FI65801C - PROTECTION OF CELLULOSE WITHOUT CELLULOSE - Google Patents

Description

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USA (US) 88M8O

(71) Purdue Research Foundation, Graduate House East, West Lafayette,

Indiana, USA (72) George T. Tsao, West Lafayette, Indiana,

The present invention relates to a method for obtaining high glucose from cellulose. as a yield from cellulose recovered from cellulosic materials, wherein the cellulosic material is hydrolyzed with dilute sulfuric acid at a temperature of about 121 ° C to remove hemicellulose and the solid residue is separated after removal of the hemicellulose.

The utilization of cellulosic materials such as corn stalks, sawdust, straw and bagasse has been of great interest recently, especially for the utilization of these waste materials for the production of fuels, nutrients, chemicals and other useful products.

Cellulosic materials contain three main components, which are cellulose, hemicellulose and lignin. Methods for extracting hemicellulose have been previously proposed and / or used, and this known extracted hemicellulose can be utilized in a number of currently used methods, such as hydrolysis, fermentation and pyrolysis.

Lignin has also been isolated from cellulosic materials. Because lignin has a higher hydrogen and carbon content and a lower oxygen content than cellulose or hemicellulose, its fuel value is the higher of the three. The separated lignin can be combusted to generate water vapor and electricity and can also be used to produce a number of useful products such as vanillin, dimethyl sulfoxide, dimethyl sulfide, methyl mercaptan and catechol.

The recovery and utilization of cellulose, for example by hydrolysis to glucose, has hitherto been difficult due to the crystalline structure of the cellulose and the lignin contained in the material.

Attempts have been made to hydrolyze cellulose with acids and / or enzymes, but these attempts have not been successful.

The use of acids such as sulfuric acid in the hydrolysis of cellulosic materials to form glucose has been known for several decades. In general, all of the previously described methods for hydrolyzing cellulose using sulfuric acid can be divided into two major groups; those using dilute sulfuric acid and those using concentrated sulfuric acid. In dilute acid processes, the sulfuric acid solution usually contains about 5 to 50 g of H2SO4 / kg of aqueous solution. At a temperature of about 150 to 350 ° C, cellulosic materials such as wood chips, when suspended in dilute acid, hydrolyze to form glucose from cellulose and sugars containing 5 carbon atoms from hemicellulose. Since the reaction temperature is usually above the boiling point of the dilute acid, the hydrolysis reaction must be carried out in pressure reactors. At high temperatures, glucose and sugars containing 5 carbon atoms decompose under the influence of acid to form furfural and its derivatives, which often continue to react to form harmful by-products. Thus, a dilute acid process is generally not useful for obtaining glucose from cellulose in high yields at low cost. Usually, a process using dilute oxygen 3 65801 poa gives a yield of about 50% or less, based on the available cellulose, and contaminated with unusable by-products. Methods using dilute acid are well known and have been extensively studied by several researchers.

There are also numerous publications on cellulose hydrolysis methods using concentrated sulfuric acid. Examples include a relatively new publication, Bose, et al. (See Bharati Bose, TR Ingle and JL Bose, "Saccharification of Groundnut Shell Pulp with Sulfuric Acid," Indian Journal of Technology, Vol. II, September 1973, pp. 391-393) and a publication by Dunning and Lathrop. (See JW Dunning and EC Lathrop, "The Saccharification of Agricultural Residues," Industrial and Engineering Chemistry, Vol. 37 (1945), pp. 24-29). Generally, concentrated sulfuric acid (e.g., 750 g H 2 SO 4 / kg acid) is added to the finely divided cellulosic material. After absorption and thorough mixing, 8-10 volumes of water are added to dilute the acid. The mixture is then refluxed for a few hours at normal pressure to form glucose. Typically, 90-93% of the available cellulose can be converted to glucose by this method and no significant by-products are formed. However, the disadvantage of the known methods is that large amounts of acid have to be used. Upon completion of the hydrolysis, both the acid and glucose are dissolved in the same aqueous solution. An equal amount of base (usually lime) must be used to neutralize the acid before sugars can be utilized, for example, as a carbon source in yeast fermentation. These methods have the difficulty of disposing of large amounts of calcium sulfate as a by-product, and the high acquisition costs of both acid and base.

The process according to the invention is characterized in that the solid residue is added to concentrated sulfuric acid at room temperature while stirring, after which the cellulose is reprecipitated by adding water or a solvent such as methanol and hydrolyzed again to give glucose.

In the process of the invention, the cellulosic feedstock, such as corn stalks, is first hydrolyzed with either fresh or reusable dilute sulfuric acid under mild conditions to remove hemicellulose. At this stage, well-known reaction conditions are used (typically 1.9% sulfuric acid at 121 ° C for 50 minutes). The liquid hemicellulose hydrolyzate can be used as a fermentation medium after neutralization with lime. This step is illustrated in the following example.

Preparation of lignocellulose 10 g of maize waste (mesh number greater than 40) are mixed with 500 ml of standard sulfuric acid solution. The mixture is heated in a cooking vessel equipped with a 2 l condenser and gently boiled for 1 hour. The mixture is then filtered and washed with 1 liter of hot water in a glass filter, and then with acetone until all the color has disappeared. The mixture is then transferred to an aluminum foil and can be air dried overnight if desired.

