NO137995B - PROCEDURE FOR THE PREPARATION OF ACETYLENE READINGS SUITABLE FOR ALKYNOL SYNTHESIS - Google Patents

Description

The present invention relates to a method for the production of acetylene solutions suitable for the synthesis of alkynol, "where one starts from a gas mixture which essentially consists of ethylene and acetylene, which is treated with acetone while forming an acetylene solution in acetone, and the peculiarity of the method according to the invention is that in order to obtain an ammoniacal acetylene solution and to separate the acetone, the acetone solution is subjected to a stripping treatment with ammonia. Methods for the catalytic production of alkynols starting from a ketone and acetylene in the presence of alkaline catalysts and a 16synthesis agent1^ e.g. .liquid ammonia, is previously known.

In the aforementioned methods, almost pure acetylene is used, and apart from the disadvantages of the high costs (as acetylene is not available under high pressure due to its stability), this entails considerable disadvantages and special tricks to bring the acetylene to the pressure required for the alkynol synthesis. In this connection, it is mentioned that British patent document 1,045,742 and German patent document 1,188,076 relate to the recovery of acetylene with high purity, and these publications teach that acetone is a good solvent for acetylene. In the present invention, the acatyl is intentionally treated without

reach a high degree of purity due to the fact that in this way the dangers of "concentrated acetylene" are avoided while avoiding expensive process steps.

The recovery of acetylene enriched in the acetone solutions is carried out by stripping with ammonia under pressure so that in all parts of the plant the concentration of acetylene is kept within safe limits.

In this way, the acetylene recovery is carried out by the method according to the invention at low costs, without particularly low condensation temperatures. The invention allows utilization and use of cheap acetylene e.g. contained in the C2 fractions obtained by steam cracking of the crude naphtha fraction in crude oil.

An object of the present invention is a method for obtaining acetylene-containing mixtures which can advantageously be used for the production of alkynols.

Another object of the present invention is a quantitative recovery of acetylene from acetylene-containing gas mixtures while obtaining a gas stream almost free of acetylene and an acetylene-containing solution usable for the production of alkynols.

The method according to the invention can advantageously be carried out in connection with treating the acetylene-containing gas in an absorption column with acetone, in order to obtain a top product comprising almost the entire amount of ethylene, and as bottom product a solution of acetylene in acetone, exposing the obtained acetylene solution to a stripping with ammonia to obtain a top fraction containing almost the entire amount of acetylene and the other components present in the feed and possibly absorbed in the first step of the process, together with the ammonia feed, feeds said top product after condensation and possible purification to the alkynol synthesis together with acetone ( or another ketone) and an alkaline catalyst, separates the resulting alkynol and recycles the ammonia, which is the reaction solvent, and the unreacted gases to the absorption step.

The method according to the invention is used to achieve

of ammoniacal solutions of acetylene by starting from gas mixtures containing acetylene together with other hydrocarbons such as methane, ethylene, ethane, propylene, propane and the like

or other gases such as hydrogen, nitrogen and the like.

As is known, acetylene is found in widely varying amounts as the main product, co-product or by-product in many gas fractions of petroleum, petrochemical or chemical origin.

Said fractions can be obtained by cracking, steam cracking, electric arc processes, partial combustion or other known methods.

The method according to the invention is also particularly suitable when the mixture already contains acetylene in high concentration, since many problems associated with compression of acetylene are eliminated. Preferably, the present invention can be used for the absorption of acetylene contained in raw ethylene streams produced by steam cracking of hydrocarbons, which then cannot in any way be characterized as "pure" acetylene streams.

It is known that one of the most interesting chemical processes for the production of ethylene is the steam cracking of hydrocarbon mixtures. The raw ethylene produced by steam cracking always contains acetylene as a by-product and the amount of acetylene is directly proportional to the severity of the operating conditions.

In general, the acetylene content in the raw ethylene produced by steam cracking is in the range 1-10%.

Said amounts of acetylene, especially at low concentrations, have not been economically usable for the production of pure acetylene, so that purification of the ethylene has been carried out by selective acetylene hydrogenation.

This practice is very expensive and there is therefore a tendency towards it

to limit the amount of acetylene to low values by limiting the severity of the steam cracking, which is also detrimental to the ethylene yield.

With the method according to the invention, it is possible to use acetylene contained in gas streams even at low concentrations for the production of alkynols, e.g. methyl-

butynol, by reacting the acetylene with acetone.

Consequently, the present invention makes it possible to carry out steam cracking of hydrocarbons into gaseous products under more suitable working conditions.

With the method according to the invention, it is possible from

a raw ethylene stream produced by steam cracking to obtain both acetylene-free ethylene and an acetylene usable for alkynol syntheses.

