Homogeneous Acid Catalysts Research Articles

Optimization and modeling of biodiesel production from oleic acid in plug flow reactor

In recent years, biodiesel has been preferable to fossil fuels because of its renewability, biodegradability, and producibility from various wastes. In this study, the esterification reaction between oleic acid and methanol was carried out in the presence of sulfuric acid, which is a homogeneous acid catalyst, to produce biodiesel. Experiments were carried out in a plug flow reactor (PFR) and a batch reactor. The experimental conditions with the highest conversion obtained in the PFR were determined and applied to the batch reactor and results were compared. The effects of temperature (45, 55, 65 in Celsius), catalyst concentration (2%, 4%, 6% by weight), and methanol/oleic acid mole ratio (3, 6, 9) on oleic acid conversion were examined in the PFR. Retention times at different flow rates were calculated to determine the reaction time in the PFR and reactions were carried out between 2 and 6 minutes. In the reactions carried out in the PFR, the highest conversion value was obtained as 97.33% under conditions where the catalyst concentration was 6% by weight, the temperature value was 55oC and the alcohol/acid mole ratio was 6:1. These conditions were applied to the batch reactor and the conversion value was found to be 50%. When the experimental results were examined, it was seen that the effect of temperature and alcohol/acid ratio on the conversion was greater than the effect of the catalyst concentration on the conversion. The modeling of oleic acid/methanol esterification, i.e., biodiesel production, at specific boundary values was found to follow a cubic dependence in the general dependence equation via Response Surface Methodology.

Heteropolyacids combined with Y zeolite as superior solid acid catalysts to accelerate lactic acid esterification

AbstractBACKGROUNDEthyl lactate produced via esterification between lactic acid and ethanol can be used in plastics, polymers and food industries and renowned for its biodegradability and low toxicity. However, lactic acid self‐catalyzed esterification presents a slow reaction process, and acid catalysts are needed to improve the catalysis. Homogeneous acid catalysts like H2SO4 are corrosive, as well as being difficult to be seperated from the reaction media; therefore, advanced heterogeneous catalysts are more ideal. In this study, two kinds of heteropolyacid–zeolite catalysts, involving loading silicotungstic acid and phosphotungstic acid onto Y zeolite, were synthesized, characterized using X‐ray diffraction, NH3 temperature‐programmed desorption and scanning electron microscopy and analyzed for their catalytic efficiency in the catalytic esterfication.RESULTSResults showed that the Keggin structures of heteropolyacids were retained during the preparation process and strong acid sites of Y zeolite were enriched, which made the main contribution to the esterification of lactic acid and ethanol. Furthermore, the initial‐stage reaction rate of esterification was significantly enhanced. During the first hour of esterification, the conversion of lactic acid increased from 18% to 65%. Exp Dec1 index model was employed to determine the activation energies of 60HSiW‐Y and 60HPW‐Y, which exhibit values of 29.3 and 28.2 kJ mol−1, respectively.CONCLUSIONThis study indicates that Keggin structures of heteropolyacids play a key role in the esterification and heteropolyacid–zeolite catalysts can effectively catalyze the esterification. Meanwhile, the results of the kinetic experiments can be of reference significance for large‐scale industrial processes involving esterification. © 2024 Society of Chemical Industry (SCI).

