Biodiesel Production with Heterogeneous Sulfonic Acid-Functionalized Mesostructured Catalysts

Abstract

Transesterification of refined and crude vegetable oils was carried out with a sulfonic acid-modified mesostructured catalyst. This catalyst has yielded fatty acid methyl ester (FAME) purity over 95 wt % for oil conversion close to 100% under best reaction conditions (temperature 180 °C, methanol/oil molar ratio 10, and catalyst loading 6 wt % with regard to the amount of oil). Interestingly, high methanol concentration leads to a detrimental effect on the catalyst activity. Regardless of the presence of free fatty acids, the sulfonic acid-modified mesostructured catalyst showed high activity toward simultaneous esterification and transesterification. These sulfonated mesostructured materials are promising catalysts for preparation of biodiesel, but some aspects related to the tuning of the adsorption properties of the silica surface and the enhancement of the catalyst's reusability must be addressed in future work.

Deactivation of sulfonated hydrothermal carbons in the presence of alcohols: Evidences for sulfonic esters formation

“…In the case of sulfonated carbons, deactivation has been attributed to leaching of soluble polycyclic aromatics with sulfonic groups [14,33], simple physical loss of catalyst [15], or hydrolysis of sulfonic groups [34]. Other acid catalysts have also shown a similar behaviour with respect to stability in esterification reactions, that have been explained by leaching problems in sulfated zirconia [35], hydrocarbon accumulation in SAC-13 [36] and organosulfonic silica [37], and several reasons, including leaching of sulfonic species, water and glycerol adsorption, and even reaction with methanol in the case of sulfonic-acid modified SBA-15 [38,39].…”

“…Both effects may be due either to a strong physisorption of molecular methanol by formation of hydrogen bonds with the highly oxygenated structure of the hydrothermal carbon or to chemical reaction of methanol with some sulfonic groups leading to surface methyl sulfonates. Some authors have proposed this possibility in the deactivation of mesoporous silicas modified with sulfonic groups [38,39], but without experimental evidences.…”

Catalysing sustainable fuel and chemical synthesis

“…Mesoporous silicas from the SBA family [73] have been examined for biodiesel synthesis, and include materials grafted with sulfonic acid groups [74,75] or SO 4 /ZrO 2 surface coatings [76]. Phenyl and propyl sulfonic acid SBA-15 catalysts are particularly attractive materials with activities comparable to Nafion and Amberlyst resins in palmitic acid esterification [77].…”

“…For example, incorporation of a secondary mesoporosity into a microporous H-b-zeolite to create a hierarchical solid acid significantly increased catalytic activity by lowering diffusion barriers [85]. Templated mesporous materials are widely used as catalyst supports [86,87], with SBA-15 silicas popular candidates for reactions pertinent to biodiesel synthesis as previously discussed [75,77,88]. However, such surfactant-templated supports possessing long, isolated parallel and narrow channels are ill-suited to efficient in-pore diffusion of bio-oil feedstocks affording poor catalytic turnover.…”

On the influence of Si:Al ratio and hierarchical porosity of FAU zeolites in solid acid catalysed esterification pretreatment of bio-oil

“…To address these issues, development of a noncorrosive and recoverable heterogeneous catalyst for esterification pretreatments is critical [5]. In this respect, various solid acid catalysts have been studied for organic acid esterification, including SO 4 / ZrO 2 [8][9][10], sulfonic acid functionalised (hierarchical) mesoporous SBA-15 [7,[11][12][13][14][15] KIT-6 [16] and PMO [17] silicas, Cs-exchanged heteropolyacids [18][19][20][21][22], tungstated zirconia [23], zirconium phosphate [24][25][26] and Nafion/SiO 2 composite (SAC-13) [27]. Among the solid acid catalysts, zeolites are efficient catalysts for esterification [28][29][30] due to their strong Brønsted acidity and tunable physical and chemical properties through altering their framework Si:Al ratio and structure.…”