A particular advantage of using the present invention in connection with raw ethylene streams produced by steam cracking is that the amount of acetone and/or the thermal level during the necessary cooling for absorption is considerably reduced, as said ethylene streams are already under high pressure.

The acetylene absorption in the acetone is carried out at pressures and temperatures which are interdependent and dependent on the necessity in each individual step to maintain the acetylene in the stability range and to achieve the desired acetylene recovery.

The absorption in the acetone is preferably carried out at temperatures in the range from -40°C to +20°C and at pressures from 2 kg/cm<2> to 40 kg/cm<2>.

Likewise, the quantity ratios between the absorbent acetone and the treated acetylene depend on the above-mentioned conditions and on the desired acetylene recovery, being preferably between 15/1 and 150/1 on a weight basis. The stripping is preferably carried out in an evaporation column at a pressure of from 1 to 20 kg/cm 2 , with heat being supplied to the bottom of the column and ammonia being introduced into the column, with the absorbed gases for the previous absorption being obtained as top product together with the introduced ammonia, preferably already in the acetylene/ammonia ratio which is necessary for a correct operation of the alkynol synthesis. The operation is carried out so that acetone is obtained as a bottom product, almost free of more volatile compounds.

The alkynol synthesis, in particular the production of methylbutynol, is then carried out by reacting the acetylene with a ketone in an ammoniacal solution and in the presence of an alkaline catalyst.

As mentioned, the possible presence of other gases absorbed together with acetylene shows no significant influence on the course of the synthesis reaction.

The presence of hydrocarbon gases, or gases which are less polar than acetylene in the mixture to be absorbed, thus causes no disadvantages as long as these components do not react with the acetone under the absorption conditions. If the said compounds are dissolved in an appreciable amount in the acetone, they must not cause the formation of compounds or complex compounds with ammonia under the conditions of the alkynol stripping and synthesis.

The conditions for the methylbutynol synthesis reaction, which are given to illustrate the method according to the invention, are as follows: Reaction temperature in the range from -40°C to +50°C, preferably from +10°C to +30°C,

The reaction pressure must be such that the reaction mixture is maintained

in liquid state and the acetylene is in the stable range, preferably the pressure is kept at between 1 and 30 kg/cm , and the molar ratio between acetylene and ammonia is kept in the range from 3:7

to 3:30,

the molar ratio between acetylene and acetone is kept in the range from 1.5:1 to 10:1, and

the molar ratio between alkaline catalyst and ketone (in this case acetone) is kept in the range from 0.005:1 to 0.1:1.

The invention will now be illustrated with the help of the accompanying drawings, figures 1, 2, 3 and 4, in which some flowcharts used in connection with the invention are reproduced.

To illustrate the flow charts, reference will be made to the treatment of gas streams containing ethylene and acetylene. It is clear, however, that the same process schemes are also applicable to other gas mixtures containing acetylene.

Among the gaseous hydrocarbons containing 1 to 3 carbon atoms, ethylene is the one that exhibits a polarity that is closest to that of acetylene, which is why it is very difficult to separate them by absorption. The other possible components present will present less separation difficulties.

In fig. 1, the gas stream consisting as mentioned of ethylene and acetylene is fed through line 1 to absorption column 2, in which the recycled gas streams are fed through lines 3 and 4. The recycled absorbing acetone from the stripping step is fed through line 5, while fresh acetone is fed through line 6 in an amount: sufficient for the synthesis reaction.

Through a line 7, a stream essentially consisting of ethylene together with a small amount of acetone corresponding to

the absorption saturation conditions. The acetone is removed and recovered from the ethylene in a manner known per se (not shown in the drawing).

From the bottom of the absorption column 2, it is taken through the line 8

out a solution of acetylene in acetone, which solution contains almost the entire amount of acetylene supplied through 1.

The absorption step requires cooling for condensation of the acetylene and the other gases dissolved in stream 8, which is provided by changing the free heat of the solution. The solution obtained is fed into the stripping column 9, where one stream of ammonia is supplied through line 10, which serves as a stripping medium for the gases lost 1 acetone.

The boiler 11 is supplied with the necessary heat for the operation which must be carried out so that the stream leaving the bottom of the column through the line 12 consists of acetone almost free of more volatile products. The top product, which is taken out through a line 13, consists of the gases released during the absorption step in the column 2 and of the ammonia introduced through the line 10. Said stream is partially condensed in the condenser 14, obtaining an ammoniacal release of acetylene and ethylene and a non -condensed fraction essentially consisting of ethylene, which fraction is recycled to column 2 through line 3.

