Alpha-pinene isomerization on acid-treated clays

WOS: 000173486300026Liquid phase isomerization of alpha-pinene was studied over a number of differently pre-treated montmorillonite clays. The effects of the acid pre-treatment parameters (acid-to-clay ratio (A/C), water-to-acid ratio (W/A), temperature and pre-treatment time) on the product distribution were investigated. It was observed that the pre-treatment with acid improved the catalytic activity of that catalyst which was activated at 200 degreesC for 4 h at A/C ratios between 0.2 and 0.4. Alpha-pinene consumption was very small over the catalysts prepared with an A/C ratio of 0.8. Characterization studies that were done by nitrogen and water vapor adsorption experiments and by IR measurements showed that catalysts with high differential pore volumes for pores around 2 nm and homogenous mesopore distributions and with low dealumination degrees were good catalysts for the production of camphene. Catalysts having heterogeneous mesoporosity were found to be the preferable ones for limonene production. (C) 2002 Elsevier Science B.V. All rights reserved

Shear-dependent rheological properties of starch/bentonite composite gels

WOS: A1997XK62700008Rheological properties of starch/bentonite gels (5.3-8.2% solids, 0-100% starch) were investigated at sheer rates 0.0083-0.33 s(-1) (Brookfield viscometer). Prior to these measurements the strain introduced during preparation of the gel was kept as low as possible. Under these conditions six different types of structural units could be identified in the gel: bentonite particles associated in a band-type structure; bands coated with starch polymers; bundles of bands interlaced and enveloped by starch polymers (strands), individual bentonite platelets dispersed in a polymer matrix; starch polymer networks; and swollen granules. A power-law model was fitted to the experimental viscosity data: mu(app) = K gamma(n-1). In all cases n was found to be less than 0.5. Its value decreased with the ability of the structural components to reorient under applied shear. K was found to be proportional to the compaction and/or entanglement of the structural units. These trends in K and n were further confirmed by the index of thixotropy (IT) and complex modulus of shear elasticity (G*) measurements

Structure of starch-bentonite gels

WOS: A1997WX40000009Mixed gels of starch and bentonite are investigated in the interval 0.056-0.089 of total solids/water ratio and 0-100% starch in the solids. The bentonite was a sodium calcium bentonite with a Na/Ca ratio of 1.76. In water it forms gels consisting of a network of band-type structures. Starch forms gels through hydrogen bonds between granules and/or amylose and amylopectin present on the external surfaces of granules and/or in fully stretched form. Mixed gels of bentonite and starch were obtained by adding corn starch granules to the already formed bentonite gels and heating the mixture above the Kofler gelatinization temperature. Amylose and amylopectin were adsorbed on strands of band-type structures of montmorillonite lamellae. Starch gellation, e.g. diffusion of amylose out of the granule, was facilitated in the presence of bentonite, On the other hand. the presence of starch favored delamination of the montmorillonite particle into thinner lamellae, Maximum gelatinization and polymer adsorption were observed for gels with 20% starch and 80% bentonite. Montmorillonite networks formed the continuous phase for 0-80% starch, At higher starch concentrations. montmorillonite flakes were dispersed within the polymer network. increase in the water content of the gels caused segregation of the bentonite and starch

Isomerization of alpha-pinene over ion-exchanged natural zeolites

15th International Conference on Chemical Reactor Modeling (CHEMREACTOR 15) -- JUN 05-08, 2001 -- HELSINKI, FINLANDWOS: 000181148600022Catalysts prepared by ion exchange of clinoptilolite-based natural zeolite tuffs; with NH4+, Ba2+ and Pb2+ were investigated in the isomerization reaction of alpha-pinene at atmospheric pressure under nitrogen flow. Activity and selectivity to mono-, bi- and tricyclic products were correlated with acidity strength. (C) 2002 Elsevier Science B.V. All rights reserved