Homogeneous Acid Catalysts Research Articles

Effect of Mixed Acid Catalysis on Pretreatment and Enzymatic Digestibility of Sugar Cane Bagasse

Aqueous pretreatment using homogeneous acid catalyst is considered as a low-cost technology in the production of lignocellulosic bioethanol. To establish the synergism of mixed acids, pilot-level aqueous pretreatments of bagasse covering a wide range of combined severity (CS) were carried out. To investigate the effect of application of mixture of acids on xylose hydrolysis as well as glucose hydrolysis via pretreatment and enzymatic hydrolysis, the following three combinations of acids were explored: (1) oxalic acid + sulfuric acid (organic + mineral acid), (2) phosphoric + sulfuric acid (mineral acids), and (3) ferric chloride + sulfuric acid (Lewis acid with a mineral acid). Of the pretreatments evaluated, the synergism was most pronounced for the combination of sulfuric and phosphoric acid, which resulted in more than 90% conversion of hemicellulose to xylose and 70% conversion of cellulose to glucose through enzymatic hydrolysis. Fourier transform infrared (FTIR) studies of pretreated samples showed ...

Production of renewable toluene from biomass-derived furans via Diels-Alder and dehydration reactions: A comparative study of Lewis acid catalysts

The Diels–Alder cycloaddition of biomass-derived furans and subsequent dehydrative aromatization are potentially valuable processes for the sustainable production of aromatic chemicals from biomass. In this paper, we have investigated the catalytic activity of a series of homogeneous and heterogeneous Lewis acid catalysts in connection with the conversion of biomass-derived 2-methylfuran (MF) and ethylene to toluene. We have used a number of Lewis acid metal chlorides, cation-exchanged Y zeolites, Sn- and Zr-containing beta zeolites to understand the role of acid sites and activity correlation in the MF reaction. The Lewis acid catalysts of AlCl3 and Na-Y zeolite demonstrated superior selectivity for toluene production with regard to the Brønsted acidic zeolites of H-Beta and H-Y, which have proven to be effective for the conversion of 2,5-dimethylfuran (DMF) to p-xylene. The high toluene selectivity of the Lewis acid catalysts was mainly attributed to their ability to retard side reactions, such as oligomerization and alkylation, as well as to accelerate the cycloaddition of MF and ethylene. In the case of Brønsted acidic zeolites, the side reactions were significantly enhanced, resulting in lower selectivity to toluene. The catalytic activity of the Lewis acidic metal chloride catalysts was correlated with an empirical scale of Lewis acid strength, showing that the strongest Lewis acid, AlCl3, gave the highest toluene yield of ∼70% at 250°C after 24h. Similarly, of the alkali cation-exchanged Y-zeolites investigated here, Li- and Na-Y were more active than K- and Cs-Y due to the smaller size of the cations, resulting in stronger Lewis acidity. Na-Y was also more active than Sn- and Zr-Beta, which have framework Lewis acidic sites, demonstrating its superiority for catalyzing the cascade of Diels-Alder and dehydrative aromatization reactions of MF. A remarkable toluene yield of ∼65% was achieved with Na-Y at the nearly complete MF conversion (>96%) under optimal reaction conditions.

Side products of methacrylic acid esterification with triethylene glycol methyl ether

Side reactions in the course of esterification of methacrylic acid with triethyleneglycol methyl ether in the presence of homogeneous acid catalyst have been studied. Chromato-mass spectrometry and authentic synthesis have revealed the chemical structure of the products; pathways of their formation have been suggested.

Effect of reaction parameters on the catalytic transesterification of cottonseed oil using silica sulfuric acid

ABSTRACTTransesterification of refined cottonseed oil was studied in the presence of silica sulfuric acid as a new heterogeneous solid acid catalyst to overcome the drawbacks of homogeneous alkali and acid catalysts. The effect of various reaction parameters, such as oil to methanol ratio, reaction temperature, reaction time, and catalyst amount, was investigated. The highest methyl ester conversion was obtained at 373 K using 5% catalyst amount and 1:20 methanol ratio within 8 h. Silica sulfuric acid was found to be a promising catalyst for cleaner biodiesel production without tedious post treatments for the product purification.

