US2206490A - Recovery of acetylene - Google Patents

Description

Patented July 2, 1940 naoovnnr F ACETYLENE Heinrich Tramm, ObeI'hausen-Holten, and Helmut Rolling, Duisburg-Hamborn, Germany, as-

signors to Ruhrchemie Aktiengesellschatt,-

Oberhausen-Holten, Germany Application February 15, 1938, Serial No. 190,674

Germany February 20, 1937 .3 Claims.

Our invention relates to the recovery of acetylene from gas mixtures containing same and more particularly from gas mixtures which contain other highly unsaturated compounds in addition to acetylene,

It is an object of our invention to recover from gas mixtures of this kind acetylene in a state of high purity.

Other objects of our invention and the manner in which they can be attained, will become clear from the following description.

It is known to extract acetylene from gas mixtures with water under increased pressure and to subsequently liberate the acetylene from the saturated solution thus obtained by exposingthe solution in a tower to a vacuum of for instance mms. mercury column. In the recovery of acetylene it is also'known to wash gas mixtures first with a small quantity of a solvent in order to extract in this preliminary wash the highly unsaturated impurities contained in the mixture from which the acetylene shall be recovered. in pure state, and to subsequently wash the thus purified gas mixture with large quan titles of the same solvent in order to completely extract from thegas the acetylene present, whereupon that portion of the acetylene which had been dissolved in the preliminary washing operation, is expelled from the small quantity of solution obtained in this operation. either by fractional dilatation or by a suitable heat treatment, tobe then recycled.

It has been found that acetylene can be extracted from gas mixtures containing same by means of water in a particularly satisfactory manner as follows: The gas mixture is washed first with a small quantity (preliminary treatment) and subsequently 'with a considerably larger quantity (main treatment) of water, these two washing treatments being carried out at normal .temperatures and under pressures ranging between 10 and atmospheres above normal. Acetylene is expelled from the solution obtained in the main treatment by exposing this solution at normal temperature to reduced pressure of not less than 30 mms. mercury column. Under these conditions the acetylene is washed out and. recovered with particular efllcacy.

The liquor may be relieved from the pressure of 10-15 atmospheres in two stages, first to about -is thereupon-freed from the dissolved acetylene at a reduced pressure of not less than mms. mercury column in a vacuum vessel into which the liquor is introduced preferably through fine nozzles. The acetylene thus obtained is compressed in the vacuum pump to normal pressure. 15 In this way a gas is obtained which, after having been freed from CO2, contains up to, but not more than, 98.5% C2H 2.

For certain purposes a gas is required containing more than 99% acetylene. We have 80 found that gases of such high degree of purity can be obtained by relieving from pressure in two or more stages the concentrated aqueous solution of acetylene obtained in the main washingtreatment mentioned above and introducing 2 into the lower part of at least one of thepreliminary stages of pressure-relief part of the pure acetylene, which is obtained as the end product of the process after reduction of the pressure to about 30 mms. mercury column and after re- .moval of'the carbon dioxide and recompression in the vacuum pump. The particular advantage offered by our process consists in the fact that the gas which has been compressed in the vacuum pump and freed from the carbon dioxide, contains a very high percentage of acetylene and not more than about 2% of gases which are more diflicultly soluble than Cal-I2. Thus almost pure acetylene is used in our process as washing-out agent and for this reason only a small quantity of this gas is required to be passed through the liquor while it is relieved from pressure in a preliminary stage. We succeed in thus obtaining acetylene o1 more'than 99%.

In order to further illustrate our invention we will now describe an example, according to which a solution of acetylene is relieved from pressure in two stages. More than two stages may be used for the pressure relief, while as a rule relief in two stages sufllces in view of the high eillcacy of the process.

