PROCESS FOR THE PRODUCTION OF PENTOSE AND HEXOSE FROM A CELLULOSIC MATERIAL CONTAINING PENTOSANS BY ACID HYDROLYSIS

Abstract: Process for the production of pentose and hexose from a cellulosic material containing pentosans by an acid hydrolysis, in which the starting material is heated to a temperature of between 210 and 250<o>C for a period of between 5 and 90 seconds in the presence of a strong acid having a concentration of between 0.2 and 2.0% by weight. A high yield of both pentose and hexose is obtained by said single step process.

Description: 1 Process for the production of pentose and hexoxe from a cellulosic material containing pentosans by acid hydrolysis i This invention relates to a process for the production of pentose and hexose from a cellulosic material containing pentosans by -> 5 acid hydrolysis, said process comprising the step of heating the cel¬ lulosic material to an elevated temperature in the presence of a ? strong acid . It is well known that glucose can be prepared from various cellulosic materials, such as straw, sawdust, wood waste and sugar 10 cane bagasse, by heating the cellulosic material to an elevated tempe¬ rature in the presence of sulphuric acid . Methods of this type have lately attracted considerable interest, partly because ' cellulosic raw materials are available in very large amounts and partly because there is a growing need for providing cheap glucose for use as a 15 starting material in the production of ethanol by fermentation . However, unless the acid hydrolysis is stopped at a proper time, the glucose formed will be converted into 5-hydroxymethyl fur¬ fural which is of no value a far as the production of ethanol is con¬ cerned. 20 It is also well known that pentosans present in various cellulosic materials, such as straw, may be converted into xylose and minor amounts of other pentoses by acid hydrolysis and that the hy- drolysate thus obtained after separation from the reaction mixture is suitable as an animal feed or as a raw material for the production of 25 xylose syrup or crystalline xylose. The hydrolysis of the pentosans to form xylose should also be carefully controlled in order to avoid that the hydrolysate, viz. xylose, is further converted into furfural . It is well known that the optimum reaction conditions of 30 the two hydrolysis reactions are different, and up to now it has been assumed that under given set of reaction conditions it is impos¬ sible to obtain both xylose and glucose in acceptable yields, cf. John A. Church and Derek Wooldridge: Continuous High-Solids Acid Hydrolysis of Bio ass in a i in . Plug Flow Reactor, Ind . Eng . 35 Chem. Prod . Res . Dev. 1981 , 20, 371 -378. Therefore, xylose and glucose are normalle prepared from cellulosic materials containing pentosans in a two step process in which the reaction conditions have been selected so as to favour the formation of xylose in the first step and glucose in the second step . O PI Since the hydrolysis is effected under strongly acidic con¬ ditions, the equipment used should be made from an acid-resistant material. Furthermore, a large scale equipment is required to handle the relatively voluminous starting material . Consequently, such a two step hydrolysis involves relatively high investments and operational costs . The object of the invention is to provide a single step process for the production of both pentose and hexose in relatively high yields. Another object of the invention is to provide a low cost process for the production of pentose and hexose from a cellulosic material containing pentosans. These objects are achieved by the method of the invention which is characterized in that the hydrolysis is effected at a tempe¬ rature of between 210 and 250°C for a period of between 5 and 90 seconds and in the presence of an acid having a concentration of from 0.2 to 2.0 % by weight. The invention will be described with reference to the pro¬ duction of xylose and glucose but it should be understood that de¬ pending on the starting material used it is also suitable for the pro- ductϊon of other combinations of a pentose and a hexose. The invention is based on the discovery that when using for example straw as starting material and by performing the hydro¬ lysis under the above mentioned operational conditions, it is possible to obtain a yield of xylose of about 50% (based on the amount of pentosans present in the starting material) together with a yield of glucose of above 50% (based on the amount of cellulose in the starting material). In view of the fact that the . above mentioned yield of glu¬ cose is close to the maximum yield obtainable in the prior art two step method, it is surprising that a yield of xylose of about 50% is obtainable under the same operational conditions. Thus, it appears from the above mentioned article by John A. Church and Derek Wooldridge that the yield of xylose obtained by the investigations described in said article Is 4% when the yield of glucose is maximum, cf. page 376, left column. The surprising technical effect obtained by the process of the invention is illustrated in the drawing which is a diagram in which the yield (%) is depicted versus reaction time (sec ). Curves 1 and 2 illustrate the theoretical yields of glucose and xylose, re- spectively, in separate acid hydrolyses of straw carried out at a temperature of 230°C and an acid concentration of 0.75±0.05%. Cur¬ ves 3 and 4 illustrate the yields of glucose and xylose, respectively, in a process according to the invention . As will appear from these curves, the yield of glucose ob¬ tained by the process of the invention is approximately equal to the theoretical yield, whereas the yield of xylose by the process of the invention is considerably higher than the theoretical yield. The highest yields of xylose and glucose are obtained by effecting the hydrolysis at a temperature of from 225 to 235°C for a period of 30-60 seconds. The reaction temperature and the reaction time should be carefully controlled and in a preferred embodiment of the method of the invention the acid hydrolysis is effected under pressure, e.g. at a pressure of 2-5 MPa in a tubular reactor and by heating the start¬ ing material by steam injection . In this manner the reaction mixture can be rapidly heated and a corresponding rapid cooling can be effected by pressure relief, e. g . to atmospheric pressure. The pressure- relieved product Is preferably further cooled or is neutral- ized by addition of base, such as Ca(OH) , in order to raise the pH value to 3 or above so as to stop the decomposition of glucose and xylose. The neutralized product may then be filtered so as to form a filtrate containing xylose and glucose and a filter cake which option¬ ally after being dried is suitable as a solid fuel. The use of the filter cake as a solid fuel decreases the energy consumption of the process. The filtrate may be separated into a xylose fraction and a glucose fraction but it is preferred to subject the filtrate to a fer¬ mentation before xylose is separated. In that case xylose is subse- quently separated, optionally in connection with part of the fermen¬ tation medium which is also suitable as animal feed together with the xylose. When using straw as starting material the straw is prefer¬ ably cut into pieces having a length of about 1-10 cm. When using other naturally occurring cellulosic materials containing pentosans, these should preferably be comminuted before the acid hydrolysis is started. Examples of other suitable starting materials are sawdust, paper waste, bagasse, oat shells, corncobs and beet pulp. The acid used is preferably a strong mineral acid, such as sulphuric acid, but also other mineral acids, such as hydrochloric acid are suitable. The invention will be described in further detail with reference to the following examples: Example 1 Barley straw was cut into lengths of about 1 cm and slurrϊed in a sulphuric acid solution . The slurry thus obtained was pumped into a tubular reactor under a pressure of 3.2-4 MPa. The temperature was raised to 230°C by direct injection of steam. After the injection of steam the acid concentration was 0.75%. The tempera¬ ture was maintained for 30 seconds and then the pressure was sud¬ denly relieved to atmospheric pressure. As a result of said pressure relief a steam phase and an aqueous phase having a temperature of 100 C were formed . The aqueous phase containing xylose and glucose was cooled to below 70°C. Xylose was separated from the cooled aqueous phase in a yield of 63% (based on the weight of the pentosans present in the straw) and glucose was separated in a yield of 35% (based on the weight of the cellulose present in the straw) . Example 2 The same procedure as described in example 1 was used used except that the reaction time was 45 seconds. The yield of cellulose was 50% (based on the weight of the pentosans present in the straw) and the yield of glucose was 56% (based on the content of cellulose in the straw) . Example 3 The same procedure as described in Example 1 was used except that the reaction time was 41 seconds. The yield of xylose was 53% and the yield of glucose 41%. Example 4 The same procedure as described in Example 1 was used, except that the concentration of the sulphuric acid solution was 0.63% and the reaction time was 45 seconds. The yield of xylose was 55% and the yield of glucose 48%. Example 5 Barley straw was cut into lengths of about 3 cm and was pumped into a reactor under a pressure of 3.2-4 MPa. To the straw was added a sulfurlc acid solution of a temperature of 180 C and the mixture thus obtained was immediately heated to a temperature of 230 C by direct injection of steam . After the injection of steam the acid concentration was 0.8%. The temperature was maintained for 59 seconds and then the pressure was suddenly relieved to atmospheric pressure. As a result of said pressure relief a steam phase and an aqueous phase having a temperature of 100 C were formed . The aqueous phase containing xylose and glucose was cooled to below 70°C . Xylose was recovered from the cooled aqueous phase in a yield of 18% (based on the weight of the pentosans present in the straw) and glucose was recovered in a yield of 53% (based on the weight of the cellulose present in the straw) .