(Invited) Carbon Sulfonation Using Plasma: Trial to Enlarge Treatment Capacity

Heterogeneous catalysis is a promising technology in conversion of biomass to biofuels because of its high reactivity, easy post-separation, and great recyclability compared to homogeneous catalysis. Various functionalized catalytic materials have emerged as promising alternatives to the homogeneous liquid acid catalyst, such as carbon materials, metal–organic frameworks, and metal nanoparticles. Among them, carbon materials such as carbon nanotube, graphene oxide, carbon black, and so on have been investigated as catalysts for cellulose hydrolysis to produce glucose.Carbon materials show considerable catalytic activity by functionalization with active acidic groups including hydroxyl groups (-OH), carboxyl groups (-COOH), and sulfonic groups (-SO3H). Hydroxyl and carboxyl groups on the carbon catalysts act as connection center to access cellulose, where sulfonic group serves as the active site to cut off the linkage between glucose units in cellulose. So, the surface modification of carbon materials with these functional groups, namely, carbon sulfonation process, becomes the determining step to producing efficient carbon acid catalysts. Conventional methods for the carbon sulfonation are the hydrothermal and reflux method, in which hazardous chemicals are necessary, such as concentrated sulfuric acid (95–98%), chlorosulfonic acid, fuming sulfuric acid, or 4-benzenediazoniumsulfonate under elevated temperature for dozens of hours.As a green and effective carbon sulfonation process, we have utilized plasma generated in contact with dilute sulfuric acid. Recently, we have investigated the mechanism of carbon sulfonation in GLIP processes. Active species produced near the gas–liquid interface such as •OH, SO3, and HOSO2• probably play important roles in carbon sulfonation. We are currently trying to enlarge the treatment capacity of carbon sulfonation by two methods, namely parallel plasma generation with ballast capacitors and large-area plasma generation by a dielectric barrier discharge. Also, effects of gases used for plasma generation such as air and Ar on the carbon sulfonation are investigated.This work was partially supported by the Environment Research and Technology Development Fund (JPMEERF20223R01) of the Environmental Restoration and Conservation Agency of Japan.

Structures and hydrogen bonds of -SO3H functionalized acid ionic liquids

Brønsted acidic ionic liquids (BAILs) are clean and versatile replacements for traditional homogeneous acid catalysts and have attracted much attention as efficient catalysts for the synthesis of valuable chemicals. It’s critically important to understand the structural properties of BAILs from the molecular level. In this work, we studied a series of −SO3H functionalized acidic ionic liquids by density functional theory (DFT) calculations, and the most stable geometries were obtained by global semiempirical quantum mechanical search. The most stable structures of cations are formed when more intramolecular H-bonds exist. For BAILs clusters, intramolecular and intermolecular H-bonds coexist and play a critical role in the stability of the system. The interaction energy decreases with increasing alkyl chain length. When the alkyl chain was replaced by −SO3H groups, the interaction energy increased due to more H-bonds formed with the anions. The quasi-3D network is formed in the BAILs clusters and the electrostatic interaction plays a critical role in stabilizing the ion clusters. This work helps to understand the microcosmic interactions of BAILs in-depth and design them in a “task-specific” way.

Liquid Hot Water (LHW) and Hydrothermal Carbonization (HTC) of Coffee Berry Waste: Kinetics, Catalysis, and Optimization for the Synthesis of Platform Chemicals

Colombia is the world’s leading producer of mildly washed arabica coffee and produces 12.6 million bags of green coffee, but at the same time, 784,000 tons of waste biomass are dumped in open fields, of which only 5% is recovered or used. The objective of this project was to evaluate the production of platform chemicals from these coffee wastes for sustainable resource management. To achieve this, biomass characterization was carried out using proximate analysis, ultimate analysis, and structural analysis. Hydrothermal valorization was carried out at a temperature range of 120–180 °C (LHW) and 180–260 °C (HTC) for one hour. The platform chemicals obtained were quantified by HPLC-RI and monitored by pH and conductivity, and the solid fraction was characterized by monitoring the functional groups in IR spectroscopy and elemental analysis. Hydrolysis processes were obtained at 150 °C, production of platform chemicals at 180 °C, and maximum concentration at 180 °C-4 h; over 200 °C, degradation of the products in the liquid fraction starts to take place. Homogeneous basic and acid catalysts were used to improve the yields of the reaction. The kinetics of the hydrolysis of lignocellulosic structures to sugars were also analyzed and described, and reaction orders of 1 (LHW), 3 (HTC), and their respective reaction rate equations were reported.

