Process for the Electrophoretic Breaking of Emulsions

The invention relates to a process for the electrophoretic breaking of electrically conductive emulsions which is characterised in that, in the case of emulsions with an electrical conductivity greater than 2,000 .mu.Mhos, the conductivity is adjusted to values in the range from about 0.1 to about 2,000 .mu.Mhos by increasing the degree of dispersion, and the emulsions are then broken by passing through a constant-voltage field of about 100 to about 1,000 volts.

Examples which may be mentioned of emulsions which can be broken by the process according to the invention are: emulsions consisting of about 3 to 7 parts by volume of nitrobenzene and about 1 to 3 parts by volume of 1 to 80% strength by weight waste sulphuric acid, such as is obtained during a nitration process. Further examples which may be mentioned are: emulsions of about 40 to 60% strength by weight phosphoric acid and nitrobenzene in a ratio of about 1:9 to 2:3 (weight volume), or 40 to 60% strength by weight phosphoric acid and 2-ethylhexanol in a ratio of about 1:9 to 2:3 (weight volume), or 5 to 20% strength by weight sodium hydroxide solution and 2-ethylhexanol in a ratio of about 1:9 to 2:3 (weight volume).

The waste sulphuric acid obtained during the nitration of benzene to give nitrobenzene consists of sulphuric acid to the extent of 60-80% by weight, the remainder being water.

Since emulsions having an electrical conductivity outside the abovementioned conductivity range are obtained during numerous washing and cleaning processes as well as during chemical production processes, it is necessary, in order to break the emulsions effectively in a constant-voltage field, to adjust the electrical conductivity of the emulsions to values in the range from about 0.1 to about 2,000 .mu.Mhos, preferably 1 to 1,000 .mu.Mhos and particularly preferably 5 to 500 .mu.Mhos.

If the electrical conductivity of the emulsions is too high, there is, in fact, the danger that a constant-voltage field of about 100 to 1,000 volts necessary for electrophoretic breaking cannot be built up, and the electrophoretic breaking changes into electrolysis.

If emulsions with an electrical conductivity from the beginning in the range from about 0.1 to about 2,000 .mu.Mhos are obtained during washing and cleaning processes, these emulsions can be broken directly, without further treatment, by passing through a constant-voltage field of about 100 to about 1,000 volts.

In order to be able to extend electrophoretic breaking of electrically conductive emulsions also to electrical conductivities in high ranges, for example up to 100,000 .mu.Mhos, it was necessary to discover methods which enable the electrical conductivity of the emulsions to be reduced.

It has been found that in the case of emulsions with electrical conductivities greater than 2,000 .mu.Mhos, the conductivity can be reduced by increasing the degree of dispersion of the emulsions.

Increasing the degree of dispersion is effected with customary physical-mechanical dispersion methods, such as stirring, circulatory pumping, ultrasound and the like. This process is sometimes accelerated by adding emulsifiers, such as sodium lauryl-sulphate, sulphonated castor oils which have been rendered neutral and sulphonated higher alcohols which have been rendered neutral.

The amount of emulsifiers to be added is not critical. It depends, inter alia, on the composition of the emulsions and can appropriately be determined by preliminary experiments.

In general, the emulsions are subjected to a dispersing process until the electrical conductivity has been adjusted to within the abovementioned conductivity range. The treatment period depends, above all, on the nature of the composition of the emulsion and can appropriately be determined beforehand.

The process according to the invention can be carried out at all temperatures in the range in which emulsions are formed.

