Acidic deterioration

The remaining anhydrides are destroyed by subsequent hydrolysis through the addition of a small amount of water [152,154]. The color of the acid deteriorates during storage and therefore should be processed as quickly as possible, usually by neutralization. The most important is product LAS, which can be found on the market in various forms. The storage and processing properties can be improved by the addition of suitable additives. From such forms (LAS Na content 80-96%) powders can be manufactured by appropriate processes... 

Acidity deterioration and coke deposition in a HZSM5 zeolite in the MTG process... 

The total acidity deterioration and the acidity strength distribution of a catalyst prepared from a H-ZSM-5 zeolite has been studied in the MTG process carried out in catalytic chamber and in an isothermal fixed bed integral reactor. The acidity deterioration has been related to coke deposition. The evolution of the acidic structure and of coke deposition has been analysed in situ, by diffuse reflectance FTIR in a catalytic chamber. The effect of operating conditions (time on stream and temperature) on acidity deterioration, coke deposition and coke nature has been studied from experiments in a fixed integral reactor. The technique for studying acidity yields a reproducible measurement of total acidity and acidity strength distribution of the catalyst deactivated by coke. The NH3 adsorption-desorption is measured by combination of scanning differential calorimetry and the FTIR analysis of the products desorbed. 

The coke deposited in the catalyst in the MTG process in the 250 450 °C range is basically soluble in pyridine and has a structure constituted by methyl-substituted polycyclic aromatics. The molecular weight of the coke components and their H/C ratio increases with time on stream and temperature. The acidity deterioration occurs simultaneously with the increase in content of coke deposited (up to 1.6 % in weight with respect to the catalyst, at 350 °C) and is attributable to the irreversible occupation of acidic Bites. The coke components preferably occupy strongly acidic sites. 

It is not possible to specify an exact limit of pH below which undue acidic deterioration may take place. Many investigators consider that paper designed for permanence should not have a pH below 5.8 to 6.0 although it is likely that there is an intermediate range of pH values in which the contribution of acidity becomes progressively less important relative to other degradative influences. 

Ohashi, A., Matsushita, Y., Shibata, H., Kimura, K., Miyashita, K., and Saito, M. 2004. Conjugated linoleic acid deteriorates insulin resistance in obese/diabetic mice in association with decreased production of adiponectin and leptin./. Nutri. Sci. Vit., 50,416-421. 

Finally, it must be mentioned that solid samples of c -cyanobenzoic acid deteriorated noticeably over the course of 2 to 3 months, i.e. a solution made from such a sample showed a significant decrease in the rate coefficient for reaction with DDM. Solutions of the acid in some of the solvents deteriorated much more rapidly c/Widequist s finding for aqueous solutions ". ... 

Most of the studies have been made with ootylpyrophosphorlc acid (OPPA). Pyrophosphorlc acids deteriorate fairly rapidly with time at room temperature. At elevated temperatures, the rate of deterioration Is even greater. Contact with mineral acid causes pyrophosphorlc acids to hydrolyze to orthophosphorlo acids. The rate of hydrolysis is slower with basic solutions... 

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