The drawing ailixed to this specification and forming part thereof is a flow sheet illustrating the two stage process. The following example will be described with reference to the drawing:

The gas mixture has the composition Per cent CO: 2.2 Call: 11.2 mm. 0.3 m 78.6 CH4 5.1 N 2.8

It contains, in additionto acetylene, a small quantity-of diacetylene and similar highly unsaturated compounds, which are designated in the above schedule as CnHm and will hereafter be termed diacetylene. The diacetylene compounds amount to about 3% of the total quantity of the acetylene present.

This starting gas is compressed in the com- .pressor A to 10 atmospheres above normal and thereafter enters the sump of the washing column B provided with 10 to 15 trays. In this column the gas is irrigated in countercurrent with water placed, in the pump S, under a pressure of 10 atmospheres above normal. If 100 cbm. (normal) of the starting gas containing about 11% CzHa are treated, approximately 3 cbm. will be sufllcient in view of a 70% capacity of the washing column for completely washing out the diacetylene. The washed gas leaves the column at C, while the water charged with acetylene, diacetylene and small quantities of the inert gases contained in the starting gas is withdrawn from the bottom of the column at D. This water con-' tains the whole of the diacetylene present, amounting to about 0.33 cbm. and about 2.4 cbm.

Cal-I2.

In order to recover the acetylene thus dissolved in the washing water, the liquor is relieved from pressure at E and is freed from the dissolved acetylene in a second washing column F. The

-water relieved from pressure is introduced into the top part of the column F, while inert gases are passed through it from below in countercurrent. Part'of the end gases which escape (at L) from the main washing treatment are employed for this purpose in column F. About 6 ohm. of these inert gases suflice to expel the acetylene almost completely. In order to reduce the quantities of diacetylene which escape during this treatment of the liquor, the washing column F is additionally supplied at T with a small quantity of fresh water which is fed to the topmost tray of the column. The water freed from acetylene is withdrawn at G from the bottom of'the column F and may be used in any suitable manher, being for instance supplied to a graduation apparatus for the regeneration of the water.

The acetylene expelled escapes from the washing column at H together with the inert gases introduced into the column and is returned to the compressor A through pipe J.

The gas which escapes from the preliminary washing apparatus at C and which contains the mainquantity of the acetylene, enters the main washing apparatus K forming a washing column with about 10 to 15 trays. This column serves for washing out and extracting the whole of the acetylene. The gas enters the: apparatus from below, under a pressure of 10 atmospheres above normal. It is irrigated with water in countercurrent and leaves the apparatus K at L free from acetylene.

If 100 cbm. (normal) of the starting gas are introduced hourly into the washing plant, about 12-13 cbm. water per hour are supplied to the main washing apparatus K in order to wash out the whole of the acetylene. The end gas escaping at L is subsequently relieved from pressure and while the greater part of this end gas is allowed to leave the plant,'a small part is passed through the washing water introduced into the washing apparatus F, as described above. Inthe main washing apparatus K here are washed out by the water, in addition to the acetylene, small quantities of carbon dioxide and hydrogen and traces of methane, ethylene and nitrogen.

The water which leaves the main washing apparatus K contains for instance, under a pressure of 10 atmospheres'above normal, the following gases:

This liquor is relieved from pressure, for instance to one atmosphere absolute, and is fed to the top of the washing column M, while acetylene, obtained as end product in the last stage of pres sure-relief and recompressed by pump P, is passed in countercurrent from below through the liquor in column M. It is important that during this treatment theliquor is thoroughly mixed .with the compressed gaseous acetylene. The liquor, while being relieved from pressure in this preliminary stage, is contacted intensively and for a suflicient period of time with the acetylene which in the first stage possesses a purity of about 98% and in the later stages a purity of more than 99% and is preferably compressed to substantially that pressure to which the liquor had previously been relieved. The intensive contacting required may for instance be secured by the use of means which enlarge the contact surface, such as Raschig rings. The acetylene forming the end product of our process is the purer, the greater the quantity of gaseous acetylene led through the liquor at this stage of the process.

