Biocomponents via Zeoforming and Hydroconversion of Vegetable Oil

Article pubs.acs.org/EF

Biocomponents via Zeoforming and Hydroconversion of Vegetable Oil: 1H NMR Analysis of Glycerides Conversion Łukasz Jęczmionek* and Wojciech Krasodomski Oil and Gas Institute, National Research Institute, Lubicz 25A, 31-503 Kraków, Poland ABSTRACT: This work describes research conducted on the zeoforming process of rapeseed oil and using zeoformat as a feedstock for hydroconversion process leading to hydrocarbon fuel biocomponents. The raw rapeseed oil and the products, including the zeoformat of the raw rapeseed oil and the hydroraffinate of the raw rapeseed oil zeoformat, were examined using 1H NMR techniques to confirm the occurrence of the oligomerization of fatty acids. Based on the tests performed, it was determined that, during the zeoforming of the vegetable oil, partial decomposition processes occurred in the triglycerides. Monoglycerides, diglycerides, and carboxylic acids were formed, followed by the occurrence of oligomerization processes that led to the creation of both branched aliphatic structures and aromatic structures, which were most likely benzene rings substituted with diverse functional groups. rapeseed oil that was not zeoformed (FBP at 334 °C). It has been hypothesized that this effect may be due to the formation of aromatic rings at the zeoforming stage because coupling (oligomerization) of the fatty acid chains takes place.14 Although a full explanation of this effect still requires a number of careful studies, many quite important pieces of information regarding analogous mechanisms can be found in the available literature.15−22 During the process of classical zeoforming (concerning the conversion of light paraffins into gasoline fractions), the nparaffin hydrocarbons are mostly converted, while the isoparaffins remain largely unchanged.23 The n-paraffins undergo the processes of cyclization and aromatization through the recombination of olefins produced at the intermediate stage of the process.15 This way, even light hydrocarbons, such as pentane and hexane, may form aromatic rings. In addition, to some extent, alkylation reactions also take place. In this case, the hydrocarbon conversion mechanism is therefore different from the conventional reforming process, which proceeds on a catalyst containing noble metals on a catalyst base with acidic centers in it. The basic reactions occurring in this process are the dehydrogenation of naphthenes and the dehydrocyclisation of paraffins.15−18 As has been already stated, the standard zeoforming process relates to light paraffin fractions being processed into gasoline components. Nevertheless, it was found during research that, in this process, much heavier molecules may also emerge from light paraffins. These molecules may contain one (or more) aromatic rings with aliphatic functional groups.16−22 In this work, the results of the rapeseed oil zeoforming process and its subsequent hydroconversion into biocomponents of hydrocarbon fuel are presented. The aim of this research was to confirm the occurrence of the oligomerization of fatty acids in the zeoforming process. According to literature,

1. INTRODUCTION Placing natural oils and fats in contact with zeolite catalysts for the purpose of decomposing them into fuel fractions or even partially finished products that can be utilized in future stages for production of such fractions is a widely addressed research topic.1−9 The ZSM-5 zeolite seems to be particularly important in these studies. It is one of the most common materials used for the production of hydrocarbon fuel fractions derived from vegetable oils. The goal of the works,1−4 in which the ZSM-5 catalyst was used to convert vegetable oils, was to achieve the highest possible conversion efficiency of the raw material. Generally, it has been found that using the ZSM-5 catalyst helps in the formation of aromatic compounds, wherein reaching a high level of conversion efficiency requires relatively high process temperatures (above 350 °C), which also gives high yields of light gaseous hydrocarbons. A similar method of triglyceride processing is the so-called triglyceride zeoforming method. In contrast to the method outlined previously for the conversion of vegetable oils into prospective gasoline fractions, the zeoforming of triglycerides refers to preliminary vegetable oil and/or animal fat processing in which they are subjected to hydroconversion into higher hydrocarbons.10−13 The purpose of this treatment is, instead of n-paraffin formation, a partial modification of the fatty acid chains causing cyclic or branched chain hydrocarbon formation during the hydroconversion. The purpose of the whole operation is to improve the performance properties of the paraffinic fraction obtained by the hydroconversion of triglycerides for use as diesel fuel biocomponents.10−13 It was found in a study14 that as a result of zeoforming rapeseed oil in a flow reactor using the HZSM-5 catalyst at a temperature of 300 °C, a pressure of 1.7 MPa and a liquid hourly space velocity (LHSV) of 1 h−1, and after its subsequent hydroconversion, the resulting hydrocarbon fraction contained predominantly n-paraffins, isoparaffins and approximately 15 wt % of aromatic compounds. The produced fraction is characterized by an increase in the final boiling point temperature (FBP at 379 °C) compared to the analogous hydrocarbon fraction obtained by the hydroconversion of © 2015 American Chemical Society

