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  • 1.Esterication of Palm Fatty Acid Distillate Using Heterogeneous Sulfonated Microcrystalline Cellulose Catalyst and Its Comparison with H2SO4 Catalyzed Reaction Deepak D. Chabukswar, Parminder Kaur K. S. Heer, and Vilas G. Gaikar* Department of Chemical Engineering, Institute of Chemical Technology, Matunga, Mumbai-400 019, India *S Supporting Information ABSTRACT: The kinetics of esterication of palm oil fatty acid distillate (PFAD) with methanol was investigated using heterogeneous carbonized microcellulose sulfonic acid as catalyst and compared with the sulfuric acid catalyzed reaction, considering liquidliquid phase split during the progress of the reaction in both the cases. The solid catalyst was characterized for acidity, thermal stability, and surface area. The residual glycerides in the PFAD were hydrolyzed prior to the esterication using sulfuric acid as a catalyst. The esterication reaction was investigated for the eect of catalyst loading, temperature, and free fatty acids (FFA) to methanol ratio, on the conversion of the fatty acids. Sulfuric acid was a better catalyst than sulfonated microcrystalline cellulose, but the solid catalyst provides the ease of recovery. The sulfonated microcrystalline cellulose rendered good conversion and reusability for esterication. The process engineering aspects of the esterication reaction are also briey discussed. INTRODUCTION Biodiesel, a mixture of fatty acid methyl esters (FAMEs), has attracted considerable attention as an alternative to petro-based transport fuels. The renewable nature of the vegetable oils feedstock and the lower sulfur value of the biodiesel resulting in the reduction of vehicular SOX emission and net carbon dioxide emissions are responsible for this increasing interest.14 The major feedstock for biodiesel comes from edible oils such as soyabean oil, palm oil, and nonedible oils such as jatropha and karanja oils. The production of biodiesel by alkali catalyzed transesterication of neat vegetable oils, which by far is the simplest method of preparing the fatty acid esters, has not been commercialized to a large extent because of the higher cost of raw materials and also because of the limited availability of the feedstock in developing countries despite bringing considerable land under cultivation for nonedible oil producing plants.5 The biodiesel manufacturing process has been under intensive study in the past decade for development of new technologies to enable the use of low cost waste oils as the feedstock as compared to more expensive neat vegetable oils. The biodiesel production from waste oils from dierent sources is a challenging job because of the presence of free fatty acids (FFAs) in such oils to varying degrees.68 The FFAs react with the alkali that is used as a catalyst in the transesterication process, to form soap that hinders subsequent phase separation of the methyl esters from glycerol formed in the reaction. The eectiveness of the alkali catalyst is signicantly reduced in the presence of moisture generated by the neutralization reaction that reduces the overall conversion in a desired time frame and thus demands larger amounts of the catalyst in the process. The fatty acid salts also dissolve in the glycerol phase making subsequent glycerol recovery cumbersome. Completely dry conditions are the most essential to produce the fatty acid methyl esters by the transesterication of triglycerides in the shortest possible time as the reaction is extremely fast in the absence of moisture and gets limited only by the mixing conditions. The conventional alkali catalyzed transesterication process, therefore, becomes inadequate to use cheaper raw materials having signicant FFA content.8 The pretreatment of the waste oil to esterify the FFAs by acid catalyzed esterication becomes a prerequisite in the biodiesel production by conventional alkali catalyzed transesterication process. On the other hand, feed stocks containing of mostly FFAs with a limited content of triglycerides can be handled by direct esterication process. Palm fatty acid distillate (PFAD) is a byproduct of the palm oil rening process and mainly consists of a mixture of fatty acids with a small percentage of mono-, di-, and triglycerides and is comparatively far cheaper than palm oil as a starting material for methyl esters production. Biodiesel synthesis, by direct esterication of waste oils with methanol, has been reported by many researchers using homogeneous and heterogeneous acid catalysts.927 Homogeneous mineral acids such as H2SO4, phosphoric acid (H3PO4), and organic acids like p-toluene sulfonic acid (p- TSA), trichloroacetic acid (TCA), and methanesulfonic acid (MSA) are routinely used as catalysts for the esterication reactions.1014 Since the recovery or post-treatment of the catalyst remains the main concern in such homogeneous catalyzed reactions, low cost sulfuric acid remains still the catalyst of choice despite its corrosive nature, as it also can be easily neutralized. The organic acids after neutralization, on the other hand, add a signicant load to the chemical oxygen demand (COD) of the waste streams that is not easy to deal with even by biological means. Received: November 10, 2012 Revised: April 4, 2013 Accepted: May 13, 2013 Published: May 13, 2013 Article 2013 American Chemical Society 7316 | Ind. Eng. Chem. Res. 2013, 52, 73167326

