Production of Motor Fuel Components by Processing Vegetable Oils Using a CoMo/Al₂O₃ Hydrotreating Catalyst and a ZSM-5 Zeolite Catalyst

Abstract

Nowadays, there is a need to search for new renewable energy sources from which it is possible to obtain hydrocarbons that are similar in composition and properties to hydrocarbons of petroleum origin. This is due to a significant increase in demand for natural minerals and, as a consequence, the depletion of their reserves. Today, the most promising alternative renewable energy sources are various vegetable oils, which are used both in their pure form, adding them to commercial mineral fuels, and as products of catalytic processing using various catalysts. However, most studies in the field of alternative energy show that the use of fuels obtained from vegetable oils is limited by their properties as well as the climatic conditions of the areas where biofuels can be used. In this work, we propose an integrated approach to the processing of vegetable oils, which allows us to obtain products of a wide fractional composition with improved operational properties. This approach consists of sequential processing of vegetable oils, first using a CoMo/Al₂O₃ hydrotreating catalyst in order to obtain classical long-chain hydrocarbons with unsatisfactory properties, and then using a zeolite catalyst, ZSM-5 type, which is characterized by the active occurrence of cracking, isomerization, and aromatization reactions, which are accompanied by a decrease in the length of the hydrocarbon chain of the hydrocarbons obtained during the hydrotreating process and, as a result, improving the physicochemical and low-temperature properties of the resulting processed products.

1. Introduction

One of the global problems of our time, which can lead to an environmental disaster, is overpopulation of the planet. In turn, overpopulation of the planet entails a significant increase in demand for natural minerals, in particular non-renewable ones. Moreover, the availability and quality of oil reserves play a critical role in shaping global energy markets, economic stability, and environmental sustainability.

Since the end of the 20th century, the world economy has been actively developing along the path of the so-called “green economy”. This economic direction is based on the need for rational use of non-renewable natural resources [1,2].

In recent decades, there has been a depletion of oil reserves and a decline in their quality. This affects various areas of activity—energy, transport, and industrial production—in all countries of the world. Most of the produced oils are heavy, sulfurous, and largely watered [3,4]. Processing such feedstock requires the modernization of equipment, which, in turn, complicates the process of obtaining commercial petroleum products and, consequently, leads to an increase in their cost. At the same time, the demand for motor fuels is increasing every year, and the vehicle fleet is growing rapidly [5].

Thus, an important task is to solve the problem of dependence on oil resources through the development of alternative and, at the same time, renewable sources for obtaining environmentally friendly motor fuel, including fuel for regions with special climatic conditions.

It is assumed that replacing petroleum fuel with an alternative one will significantly reduce the costs of production and processing of hard-to-recover oils, preserve their reserves, and also reduce emissions of harmful substances into the atmosphere [6,7,8].

One of the promising areas that is actively developing is the catalytic processing of mixtures of petroleum and plant feedstocks [9,10,11,12].

The work [9] presents the results of the joint processing of vegetable oil and vacuum gasoil and shows that the involvement of up to a 5% mass of oil allows for increasing the conversion of raw materials, as well as the yield of the gasoline fraction.

The authors of [10] studied the process of joint processing of vacuum gasoil and its mixtures containing 10% cottonseed and sunflower vegetable oils. The processing was carried out in a microreactor for catalytic cracking with a fluidized bed using a zeolite catalyst. It was found that the resulting product could only be used as an additive to petroleum fuel.

In the work [11], as a result of joint processing of straight-run diesel fraction and a 10% vol. of sunflower oil, products were obtained that meet the requirements for Arctic diesel fuel [13].

The authors of [12] investigated the possibility of obtaining a gasoline fraction as a result of processing vacuum gasoil and cottonseed oil. The maximum proportion of oil that could be involved in processing without significant deterioration in the properties of the target product was a 5% vol.

As can be seen, the joint processing of petroleum and plant feedstock allows the use of only a small proportion of renewable feedstock. This necessitates research based on the possibility of obtaining fuel hydrocarbons as a result of catalytic processing of pure (100%) plant feedstock [14,15,16,17].

