DE1095448B - Process for removing substances such as acetylene and its homologues from gases - Google Patents

Description

Process for removing substances1 such as acetylene and its homologues, from gases The invention relates to a method for removing substances such as acetylene and its homologues, mercaptans, COS, Cis2, 2 nitrogen oxides, cyclopentadiene, Butadiene and styrene, from gases produced by fractional liquefaction, namely can be cleaned by means of pressure and cold.

It is known that apparatus for the fractionation of gas mixtures are limited in their service life at low temperature, which is due to the im Gas mixture still contained impurities is conditioned, which are in the apparatus as deposit solid substances, these initially reducing the effectiveness of the heat exchange decrease and eventually lead to constipation.

It is also known that heavy contaminants, including water, Benzene and its homologues, various hydrocarbons of similar volatility etc. are to be understood in the first zone of the apparatus, i.e. in the zone which the gas generally cools from -45 to -90 to -110 "C, condense. After the current state of the art, this disadvantage is addressed by various arrangements, avoided, among other things, by using two alternating heat exchangers.

In the exit from the first zone indicated above, the gas contains the temperature of which is generally very close to the point at which the liquefaction occurs of the ethylene begins, there are still residues of the aforementioned impurities and others lighter impurities such as acetylene and its homologues, mercaptans, COS, CS2, C02 etc. These impurities would form solid deposits in the second zone of the Apparatus, i.e. in the zone which the gas from -90 to -110 to -150 to -165 "C and cools below, form if the formation occurs at the same time in this zone the ethylene liquid would not turn on, its dissolving power these impurities is known.

However, experience in industrial practice has shown that the solvency of the ethylene liquid alone is not sufficient, solid deposits to avoid inside the apparatus and a longer period of operation of the latter to ensure. Solid deposits and blockages in both the high-pressure circuits from the second zone as well as in low-pressure circuits in which the Äthvlenlösungs-solvent is expanded, occur as a result of the evaporation of the latter and the resulting Temperature decrease still on.

In the course of investigations and industrial, with fractionators Tests carried out for the treatment of coke oven gas have been found to that the washing efficiency of the ethylene liquid with regard to the aforementioned impurities due to the presence of methane, ethane and their homologues in the ethylene liquid decreases.

It is possible in and of itself through various measures, inside the apparatus to obtain a low-methane ethylene liquid, on the other hand, succeeds It is not possible to eliminate ethane and its homologues because their boiling point is very close is at the boiling point of ethylene.

The above disadvantages, which are known to occur individually or together can be remedied by the method according to the invention.

In the method according to the invention, various are known per se Process steps in a special order and under newly developed conditions carried out, above all about the operating time of the facility, be it through The best possible removal of the impurities from the gas, be it through modification the composition of the latter, increasing, creating inside the facility an ethylene liquid is then condensed, which is opposite to the rest Impurities has an increased solvency. The inventive method consists of a combination of the following process steps: 1. The gas is after the excretion of CO2, H2S, benzene and its homologues with kerosene washed at 12 atm and -40 "C, whereby mainly ethane is removed; 2. the after t washed gas is at 10 to 12 atü and -35 to -50 "C by porous adsorbents, such as activated charcoal, silica gel or aluminum oxide, passed, except for the vaporous Kerosene, the main amounts of the resin formers are retained, and 3. the gas thus obtained is introduced into the fractionation device and here to cooled down to the dew point of the ethylene, whereby the liquid ethylene fraction, which consists essentially of ethylene accompanied by methane, methane, acetylene and washes the remaining contaminants out of the gas.

For example, when using about 1 m3 Kem sin to about 500 to 1000 mp of gas when washing coke oven gas is the gas changed in such a way that the ethylene liquid which is excreted in a continuous manner at the Fralrtíon a significant in terms of a more effective washing out of harmful contaminants has a more favorable ethylene-thane ratio. The ethylene concentration reached is 50 to 650 / o, thus exceeding the usual concentration of 25 to 35010 very largely.

The washing also exercises against numerous contaminants, under other unsaturated substances such as cyclopentadiene, butadiene, styrene, etc., a cleaning effect the end; These substances can form resins in the interior of the apparatus, which in the event of condensation with nitrogen oxides are particularly dangerous, i.e. further impair the service life. The exhausted absorption liquid is in a known manner by heating in a special system regenerated.

