Heterogeneous Acid Catalysis Research Articles

Preliminary Analysis of Heterogeneous Superacid Catalysts in Biodiesel Production

Biodiesel is a renewable biofuel that has been studied as a possible successor to conventional diesel. Currently, biodiesel is predominantly produced on a commercial scale by means of methyl transesterification via basic catalysis. This production route provides high conversions, however, the alkaline catalyst in the presence of free fatty acids provides the formation of soaps, making it difficult to separate and purify the products, thus making the process more expensive. In this way, studies have been developed with the purpose of replacing conventional basic catalysis with production routes that reduce the formation of by-products and that are simultaneously economically, technically and environmentally viable. According to studies, one of the possible routes with substitution potential is heterogeneous acid catalysis. The objective of this work was to carry out a preliminary analysis with the purpose of verifying the possibility of producing biodiesel through heterogeneous superacid catalysis using niobium oxide supported in gamma alumina as catalysts. Two methods of preparation of the catalysts were evaluated, impregnated and co-precipitate. The catalyst masses were varied in 1%, 2%, 3%, 4%, 5% and 6% in order to find the optimum concentration. The transesterification reaction was conducted at a temperature of 65 ° C with an oil/methanol molar ratio of 1:12 and a reaction time of 5 hours. The results demonstrate that the occurrence of the transesterification reaction. The optimum concentration for both catalysts was 5% and the catalyst that presented the highest conversion was the catalyst obtained by the co-precipitation method.

Exergetic Analysis of Biodiesel Production Routes

Biodiesel is a possible successor to conventional diesel. Several methods, with the most varied raw materials and different routes, are available in the literature, directed to the production of biodiesel. In this way, the objective of this work was to evaluate the energetic conversion process from two routes: via basic homogeneous catalysis and via heterogeneous acid catalysis. The purpose of the study was to verify which of the two routes spends (or destroys, from the exergetic point of view) less energy. Since the route that destroys less energy becomes more energetically viable than the other. Due to the particularity of each method, the operational parameters were different, but for a concise analysis, the same raw materials were used for both cases.

Esterification Optimization of Crude African Palm Olein Using Response Surface Methodology and Heterogeneous Acid Catalysis

In this work, the effect of zeolite montmorillonite KSF in the esterification of free fatty acids (FFAs) of crude African palm olein (Eleaias guinnesis Jacq) was studied. To optimize the esterification of FFAs of the crude African palm olein (CAPO), the response surface methodology (RSM) that was based on a central composite rotatable design (CCRD) was used. The effects of three parameters were investigated: (a) catalyst loading (2.6–9.4 wt %), (b) reaction temperature (133.2–166.2 °C), and (c) reaction time (0.32–3.68 h). The Analysis of variance (ANOVA) indicated that linear terms of catalyst loading (X1), reaction temperature (X2), the quadratic term of catalyst loading ( X 1 2 ), temperature reaction ( X 2 2 ), reaction time ( X 3 2 ), the interaction catalyst loading with reaction time ( X 1 * X3), and the interaction reaction temperature with reaction time ( X 2 * X3) have a significant effect (p < 0.05 with a 95% confidence level) on Fatty Methyl Ester (FAME) yield. The result indicated that the optimum reaction conditions to esterification of FFAs were: catalyst loading 9.4 wt %, reaction temperature 155.5 °C, and 3.3 h for reaction time, respectively. Under these conditions, the numerical estimation of FAME yield was 91.81 wt %. This result was experimentally validated obtaining a difference of 1.7% FAME yield, with respect to simulated values.

New Nb-P-Si ternary oxide materials and their use in heterogeneous acid catalysis

The surface and catalytic properties of oxide ternary materials consisting of niobium-phosphorus-silicon, Nb-P-Si, with Nb/P=1 and general formula xNb2O5·xP2O5·(100–2x)·SiO2, with x=2.5, 5, 7.5, and 10, and Si content ranging from 95 to 80mol% are presented. Amorphous gel-derived samples were obtained, characterized by a very high degree of silicon cross-linking with presence of SiONb bridges, allowing phosphorus to be stably anchored to the matrix through NbOP bonds.The morphology (surface area and porosity), the intrinsic acidity (density and average strength of the surface acid sites, by PEA-TPD in a TGA-DSC coupled instrument), and the nature of the acid sites were determined. The LAS/BAS ratio has been evaluated by FTIR of adsorbed pyridine in absence/presence of water to discover the differences between the intrinsic and effective nature of the acid sites. The amount of acid sites decreased with the Nb-content in the samples as well as the surface average acid strength. Both LAS and BAS are maintained in the presence of water, even if BAS are predominant in any case.The catalytic performances of the Nb-P-Si samples in the reaction of inulin hydrolysis were investigated in aqueous solution under mild conditions (below 100°C).

