotreated Vegetable Oils As Novel Feedstocks for Steam-Cracking Process

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Article Experimental Evaluation of Hydrotreated Vegetable Oils as Novel Feedstocks for Steam-Cracking Process

Adam Karaba 1,* , Jan Patera 1, Petra Dvorakova Ruskayova 1 ,Héctor de Paz Carmona 2 and Petr Zamostny 1,*

1 Department of Organic Technology, Faculty of Chemical Technology, University of Chemistry and Technology, Technicka 5, 166 28 Prague, Czech Republic; [email protected] (J.P.); [email protected] (P.D.R.) 2 ORLEN UniCRE a.s., Block 2838, 436 70 Litvínov-Záluží, Czech Republic; [email protected] * Correspondence: [email protected] (A.K.); [email protected] (P.Z.); Tel.: +420-22044-4300 (A.K.); +420-22044-4301 (P.Z.)

Abstract: Hydrotreated vegetable oils (HVOs) are currently a popular renewable energy source, frequently blended into a Diesel-fuel. In the paper, HVO potential as feedstock for the steam- cracking process was investigated, since HVOs promise high yields of monomers for producing green polymers and other chemicals. Prepared HVO samples of different oil sources were studied experimentally, using pyrolysis gas chromatography to estimate their product yields in the steam- cracking process and compare them to traditional feedstocks. At 800 ◦C, HVOs provided signiﬁcantly elevated ethylene yield, higher yield of propylene and C4 oleﬁns, and lower oil yield than both atmospheric gas oil and hydrocracked vacuum distillate used as reference traditional feedstocks. The

HVO preparation process was found to inﬂuence the distribution of steam-cracking products more than the vegetable oil used for the HVO preparation. Furthermore, pyrolysis of HVO/traditional

Citation: Karaba, A.; Patera, J.; feedstock blends was performed at different blending ratios. It provided information about the Ruskayova, P.D.; Carmona, H.d.P.; product yield dependence on blending ratio for future process design considerations. It revealed that Zamostny, P. Experimental some product yields exhibit non-linear dependence on the blending ratio, and therefore, their yields Evaluation of Hydrotreated Vegetable cannot be predicted by the simple principle of additivity. Oils as Novel Feedstocks for Steam-Cracking Process. Processes Keywords: hydrotreated vegetable oil; steam-cracking; oleﬁns production; green chemicals; 2021, 9, 1504. https://doi.org/ laboratory pyrolysis 10.3390/pr9091504

Academic Editor: Ambra Giovannelli 1. Introduction Received: 14 July 2021 Biomass is considered a renewable source of energy and automotive fuel. Among Accepted: 23 August 2021 Published: 26 August 2021 all biomass sources, vegetable oils often play a role of a pioneering feedstock because of their similarity to traditional crude-oil-based resources. Speciﬁcally, hydrotreated (or

Publisher’s Note: MDPI stays neutral hydrogenated) vegetable oils (HVOs), also called “green Diesel”, are currently popular for with regard to jurisdictional claims in use as components blended into Diesel-fuels [1,2]. Production of HVOs involves catalytic published maps and institutional affil- hydro-deoxygenation of triacylglycerols contained in vegetable oils, followed by separation iations. of water and undesired light components [1,3]. Produced HVO then typically represents a mixture of linear-chain alkanes corresponding to fatty acids comprised in form of glycerol esters in the vegetable oil. The resulting mixture has sharp hydrocarbon distribution peaking in C17–C18 fractions and contains a small amount of lighter (C12–C16) and heavier hydrocarbons (~C ) formed by side-reactions running during the process [4]. Copyright: © 2021 by the authors. 20 Licensee MDPI, Basel, Switzerland. While the exploitation of HVOs as automotive fuels is commonplace nowadays, they This article is an open access article should also be considered a potential feedstock for other processes. Since HVOs are formed distributed under the terms and predominantly by long-chain linear hydrocarbons, they promise high yields of desired conditions of the Creative Commons products in the steam-cracking process. Steam-cracking of HVOs would be an attractive Attribution (CC BY) license (https:// alternative to their common energetic use. It represents an opportunity to produce green creativecommons.org/licenses/by/ monomers and other green chemicals, specifically petrochemicals, as Kubicka et al. [5] 4.0/). indicated. Besides the hydrotreatment of vegetable oils, significant attention was paid to

Processes 2021, 9, 1504. https://doi.org/10.3390/pr9091504 https://www.mdpi.com/journal/processes Processes 2021, 9, 1504 2 of 11

hydrotreatment of oil (tar) originated from biomass pyrolysis [6–9]. Derived hydrogenate expresses similar properties as HVOs prepared from primary biomass. Other studies were aimed at catalytic cracking of oils obtained from biomass pyrolysis [10,11]. All mentioned technological pathways lead to the production of fuels, but not chemicals. Methyl-esters of vegetable oils and vegetable oil itself were studied as a potential feedstock for the steam-cracking process [12], but this pathway faces serious technical difficulties given by currently used technology, which cannot handle hydrocarbon feedstock with significant oxygen content due to the formation of carbon oxides during the cracking process. The limitation is given by the arrangement of separation parts of steam-cracking facilities, designed for low content of carbon oxides in the product stream. On the other hand, there is an obvious lack of sources studying the steam-cracking or pyrolysis of HVOs or similar materials mentioned above. There are sparse sources aimed at experimental pyrolysis of pure components, similar to those contained in HVOs. For example, Bartekova and Bajus [13] examined the thermal decomposition of n-hexadecane. However, the conversion was only in the range of 10–50%, which is not comparable to conditions in the process scale. Depeyre et al. [14] investigated n-hexadecane steam-cracking with reaction conditions varying in the wide range. In dependence on conditions, they observed 28.3–100% conversion and ethylene yield up to 48.2 wt.%. Depeyre then extended the study by the modeling of n-hexadecane pyrolysis [15]. Billaud and Freund studied the steam- cracking of a mixture containing C12–C20 alkanes, but its composition significantly differs from typical HVO [16]. However, to the best of our knowledge, there is no published study evaluating HVOs as steam-cracking feedstock, nor providing quantitative data needed for consideration before introducing HVOs as feedstock to the industrial scale. Therefore, the objective of this study is an experimental examination of HVO pyrolysis and a comparison of pyrolysis products’ distribution to traditional feedstock for the steam- cracking process. Considering the given nature of HVO (its density and boiling point), atmospheric gas oil (AGO) and hydrocracked vacuum distillate (HCVD) were chosen as traditional feedstocks for the comparison and reference purposes. This comparison should provide a quantitative evaluation of the HVOs as potential steam-cracking feedstock. Our well-established pyrolysis chromatography technique was utilized to achieve these goals. In our previous papers, the technique was established as a laboratory method suitable for studying the effect of feedstock composition on the yield of pyrolysis products, as demonstrated in the example of evaluation of Fischer-Tropsch waxes as a potential feedstock for the steam-cracking process [17]. Furthermore, the effect of light/heavy naphtha blending on its cracking products yield was examined by this technique [18]. It was also applied in a study evaluating the impact of different structural elements on the pyrolysis behavior of individual components [19]. As the technique is markedly sensitive to the feedstock composition, it is an appropriate tool for the intended evaluation. Moreover, a significant correlation was shown between experimental results from the lab-scale pyrolysis and products yields obtained in the process-scale [20].

2. Materials and Methods 2.1. Materials The samples of HVOs were prepared by the research centre ORLEN UniCRE (Litvínov, Czech Republic) in a pilot scale for HVO testing. Although the current article is focused on the HVOs utilization in the steam-cracking process, not the HVOs’ preparation, here we provide a brief description of HVOs’ origin, including characterization of vegetable oils, prepared HVOs, and hydrotreatment conditions. However, all the HVO preparation procedures were already published in the previous paper [21]. The feedstocks used for the HVOs’ preparation were rapeseed oil (RSO), sunflower oil (SFO), and used cooking oil (UCO). The UCO was supplied by a local waste manager, while SFO and RSO were food quality commercial vegetable oils (provided by ARO). Before the preparation, UCO was filtered using a standard diesel filter to remove solid impurities. Table1 shows the basic characterization of these materials. The hydrotreating of vegetable oils to produce Processes 2021, 9, 1504 3 of 11

HVOs was performed in the same unit used by the authors in previous co-hydroprocessing experiments [21]. The unit is placed in the experimental facility of ORLEN UniCRE a.s., Litvínov-Záluží, Czech Republic. The catalyst bed consisted of commercial hydrotreating sulfide catalysts (NiMo/Al2O3 and CoMo/Al2O3). To maintain the catalyst activity constant even during the long-term experiment, it was necessary to add 0.5 wt.% content of dimethyl-disulfide into the raw oils. This served as a continual sulfur source preventing catalyst from deactivation. The sulfur is then in the form of hydrogen sulfide contained in resulting HVOs, which makes the S-content in the HVOs virtually higher than the original content of sulfur in raw oils. Normally, the hydrogen sulfide would be removed from the HVOs after the reactor. Table2 shows the used operating conditions for the synthesis of HVO with different vegetable oil feedstocks. The HVO obtained at the steady-state was characterized using the same analytical techniques employed for the feedstocks and was stored for its use as a pyrolysis feedstock. The paraffin content in HVO was determined by gas chromatography with a flame ionization detector. Table3 shows the basic characteristics of the HVOs obtained from the hydrotreating of different vegetable oils.