Received: September 26, 2014 Revised: March 11, 2015 Published: March 11, 2015 2372

DOI: 10.1021/ef502148g Energy Fuels 2015, 29, 2372−2379

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Energy & Fuels 13

C NMR and 1H NMR spectroscopies are useful for the study of hydrocarbon structures in oil fractions.24−26 In this work 1H NMR technique was applied because the triglycerides proton structure is well-defined,27 and even slight changes could be detectable. The effect of zeoforming vegetable oil on the quality of the final product was analyzed.

conditions, the process itself was conducted for 6 h allowing the zeoformat to be sampled in the amounts necessary for further studies. In the second part of the experiment, the obtained zeoformat was subjected to hydroconversion under fixed conditions. As in the zeoforming, for the hydroconversion a flow reactor with a capacity of 100 mL equipped with the necessary equipment was used. The NiMo catalyst employed in this step was sulfurized in accordance with the typical research procedure by using diesel fuel with 2% sulfur added (in the form of DMDS).13 After finishing the process of catalyst sulfurization, the test system was rinsed out with a middle petroleum fraction with a low sulfur content for 24 h in order to flush the system. The hydroconversion conditions applied were as follows: a temperature of 340 °C, a LHSV of 0.5 h−1, a pressure of 4.5 MPa, and a hydrogen feed of 1500 Nm3/m3. The hydroconversion process was conducted for 5 h for each type of raw material (zeoformat and fresh rapeseed oil). The process stabilization periods (2 h) were applied between the points of measurement (collection of the converted product). All stages of the experiment are shown in Scheme 1. The obtained hydroraffinates (liquids) were purged with nitrogen for 1 h (gas stripping) to remove the dissolved gases. 2.4. Analytical Techniques. The fatty acid composition of the rapeseed oil was determined according to the EN ISO 5508 and the EN ISO 5509 methodologies (results presented in Table 1). The raw rapeseed oil and the products, including the zeoformat of the raw rapeseed oil and the hydroraffinate of the raw rapeseed oil zeoformat, were examined using NMR techniques. NMR spectra were recorded in CDCl3 on a Bruker AVANCE III 600 MHz spectrometer (with 1H NMR, relaxation delay of 2.0 s, pulse with 8.0 μs, and acquisition time of 3.8 s; with 13C NMR, 150 MHz, relaxation delay of 1.0 s, pulse width of 13.2 μs, and acquisition time 0.84 s, with proton decoupling). The processing and analysis of the spectra were carried out using the program MestReNova 8.1.2 from the Mestrelab Research S.L. Co.