In the work [14], the process of joint processing of biomass and waste vegetable oil using various zeolite catalysts was studied, and it was shown that the maximum yield of C8-C14 hydrocarbons was 87.28%.

The authors of [15] investigated the possibility of producing biofuel from dogwood oil using zeolite catalysts. The results showed that the composition of the biofuel obtained during processing was mainly represented by hydrocarbons with a small content of acids, alcohols, esters, and ketones, and the highest total yield of hydrocarbons was 89.07%.

The works [16,17] reflect the results of the catalytic processing of non-edible sunflower oil. The maximum yield of the product in the work [17] was 30.1%. The composition of the product was represented by hydrocarbons of the C₇-C₄₃ series and oxygenates. Also, in the work [17], the catalytic processing of sunflower oil made it possible to obtain a product in which n-octadecane makes up 65% wt.; the rest is a mixture of alkenes and isoalkanes C₁₈ (18 wt.%).

The authors of [18], as a result of processing rapeseed oil using a zeolite catalyst, managed to obtain a product in which the proportion of hydrocarbons was 64% wt., of which 43% wt. were aromatic hydrocarbons.

In the work [19], rapeseed oil was processed using a catalyst containing the hydrogen form of ZSM-5. As a result, hydroraffinates were obtained. It was found that increasing the temperature of the rapeseed oil processing process leads to a deeper change in the structure of triglycerides of fatty acids, which reduces the cloud point of the resulting fuel.

The authors of [20] explored various methods for producing “green” fuel. The production of “green” diesel fuel from palm oil was realized by a deoxygenation reaction in a reactor at 500 °C for 2 h using ZSM-5 zeolite. As a result, it was possible to achieve a 100% conversion of palm oil. The secondary products of the process are biokerosene and biogasoline, but their independent use is impossible due to their high viscosity and density.

It is worth noting that the processing of pure vegetable oil with zeolite catalysts, without additional mixed components, including mineral components, is complicated by its high viscosity, density, and molecular weight.

Another way to process vegetable oils to produce hydrocarbons is to process them using hydrotreating catalysts.

So, the work [21] shows that the products obtained from rapeseed oil (with complete oil conversion at 360 °C) using a hydrotreating catalyst (NiO—3.8% wt., MoO₃—17.3% wt., and P₂O₅—6.7% wt.) were water, gaseous hydrocarbons, and liquid organic products. The composition and physicochemical properties of the liquid product, obtained by hydrotreating rapeseed oil, allowed the characterization of this product as high-cetane diesel fuel, but its unsatisfactory low-temperature properties (pour point above 20 °C) do not allow its use in its pure form.

The authors of [22], as a result of the hydrotreating process (using a Co-Mo/Al₂O₃ catalyst), managed to obtain from vegetable oil a product similar to mineral diesel fuel, with a maximum cold filter plugging point of 11 °C and a cloud point of 14 °C. Despite the unsatisfactory low-temperature properties, the resulting product has a high cetane number and therefore can be used only in a mixture with mineral diesel fuel.

Based on the presented literature review, it can be concluded that the processing of vegetable oils using only a zeolite catalyst or a hydrotreating catalyst makes it possible to obtain hydrocarbons. However, regardless of the catalyst used, the products obtained through processing have physicochemical and low-temperature characteristics that do not allow their use as commercial motor fuels.

A possible solution for obtaining fuel hydrocarbons with improved physicochemical and low-temperature properties (components of motor fuels) may be the process of processing vegetable oils using two catalysts sequentially—a hydrotreating catalyst and a zeolite catalyst.

The purpose of the work is to evaluate the feasibility of obtaining motor fuel components by processing vegetable oils using both a CoMo/Al₂O₃ hydrotreating catalyst and by processing using a hydrotreating catalyst and a zeolite catalyst of the ZSM-5 type sequentially.