Fabrication of −SO3H functionalized aromatic carbon microspheres directly from waste Camellia oleifera shells and their application on heterogeneous acid catalysis

Sulfonic acid groups functionalized aromatic carbon microspheres (Ar-CMSs–SO3H) were first successfully fabricated directly from waste Camellia oleifera shells by simple steps in the assistance of phloroglucinol. As a heterogeneous solid Brønsted acid catalyst, the as-prepared Ar-CMSs–SO3H showed considerably high activity because of its numerous spherical microstructure and abundant surface sulfonic acid groups (–SO3H). Subsequently, the as-prepared Ar-CMSs–SO3H was applied to the synthesis of biofuels 5-ethoxymethylfurfural (EMF) from biological platform compounds 5-hydroxymethylfurfural (HMF). The catalytic results showed that both sulfonation conditions in the course of Ar-CMSs–SO3H preparation and catalytic reaction conditions in the course of EMF synthesis had a significant effect on the EMF yield and HMF conversion rate.

Synergetic effect in heterogeneous acid catalysis by a porous ionic crystal based on Al(iii)-salphen and polyoxometalate.

A porous ionic crystal is synthesized with a cationic Al(iii)-salphen complex (Al(iii)-salphen) and a α-Keggin-type polyoxometalate (POM). The compound possesses stable three dimensional porous structure and shows high activity as a heterogeneous catalyst in pinacol rearrangement, which is a typical acid reaction. Notably, Al(iii)-salphen, POM, and a physical mixture of the two components are much less active, suggesting a synergetic effect of Al(iii)-salphen and POM in a porous framework.

Willgerodt-Kindler Reaction’s Microwave-Enhanced Synthesis of Thiobenzamides Derivatives in Heterogeneous Acid Catalysis with Montmorillonite K-10

The Willgerodt-Kindler (WK) reaction of is one of most synthesis methods used to access the thioamides. The known to thioamides have made this reaction more attractive in catalytic synthesis methods. Heterogeneous catalysis acid with the montmorillonite K-10 applied to this reaction under activation microwave for the synthesis of phenyl (morpholino) methanethiones derivatives shows that the mixture (aldehyde, sulfur, morpholine and K-10) is not only appropriate, but optimizes the reaction. This solid catalyst was easily separated from the reaction mixture and was recycled at least twice (02) without any loss of activity. Operational simplicity, short reaction times, excellent yields and benign environmental conditions are other advantages of this protocol, thus respecting the principles of green chemistry. Among the thioamides synthesized, 4-(morpholine-4-carbonothioyl)benzoic acid (h) is a novel molecule which to our knowledge has never before been synthesized. We obtained it with a yield of 68%. In summary, we can be concluded that the heterogeneous catalysis acid conditions with the montmorillonite K - 10 favourable to the Willgerodt-Kindler reaction for carbonyl compounds. The structures of thioamides synthesized were characterized and confirmed by highresolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) 1D and 2D (COSY, HSQC, HMBC).

Erbium-Organic Framework as Heterogeneous Lewis Acid Catalysis for Hantzsch Coupling and Tetrahydro-4H-Chromene Synthesis

An Erbium-organic framework was prepared by hydrothermal reaction. The prepared framework was characterized by Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), and X-ray powder diffraction (XRD). The framework has open metal sites at Er(III) centers, thus providing an accessible Lewis acid center for electrophile activation. Accordingly, the synthesized framework was used as Lewis acid heterogeneous catalyst for Hantzsch coupling reaction and tetrahydro-4H-chromene synthesis. The reaction condition has been optimized by variation of the reaction time, temperature, solvent and catalyst concentration. A variety of tetrahydro-4H-chromenes was synthesized and characterized by FT-IR and 1H NMR spectroscopy. Er-MOF, as a Lewis acid heterogeneous catalyst, showed excellent selectivity and high yield for these transformations.

Synthesis of poly(lactic acid) by heterogeneous acid catalysis from d,l-lactic acid

Poly(lactic acid) (PLA) is an important polymer because of its significant biocompatibility and biodegradability. Supported H3PW12O40 (H3PW) on activated carbon was utilized for the catalytic polymerization of D,L-lactic acid, resulting in blends of PLA. The stability of the polymer was monitored by thermogravimetry (TGA), and the decomposition temperature (Td) was used to determine the optimal production conditions (i.e., temperature of 180 °C for 15 h; 0.1 wt. % catalyst; 20 wt. % H3PW/carbon calcined at 400 °C). The best catalyst was reused three times with good activity and recovery (95 %) and was analyzed to confirm the consistency of its Keggin structure, dispersion, and acidity, which are important parameters that affect the catalyst’s activity. The obtained polymer was characterized by gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FT-IR), 1H/13C nuclear magnetic resonance (NMR) spectroscopy, specific optical rotation ([α]D 25), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The average molar mass of the polymer was 17,400 g mol−1. Blends of poly(lactic acid) with 85 % poly(L-lactic acid) stereospecific isomer were obtained.

