K. Lourvanij et Gl. Rorrer, DEHYDRATION OF GLUCOSE TO ORGANIC-ACIDS IN MICROPOROUS PILLARED CLAY CATALYSTS, Applied catalysis. A, General, 109(1), 1994, pp. 147-165
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.