Simple Dilute-acid Hydrolysis of Wood, Sulphur Dioxide, Lignocellulose, Saccharification, Pentoses, Glucose, Hydrolysis

Simple Dilute-acid Hydrolysis of Wood

	Simple Dilute-acid Hydrolysis of Wood The single-stage batch process of wood hydrolysis was the first commercial method for making sugars from wood. The process has the advantage of great simplicity, and, with improvement, it might still be the method of choice in certain situations. The wood is processed on a 1-hour cycle in four spherical digesters, each holding 4,700 pounds of dry wood. The sugar is extracted in a battery of eight 150-cubic-foot cells arranged for countercurrent extraction.
About 96 percent of the sugar is extracted to give a solution containing about 12 percent total solids, nearly 9 percent reducing sugar, and roughly 6 percent fermentable sugar. A process used in Sweden during World War II for the continuous hydrolysis of wastewood is described as follows. The wood chips are impregnated in a tower with sulphur dioxide gas. The bottom of the tower is connected to the feeder mechanism of a de-fibrator. The chips are heated in the pre-heater at 180° C for 2 to 3 minutes, ground in the de-fibrator, and the pulp pressed out continuously through an expansion valve. Seven such units operate in parallel. The pulp is washed in centrifuges and the solubles are re-acidified and hydrolysed further. The sugar solution at a concentration of 8 percent is fermented with the spent sulphite liquor of the plant. The residual lignocellulose is used as a fuel.
The following conclusions can be arrived at regarding the saccharification process involving wood: 1. A fairly good yield of sugar (48-50 percent); 2. A high concentration of sugar (10-12 percent); 3. All pentoses enriched in the first stage solution which facilitates the utilization of the pentoses: the sugar formed in the second stage consists entirely of glucose; 4. The total consumption of sulphuric acid is low, and amounts to 20-25 kilograms per ton of wood;
5. The consumption of steam without heat recovery amounts to 1.3 tons per ton of wood; 6. The digesters for carrying out the hydrolysis are of small size, because of the short time of hydrolysis. Fifty tons of wood a day may be converted to sugar by using two digesters of 3 cubic metres each and two of 2 cubic metres each. The hydrolysis is carried out under the following conditions: 1. The wood is used in the form of thin shavings, chips or sawdust. 2. The wood is impregnated with weak acid and freed from excess of liquor prior to hydrolysis. 3. The hydrolysis is carried out in an atmosphere of steam.

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Simple Dilute-acid Hydrolysis of Wood