Table 1. Basic feedstock properties.

Feedstock UCO SFO RSO Density at 1, kg/m3 918.3 920.8 920.8 Ref-index 1 1.4732 1.4750 1.4749 Acid number 2, mg/g 1.13 0.75 0.19 Br-index 2, mg/g 55,384 47,243 42,113 Elemental analysis C content, wt.% 76.9 77.6 76.2 H content, wt.% 11.7 11.7 11.7 S content, ppm 4.3 2.1 2.3 N content, ppm 22.3 4.3 2.1 Simdis 3, ◦C 10 wt.% 596.20 595.84 596.40 30 wt.% 606.06 605.17 605.90 50 wt.% 609.55 608.83 609.14 70 wt.% 611.83 611.04 611.32 90 wt.% 613.77 612.84 613.08 95 wt.% 616.17 614.76 615.28

1 Liquid density and refractive index were determined at 20 ◦C. 2 Acid number and bromine-index were determined in milligrams of reagent (KOH or Br) per gram of sample. 3 Distillation curves obtained by simulated distillation according to standards listed in the text.

Table 2. Description of reaction conditions during HVOs preparation.

◦ −1 3 3 1 Feedstock T, C LHSV, h H2:Feed, Nm /m p, MPa Catalyst HVO Sample Rapeseed oil 340 1 4150 12.5 CoMoS HRSO1 Rapeseed oil 340 1 4150 12.5 CoMoS HRSO2 Rapeseed oil 320 2 2400 5.5 NiMoS HRSO3 Sunﬂower oil 330 2 2400 5.5 NiMoS HSFO Used cooking oil 335 2 2400 5.5 NiMoS HUCO 1 Supported by Al2O3. Sample of traditional feedstock, hydrocracked vacuum distillate (HCVD), is a real sample of vacuum residue of hydrocracked vacuum distillate from the crude-oil distillation supplied by Uniperol RPA (Litvínov, Czech Republic). The second traditional feedstock, atmospheric gas oil (AGO), is a real AGO sample from primary crude-oil distillation, which underwent hydrodesulfurization and the following stabilization and was obtained from the same facility. Both samples represent the steam-cracking feedstock in the mentioned facility, where the HCVD is processed on a much larger scale than AGO. The characterization of these samples is provided in Table3. Processes 2021, 9, 1504 4 of 11

Table 3. Basic properties of traditional (HCVD and AGO) and HVOs (hydrotreated rapeseed oil HRSOx, hydrotreated sunﬂower oil HSFO and hydrotreated used cooking oil HUCO) feedstock for pyrolysis experiments.

Variable HCVD AGO HRSO1 HRSO2 HRSO3 HSFO HUCO Density 1, - 852.6 753.0 752.9 761.3 761.0 762.0 kg/m3 Ref-index 1 - 1.4759 1.4203 1.4204 1.4264 1.4263 1.4267 Acid number 2 - 0.04 0.02 0.02 0.02 0.02 0.02 Br-index 2 - 8534 - - 4486 4834 3532 Elemental C, wt.% - 86.1 85.0 84.9 84.0 85.0 85.1 H, wt.% - 13.3 15.0 15.1 15.0 14.6 15.0 S, ppm - 12000 2.5 2.5 21.8 41.0 26.3 N, ppm - 232 0.5 0.5 0.5 0.5 0.5 Simdis 3, ◦C 10 wt.% 345.1 206.1 295.6 295.8 300.4 300.0 299.7 30 wt.% 390.8 256.8 305.4 306.1 304.6 304.3 304.2 50 wt.% 419.0 289.5 310.2 311.6 310.5 315.1 308.2 70 wt.% 448.8 318.0 320.5 321.4 319.6 319.8 319.3 90 wt.% 494.3 359.7 323.1 324.3 323.4 327.6 324.9 95 wt.% 512.5 378.2 330.3 330.9 352.6 355.5 365.4 Parafﬁns n-C15, wt.% - - 2.09 2.03 2.56 2.56 3.33 n-C16, wt.% - - 2.65 2.65 2.39 2.77 3.04 n-C17, wt.% - - 36.97 36.57 47.53 43.33 47.77 n-C18, wt.% - - 42.24 42.97 41.75 44.62 41.10 1 Liquid density and refractive index were determined at 20 ◦C, 2 Acid number and bromine-index were determined in milligrams of reagent (KOH or Br) per gram of sample. 3 Distillation curves obtained by simulated distillation according to standards listed in the text.

All samples were analyzed using simulated gas chromatography distillation (SIMDIS) following ASTM D2887 for samples with a boiling point up to 520 ◦C and ASTM D6352, D7169, D1160, and D2892 for samples with a boiling point higher than 520 ◦C. Density, refractive index, and the acid number of samples were measured according to ASTM D4052, D1218, and D664. Elemental analysis was performed according to ISO 29,541 for the characterization of both vegetable oils and HVOs. The content of sulfur and nitrogen was determined according to ASTM D1552 and D5291.

2.2. Procedures All samples for pyrolysis experiments were melted and homogenized. The pure feedstock samples were used without any modification, while the blended samples were prepared by differential weighing of components into 10-mL vials with content 10, 20, 40, 60, and 80 wt.% of HVO in HCVD, or 10 wt.% of HVO in AGO. Prepared samples were maintained cold and stored until needed for experimentation. Before the experiment, prepared samples were melted and then maintained liquid at 60 ◦C in the thermostatic block. Pyrolysis experiments were performed using the laboratory pyrolysis unit (Shimadzu Pyr-4A), directly connected to two gas chromatographic units (Shimadzu GC-17A) for the separation of products on the system of switched columns and detection on flame ionization detectors. The pyrolysis reactor is a straight quartz plug-flow reactor 18 cm long, 2.9 mm in diameter, filled by SiC, placed in an electrical furnace. A control system limits the peak of the parabolic temperature profile. The apparatus allows quantitative determination of all pyrolysis products C1–C6 individually, the most important products C7–C10 and the rest of the reaction mixture forming the oil C11+. The method was explained in deep detail and validated on pyrolysis data in our former paper [19]. Furthermore, the reproducibility and accuracy of the experimental technique were determined on an extensive dataset obtained from naphtha pyrolysis experiments [22]. Processes 2021, 9, 1504 5 of 11

The reactor was operated under 400 kPa and 800 ◦C with a 65 NmL/min carrier-gas flow (nitrogen). Residence time at the hot zone is 0.35 s under these conditions [18,23]. These conditions were selected as the standard conditions on the apparatus, allowing the comparison of obtained results with an extensive database of already measured data. Samples were fed as a liquid into the reactor in the amount of 0.2 µL by micro-syringe. The injected sample is vaporized and passes through the reactor (plug flow) as an undiluted pulse of the reaction mixture. Pyrolysis products are then carried into the analytical system in the flow of carrier gas (nitrogen), where their separation occurs as well as a final determination on detectors. Our results report the composition of product stream as products mass fractions, which are referred to as process yields (Y). Notably, this definition of yields may differ from the traditional chemical engineering one; it is widely used in papers related to steam-cracking process. Since experiments were repeated (3×), we report ranges of product yields in plots. These ranges shown as error bars represent the minimum-maximum range of the displayed variable obtained from experiments.

3. Results The summary and discussion of experimental results obtained during the study are divided into two sections. At ﬁrst, the results of pure feedstocks pyrolysis are presented, and the desired comparison of HVOs to traditional feedstocks is performed. Presented results are discussed in the context of other experimental work with similar feedstock at the end of the ﬁrst part. In the next part, results obtained in experiments with the blended feedstocks are presented and discussed. Data obtained from pyrolysis experiments as the composition of product stream are shown and discussed as yields of individual products; error bars represent range min-max from repeated experiments.

3.1. Pure Feedstocks Pyrolysis Here we report the analysis of experimental data to evaluate HVOs as a potential feedstock for the steam-cracking process compared to traditional feedstocks, HCVD, and AGO. The most important products are ethylene and propylene, followed by desired C4 fraction and benzene, in the steam-cracking process. On the contrary, pyrolysis oil is generally not desired product [24]. A simple comparison of the main pyrolysis products yield is provided in Figure1. The experiments were carried out under constant reaction conditions with all the studied feedstocks. The pyrolysis of HVOs provided a remarkably elevated yield of ethylene (39.9–45.6 wt.%) compared to both traditional feedstocks, HCVD (30.0 wt.%) and AGO (19.8 wt.%), at reaction temperature 800 ◦C. HVOs also provided a significantly higher yield of propylene (18.7–19.2 wt.%) than HCVD (15.3 wt.%) and AGO (11.3 wt.%), and a higher yield of C4 fraction (15.2–18.2 wt.%) than ones obtained of HCVD and AGO (14.9 wt.% and 8.3 wt.%). Moreover, the pyrolysis oil yield was significantly lower in all cases of HVOs (1.5–3.6 wt.%) compared to both HCVD and AGO (9.7 and 28.1 wt.%). On the other hand, the yield of benzene obtained from HVOs (1.3–3.4 wt.%) is lower than that of HCVD (3.9 wt.%) and approximately comparable to AGO (2.7 wt.%). Besides the decreased yield of benzene, all trends mentioned above are beneficial. The differences in the HVOs’ composition (see Table3) are not large enough to expect any significant difference in their pyrolysis behavior, but the yields are surprisingly different. As evident from Figure1, HRSO1 provided higher yields of ethylene and C4 fraction and a lower yield of benzene than all remaining HVO samples. Both HRSO1 and HRSO2 samples were obtained from rapeseed oil during the same long-term experiment of HVO preparation and under the same conditions. The HRSO2 sample was collected after the preparation process safely achieved steady-state, but the sample HRSO1 was collected much later. This fact is the only known difference between these two samples. We assume that catalyst deactivation influenced the preparation process and consequently caused these two samples to differ in composition. Despite no significant difference analytically determined in these two samples’ composition, they still can differ in the part of mass “invisible” for the performed analytical techniques, namely, non-linear alkanes. ProcessesProcessesProcesses 2021 20212021,, , ,9 99,, , ,x x xx FOR FOR FORFOR PEER PEER PEERPEER REVIEW REVIEW REVIEWREVIEW 666 ofofof 111111

