Dehydration of Ethanol Using other Adsorbents
A number of researchers have studied the use of other adsorbents for dehydration of ethanol. Some examples from recent literature are natural materials such as corncobs, activated palm stone, oak [3], starch (corn and potato), xylan, pure cellulose, corn residue [11, 12], bleached wood pulp, sawdust, kenaf core [13], cassava starch, cassava pulp [14], corn (Zea mays), upright elephant ear (Alocasia macrorrhiza), cassava (Manihot esculenta), sugarcane bagasse [15], rice flour and maize flour [16].
In a comparison study Benson and George used three lignocel — lulosic material-based adsorbents, bleached wood pulp, oak sawdust and kenaf core, where a thermal swing adsorption column was used to evaluate the effectiveness on the removal of water from ethanol-water mixtures of 90, 95 and 97 wt% ethanol. They generated breakthrough curves to determine the effectiveness of these adsorbents and to compare them. These researchers observed that water is preferentially adsorbed allowing for complete dehydration of ethanol and also presented the mass transport properties for the diffusion of water molecules into porous matrices of the adsorbents as well as the length and velocity of mass transfer zone.
The adsorption capabilities of rice flour and maize flour for gaseous-phase selective water adsorption for ethanol dehydration was investigated by Chang and coworkers via a bench-test fixed-bed absorber at constant temperature [16]. In this experiment, ethanol concentration in the feed was 93.4% (mass) and each of the dried biomass was used as adsorbent; breakthrough curves and temperature distribution in adsorptive bed were obtained for different bed depths, superficial velocities, granularities of adsorbent and temperatures. Bed pressure drop curves for different bed depths and superficial velocities were also measured. Additionally, they found that ethanol product purity of 99.5% (mass) could be achieved through both kinds of biomass adsorbents. When 99.5% (mass) of ethanol purity is defined as the breakthrough point, the capacity for adsorbent was within 0.0915-0.2256 gram water/gram adsorbent [16].
The application of corn (Zea mays), upright elephant ear (Alocasia macrorrhiza), cassava (Manihot esculenta), and sugarcane bagasse (Saccharum) for dehydration of ethanol was evaluated by Quentero and coworkers [15]. In this study enzymes (R-amylase and cellulase for starch and cellulose, respectively) were evaluated as modifying agents with the aim of increasing water adsorption capacity of these cellulosic materials as well. Water adsorption capacity ranges from 4 to 19g/100g adsorbent were found for evaluated materials. Cornstarch had the highest water adsorption capacity (19g/100g ads), while upright elephant ear starch presented the lowest (4.2g/100g ads). Tested materials showed affinity with water for both native and enzyme-treated cases.