The invention relates to carrying out biotechno- logical processes by means of a multiphase system in a loop reactor, which system comprises an aqueous phase. Loop reactors are described in detail in "Bio¬ technology" by H.J. Rehm and G. Reed, vol. 2, "Funda¬ mentals of Biochemical Engineering", VCH, einhei (1985), chapter 21 entitled "Biochemical Loop Reactors", pages 465-517. More particularly, in a loop reactor, at least one defined circulatory flow of a liquid medium present therein takes place and loop reactors have in principle either an "internal circulation" (see Figure 1a) or an "external circulation" (see Figure 1b). As the driving force for the circulatory flow, in such loop reactors use is made of a gaseous medium and, in particular, usually air which is introduced into the riser pipe of the reac¬ tor (see Figure 1a and 1b). Owing to the introduction of the gaseous medium, ±he liquid medium passes through the riser pipe until it reaches the top section of the reactor and then travels through the dowπcomer pipe (see Figure 1a and 1b) after which it again finishes up in the riser pipe via the bottom section under the influence of the driving force generated by the gaseous medium. In a loop reactor permanently fitted elements may be present which are usually situated in the riser pipe. Examples of such elements are sieve plates for redispersing co¬ alesced gas bubbles or packings which serve as carrier material for immobilized cells or enzymes. A more detailed explanation of the process con¬ ditions in the loop reactor which is at present of con¬ siderable importance and which is driven with air and also termed an "air lift loop reactor", is given for example in PT process technique 40, no. 10, (1985), pages 60-63. With respect to stirred reactors used tradition¬ ally in biotechnology such as are described, for example, in the Swiss Patent 478,282, air Lift loop reactors have a number of important advantages such as a relatively

simple construction and a low susceptibility. to malfunc¬ tion, a good and regulable phase separat on in the top section of the loop reactor, a large specific surface ith low energy input, a heat exchange which is relatively easy to control, a unique combination of a controlled flow and good mixing properties and also a good accessi¬ bility for measuring and regulating equipment, certainly if the air lift loop reactor is constructed with an ex¬ ternal loop (see Figure 1b ⁾ . Although the presence of water in biotechnolog cal processes is essential, the use thereof as a reaction medium, however, involves various disadvantages. The following may be mentioned as examples of such dis¬ advantages: the difficulty of achieving high conceπtra- tions of substrates in the reaction medium which are sparingly soluble in water, the unfavourable position of reaction equilibria, water being one of the reaction products, and also the occurrence of hydrolysis of sub- ^• strates or reaction products. It has been found that the abovement ioned dis¬ advantages can be completely or partially eliminated if, to carry out biotechnological processes in a loop reactor, use is made of at least one organic solvent which is immiscible with water and which has a different density from water instead of a gaseous medium so that one of the liquid components acts as the continuous phase and the other as the disperse phase. In this connection, an organic solvent which is immiscible with water is under¬ stood to mean a solvent which is not miscible with water or soluble in water in all proportions so that a liquid multiphase system can be created.

The method according to the invention d ffers in principle from the method described in the abovement ioned Swiss Patent 478,282. The reason is that, according to said Swiss patent, two liquids which are immiscible with each other are subjected to a mixing action by means of a stirring device, i.e. the stirring device provides the driving force for the mixing action, whereas, in the method according to the invention, the difference in

density between the liquid components used functions as driving force.

The reaction systems according to the invention are very readily. usable in biocatalysis, use being made of organic media. By replacing a portion of the aqueous phase by an organic solvent which is immiscible with water, it is possible, in addition to eliminating com¬ pletely or partially the abovement i oπed disadvantages, also to obtain a number of additional advantages, namely: a displacement of reaction equilibria as a consequence of modified distribution of substrates and reaction pro¬ ducts between the phases present, a lowering of the sub¬ strate/reaction product inhibition, an improved product and biocatalyst working up and a stabilization of the biocatalyst.

Advantageously, use is made of an organic solvent which is immiscible with water and which has a lower density than water. At the same time, the possibility is, however, also available of using an organic solvent which is i miscible with water and which has a higher dens i ty than water .

Examples of organic solvents which can be used in the method according to the invention are listed in the table belo .

TABLE

Organic solvent _. Specific Solubility density in water

(20°C) (20°C) (g/m3 ⁾ (wt. %) π-hexane 0.660 0.00095 n-hexadecaπe 0.7733 toluene 0.8669 0.052 ethylbenzeπe 0.867 0.0152 styreπe 0.906 0.031