Levulinic Acid Production Using Solid-Acid Catalysis

Levulinic acid (LA) is one of the compounds included in the list of the 12 chemicals, known as “building blocks” obtained from biomass. One route to synthesize levulinic acid is from furfuryl alcohol (FA), which is a compound that can be obtained from biomass. For this route, the hydration and ring opening of FA is necessary. Usually, the hydration takes place using homogeneous strong acid catalysts, being the disadvantages of using homogeneous acid catalysts well-known. Therefore, this work has studied the production of LA using heterogeneous catalysts such as ion exchange resins, zeolites, and acidic clays. The LA yield was increased by the optimal control of FA feed. The initial catalyst screening study showed results up to 62% in LA yield. Then, an optimization procedure was developed using the ZSM-5 catalyst, reaching a maximum LA yield of 77%.

Enhanced Activity of Nanocrystalline Beta Zeolite for Acylation of Veratrole with Acetic Anhydride.

Friedel-Craft acylation of veratrole using homogeneous acid catalysts such as AlCl3, FeCl3, ZnCl2, and HF etc. produces acetoveratrone, (3',4'-dimethoxyacetophenone), which is the intermediate for synthesis of papavarine alkaloids. The problems associated with these homogeneous catalysts can be overcome by using heterogeneous solid catalysts. Since acetoveratrone is a larger molecule, large pore Beta zeolites with smaller particle sizes are beneficial for the liquid-phase acylation of veratrole, for easy diffusion of reactants and products. The present study aims in the acylation of veratrole with acetic anhydride using nanocrystalline Beta Zeolite catalyst. A systematic investigation of the effects of various reaction parameters was done. The catalysts were characterized for their structural features by using XRD, TEM and DLS analyses. The catalytic activity of nanocrystalline Beta zeolite was compared with commercial Beta zeolite for the acylation and was found that nanocrystalline Beta zeolite possessed superior activity.

Application of Tin(II) Chloride Catalyst for High FFA Jatropha Oil Esterification in Continuous Reactive Distillation Column

The application of heterogeneous solid acid catalysts in biodiesel production has become popular and gained significant attention over the last few years. It is since these types of catalysts hold the benefits in terms of easy separation from the product, reusability of the catalyst, high selectivity of the reaction. They are also considered sustainable and powerful particularly in organic synthesis. This work studied the use of tin(II) chloride as solid Lewis acid catalyst to promote the esterification reaction of high Free Fatty Acid (FFA) jatropha oil in continuous reactive distillation column. To obtain the optimum condition, the influences of reaction time, molar ratio of the reactant, and catalyst were investigated. It was revealed that the optimum condition was achieved at the molar ratio of methanol to FFA at 1:60, catalyst concentration of 5%, and reaction temperature of 60°C with the reaction conversion of 90%. This result was significantly superior to the identical reaction performed using batch reactor. The esterification of high FFA jatropha oil using reactive distillation in the presence of tin(II) chloride provided higher conversion than that of Amberlyst-15 heterogeneous catalyst and was comparable to that of homogenous sulfuric acid catalyst, which showed 30 and 94.71% conversion, respectively. The esterification reaction of high FFA jatropha oil was subsequently followed by transesterification reaction for the completion of the biodiesel production. Transesterification was carried out at 60 °C, molar ratio of methanol to oil of 1:6, NaOH catalyst of 1%, and reaction time of one hour. The jatropha biodiesel product resulted from this two steps process could satisfy the ASTM and Indonesian biodiesel standard in terms of ester content (97.79 %), density, and viscosity.

First Examples of Doebner-Miller Reaction in Flow: Efficient Production of 2-Methylquinoline Derivatives in Water

Production of quinaldine and derivatives is proposed using sulfuric acid as commercial homogeneous acid catalyst in water in continuous flow chemistry. This approach is a rapid, practical and green route for the synthesis of 2-methylquinolines and permit to obtain the target compounds in 39–91% yields.

