Acid functionalized carbons as catalyst for glycerol etherification with benzyl alcohol

María E Chiosso,Mónica L Casella,Andrea B Merlo,Ileana D Lick

doi:10.1007/s43153-019-00002-z

Abstract

In this paper, the catalytic behaviour of two different carbonaceous systems, commercial carbon (Cc) and synthetic carbon (Cs) functionalized with concentrated sulfuric acid (–SO3H) and with reduced aryl diazonium salt (–PhSO3H), was studied in the etherification of glycerol (Gly) with benzyl alcohol (BA). The catalytic activity and selectivity were studied varying the catalyst percentage (5, 10 and 15 wt%) and the initial reactant mass ratio. Taking into account the results obtained, the experimental conditions selected to continue with the catalytic studies were: temperature 393 K, Gly:BA molar ratio 3:1 and a catalyst loading of 10 wt%. Mono- and diethers were the main products. For the Cc-based catalysts, higher conversion (66%) and selectivity (90%) were obtained with the most acidic system, Cc–PhSO3H. Changing the carbon functionalization method (–PhSO3H for –SO3H groups) produced a considerable increase in glycerol conversion (from 23 to 66%) and in selectivity to ME + DE (from 62 to 90%). On the other hand, for both Cs-based systems a great increase in performance was obtained, about 95% conversion after 360 min of reaction. Monoether was the major product of the reaction with a selectivity of 79% for Cs–SO3H and 87% for Cs–PhSO3H, which was maintained with reuse. Etherification of glycerol (Gly) with benzyl alcohol (BA) with two carbonaceous systems synthesized in the laboratory and functionalized with –SO3H and –PhSO3H.

Highlights

Current problems of the energetic crisis due to the depletion of fossil fuels, high oil prices and the effects on the environment caused by the emission of hazardous and chemicals products into the atmosphere have forced us to look for alternatives to replace these fuels
The amount of acid sites is very important in the glycerol etherification reaction
It can be seen that, when comparing Cs and commercial carbon (Cc) carbons, a higher acid density is obtained with the first one (0.4 vs. 0.05 mmol g−1), a fact that can be attributed to the additional contribution of –COOH and –OH groups generated as products of the incomplete carbonization of the starting sugar

Summary

Introduction

Current problems of the energetic crisis due to the depletion of fossil fuels, high oil prices and the effects on the environment caused by the emission of hazardous and chemicals products into the atmosphere have forced us to look for alternatives to replace these fuels. One of the main obstacles to the commercialization of biodiesel is the by-product glycerol, since each ton of biodiesel originates 100 kg of glycerine that saturates the market, causing a dramatic reduction in prices and, negatively effects biodiesel economy (Anitha et al 2016; Janaun and Ellis 2010). In recent years several processes to produce value-added chemicals from glycerol have been reported, such as hydrogenolysis, etherification, esterification, dehydratation, oxidation and others (Len and Luque 2014; Faroppa et al 2016; Jaworski et al 2015; Pagliaro et al 2007; Alonso et al 2012)

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