Preparation of solid acid catalyst from glucose–starch mixture for biodiesel production

Abstract

The aim of this work is to study the catalyst prepared by glucose–starch mixture. Assessment experiments showed that solid acid behaved the highest esterification activity when glucose and corn powder were mixed at ratio of 1:1, carbonized at 400 °C for 75 min and sulfonated with concentrated H₂SO₄ (98%) at 150 °C for 5 h. The catalyst was characterized by acid activity measurement, XPS, TEM and FT-IR. The results indicated that solid acid composed of CS_0.073O_0.541 has both Lewis acid sites and Broˇnsted acid sites caused by SO₃H and COOH. The conversions of oleic acid esterification and triolein transesterification are 96% and 60%, respectively. Catalyst for biodiesel production from waste cottonseed oil containing high free fatty acid (FFA 55.2 wt.%) afforded the methyl ester yield of about 90% after 12 h. The catalyst deactivated gradually after recycles usage, but it could be regenerated by H₂SO₄ treatment.

Introduction

Developing renewable energy has become an important worldwide energy policy to reduce greenhouse gases caused by fossil fuel. Biodiesel is an alternative fuel consisting of fatty acid methyl esters (FAME). Biodiesel is environmentally beneficial because it is biodegradable, nontoxic and has low emission profiles. Biodiesel can be produced by chemical or biochemical processes from various types of biomass including vegetable oils, animal fats, waste edible oil and algae oil. Biodiesel can be produced by using both acid and base catalysts (Agarwal, 2007). The basic homogeneous catalyst (NaOH or NaOCH₃) is commonly used in the most of technology for triglycerides transesterification due to short reaction time. But base-catalyzed process requires an extra step to convert free fatty acids to methyl esters, thus avoiding soap formation when the amount of free fatty acids in the oil exceeds 1% (Meher et al., 2006). Although the acid-catalyzed reaction requires a longer reaction time than base-catalyzed one, acid-catalyzed procedure is more economical for one-step process of esterification and transesterification when high FFA-containing oil is used as feed stock (Canakci and Van Gerpen, 1999). The problem with liquid acid process is the discontinuous operation mode that also involves a costly separation and corrosion of liquid acid. In contrast, solid acid catalysts are easily removed from the reaction mixture, making the purification and continuous operation much simpler (Vicente et al., 2004, Kiss et al., 2006). Among strong solid acid catalysts, sulfated zirconia (SZ) (Chen et al., 2007) and Nafion resin catalysts (Russbueldt and Hoelderich, 2009) have been shown to catalyze biodiesel forming reactions as efficiently as sulfuric acid on a site activity. The solid acid catalysts from sulfonated polystyrene compounds (SPS) (Soldi et al., 2009) and poly(vinyl alcohol) cross-linked with sulfosuccinic acid (SSA) (Caetano et al., 2009) also showed good activity in esterification of fatty acid with methanol. Recently, Toda et al. (2005) and Zong et al. (2007) reported another study about the use of sulfonic acid-containing catalysts on the esterification of free fatty acids with methanol. The catalyst consisted of sulfonated carbons previously obtained by pyrolysis of sugars in nitrogen atmosphere. A mesoporous solid acid was prepared through first adding calcinated mesoporous silica SBA-15 into aqueous sucrose solution, second pyrolizing to form Si/C material and then sulfonating to introduce SO₃H (Dhainaut et al., 2010). The results of deactivation studies by Mo et al. indicate that leaching of active species substantially affected catalyst activity (Mo et al., 2008). Lou et al. (2008) presented the preliminary characterization of this novel d-glucose-derived solid acid catalyst and its successful use for biodiesel production from higher fatty acids and especially waste oils with a high acid value.

The goal of this work is to characterize the solid acid catalyst prepared by glucose–starch mixture and to synthesize biodiesel from high FFA waste oil by using the catalyst.

In this work, we followed the method reported by Toda et al. (2005) to synthesize sulfated carbon-base catalysts. We modified the process of catalyst preparation from mixture of glucose and starch, and then characterized the catalyst. The amylopectin ratio in starch is important in the formation of small polycyclic aromatic carbon rings that provided anchoring points for sulfonite groups (−SO₃H), which affected the final catalyst activity. The starches with different percent of amylopectin were investigated. The catalytic activities of esterification and transesterification were examined. The simultaneous esterification and transesterification of waste cottonseed oil (high FFA) with methanol was carried out using the starch-derived solid acid. Finally, the reuse and reactivation of catalyst were presented.