DE1950598A1 - Process for preventing the formation of emulsions in mixtures of hydrocarbons and water when cooling acetylene- and olefin-containing fission gases - Google Patents

Description

Badische Anilin- & Soda-Fabrik AG 1950598

Our reference: O.Z. 26,378 g / hip ■ 6700 Ludwigshafen, October 6th. 1969

Process for preventing emulsification in mixtures of hydrocarbons and water in the cooling of acetylene and olefin-containing fission gases

The invention relates to a method for preventing emulsification in mixtures of hydrocarbons and water, such as are obtained in the cooling of acetylene- and olefin-containing fission gases from the immersion flame method with water. In the thermal cracking of crude oil or its fractions by the immersion flame process, unsaturated low molecular weight hydrocarbons are obtained from higher hydrocarbons in a mixture with incompletely split saturated hydrocarbons such as methane, ethane and combustion products, nitrogen, sulfur compounds and soot. It is known that the cracked gas mixture is passed through a water scrubber before being worked up in a low-temperature system, which, in addition to removing solid particles, has the task of cooling the cracked gas before it enters the gas separation. Depending on the gas composition, selected pressure and temperature, hydrocarbons are brought to condensation in this scrubbing process, which, after passing through a separation vessel, are either withdrawn for further use or returned to the cracking furnace.

In the latter case it is of the greatest importance for the process that the recirculated hydrocarbon stream is homogeneous and anhydrous, since the water entrained by emulsion formation triggers strong foaming in the reactor. Furthermore, an emulsion formation in the separation vessel leads to considerable hydrocarbon losses, some of which leave the system with the discharged water. It has also tried to prevent the interference by adding Emulsionsihhibitoren in the water scrubbing of other fission gases. In the immersion flame process, however, these inhibitors only have a short-term effect, since they are either discharged with the water or, if they are more soluble in the hydrocarbons, returned to the cracking furnace, where they are built up thermally and oxidatively.

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It has now been found that when cooling hot Fission gases as they are formed in the immersion flame process, the emulsion formation described above through a water wash Can be completely suppressed if you use it to cool the fission gases .Used water adds such amounts of alkaline substances that a pH of 7.5 to 12.5 im circulating water adjusts,

This result is surprising insofar as it could be expected that in the immersion flame process by oxidation in Small amounts of long-chain acids formed are converted into the form of their sodium salts and act as foam-forming Soaps would behave. .

In general, the fission gases are washed with water after they have been passed through the same through a mechanical scrubber and cyclone to remove the bulk of the soot and prior to the removal of acidic components of the fission gas e.g. with alkanolamine solutions, and a methanol wash carried out. You can do the laundry in in a known manner in columns or trickle coolers with a subsequent. Separation vessel in a known manner, e.g. by the gases in countercurrent to the aqueous solution from below heads up through the washing tower.

As alkaline reacting substances that are circulated Wash water in amounts of 1 to 4 wt. $ Are added e.g. sodium or potassium hydroxide, soda, sodium bicarbonate, Ammonia or ammonium carbonate or mixtures of these substances are suitable. You can also use alkaline washing solutions, such as those used, for example, for delicate washes, and some of them used for this purpose.

The alkaline compounds are preferably mixed with the Water in such amounts that a pH of 8.0 to 8.9 sets. If the gas to be cooled contains carbonic acid, then e.g. alkali or ammonia depending on the reaction conditions partially converted into the corresponding carbonates or bicarbonates with lowering of the pH value. This carbonate or bicar

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Tdonate solutions still have a carbonic acid effect Sufficient alkaline reaction to prevent emulsification in the water / hydrocarbon system. E.g. the pH of a 0.1 N soda solution at 11.6 and a 0.1 N sodium bicarbonate solution at 8.4. The use of carbonate or bicarbonate solutions from waste alkalis, which e.g. in the pain wash to remove small amounts of carbon dioxide using caustic soda in the same process before the methanol wash attack.

The method according to the invention offers over other methods the advantage that those listed above have an alkaline effect Compounds in the hydrocarbon fractions are insoluble and therefore no longer subject to thermal cleavage in the reactor hike. The method also has the advantage that the organic acids present in the cracked gas are in the alkaline cooling liquid be bound, and thus with the following Gas separation process significant disruptions, especially in diethanolamine scrubbing, can be excluded. In the diethanolamine wash the organic acids would be bound in a salt-like manner and correspondingly reduce the activity of the washing solution. One The solution consumed in this way cannot be freed from the acids by means of conventional thermal regeneration, but rather it must be purified by distillation in a very complex process stage in the presence of alkali metal hydroxides.

example

In a washing tower, 200,000 parts by volume of a 120 ^° C. cracked gas with the following gas composition are introduced every hour from below.

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component

Fission gas composition in volume?

acetylene

Ethylene

Ät.han

C, - + higher hydrocarbons S compounds methane

Carbon dioxide carbon monoxide hydrogen nitrogen oxygen

7.0

6.5

0.5

3.7

4.0

7.0

41.2

29.3

0.6

0.2

At the same time the washing tower is 3,000 Raimteile water of 3O ⁰ C added at the top. The system is under the pressure of

8 at. ■ "■ -'- · '-

The water that collects in the sump of the wash column contains 50 parts by volume of hydrocarbons, which are ionized out every hour in the wash tower; and be absorbed by the water. Hourly the Wasohwasserkreislauf be 1 kg of soda in the form of a 2 follow aqueous solution. Most of the sodium carbonate is converted to sodium bicarbonate by the carbon dioxide in the cracked gas. This results in a pH of 8.7. The contents of the bottom of the column, which consist of two phases, are passed into a separation vessel in which the hydrocarbon gas is separated off from the aqueous phase. The water introduced into the washing circuit by the addition of the soda solution is discharged again in the appropriate amount after passing through the separation vessel. ■

If, however, the hourly addition of 1 kg of soda is reduced to 0.25 kg of soda, the soda content in the added aqueous solution again being 2% by weight, the pH can no longer be maintained at 8.7 because the organic acids contained in the cracked gas ^: * "ft! rt 'the sodium bicarbonate react and this

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neutralize for the most part »This results in a pH value from 7 »1 Ms 7.3 a. There is emulsion formation and the Separation of the two phases in the separation vessel is no longer possible.

As a result of this emulsion formation, the contain from the separation vessel Hydrocarbons returned to the reactor in such amounts of water that the oil bath is caused to foam, thereby constant operation of the submerged flame process is not more guaranteed.

BATH ORIGINAL

109816/2258

Claims (1)

- 6 - - O, Z ₅ 26 378 Patent entitlement ~ Process for preventing the formation of emulsions in mixtures of hydrocarbons and water, which are obtained in the immersion flame process when the acetylene- and olefin-containing cracking gases are cooled by washing with water, characterized in that the water used for cooling the cracking gases is added in such amounts of alkaline substances that When washing, a pH of 7.5 to 12 ^ 5 im. the circulating water. Badische Anilin- & Soda-Fäbrik AG SAD ORIGINAL 109816/2258