2. EXPERIMENTAL SECTION 2.1.. Catalyst Characterization. To study the zeoforming of vegetable oil, a commercially available H-ZSM-5 zeolite material was used as the catalyst. An analogous material was previously used in studies on the zeoforming of light paraffinic fractions.17,18 The catalyst was characterized by a silicon module of approximately 80−90, external surface area of 150 m2/g, and total pore volume of 0.6 cm3/g (0.5 cm3/g meso- and macropore volume).17,18 The acidity (by NH3 temperature-programmed desorption (NH3-TPD)) was 0.25 mmol/g. The catalyst had the form of circular extrusions: 2 mm in diameter and 3−5 mm in length. It is worth recalling that the another H-ZSM-5 catalyst with a silicon module of 70−80 and a significantly reduced volume of meso- and macropores was used to study the zeoforming of rapeseed oil.10 In this work, a NiMo type of catalyst on an Al2O3 carrier was used for the hydroconversion of the zeoformat and fresh vegetable oil.10 The catalyst has been developed for the deep hydrotreatment of middle distillates and especially for deep hydrodesulfurization. 2.2. Feedstock. In the tests, edible, refined, and commercially available rapeseed oil produced by the Kruszwica ZPT Co. was used,11 and its triglyceride fatty acid composition is indicated in Table 1.

Table 1. Triglyceride Fatty Acid Content in the Rapeseed Oil Used in the Research, wt %11 fatty acid

triglyceride fatty acid content in the rapeseed oil used in the test (wt %)

mirystic C14:0 palmitic C16:0 palmitoleic C16:1 stearic C18:0 oleic C18:1 linoleic C18:2 linolenic C18:3 arachidic C20:0 eicozenoic C20:1 behenic C22:0 erucic C22:1 lignoceric C24:0 nervonic C24:1 unidentified

0.1 4.3 0.2 1.9 63.2 18.5 7.4 0.6 1.6 0.4 1.4 0.2 0.1 0.1

3. RESULTS AND DISCUSSION It is possible to identify the peaks clearly and calculate the average quantities of different protons in a single triglyceride molecule by analyzing the chemical shifts and signal integration in the 1H NMR spectrum (Figure 1; Table 2). An important parameter describing the analyzed structures is the ratio of the average number of methylene and vinyl carbon atoms to the number of methyl groups, which is calculated based on the integration of the 1H NMR signals after taking into account the quantity of protons in the individual structural groups. In the case of crude rapeseed oil, this ratio is approximately 15.83:1, which corresponds with the triglyceride structure. It correlates very well with the values calculated for the fatty acids present in amounts greater than 0.5 wt % in the triglycerides based on the data from Table 1. Additionally, signals that were difficult to interpret because they are at the noise level in the range of aromatic compound signals are shown in the spectrum (enlarged detail in Figure 1). They come from unidentified structures and are most likely from tocopherols or other phenolic compounds.29 The integrations of 1HNMR signals correlated to appropriate structural groups of obtained substances are shown in Table 2. Analyzing the 1H NMR spectrum of the hydrocarbon fraction obtained from rapeseed oil (Figure 2), it can be observed that the carboxylic acid tails were hydrogenated with hardly any isomerization of the carbon chains. In this case, the ratio of the average number of carbon atoms in the methylene and vinyl structures to the number of methyl groups is approximately 7.41:1, which corresponds to the hydrocarbon structure produced by the decarboxylation and hydrogenation of the fatty acids in a triglyceride. The obtained mixture, according to GC analysis, had a content of over 96% saturated hydrocarbons28 which have an average chain length, calculated

The hydrogen used in the hydroconversion process was of 99.99% purity. The raw materials (zeoformed and nonzeoformed rapeseed oil) were mixed with dimethyl disulfide (DMDS) to protect the surface of the NiMo/Al2O3 catalyst with sulfur on it from deactivation in the second part of the experiment. The DMDS was applied in such a way that the sulfur content in the raw materials was approximately 600 mg/ kg. 2.3. Experimental Approaches. The process was conducted in two stages.28 In the first stage, the rapeseed oil was zeoformed over the H-ZSM-5 catalyst under the following conditions: a raw material feeding in relation to the catalyst volume (LHSV) of 1.0 h−1, a pressure of 1.7 MPa, and a temperature of 300 °C. The rapeseed oil zeoforming was performed using an OL-105 apparatus containing a flow reactor with a 100 mL capacity. The device was equipped with a raw material pump, a separator, and a system with receptacles for the converted fractions, i.e., the liquid and gas fractions. The feed rate was controlled by an automatic measuring system. After stabilizing the 2373


