Pervaporation membrane based on laterite zeolite-geopolymer for ethanol-water separation

Abstract

In recent years, the worldwide production of ethanol as a liquid biofuel has reached 27 billion gallons per year. The United States and Brazil are the main producers of ethanol, which account for 58% and 27% of total production, respectively. Ethanol has been known as a leading biofuel and as an additive to gasoline. In the USA, ethanol was produced from corn, from sugarcane in Brazil, and grains in Europe. The price of corn, sugarcane, grains and crude oil (gasoline) have a direct impact on the price of ethanol. The most common purification technique utilized in the ethanol industry is rectification followed by azeotropic distillation. This method is energy consume and its separation capacity is inadequate. Pervaporation system with inorganic membrane has been proposed as a new method for ethanol purification. The main objective of this research is to produce and characterize the performance of inorganic membrane made from a zeolite-geopolymer for pervaporation of ethanol-water separation. Zeolite was produced through geopolymerisation route using laterite as raw material. The aluminous iron type of laterite was dehydroxylated at 750 °C for 4 h to enhance its reactivity in a high alkali environment. The elemental compositions of laterite were examined by using x-ray fluorescence (XRF). The structure, phase and chemical compositions of zeolite-geopolymer were measured by using the x-ray diffraction (XRD) technique. The microstructure of the resulting membrane was investigated by using scanning electron microscopy (SEM). Liquid N2 absorption based on the Brunauer-Emmett-Teller (BET) method was used to determine the pore size distribution of the zeolite-geopolymer membrane. The pervaporation experiment was performed by using two membranes having different compositions (designated as K1 and K2) at temperature 50 °C and 70 °C. The measurement results showed that there are two types of zeolites produced namely sodalite and sodium silicate hexahydrate. The crystalline level of both zeolites is very high and regular in shape based on SEM examination. BET measurements showed that the pore size of K1 ranging from 15 to 900 Å and K2 ranging from 15 to 2000 Å. The results of pervaporation experiments showed that the selectivity of both membranes was very low due to high permeation flux. It is proposed that zeolite-geopolymer membranes should be coated with hydrophobic materials to reduce the hydrophilic properties of geopolymer and hence become more feasible for ethanol purification through pervaporation system.