SO3H‐Functionalized Carbon Materials: A Versatile and sustainable heterogeneous Catalyst for Diverse Organic Transformations

AbstractDue to their fascinating biological features, heterocyclic compounds and their derivatives have long been recognized as promising molecules with potential pharmaceutical applications. The significance of heterocyclic compounds in drug discovery and development is evident from the fact that a majority of drugs in the pharmaceutical market incorporate heterocyclic compounds as active substances or ingredients. Various synthetic methods and advancements have been devised to prepare these heterocyclic compounds using diverse catalysts under mild reaction conditions. SO3H functionalized carbon material (C‐SO3H) is heterogeneous green solid catalyst that has been employed to catalyze diverse organic reactions including construction of three‐, four‐, five‐, six‐member and fused heterocycles as well as other open chain organic transformations. The C‐SO3H catalyst works under relatively mild reaction conditions and recovered from the reaction mixtures for reuse. Various cheap carbon sources covering natural organic carbon matter and industrial waste already being used to synthesize SO3H‐functionalized acidic carbon catalyst for replacement of various homogeneous acid catalysts. The present review aims to highlight the organic reactions especially those connecting for heterocyclic synthesis catalyzed by sulfonated carbons (C‐SO3H) from 2010 to till date.

Esterification of butyric acid with n‐butanol: Kinetic study using experimental data and modeling

AbstractPresent study involves the investigation of the esterification kinetics between butyric acid and n‐butanol. This reaction was conducted in a batch reactor, utilizing homogeneous methanesulfonic acid (MSA) catalyst. Response surface methodology (RSM) was conducted prior to the kinetic study using “Design Expert; version‐11.0” for finding the causal factors influencing the conversion of butyric acid. Most important factors identified with their limits against conversions (during optimization of the process using RSM) were taken up to critically analyze the effect of them on butyric acid conversion. Concentration and activity‐based model of the process were proposed assuming second order reversible reaction scheme using homogeneous MSA catalyst. During the study of non‐ideal behavior of the system, UNIFAC model was adapted for assessing the activity coefficients of species present in equilibrated liquid phase. Experimental data were used to evaluate kinetic and thermodynamic parameters such as rate constants, activation energy, enthalpy, and entropy of the system. The endothermic nature of esterification was confirmed by positive value of enthalpy obtained. The effect of various levels of causal variables like temperature (60–90°C), catalyst concentration (0.5–1.5 wt.%), and molar ratio of n‐butanol to butyric acid (1–3) on conversion kinetics of butyric acid was investigated during transient and equilibrium phase of the reaction. It has been observed that molar ratio of butanol to butyric acid has the highest influence on the conversion. The rate equation derived offered a kinetic and thermodynamic framework to the generated data. It also exhibits a notable degree of conformity of predicted data to the experimental ones and effectively characterizes the system across different reaction temperatures, reactant molar ratio, and catalyst concentration.

A Collaborative Study: Greener Synthesis of Heterocyclic Compounds Using Rice Husk-Based Catalyst

An efficient, straight forward and sustainable synthetic procedures for the synthesis of few important class of bioactive heterocyclic compounds like dihydro-dichromeno-pyridine-6,8-diones, tetrahydrotetrazolo[5,1-b]quinazolinones and2,4-diaryl hexahydroquinoline-5-ones have been designed using a novel bio-degradable heterogeneous catalyst-sulphonated rice-husk (SRH). The greener catalyst has high porosity and high density of acid groups along with bio-degradable characteristics which has made it different and advantageous material for catalysis as compared to other conventional homogenous solid acid catalyst. We report primarily a new protocol for the synthesis of a group of biologically active compounds such as dihydro-dichromeno-pyridine-6,8-dione, tetrahydrotetrazolo[5,1-b]quinazolinone and2,4-diaryl hexahydroquinoline-5-ones derivatives using sulphonated rice husk (SRH) under greener condition. Operational simplicity, easy recovery of the product, metal free technique and reusability of the catalyst with excellent yield are the important and promising features of this procedure. The prepared solid heterogeneous catalyst was subjected for characterization using different spectroscopic techniques like FTIR, SEM, EDX, Powder XRD before its application for desired reaction.

