Study On The Modification And Adsorption Characteristics Of Cassava Adsorbents

Due to energy shortage and environmental deterioration, the biomass-based fuelethanol（BFE）has drawn increasing attention in the past few decades. As a step ofhuge energy consumption in the preparation of fuel ethanol, ethanol dehydration hasalways been a research highlight. Currently, the industrial adsorbents for ethanoldehydration are generally molecular sieves, but they also have their own deficienciesand drawbacks, such as the high temperature of regeneration. Therefore, a new kindof adsorbent-biomass adsorbent slowly got people`s attention. It also had a goodadsorption performance and, more importantly, low regeneration temperature.Moreover under certain circumstances, it could even be recycled directly back to thefermentation process without regeneration, which can save more energy.In this thesis, one of the feedstock of fuel ethanol, cassava starch, was chosen asthe biomass adsorbent to be studied. The cassava starch was modified to porous starchvia the enzymatic reaction. Glucoamylase, α-amylase, and ultrasonic technique wereused to facilitate the process of enzymatic reaction. Fractional factorial design wasused to analyze the influential factors in porous cassava starch production. Theoptimal enzymatic hydrolysis conditions in terms of maximum adsorption capacitywere obrainer, and the statistical equation of the adsorption capacity was regressed aswell. The optimal conditions are as follows the mass ratio of glucoamylase toα-amylase (5:1), the mass ratio of total amount of enzymes to starch (1:40), pH valueof the reaction solution (4.5), enzymatic reaction temperature (45℃), enzymaticreaction time (10h), particle size (60-80mesh), and ultrasonic time (10min).The chemical properties and surface characteristics of adsorbents aftermodification were analyzed via a series of methods, such as Scanning electronmicroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction andDifferential scanning calorimetry. The results not only explained why the adsorptioncapacity of the modified starch was higher than that of the natural starch, but alsoshowed that the performance in fermentation of the modified starch almost had nochange compared with the natural starch. So this modified cassava adsorbent could bereused in fermentation as fresh feedstock after adsorption, which is an efficient way tosave energy and natural resources. Finally, an adsorption experiment of water form liquid-phase ethanol-watermixtures was designed to study the adsorption ability of the modified and nativecassava adsorbents, which can prove that the modified cassava adsorbents had betterabsorptive properties than the native ones. The time of adsorption as well as the waterremoved under different ethanol concentrations were investigated. The modifiedcassava adsorbent was compared with the commercial molecular sieves in terms ofadsorption capacity form liquid-phase ethanol-water mixtures. And it was proved thatthe modified cassava adsorbent had capacities similar to commercial molecular sieves,and even bigger than commercial molecular sieves under some certain waterconcentration of ethanol-water mixtures. The physical strength of the modified starchadsorbents was proved to meet the need of normal application when the water massconcentration of the ethanol-water solution was less than20%.