Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Patent
1997-11-10
1999-03-09
Brunsman, David
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
127 1, C13K 104
Patent
active
058794638
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for acid hydrolysis of lignocellulosic material, such as wood, sugar cane bagasse, straw, vegetables, etc., for the obtention of sugars and lignin, among other products, as well as to a reactor for carrying out the referenced process.
BACKGROUND OF THE INVENTION
For the effect of hydrolysis, the lignocellulosic materials may be described as a celullosic, hemicellulose and lignin complex further containing lower organic components, such as taninnes, waxes, oils, etc, said "extractive" and mineral substances (silica, calcium, potassium, sodium, etc, the ashes). The cellulose (or glicane, 36 to 40% in mass) is a glucose polymer found in the amorphous form (its greater part) and in the microcrystalline form. The hemicellulose (34%) is a complex amorphous polymer containing glicane (-8%), xylane (22%), arabinane and galactane (total 4%). It has been shown that hemicellulose hydrolyzes almost instantly, microcrystalline cellulose is quite resistant to acid attacks and that amorphous cellulose is intermediary. The lignin (a polymer derived from phenyl propene containing active phenolitic functions) is not soluble in an exclusive acid medium, but may be dissolved by certain organic solvents. The ashes constitute of silica and aluminum and iron oxides that are very little soluble in hydrolytic means, and of potassium, sodium oxides, etc., that are soluble in acids. Such characteristics require desirable conditions for the hydrolysis apparatus and processes.
Acid hydrolysis processes of lignocellulosic materials produce, among others: hexoses (sugars with 6 carbons), such as glucose, galactose and mannose; pentoses (sugars with 5 carbons), such as xylose and arabinose: lignin; furfural; 5-hydromethil furfural; acetic acid; and methanol among others, in variable proportions, depending on the raw material being processed. Known acid hydrolysis processes of lignocellulosic materials are divided into two major groups: processes using concentrated acids and processes utilizing dilute acids.
From the first group, the "Bergius" and "Udic Rheinau" processes stand out, which use 40-45% hydrochloric acid, and the "Riga" process, which uses 75% sulfuric acid.
Although such processes present elevated hydrolysis yields (approximately 94% of the estoichiometrical value), high investments in equipment are required once they should be constructed with material resistant to such strongly concentrated acids. In addition, the manipulation of said acids makes the operation of the process extremely difficult.
Among processes which use dilute acids developed to overcome the drawbacks exposed hereinabove, the "Schoeller" process should be mentioned. According to this process the wood is heated in percolators at 134.degree. C. with the aid of sulfuric acid, thus obtaining, through repeated extractions, sugars with concentration of 2 to 4% in the resulting hydrolysis solution.
It is evident that this process, which is carried out in a batch procedure, presents a yield that is rather below that commercially expected.
In order to improve the process with dilute acid described above, a process namely "Madison" has been developed by the Laboratory of Forest Products of the United States, which uses 0.6% dilute sulfuric acid within the range of 18 m.sup.3 by ton of the dried treated material and is carried out in 3 to 5 hours, reaches a maximum yield of 67% of its estoichiometrical value. Although the "Madison" process is substantially improved relatively to the "Scholler" process, it presents a yield still below the desired. Further, due to the elevated temperature at which it is carried out, the equipment, even when dilute acid is used, must be made from special materials, such as titanium and zirconium, thus elevating the investment value therefor, even though below the investment made in processes wherein strong acids are used.
Apart from the drawbacks evidenced above, which are specific to each type of process, both present a common problem: during the saccharification op
REFERENCES:
patent: 4025356 (1977-05-01), Nyman et al.
patent: 4470851 (1984-09-01), Paszner et al.
patent: 4941944 (1990-07-01), Chang
Brunsman David
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