Modeling and simulation of an ideal plug flow reactor for synthesis of ethyl oleate using homogeneous acid catalyst

Modeling and simulation of an ideal plug flow reactor for synthesis of ethyl oleate using homogeneous acid catalyst

Transesterification of Microalgae from Food Waste via Acid Catalyst for Biodiesel Production

Recently, numerous studies have presented the potential of various feedstock of biodiesel catalysed with acid catalysts and its performance. This study examines the potential of microalgae from food waste for biodiesel production by a homogeneous acid catalyst in a transesterification reaction. Initially, lipid was extracted from the microalgae using the microwave-assisted extraction (MAE) method. Then, the lipid was transesterified using a sulphuric acid catalyst under different conditions to decide the optimum condition. About 50% of the lipid was extracted from the microalgae when 400 W of microwave power was used for 15 minutes. The biodiesel yield of 76% has been attained from transesterifying the extracted lipid with methanol using 9:1 of methanol to oil molar ratio, 2.5 wt% of catalyst dosage for 3 hours at 65°C. Overall, this study has shown the potential of microalgae from food waste as one of the options for biodiesel’s feedstock catalysed by acid.
 Keywords: Biodiesel, food waste, microalgae, transesterification, acid catalyst, microwave assisted extraction (MAE)

Kinetics of esterification of acetic acid with n‐butanol over different homogeneous acid catalysts

AbstractThe esterification reaction of n‐butanol and acetic acid has been performed in batch reactor in the presence of different homogeneous acid catalyst, namely sulfuric acid, nitric acid, and para toluene sulfonic acid (p‐TSA). The objective of present research work is to investigate kinetic behavior of esterification reaction over the temperature range of 60°C–80°C. The effect of reaction parameter such as catalyst loading varied from 1% to 5% v/v and acid to alcohol molar ratio of 1:1, 1:3, and 1:5 has been observed. A pseudo homogeneous kinetic model has been applied. Kinetic parameters such as equilibrium constant, reaction rate constant, enthalpy, activation energy, and entropy were calculated by the experimental data for different acid catalyst system. It was observed that sulfuric acid gives higher conversion 73% than p‐TSA 68.5% and nitric acid 66.25% at temperature of 80°C, 1:1 molar ratio and 3% catalyst concentration. The activation energy was estimated 36448.49, 23324.31 and 19060.156 J/mol K for three different catalyst sulfuric acid, nitric acid and p‐TSA respectively. The enthalpy and entropy of the esterification reaction of acetic acid with n‐butanol over three different catalysts has been calculated (Enthalpy: 25.788 KJ/mol, 12.256 KJ/mol, 28.320 KJ/mol, Entropy: 88.1 J/mol K, 45.298 J/mol K, 91.44 J/mol K) and found enthalpy is having positive value that shows reaction is endothermic.

Production of high-carbon-number bio-aviation fuels from furans using sulfated zirconia and silica-alumina aerogel catalysts

Lignocellulose can help produce fuels in biorefineries through its fractionated components such as cellulose, hemicelluloses, and lignin. For instance, hemicellulose-derived xylose has been studied for obtaining petroleum-substituting fuels. Therefore, in this study, catalytic hydroalkylation/alkylation (HAA) of xylose-derived 2-methylfuran (2-MF) with butanal was targeted to selectively produce high-carbon-number diesel fuels. To that end, silica–alumina (SiAl) aerogels with different Si/Al ratios and a series of sulfated zirconia (SZ) compounds calcined at various temperatures were prepared as catalysts to overcome the limitations of conventional hazardous homogeneous acid catalysts. The activity of the SiAl catalysts in forming the desired HAA product, 5,5-bissylvylbutane (denoted as BB), was found to be directly related to the number of acid sites and acid density. Moreover, increasing the Si/Al molar ratio, which reduced the acid density and number of acid sites, led to lower 2-MF conversions and BB yields. The optimal 2-MF conversion and BB yield with the SiAl catalysts (67 % and 45 %, respectively) were achieved using a Si/Al ratio of 8:2 mol/mol. Furthermore, SZ calcined at 700 °C (denoted as SZ-700) exhibited the highest activity among the SZ catalysts (72 % 2-MF conversion, 63 % BB yield), despite having the fewest acid sites and lowest acid density. This was presumably because of the physical structure of SZ-700, which featured mixed monoclinic and tetragonal phases, many oxygen vacancies, and a large accessible external surface area, which facilitated the HAA reactions. Hydrogenation and hydrodeoxygenation (HDO) of BB were performed thereafter using Pd/C and Ru/SiO2–Al2O3 catalysts, respectively. The resulting deoxygenated hydrocarbons comprised 15.1 % light hydrocarbons (C4–C8) and 83.1 % heavier hydrocarbons (C9–C20). Simulated distillation analysis of the post-HDO product distribution indicated that the liquid-phase product contained 70 % high-carbon-number bio-aviation fuels.