The solid residue containing mainly cellulose and lignin is filtered or centrifuged to remove the hemicellulose hydrolyzate.

Concentrated sulfuric acid is then added, the acid intensity being preferably 60 to 90% (60% acid contains 600 g of 1 SO 2 / kg of acid solution). At this acid strength, the cellulose can be dissolved in an acid solution. This step is illustrated in the following Examples 1-3.

Example 1 1 ml of 70% sulfuric acid is periodically mixed with 0.4 g of Avicel (microcrystalline cellulose, manufactured by FMC Corporation, type PH101) for half an hour at room temperature and then diluted with 3 ml of methanol (99%, reagent grade). ). The mixture is filtered to give a sugar loss in the filtrate of 0.3% (determined by the Anthrone method). The mixture is then washed with water until it is only slightly acidic. 3.6 mg of this pretreated amorphous cellulose are poured into a mixture of 0.4 ml of NaCH 2 COO buffer solution having a pH of 5 and 0.04 ml of cellulase enzyme to give a 90% conversion of cellulose to glucose in 3 hours.

Example 2

The procedure and reagents are the same as in Example 1, except that 4 ml of water is used to dilute the acid mixture instead of 3 ml of methanol. The sugar loss in the filtrate is 7.8% and the effect of the enzyme on the solid residue is the same as in Example 1.

5,65801

Example 3 0.6 ml of 65% sulfuric acid is mixed with 0.1 g of ligno-cellulose (prepared according to the above pretreatment) and the mixture is subjected to the treatment of Example 1, except that the dilution is made with 2 ml of methyl alcohol, in which case the sugar loss is reduced. the dose is 1.03% and a 90% change in cellulose is obtained in 10 hours.

The moist mixture is then mixed with concentrated sulfuric acid (during this mixing, most of the cellulose dissolves in concentrated sulfuric acid), carefully monitoring the reaction conditions including temperature, time, acid strength, and acid to solid ratio. The cellulose is then reprecipitated by diluting the acid with 2-5 volumes of water or an organic solvent such as methanol at the end of the mixing.

Careful control of the reaction conditions is important and the key is the successful recovery of sulfuric acid and the efficient hydrolysis of the reprecipitated cellulose to obtain glucose. For example, if the reaction time is too long, the cellulose may hydrolyze too far and much of it will dissolve because cellodextrins having a degree of polymerization of less than 7 are soluble in water. When this happens, that portion of the carbohydrates is lost because there is no easy and inexpensive way to separate dissolved sugars from sulfuric acid. It is assumed that this is the main reason for rendering the known methods using concentrated sulfuric acid unusable, due to the high cost of the acid and the base required to neutralize it, for the use of dissolved sugars.

When the reaction conditions are monitored according to the invention when mixing the cellulose-lignin mixture with concentrated sulfuric acid, approximately 97% by weight of the original cellulose is in solid form after the addition of 2-5 volumes of water at the end of the mixing. If an organic solvent such as methanol is added instead of water, an even larger portion (i.e., 97% or more) of the original cellulose is reprecipitated. By filtering or centrifuging the mixture immediately after the addition of water or an organic solvent such as methanol, about 90% of the sulfuric acid is recovered, which dilute sulfuric acid can be concentrated in an evaporator to remove excess water or added methanol before returning to the process. The cellulose obtained by filtration or centrifugation is washed with water to form a dilute acid which can be returned to the initial stage of the process to hydrolyze the hemicellulose.

The resulting solid cellulose is partially hydrolyzed to a lower degree of polymerization than the original and has a completely broken internal structure and lignin seams, and can thus be easily and completely hydrolyzed to glucose by dilute acid and / or cellulase enzymes after pH adjustment.

As can be seen from the above, the process of the present invention takes advantage of the fact that prior to solubilizing hydrolysis, cellulose can be precipitated from a concentrated sulfuric acid solution by dilution with water or as an organic solvent such as methanol. The cellulose thus precipitated can be easily and completely hydrolyzed to glucose by enzymes and / or dilute acids. Precipitation enables the separation and recovery of the acid, i.e., the efficient recycling of the acid, which significantly reduces chemical costs.

Claims (4)

7 65801 A process for obtaining glucose in high yield from cellulose recovered from cellulosic materials, wherein the cellulosic material is hydrolyzed with dilute sulfuric acid at about 121 ° C to remove hemicellulose and the solid residue is separated after removal of the hemicellulose at room temperature, characterized in that said residue is added after which the cellulose is again blended by the addition of water or a solvent such as methanol, and the reprecipitated cellulose is hydrolyzed to obtain glucose. Process according to Claim 1, characterized in that the precipitated cellulose is hydrolysed by the action of cellulase enzymes in order to obtain glucose. Process according to Claim 1, characterized in that the precipitated cellulose is hydrolysed with a dilute acid. Process according to Claim 1, characterized in that the precipitated cellulose is hydrolysed by means of cellulase enzymes and a dilute acid.