different.different.different. As AsAs evident evidentevident from fromfrom Figure FigureFigure 1, 1,1, HRSO1 HRSO1HRSO1 provided providedprovided higher higherhigher yields yieldsyields of ofof ethylene ethyleneethylene and andand C4 C4C4 fractionfractionfractionfraction andand andand aa aa lowerlower lowerlower yieldyield yieldyield ofof ofof benzenebenzene benzenebenzene thanthan thanthan allall allall remainingremaining remainingremaining HVOHVO HVOHVO samples.samples. samples.samples. BothBoth BothBoth HRSO1HRSO1 HRSO1HRSO1 andand andand HRSO2HRSO2HRSO2 samples samplessamples were werewere obtained obtainedobtained from fromfrom rapeseed rapeseedrapeseed oil oiloil during duringduring the thethe same samesame long-term long-termlong-term experiment experimentexperiment ofofof HVO HVOHVO preparation preparationpreparation and andand under underunder the thethe same samesame conditions. conditions.conditions. The TheThe HRSO2 HRSO2HRSO2 sample samplesample was waswas collected collectedcollected afterafterafter the thethe preparation preparationpreparation process processprocess safely safelysafely achieved achievedachieved steady-state, steady-state, steady-state,steady-state, but but butbut the the thethe sample sample samplesample HRSO1 HRSO1 HRSO1HRSO1 was was waswas col- col- col-col- lectedlectedlectedlected muchmuch muchmuch later.later. later.later. ThisThis ThisThis factfact factfact isis isis thethe thethe onlyonly onlyonly known knownknown difference differencedifference between betweenbetween these thesethese two twotwo samples. samples.samples. We WeWe assumeassumeassume that thatthat catalyst catalystcatalyst deactivation deactivationdeactivation influenced influencedinfluenced the thethe preparation preparationpreparation process processprocess and andand consequently consequentlyconsequently Processes 2021, 9, 1504 6 of 11 causedcausedcaused these thesethese two twotwo samples samplessamples to toto differ differdiffer in inin composition. composition.composition. Despite DespiteDespite no nono significant significantsignificant difference differencedifference ana- ana-ana- lyticallylyticallylyticallylytically determineddetermined determineddetermined inin inin thesethese thesethese twotwo twotwo samples’samples’ samples’samples’ composition,composition, composition,composition, theythey theythey stillstill stillstill cancan cancan differdiffer differdiffer inin inin thethe thethe partpart partpart ofof ofof massmassmass “invisible” “invisible”“invisible” for forfor the thethe performed performedperformed analytical analyticalanalytical techniques,techniques, techniques,techniques, namely,namely, namely,namely, non-non- non-non-linearlinearlinearlinear alkanes. alkanes. alkanes.alkanes. TheThe TheThe relativelyTherelativelyrelatively relatively many manymany many differences differencesdifferences differences between betweenbetween between studied studiedstudied studied samples samplessamples samples also alsoalso document documentdocument also document the thethe merit meritmerit the of ofofmerit the thethe py- py-py- of rolysisrolysistherolysis pyrolysis chromatographychromatographychromatography chromatography techniquetechniquetechnique technique utilizationutilizationutilization utilization tototo characterizecharacterizecharacterize to characterize thethethe samples,samples,samples, the samples, asasas thisthisthis as tech-tech-tech- this niqueniquetechniquenique can cancan reveal canrevealreveal reveal the thethe thedifferences differencesdifferences differences that thatthat that would wouldwould would be bebe be normally normallynormallynormally normally difficult difficultdifficultdifficult difﬁcult to tototo to detect detectdetectdetect detect by byby by standard standardstandard standard analyticalanalyticalanalytical techniques.techniques. techniques. TheTheThe nextnextnext interestinginteresting interesting factfact fact isis is thatthat that the thethe HUCO HUCOHUCO sample samplesample provided providedprovidedprovided the thethethe lowestlowestlowestlowest yieldyield yield yield ofof of of ethyleneethylene ethyleneethylene ofof ofof allall allall HVOsHVOs HVOsHVOsHVOs samplesample samplessamplesamplesss and andand a aa lower lowerlowerlower yield yieldyieldyield of ofofof C4 C4C4C4 fractionfractionfraction comparedcomparedcompared totototo HRSO1 HRSO1 HRSO1HRSO1 and and andandand HRSO2. HRSO2. HRSO2.HRSO2.HRSO2. All All AllAll remaining remaining remainingremaining differences differences differencesdifferences between between betweenbetween HVOs HVOs HVOsHVOs can can cancan be be bebe considered consideredconsideredconsidered not notnotnot significant.significant.signiﬁcant.significant. We We We believe believebelievebelieve the thethethe explanation explanationexplanationexplanation above aboveaboveabove is isisis valid validvalid also alsoalso for forfor those thosethose two twotwo samples. samples.samples.

505050

404040

303030

202020 Y(Product), wt. % wt. % wt.Y(Product), Y(Product), Y(Product), wt. % wt. Y(Product), % wt. Y(Product), Y(Product), wt. % wt. Y(Product), Y(Product), wt. % wt. Y(Product),

101010

000 HCVDHCVDHCVD AGO AGO AGO HRSO1 HRSO1 HRSO1 HRSO2 HRSO2 HRSO2 HRSO3 HRSO3 HRSO3 HSFO HSFO HSFO HUCO HUCO HUCO FeedstocksFeedstocksFeedstocks FigureFigureFigure 1. 1.1. Yields YieldsYields of ofof main mainmain pyrolysis pyrolysispyrolysis products: products:products: ■ ■■ ethylene,ethylene, ethylene,ethylene, ■ ■■ propylene,propylene, propylene,propylene, ■ ■■ C4C4 C4C4 fraction,fraction, fraction,fraction, ■ ■■ benzenebenzene benzenebenzene andand andand ■■■ oiloil oiloil obtainedobtained obtainedobtained fromfrom from from purepure purepure feedstockfeedstock feedstockfeedstock pyrolysispyrolysis pyrolysispyrolysis underunder underunder constant constantconstant reaction reactionreaction conditions conditionsconditions (400 (400(400 kPa, kPa,kPa, 800 800800 °C, ◦°C,°C,C, 656565 NmL/min). NmL/min).NmL/min).

