The presence of organic acids in thermal-pyrolysis bio-oils can lead to serious corrosion to process devices and lower storage stability. Esterification reactions between acids and alcohols are considered to be a promising approach to remove organic acids in thermal-pyrolysis bio-oils. The transition metal sulphides (TMSs) with versatile catalytic properties endow themselves potential candidates as esterification catalysts. To the best of our knowledge, however, there is no report on the application of TMSs such supported tungsten and vanadium sulphides to esterification reactions. In this contribution, we for the first time describe a novel class of alumina supported tungsten-vanadium sulphide catalysts for the esterification of acetic acid with sec-butyl alcohol, which is used as a model reaction representing the stabilization of bio-oils. We found that, over a sulphided catalyst (Al2O3-14W6V) pre-sulphided from its oxidic precursor containing 14 wt% WO3, 6 wt% V2O5 and 80% Al2O3, the conversion of acetic acid reached up to 42.2% at 150 oC and a sec-butanol to acetic acid molar ratio 2:1. Interestingly, we found that the conversion rate of acetic acid obtained over the different catalysts increases with the increasing total acidity of the catalyst, indicating that both Brönsted and Lewis acid sites catalyse the esterification reaction. Furthermore, the effects of reaction conditions such as temperature and weight hourly space velocity (WHSV) were investigated in a continuously flowing fixed-bed microreactor. The optimum reaction conditions determined are: 150 oC, 2.5 MPa, and WHSV 0.8 h-1. As shown in Fig. 1, the selectivity to sec-butyl acetate obtained over Al2O3-14W6V is nearly 100%, dramatically higher than that obtained over Amberlyst 15 which is a heavily used commercial esterification catalyst. Figure 1. Schematic presentation of the esterification reaction path of acetic acid with sec-butanol over Amberlyst 15 and Al2O3-14W6V catalysts.

Removal of organic acids from bio-oils by catalytic esterification

253rd National Meeting (2017)

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