DEHYDRATION OF GLUCOSE TO ORGANIC-ACIDS IN MICROPOROUS PILLARED CLAY CATALYSTS

Glucose is an abundant and renewable feedstock for chemicals productio n. The objective of this study was to determine if microporous pillare d-clay catalysts could promote the shape-selective, partial dehydratio n of glucose to organic acids. Iron-, chromium-, and aluminum-pillared montmorillonite catalyst powders were prepared. The iron-pillared mon tmorillonite had the most open pore structure in the > 10 Angstrom ran ge. Pore slit widths of at least 10 Angstrom allowed the 8.6 Angstrom glucose molecule to diffuse and react directly within the catalyst mic ro- and meso-pores. Each catalyst powder was reacted with 0.75 M gluco se solution (4 g catalyst/150 ml) within a well-mixed Parr autoclave r eactor for 0-24 h at temperatures ranging from 130-170 degrees C. All of the catalysts tested promoted four acid-catalyzed reactions: isomer ization of glucose to fructose, partial dehydration of glucose to 5-hy droxy-methylfurfural (HMF), rehydration and cleavage of HMF to formic acid and 4-oxopentanoic acid, and coke formation. The Fe-pillared mont morillonite provided the highest glucose conversion rate, with 100% gl ucose conversion attained within 12 h at 150 degrees C. This catalyst also provided the lowest selectivity of the HMF (the reaction intermed iate) and the highest selectivity of formic acid (the final product) i n the bulk phase at an optimum temperature of 150 degrees C. Apparentl y, the fraction of pores in the 10-25 Angstrom range allowed glucose t o diffuse into the microporous matrix, but also trapped the bulky HMF molecule within the micropores, thus directing the reaction scheme to the final organic acid products. However, 4-oxopentanoic acid selectiv ities were low ( < 20%), and coke formation was as high as 0.4 g coke/ g catalyst, implying carbonization of final reaction products.