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Energy & Fuels Scheme 1. Schematic Diagram of the Experiment

Figure 1. 1H NMR spectrum of fresh rapeseed oil.

from 1H NMR spectra, of 16.83 carbon atoms. The weak signals in the range of 1.4−1.8 ppm, except 1.55 typical of water as impurity, indicate a low isoparaffinic content (see enlarged detail in Figure 2). Moreover, low signals present in the 1H NMR spectrum at the noise level (see enlarged detail in Figure 2) in the range from 3.5 ppm to approximately 6.0 ppm indicate that the hydrogenation of the unsaturated structures was not complete, and there was probable contamination with traces of ester structures of mono-, di-, and triglycerides. The observed aromatic signals in the raw material were strongly reduced and shifted downward (see enlarged detail in Figure 2), which indicates the instability of aromatic compounds present in vegetable oil during the processing conditions. Analyzing the 1H NMR spectrum of the zeoformed oil (Figure 3), many significant changes in the structure of the triglycerides during that process can be detected. First of all, the

methylene protons in the glyceride structure were altered (signals in the range of 4.0−4.5 ppm), and it was most likely transformed into partial di- and monoglycerides through the cleavage of carboxylic acids (see enlarged detail in Figure 3). This hypothesis regarding the partial decomposition of the triglycerides is supported by the relatively high acidity of the zeoformat (about 10 mg of KOH/g), which indicates the presence of more than 50 mg of carboxylic acids recalculated as oleic acid per gram of zeoformat. In addition, the increase in the ratio of the integration of the α-CH2 signal (2.3 ppm) to the sum of glyceride proton signals from 1.2:1 in fresh oil to 3.9:1 in zeoformat confirms this assumption. Significant changes also occurred in the acids’ hydrocarbon tails. In the case of the zeoformed vegetable oil, the ratio of the average amounts of methylene, methine, and vinyl carbon atoms to the amount of methyl groups is approximately 9.2:1, which indicates a strong reduction in the average length of the linear acids’ carbon tails, 2374


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Table 2. Comparison of Proton Signal Integrations on Typical Functional Groups in Triglycerides, Zeoformates, and HVO Products 1

H NMR signal integration of various rapeseed oils

structural groupa

chem shift (ppm)

Ar−H Ar−H -CHCH-O−CH(CH2O-)2 -O−CH(CH2O-)2 -CHCH−CH2−CHCHAr−CH2R−CH2−COO-CHCH−CH2R−CH2−CH2−COO− Ar−CH2−CH2− R−CH(R′)−R″ H2O R−CH2−R′, R−CH(R′)−R″ CH3−CH2−Rd

7.23−8.2 6.0−7.2 5.3−5.5 5.2−5.3 4.0−4.4 2.7−2.9 2.5−2.7 2.3 2.0 1.4−1.8 1.5c 1.0−1.4 0.5−1.0

freshb

fresh

2.54 0.33 1.33 0.70

0.01 0.01 2.53 0.35 1.32 0.72

2.00 3.68 2.00 18.31 3.00

2.05 3.83 2.04 0.31 17.96 3.00

zeoformed 0.25 0.50 0.08 0.31 0.16 0.38 1.53 1.78 2.36 11.68 3.00

hydroconverted fresh

hydroconverted zeoformed

0.004 0.01

0.14 0.03 0.007 0.04 0.06 0.17 0.18 0.22 0.87

0.003 0.01 0.02 0.04 0.20 0.24 14.55 3.00

9.68 3.00

a

To recalculate integration to the number of carbon atoms in the indicated structural group, per one methyl group the integration should be divided by the number of hydrogen atoms bonded to one carbon atom. bCalculated based on the balance of carboxylic acids amounts identified by the GC method (Table 1). cSharp signal. dThe integration of methyl group signals was set as 3.00 to compare all obtained products.

