FI58944B - FRAMEWORK FOR FRAMSTAELLNING AV EN XYLOSLOESNING - Google Patents

Description

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Patent- och ragisterstyralsan '' Anaekan utla | d oeh utl.ikrlfun publtorad 30.01.8l (32) (33) (31) Pyydetty MuoHmm · —B * jlrd priority 0U. 05.73 13.11.73 Switzerland-Switzerland (CH) 6335/73 15918/73 (71) Sulzer Brothers Limited, Winterthur, Switzerland-Switzerland (CH) (72) Renato Maspoli, Zurich, Switzerland-Switzerland (CH) (7U) Oy Kolster Ah (5U) Method for preparing a xylose solution - Förfarande för framställning av en xyloslosning

The invention relates to a process for preparing a xylose solution from xylan-containing raw materials, in which the xylan is hydrolyzed with an acid solution at an elevated temperature and the xylose formed is extracted with water.

It is known that a xylose solution can be prepared from xylan-containing plant-derived raw materials or waste, such as beech or bagasse, by contacting the raw material with an acid solution in a closed vessel at elevated temperature and overpressure so that the xylose is hydrolyzed. The xylose formed is then extracted with water. The disadvantage of the known method is that the impregnation, the reaction and often also the extraction take place together. This makes it much more difficult or even impossible to monitor and optimize the private phases. Due to the overpressure of the air in the pores and the water vapor, the capillary absorption of the hot acid solution into the pores becomes considerably more difficult and it is therefore not possible to saturate the raw material base in the acid solution. The reaction surface between the raw material and the acid solution is then only negligible, so that the hydrolysis of the xylan contained in the raw material takes place only slowly. The known method thus becomes long-lasting and uneconomical. In addition, the purity of the obtained xylose solution is not particularly high.

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The object of the invention is to eliminate these drawbacks and to provide a process for the preparation of xylose solutions which is economical and thus gives a xylose solution of high purity. The invention is characterized in that the process is carried out in four mutually separate and completely continuous steps, in the first step the xylan-containing raw materials are heated with steam and deaerated, in the second step the heated raw materials are treated with an acid solution at a temperature of up to 50 ° C; the raw materials treated in step 4 are preferably subjected to a water vapor atmosphere at atmospheric pressure, for a maximum of 90 minutes, and finally, in the fourth step, the xylose thus formed is extracted with water.

The advantages of the invention are based on the fact that the various steps can be carefully monitored and optimized so that the duration of the process is short and the purity of the product is very high. According to the invention, since the impregnation of the raw material takes place after and separately from the steam treatment and because the temperature of the acid solution is low, condensation of water vapor is initially achieved in the pores so that a vacuum is created and the pores rapidly and completely absorb the acid solution. The subsequent hydrolysis therefore proceeds rapidly and thoroughly. A further advantage of the method according to the invention is that the raw material, for example beech chips, is not destroyed and the residual components of the wood remain essentially untouched. They can therefore be further processed immediately, for example as starting materials for the production of cellulose.

As a saturating solution, preferably up to 3% by weight of hydrochloric acid is used.

The recommended impregnation time is 2-10 minutes.

The method is used continuously, in which case the process substances pass through a feeder which transfers them to the stern and continuously from one stage to the next. In this case, the feed device is preferably formed as a helical conveyor.

Some embodiments of the method according to the invention will be examined in more detail with reference to the drawing.

The drawing shows a flow chart according to which a xylose solution can be prepared according to the invention. A xylan-containing raw material, e.g. beech chips, is fed through a pipe 1 to a spiral conveyor 2. The coil 3 is driven by a motor M. Steam 3 is supplied to the spiral conveyor 2 via a pipe U with a shut-off tap U ', whereby the beech chips are heated. In this case, the air leaving the beech chips exits through the ventilation pipe 5. When the shut-off valve 5 'in the ventilation pipe 5 is fully open, heating takes place at an external pressure. To promote ventilation, the ventilation pipe 5 can be connected to a vacuum source. The described event represents the first step of the method. The helical conveyor 2 transfers the heated beech chips through the connecting pipe 6 to the helical conveyor 8. In this case, an acid solution at room temperature is mixed with the beech chips through the pipe 7. As the wetted beech chips pass through the helical conveyor 8, the beech chips are completely saturated with the acid solution. Since the acid solution is cold, water vapor penetrating the pores of the night chips by the first helical conveyor 2 condenses and a vacuum is created in the pores. In this case, the acid solution penetrates quickly and completely into the pores so that the walls of the pores become completely wet. A dam ring 9 is mounted at the end of the helical conveyor 8, which causes the liquid and solid components of the incoming mass to separate. The part of the acid solution which is not absorbed in the beech chips can be removed via the line 10. The impregnated beech chips leave the helical conveyor 8 and four helical conveyors installed in parallel. of which only one helical conveyor 13 is shown, via an intermediate connecting line 11. As it passes to the helical conveyor 13, the mass passing through the connecting line 11 is heated by the water vapor from the line 12. In the helical conveyor 13, the actual hydrolysis of the beech chips takes place at the water vapor atmosphere and xylose is formed. The helical conveyors 13 are provided with a ventilation line li so that when the shut-off valve is fully open, hydrolysis takes place at ambient pressure. By restricting the shut-off valve 11 ', the hydrolysis pressure can be increased. As the pulp is transferred via line 15 to the helical conveyor 17, deionized water from line 16 is mixed to extract the xylose formed therein. The xvloo solution formed passes through the connecting line 18 to the last helical conveyor 19 · This contains a battery ring 20, where solids still separate from the xylose solution. The formed silose solution is directed via line 21 to a crystallization device 22 for further purification, the beech chips exit via an outlet pipe 23 to helical conveyors 19.

It follows from the above that, despite the steps separated, the process shown can be used in a completely continuous manner, which results in a good economy of the process and a high purity of the final product. Each step can be carefully monitored and optimized individually. The speeds of the helical conveyors are chosen so that the various process steps take place optimally. beech chips are not destroyed during processing, but retain their original shape and the other components of the wood remain essentially unchanged. They can therefore be further processed, eg in the manufacture of cellulose »

The following example illustrates the invention.

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Example n x 50 kg of beech chips with a solids content of 7% by weight were heated in the first process step with steam for about 2 minutes at 100 ° C, ensuring that air could escape. As a second step, the heated material was saturated for about U minutes with about n x 100 kg of 2.2 wt% hydrochloric acid at room temperature. In the third step, the actual reaction step, the saturated beech chips were heated as soon as possible with steam to 100 ° C and reacted for about 60 minutes in a steam atmosphere. In the fourth and final step of the process, beech chips were extracted with about n x 60 kg of deionized water at about 60 ° C for about 20 minutes. The final product contains about 10 kg of xylose solution containing about 10% by weight of xylose. Xylose was thus obtained from about 10.8 # of starting material. The proportion of xylose in the extract was greater than 96% by weight.