GB2028332A

GB2028332A - Process and apparatus for degrading starting materials containing cellulose and/or lignin

Info

Publication number: GB2028332A
Application number: GB7928194A
Authority: GB
Original assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Priority date: 1978-08-16
Filing date: 1979-08-14
Publication date: 1980-03-05
Also published as: DE2837904A1; NO792637L; SE7906757L; FI792506A; FR2433577A1; BR7905208A; NL7906179A

Abstract

A process for the manufacture of chemical raw materials by treating starting materials containing cellulose and/or lignin with ozone, followed by biochemical degradation processes, is simplified in that the starting materials are treated with the ozone immediately after a mechanical pre-treatment and without a prior chemical treatment. Preferably an aqueous suspension of the material is made and this is first passed via valve 7 into a first reaction vessel 1' and subsequently via valve 8 into a second reaction vessel 1'', finally leaving via valve 9, ozone from generator 2 passing first through reaction vessel 1'' and then through reaction vessel 1'. <IMAGE>

Description

SPECIFICATION Process and apparatus for degrading starting materials containing cellulose and/or lignin The invention relates to a process for the manufac ture of chemical raw materials by means of biochem ical degradation processes on starting materials con taining cellulose and/or lignin. The invention also relates to an apparatus for carrying out a process of this type.

In the biological synthesis of chemical raw materi als, considerable importance attaches to the utilisation of straw and similar materials containing cellul ose and lignin. These starting materials are mainly produced in the form of unused waste products (for example the burning of straw in cereal and sugar cane fields). In the fermentation of such wastes by means of microorganisms, the fermentation product which results is, for example, ethyl alcohol. The microorganisms which multiply in the course of the fermentation are utilised as a feeding stuff containing protein.

Without chemical pre-treatment, the wood-like starting material is only degraded biologically to the extent of about 30%. This is principally amorphous cellulose. The residue consists of crystalline cellulose (about 20%), hemicellulose (approx. 20%) and lignin (20-30%), all these being substances which are difficult to degrade biologically.

In order also to render these substances accessible to the microorganisms, in known processes the start ing materials are first treated with a hot alkali solution (compare C.E. Dunlop, A.J., CH.E. Synposium, Series 158,72,58(1976)). Treatment with steam or with y-irradiation is also known.

However, these known processes exhibit various disadvantages. In the alkali treatment, for example, the substrate must be neutralised with an acid before biological degradation. This leads to a high outlay on chemicals and to an undesirable formation of salts. Furthermore, both this process and treatmentwith steam ory-irradiation exhibit the disadvantage that they also attack substances in the starting material which, in their original form, are desirable and can readily be degraded biologically.

French Patent Specification 343,745 also describes a process for the manufacture of chemical raw materials, in which the starting materials are treated in an alkaline or acid medium under pressure and at high temperatures (the boiling point) by treatment with ozonised oxygen or hydrogen peroxide.

It is the object of the present invention to provide a process of the type initially mentioned in which neither an alkali or steam treatment nor y-irradiation is necessary and in which only the substances which are difficult to degrade are converted, and are converted into substances which can readily be biologically degraded. It is furthermore intended to provide an apparatus for carrying out a process of this type.

In accordance with this invention, there is provided process for the manufacture of chemical raw materials by treating starting materials containing cellulose and/or lignin with ozone, followed by biochemical degradation processes, in which the starting materials are treated with ozone immedi ately after a physio-mechanical pre-treatment of the starting materials and without a prior chemical pretreatment.

It must be regarded as a substantial advantage of the invention that it is possible to dispense with a chemical treatment, by means of acids or caustic alkalis, of the starting materials which have been processed by mechanical and physical means, since it has been found that the digestion of the cellulose can be achieved by means of the ozone treatment on its own, to the extent required for the biochemical degradation processes subsequent to the ozone treatment, whilst in the prior art the prior chemical digestion at elevated temperatures and pressure has been regarded as indispensable.

Further details and advantages of the invention can be seen from the illustrative embodiments which will now be described by reference to the accompanying drawings, in which: FIGURE 1 and FIGURE 2 show apparatus, represented diagrammatically, for carrying outthe process according to the invention.

An experiment which makes the advantages of the invention particularly clear is described with the aid of Figure 1: An aqueous suspension of straw ground to a particle size of not more than 1 mm, and having a concentration of 50 g of straw/litre of water, was treated for 12 hours with ozone-containing air in a reaction vessel 1 with a capacity of 15 litres (the carrier gas used can also be oxygen or nitrogen instead of air).