Figure 2. 1H NMR spectrum of hydroconverted fresh rapeseed oil.

radicals and the protons of the methylene groups bonded with benzyl structures. Moreover, a decreased total amount of unsaturated structures was observed, and some new alkene structures occurred. Formation of the unsaturated structures depicted in Scheme 2A confirms the changes in integration of vinyl (5.3−5.5 ppm) and allyl (∼2.0 and ∼2.8 ppm) proton signals in zeoformat. In the case of fresh oil, the ratio of vinyl to allyl protons is 1.2:1, whereas in the case of zeoformat this ratio is 2.7:1. This is due to a lack of vinyl proton in the newly formed unsaturated dimer of free acids as well as glycerides. Evidence for the formation of

or even partial decarboxylation. This is due to both the classical isomerization linear structures on zeolite and the triglyceride transformations: decomposition and the subsequent oligomerization of carboxylic acids structures toward the formation of branched and aromatic structures in the products (Scheme 2). The presence of branched aliphatic structures is indicated by an increase in the integration of the methine proton signals in the range of 1.4−1.6 ppm in relation to the methyl protons. An unequivocal calculation of that ratio is somewhat difficult to conduct due to the presence of broad signals coming from the protons attached to the β carbon atoms of the carboxylic acid 2375


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Figure 3. 1H NMR spectrum comparison of fresh (A) and zeoformed (B) rapeseed oil.

aromatic structures is provided by the complex structure of 1H NMR signals in the range of 6.5−7.2 ppm (see enlarged detail in Figure 3). The lack of signals above 7.3 ppm indicates that there exist variously alkyl substituted monoaromatic derivatives in zeoformat. The substituted benzene derivatives are probably the products of double bond migration and then subsequent Diels−Alder cycloaddition19−22 between the unsaturated fatty acid tails. The ratio of the integration of their signals, assuming that the six carbon atoms of the aromatic carbon ring correspond to only two hydrogen atoms, according Scheme 2B, indicates the presence of an average ratio of approximately 0.75 of an aromatic carbon atom per one methyl group.

Their formation is most likely a result of the isomerization process, chain shortening, and the subsequent cyclization, which follow oligomerization. Experiments conducted in this work allow one to propose, in accordance with previous literature data,16−22 the mechanisms depicted in Scheme 2 for the oligomerization processes of unsaturated fatty acids conducted on solid catalysts running at a temperature within the range of 200−300 °C. Formation of a secondary carbocation is the key step of the proposed mechanism of the oligomerization process of unsaturated fatty acids conducted on solid catalysts that resulted in the creation of high molecular weight compounds. 2376


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Scheme 2. Reaction Scheme for the Formation of Aliphatic Dimers from Unsaturated Fatty Acids: Via Cationic Intermediates (A) and via [4 + 2] Cycloaddition (B)19−22

Figure 4. 1H NMR spectrum of the hydroconversion product of zeoformed rapeseed oil.

(i.e., free oleic acid or glycerides). This secondary carbocation attacks the unsaturated bond of the second molecule, resulting in the formation of another carbocation with double the mass of the initial acid. From that carbocation, as the result of proton

The oligomerization process can be carried out in two paths. In the first reaction path, a secondary carbocation is formed as a result of proton attachment to the double CC bond; this commonly occurs with monounsaturated fatty acids structures 2377


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Figure 5. 13C NMR spectra comparison of HVO obtained from fresh (A) and zeoformed (B) rapeseed oil.

