Solid acid catalysts

The major challenges facing the commercialization of biodiesel are: readily available and profitable feedstock and cost-effective production process. Although conventional oilseed feedstocks provided biodiesel yields of more than 98%, sufficient land for cultivating such feedstocks is a major challenge. Moreover, the use of refined feedstocks is uneconomical because of refining costs and priority as food. Algae (including macro- and microalgae) are the focus of many current research interests because they have the potential to provide sufficient fuel for global consumption. Beside their high lipid contents and fast growth rate, microalgae have the potential to mitigate the competition for land-use and food-for-fuel conflicts. They are also able to reduce the greenhouse effects via CO2 sequestration. Critical survey of the literature suggests that microalgal oil has the potential to produce higher biodiesel yields with about 25% reduction in production costs. However, the oil from microalgae contains high free fatty acids which require pretreatment if conventional homogeneous catalysts are employed. Heterogeneous base catalysts are also not suitable due to soap formation and post-production processes, hence the need for solid acid catalysts. Therefore, this article provides a review on solid-acid catalysts used in processing microalgal oil for biodiesel production. Also discussed in details are the challenges and prospects of the production process. With more advances in technology and long-term commitment to investments, heterogeneous acid-catalyzed microalgal-biodiesel can become the ideal process for the future. © 2013 Elsevier Ltd. All rights reserved.

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http://www.sciencedirect.com/science/article/pii/S2213343713000183

Malaysian oil palm industry produces a significant amount of oil palm residue as solid wastes. These solid wastes are comprised of oil palm residue which contains the stem, fronds from the farms, empty fruit bunch (EFB), mesocarp fibre (MF), and palm kernel shell (PKS) from the oil palm–processing factories. These residues are not successfully reused for other purposes, and the current dumping methods can possibly trigger unfavourable effects to the environment. As oil palm residues are a readily available waste biomass, it has a high potential to be converted into valuable energy-derived products. Hydrothermal carbonization (HTC), which is a thermochemical process, is a method used to treat biomass to produce hydrochar under hot-compressed water. Oil palm residues (palm leaves, palm fronds, and palm shell) were used as the feedstock for producing carbonaceous hydrochar. The key objective of this study is to examine the effect of the reaction temperature, residence time, and acid catalysts on the HTC process. HTC of oil palm residues was optimized at different operating temperatures from 140 to 300 °C and different reaction times between 30 and 240 minutes with a biomass-to-water ratio of 1:10 wt%. Acid catalysts such as citric acid and ascorbic acid were used for the HTC process. The hydrochar produced is further characterized using heating value and elemental and Fourier transform infrared (FTIR) analysis. The yield of hydrochar reduces with the rise of temperature and time but it increases in the presence of acid catalysts. The carbon content of hydrochar is observed to be between 44.36 and 49.50%. The FTIR analysis showed that a high intensity at 1423 cm−1 indicates a high content of lignin and cellulose in the hydrochar. A considerable decrease in the H/C and O/C atomic ratio shows that the dehydration and decarboxylation take place during the HTC process.

Herein, an in situ DRIFT technique was used to study the reaction mechanism of methanol dehydration to dimethyl ether (DME). Moreover, the effect of silver loading on the catalytic performance of η-Al 2 O 3 was examined in a fixed bed reactor under the reaction conditions where the temperature ranged from 180 to 300 °C with a WHSV = 48.4 h −1. It was observed that the optimum Ag loading was found to be 10% Ag/η-Al 2 O 3 with this novel catalyst also showing a high degree of stability under steady-state conditions, and this is attributed to the enhancement in both the surface Lewis acidity and the hydrophobicity.

A carbonization-sulfonation method was utilized in synthesizing sulfonated mesoporous catalysts from palm tree biomass. Brunauer-Emmet-Teller (BET), powder X-ray diffraction (XRD), energy dispersive X-ray (EDX), and field emission scanning emission microscopy (FE-SEM) analyses were used to evaluate the structural and textural properties of the catalysts. Further, Fourier transform infrared (FT-IR) spectroscopy and titrimetric analyses measured the strong acid value and acidity distribution of the materials. These analyses indicated that the catalysts had large mesopore volume, large surface area, uniform pore size, and high acid density. The catalytic activity exhibited by esterifying used frying oil (UFO) containing high (48%) free fatty acid (FFA) content further indicated these properties. All catalysts exhibited high activity, with sPTS/400 converting more than 98% FFA into fatty acid methyl esters (FAMEs). The catalyst exhibited the highest acid density, 1.2974 mmol/g, determined by NaOH titration. This is outstanding considering the lower reaction parameters of 5 h, 5:1 methanol-to-oil ratio, and a moderate temperature range between 100 and 200 degrees C. The study further illustrates the prospect of converting wastes into highly efficient, benign, and recyclable solid acid catalysts.

