Kenjiro Tokami

Continuous surface modification of silica particles for enzyme immobilization

Abstract A novel reaction process for surface modification of ceramic particles is investigated for enzyme immobilization. The surface modification of the support particles can be carried out continuously in a flow reactor. The proposed continuous surface modification process (CSMP) is advantageous for the handling of particles in the catalyst preparation process. Using this reaction method, the surface of silica particles was easily modified for enzyme immobilization. The degree of surface modification could be controlled by the reaction conditions and the amount of immobilized enzyme was also controlled. Lysozyme and catalase were immobilized on the silica particles modified by the CSMP method. The adsorption of lysozyme was studied as an example of enzyme adsorption on the modified particles. The enzyme activity of prepared particles was tested for decomposition of H 2 O 2 by immobilized catalase. It was shown that the obtained particles indicated the enzyme activity and CSMP is a useful method for preparing enzyme catalysts.

Rates of alkoxylation and hydrolysis of alkoxyl groups on silica surfaces

Abstract The rate of reactions on silica surfaces was investigatedfor the alkoxylation and hydrolysis of alkoxyl groups. Silica gel particles were contacted with vapors of several alcohols and water in a flow-type reactor at various temperatures. The surface concentrations of alkoxyl groups were measured by thermogravimetric analyses to determine the rates of reactions. The apparent rate constants could be calculated by applying the progressivereaction model. The apparent rates based on the total number of surface groups were determined for alkoxylation reactions. Among the alcohols investigated, alkoxylation with methanol showed the smallest activation energy and the largest rate constant. The rates of hydrolysis of alkoxyl groups were also measured on samples which had been alkoxylatedto about 10% of the initial surface groups. The activation energy of hydrolysis was almost constant for all alkoxyl groups. However, the hydrolysis of methoxy groups showed the largest rate constant. The influence of preheating treatment on the rate of alkoxylation was examined for the reaction with 1-butanol. Even when the reaction temperature was the same, the rate constant increased with increasing preheating temperature. The increase in the rate constant could be attributed to the increase in the frequency factor, since the preheating treatment increased the activation energy.

Kinetic study of alkoxylation and rehydroxylation reactions on silica surfaces

The rates of alkoxylation and rehydroxylation reactions were investigated on silica surfaces preheated at various temperatures. The effect of preheating temperature was examined for both reactions. The initial rate of reaction was analyzed and discussed as a representative reactivity of the silica surface. For the alkoxylation reaction, the apparent rate of reactions on the total active sites was analyzed by measuring the alkoxyl groups formed on the surface. The rate of the alkoxylation reaction increased with the preheating temperature, which could be attributed to the increase in the number of reactive siloxane bridges. It was shown that the preheating treatment caused the compensation effect for the surface alkoxylation reactions. An analysis for the state of the activated complex in the reaction was proposed to discuss the kinetic characteristics. For the rehydroxylation reaction, the rate of reaction forming hydroxyls from siloxane bridges was measured. The rate of rehydroxylation decreased with increasing the preheating temperature. For both the alkoxylation and rehydroxylation, the reactivity of siloxane bridges decreased with increasing the preheating temperature.

Rehydroxylation of dehydrated silica surfaces by water vapor adsorption

Abstract The rehydroxylation reaction of siloxane bridges was studied for silica gel particles dehydrated by preheating. Adsorption isotherms of water vapor at 298 K were measured for the samples which were preheated at different temperatures. The amounts of total adsorption and irreversible adsorption were examined against the preheating temperature and vapor pressure. The number of the hydroxyl groups produced by the rehydroxylation of siloxane was measured by thermogravimetrican alysis to determine the adsorption isotherms for chemisorption of water. For the surface preheated at 673 K, the siloxane bridges were fully rehydroxylated for about 3 h at a relative pressure of 0.3. The surface preheatedat 873 K was gradually rehydroxylated with increasing pressure and the rehydroxylation was not complete even for 90 h at a relative pressure lower than 0.7. In the high-pressure region, the rehydroxylation was promoted by condensed water. The number of surface hydroxyls after rehydroxylation became greater than that on the original surface. The possibility of the generation of the geminal hydroxyls was suggested from the degree of rehydroxylation on the surface.

Control of the bulk flow of granular materials by an aeration technique

Abstract Discharge of granular materials through a standpipe against an imposed overall gas pressure difference has been studied experimentally. The particles were transported from a low pressure region to a high pressure region and discharged through an orifice by aeration. With air introduced to aerate the particles, particle flow against the pressure difference was found to be more stable than without aeration. The particles can be discharged through the orifice stably even when the overall pressure difference in the pipe is just below that for fluidization. The mass flow rate of particles is correlated to the pressure difference across the discharging orifice and to its diameter. Effects of aeration on discharging rate were examined. An experimental equation which correlates the particle flow rate to the pressure difference across the orifice was obtained.