Claims: a i m s 1. A process for the production of pentose and hexose from a cellulosic material containing pentosans by acid hydrolysis, said process comprising the step of heating the cellulosic material to an elevated temperature in the presence of a strong acid, c h a r ¬ a c t e r i z e d in that the hydrolysis is effected at a temperature of between 210 and 250 C for a period of between 5 and 90 seconds and at an acid concentration of between 0.2 and 2% by weight. 2. A process according to claim 1, c h a r a c t e r i z - e d in that the hydrolysis is effected at a temperature of between 225 and 235 C for a period of between 30 and 60 seconds. 3. A process according to claim 1, c h a r a c t e r i z ¬ e d in that the acid hydrolysis is effected under pressure in a tubular reactor and that the reaction mixture is heated by steam injection. 4. A process according to claim 3, c h a r a c t e r i z ¬ e d in that the acid hydrolysis is stopped by pressure relief follow¬ ed by a further cooling of the reaction mixture. 5. A process according to claim 1, c h a r a c t e r i z - e d In that the hydrolysate is filtered before it is converted into a pentose and a hexose fraction. OMPI

Inventors: BUUS LASSE, NIELSEN WERNER KOFOD, BUUS, LASSE, NIELSEN, WERNER, KOFOD
Applicants: DANSKE SPRITFABRIKKER, DANSKE SUKKERFAB, AKTIESELSKABET DE DANSKE SPRITFABRIKKER, AKTIESELSKABET DE DANSKE SUKKERFABRIKKER
Application year: 1982
Main classification: C13K1
IPC codes: C13K1, C13K13