Preparation, characterisation and evaluation of brazilian clay-based catalysts for use in esterification reactions

Abstract

Catalisadores a base de argilas naturais brasileiras foram preparados, caracterizados, e sua atividade catalítica foi avaliada em reações de esterificação. As argilas naturais foram ativadas por tratamento ácido como recebidas, sem qualquer tratamento prévio. As argilas naturais e as argilas ácidas foram caracterizadas por DRX, TPD-NH 3 , termodessorção de n-butilamina, análise de adsorção de N 2 , FT-IR, TGA e DTA. O desempenho catalítico foi investigado em reações de esterificação de diversos ácidos carboxílicos com diferentes álcoois. As reações foram realizadas com razão molar ácido carboxílico/álcool 1:3, a 100 °C e pressão atmosférica, por 3 h. As argilas ácidas forneceram boas conversões e apresentaram desempenho melhor que a argila comercial K10. Natural Brazilian clay-based catalysts were prepared, characterised, and their catalytic activity was assessed in esterification reactions. The natural clays were acid activated as received, without any previous treatment. Both natural and acid-activated clays were characterised by XRD, NH 3 -TPD, thermodesorption of n-butylamine, N 2 adsorption analysis, FT-IR, TGA and DTA. The catalytic performance was investigated in the esterification of several carboxylic acids with different alcohols. The reactions were carried out in a 1:3 carboxylic acid/alcohol molar ratio at 100 °C and atmospheric pressure for 3 h. The acid-activated clays provided good yields and better performance than commercial clay K10. Keywords: acid activation, clay, smectite, esterification IntroductionEsterification reactions are widely employed in a variety of chemical industries. 1 The procedure generally uses either sulfuric, hydrochloric or sulfonic acid as catalyst. These catalysts generate large quantities of acidic waste, which require appropriate treatment before disposal. The most widely used catalyst is sulfuric acid. It is a low cost reagent and is very active. However, it is also corrosive and presents problems of storage and control. 2 To minimise the problems associated with the homogeneous process, intensive research has been recently devoted to the development of heterogeneous catalysts for esterification. Some examples include functionalised mesoporous materials, 3,4 ion-exchange resin, 1 oxides 5-7 and metal complexes. 8,9 There is considerable interest in developing catalysts based on clays. In terms of their environmental aspect, these materials are one of the most friendly solid catalysts. Additionally, clay-based catalysts are very promising because of the low cost of the raw material, ease of properties manipulation and ease of recovery and reuse. 10 Ion exchange capacity and the potential for increased interlayer spacing are important characteristics of clay minerals that strongly influence their physical-chemical and technological properties. These characteristics, as well as their high surface area, have lead clay minerals to be explored as catalysts. The acid activation method is usually employed to modify the textural characteristics of clays.Clays are being employe...

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