The concentration of ozone in the air was 40 mg/litre, relative to standard conditions (237on and 1 atmosphere). The ozone-containing air was fed into the reactor through a frit 3 from an ozone generator 2 at a volumetric rate of 260 litres/hour (under standard conditions). The bubbles of gas thus generated in the suspension of straw 4 made it possible for the ozone to pass rapidly into the aqueous phase, where the chemical reaction took place, first with the lignin and, after the disappearance of the latter, with the hemicellulose. The utilisation of the ozone in this process was 75%. The quantity of ozone reacting per kg of straw was 125 g of ozone. In the course thereof, 60% of the lignin was removed.A subsequent enzymatic hydrolysis with cellulose in the same reaction vessel 1 led, within 24 hours at 50"C and with continuous stirring by means of the stirrer 5, to a saccharification with a yield of 240 g of reducing sugar/kg of straw. On the other hand, straw which had not been pre-heated with ozone gave only 50 g of reducing sugar/kg of straw. The sugars produced (glucose, xylose and cellobiose) can readily be biologically degraded.

In another experiment, instead of the enzymatic hydrolysis, the suspension 4 was treated with ozone at 28"C and was then treated for4 days, while being aerated via the frit 3, with an inocculation culture of fungi, of the species Trichoderma vi ride, with the addition of 0.1% of peptone. It was possible to determine an 85% degradation of the cellulose, whilst untreated straw merely exhibited a decrease of 15% in cellulose content A particular apparatus for carrying out the process according to the invention is shown in Figure 2.

The equipment consists essentially of two reaction vessels 1' and 1", an ozone generator 2' and several valves 7,8 and 9, connected to the inlet and outlet lines of the reaction vessels. This equipment is suitable for both continuous and intermittent operation.

When the equipment is operated continuously, the straw-like or wood-like mass 4', present in the form of a suspension, flows into the reaction vessel 1'.

The ozone produced by the ozone generator 2' passes first into the second reaction vessel 1" and only afterwards into the first reaction vessel 1'. By this means, the fresh suspension with a high concentration of substrate reacts first with ozone at a low concentration and then, in the second reaction vessel 1", the remainder of the suspension, which has a low concentration of substrate, reacts with ozone at a high concentration. A particularly advantageous utilisation of the ozone is achieved by means of this measure. The circulation of the suspension in the reaction vessels 1' and 1" is effected, on the one hand, by means of the gas flow and, on the other hand, by means of a circulation tube 6 which is provided in each ofthe reaction vessels.

The valves 7,8 and 9 are used for carrying out intermittent operation (frequently also designated batch operation), in order to make it possible to carry out the filling and emptying operations. When refilling, the valve 9 is first opened, permitting the completelytreated suspension to leave the reaction vessel 1". Afterthe reaction vessel 1" has been emptied, the valve 9 is closed and valve 8 is opened. The pretreated suspension in the reaction vessel 1' flows into the second reaction vessel 1". When the reaction vessel 1' is empty, the valve 8 is closed and the valve 7 opens, permitting fresh suspension to enter the reaction vessel 1'.

The point of time for refilling is either determined by a previously decided reaction time or is reached when the concentration of ozone in the exit gas line 10 of the first reaction vessel 1' reaches a known value for the final state desired.

Claims

1. Processforthe manufacture of chemical raw materials by treating starting materials containing cellulose and/or lignin with ozone, followed by biochemical degradation processes, in which the starting materials are treated with ozone immediately after a physico-mechanical pre-treatment of the starting materials and without a prior chemical pretreatment.

2. Process according to claim 1, in which an aqueous suspension is first prepared from the starting materials and this suspension is then treated with a carrier gas containing ozone, such as air, oxygen or nitrogen.

3. Process according to claim 2, in which the ozone-containing carrier gas coming into contact with the suspension consists of a large number of gas bubbles.

4. Apparatus for carrying outthe process accord ing to any preceding claim, comprising at least two reaction vessels and an ozone generator which are connected with one another by pipelines in such a way that a suspension of material to be treated with ozone flows first through the first reaction vessel and then through the second reaction vessel, and the ozone from the ozone generator reaches the second reaction vessel first and only then reaches the first reaction vessel.

5. A process as claimed in claim 1 and substantially as herein described.

6. Apparatus for the manufacture of chemical raw materials substantially as herein described with reference to Figure 2 of the accompanying drawings.