Nano-crystalline, mesoporous aerogel sulfated zirconia as an efficient catalyst for esterification of stearic acid with methanol

Aerogel sulfated zirconia (A-SZr) solid acid catalyst was prepared by sol–gel method followed by supercritical drying (SCD) using n-propanol as alcoholic solvent. For comparison, xerogel sulfated zirconia (X-SZr) was also prepared by sol–gel followed by conventional thermal drying method. A-SZr catalyst has lower nano-crystallite size, higher BET surface area, pore volume and ordered mesoporous structure with complete absence of micropores along with more number of scattered and accessible Brönsted and Lewis acid sites as compared to X-SZr. The evaluation of its catalytic performance for esterification of stearic acid with methanol exhibited 88% yield of methyl stearate at 60°C after 7h. A-SZr catalyst showed significant higher reaction rate (18.94mmolh−1g−1) and TOF (8.55h−1) than X-SZr (12.94mmolh−1g−1 and 3.92h−1, respectively). A-SZr catalyst also exhibited higher activity than other heterogeneous acid catalysts such as ion-exchange resins, Nafion and acid clay under the similar reaction conditions; as well as it showed comparable activity with conventional Brönsted (H2SO4) and Lewis (ZrOCl2) acids indicating its potential to replace the homogeneous acid catalysts.

ChemInform Abstract: State of the Art of Biodiesel Production Processes: A Review of the Heterogeneous Catalyst

AbstractReview: 183 refs.

Selective oxidation of furfural in a bi-phasic system with homogeneous acid catalyst

The selective catalytic oxidation of furfural to 2(5H)-furanone, succinic acid (SA) and maleic acid (MA) was studied. Under optimized conditions, furfural was oxidized to 2(5H)-furanone with a yield of 60–62% in an aqueous/organic bi-phasic system using 1,2-dichloroethane or ethyl acetate as the solvent and formic acid as the catalyst, while the total yield of SA and MA was 15–20%. Compared with other homogeneous and heterogeneous acid catalysts, formic acid gave a much higher selectivity to 2(5H)-furanone because it reacted with hydrogen peroxide to generate performic acid that had a strong oxidizing nature and good solubility in both the aqueous and organic phases. The solvent had a significant influence on the product distribution. A simplified reaction network was established to quantitatively analyze the solvent effect based on the reaction rate constants. In the homogeneous system, the yield of 2(5H)-furanone decreased while the yield of SA increased with an increasing dielectric constant of the solvent. The formic acid/furfural molar ratio, reaction temperature and furfural concentration were optimized for the selective oxidation of furfural to 2(5H)-furanone in the bi-phasic reaction system.

Fe3O4@MCM-41-SO3H@[HMIm][HSO4]: An effective magnetically separable nanocatalyst for the synthesis of novel spiro[benzoxanthene-indoline]diones

Synthesis of novel spiro[benzo[a]xanthene-12,3′-indoline]-2′,11(8H)-diones and spiro[benzo[c]xanthene-7,3′-indoline]-2′,8(9H)-diones were evaluated by three type of MCM-41 mesoporous magnetite nanoparticles Fe3O4@MCM-41-(CH2)3–SO3H, Fe3O4@MCM-41-SO3H and Fe3O4@MCM-41-SO3H@[HMIm][HSO4] as heterogeneous solid acid catalysts and 1-methylimidazolium hydrogen sulfate ([HMIm][HSO4]) as homogeneous acid catalyst in terms of activity and recyclability. The activity of Fe3O4@MCM-41-SO3H@[HMIm][HSO4] was comparable to those of the other heterogeneous and homogeneous catalysts. The structures of the products were characterized by their physical constants, IR, 1H NMR and 13C NMR spectroscopy. The ability to reuse the magnetite nanoparticle, high yield, short reaction time, solvent free conditions and ease of purification of products are the important features of this process.