2. Materials and Methods

The objects of research in the work are vegetable oils, such as corn (F_CO), sunflower (F_SO), and rapeseed (F_RO), products of their processing using a CoMo/Al₂O₃ hydrotreating catalyst (P_CO, P_SO, and P_RO), as well as a product of processing rapeseed oil using two catalysts, a (P_2RO): CoMo/Al₂O₃ hydrotreating catalyst and zeolite catalyst type ZSM-5.

The subject of the study is the composition and properties of feedstock and products of catalytic processing, as well as the regularities of the transformation of substances included in vegetable oils in processing with a CoMo/Al₂O₃ hydrotreating catalyst/hydrotreating catalyst and a zeolite catalyst of the ZSM-5 type.

The physicochemical and low-temperature characteristics, as well as composition, were determined for the feedstock and products of catalytic processing using the following methods and equipment:

1. Kinematic and dynamic viscosity at temperatures of 20 and 40 °C—determination was carried out on a Stabinger viscometer in accordance with the method presented in [23].

2. The hydrocarbon composition of the processed products was determined by gas chromatography–mass spectrometry using a Chromatek Crystal 5000.2 device with an HP-1-MS column (30 m; 0.25 mm; 0.25 μm).

3. Density at a temperature of 15 °C was determined on a Stabinger viscometer SVM 3000 Anton Paar, according to [24].

4. Cloud point, cold filter plugging point (CFPP), and pour point were determined using a low-temperature liquid thermostat, KRIO-T-05-01, and unit for the cold filter plugging point, according to [25,26,27].

5. Molecular mass was determined on an automatic device, KRION-1, in accordance with the method presented in [28].

6. The sulfur content was determined using a SPECTROSCAN S apparatus, according to [29].

7. The hydrocarbon composition of the gasoline fraction was determined by gas chromatography on a Chromatek Crystal 5000 device with a quartz capillary column 25 m × 0.22 mm, stationary phase—SE-54, and carrier gas—helium.

8. Research octane number (RON), motor octane number (MON), saturated vapor pressure (SVP), and density at 15 °С for the separated gasoline fraction were calculated using the development of Tomsk Polytechnic University—the Compounding Software package (ver. 7.0)—based on the results of chromatographic analysis [30].

9. The fractional composition was determined according to the requirements of the standard [31] using an ARNS-1E unit for distilling petroleum products. This method was also used to separate the processed product into fuel fractions.

Catalytic Processing Techniques

The catalytic processing was implemented using a laboratory catalytic unit (in a pure hydrogen environment) (Figure 1), which is designed to study processes occurring under high-pressure conditions, in a flow reactor at a maximum pressure of 9 MPa and a maximum temperature of 700 °C.

During the process, the feedstock is fed by a piston liquid dosing pump into a high-pressure reactor located in a thermal box, after which the obtained product is sent to a water cooler, and then to a high-pressure separator, in which light hydrocarbon gases are separated, that is, the processed product is stabilized. After stabilization, the liquid product enters the receiving container. The monitoring of technological parameters of the process implementation is carried out using pressure sensors and a multi-channel microprocessor temperature controller.

The processing of vegetable oils using a hydrotreating catalyst was carried out under the following parameters: temperature of 375 °C, pressure of 7 MPa, feed volumetric flow rate of 0.5 h⁻¹, and hydrogen consumption of 2.1 L/h.

Table 1. Characteristics of the hydrotreating catalyst.

Characteristic	Value
Nominal particle size	1.2 × 1.4
Compound	Co/Mo on active Al oxide
Stoichiometric amount of sulfur, % wt.	11
Form	Quatrefoil
Bulk density, kg/m3	37.0
Average length, mm	1.2
Mechanical strength at crushing, lb/mm	4.0
Abrasion losses, % wt.	2.0

shows the characteristics of the hydrotreating catalyst [32].

The processing of rapeseed oil using a hydrotreating catalyst and a zeolite catalyst sequentially was implemented under similar technological parameters (temperature of 375 °C, pressure of 7 MPa, feed volumetric flow rate of 0.5 h⁻¹, and hydrogen consumption of 2.1 L/h).

