GB2070580A - Oxidation of organic wastes - Google Patents

Abstract

In the wet oxidation of organic wastes oxygen is produced within the oxidation reactor from hydrogen peroxide by contact with the enzyme catalase.

Description

SPECIFICATION Oxidation of organic wastes This invention relates to the wet oxidation or organic wastes.

Various processes exist for the wet oxidation of organic wastes. Such processes are important as part of an effluent treatment process particularly for organic wastes in aqueous solution at concentrations of between 1.5% and 20%.

It is the object of this invention to minimise the energy requirement of the wet oxidation process which are normally carried out between 2000C and 3000C and under pressures of 400 to 800 p.s.i.

The use of high temperature and pressure conditions ensure rapid oxidation with the production of excess thermal energy. It is the practice to reduce the energy usage by exchanging heat between the incoming organic waste and the treated effluent. Two other aspects of the process demand a high energy use. There is the need to raise the pressure of the incoming waste to the pressure condition of the reactor, and also there is the need to compress air or oxygen which is essential to the reaction.

In order to reduce the energy requirement in raising the reactants to the operating pressures, according to the invention there is provided a process of wet oxidation of organic wastes in which the required oxygen is produced in situ from hydrogen peroxide by contact with the enzyme catalase.

The requirement of this process will demand one or more batch treatment stages which will allow near-continuous operation in which the reactants, namely the organic waste, hydrogen peroxide and catalase, are added either at atmospheric pressure or at some intermediate pressure between the feedstock and the final reactor pressure. The pressure rise is created by the action of the catalase upon the hydrogen peroxide restrained within a closed reactor which becomes a stage in the total process of wet oxidation.

Clearly in a multi-stage system the contribution to pressure rise caused by temperature change in the reactor is small whereas the contribution from the release of oxygen following the catalase reaction with peroxide is high.

The proposed system involving probably three stages would utilise intermediate heat exchangers to allow a staged preheating of the feed and intermediate materials with the final hot effluent from the final and main reactor.

In a proposed form of the invention the catalase may be immobilised on a suitable substrate and held in a fixed bed. Such a device would conveniently separate the catalase reaction from that of the wet oxidation stage.

In an alternative form the wet oxidation process follows more closely the traditional continuous process merely utilising one or more catalase reactor stages in series i.e. utilising one or more catalase reactor stages in series i.e. utilising hydrogen peroxide as an alternative to air or oxygen but retaining the more usual concept of continuous flow and pumping pressures to reach the required reactor pressure.

The invention will be further described with reference to the accompanying simplified diagrammatic drawings, in which: Figure 1 and 2 are flow diagrams of two possible forms of apparatus for carrying out the invention.

Figure 1 shows a three-stage near-continuous process. The feed liquid is fed from a line 1 by a pump 2 to a first heat exchanger 3 where it is given a first stage of pre-heating in exchange with product liquid on its way from a main reactor 4 to an output line 5 leading to a settling tank. From the heat exchanger 3, the incoming liquid is fed alternatively to a pair of catalytic reactors 6a and 6b wherein hydrogen peroxide in the feed liquid is contacted with catalase to generate oxygen and raise the pressure. A suitable arrangement of valves (not shown) ensures both alternate feeding of the reactors 6a and 6b and alternative dsicharge of them to utilise this increase in pressure.From the reactors 6a and 6b, the feed liquid passes through a second heat exchanger 7 and them alternately to one of a pair of catalytic reactors 8a and 8b wherein a further higher pressure and higher temperature stage of contact with catalase takes place. Again, appropriate valving (not shown), is provided. A third stage of pre-heating takes place in a heat exchanger 9, and from here the feed liquid is fed to a third and final pair of catalytic reactors 1 Oa and 1 Ob. The output from these reactors is again taken alternately via a pump 12 into the final high pressure reaction vessel wherein the feed liquid is held at the appropriate high temperature and pressure for oxidation to take place. The diagram shows an agitator 13 within the vessel 4.A substantially continuous draw-off of liquid from the vessel 4 provides flow of heating liquid through the heat exchangers 3, 7 and 9 in counter-current with the incoming near continuous flow.

In the reactors 6a, 6b, 8a, Sb, 1 0a and 1 Ob, the catalase is immobilised on a suitable substrate and held in a fixed bed through which the incoming feed liquid comes for exposure of its hydrogen peroxide to the catalase for the release of oxygen to generate the required pressure and oxide potential.

By appropriate choice of the valving arrangements and controls, the feed liquid and the oxygen generated in it can be brought to the high operating pressures required in the reactor 4 with the minimum use of pumping energy, while at the same time maintaining an almost continuous flow of liquid in and out of the reactor 4.

Figure 2 shows a continuous form of process in which the apparatus more nearly resembles a convential continuous flow apparatus, but in which pumping has to operate against full reaction pressure, so that the energy saving in somewhat reduced. In Figure 2, the feed liquid enters via a line 21 to a mixing vessel 22 also fed with a supply of hydrogen peroxide along the line 23.

From the mixing vessel 22, a pump 24 passes the mixture through a heat exchanger 25 in countercurrent with out-going product, and the hot mixture leaving the heat exchanger passes through one or more catalase reactor stages 26 and into a reaction vessel 27 from which there is continuous draw-off via a line 28 leading to the heat exchanger 25.

Various modifications may be made within the scope of the invention.

Claims (7)

1. A process of wet oxidation of organic wastes under conditions of high temperature and pressure, in which the oxygen required for the oxidation is produced within the reactor system from hydrogen peroxide by contact with the enzyme catalase.

2. A process as claimed in claim 1, in which the oxygen is produced in one or more batch treatment stages in which a pressure rise is induced by the generation of oxygen from the hydrogen peroxide within a closed reactor.

3. A process as claimed in claim 2, in which each batch treatment stage is associated with a heat exchanger for staged pre-heating of the incoming materials.

4. A process as claimed in claim 3, in which the incoming materials are heated in indirect heat exchangers with the reaction product from the process.

5. A process as claimed in claim 1, in which the process in continuous and the oxygen is generated in a catalase reactor stage immediately prior to a reactor vessel.

6. A process as claimed in any of the preceding claims, in which the catalase is immobilised in one or more fixed beds.

7. A process for the wet oxidation of organic wastes substantially as hereinbefore described with reference to the accompanying drawing.