The process according to the invention can be carried out as follows: An emulsion which consists, for example, of 3 parts by volume of nitrobenzene and 2 parts by volume of 70% strength by weight waste sulphuric acid, such as is obtained, for example, during the nitration of benzene in the presence of sulphuric acid, and has an electrical conductivity of 10,000 to 20,000 .mu.Mhos is brought to an electrical conductivity of about 300 to 400 .mu.Mhos by stirring or circulatory pumping with a high-speed pump (1,500 to 2,500 revolutions per minute), and then flows through, for example, a tubular electrode chamber. The emulsion thereby passes through a constant-voltage field of about 100 to 1,000 volts, preferably 300 to 500 volts. The current is about 0.5 to 1 ampere. Steady flooding of the electrode chamber is ensured by simple regulation of the flow of emulsion, so that even if any electrical flashovers occur between the electrodes, there is no danger of ignition of any ignitable gas mixtures in the electrode chamber. After a residence time of about 5 to about 30 minutes in a separation tank, the separated phases of nitrobenzene and 70% strength by weight waste sulphuric acid can be removed from the tank.

Compared with other processes for breaking emulsions, the process according to the invention is distinguished by the following advantages:

The process according to the invention is virtually maintenance-free and free from mechanical wear. This makes the process particularly economical. There is no restriction on the amount of emulsion to be passed through per hour. The process can be applied in areas where there is an explosion hazard and is not sensitive to fine or coarse impurities in the emulsions. The separation effect is high and, apart from the actual solubility of the components in one another, the constituents are obtained in a pure form. Since the electrophoretic breaking of emulsions already takes place extremely rapidly in very small electrode chambers, the space/time yield is particularly high.

The examples which follow serve to illustrate the process according to the invention.

An emulsion of 3 parts by volume of crude nitrobenzene and 2 parts by volume of 70% strength by weight waste sulphuric acid, consisting of 70% by weight of sulphuric acid and 30% by weight of water, was pumped, at 50.degree. C., round in a simple circulatory apparatus consisting of a receiver with a stirrer and circulation pump, an electrophoresis cell and a separation tank. After the conductivity has fallen from about 15,000 .mu.Mhos to 400 .mu.Mhos, the emulsion could be broken in the electrophoresis cell by applying a constant-voltage of 300 volts at 0.6 to 0.8 ampere. The nitrobenzene discharged from the separation tank after a residence time of 20 minutes had a residual acid content of 0.3% by weight. The acid content in the case of other separation processes, for example passing through a separator or coaleser, is 0.6 to 0.8% by weight.

The tables below show the decrease in the electrical conductivity of emulsions consisting of various components. The experiments on which the results are based were carried out as follows:

The components were stirred at 700 revolutions per minute in a 2 liter beaker using a twin-bladed stirrer. The degree of dispersion was thereby increased. The conductivity was measured at certain intervals of time during the stirring.

(a) 1% strength by weight waste sulphuric acid: nitrobenzene=2.3.

Temperature 23.degree. C.

After 5 seconds: 1,499 .mu.Mhos

After 15 seconds: 968 .mu.Mhos

After 30 seconds: 158 .mu.Mhos

After 60 seconds: 37 .mu.Mhos

After 90 seconds: 26 .mu.Mhos

After 120 seconds: 26 .mu.Mhos (final value)

(b) 10% strength by weight waste sulphuric acid: nitrobenzene=2:3.

Temperature 23.degree. C.

After 5 seconds: 1,056 .mu.Mhos

After 15 seconds: 361 .mu.Mhos

After 30 seconds: 246 .mu.Mhos

After 60 seconds: 211 .mu.Mhos

After 90 seconds: 202 .mu.Mhos

After 120 seconds: 141 .mu.Mhos

After 150 seconds: 132 .mu.Mhos

After 180 seconds: 114 .mu.Mhos (final value)

(c) 30% strength by weight waste sulphuric acid:nitrobenzene=2:3.

Temperature 23.degree. C.

After 5 seconds: 2,816 .mu.Mhos

After 15 seconds: 1,364 .mu.Mhos

After 30 seconds: 361 .mu.Mhos

After 60 seconds; 317 .mu.Mhos

After 90 seconds: 255 .mu.Mhos

After 150 seconds: 246 .mu.Mhos

After 180 seconds: 238 .mu.Mhos (final value)

(d) 50% strength by weight waste sulphuric acid:nitrobenzene=2:3.