(Invited) Efficient Carbon Sulfonation Using Plasma in Contact with Dilute Sulfuric Acid

Heterogeneous catalysis is a promising technology in biomass valorization because of its high reactivity, easy post-separation, and great recyclability compared to homogeneous catalysis. Various functionalized catalytic materials have emerged as promising alternatives to the homogeneous liquid acid catalyst, such as carbon materials, metal–organic frameworks, and metal nanoparticles. Among them, carbon materials such as carbon nanotube, graphene oxide, carbon black, and so on have been investigated as catalysts for cellulose hydrolysis to produce glucose.Carbon materials show considerable catalytic activity by functionalization with active acidic groups including hydroxyl groups (-OH), carboxyl groups (-COOH), and sulfonic groups (-SO3H). Hydroxyl and carboxyl groups on the carbon catalysts act as connection center to access cellulose, where sulfonic group serves as the active site to cut off the linkage between glucose units in cellulose. So, the surface modification of carbon materials with these functional groups, namely, carbon sulfonation process, becomes the determining step to producing efficient carbon acid catalysts. Conventional methods for the carbon sulfonation are the hydrothermal and reflux method, in which hazardous chemicals are necessary, such as concentrated sulfuric acid (95–98%), chlorosulfonic acid, fuming sulfuric acid, or 4-benzenediazoniumsulfonate under elevated temperature for dozens of hours. As a green and effective carbon sulfonation process, we have utilized gas–liquid interfacial plasma (GLIP).In the GLIP process, plasma is generated between the tips of multi-needles and the surface of dilute sulfuric acid which contains carbon particles in N2/Ar gas mixture. The optimized catalyst synthesized from graphene nanoplatelets by the GLIP process achieved a conversion rate of 41.5% with high glucose selectivity of 84.3%, which is superior to performance of catalysts synthesized by the hydrothermal method. The concentration of sulfuric acid, reaction temperature, and reaction time for the GLIP process were 1 M, 40℃, and 0.75 h, respectively while those of the hydrothermal method were 18 M, 200℃, and 24 h, respectively. Thus, the GLIP process is less hazardous and more efficient. Significantly, the catalyst synthesized by the GLIP process also exhibited superior recyclability of 95.9% in 3 times cycle tests for cellulose hydrolysis.Recently, we have investigated the mechanism of carbon sulfonation in GLIP processes. Active species produced near the gas–liquid interface such as ·OH, SO3, and HOSO2· probably play important roles in carbon sulfonation. We are trying to observe gas-phase active species by Fourier transform infrared spectroscopy and quadrupole mass spectrometer, and liquid-phase active species by electron spin resonance spectroscopy.

Aspect elucidation of a physicochemical pretreatment for continuous decrystallization

The purpose of this study is to understand the operating conditions of a physicochemical pretreatment process for lignocellulosic biomass using homogeneous acid catalysts. Four parameters were studied: moisture content, acid catalyst, type of biomass and reactor morphology. The different types of biomass (perennial grasses: sugarcane bagasse, corn stover; flowering plants: cannabis (stalks and leaves); hardwoods (pulp and bark): poplar, sugar maple; softwood bark) were processed in a meat grinder with sulfuric acid. Furthermore, softwood bark was used to change the moisture content, acid catalyst and reactor morphology. Biomass moisture above 17 wt% yielded less than 50 wt% glucose. Sulfuric acid, by far, had the best performance with a 74.5 wt% glucose yield in the meat grinder. The glucose yield showed a direct relationship with the non-carbohydrate components of biomass (lignin, ash, etc).