Porous carbonaceous solid acids derived from farm animal waste and their use in catalyzing biomass transformation

We demonstrate here the transformation of waste cow manure into N rich porous carbons (NPC) with large amount of micropores and large Brunauer–Emmett–Teller (BET) surface areas. The transformation process was achieved via carbonization of cow manure in presence of ZnCl2 and FeCl3 additives, without using additional templates. The resultant NPC could be converted into microporous carbonaceous solid acids (NPC-[C4N][X]) by quaternary ammonization of samples with 1,4-butane sultone, and ion exchanging with strong acids such as HSO3CF3 and H2SO4. X-ray diffraction patterns and Raman spectra showed that NPC-[C4N][X] exhibit amorphous carbon network. N2 isotherms and SEM images showed that NPC-[C4N][X] have abundant nanopores with large BET surface areas. XPS, FT-IR and elemental analysis results showed the N rich network in NPC support, has been successfully and homogeneously functionalized with strongly acidic ionic liquid and sulfonic groups. 31P solid NMR spectra confirmed that NPC-[C4N][X] have typical Brønsted acid centers with strong and controllable acidity. Catalytic tests showed that NPC-[C4N][X] exhibits excellent activity and reusability in production of biofuels and fine chemicals through esterifications, transesterifications, and depolymerization of microcrystalline cellulose. This approach may provide a novel and cost effective way to recycle the waste cow manure into efficiently porous carbon based solid acids for heterogeneous acid catalysis.

Synthesis of Triacetin and Evaluation on Motor

Triacetin (or glycerol triacetate) was obtained by acetylating the glycerol by-product of biodiesel production process. This procedure is an interesting alternative that follows the principles of green chemistry. In this work, triacetin was synthesized using reactions between glycerol and acetic acid, as well as glycerol and acetic anhydride, using homogeneous and heterogeneous acid catalysis. The goal is to use this product as an additive for biodiesel produced from palm oil, which is a fuel with physical properties that require improvement. The products were characterized by Fourier transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance (NMR) and gas chromatography (GC). The reaction between glycerol and acetic anhydride was the most effective for obtaining the desired product, with an approximate selectivity of 98% for triacetin. The triacetin was added to diesel fuel oil and biodiesel in proportions from 5 to 10% v/v, and the mixtures were tested in an electrical generator. In the test, the engine showed no problems during operation, and incorporating the mixtures did not result in significant consumption. Small reductions were detected in CO, O2 and opacity, but no changes were observed in the emissions of NOx and CO2.

Graphene-based nanomaterials as heterogeneous acid catalysts: a comprehensive perspective.

Acid catalysis is quite prevalent and probably one of the most routine operations in both industrial processes and research laboratories worldwide. Recently, “graphene”, a two dimensional single-layer carbon sheet with hexagonal packed lattice structure, imitative of nanomaterials, has shown great potential as alternative and eco-friendly solid carbocatalyst for a variety of acid-catalyzed reactions. Owing to their exceptional physical, chemical, and mechanical properties, graphene-based nanomaterials (G-NMs) offer highly stable Brønsted acidic sites, high mass transfer, relatively large surface areas, water tolerant character, and convenient recoverability as well as recyclability, whilst retaining high activity in acid-catalyzed chemical reactions. This comprehensive review focuses on the chemistry of G-NMs, including their synthesis, characterization, properties, functionalization, and up-to-date applications in heterogeneous acid catalysis. In line with this, in certain instances readers may find herein some criticisms that should be taken as constructive and would be of value in understanding the scope and limitations of current approaches utilizing graphene and its derivatives for the same.

Recent Progress Towards Transition Metal-Catalyzed Direct Conversion of Cellulose to 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) has been considered as a green platform chemical with a wide range of applications due to its rich chemistry and potential availability from renewable biomass resources. In recent years, considerable efforts have been made to transform carbohydrates into HMF using homogeneous and heterogeneous acid catalysis. In this critical review, the direct conversion of cellulose into HMF catalyzed by transition metals is described because of the present important utility of such metals. Since solid acids are deemed less noxious than traditional liquid acids, significant attention is given to hydrolysis, isomerization, and dehydration reactions successively carried out in a one-pot mode from the polysaccharide using heterogeneous catalysts. Keywords: 5-hydroxymethylfurfural (HMF), cellulose, lignocellulosic biomass, transition metals, homogeneous catalysis, heterogeneous catalysis, organic material, hydrolytic hydrogenation, hydrogenolysis, oligosaccharides, non-catalytic processes, TRS, Lignin-derived solvents, ignocellulose, sulfur-doping