Temperature 23.degree. C.

After 5 seconds: 3,872 .mu.Mhos

After 15 seconds: 1,716 .mu.Mhos

After 30 seconds: 651 .mu.Mhos

After 60 seconds: 422 .mu.Mhos

After 120 seconds: 255 .mu.Mhos

After 180 seconds: 220 .mu.Mhos (final value)

(e) 70% strength by weight waste sulphuric acid:nitrobenzene=2:3.

Temperature 23.degree. C.

After 5 seconds: 3,344 .mu.Mhos

After 15 seconds: 2,992 .mu.Mhos

After 30 seconds: 2,552 .mu.Mhos

After 60 seconds: 1,672 .mu.Mhos

After 120 seconds: 1,144 .mu.Mhos

After 180 seconds: 924 .mu.Mhos

After 240 seconds: 748 .mu.Mhos

After 270 seconds: 638 .mu.Mhos

(f) 80% strength by weight waste sulphuric acid:nitrobenzene=2:3.

Temperature 23.degree. C.

After 5 seconds: 2,464 .mu.Mhos

After 15 seconds: 2,156 .mu.Mhos

After 90 seconds: 704 .mu.Mhos

After 150 seconds: 554 .mu.Mhos

After 270 seconds: 343 .mu.Mhos

After 360 seconds: 220 .mu.Mhos

After 480 seconds: 189 .mu.Mhos (final value)

(g) 70% strength by weight waste sulphuric acid:nitrobenzene=3:7.

Temperature 23.degree. C.

After 5 seconds: 1,584 .mu.Mhos

After 15 seconds: 616 .mu.Mhos

After 60 seconds: 422 .mu.Mhos

After 120 seconds: 361 .mu.Mhos

After 180 seconds: 326 .mu.Mhos (final value)

(h) 70% strength by weight waste sulphuric acid: nitrobenzene=1:4.

Temperature 23.degree. C.

After 5 seconds: 880 .mu.Mhos

After 15 seconds: 282 .mu.Mhos

After 30 seconds: 194 .mu.Mhos

After 60 seconds: 158 .mu.Mhos

After 90 seconds: 132 .mu.Mhos (final value)

(i) 40% strength by weight phosphoric acid:nitrobenzene=2:3.

Temperature 23.degree. C.

After 5 seconds: 2,904 .mu.Mhos

After 15 seconds: 1,584 .mu.Mhos

After 30 seconds: 968 .mu.Mhos

After 60 seconds: 739 .mu.Mhos

After 150 seconds: 642 .mu.Mhos

After 300 seconds: 572 .mu.Mhos

After 360 seconds: 554 .mu.Mhos (final value)

(j) 60% strength by weight phosphoric acid:nitrobenzl=2:3.

Temperature 23.degree. C.

After 5 seconds: 4,200 .mu.Mhos

After 15 seconds: 968 .mu.Mhos

After 30 seconds: 598 .mu.Mhos

After 60 seconds: 519 .mu.Mhos

After 120 seconds: 431 .mu.Mhos

After 180 seconds: 396 .mu.Mhos (final value)

(k) 40% strength by weight phosphoric acid:2-ethylhexanol=2:3.

Temperature 23.degree. C.

After 5 seconds: 1,144 .mu.Mhos

After 15 seconds: 1,056 .mu.Mhos

After 30 seconds: 704 .mu.Mhos (final value)

(1) 10% strength by weight sodium hydroxide solution: 2-ethylhexanol=2:3.

Additive: "Brillant" emulsifier.

Temperature 23.degree. C.

After 5 seconds: 1,816 .mu.Mhos

After 15 seconds: 1,144 .mu.Mhos

After 30 seconds: 704 .mu.Mhos

After 60 seconds: 176 .mu.Mhos

After 180 seconds: 106 .mu.Mhos

After 300 seconds: 70 .mu.Mhos (final value)