TheTheThe pyrolysis pyrolysis pyrolysis behavior behavior behavior of of of HVOs HVOs HVOs has has has not not not been been been studied studied studied prior prior prior to to to our our our study. study. study. Therefore, Therefore, Therefore, wewewe decided decideddecided to toto extend extendextend our ourour study studystudy of ofof its itsits behavior behaviorbehaviorbehavior by byby analyzing analyzinganalyzinganalyzing yields yieldsyields sensitivity sensitivitysensitivity to toto reaction reactionreaction temperature.temperature.temperature.temperature. Here HereHereHere we wewe we demonstrate demonstratedemonstrate demonstratedemonstrate the thethe the temp temptemp temperaturetemperatureeratureerature dependency dependency of of of pyrolysis pyrolysis products’ products’ products’ yieldyieldyield on on on the the the example exampleexample of ofof of HRSO1. HRSO1.HRSO1. HRSO1. The TheThe The behavior behaviorbehavior behavior of ofof ofremaining remainingremaining remaining HVOs HVOsHVOs HVOs in inin dependence dependence independence dependence on onon re- onre-re- actionactionreactionaction temperature temperaturetemperature temperature was waswas was similar. similar.similar. similar. In InIn In Figure FigureFigure Figure 2, 2,2,2 , thethe the the yieldyield yield yield ofof of of thethe thethe selectedselected selectedselectedselected productsproducts productsproducts of of ofof HRSO1HRSO1 HRSO1HRSO1 obtainedobtainedobtained under under under various variousvarious reaction reactionreaction temperature temperaturetemperature isis isis shown,shown, shown,shown, while while whilewhile all all allall other otherotherother variables variablesvariablesvariables remain remainremainremain constant.constant.constant. As AsAs As it itit itis isis isclearly clearlyclearly clearly visi visivisi visible,ble,ble,ble, the thethe the yield yieldyield yield of ofof light lightlight of light products productsproducts products increasesincreases increasesincreases increases withwith withwith with increasingincreasing increasingincreasing increasing tem-tem- tem-temperature,perature,temperature,perature, and andand and this thisthis this increase increaseincrease increase is isis approximately approximately isapproximately approximately convex convexconvex convex in inin in the thethe the case casecase case of ofof of ethylene. ethylene.ethylene. ethylene. In InIn contrast, contrast, the increase of methane, propylene, and butadiene is concave at higher temperatures. thethethethe increaseincreaseincreaseincrease ofofofof methane,methane,methane,methane, propylene,propylene,propylene,propylene, andandandand bubububutadienetadienetadienetadiene isisisis concaveconcaveconcaveconcave atatatat higherhigherhigherhigher temperatures.temperatures.temperatures.temperatures. Therefore, we can estimate that these products approached maximum. It testifies that the Therefore,Therefore,Therefore, we wewe can cancan estimate estimateestimate that thatthat these thesethese products productsproducts approachedapproached approachedapproached maximum.maximum. maximum.maximum. ItIt ItIt testifiestestifies testifiestestifies thatthat thatthat thethe thethe reaction temperature is approximately optimal, and with more increased temperature (or reactionreactionreaction temperature temperaturetemperature is isis approximately approximatelyapproximately optimal, optimal,optimal, and andand with withwith more moremore increased increasedincreased temperature temperaturetemperature (or (or(or residence time), HVO would become “overcracked”. residenceresidenceresidence time), time),time), HVO HVOHVO would wouldwould become becomebecome “overcracked”. “overcracked”.“overcracked”. Based on data obtained during the products’ chromatographic analysis and the BasedBasedBased on onon data datadata obtained obtainedobtained during duringduring the thethe produc producproducts’ts’ts’ts’ chromatographicchromatographic chromatographicchromatographic analysisanalysis analysisanalysis andand andand thethe thethe rec-rec- rec-rec- recorded chromatograms, we confirm that peaks belonging to main components of HVOs ordedordedorded chromatograms, chromatograms,chromatograms, we wewe confirm confirmconfirm that thatthat peaks peakspeaks belonging belongingbelonging to toto main mainmain components componentscomponents of ofof HVOs HVOsHVOs (n-paraffins) were visible on the FID detecting oil fraction when the sample underwent low- temperature experiments (725–700 ◦C). Therefore, non-converted HVOs are just included in the oil fraction of products. But at 800 ◦C, these peaks disappeared in the mixture of pyrolysis oil, which indicates that the conversion of HVO is approaching total conversion at 800 ◦C. As stated in the introductory section, we did not find any source focused on the experimental investigation of HVO pyrolysis. However, Depeyre et al. [14] investigated the pyrolysis of n-hexadecane, which is structurally similar to C17–C18 paraffins contained in HVOs. When Depeyre approached the total conversion of n-hexadecane (95–100%) at temperatures 750–800 ◦C, ethylene yield varied in the range 41.3–47.6 wt.% depending on dilution of feedstock by steam, and therefore with varying residence time (0.6–1.0 s). Processes 2021, 9, 1504 7 of 11

This ethylene yield approximately ﬁts our data. In the middle of this conditions sub- ProcessesProcessesProcessesProcesses 2021 2021 20212021,,, , , ,9 9 99,,, , , ,x x x xxx FOR FOR FOR FORFORFOR PEER PEER PEER PEERPEERPEER REVIEW REVIEW REVIEW REVIEWREVIEWREVIEW 7777 ofofofof 11111111 range, under total conversion, Depeyre observed yields ~43 wt.% of ethylene, ~12 wt.% of propylene, ~2.5 wt.% of benzene, and ~6 wt.% of C4 fraction that approximately agree with our results. This provides partial validation of our data, even though they were obtained by(n-paraffins)(n-paraffins)(n-paraffins)(n-paraffins) experimentation were werewerewere visible visiblevisiblevisible with only on ononon the thethe similarthe FID FIDFIDFID feedstock,detect detectdetectdetectinginginging oil oil onoiloil fraction fractionsigniﬁcantlyfractionfraction when whenwhenwhen different the thethethe sample samplesamplesample equipment, underwent underwentunderwentunderwent but underlow-temperaturelow-temperaturelow-temperaturelow-temperature comparable experiments experimentsexperimentsexperiments feedstock conversion (725–700 (725–700(725–700(725–700 and°C). °C).°C).°C). with Th ThThTherefore,erefore,erefore,erefore, similar non-converted non-convertednon-convertednon-converted ethylene yield. HVOs HVOsHVOsHVOs Another are areareare support just justjustjust inin-in-in- cancludedcludedcludedcluded be in takenin inin the the thethe oil oil oil fromoil fraction fraction fractionfraction Billaud of of ofof products. products. products.products. and Freund But But ButBut at[ at at16at 800 800 800].800 They °C, °C, °C,°C, these these thesethese cracked peaks peaks peakspeaks a disappeared disappeared disappeareddisappeared C12–C20 alkanes in in inin the the thethe mixture, mixture mixture mixturemixture atofofofof pyrolysiswhich pyrolysispyrolysispyrolysis C14 oil, oil,oil,–Coil, 17 which whichwhichwhichformed indicates indicatesindicatesindicates 89%, that andthatthatthat the theythethethe conversion conversionconversionconversion obtained 42.4of ofofof HVO HVOHVOHVO wt.% is isisis approachingof approachingapproachingapproaching ethylene, 18.4 total totaltotaltotal wt.% conver- conver-conver-conver- of ◦ propylene,sionsionsionsion atat atat 800800 800800 °C.16.8°C. °C.°C. wt.% of C4 faction, 1.8 wt.% of benzene, and ~1 wt.% of oil at 780 C.

90909090

80808080 70707070 60606060 50505050 40404040 30 Y(Product), wt. % wt. Y(Product), 30303030 Y(Product), wt. % wt. Y(Product), Y(Product), wt. % wt. Y(Product), % wt. Y(Product), Y(Product), wt. % wt. Y(Product), % wt. Y(Product), 20202020 10101010 0000 MethaneMethaneMethaneMethane Ethylene Ethylene Ethylene Ethylene Propylene Propylene Propylene Propylene 1-butene 1-butene 1-butene 1-butene Butadiene Butadiene Butadiene Butadiene Benzene Benzene Benzene Benzene Oil Oil Oil Oil (C11+) (C11+)(C11+)(C11+) Products ProductsProductsProductsProducts FigureFigureFigureFigure 2. 2. 2.2. SelectedSelected SelectedSelected productsproducts productsproducts yield yield yieldyield of of ofof HRSO1 HRSO1HRSO1 HRSO1HRSO1 pure purepure purepure feedstock ff feedstockfeedstockeedstockeedstock pyrolyzed pyrolyzedpyrolyzed pyrolyzedpyrolyzed under underunder underunder 400 400400 400400 kPa, kPa,kPa, kPa,kPa, 65 6565 6565 NmL/min NmL/minNmL/min NmL/minNmL/min andandandand variousvarious variousvarious temperature: temperature: temperature:temperature: ■■ ■■ 700 700700 700700700 °C,◦ °C,°C, °C,°C,°C,C, ■ ■ ■■ 725 725725 725725725 °C, °C,°C,◦ °C,°C,°C,C, ■ ■ ■■ 750 750750 750750750 °C, °C,°C, °C,◦°C,°C,C, ■ ■ ■■ 775 775775 775775775 °C, °C,°C, °C,°C,◦°C,C, and andand andand and ■ ■ ■■ 800 800800 800800800 °C. °C.°C. °C.°C.°C.◦C.