Application of sulfonated biochar-based magnetic catalyst for biodiesel production: Sensitivity analysis and process optimization

The sulfonated magnetic porous biochar-based solid catalysts have a significant potential to replace homogeneous acid catalysts in order to decrease corrosion issues and the environmental risks brought on by homogeneous acid catalysts. For this purpose, produced biochar from the rice husk pyrolysis at 700 °C was employed for the synthesis of a biochar-based magnetic acid catalyst. The base structure of the catalyst was modified and magnetized using different ratios of ZnCl2 and FeCl3. The magnetic porous biochar was sulfonated with two sulfonation agents including H2SO4 and ClSO3H. Characteristic analyzes of BET (Brunauer, Emmett, and Teller), Scanning Electron Microscopy, vibrating-sample magnetometer, Fourier Transform Infrared Spectroscopy, Energy-Dispersive X-ray Spectroscopy, and elemental analysis were used to investigate the physicochemical properties of the synthesized catalysts. The magnetic biochar-sulfonated with ClSO3H was evaluated as the selected catalyst in the biodiesel generation process from oleic acid (OA) as a representative of bio-oils. The central composite design (CCD) based on the response surface methodology (RSM) was used to optimize the process and examine the effectiveness of various parameters, including catalyst concentration based on the OA weight (3–15 wt.%), experiment duration (1–5 h), MeOH: Oil molar ratio (5–25), and reaction temperature (40–100 °C), on the efficiency of biodiesel generation. The optimum yield was achieved at 98.11% under the optimal condition, which included an experiment duration of 4.8 h, catalyst concentration of 9.9 wt.%, MeOH: Oil ratio of 16:1, and reaction temperature of 74.8 °C.

Conversion of wet microalgae to biodiesel with microalgae carbon based magnetic solid acid catalyst

A microalgae carbon based magnetic solid acid catalyst (MCMSA) was prepared using microalgal residue after lipids extraction as carbon source through magnetization, carbonization and sulfonation. The effects of three preparation conditions of pore-forming agent type, carbonization temperature, and sulfonation agent type on the MCMSA were studied. The specific surface area, functional group, acidity and magnetism of MCMSA were studied to determine the optimized catalyst. The MCMSA prepared under the condition that the pore-forming agent is NaCl (1:1 m/m), the carbonization temperature is 800 °C, and the sulfonation agent is H2SO4 (1:10 m/v, 150 °C) has a high specific surface area (124.70 m2/g), high acidity (3.64 mmol/g) and high magnetism (1.042 emu/g), and shows good thermal stability at transesterification temperature of 90 °C with low loss of acid groups. MCMSA showed high conversion efficiency (98.51 %) in the microwave-assisted catalytic transesterification at 90 °C with MCMSA dosage of 5 wt% and methanol to wet microalgae ratio of 6.25:1 (v/m). It could maintain catalytic activity in five consecutive cycles without further treatment, and the average conversion efficiency was approximately 85.5 %. The results showed that the MCMSA could replace the traditional homogeneous acid catalyst for the preparation of microalgae biodiesel.

Enabling Catalysts for Biodiesel Production via Transesterification

With the rapid development of industry and the increasing demand for transportation, traditional sources of energy have been excessively consumed. Biodiesel as an alternative energy source has become a research focus. The most common method for biodiesel production is transesterification, in which lipid and low carbon alcohol are commonly used as raw materials, in the presence of a catalyst. In the process of transesterification, the performance of the catalyst is the key factor of the biodiesel yield. This paper reviews the recent research progress on homogeneous and heterogeneous catalysts in biodiesel production. The advantages and disadvantages of current homogeneous acid catalysts and homogeneous base catalysts are discussed, and heteropolyacid heterogeneous catalysts and biomass-derived base catalysts are described. The applications of the homogeneous and heterogeneous catalyst derivatives ionic liquids/deep eutectic solvents and nanocatalysts/magnetic catalysts in biodiesel production are reviewed. The mechanism and economic cost of current homogeneous acid catalysts and homogeneous base catalysts are also analyzed. The unique advantages of each type of catalyst are compared to better understand the microscopic details behind biodiesel. Finally, some challenges of current biodiesel catalysts are summarized, and future research directions are presented. This review will provide general and in-depth knowledge on the achievements, directions, and research priorities in developing novel homogeneous/heterogeneous catalysts for the green and cost-effective production of biodiesel.

Room temperature esterification of high-free fatty acid feedstock into biodiesel.