I sure and had been treated in the washing column M with pure acetylene passed therethrough, is subsequently placed under reduced pressure in the degasifier N. We have found it advantageous not to operate under an absolute pressure below -30 mms. mercury column. In order to expel the whol of the gas contained in the liquor, it is necessary to very finely disperse the water and to expose it to the vacuum for a sufliciently long period of time. The water saturated with acetylene may for instance be freed from it by atomizing in suitable nozzles, such as spiral nozzles, the

liquor entering the degasifler tower N, and sub- 5 sequently causing it to flow down in thin layers on the inner walls of long and rather narrow tubes, or to fall in atomized state through the vacuum. Atomization may also be performed by supplying the water to rapidly rotating disks. Towers charged with suitable filling bodies which secure a fine dispersion of the water, may be used alsoinstead of the tubes.

In the practical operation of our process it is easily possible to attain a degasifying efiect'of about 99.5%. This expulsion of gas is efiected not only by the reduced pressure employed, but to a remarkable extent by the water vapor which is simultaneously expelled and which acts as an indifierent gas, passing through the liquor which contains the acetylene.

The expelled gas leaves the degasifier N at 0. About 22-23 cbm. (normal) of a mixture of gas and vapor escape per hour, consisting of about 10.5 cbm. (normal) CzHz, 2.9 cbm., CO2 and 10 ohm. steam. The main portion of the vapor is condensed in the vacuum pump P, into which the gases are led. The gas which leaves the .vacuum pump and which consists of acetylene and carbon dioxide and a small quantity of moisture, is subsequently subjected to some washing treatment by which the carbon dioxide is separated from the gas mixture, whereby acetylens of high purity is recovered. ii

The water havingsbeen freed from gas in the tower N is led into a vessel .Q and is subsequently recompressed in the pump R to 10 atmospheres, whereupon it may be employed anew for the extraction of acetylene inthe main washing column K.

As has been mentioned above, the acetylene forming the end product is the purer, the larger the quantity of compressed acetylene with which the liquor is treated while being relieved from pressure in the preliminary stage. In -a case where 20 litres gas of the second stage of pressure relief were used for the treatment of 120 litres water employed per hour for the main washing step, the end gas contained for instance 98.'7% CzHz, while acetylene of 99.5% was obtained by treating the same quantity of water with 27 litres per hour of the gas recovered in the second stageof pressure relief. These 20 litres of gas corresponded to about 19% of the pure acetylene obtained per hour, while the 27 litres corresponded to about 26% acetylene and other highly unsaturated com-- .T.

pounds, which comprises the steps of washing such gas mixture, at normal temperature and under a p essure ranging between about 10 and 15 atmos heres, with a small quantity of water sufiicient for practically completely extracting the highly unsaturated compounds other than acetylene, treating the washed gas at normal temperatures and under a pressure ranging between about 10 and 15 atmospheres with a quantity of water sufiicient for extracting substantial-- ly the whole of the acetylene present, relieving the aqueous solution thus obtained from pressure at normal temperature in several stages up to a reduced pressure of not less than 30 mms. mercury column, compressing the gas thus obtained and freeing it from carbon dioxide and recycling part of the substantially pure acetylene with a content of at least -98% 02H: thus obtained by passing it through, and intensively contacting it with, the aqueous solution during a preliminary stage of pressure relief at which the pressure is substantially equal to that of the recycled gas.

2. The method of claim 1, wherein the aqueous solution of acetylene is relieved from pressure in two stages, first to about normal pressure and subsequently to a reduced pressure not below 30 mms. mercury column, while part 01' the substantially pure acetylene obtained as end product and compressed to about normal pressureis conducted in countercurrent through the aqueous solution between the first and second stages of pressure relief.

3. The method of claim 1, wherein the gases escaping from the aqueous solution of acetylene during a preliminary stage of pressure relief are compressed and introduced into the first washing step.

HEINRICH TRAMM. HELMUT KOLLING.

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