3.2. BlendedAsAsAsAs stated statedstatedstated Feedstocks in ininin the thethethe introductory introductoryintroductory Pyrolysisintroductory section, section,section,section, we wewewe did diddiddid not notnotnot find findfindfind any anyanyany source sourcesourcesource focused focusedfocusedfocused on ononon the thethethe ex- ex-ex-ex- perimentalperimentalperimentalperimentalIt is expected investigationinvestigation investigationinvestigation that for ofof of pilotof HVOHVO HVOHVO testing pyrolysis.pyrolysis. pyrolysis.pyrolysis. or process-scale However,However, However,However, experiments, DepeyreDepeyre DepeyreDepeyre etet etet al.al. al.al. an [14][14] [14][14] industrial investigatedinvestigated investigatedinvestigated producer thethe thethe cannotpyrolysispyrolysispyrolysispyrolysis allocate of ofofof n-hexadecane, n-hexadecane,n-hexadecane,n-hexadecane, the full capacity which whichwhichwhich of is theisisis structurally structurallystructurallystructurally steam-cracker similar similarsimilarsimilar (typically to tototo C CCC17171717–C–C–C 20–30–C18181818 paraffinsparaffins paraffinsparaffinsparaffins t/h), or containedcontained suchcontainedcontainedcontained a large inin ininin sourceHVOs.HVOs.HVOs.HVOs. of WhenWhenWhenWhen HVO DepeyreDepeyreDepeyre mayDepeyre not beapproachedapproachedapproachedapproached available. theTherefore,thethethe totaltotaltotaltotal cocococo wenversionnversionnversionnversion decided ofofofof to n-hexadecanen-hexadecanen-hexadecane investigaten-hexadecane the (95–100%)(95–100%)(95–100%)(95–100%) pyrolysis of atatatat blendstemperaturestemperaturestemperaturestemperatures containing 750–800750–800 750–800750–800 HVO °C,°C, °C,°C, blended ethyleethyle ethyleethylenene intonene yieldyield yieldyield HCVD variedvaried variedvaried or AGO inin inin thethe thethe on rangerange rangerange selected 41.3–47.641.3–47.6 41.3–47.641.3–47.6 examples. wt.%wt.% wt.%wt.% It dependingdepending dependingdepending will provide onon onon adilutiondilutiondilutiondilution quantitative ofof ofof feedstockfeedstock feedstockfeedstock evaluation byby byby steam,steam, steam,steam, of blends andand andand as thereforetherefore thereforetherefore the input withwith withwith material varyingvarying varyingvarying for residenceresidence residenceresidence the steam-cracking timetime timetime (0.6–1.0(0.6–1.0 (0.6–1.0(0.6–1.0 process. s).s). s).s). ThisThis ThisThis ethyleneethyleneethyleneethyleneWith yield yieldyieldyield respect approximately approximatelyapproximatelyapproximately to previously fits fitsfitsfits presented our ourourour data. data.data.data. results, In InInIn the thethethethe HRSO1 middle middlemiddlemiddlemiddle and of ofofofof this thisthisthisthis HRSO2 conditions conditionsconditionsconditionsconditions were selected sub-range, sub-range,sub-range,sub-range,sub-range, as exampleunderunderunderunder total totaltotaltotal feedstocks conversion, conversion,conversion,conversion, due to Depeyre DepeyreDepeyreDepeyre their high observed observedobservedobserved yield of yiel yielyiel lightyieldsdsdsds products ~43 ~43~43~43 wt.% wt.%wt.%wt.% and of ofofof ethylene, theethylene,ethylene,ethylene, availability ~12 ~12~12~12 wt.% wt.%wt.%wt.% of rapeseed of ofofof pro- pro-pro-pro- oil.pylene,pylene,pylene,pylene, HCVD ~2.5 ~2.5~2.5~2.5 was wt.% wt.%wt.%wt.% selected of ofofof benzene, benzene,benzene,benzene, as a traditional and andandand ~6 ~6~6~6 wt.% wt.%wt.%wt.% feedstock of ofofof C4 C4C4C4 due fraction fractionfractionfraction to its that thatthat commonthat approximately approximatelyapproximatelyapproximately use by our agree agreeagreeagree industrial with withwithwith partner.ourourourour results. results.results.results. In Figure This ThisThisThis provides provides2providesprovides, there are partial partialpartialpartial yields validation validationvalidationvalidation of main products of ofofof our ourourour data, data,data,data, shown even eveneveneven in though dependencethoughthoughthough they theytheythey on were werewerewere the obtained obtainedobtained contentobtained ofbybybyby HVO experimentationexperimentation experimentationexperimentation (HRSO1 or HRSO2) withwith withwith onlyonly onlyonly in similarsimilar thesimilarsimilar blend feedstock,feedstock, feedstock,feedstock, with HCVD. onon onon significantlysignificantly significantlysignificantly The results different weredifferentdifferentdifferent obtained equipment,equipment, equipment,equipment, under butthebut butbut constantunderunderunderunder comparable comparable comparablecomparable reaction conditions. feedstock feedstock feedstockfeedstock conversion Theconversion conversionconversion dependence and and andand wi wi wiwi overthththth similar similar similarsimilar the whole ethylene ethylene ethyleneethylene blending yield. yield. yield.yield. ratio Another Another AnotherAnother clearly support support supportsupport shows general trends: yield of light oleﬁns (ethylene, propylene and C4 fraction) increases with cancancancan be bebebe taken takentakentaken from fromfromfrom Billaud BillaudBillaudBillaud and andandand Freund FreundFreundFreund [16]. [16].[16].[16]. They TheyTheyThey cracked crackedcrackedcracked a aaa C CCC12121212–C–C–C–C20202020 alkanes alkanesalkanesalkanesalkanes mixture, mixture,mixture,mixture,mixture, at atatatat the increasing content of HVO in the feedstock, and the yield of oil signiﬁcantly decreased whichwhichwhichwhich CC CC14141414–C–C–C–C17171717 formed formed formedformedformed 89%, 89%, 89%,89%,89%, and and andandand they they theytheythey obtained obtained obtainedobtainedobtained 42.4 42.4 42.442.442.4 wt wt wtwtwt.%.%.%.%.% of of ofofof ethylene, ethylene, ethylene,ethylene,ethylene, 18.4 18.4 18.418.418.4 wt.% wt.% wt.%wt.%wt.% of of ofofof propyl- propyl- propyl-propyl-propyl- over the blending ratio. ene,ene,ene,ene, 16.816.8 16.816.8 wt.%wt.% wt.%wt.% ofof ofof C4C4 C4C4 faction,faction, faction,faction, 1.81.8 1.81.8 wt.%wt.% wt.%wt.% ofof ofof benzene, benzene, benzene,benzene,benzene, and and andandand ~1 ~1 ~1~1~1 wt.% wt.% wt.%wt.%wt.% of of ofofof oil oil oiloiloil at at atatat 780 780 780780780 °C. °C. °C.°C.°C. While previously commented trends seem to be approximately linear, benzene yield ex- pressed3.2.3.2.3.2.3.2. BlendedBlended BlendedBlended an interesting FeedstocksFeedstocks FeedstocksFeedstocks trend: PyrolysisPyrolysis PyrolysisPyrolysis starting from the 3.9 wt.% (for pure HCVD), a maximum >5 wt.% of benzene was achieved around content ~20 wt.% of HVO in the blend, and then decreased It is expected that for pilot testing or process-scale experiments, an industrial pro- againItItItIt with is isisis expected expectedexpectedexpected highercontent that thatthatthat for forforfor of pilot pilotpilotpilot HVO testing testingtestingtesting in the or or feedstockoror pr prprprocess-scaleocess-scaleocess-scaleocess-scale to final experiments, experiments,experiments,experiments, benzene yield an ananan for industrial industrialindustrialindustrial pure HRSO1 pro- pro-pro-producer cannot allocate the full capacity of the steam-cracker (typically 20–30 t/h), or such a orducerducerducerducer HRSO2 cannotcannot cannotcannot (2.1 allocateallocate allocateallocate or 3.1 thewt.%,the thethe fullfull fullfull resp.). capacitycapacity capacitycapacity This ofof ofof thecouldthe thethe steam-cracker steam-crackersteam-crackersteam-cracker be caused by (typically(typically (typically(typically the fact 20–3020–30 that20–3020–30 both t/h),t/h), t/h),t/h), feedstock oror oror suchsuch suchsuch aa aa large source of HVO may not be available. Therefore, we decided to investigate the pyrol- componentslargelargelargelarge sourcesource sourcesource produce ofof ofof HVO HVO HVOHVO maybenzene,may maymay notnot notnot bebe be butbe available. available. available.available. through different Therefore,Therefore, Therefore,Therefore, mechanisms, we we wewe decideddecided decideddecided and toto toto investigateinvestigate investigateinvestigate therefore in thethe thethe different pyrol-pyrol- pyrol-pyrolysis of blends containing HVO blended into HCVD or AGO on selected examples. It will quantities.ysisysisysisysis of ofofof blends blendsblendsblends HCVD containing containingcontainingcontaining contains HV HVHVHV substitutedOOOO blended blendedblendedblended saturated into intointointo HCVD HCVDHCVDHCVD cyclic or ororor AGO AGOandAGOAGO polycyclic on ononon selected selectedselectedselected hydrocarbons, examples. examples.examples.examples. It ItItIt and will willwillwill provide a quantitative evaluation of blends as the input material for the steam-cracking theseprovideprovideprovideprovide provide a aaa quantitative quantitativequantitativequantitative benzene by evaluation evaluationevaluationevaluation dealkylation. of ofofof blends blendsblendsblends At the as asasas same the thethethe input inputinputinput time HVOmaterial materialmaterialmaterial can for forfor formfor the thethethe the steam-cracking steam-crackingsteam-crackingsteam-cracking benzene as a process. secondaryprocess.process.process.process. product from ethylene and butadiene, which are both formed with high yields WithWithWithWith respect respectrespectrespect to tototo previously previouslypreviouslypreviously presented presentedpresentedpresented resu resuresuresults,lts,lts,lts, HRSO1 HRSO1HRSO1HRSO1 and andandand HRSO2 HRSO2HRSO2HRSO2 were werewerewere selected selectedselectedselected as asasas exampleexampleexampleexample feedstocks feedstocksfeedstocksfeedstocks due dueduedue to tototo their theirtheirtheir high highhighhigh yield yieldyieldyield of ofofof light light lightlightlight productsproducts productsproductsproducts andand andandand thethe thethethe availabilityavailability availabilityavailabilityavailability of of ofofof rape-rape- rape-rape-rape- seedseedseedseed oil. oil.oil.oil. HCVD HCVDHCVDHCVD was waswaswas selected selectedselectedselected as asasas a aaa traditional traditionaltraditionaltraditional feedstock feedstockfeedstockfeedstock due dueduedue to tototo its itsitsits common commoncommoncommon use useuseuse by bybyby our ourourour inin-in-in- dustrialdustrialdustrialdustrial partner. partner.partner.partner. In InInIn Figure FigureFigureFigure 2, 2,2,2, there theretherethere are areareare yiel yielyielyieldsdsdsds of ofofof main mainmainmain products productsproductsproducts shown shownshownshown in ininin dependence dependencedependencedependence on ononon

