Saeman hydrolysis

Selvendran and coworkers hydrolyzed plant cell-wall materials by using 2 M CF3CO2H for 2 h at 120°, and M sulfuric acid for 1, 2, 5, and 8 h at 100° with (Saeman hydrolysis), or without, a prior 72% H2SO4 step for... 

The silk floss was defatted and hydrolyzed by Saeman s method [10] giving rise to xylose (73 %) and glucose (27 %), Aus indicating the presence of xylan. When the time of hydrolysis was up to 24 h, the presence of rhamnose (5 %) was also evident. However, degradation of xylose was observed after 8 h at 100 °C. 

Further insight into the decomposition of sugars which precedes formation of humic substances has been supplied by Saeman.85 Investigating the hydrolysis of wood in the temperature range 170-190°C. with... 

The importance of time, temperature and acid concentration in the hydrolysis of cellulose with dilute acid was recognized by early investigators and applied in the investigations of Simonsen in 1898. Further study was made by Kressman and reported in U. S. Department of Agriculture Bulletin No. 983. Reviews of the quantitative aspects have been made by Doree. Liiers pointed out that the conversion of cellulose dextrin to D-glucose by dilute sulfuric acid was a monomolecular reaction. The constants of the hydrolysis of wood cellulose have been determined by Saeman. The reaction rate (A ) was found to be expressed by the following equation ... 

Values determined by Saeman for the hydrolysis of Douglas fir are shown in Table II. 

The curves in Fig. 1 by Saeman show the production of sugars by hydrolysis of the carbohydrate and the decomposition of the sugars in the presence of an acid. 

Several procedures have been used to hydrolyze polysaccharides in cell walls and cell wall fractions. For example, the noncellulosic polysaccharides can be hydrolyzed using 1 M sulfuric acid for 2 to 3 hr at 100°C (Selvendran and Ryden, 1990). One of the simplest procedures is that of Albersheim et al. (1967) in which hydrolysis of the noncellulosic polysaccharides is achieved by incubating in 2 M trifluoroacetic acid (TFA) at 121 °C for 1 hr. The advantage of the TFA procedure is that it is quick and the acid can be removed by evaporation in a gentle stream of air or nitrogen. However, neither the 1 M sulfuric acid or TFA procedures hydrolyze cellulose. Hydrolysis of cellulose can be achieved by an initial dispersion in 72% (w/w) sulfuric acid (Saeman et al., 1963 Selvendran et al., 1979 Fry, 1988 Harris et al., 1988 Selvendran and Ryden, 1990) followed by hydrolysis in 1 M sulfuric acid. 

Saeman, J.F., Moore, W.E., and Millet, M.A. 1963. Sugar units present. Hydrolysis and quantitative paper chromatography. In Methods in Carbohydrate Chemistry, Vol. 3, Cellulose (R.L. Whistler, ed.) pp. 54-69. Academic Press, New York. 

A considerable amount of experimentation has been done on the kinetics of acid hydrolysis of pure cellulose substrates. Little experimentation has been done on natural cellulosic materials. Typical examples of kinetic studies of acid hydrolysis of cellulose can be found in the papers of Saeman (33) and Grethlein (13). These researchers depict the acid hydrolysis process as a pseudo-first-order sequential process, with the rate constants as a function of the acid concentration raised to a power, i.e.,... 

Grethlein (13) and Saeman (33) have estimated values of the various constants for acid hydrolysis of Solka Floe and Douglas Fir. These are given in Table III. 

Saeman, J. F. Kinetics of Wood Saccharification—Hydrolysis of Cellulose... 

The standard procedure by Saeman et al. (I) involves manual stirring of the polysaccharide with 72% H2S04, standing at 30°C, and secondary hydrolysis at 100° or 120°C in a steam autoclave. While certain resistant polysaccharides are still incompletely depolymerized, decomposition of the more sensitive monosaccharides formed cannot be avoided. An alternative method by using trifluoroacetic acid was applied successfully for plant cell wall polysaccharides by Albersheim et al. (2) and for dissolving pulps and hemicelluloses by Fengel et al. (3). Highly crystalline cellulose was not well dissolved and not completely hydrolyzed by CFsCOOH. 

The hydrolysis of polysaccharides into monomeric sugars is a well-studied process its mechanism is still believed to be accurately described by the work of Saeman in 1945.432 Its significance is linked to the production of fermentable sugars for ethanol manufacture. Many of these processes are based on acid catalysis and overlap closely the pretreatment methods described earlier.363,364,373 Treatments with both concentrated and dilute acids are well known as methods for the hydrolysis of cellulose and hemicellulose, as is the use of organic dicarboxylic acids as alternative catalysts to mineral acids.433... 

Luers erred, however, in concluding that changing the acid concentration and temperature changed the rate but not the course of the reaction nor the maximum yield attainable. Saeman W showed that the hydrolysis reaction is accelerated more than the decomposition reaction by both increased temperature and acid concentration. Hence, the sugar yield increases with both acid concentration and temperature. This observation is applicable to both the percolation process and to the much simpler batch process. 

Figure I shows the maximum yield of "B" and the residual "A" in consecutive first-order reactions A C for various ratios of ki k2 kr. Parameters for cellulose hydrolysis were determined by Saeman (4) and redetermined by Kirby j. It might be noted that despite analytical and experimental problems, the general model has been repeatedly confirmed.

Data and kinetic models of dilute acid pretreatment ate vital to provide a foundation for undostanding hemicellulose hydrolysis and the cause of enhanced performance by flow system systems. Initial hemicellulose hydrolysis models were adapted from Saeman s first-order homogeneous kinetic model of cellulose hydrolysis in a dilute acid batch system (30) and later modified to include two different fractions of hemicellulose, one of which is more easily... 

Saeman, J.F., 1945. Kinetics of wood saccharification. Hydrolysis of cellulose and decomposition of sugars in dilute acid at high temperature. Industrial and Engineering Chemistry 37, 43-52. 

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