In a fixed-bed reactor with an internal diameter of 12 mm, catalysts with a total volume of 10 cm³ (5 + 5 cm³) were placed one by one. The catalysts were arranged in two layers so that the feedstock first went to the hydrotreating catalyst and then to the zeolite catalyst. Before testing, the catalysts were calcined for 3 h in a stream of hydrogen at the process temperature.

The zeolite catalyst used in the processing is a catalyst of the ZSM-5 structural type, and the mass fraction of zeolite in the finished catalyst is at least 80% by weight (

Table 2. Characteristics of the zeolite catalyst.

Characteristic	Value
Structural type	ZSM-5
Mass fraction of zeolite not less than, %	80
Mass fraction in zeolite powder, %:
SiO2	90.0–97.6
Al2O3	1.4–2.7
Na2O	no more 0.1
Fe2O3	0.35–1.25
Granule diameter, mm	3.0–4.3
Specific surface, m2	300
Mileage period before regeneration, h	150–300
Bulk density, g/cm3	0.60–0.86

).

The catalysts used in this work were commercial catalysts used in real production. The catalysts were provided by their manufacturers for research.

3. Results

3.1. Characteristics and Composition of Vegetable Oil Processing Products Using a Hydrotreating Catalyst

For the feedstock vegetable oils and their processed products using a hydrotreating catalyst, their physicochemical and low-temperature characteristics were determined (

Table 3. Characteristics of feedstock and products of catalytic processing using a hydrotreating catalyst.

Characteristic	FRO	PRO	FSO	PSO	FCO	PCO
Kinematic viscosity at 40 °C, mm2/s	32.95	13.77	33.42	16.32	33.82	17.10
Dynamic viscosity at 40 °C, mPa∙s	29.78	11.72	30.23	13.95	30.59	14.73
Density at 40 °C, kg/m3	904.0	851.4	905.0	854.8	905.0	861.2
Molecular weight, g/mol	743.9	333.0	707.4	376.2	732.1	425.5
Cloud point, °C	−2	24	−7	27	−5	25
Pour point, °C	−15	0	−12	3	−15	0

).

From the data presented in Table 3, it can be seen that as a result of processing vegetable oils using a CoMo/Al₂O₃ hydrotreating catalyst, there is a more than two-fold decrease in kinematic and dynamic viscosity, a more than 1.5-fold decrease in molecular weight, and a decrease in the density of the products versus the raw materials.

In addition, it can be seen that when processing vegetable oils using a hydrotreating catalyst, the low-temperature properties of the products deteriorate, which is due to the formation of long-chain n-paraffins from fatty acids in the vegetable oils, which become cloudy and solidify at positive temperatures.

Table 4. Material balance of vegetable oil processing using a hydrotreating catalyst and water content in liquid products.

Product	Feedstock, % vol.	Yield of Gaseous Products, % vol.	Yield of Liquid Products, % vol.	Water Content in Liquid Product % vol.
PRO	100	1.8	98.2	11.3
PSO	100	10.7	89.3	9.1
PCO	100	6.8	93.2	10.7

presents the yields of liquid and gaseous products resulting from the processing of various vegetable oils using a hydrotreating catalyst.

As can be seen from the results presented in Table 4, the highest yield of liquid products is observed when processing rapeseed oil.

The presence of hydrocarbons, in particular n-paraffins, in the products of vegetable oil processing using a hydrotreating catalyst is clearly reflected in the results of determining the component hydrocarbon composition of the resulting products using gas chromatography–mass spectrometry (

Table 5. Component composition of processed products using a hydrotreating catalyst.

Group	Content in the Product, % wt.
	PRO	PSO	PCO
N-paraffins	43.33	40.47	40.40
Isoparaffins	3.18	5.47	4.08
Olefins	5.38	1.55	1.36
Organic acids	32.37	36.58	42.17

).

