Probing the Catalytic Efficiency of Supported Heteropoly Acids for Esterification: Effect of Weak Catalyst Support Interactions

Abstract

Supported heteropoly acids are an interesting class of solid acid catalysts which possess flexible structure and super acidic properties essentially required for the oil-based biodiesel production. In this study, a series of catalysts containing 25 wt.% of heteropolytungstate (HPW) supported on various clays or SiO2 were prepared, and their catalytic efficiency was evaluated for esterification of acetic acid with heptanol. The as-prepared catalysts were characterized by various techniques including FT-IR spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and BET. The catalytic efficiency of both bulk and supported HPW catalysts for the esterification activity strongly depends on the type of support and amount of catalyst; the bulk HPW catalyst and the catalyst supported by kaolinite with 25 wt.% of HPW exhibited highest activity. In order to study the effect of temperature on conversion, all the catalysts were subjected to different reaction temperatures. It was revealed that esterification activity of both bulk and supported HPW catalysts strongly depends upon the temperature variations of the reaction. Besides, the effect of leaching of active sites on the catalysts performance for biodiesel production was also evaluated by inductively coupled plasma studies (ICP). The kaolinite-supported catalyst (25% HPW/kaolinite) demonstrated higher amount of leaching which is also confirmed by the significant decrease in its catalytic activity when it is used for the second time. However, the higher activity demonstrated by HPW/kaolinite maybe because of some homogeneous reaction indicating a weak catalyst support interaction (WCSI) resulting in the leaching of the catalyst during the test. Furthermore, the effects of other reaction variables such as catalyst loading and reaction time on the conversion of acetic acid were also studied.

Kinetics for the biodiesel production from lauric acid over Keggin heteropolyacid loaded in silica framework

“…For this reason and in order to overcome these problems, different supports were employed to immobilize HPAs, for example activated carbon, zeolites, silica, zirconium, titanium, MCM-41, and polymers among others [24,25]. Different HPAs in heterogeneous form have been tested in biodiesel production such as cesium-doped heteropoly tungstate (HPW), HPW/ZrO2, HPW/γ-Al2O3 and HPW/SiO2 for the simultaneous esterification and transesterification of 10% oleic acid-soybean oil mixture [26]; core-shell nanostructured heteropoly acidfunctionalized zeolitic imidazolate frameworks-8 (ZIF-8) for rapeseed oil transesterification [18]; HPW/kaolinite, HPW/bentonite and HPW/montmorillonite for acetic acid esterification [27]; HPW/SiO2 and cesium-doped HPW for rapeseed oil transesterification [28]; H3PMo12O40/bentonite [29] for esterification of a waste from palm oil; H3PW12O40/KIT-6 for neem oil transesterification [30]; 12-tungstophosphoric HPA/ZrO2 [31], and H3PW12O40 and H3PMo12O40 supported on activated carbon fibers [32] for palmitic acid esterification; Ni0.5H3SiW/SiO2 [33], NiHSiW/UiO-66 [34] and Sn1.5PW12O40/Cu-BTC [35] for oleic acid esterification.…”

New Task-Specific and Reusable ZIF-like Grafted H6P2W18O62 Catalyst for the Effective Esterification of Free Fatty Acids

“…However, the unsupported heteropolyacids are typically soluble in polar reaction media and, hence, unsuitable for chemical manufacturing due to the difficulty in separating them from the product stream. Several recent studies have shown that the catalytic efficiency of heteropolyacids can be improved following their dispersion over solid supports. − …”

Influence of phenolic compounds on color formation at different stages of the VHP sugar manufacturing process

“…The most common and the only commercially available chlorogenic acid is 5- O -caffeoylquinic acid (5-CQA), which is formed by esterifying caffeic acid (3,4-hydroxycinnamic acid) with quinic acid (1 L −1 (OH), 3,4/5-tetrahydroxycyclohexane carboxylic acid) 34 , 35 . The hypothesis that this reaction occurred in the clarification stage was considered for some reasons: the sugarcane juice has quinic acid 36 ; the pH close to neutrality and the high temperature (105 °C) favor the reaction 37 ; and calcium added to the juice in the form of Ca(OH) 2 in the liming step is proven to be a good catalyst 38 , 39 . Therefore, it may be inferred that the juice clarification stage promoted the formation of CGA by the degradation of CAF.…”