The esterification of a high-free fatty acid feedstock to biodiesel is often performed in high-temperature conditions using either homogeneous or heterogeneous acid catalysts. Thus, this study attempts to esterify oleic acid to biodiesel in room temperature conditions using sulphuric acid as a catalyst and a homogenizer device. The influences of process parameters including the molar ratio of oleic acid to methanol, catalyst concentration and rotational speed on biodiesel conversion were determined in different reaction times. The maximum conversion of 96.1 ± 0.4% was obtained in the presence of a molar ratio of 1 : 12, catalyst concentration of 0.7 mol L-1, a rotational speed of 4000 rpm and a reaction time of 30 minutes. The catalytic reusability test showed that the addition of fresh methanol is required to maintain the catalytic activity. However, the homogenizer-intensify esterification of oleic acid to biodiesel showed better performance than other methods as the reaction could conducted at room temperature and at a short reaction time. The predicted biodiesel properties meet the international standard except for oxidative stability. However, the flow properties revealed that the biodiesel can be used in winter season.

Heterogenization of a Tungstosilicic Acid Catalyst for Esterification of Bio-Oil Model Compound

Based on a prior demonstration of the high activity of a homogeneous tungstosilicic acid catalyst for the esterification of acetic acid as bio-oil model compound, a further study has been undertaken in an attempt to heterogenize the catalyst. Tungsten oxide was supported on amorphous silica (W/A150) using incipient wetness impregnation and incorporated into the structure of structured silica (W-KIT-5) via a one-step hydrothermal synthesis. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), physisorption (BET), and temperature-programmed desorption of ammonia (NH3-TPD). Both series were evaluated for the esterification of acetic acid with ethanol and compared with the homogeneous 12-tungstosilicic acid catalyst. The result of XRD analysis suggests the average crystallite size of the W oxide nanoparticles on both supports to be less than 2 nm, while XPS analysis revealed that all W existed in the W 6+ oxidation state. From the BET and NH3-TPD analyses, it was shown that the KIT-5 series had higher surface area and acidity than the W/A150 catalyst. The 10% W-KIT-5 was shown to be the best heterogeneous catalyst with the highest activity and acid conversion of about 20% and 93% of the homogeneous catalyst. Significant leaching of tungsten from both the supports occurred and will have to be solved in the future.

TRANSESTERIFICATION OF TRIGLYCERIDES WITH PROPAN-2-OL CATALYSED BY SULFURIC ACID

Transesterification of sunflower oil triglycerides with propan-2-ol catalyzed by sulfuric acid has been studied. The effect of the homogeneous acid catalyst content and the triglycerides of sunflower oil : propan-2-ol molar ratio on the reagents conversion, selectivity of diisopropyl ether formation, the acid number and the color of reactions products on the iodine scale was determined. It was established that an increase in the sulfuric acid content from 1 wt. % up to 3 wt. % leads to a slight increase in the triglycerides conversion and a significant increase in the propan-2-ol conversion. A further increase in the acid catalyst content causes a decrease in the conversion of both triglycerides and alcohol. Comparison of the obtained results with the data on the reaction products composition allowed us to conclude that a significant increase in the propan-2-ol conversion with an increase in the sulfuric acid content to 3–4 wt. % due to the increase in the diisopropyl ether selectivity formation from 5% by an acid catalyst content of 1 wt. % to almost 65% by a sulfuric acid content of 4 wt. %. It is shown that an increase in the sulfuric acid content in the reaction mixture also leads to a significant increase in the reaction product's color according to the iodine scale - almost 5 times, which also indicates the course of side condensation reactions with the double bonds of higher fatty acids participation, which are part of triglycerides composition. It is established that the reaction product's acid number regularly increases with an increase in the acid catalyst content in the reaction mixture. It is shown that the reaction products acid number value is determined by the amount of acid catalyst used. It is established that the activity of the sulfuric acid in the sunflower oil triglycerides transesterification reaction is slightly lower than the activity of cation exchange resin KU-2-8. The cation exchange resin under the same conditions provides more than 15% higher triglycerides conversion with a lower reaction product's color on the iodine scale value and the absence of a diisopropyl ether formation side reaction. It is concluded that using sulfuric acid as a catalyst for triglyceride transesterification by propan-2-ol is entirely possible.