The ammoniacal solution of acetylene and ethylene is then supplied through line 15 to the reaction zone 16. The catalyst is fed in through line 17. From the bottom of column 9, the acetone required for the reaction to 16 is fed through lines 12 and 18 after cooling in the heat exchangers 19 and 20 .

In general, the acetone used in the synthesis can be completely separated from the acetone used in the absorption step, but the integration of the acetone used in the absorption step and in the synthesis simplifies the operation considerably.

From the reaction zone 16, the reaction product flows out through the line 21. This product consists of methylene butynol, ammonia, unreacted acetylene, unreacted acetone and ethylene which has remained unchanged. This mixture is expanded in a first separation column 22 where vapors consisting of ethylene, acetylene and ammonia are taken out from the top through line 23. These vapors are then introduced into the partial condenser 24 in which a condensate consisting mainly of ammonia is produced which is recycled to the column 9 through the line 10 after prior evaporation in the heat exchanger 19. The non-condensed part, which mainly consists of ethylene and acetylene, is recycled to the column 2 through the line 4.

From the bottom of the column 22, a stream consisting of methylbutynol, unreacted acetone and traces of ammonia is taken out through line 25. This mixture quickly goes to the separation column 26, from which a top product essentially consisting of acetone and ammonia is taken out through line 27, which is recycled to column 9, and a bottom product through line 28 essentially consisting of the methylbutynol product.

The flowchart in fig. 2 shows a variant of fig. 1.

According to fig. 2, the vapors obtained in column 9 are fed to column 29 in which the acetylene recovery is completed by using part of the ammonia condensed in 24 and which is fed through line 30 and cooled in heat exchanger 31.

To relieve the current 30, e.g. both to limit the flow rate and its heat content, part of the ammoniacal discharge of acetylene obtained through line 15 is cooled in the heat exchanger 32 and reintroduced in 29 through line 33.

Fig. 3 shows a simplified diagram in which a number of modifications have been made in relation to fig. 1.

The vapors obtained at the top of column 9 are sent in their entirety

to the reaction zone 16 after prior condensation in 14, and the top product from column 26 is recycled in vapor phase to column 9 through line 27.

The form in fig. 3 is particularly suitable when hydrocarbons dissolved in acetone in stream 8 already contain a large amount of acetylene. In this case, a further purification step by partial condensation is not necessary.

Recycling of ethylene to the absorption stage occurs through line 4. When the solution obtained in the absorption stage essentially contains only acetone and acetylene, scheme 3 can be further simplified to scheme 4 in which line 34 and heat exchanger 35 serve to provide most of the necessary cooling for the absorption step without using very high flow rates and temperatures.

The small amount of light, non-acetylenic compounds present as impurities in the stream 8 can be removed by emptying said compounds out through the line 36.

Of the forms shown as examples, form 1 can be used with advantage when feeds containing small amounts of acetylene are to be processed, as the amount of ethylene is not very high either.

The form in fig. 2 is typical for an ethylene-acetylene mixture with a low acetylene content.

When the amount of acetylene is higher, scheme 3 is preferable.

Form 4 is used with advantage when the acetylene is free of diluents which have appreciable solubility in the acetone under the absorption conditions.

As an example of the gas compositions that it can be

in the various parts of the plant, during a process in which the method according to the invention is included, the following example is shown which refers to a plant corresponding to that shown in fig. 1.

Here, a gas mixture consisting of 95 volume percent ethylene and 5 volume percent acetylene is supplied to a filled absorption column 2, which consists of four sections with a diameter of approx. 15 cm and each with a height of 2 metres.

The following table indicates approximate molar equilibrium with

new addition of 100 gram-mol gaseous mixture per hour.

The absorption is carried out with approximately 15 atmospheres absolute

pressure and the bottom temperature is approximately 10°C. The solvent is supplied through lines 5 and 6 at approximately 0°C.

The stripping column 9 consists of an approx. 15 cm column equipped with 33 bubble clock plates. The stripping is carried out at approximately 5 atmospheres absolute pressure and the condensation temperature is approximately -10°C.

The composition obtained at stream 15 is directly fed to the synthesis reactor 16.

Claims (2)

1. Process for the production of acetylene solutions suitable for the synthesis of alkynol, where one starts from a gas mixture which essentially consists of ethylene and acetylene, which is treated with acetone while forming an acetylene solution in acetone, characterized in that in order to obtain a ammoniacal acetylene solution and separation of the acetone subject the acetone solution to a stripping treatment with ammonia. 2. Method as stated in claim 1, characterized in that the stripping treatment is carried out in an evaporation column, preferably at a pressure of from 2 1 to 20 kg/cm .