The regeneration of a commercial hydrotreating catalyst was investigated by means of a thermobalance reactor. The kinetics of combustion of carbonaceous deposits were measured over a wide range of conditions. The rate controlling mechanism changed from the intrinsic chemical kinetics to pore diffusion as operating variables were changed. The thermogravimetric method proved to be a quick and reliable means of measuring catalyst regeneration kinetics.
Various titrimetric and manometric methods have been proposed for the quantitative measurements of enzymatic activity of pancreatic and other lipases. Since these procedures have been recently reviewed by Bradshaw ( 4 ) and by Ammon and Jaarma ( I ) , the details of the methods will not be discussed in this paper, except to call attention to certain features which adversely affect the precision and accuracy of the determination. Thus, it appears that such procedures include one or more of the following undesirable practices : the use of poorly dispersed, unstable fat emulsions which prevents the maximum interaction of the enzymesubstrate complex; the inadequate control of the p H during the course of reaction which introduces important variables affecting the precision of the results; and the resort to solvent extraction of the fatty acids from the digest mixture which permits manipulative errors and time-consuming labors.The present investigation was undertaken to develop a more sensitive and convenient method for determining the digestibility of fat by pancreatic and other lipases. A technique for dispersing lipid substrates in a finely divided and stable emulsion was employed, using a soy phospholipid preparation as the emulsifying agent and carrying out the emulsification in a high-pressure dairy homogenizer ( Cherry-Burrell Junior Viscolizer) .The details for preparing the emulsion were the same as those previously described for studies on the bacterial hydrolysis of fats by the present authors (7). Emulsions so prepared show n o oil separation during prolonged storage, and the uniform globule size of less than 0.5 micron makes available an enormous surface for lipase action.Since the fat-splitting action of lipase is greatly affected by changes in pH, it seemed advisable to maintain the optimum p H level by continually adding dilute alkali to the digestion mixture during reaction, a s was done by Koch and Duellman (9), and Bullock (5). The addition of an indicator to the digestion mixture was found in the present work to be unsatisfactory in controlling the pH, partly because of the interfering turbidity of the digest. Also, Bamann and Schmeller ( 3 ) have indicated the possibility of significant errors inherent in the use of indicators in the esterase determination because of their inhibitory effect on the enzyme-substrate system. Therefore, the pH was maintained in this study b y the use of the glass electrode as described by Glick (6) for the determination of choline esterase. With this procedure, the functions of both p H control and titra-
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