A large share in the composition of the products obtained using a hydrotreating catalyst is accounted for by n-paraffins, as well as unreacted and partially reacted fatty acids, which are part of the original vegetable oils. In addition, a small amount of isoparaffins and olefins was found in the obtained products.

A more detailed composition of the vegetable oil product processed using a hydrotreating catalyst, which demonstrates the length of the hydrocarbon chain of n-paraffins included in the product, is presented in Figure 2, Figure 3 and Figure 4.

The results presented in Figure 2, Figure 3 and Figure 4 show that for all the oils, the differences in the paraffin profile are not significant. The highest contents are accounted for by octadecane (n-C18), heptadecane (n-C17), hexadecane (n-C16), eicosane (n-C21), and heneicosane (n-C20).

At the same time, from the processing products obtained by using a hydrotreating catalyst, the product obtained from rapeseed oil has the best physicochemical and low-temperature properties (Table 3), the highest yield of liquid products (Table 4), and a more complete conversion of fatty acids (Table 5), which indicates the prospects for using rapeseed oil in further processing. It is also important to note that when using rapeseed oil, the “food vs. fuel” issue is not as acute.

From the results presented in Figure 2, it can be seen that n-paraffins are represented, predominantly, by molecules with a hydrocarbon chain length of C₉-C₂₆. Moreover, the largest share is accounted for by n-paraffins with a C₁₈ hydrocarbon chain length (22.94% wt.), which is due to the composition of rapeseed oil—oleic, linoleic, and linolenic acids— that predominate in the composition of rapeseed oil, with the number of carbon atoms in the chain equal to 18 [33].

The results of determining the component composition of the resulting products are explained in the reactions that fatty acids undergo using hydrotreating catalysts (Figure 5).

Thus, in accordance with [34,35], fatty acids that are part of vegetable oils, in particular rapeseed oil, are first hydrogenated during hydrotreating and then undergo thermal decomposition reactions with the formation of predominantly monobasic fatty acids. The resulting monobasic acids, in turn, undergo decarbonization, decarboxylation, and hydrodeoxygenation reactions, resulting in the formation of long-chain n-paraffins. Long-chain n-paraffins undergo cracking reactions, resulting in the formation of n-paraffins with a shorter hydrocarbon chain length (Figure 2, Figure 3, Figure 4 and Figure 5). N-paraffins obtained as a result of decarboxylation and decarbonylation reactions contain an odd number of carbon atoms in the chains. Decarboxylation reactions do not require hydrogen, and saturated fatty acids are converted to n-paraffins and carbon dioxide. In decarbonylation reactions, saturated fatty acids react with hydrogen and form n-paraffins, carbon dioxide, and water. At the same time, hydrodeoxygenation reactions produce n-paraffins with an even number of carbon atoms and water as a by-product of the reaction.

3.2. Characteristics and Composition of Products Obtained by Co-Processing Rapeseed Oil Using a Hydrotreating Catalyst and a Zeolite Catalyst

Section 3.1 established that the processing of vegetable oils using a hydrotreating catalyst makes it possible to obtain linear long-chain hydrocarbons with physicochemical and low-temperature characteristics that do not allow their use as motor fuels. It is possible to improve the characteristics of the obtained products by implementing an additional process for processing the obtained long-chain hydrocarbons using a zeolite catalyst of the ZSM-5 type.

To implement the process using two catalysts sequentially: hydrotreating and zeolite, rapeseed oil was used. Rapeseed oil was chosen as the oil giving the highest yield of the best quality product. The material balance of the process was: 100% vol. feedstock (rapeseed oil), 60.4% vol. (P_2RO)—yield of liquid products, and 39.6% vol.—yield of gaseous products.

Table 6. Comparison of the rapeseed oil and its processed product characteristics using two catalysts sequentially.

Characteristic	FRO	PRO	P2RO
Density at 15 °C, kg/cm3	920.0	–	794.0
Kinematic viscosity at 20 °C, mm2/s	64.77	–	1.52
Molecular weight, g/mol	743.9	333.0	332.0
Sulfur content, mg/kg	0	0	0
Cloud point, °C	−2	24	−67
Pour point, °C	−15	0	low than −70
CFPP, °C	–	–	−57
Water content, % wt.	–	11.3	16.0
Yield of liquid product, % vol.	–	98.2	60.3
Cetane index, point	40	-	34

shows the characteristics of the feedstock and the resulting rapeseed oil processed product.

