Organic dehydration, with zeolite membranes

The inorganic silica membranes, also commercial, have solved the problem of thermal and chemical stability however, these membranes are only used for dehydration purposes, leaving the problem of separation of organic mixtures unsolved. As we have seen previously, due to the versatility and special feamres of zeolites, new applications in pervaporation that are not possible with other membranes could be developed with zeolite membranes. GaUego-Lizon et al. [110] compared different types of commercial available membranes zeolite NaA from SMART Chemical Company Ltd., sUica (PERVAP SMS) and polymeric (PERVAP 2202 and PERVAP 2510) both from Sulzer Chemtech GmbH, for the pervaporation of water/f-butanol mixtures. The highest water flux was obtained with the silica membrane (3.5 kg/m h) while the zeolite membrane exhibited the highest selectivity (16,000). 

Pervaporation Performance in Organic Dehydration of Solvents with Zeolite Membranes... 

According to a recent conference given by Prof. Kita [162], the classical synthesis method currently used by Mitsui allows to produce about 250 zeolite membranes per day. Both the LTA and T types (Na K) membranes are now commercial and more than 80 pervaporation and vapor permeation plants are operating in Japan for the dehydration of organic liquids [163]. A typical pervaporation system, similar to the one described in [8], is shown in Fig. 11. One of the most recent applications concerns the production of fuel ethanol from cellulosic biomass by a vapour permeation/ pervaporation combined process. The required heat is only 1 200 kcal per liter of product, i.e. half of that of the classical process. Mitsui has recently installed a bio-ethanol pilot plant based on tubular LTA membranes in Brazil (3 000 liters/day) and a plant with 30 000 liters/day has been erected in India. The operating temperature is 130 °C, the feed is 93 % ethanol, the permeate is water and the membrane selectivity is 10 000. 

Zeolite membranes represent a new branch of inorganic membranes. Significant progress has been made so far in the synthesis of thin, high-flux, defect-free zeolite membranes with new techniques of preparation and modification. In fact, the hydrophilic LTA zeolite membranes have already been applied in industry for dehydration from organic solutions... 

Chen et al. (2001b) reported the preparation and characterization of HY zeolite-filled chitosan membrane for the dehydration of organic-water mixtures using PV. A flux of 353 g/m h and a selectivity of 102 were obtained for an EtOH-water mixture with 10 wt% of water at room temperature, when the HY zeolite content in the membrane was 20 wt%. 

---