1-butanol 0.8098 9

1-hexaπol 0.814 0.594 diisopropyl ether 0.723 1.197 diisopentyl ether 0.777 0.020 methylphenyl ether 0.993 1.04 dipheπyl ether 1.0748 0.39 hexanal 0.815 0.5 methylisobutyl ketoπe 0.798 1.693 methyloctyl ketone 0.825 butyl acetate 0.883 0.43 ethyltri chloro acetate 1.3836 butyl acrylate 0.898 butyl benzoate 1.004 diethyl aleate 1.065 1.4 dibutyl adipate 0.962 dimethyl phthalate 1.188 0.43 diethyl phthalate 1.117 dibutyl phthalate 1.045 0.040 dioctyl phthalate 0.985 didecyl phthalate 0.966 di (2-methoxyethyl) phthalate 1.171 diallyl phthalate 1.119 tri-n-butyl phosphate 0.976 0.039 tri-2-tolyl phosphate 1.16 (approx) 0.000050 chloroform 1.4832 0.815 tetrachloromethane 1.5940 0.077

1,1,2,2-tetrachloroethaπe 1.594 0.287

FC-40* 1.87 (approx)

FC-70* 1.94 (approx) -

*FC-40 and FC-70 are fluoriπated hydrocarbons which are marketed by 3M.

In view of the abovement i oned use of an organic solvent which is immiscible with water and which has either a Lower or a higher density than water, eight embodiments of the method according to the invention can be distinguished on the basis of loop reactors with an internal or external loop. These are illustrated in Figures 2a-d and Figures 3a-d.

Figure 2a illustrates an internal loop reactor which contains water (1) as the continuous phase and an organic solvent (2) having a density lower than water as the disperse phase.

Figure 2b illustrates an external loop reactor which contains water (1) as the continuous phase and an organic solvent (2) having a density lower than water as the disperse phase.

Figure 2c illustrates an internal loop reactor which contains water (3) as the disperse phase and an organic solvent (4) having a density higher than water as the continuous phase. . Figure 2d illustrates an external loop reactor which contains water (3) as the disperse phase and an organic solvent (4) having a density higher than water as the continuous phase.

Figure 3a illustrates an internal loop reactor which contains water (5) as the continuous phase and an organic solvent (6) having a density higher than water as the disperse phase.

Figure 3b illustrates an external loop reactor which contains water (5) as the continuous phase and an organic solvent (6) having a density higher than water as the disperse phase.

Figure 3c illustrates an internal loop reactor which contains water (7) as the disperse phase and an organic solvent (8) having a density lower than water as the continuous phase.

Figure 3d illustrates an external loop reactor which contains water (7) as the disperse phase and an organic solvent (8) having a density lower than water as the continuous phase.

For completeness. Figure 4 shows a special em¬ bodiment of the method according to the invention in which use is made of two organic solvents which are im¬ miscible with water, one (9) having a higher density and the other (10) a lower density than the water (11) pre¬ sent. The use of this three-phase system in a loop reactor with an "internal" circulation is in principle also poss ible.

The loop reactor used for carrying out the method according to the invention may, if desi.red, be provided with solid particles such as immobilized catalyst particles and the Like which are dispersed in the con¬ tinuous phase or may be provided in another manner (see the abovemeπtioπed book entitled "B otechnology" by H.J. Rehm and G. Reed, vol. 2, chapter 21 entitled

"Biochemical loop reactors"). In the event that the disperse phase has a higher density than the continuous phase, air can be introduced into the riser pipe in order to intensify the upwards movement of the liquid medium in said riser pipe. In addition, provision of the reaction system in the loop reactor with oxygen can be implemented with this embodiment of the method according to the invention.

Loop reactors in which the method according to the invention is carried out may therefore be used as continuous extractors, fer enters and biological reactors using (b o)catalysts.

The invent on is illustrated in more detail by reference to the examples below which should not be interpreted as restrictive. Example I

An "internal" loop reactor according to Figure 2a with a capacity of 1.7 dm , of which the internal pipe had a diameter of 39 mm and the external pipe a d i - ameter of 60 mm, was filled with water (9 g/dm NaC Ll) 3

Petroleum ether 40/60 having a density of 0.65 g/cm ^" was pumped in at the bottom of the riser pipe by means of the porous filter fitted in the bottom of the loop re¬ actor and having a diameter of 25 mm (pore size < P4).

The circulation in the Loop reactor was made visible with alginate spherules suspended in the aqueous phase and having a diameter of 2 mm. The circulation time of said alginate spherules was appro imately 3 seconds. Example 11

An "internal" loop reactor according to Figure 3c having the dimensions mentioned in Example I was filled with petroleum ether 40/60. Water (9 g/dm NaCl) was pumped into the internal pipe by means of the porous filter fitted in the top of the loop reactor and having a diameter of 25 mm (pore size < P4). The circulation in the Loop reactor was made visible with alginate sphe¬ rules having a diameter of 2 mm. Examp Le III An "external" loop reactor according to Figure-

2b with a capacity of 1.5 dm , of which the riser pipe

_ had a diameter of 65 mm and the downcomer pipe a diameter of 30 mm, was filled with water (9 g/dm NaCl ⁾ . Petroleum ether 40/60 was pumped into the riser pipe by means of a glass filter fitted in the bottom of the loop reactor and having a diameter of 25 mm. The circulation in the loop reactor was made visible with alginate spherules suspended in the aqueous phase and having a diameter of 2 mm. The circulation time of said alginate spherules was appro imately 3 seconds.