Hydrothermal gasification of a biodiesel by-product crude glycerol in the presence of phosphate based catalysts

Energy from biomass can be provided in various ways, such as burning the solid wastes, production of biogas (by anaerobic digesters), biofuels (i.e. methanol, ethanol, biodiesel, and derivatives), and methane via the utilization of landfills. Biodiesel is a widely used biofuel produced by the conversion of first-generation biomass feedstock via bio-chemical conversion platforms.Crude glycerol is the by-product of biodiesel production being 10 wt.% of the produced biodiesel. The objective of this study is to utilize this glycerol fraction by converting it to fuel gas or to chemical feedstock.In this study, the concentration of glycerol feedstock solution and the catalyst concentration were 50 g/L and 5 g/L, respectively. Crude glycerol was gasified in a sub and supercritical water medium by using a batch autoclave with an inner volume of 100 ml. A temperature range from 300 to 600 °C was studied. Experiments were performed with pure and crude glycerol samples in the absence and the presence of homogeneous acidic and alkali catalysts, namely H3PO4, KH2PO4, K2HPO4, and K3PO4. These were used to obtain higher gasification efficiencies and hydrogen and/or methane yields.Subsequent to each experiment liquid, solid, and gaseous products were collected and analyzed by GC, TCA (total carbon analyzer), HPLC, and GC/MS.The order of the effectiveness of the catalysts on gasification was found as: K3PO4 > K2HPO4 > H3PO4 > KH2PO4 for crude glycerol and K3PO4 > K2HPO4 > KH2PO4 > H3PO4 for pure glycerol. K2HPO4 and K3PO4 were found to be more effective in terms of hydrogen production while H3PO4 and KH2PO4 showed the best performance for the maximized methane production.

Transesterification of Triolein over Hydrophobic Microporous Carbon with SO3H Groups

AbstractSO3H‐bearing microporous amorphous carbon with a large BET surface area (≈2000 m2 g−1) and a high density of SO3H groups (0.5 mmol g−1) was investigated as a solid acid catalyst for the transesterification of triolein and esterification of oleic acid with methanol. The separable and reusable carbon catalyst exhibits higher catalytic performance for both reactions than conventional homogeneous and heterogeneous acid catalysts, including sulfuric acid, at 353 K. This carbon catalyst can provide methyl oleate yields over 99 %, even in a triolein–oleic acid mixture that resembles a crude vegetable oil, owing to efficient transesterification and esterification reactions. The carbon material is sufficiently hydrophobic to be distributed throughout the hydrophobic triolein phase, resulting in high catalytic performance for both reactions.

Amidation of Carboxylic Acids with Amines by Nb2O5 as a Reusable Lewis Acid Catalyst

AbstractAmong 28 types of heterogeneous and homogenous catalysts tested, Nb2O5 shows the highest yield for direct amidation of n‐dodecanoic acid with a less reactive amine (aniline). The catalytic amidation by Nb2O5 is applicable to a wide range of carboxylic acids and amines with various functional groups, and the catalyst is reusable. A comparison of the results of the catalytic study and an infrared study of the acetic acid adsorbed on the catalyst suggests that activation of the carbonyl group of the carboxylic acid by Lewis acid sites on Nb2O5 is responsible for the high activity of the Nb2O5 catalyst. Kinetic studies show that Lewis acid sites on Nb2O5 are more water‐tolerant than conventional Lewis acidic oxides (Al2O3, TiO2). In comparison with the state‐of‐the‐art homogeneous Lewis acid catalyst for amidation (ZrCl4), Nb2O5 undergoes fewer negative effects from basic additives in the solution, which indicates that Nb2O5 is a more base‐tolerant Lewis acid catalyst than the homogeneous Lewis acid catalyst.

Formation of 5-(Hydroxymethyl)furfural by Stepwise Dehydration over TiO2 with Water-Tolerant Lewis Acid Sites

The reaction mechanism for the formation of 5-(hydroxymethyl)furfural (HMF) from glucose in water over TiO2 and phosphate-immobilized TiO2 (phosphate/TiO2) with water-tolerant Lewis acid sites was studied using isotopically labeled molecules and 13C nuclear magnetic resonance measurements for glucose adsorbed on TiO2. Scandium trifluoromethanesulfonate (Sc(OTf)3), a highly active homogeneous Lewis acid catalyst workable in water, converts glucose into HMF through aldose–ketose isomerization between glucose and fructose involving a hydrogen transfer step and subsequent dehydration of fructose. In contrast to Sc(OTf)3, Lewis acid sites on bare TiO2 and phosphate/TiO2 do not form HMF through the isomerization–dehydration route but through the stepwise dehydration of glucose via 3-deoxyglucosone as an intermediate. Continuous extraction of the evolved HMF with 2-sec-butylphenol results in the increase in the HMF selectivity for phosphate/TiO2, even in highly concentrated glucose solution. These results sugges...