Processes 2021, 9, 1504 8 of 11

from HVO. It can be hypothesized that around 20 wt.% of HVOs, the feedstock composition is suitable for benzene formation with maximal yield from both components present in the feedstock under these conditions. Even the 10 wt.% content of both HVOs in the feedstock slightly improved the yield of the main products, as visible in Figure3. In Table4, there are listed yields of products from experiments done under constant conditions for both pure traditional feedstocks, all pure HVOs followed by mixtures containing 10 wt.% of HRSO1 or HRSO2 blended in HCVD or AGO. In contrast to the already presented results, Table4 provides products distribution in full detail. For example, it was already discussed that HVOs generally provided a high yield of C4 fraction, which is one of the desired side-products of the steam-cracking process. The most desired components of C4 fractions are butadiene and 1-butene. According to the data in Table4, summed content of 1-butene and butadiene is 14.3–17.0 wt.% for HVOs, while only 12.6 wt.% and 6.6 wt.% for HCVD and AGO. Therefore, the C4 fraction obtained of HVOs in more significant amounts is more valuable than that of HCVD and AGO. It is also visible that the benzene yield obtained from 10% blends (4.1–4.7 wt.%) is higher than benzene yield obtained from pure HVOs (1.3–3.4 wt.%) as well as both traditional feedstock HCVD and AGO (3.9 and 2.7 wt.%). Detailed composition table also provides yields of toluene, xylenes, styrene, and naphthalene. Toluene, xylenes, and styrene are usually not isolated as steam-cracking products, but rather they are reprocessed by hydrodealkylation to benzene (or by a similar process), which finally leads to their beneficial use. From this perspective, it would also be beneficial to process HCVD or AGO feedstock with only 10 wt.% content of HVO, since these mixtures provided a higher yield of ethylene, ProcessesProcessesProcessesProcessesProcesses 2021 20212021 2021 2021 2021,, , 9 9,9 ,,9 , ,x 9x, x 9 , xFOR FOR,FORx FORx FOR FOR PEER PEERPEER PEER PEER PEER REVIEW REVIEWREVIEW REVIEW REVIEW REVIEW 999 9 of9of of9 of of 11of11 11 11 11 11 propylene, and C4 fraction than HCVD or AGO, but also elevated yield of benzene, and elevated or equal summary yield of toluene, xylenes, and styrene.

505050505050 202020202020

454545454545 161616161616 404040404040

121212121212 353535353535

303030303030 888888 Y(product),% wt. Y(product), % wt. Y(product),% wt. Y(product),% wt. Y(product), % wt. Y(product), % wt. Y(product),% wt. Y(product), % wt. Y(product),% wt. Y(product), % wt. Y(product),% wt. Y(product), % wt. 252525252525 444444 202020202020

151515151515 000000 000000 20406080100 20406080100 20406080100 20406080100 20406080100 20406080100 000000 0,2 0,2 0,2 0,2 0,2 0,2 0,4 0,4 0,4 0,4 0,4 0,4 0,6 0,6 0,6 0,6 0,6 0,6 0,8 0,8 0,8 0,8 0,8 0,8 1 1 1 1 1 1 w(HVO),w(HVO),w(HVO),w(HVO),w(HVO), wt. wt. wt. wt. %wt. % % % % w(HVO),w(HVO),w(HVO),w(HVO),w(HVO), wt. wt. wt. wt. %wt. % % % % w(HVO), wt. % w(HVO), wt. % ◦ FigureFigureFigureFigureFigure 3.3. 3. 3.PyrolysisPyrolysis3. Pyrolysis Pyrolysis Pyrolysis productsproducts products products products yieldyield yieldyield yield yield obtainedobtained obtainedobtained obtained obtained underunder under under under constaconsta consta constantconsta constantntnt nt reactionntreaction reaction reactionreaction reaction conditionsconditions conditions conditionsconditions conditions (400(400 (400 (400(400 kPa,kPa, kPa, kPa, kPa, 800800 800 800 800800 °C,°C, °C, °C, °C, 65C,65 65 65 65 65NmL/min)NmL/min)NmL/min)NmL/min)NmL/min) inin in in dependenceindependence independence dependence dependence dependence onon on on on thethe onthe the the HRSO1 theHRSO1 HRSO1 HRSO1 HRSO1 HRSO1 (solid,(solid, (solid, (solid, (solid, (solid, fillefille fille fille filled)d) ﬁlled)d) d) ord)or or or HRSO2orHRSO2 HRSO2 orHRSO2 HRSO2 HRSO2 (dashed,(dashed, (dashed, (dashed, (dashed, (dashed, empty)empty) empty) empty) empty) empty) contentcontent content content content content inin in in feed-infeed- feed- feed- infeed- feedstockstockstockstockstockstockstock blendedblendedblended blended blended blended blended ininin in in HCVD.HCVD.inHCVD. inHCVD. HCVD. HCVD. HCVD. LeftLeft Left Left Left::: ○●:○● :○● :○● ○● ethylene,ethylene,ethylene, ethylene, ethylene, ethylene, ▲∆▲∆ ▲∆ ▲∆ ▲∆ propylenepropylenepropylene propylene propylene,propylene propylene,,, Right,Right ,Right ,Right RightRight::: ▲∆::▲∆ :▲∆ : ▲∆▲∆ C4C4C4 C4 C4 C4 fraction,fraction,fraction, fraction, fraction, fraction, ■□■□ ■□ ■□ ■□ C4C4C4 C4 C4 C4 BenzeneBenzene Benzene,Benzene Benzene Benzene Benzene,,, , , , ♦◊♦◊♦◊♦◊ Oil.♦◊Oil.Oil. Oil. Oil. Oil.