The hydroconversion product of the zeoformed oil was a subject of the next step of the research. An analysis of the 1H NMR spectrum of the hydroconversion product (Figure 4) has shown that decarboxylation and hydrogenation of the unsaturated bonds have occurred in the structures during the process. The branched structures of the saturated hydrocarbon chains formed during the zeoforming process remained without any significant changes; however, some hydrogenation of the aromatic structures took place. In this case, in the obtained hydrocarbon fraction, the average ratio of the amount of methylene, methine, and vinyl carbon atoms to the amount of methyl groups is approximately 6:1. This indicates a shortening of the average length of the compounds’ linear carbon chains. This shortening is caused by the previously mentioned processes of triglyceride decomposition and isomerization. The presence of branched aliphatic structures is indicated by an increase in the integration of the methine proton signals in the range of 1.4−1.6 ppm in relation to the methyl protons. Similarly, as in the case of the zeoformat, an unequivocal calculation of that ratio is somewhat difficult to conduct due to the presence of broad signals coming from the protons attached to the β carbon atoms of the carboxylic acid radicals and the protons of the methylene groups bonded with benzyl structures. The formation of aromatic structures is indicated by the signals in the range of 6.5−7.2 ppm (see enlarged detail in Figure 4). The ratio of their signal integrations, assuming, as in the zeoformat case, that the six atoms of the carbon aromatic ring only correspond to two hydrogen atoms, indicates the presence of an average of 0.42 of an aromatic carbon atom per 1 methyl group.

separation, a new branched dimer molecule is formed that still contains the double bond, carboxyl groups, and n-alkyl chains (Scheme 2A). During further zeoforming processes some double bonds may become saturated. The second category of reactions comprises the processes that occur in the presence of acids containing at least two double bonds. For example, in the case of linoleic acid containing double bonds between C9−C10 and C12−C13, under the influence of an acid catalyst, the double bond structure can easily create a secondary carbocation and double bond migration may occur, resulting in the creation of a coupled diene structure. Then, that diene structure can participate in a Diels−Alder type of reaction with a dienophile, another fatty acid molecule with at least one double bond. As a result of this transformation, an oligomer is formed, which is a dicarboxylic acid containing the substituted cyclohexene structure. This product, particularly in the presence of double bonds in the immediate vicinity of the ring, may aromatize itself by isomerization or dehydrogenation (Scheme 2B). In the case of both reaction mechanisms (Scheme 2), a decrease in the level of unsaturation structures and increase in the level of aromatic structures in the zeoformated product are observed. Each reaction cycle diminishes the structures by one or two double bonds. It should be noted here that, in the case of polymolecular highly branched structures, their thermal decomposition and isomerization must also be taken into account. The process must lead to a reduction in the molecular size while maintaining their structural composition, especially of the branched structures. This is confirmed by observed differences between the CH3:CH2 ratio in fresh and zeoformed oil. 2378