Production and Upgradation of Cotton Shell Pyrolytic Oil for Biofuel from Flash Pyrolysis by Fluidized Bed Reactor

In this study the flash pyrolysis of the cotton shell on the electrically heated fluidized bed has been conducted for producing cotton shell pyrolytic oil and with the presence of homogenous acid catalyst the cotton shell pyrolytic oil is converted into biofuel. Cotton shell was procured from resources available in India. The various physical properties such as density, viscosity, flash point and elemental analysis have been done for the bio oil. For the baseline data analysis, the same characteristics study has been carried out on the biofuel and an acceptable agreement is observed.

Optimization of Pyrolysis Operating Condition for Deriving Corn Starch Heterogeneous Acid Catalyst for Biodiesel Production

Biodiesel can be produced from various oils and fats. Due to possibility of diversion of edible oils from feedstocks to raw materials for biodiesel production, which may lead to food crisis, it is preferable to choosenon-edible oils as raw material for biodiesel production. As a country rich in natural resources, Indonesia has avast amount and variety of non-edible fatty-oil production plants. However, non-edible oils usually have highfree fatty acid (FFA) contents. Oils with high FFA contents cannot be converted directly to biodiesel using aconventional alkaline catalyzed process due to saponification problem. To avoid this problem, the high FFAcontents in the oils must be reduced via esterification process using acid catalyst. The use of homogeneous acidcatalyst in this process can be very corrosive and not environmentally friendly while the use of commerciallyavailable heterogeneous acid catalyst can be very expensive. In this research, a heterogeneous acid catalystsuitable for biodiesel production will be derived from corn starch through pyrolysis followed by sulphonationprocesses. The purpose of this research is to study the effects of pyrolysis temperature and time to the aciddensity of the catalyst and the activity of the catalyst in the esterification of oleic acid using a 22 factorial designwith 3 center points experimental design. It is found that the catalyst obtained from pyrolysis at 400°C for 15hours has the optimum–HSO3 content of 5.9% which corresponds to the highest average conversion of theesterification of oleic acid of 97.45%.

Synthesis of spiro[benzochromeno[2,3-d]pyrimidin-indolines] using Fe3O4@MCM-41-SO3H@[HMIm][HSO4] as a magnetically separable nanocatalyst

Three types of MCM-41 mesoporous magnetite nanoparticles Fe3O4@MCM-41-(CH2)3-SO3H, Fe3O4@MCM-41-SO3H and Fe3O4@MCM-41-SO3H@[HMIm][HSO4] as heterogeneous solid acid catalysts were evaluated for the synthesis of spiro[benzochromeno[2,3-d]pyrimidin-indolines] in terms of activity and recyclability. Their catalytic activities were compared with those of the homogeneous acid catalyst 1-methylimidazolium hydrogen sulfate ([HMIm][HSO4]). The activity of Fe3O4@MCM-41-SO3H@[HMIm][HSO4] was comparable to those of the other heterogeneous and homogeneous catalysts.

Liquid-Phase Catalytic Transfer Hydrogenation of Furfural over Homogeneous Lewis Acid-Ru/C Catalysts.

The catalytic performance of homogeneous Lewis acid catalysts and their interaction with Ru/C catalyst are studied in the catalytic transfer hydrogenation of furfural by using 2-propanol as a solvent and hydrogen donor. We find that Lewis acid catalysts hydrogenate the furfural to furfuryl alcohol, which is then etherified with 2-propanol. The catalytic activity is correlated with an empirical scale of Lewis acid strength and exhibits a volcano behavior. Lanthanides are the most active, with DyCl3 giving complete furfural conversion and a 97 % yield of furfuryl alcohol at 180 °C after 3 h. The combination of Lewis acid and Ru/C catalysts results in synergy for the stronger Lewis acid catalysts, with a significant increase in the furfural conversion and methyl furan yield. Optimum results are obtained by using Ru/C combined with VCl3 , AlCl3 , SnCl4 , YbCl3 , and RuCl3 . Our results indicate that the combination of Lewis acid/metal catalysts is a general strategy for performing tandem reactions in the upgrade of furans.