TableTableTableTableTable 4. 4. 4. Products 4.Products4. Products Products Products distribution distribution distribution distribution distribution (in (in (in (in A (inwt.%) wt.%) wt.%) precisewt.%) wt.%) obtained obtained obtained obtained obtained economic at at at at800 800at 800 800 800 °C, °C, analysis°C, °C, °C, unde unde unde unde underrr r400 400 should400r 400r 400 400 kPa kPakPa kPa kPa kPa and andand beand and and 65 performed6565 65 65 NmL/min 65NmL/minNmL/min NmL/min NmL/min NmL/min tofor forfor for for forevaluate pure purepure pure pure pure traditional traditionaltraditional traditional traditional traditional the most feedstocks feedstocksfeedstocks feedstocks feedstocks feedstocks proﬁtable (HCVD(HCVD(HCVD(HCVD(HCVD(HCVD andandand and andand AGO),AGO),AGO), AGO), AGO),AGO), purepurepure pure purepure HVOsHVOsHVOs HVOs scenarioHVOs HVOs (HRSO1,(HRSO1,(HRSO1, (HRSO1, (HRSO1,(HRSO1, for theHRSO2,HRSO2,HRSO2, HRSO2, HRSO2, HRSO2, current HRSO3,HRSO3,HRSO3, HRSO3, HRSO3,HRSO3, situation HSFOHSFOHSFO HSFO HSFOHSFO inandandand and andand the HUCO)HUCO)HUCO) HUCO) HUCO)HUCO) merchant andandand and andand blendsblendsblends blends products blendsblends containingcontainingcontaining containing containingcontaining market. 101010 10 10 10wt.%wt.%wt.% Therewt.% wt.%wt.% ofofof of of areHRSO1HRSO1ofHRSO1 HRSO1 HRSO1HRSO1 already ororor or HRSO2orHRSO2 HRSO2 HRSO2 HRSO2 inin in in HCVDinHCVD HCVD HCVD HCVD oror or or AGO.orAGO. AGO. AGO. AGO.established methods available [25] for this kind of evaluation, demonstrated in the example of light/heavy naphtha cracking [18]. It uses total economic value of products produced HRSO1HRSO1HRSO1HRSO1HRSO1 HRSO2HRSO2 HRSO2HRSO2HRSO2 HRSO1HRSO1 HRSO1HRSO1HRSO1 HRSO2HRSO2 HRSO2HRSO2HRSO2 FeedstockFeedstockFeedstockFeedstockFeedstock HCVDHCVDHCVDHCVDHCVD AGO AGOperAGOAGOAGO one HRSO1HRSO1 tonHRSO1HRSO1HRSO1 of investigated HRSO2HRSO2 HRSO2HRSO2HRSO2 HRSO3HRSO3 feedstockHRSO3HRSO3HRSO3 HSFO HSFO HSFO inHSFOHSFO relation HUCO HUCO HUCOHUCOHUCO to the products value obtained from a ton +HCVD+HCVD+HCVD+HCVD+HCVD +HCVD +HCVD +HCVD +HCVD+HCVD +AGO +AGO +AGO+AGO+AGO +AGO+AGO+AGO+AGO+AGO of referential (well known) feedstock, which forms referential economic value. However, MethaneMethaneMethaneMethane 5.2 5.2 5.2 5.2 6.36.36.36.3 4.94.94.94.9 6.16.16.16.1 7.17.17.17.1 7.27.27.27.2 7.07.07.07.0 5.55.55.55.5 5.45.45.45.4 6.16.16.16.1 5.95.95.95.9 MethaneMethane 5.2 5.2 such6.36.3 an analysis4.94.9 must6.16.1 consider 7.17.1 current 7.2 or7.2 predicted 7.07.0 prices5.55.5 of products.5.45.4 We6.1 used6.1 the5.9 same5.9 EthaneEthaneEthane 1.5 1.5 1.5 1.81.81.8 1.51.51.5 1.91.91.9 2.72.72.7 2.92.92.9 2.92.92.9 1.61.61.6 1.71.71.7 1.61.61.6 1.51.51.5 EthaneEthaneEthane 1.5 1.5 1.5 method1.81.81.8 for1.51.5 the1.5 evaluation1.91.91.9 as2.72.7 in2.7 the previous2.92.92.9 2.9 paper2.92.9 [251.61.6],1.6 and products1.71.71.7 prices1.61.61.6 valid1.51.51.5 for Ethylene 30.0 19.8 45.6 41.4 41.3 40.4 39.9 29.9 30.4 22.2 22.2 EthyleneEthyleneEthyleneEthyleneEthylene 30.0 30.0 30.0 30.0 30.0 19.806/201719.819.819.819.8 in45.645.645.645.6 the45.6 central 41.441.441.441.441.4 Europe 41.341.341.3 to41.341.3 demonstrate 40.440.440.440.440.4 the39.939.939.939.939.9 impact 29.929.929.929.9 of29.9 HVOs 30.430.430.430.4 to30.4 the process22.222.222.222.222.2 economy.22.222.222.222.222.2 AcetyleneAcetyleneAcetyleneAcetyleneAcetylene 0.60.60.60.60.6 Based0.20.20.20.20.2 on experimental0.40.40.40.40.4 0.30.30.30.30.3 results 0.20.2 from0.20.20.2 lab-pyrolysis0.20.20.20.20.2 0.20.20.20.2 in0.2 the Table0.40.40.40.40.4 4 , and0.40.40.4 considering0.40.4 0.20.20.20.20.2 the HCVD0.20.20.20.20.2 PropanePropanePropanePropanePropane 0.6 0.6 0.6 0.6 0.6 0.30.30.30.30.3 0.40.40.40.40.4 0.50.50.50.50.5 0.50.50.50.50.5 0.50.50.50.50.5 0.50.50.50.50.5 0.40.40.40.40.4 0.50.50.50.50.5 0.30.30.30.30.3 0.30.30.30.30.3 PropylenePropylenePropylenePropylenePropylene 15.3 15.3 15.3 15.3 15.3 11.311.311.311.311.3 18.818.818.818.818.8 18.718.718.718.718.7 19.219.219.219.219.2 19.119.119.119.119.1 19.119.119.119.119.1 15.515.515.515.515.5 15.415.415.415.415.4 12.112.112.112.112.1 12.112.112.112.112.1 Propa-1,3-dienePropa-1,3-dienePropa-1,3-dienePropa-1,3-dienePropa-1,3-diene 0.20.20.20.20.2 0.00.00.00.00.0 0.10.10.10.10.1 0.20.20.20.20.2 0.20.20.20.20.2 0.20.20.20.20.2 0.20.20.20.20.2 0.00.00.00.00.0 0.00.00.00.00.0 0.00.00.00.00.0 0.00.00.00.00.0 PropynePropynePropynePropynePropyne 0.5 0.5 0.5 0.5 0.5 0.20.20.20.20.2 0.20.20.20.20.2 0.20.20.20.20.2 0.20.20.20.20.2 0.20.20.20.20.2 0.10.10.10.10.1 0.40.40.40.40.4 0.40.40.40.40.4 0.30.30.30.30.3 0.30.30.30.30.3 i-butanei-butanei-butanei-butanei-butanei-butane 0.2 0.2 0.2 0.2 0.2 0.2 0.00.00.00.00.00.0 0.40.40.40.40.40.4 0.20.20.20.20.20.2 0.00.00.00.00.00.0 0.00.00.00.00.00.0 0.00.00.00.00.00.0 0.00.00.00.00.00.0 0.00.00.00.00.00.0 0.00.00.00.00.00.0 0.00.00.00.00.00.0 nnn-butane-butane-butanen-butanen-butane-butane 0.3 0.3 0.3 0.3 0.3 0.3 0.20.20.20.20.20.2 0.00.00.00.00.00.0 0.10.10.10.10.10.1 0.10.10.10.10.10.1 0.10.10.10.10.10.1 0.10.10.10.10.10.1 0.40.40.40.40.40.4 0.50.50.50.50.50.5 0.20.20.20.20.20.2 0.20.20.20.20.20.2 transtranstranstranstranstrans-but-2-ene-but-2-ene-but-2-ene-but-2-ene-but-2-ene-but-2-ene 0.00.00.00.00.00.0 0.30.30.30.30.30.3 0.20.20.20.20.20.2 0.00.00.00.00.00.0 0.30.30.30.30.30.3 0.30.30.30.30.30.3 0.30.30.30.30.30.3 0.00.00.00.00.00.0 0.00.00.00.00.00.0 0.30.30.30.30.30.3 0.10.10.10.10.10.1 But-1-eneBut-1-eneBut-1-eneBut-1-eneBut-1-ene 4.8 4.8 4.8 4.8 4.8 1.91.91.91.91.9 10.010.010.010.010.0 8.28.28.28.28.2 6.6 6.6 6.6 6.6 6.6 6.46.46.46.46.4 6.86.86.86.86.8 5.95.95.95.95.9 5.7 5.7 5.7 5.7 5.7 3.0 3.0 3.0 3.0 3.0 3.4 3.4 3.4 3.4 3.4 iii-butene-butene-butenei-buteneii-butene-butene 1.3 1.3 1.3 1.3 1.3 1.3 0.90.90.90.90.90.9 0.30.30.30.30.30.3 0.30.30.30.30.30.3 0.20.20.20.20.20.2 0.20.20.20.20.20.2 0.20.20.20.20.20.2 1.61.61.61.61.61.6 1.61.61.61.61.61.6 1.41.41.41.41.41.4 1.41.41.41.41.41.4 cisciscisciscis-but-2-enecis-but-2-ene-but-2-ene-but-2-ene-but-2-ene-but-2-ene 0.40.40.40.40.40.4 0.30.30.30.30.30.3 0.30.30.30.30.30.3 0.30.30.30.30.30.3 0.30.30.30.30.30.3 0.40.40.40.40.40.4 0.40.40.40.40.40.4 0.40.40.40.40.40.4 0.40.40.40.40.40.4 0.30.30.30.30.30.3 0.30.30.30.30.30.3 Buta-1,3-dieneButa-1,3-dieneButa-1,3-dieneButa-1,3-dieneButa-1,3-diene 7.97.97.97.97.9 4.74.74.74.74.7 6.96.96.96.96.9 7.77.77.77.77.7 7.97.97.97.97.9 7.97.97.97.97.9 7.87.87.87.87.8 7.67.67.67.67.6 7.57.57.57.57.5 5.15.15.15.15.1 5.15.15.15.15.1 CPDCPDCPDCPDCPD 2.4 2.4 2.4 2.4 2.4 1.31.31.31.31.3 0.70.70.70.70.7 1.51.51.51.51.5 1.51.51.51.51.5 1.61.61.61.61.6 1.51.51.51.51.5 3.03.03.03.03.0 2.72.72.72.72.7 2.22.22.22.22.2 2.22.22.22.22.2 CCC55C5–CC–C5–C55–C–C777 7non-id.non-id.non-id. 7non-id.7 non-id. non-id. 7.37.37.37.37.37.3 7.27.27.27.27.27.2 3.43.43.43.43.43.4 4.94.94.94.94.94.9 4.54.54.54.54.54.5 4.84.84.84.84.84.8 5.45.45.45.45.45.4 4.64.64.64.64.64.6 4.04.04.04.04.04.0 3.23.23.23.23.23.2 3.43.43.43.43.43.4 BenzeneBenzeneBenzeneBenzeneBenzene 3.9 3.9 3.9 3.9 3.9 2.72.72.72.72.7 1.31.31.31.31.3 2.12.12.12.12.1 3.13.13.13.13.1 3.43.43.43.43.4 3.13.13.13.13.1 4.74.74.74.74.7 4.74.74.74.74.7 4.44.44.44.44.4 4.14.14.14.14.1 TolueneTolueneTolueneTolueneToluene 2.7 2.7 2.7 2.7 2.7 3.33.33.33.33.3 0.30.30.30.30.3 0.00.00.00.00.0 0.90.90.90.90.9 1.01.01.01.01.0 1.01.01.01.01.0 2.72.72.72.72.7 1.61.61.61.61.6 2.92.92.92.92.9 2.72.72.72.72.7 EBEBEBEBEB 0.2 0.2 0.2 0.2 0.2 0.00.00.00.00.0 0.00.00.00.00.0 0.00.00.00.00.0 0.10.10.10.10.1 0.10.10.10.10.1 0.10.10.10.10.1 0.00.00.00.00.0 0.00.00.00.00.0 0.00.00.00.00.0 0.00.00.00.00.0 mmm+m+mp+p+-xylenesp-xylenes+-xylenesp-xylenesp-xylenes-xylenes 0.70.70.70.70.70.7 1.31.31.31.31.31.3 0.00.00.00.00.00.0 0.00.00.00.00.00.0 0.10.10.10.10.10.1 0.10.10.10.10.10.1 0.10.10.10.10.10.1 0.90.90.90.90.90.9 0.90.90.90.90.90.9 1.21.21.21.21.21.2 1.21.21.21.21.21.2 StyreneStyreneStyreneStyreneStyrene 1.0 1.0 1.0 1.0 1.0 1.51.51.51.51.5 0.30.30.30.30.3 0.00.00.00.00.0 0.50.50.50.50.5 0.50.50.50.50.5 0.50.50.50.50.5 1.01.01.01.01.0 1.01.01.01.01.0 1.31.31.31.31.3 1.31.31.31.31.3 NaphthaleneNaphthaleneNaphthaleneNaphthaleneNaphthalene 0.40.40.40.40.4 1.01.01.01.01.0 0.00.00.00.00.0 0.00.00.00.00.0 0.00.00.00.00.0 0.00.00.00.00.0 0.00.00.00.00.0 0.50.50.50.50.5 0.30.30.30.30.3 1.01.01.01.01.0 0.90.90.90.90.9 CCC77C7–CC–C7–C77–C–C12121212 non-id.12non-id.non-id. 12non-id. non-id. non-id. 2.82.82.82.82.82.8 5.35.35.35.35.35.3 1.21.21.21.21.21.2 1.81.81.81.81.81.8 1.01.01.01.01.01.0 1.01.01.01.01.01.0 1.21.21.21.21.21.2 3.23.23.23.23.23.2 3.63.63.63.63.63.6 4.94.94.94.94.94.9 5.15.15.15.15.15.1 OilOilOilOilOil (C(C (C (C 1111(C1111+)+)11+)11 +) +) 9.79.79.79.79.7 28.128.128.128.128.1 2.72.72.72.72.7 3.63.63.63.63.6 1.61.61.61.61.6 1.51.51.51.51.5 1.71.71.71.71.7 9.79.79.79.79.7 11.211.211.211.211.2 25.625.625.625.625.6 26.026.026.026.026.0