2. Heterogeneous catalysts oer major advantages of facile separation from the reaction mixture and reusability and substantial benets from an environmental pollution point of view. Inorganic solid acids such as niobic acid, silica and zeolite supported Lewis acids, zirconium sulfate, and super acid catalysts have been extensively studied for the esterication reaction.1620 Lipase catalyzed enzyme esterication has been also reported, but the reaction rates are much slower as the temperature and pressure conditions are too mild, usually not exceeding 4045 C as enzyme denaturation leads to the loss of its activity at higher temperatures. This is a serious drawback of the enzymatic reaction in industrial conditions because of poor volumetric productivity although enzymes can work very well in the presence of water formed in the reversible esterication reaction. Acidic ion-exchange resin catalysts, such as CT-175 cation exchage resin, Dowex monosphere 550A, Amberlyst-15, and Naon NR50, in H+ form, have all been reported, sometimes even with supercritical methanol conditions to take advantage of higher rates of the reaction at higher operating temperatures.2027 Many of these resin catalysts, however, retain the water of esterication that often decreases the reaction rates and conversions. The prior literature indicates that cheaper feedstock, driving reaction to completion, easily available and recyclable catalyst, and moderate reaction times are the major concerns of the biodiesel manufacturing process. Kinetic modeling of esterication of fatty acids using homogeneous and heterogeneous catalysts also has been performed by several authors.2835 Most of these papers refer to a homogeneous liquid phase reaction using a large excess of methanol and, therefore, use of a pseudohomogeneous power law model or EleyRideal or LangmuirHinshelwood model to describe the kinetics of homogeneous and heterogeneous catalyzed reactions, respectively, is very common. However, generation of water during the esterication reaction and limited miscibility of methyl esters with methanol lead to a biphasic reaction medium in both of these cases. The two liquid phases attain equilibrium with respect to each other very quickly. Therefore, it becomes necessary to understand the thermodynamic framework of the reaction system, and the eect of phase equilibrium between the two liquid phases on the reaction kinetics of the esterication. Very few papers have analyzed the kinetics of the esterication considering the biphasic nature of the system.36,37 In this paper, PFAD is used for the production of FAMEs by acid catalyzed esterication, after hydrolysis of residual glycerides in the feed. The esterication reaction is conducted with concentrated sulfuric acid as the homogeneous catalyst for comparison with the esterication using a carbonized sulfonated microcrystalline cellulose solid acid (CSMC) as a heterogeneous catalyst. Sulfonation and incomplete carbon- ization of natural products results in a rigid carbon framework composed of small polycyclic carbon sheets in a three- dimensional sp3 -bonded structure.3842 Microcrystalline cellu- lose is a very strong organic material consisting of polysaccharide linear chains of (1 4) linked D-glucose units. Cellulose, as such, has hydrophobic surface and a high amount of amorphous regions. Microcrystalline cellulose material has a lower content of amorphous regions and a higher degree of crystallinity and is usually obtained by partially hydrolyzing cellulose with a mineral acid or by steam explosion process. Sulfonation of such carbonaceous materials, such as microcrystalline cellulose, is expected to aord a highly stable solid with a high density of active sites, allowing high- performance catalysts to be prepared from natural products. The esterication of PFAD, with CSMC, is compared with that using Amberlyst-15 under similar conditions. EXPERIMENTAL SECTION Materials. The palm fatty acid distillate (PFAD) was procured from Royal Energy Ltd., Mumbai, as a yellow color solid having melting point of 40 C. Methanol (AR grade), sulfuric acid (98%), and Amberlyst-15 were procured from SD, Fine Chemicals, Mumbai. A crystalline powder sample of microcrystalline cellulose (MC; surface area = 105.1 m2 /g, pore size = 1.3 nm) was supplied by Godavari Bioreneries Ltd., Mumbai. The HPLC grade acetonitrile and acetone were procured from Thermo Fischer Scientic, Mumbai, for the analysis. Catalyst Preparation. In a typical run, MC (10 g) was taken along