Link to Full-Text Articles :
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http://www.ncsu.edu/bioresources/BioRes_10/BioRes_10_2_3393_Sani_RAAW_Palm_Frond_Spikelet_Catal_Biodiesel_6824.pdf

Catalytic transesterification of triglycerides and esterification of free fatty acids underpins sustainable biodiesel production, wherein efficient heterogeneous catalysts are sought to replace mineral acids. A robust, magnetic core-shell SO 4 /Mg-Al-Fe 3 O 4 catalyst was synthesised by stepwise co-precipitation, encapsulation, and surface functionalisation. The resulting magnetically-separable catalyst has a surface area of 123 m 2 g −1 , uniform 6.5 nm mesopores, and a high total acid site loading of 2.35 mmol g-1. Optimum conditions for the (trans) esterification of waste cooking oil (WCO) over the sulfated solid acid catalyst were 95 °C, a methanol:WCO molar ratio of 9:1, and 300 min reaction to achieve 98.5% FAME yield. Esterification of oleic acid to methyl oleate resulted in an 88% yield after 150 min under the same reaction conditions. The magnetic solid acid catalyst exhibited good thermal and chemical stability and enabled facile catalyst separation post-reaction and the production of high quality biodiesel.

Highly efficient, robust and mesoporous sulfated zirconia, SZ catalysts were prepared by co-precipitation and incipient-wetness routes with sufficient and in-excess acid. The study investigated the effect of pH, precursor type, and concentration, on SZ and compared their acidity and performance with ytterbium-doped SZ toward transesterification. N2 sorption, elemental analysis, XRD, and ammonia temperature-programmed desorption (NH3-TPD) revealed the properties of the catalytic materials. The specific surface area increases independently of the presence of Ti up to 60.33 m2/g, with increasing pH while pore size of the tetragonal crystallites decreases from 37.04 to 6.83 nm. Soaking the material in sufficient 0.5-M H2SO4 produced 37.04 nm SBET in contrast to 21.21 nm from soaking in excess. Double sulfation ensured sulfate incorporation while moderate precursor amounts enhanced activity of the materials. Interestingly, despite low specific surface area, which was due to short aging p...

Heterogeneous catalysts are promising for the transesterification reaction of vegetable oils to produce biodiesel. Unlike homogeneous, heterogeneous catalysts are environmentally benign and could be operated in continuous processes. Moreover they can be reused and ...

Heterogeneous catalysts are promising for the transesterification reaction of vegetable oils to produce biodiesel. Unlike homogeneous, heterogeneous catalysts are environmentally benign and could be operated in continuous processes. Moreover they can be reused and regenerated. However a high molar ratio of alcohol to oil, large amount of catalyst and high temperature and pressure are required when utilizing heterogeneous catalyst to produce biodiesel. In this paper, the catalytic activity of several solid base and acid catalysts, particularly metal oxides and supported metal oxides, was reviewed. Solid acid catalysts were able to do transesterification and esterification reactions simultaneously and convert oils with high amount of FFA (Free Fatty Acids). However, the reaction rate in the presence of solid base catalysts was faster. The catalyst efficiency depended on several factors such as specific surface area, pore size, pore volume and active site concentration. © 2009 Elsevier B.V. All rights reserved.

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http://www.sciencedirect.com/science/article/pii/S0378382009000629

Homogeneous acid catalysts received wide acceptability because of their fast reaction rates. However, postproduction costs incurred from aqueous quenching, wastewater and loss of catalysts led to the search for alternatives. Until recently, heterogeneous base catalyzed-biodiesel production also gained the attention of most researchers. This was because the process minimized the problems of homogeneous catalysis in terms of catalyst regeneration and recycling in continuous processes. However, despite these advances, the ultimate aim of producing biodiesel at affordable cost is yet to be realized. Further, the process requires refined feedstocks which account for as high as 88% of the final production costs. Thus, the focus of many research efforts is towards the rational design and development of solid acid catalysts aimed at reducing biodiesel production costs. Therefore, this study reviewed current literature on the activities and advantages of solid acid catalysts used in biodiesel production. It discussed in details how the preparation method and prevailing reaction conditions affect the catalytic activity of the catalyst. The review concluded by suggesting way forward from the traditional trial-and-error method to a rational means of determining catalytic activities. © 2013 Elsevier Ltd. All rights reserved.

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http://www.sciencedirect.com/science/article/pii/S0926860X13006716

A carbon-based solid acid with high acid density was successfully prepared using camphor tree branches as raw materials through a novel method including dilute sulfuric acid activation, carbonization in refluxing solvent and sulfonation. Physical characterization was detected to show that the carbon-based acid is amorphous with polycyclic aromatic carbon sheets attached plentiful -OH, -COOH, and -SO3H groups. The sulfonic acid density and total acid density of it reached 2.05 mmol·g-1 and 5.63 mmol·g-1, respectively by acid-base titration. As a solid acid catalyst, it showed excellent performance in the ketalization of cyclohexanone with glycol.