Processes 2021, 9, 1504 9 of 11

as referential feedstock, pure HRSO1 provided strongly positive value 98 EUR/t. It means that HRSO1 pure would provide products with total sale price by 98 EUR/t higher than HCVD. The remaining pure HVOs provided values in range 70–80 EUR/t. The examined content 10 wt.% of HVOs in HCVD, affected the resulting value only slightly, in interval −0.8–1.3 EUR/t. But the same addition of 10 wt.% of HVOs into the AGO caused signiﬁcant change of products value, by +27 and +25 EUR/t, compared to pure AGO.

Table 4. Products distribution (in wt.%) obtained at 800 ◦C, under 400 kPa and 65 NmL/min for pure traditional feedstocks (HCVD and AGO), pure HVOs (HRSO1, HRSO2, HRSO3, HSFO and HUCO) and blends containing 10 wt.% of HRSO1 or HRSO2 in HCVD or AGO.

HRSO1 HRSO2 HRSO1 HRSO2 Feedstock HCVD AGO HRSO1 HRSO2 HRSO3 HSFO HUCO +HCVD +HCVD +AGO +AGO Methane 5.2 6.3 4.9 6.1 7.1 7.2 7.0 5.5 5.4 6.1 5.9 Ethane 1.5 1.8 1.5 1.9 2.7 2.9 2.9 1.6 1.7 1.6 1.5 Ethylene 30.0 19.8 45.6 41.4 41.3 40.4 39.9 29.9 30.4 22.2 22.2 Acetylene 0.6 0.2 0.4 0.3 0.2 0.2 0.2 0.4 0.4 0.2 0.2 Propane 0.6 0.3 0.4 0.5 0.5 0.5 0.5 0.4 0.5 0.3 0.3 Propylene 15.3 11.3 18.8 18.7 19.2 19.1 19.1 15.5 15.4 12.1 12.1 Propa-1,3-diene 0.2 0.0 0.1 0.2 0.2 0.2 0.2 0.0 0.0 0.0 0.0 Propyne 0.5 0.2 0.2 0.2 0.2 0.2 0.1 0.4 0.4 0.3 0.3 i-butane 0.2 0.0 0.4 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 n-butane 0.3 0.2 0.0 0.1 0.1 0.1 0.1 0.4 0.5 0.2 0.2 trans-but-2-ene 0.0 0.3 0.2 0.0 0.3 0.3 0.3 0.0 0.0 0.3 0.1 But-1-ene 4.8 1.9 10.0 8.2 6.6 6.4 6.8 5.9 5.7 3.0 3.4 i-butene 1.3 0.9 0.3 0.3 0.2 0.2 0.2 1.6 1.6 1.4 1.4 cis-but-2-ene 0.4 0.3 0.3 0.3 0.3 0.4 0.4 0.4 0.4 0.3 0.3 Buta-1,3-diene 7.9 4.7 6.9 7.7 7.9 7.9 7.8 7.6 7.5 5.1 5.1 CPD 2.4 1.3 0.7 1.5 1.5 1.6 1.5 3.0 2.7 2.2 2.2 C5–C7 non-id. 7.3 7.2 3.4 4.9 4.5 4.8 5.4 4.6 4.0 3.2 3.4 Benzene 3.9 2.7 1.3 2.1 3.1 3.4 3.1 4.7 4.7 4.4 4.1 Toluene 2.7 3.3 0.3 0.0 0.9 1.0 1.0 2.7 1.6 2.9 2.7 EB 0.2 0.0 0.0 0.0 0.1 0.1 0.1 0.0 0.0 0.0 0.0 m+p-xylenes 0.7 1.3 0.0 0.0 0.1 0.1 0.1 0.9 0.9 1.2 1.2 Styrene 1.0 1.5 0.3 0.0 0.5 0.5 0.5 1.0 1.0 1.3 1.3 Naphthalene 0.4 1.0 0.0 0.0 0.0 0.0 0.0 0.5 0.3 1.0 0.9 C7–C12 non-id. 2.8 5.3 1.2 1.8 1.0 1.0 1.2 3.2 3.6 4.9 5.1 Oil (C11+) 9.7 28.1 2.7 3.6 1.6 1.5 1.7 9.7 11.2 25.6 26.0

4. Conclusions Hydrotreated vegetable oil (HVO) is currently widely applied as a renewable energy source, mainly as a component of Diesel-fuel. However, it is also a very promising feedstock for the steam-cracking process. Our experimental results indicate that HVOs provide much higher yields of desired steam-cracking products, namely ethylene, propylene, and C4 olefins, than comparable traditional feedstocks (HCVD and AGO). Moreover, HVOs provide a significantly lower yield of undesired pyrolysis oil. Based on our comparison of five different HVOs, we estimate that the HVOs’ preparation process may influence the HVOs properties and consequently the distribution of steam-cracking products more than the vegetable oil used for the preparation. Markedly, even the HVO prepared from used cooking oil represents interesting candidate feedstock for steam-cracking process. Experimental investigation of blended samples over the whole blending ratio with HCVD revealed that several products exhibit non-linear dependence on the blending ratio, and therefore, their yields cannot be predicted by the simple principle of additivity. Blends containing 10 wt.% of HVO in traditional feedstock showed slightly enhanced product yields, but the difference is more significant when HVO is blended into the AGO than HCVD. The blended samples investigation provided information about the product yield dependence on blending ratio for future process design considerations. Processes 2021, 9, 1504 10 of 11

Author Contributions: Conceptualization, P.Z.; methodology, J.P.; validation, A.K. and J.P.; investigation P.D.R. and H.d.P.C., writing—original draft preparation, A.K.; visualization, A.K.; supervision, P.Z.; project administration, P.Z.; Material preparation H.d.P.C., Experimentation P.D.R. and H.d.P.C., Analytics H.d.P.C. All authors have read and agreed to the published version of the manuscript. Funding: This paper is a result of the project reg. no. FV30083. This project has been funded with financial support from the state budget through the Ministry of Industry and Trade within the TRIO program. Part of the work is a result of the project which was carried out within the financial support of the Ministry of Industry and Trade of the Czech Republic with institutional support for long-term conceptual development of research organization. The result was achieved using the infrastructure included in the project Efficient Use of Energy Resources Using Catalytic Processes (LM2018119) which has been financially supported by MEYS within the targeted support of large infrastructures. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Data is contained within the article. Acknowledgments: The authors acknowledged significant contribution of Grabriela Horackova to the HVO preparation process. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study, in the collection, analyses, or interpretation of data, in the writing of the manuscript, or in the decision to publish the results.

Abbreviations and Symbols

LHSV h−1 Liquid hourly space velocity p kPa, MPa absolute pressure T ◦C temperature w(i) wt.% mass content of component i Y(i) wt.% yield (in the sense process yield of product i) AGO atmospheric gas oil HCVD hydrocracked vacuum distillate HVO hydrotreated vegetable oil RSO rapeseed oil SFO sunﬂower oil SIMDIS simulated gas chromatography distillation UCO used cooking oil

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