Based on the results presented in Table 6, it can be seen that as a result of processing rapeseed oil using two catalysts sequentially: hydrotreating and zeolite, there is a significant improvement in its physicochemical and low-temperature characteristics. Thus, the obtained product is characterized by a decrease in density of 126 kg/m³, viscosity by more than 40 times, molecular weight by more than 2 times, cloud point by 55 °C, and pour point by more than 55 °C compared with the feedstock.

Compared with the product of rapeseed oil processing using a hydrotreating catalyst, the product of rapeseed oil processing using two catalysts is characterized by a significant improvement in its low-temperature properties; in particular, the cloud point is reduced by more than 81 °C, and the pour point is reduced by more than 70 °C. It is not possible to assess the change in density at 15 °C and viscosity at 20 °C since, at temperatures of 15 °C and 20 °C, the product of rapeseed oil processing using a hydrotreating catalyst is in a solid state because the long-chain paraffins included in its composition solidify at positive temperatures.

Processing rapeseed oil using two catalysts sequentially: a hydrotreating catalyst and a zeolite catalyst of the ZSM-5 type, made it possible to obtain a product whose low-temperature characteristics meet the requirements [12] for Class 4 diesel fuel for Arctic climatic zones (cloud point no higher than −34 °C, CFPP no higher than −44 °C). In addition, the product of rapeseed oil processed using two catalysts sequentially is characterized by a significant decrease in density and viscosity below the limit established in accordance with the requirements (density at 15 °C from 800 to 840 kg/cm³, kinematic viscosity at 20 °C from 1.2 to 4.0 mm²/s) [12].

For the rapeseed oil product processed using two catalysts sequentially, the fractional composition was also determined;

Table 7. Fractional composition of rapeseed oil product processed using two catalysts sequentially.

Condensate Volume, % vol.	Temperature, °С	Condensate Volume, % vol.	Temperature, °С
IBP	38	50	154
10	61	60	180
20	84	70	270
30	110	80	307
40	133	90	322

presents the results.

From the obtained results, it follows that the rapeseed oil product processed using two catalysts sequentially has a wide fractional composition and includes a 60% vol. of gasoline fraction (boiling point—IBP—180 °C), a 7% vol. of kerosene fraction (boiling point—180 °C–240 °C), and a 33% vol. of heavy diesel fraction (boiling point—240 °C—EBP). Due to the low content of kerosene fraction in the product, it was decided to isolate only two fuel fractions from the obtained product: the gasoline and diesel (boiling point—180 °C—EBP) fractions.

Using gas chromatography–mass spectrometry analysis, the component hydrocarbon composition of the rapeseed oil product processed using two catalysts sequentially was determined.

Table 8. Component composition of rapeseed oil product processed using two catalysts sequentially.

Hydrocarbon Group	Content, % wt.
Isoparaffins	2.83
N-paraffins	3.47
Naphthenes	1.81
Aromatic hydrocarbons	68.31
Not identified	19.50

shows the summary results (group hydrocarbon composition). Appendix A shows the individual hydrocarbon composition of the product of rapeseed oil processing obtained using two catalysts sequentially.

From the results presented in Table 8, it follows that aromatic hydrocarbons predominate in the composition of the resulting product.

The resulting composition of the rapeseed oil product processed using two catalysts sequentially is consistent with the concepts of chemical reactions occurring using a hydrotreating catalyst and a zeolite catalyst.

The hydrotreating process includes the following reactions: hydrogenation, the cracking of fatty acid triglycerides, decarboxylation, and decarbonylation or hydrodeoxygenation; a description of the reactions is presented in Section 3.1. The long-chain hydrocarbons obtained during these reactions are then subjected to a cracking process using a zeolite catalyst.