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(12) Jęczmionek, Ł. Pol. J. Environ. Stud. 2014, 23 (1), 103−108. (13) Jęczmionek, Ł. Prace Naukowe Instytutu Nafty i Gazu w Krakowie, Monographic Vol. No. 185; Instytut Nafty i Gazu: Kracow, Poland, 2012; ISSN 0209-0724. (14) Jęczmionek, Ł.; Porzycka-Semczuk, K. Proceedings of the International XIX Zeolite Forum, Małe Ciche, Poland, Sep. 11−15, 2012; Polish Zeolite Association: Krakow, 2012, 11−19. (15) Stepanov, V. G.; Ione, K. G.; Snytnikova, G. P. Catalysts in petroleum refining and petrochemical industries; Elsevier: Amsterdam− Lausanne−New York−Oxford−Shannon−Tokyo, 1996; pp 477−482. (16) Jęczmionek, Ł.; Lubowicz, J. Pol. J. Environ. Stud. 2009, 18 (1B), 56−61. (17) Kornblit, L.; Marchut, A.; Jęczmionek, Ł.; Lenartowicz, L.; Mikrut, G. Sci. Pap. Inst. Chem. Technol. Pet. Coal Tech. Univ. Wrocław 2002, 57. (18) Kornblit, L.; Marchut, A.; Jęczmionek, Ł.; Bożek, S.; Lenartowicz, L.; Mikrut, G. Proceedings of the 41st International Petroleum Conference, Bratislava, Slovak Republic, Oct. 6−8, 2003. (19) Tolvanen, P.; Maki-Arvela, P.; Kumar, N.; Eränen, K.; Sjöholm, R.; Hemming, J.; Holmbom, B.; Salmi, T.; Murzin, D. Y. Appl. Catal., A 2007, 330, 1−11. (20) Link, W.; Spiteller, G. Eur. J. Lipid Sci. Technol. 1990, 92, 135− 138. (21) Link, W.; Spiteller, G. Eur. J. Lipid Sci. Technol. 1992, 94, 9−13. (22) Brütting, R.; Spiteller, G. Eur. J. Lipid Sci. Technol. 1993, 95, 193−199. (23) Ono, Y. Catal. Today 2003, 81, 3−16. (24) Wauquier, J.-P. Petroleum Refining, Vol. 1: Crude Oil, Petroleum Products, Process Flowsheets; Editions Technip; Paris, 1995; pp 62−71. (25) Huc, A. Y. Heavy Crude Oils From Geology to Upgrading. An Overview; Editions Technip: Paris, 2010; pp 40−41. (26) Michon, L.; Martin, D.; Planche, J. P.; Hanquet, B. Fuel 1997, 76, 9−15. (27) Gunstone, F. D.; Knothe, G. H. NMR Spectroscopy of Fatty Acids and Their Derivatives, The AOCS Lipid Library; The American Oil Chemists’ Society, Urbana, IL, USA, 2014; http://lipidlibrary.aocs. org/nmr/nmr.html, accessed Jun. 18, 2014. (28) Jęczmionek, Ł.; Burnus, Z.; Ż ak, G.; Ziemiański, L.; Wojtasik, M.; Krasodomski, W.; Stępień, Z.; Rutkowska, M.; Węgrzyn, A. Zeoforming of Triglycerides Can Improve Some Properties of Hydrorefined Vegetable Oil Biocomponents. Energy Fuels 2014, 28, 7569−7575. (29) Balasundram, N.; Sundram, K.; Samman, S. Food Chem. 2006, 99, 191−203.

The 13C NMR spectra of hydroconverted oils have been recorded to confirm structural changes (Figure 5). All observed signals are in the aliphatic range of 3−60 ppm. An increase of the number of signals suggests the presence of branched aliphatic structures in HVO from zeoformated oil. Especially significant are 32.7 and 34.4 ppm typical for methine groups CH in hydrocarbon chains, and 37.2 characteristic for methylene groups branched in the α or β position from aromatic rings, or in α position from a naphthenic ring.26 Lack of signals of aromatic carbons is due to the low sensitivity of 13 C NMR relative to 1H NMR spectroscopy. According to the authors of this work, there are reasonable grounds for claiming that oligomerization and isomerization of fatty acids occur during the process of vegetable oil zeoforming on a catalyst containing the hydrogen form of ZSM-5.14 Using this product as the feedstock for hydroconversion allows one to improve the quality of obtaining fuel fractions, containing branched alkanes and alkylsubstituted aromatic hydrocarbons.

4. CONCLUSION The 1H NMR study of the products obtained in the zeoforming process followed by hydroconversion of vegetable oil confirms the hypothesis that the triglycerides are oligomerized into branched aliphatic and alkyl substituted benzene structures during the zeoforming process. The direct hydroconversion process results in the synthesis of predominantly n-paraffinic structures. The hydroconversion products obtained from the zeoformed vegetable oil include branched and aromatic structures that are responsible for fuel properties corresponding to the EN 590 standard requirements for diesel fuel.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +48 12 617 75 14. Fax: +48 12 430 38 85. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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Biocomponents via Zeoforming and Hydroconversion of Vegetable Oil

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