Sugar – starch – and carbohydrates – Apparatus – Hydrolyzing
Patent
1981-10-15
1984-01-24
Marantz, Sidney
Sugar, starch, and carbohydrates
Apparatus
Hydrolyzing
127 37, C13K 102
Patent
active
044274530
DESCRIPTION:
BRIEF SUMMARY
The invention is concerned with a process for the continuous hydrolysis into sugars of pentosan-containing hemicelluloses, cellulose, and corresponding compounds of plant biomass. As a first step the appropriately pre-crushed biomass is treated in the presence of dilute acid at a specific temperature and pressure. Under these conditions mainly hemicellulose but partially cellulose, are hydrolyzed into pentoses and hexoses during the initial reaction. The reaction pressure is suddenly released and the hydrolysate is separated from the biomass.
In at least a further step, the cellulose in the biomass is hydrolyzed to hexoses in the presence of dilute mineral acid and under increased temperature and pressure. Again the pressure on the reaction mixture is suddenly released and the hydrolysate is separated from the biomass.
The neutralized hydrolysate is then appropriately processed for the production of sugars. The invention is further concerned with an apparatus for carrying out such a process.
The industrial production of sugar from cellulose-containing raw materials, especially from wood chips, was carried out for many years during the last war, until better economic conditions after the war made it unprofitable with conventional installations. The recent price increases of crude oil on the world market have led to the consideration of alternative raw materials for the production of fuels for combustion engines. In this connection sugar production from plant biomass, previously abandoned for economic reasons, now takes on new importance as the sugars may be fermented to ethyl alcohol, which can be used as fuel.
Sugar production from wood, as used during the war, was based on Scholler's percolator principle described in German Patent No. 640,775. In this discontinuous percolation process approximately 100 m.sup.3 containers are used. The wood is boiled at 160.degree. to 180.degree. C. for several hours with dilute sulfuric acid and then the produced xyloses and glycoses are washed out. The rinsing is performed according to the principle known as percolation. This known process has the disadvantage that it requires long boiling times and does not permit the use of waste such as remnants of annual plants, old papers and other garbage because the strainers built into the boilers, which are needed for the recycling of the boiling acid, become plugged and the percolation stops. In addition the long boiling times require very large boiling volumes. For this reason, the installations previously used in West Germany contained approximately 30 to 40 percolators, each with 60 m.sup.3 capacity. This lead to a substantial capital investment and to unjustifiably high energy consumption; for these reasons and others it became necessary to close installations.
A further process, based on the Scholler process, was developed by Eickemeyer and is described in German Patent No. 15 67 335. With the improved process, with discontinuously operating percolators, the initial impregnation of the biomass is said to be improved and steam use is reduced. This saves energy and gives a higher sugar concentration in the hydrolysate.
Because of the economic disadvantages of a discontinuous hydrolysis process one finds in the literature suggestions for continuous processes. However, so far it has not been possible to put these processes into practice. Currently there is no continuously operating sugar-producing process in operation.
Further improved hydrolysis processes are described in U.S. Pat. Nos. 2,801,939 and 3,212,932. The key point of these two patents concerns the conditions for the reactions. In both patents it is mentioned that the processes may be used continuously but the patents give no details of how this is to be achieved economically. U.S. Pat. No. 2,801,939 indicates that the biomass has to be sufficiently chopped up and mixed with a high excess of liquid so that it can be pumped. A high dilution however, leads to high energy costs and, more importantly, to lower concentrations of sugar in the hydrolysate which requires a
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