Modification in Properties of Fly Ash through Mechanical and Chemical Activation

This paper is a critical overview on chemical, structural, and morphological changes in fly ash properties with mechanical activation using high energy planetary ball mill and chemical activation by digesting with various mineral acids (HCl, HNO3, H2SO4 and HClO4) at 110oC. Mechanical activation results in increase in silica percentage, amorphous nature, specific surface area and surface roughness, as evident by analytical measurements using XRF, XRD, FT-IR, BET surface area and SEM techniques. The chemical activation of Fly ash performed by different acids results in increased silica content and surface area due to leaching of several metal ions from silico-aluminate skeleton. The surface silanol groups responsible for generating Bronsted acidity are enhanced as evident by pyridine adsorbed FT-IR. Activation with HClO4 is also evident to generate surface active Lewis acid sites due to formation of Al-OH phases on the surface. The mechano-chemical activation can generate sufficient activity on fly ash surface rendering its potential application in heterogeneous acid catalysis.

Solvothermal synthesis and characterization of two inorganic–organic hybrid materials based on barium

Two metal-organic frameworks containing barium were synthesized hydrothermally and investigated for their catalytic properties. Ba(2)F(2)[O(3)SC(2)H(4)SO(3)] has barium fluoride layers linked by organic 1,2-ethanedisulfonate molecules. Ba[O(3)SC(2)H(4)SO(3)] has discrete barium centers arranged in layers and connected covalently by ethanedisulfonate bridges. Thermogravimetric analysis showed that Ba(2)F(2)[O(3)SC(2)H(4)SO(3)] is stable to ca. 325 °C and Ba[O(3)SC(2)H(4)SO(3)] to ca. 375 °C. These materials expand the metal-organic frameworks available for group II metals bound to organodisulfonate linkers and are potentially useful for a range of heterogeneous acid catalysis reactions.

Acid-catalyzed transformations of diepoxy derivatives of terpinolene

Transformations of diepoxy derivatives of terpinolene under conditions of homogeneous and heterogeneous acid catalysis were studied. Qualitative and quantitative compositions of the reaction mixtures were found to depend on the acidity of the medium and mutual orientation of the epoxide rings in the p-menthane skeleton. The experimental data were compared with the results of computer simulation of the most probable transformation pathways in terms of molecular mechanics and quantum-chemical methods.

Mechanistic Modeling of Palmitic Acid Esterification via Heterogeneous Catalysis

Biodiesel has emerged as a promising renewable and clean energy alternative to petrodiesel. While biodiesel has traditionally been prepared through homogeneous base catalysis, heterogeneous acid catalysis has been investigated recently due to its ability to convert cheaper but high “free fatty acid” content oils such as waste vegetable oil while decreasing production cost. In this work, the esterification of free fatty acid over sulfated zirconia and activated acidic alumina was studied experimentally in a batch reactor. The models of the reaction over the catalysts were developed in two parts. First, a kinetic study was performed using a deterministic model to develop a suitable kinetic expression, and the related parameters were estimated. Second, a stochastic model was developed as a pseudo-verification of the nature of the reaction at the molecular level. The esterification of palmitic acid obeyed the Eley−Rideal mechanism in which palmitic acid and methanol are adsorbed on the surface for SO4/ZrO2−55...

Ethyl oleate production by means of pervaporation-assisted esterification using heterogeneous catalysis

Pervaporation-assisted esterification of oleic acid and ethanol was investigated by means of heterogeneous acid catalysis with the aim of increasing the ethyl oleate yield. The experimental strategy comprised kinetic tests with Amberlyst 15 Wet (Rohm & Haas), the characterization of hydrophilic Pervap 1000 membrane (Sulzer) and the evaluation of the membrane-assisted reactor. Kinetic tests were carried out to study the effect of temperature, catalyst loading and ethanol/organic acid molar ratio for the esterification of oleic acid and ethanol. The ester yield and initial reaction rate were used as response. The hydrophilic poly(vinyl alcohol) membrane was able to remove water from the reaction medium and, hence, the ester yield was increased. The potential of coupling esterification and pervaporation was demonstrated, with a two-fold increase in the reaction yield of ethyl oleate.

Recent Advances in the Catalytic Conversion of Cellulose

Shift happens: Concerns about the depletion of fossil fuel reserves and the environmental problems related to its use have encouraged the development of new catalytic approaches for producing carbon-based chemicals from cellulosic biomass. Here, recent progress in the implementation of (mainly) heterogeneous acid, bifunctional, and multistep catalysis is reviewed.

ChemInform Abstract: Sustainable Heterogeneous Acid Catalysis by Heteropoly Acids

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