The chemical transformations occurring using a zeolite catalyst of the ZSM-5 type made it possible to significantly improve the properties of the product obtained as a result of the hydrotreating process due to the following reactions: the splitting of high molecular weight hydrocarbons (cracking), isomerization, hydrogen redistribution, and synthesis of dienes [36,37].

Using a zeolite catalyst, n-paraffins undergo skeletal isomerization and cracking. These reactions lead to the formation of iso-structure paraffins and olefins. Olefins, in turn, enter into diene synthesis reactions, with the formation of naphthenes, and hydrogen transfer reactions, with the formation of aromatic and paraffinic hydrocarbons, as well as hydrogen (Figure 6).

The occurrence of hydrogen transfer reactions in olefins with the formation of aromatic hydrocarbons in turn explains the high content of aromatic compounds in the resulting product [37]. In addition, it is known that when zeolite catalysts are used, high process pressure favors the formation of aromatic hydrocarbons [38].

3.3. Characteristics and Composition of the Separated Fuel Fractions

The wide fractional composition, as well as the low density and viscosity values of the rapeseed oil product processed using two catalysts sequentially: a hydrotreating catalyst and a zeolite catalyst, determined the feasibility of it being separated into narrower fuel fractions—gasoline (boiling point IBP—180 °C) and diesel (boiling point 180 °C-EBP) fraction.

The results of determining the main characteristics and hydrocarbon composition of the gasoline fraction separated from the processed product are presented in

Table 9. Main characteristics of the separated gasoline fraction.

Characteristic	Value
Density at 15 °C, kg/m3	758.7
SVP at 38 °C, kPa	41.4
RON, points	75.0
MON, points	71.2
Sulfur content, mg/kg	0

and

Table 10. Hydrocarbon composition of the separated gasoline fraction.

Group	Content, % vol.
N-paraffins	26.89
Isoparaffins	33.04
Naphthenes	3.35
Olefins	10.71
Aromatic hydrocarbons	26.01

.

In accordance with [39], the SVP value of the resulting gasoline fraction is within the required limits (35–80 kPa for summer and 35–100 kPa for winter). The density at 15 °C of the resulting fraction meets the requirements [24] (725.0–780.0 kg/m³). The requirements for the hydrocarbon composition are also met: the benzene content for class K5 is no more than 1% vol., the content of olefin hydrocarbons is no more than 18% vol., and the content of aromatic hydrocarbons is no more than 35% vol. In addition, the separated gasoline fraction is characterized by a high octane number, which exceeds the octane number of straight-run fractions used in the production of commercial gasoline. Thus, the gasoline fraction separated from the rapeseed oil product processed using two catalysts sequentially can be used as a blending component in the production of commercial motor gasoline.

The main characteristics of the diesel fraction separated from the rapeseed oil product processed using two catalysts sequentially are presented in

Table 11. Main characteristics of the separated diesel fraction.

Characteristic	Value
Density at 15 °C, kg/m3	857.9
Dynamic viscosity at 40 °C, mPa/s	2.48
Kinematic viscosity at 40 °C, mm2/s	2.60
Sulfur content, mg/kg	0
Cloud point, °C	−18
CFPP, °C	−20
Pour point, °C	−27
Cetane index, point	50

.

In accordance with [12], there are no requirements for the hydrocarbon composition of diesel fuel. The value of the kinematic viscosity and density of the separated diesel fraction, as well as the CFPP value, meets the requirements [12] for Class F diesel fuel for temperate climatic zones (kinematic viscosity—2.00–4.50 mm²/s, density—820.0–860.0 kg/m³, CFPP not higher than −20 °C, cetane index not less than 46 points).

In addition, unlike mineral diesel fractions, which, as a rule, contain a significant amount of sulfur and require additional refining, the separated diesel fraction is characterized by the complete absence of sulfur-containing compounds in its composition. Thus, the diesel fraction of the rapeseed oil product processed using two catalysts sequentially is a promising component for the production of commercial diesel fuels.

4. Conclusions and Prospects

During the study, the processing of vegetable oils, such as rapeseed, corn, and sunflower, was carried out on a CoMo/Al₂O₃ hydrotreating catalyst at a temperature of 375 °C, a pressure of 7 MPa, a feedstock space velocity of 0.5 h⁻¹, and a hydrogen consumption of 2.1 L/h.

It has been shown that the processing of vegetable oils using a hydrotreating catalyst makes it possible to obtain long-chain hydrocarbons similar to those included in petroleum fractions. The largest share in the composition of the processed products is accounted for by n-paraffins C9-C26. The formation of paraffins occurs during the sequential reactions of hydrogenation of fatty acids of vegetable oils, and their thermal decomposition with the formation of monobasic fatty acids, which, in turn, undergo decarbonization reactions, decarboxylation, and hydrodeoxygenation to form long-chain n-paraffins. In addition, the products contain a significant share of unreacted organic acids, which necessitates the selection of optimal process parameters in order to increase the conversion of feedstock and the yield of target process products—hydrocarbons. It has been established that the resulting products of vegetable oil processing using a hydrotreating catalyst are characterized by unsatisfactory physicochemical and low-temperature characteristics. Thus, from the point of view of using the resulting products as components of motor fuels, the necessitates further catalytic processing of its.

The work also involved the processing of rapeseed oil using two catalysts sequentially—a hydrotreating catalyst and a ZSM-5 type zeolite catalyst at a temperature of 375 °C, a pressure of 7 MPa, a feedstock space velocity of 0.5 h⁻¹, and a hydrogen consumption of 2.1 L/h—to improve the physicochemical and low-temperature characteristics of the rapeseed oil hydrotreating product.

It was shown that the predominant group of hydrocarbons in the composition of the resulting product are aromatic hydrocarbons.

It was established that adding ZSM-5 zeolite catalyst allowed n-paraffins, formed as a result of processing using a hydrotreating catalyst, to undergo skeletal isomerization and cracking with the formation of isoparaffins and olefins. Olefins, in turn, enter into diene synthesis reactions, with the formation of naphthenes, and hydrogen transfer reactions, with the formation of aromatic and paraffinic hydrocarbons, as well as hydrogen, which, in turn, explains the high content of aromatic compounds in the composition of the resulting product.

It was shown that the product of rapeseed oil processed using two catalysts sequentially, in terms of low-temperature characteristics, meets the requirements for Class 4 diesel fuel for Arctic climatic zones [12]; however, the density and viscosity of the resulting product is below the limit established in accordance with the requirements [12]. It was also established that the rapeseed oil product processed using two catalysts sequentially has a wide fractional composition.

The wide fractional composition, as well as the low density and viscosity of the resulting product, necessitated its separation into narrower fuel fractions—gasoline (boiling point IBP—180 °C) and diesel (boiling point 180 °C—EBP). The resulting gasoline fraction meets the requirements of modern standards in its properties and composition and can be used as a component in the production of commercial motor gasoline. It was established that the resulting diesel fraction meets the requirements of modern standards in its properties and can be used as a component in the production of Class F commercial diesel fuels for temperate climatic zones.

The feasibility of processing vegetable oils using two catalysts sequentially was shown; a CoMo/Al₂O₃ hydrotreating catalyst and a ZSM-5 type zeolite catalyst were used to obtain components of commercial gasoline and diesel fuels with improved low-temperature properties. It has been established that motor fuel components obtained by processing rapeseed oil using two catalysts sequentially are promising replacements for petroleum components of motor fuels and are characterized by improved environmental properties since their composition is completely free of sulfur-containing compounds. The use of vegetable oils as a feedstock in a processing process using two catalysts sequentially will allow motor fuel producers to reduce their dependence on non-renewable feedstock and expand the feedstock pool for the production of motor fuel components through the involvement of renewable feedstock. In addition, the regularities identified during the study and the obtained results will become the basis for further study of the processes of producing hydrocarbons similar to oil from renewable feedstock.