That which is to be fractionated comes from the washing process with kerosene In addition to the vapors of the organic liquid, the gas mixture also contains all of them not excreted during washing, including heavier impurities that in a solid state in the first zone of the apparatus, i.e. before the formation of the Ethylene liquid, would deposit.

This disadvantage is increased by using the above-mentioned porous adsorbents, such as activated carbon, silica gel, aluminum oxide, etc., fixed.

The second step is to use those mentioned above porous adsorbents, but among the particulars detailed below Conditions because this procedure leads to a condensation of the impurities and KerQsin fumes in the first zone of the facility not only avoided, but causes the impurities to reach the second zone to a lesser extent, on which the ethylene liquid, the solvency of which has already been increased, condensed.

The use of porous adsorbents is known per se. Known is also that the amount of impurities that these adsorbents hold back, the nature of the impurities in question and the degree of saturation of the Adsorbierraittels depends.

However, the apparatus cannot use the adsorbents alone to protect effectively, as the adsorbing effect of these substances is limited to the dew point in the vapor state, i.e. below its critical temperature in Gas mixture inflicts contamination, to be reduced to a maximum of 50 to 80 ° C.

Treatment would have to be carried out to completely remove the impurities theoretically be carried out in successive stages.

For these reasons, the use of adsorbents alone, as it occurs in numerous processes, is not a technically useful result achieved.

In the present process, in which the ethylene liquid of by washing with kerosene improved composition, as set out above, has the task of absorbing the remaining impurities contained in the gas and to dissolve, the use of adsorbents is particularly advantageous, with the same come into effect under technically favorable conditions, since their effect on the Lowering of the dew point of the impurities contained in the gas mixture up to Temperature at which the condensation of the ethylene liquid itself begins, is limited.

To do this, it is sufficient to carry out the adsorption at a temperature which by 50 to 80 "C exceeds that at which the ethylene liquid increases begins to condense.

For example, this condensation temperature is fd coke oven gas approximately -110 to -1200C at 10 to 12 at. Purification by adsorbents should therefore take place at at least 35 to -50 "C. Finally, the gas enters the fractionation device one, in which it, as stated above, up to the condensation temperature of the ethylene liquid is cooled, which with a higher percentage due to the prewash of ethylene with respect to ethane is capable of Xe residual impurities, in particular Acetylene, which tends to harden, to dissolve and remove completely.

By applying the above measures, larger fractionators for coke oven gas, continuous operating times of several years as well as increased output achieved by keeping the heat exchange surfaces completely clean for a longer period of time can be obtained.

The following example of the application of the method according to the invention explains the invention .dungsSegth in application to a large industrial plant below Referring to the schematic drawing in more detail: Example A coke oven gas from normal Composition is known at an operating pressure of 12 Atm. After it is in Way of a pre-cleaning for the elimination of CO2, H2S and benzene has been, in the usual way in the heat exchanger 1 by means of the fractionator Exiting cold gases to about -15 "C and then to -450C in the cooler 2, its cooling effect is maintained by a special cooling machine, cooled.

The heat exchanger 1 and the cooler 2 consist of as usual exchangeable pairs, as the heavy impurities, such as water, Benzene and its homologues.

When it emerges from the cooler 2, the gas mixture still contains residues the heavy contaminants and the other lighter contaminants, such as COS, Mercaptans and similar organic sulfur compounds, various light hydrocarbons, especially acetylene.

This gas mixture is introduced into a tower 3, in which it at -45 "C in its lower part by sprinkling with kerosene, which by a pump 4 is kept in circulation in a closed circuit, and regenerated in the upper part and kerosene enriched with ethylene is washed from a regeneration column 15 and from the apparatus 12, 22, as will be described in more detail below.

In the tower, the kerosene not only absorbs from the gas, as usual, various impurities such as benzene, its higher homologues and the like also ethane in proportionally larger quantities than ethylene because of its higher solubility in kerosene.

Part of the washing liquid is removed from the bottom of the tower 3 and fed to the apparatus 12, 22, which in a known manner has the task of to separate the ethane from the ethylene, the former being derived, while the the latter withheld and returned to the cycle either immediately or in Solution in fresh kerosene fed to the upper end of the tower 3 is returned.

The column 12 is a heat regeneration column with its accessories downstream, which has the task, in a manner known per se, from the kerosene to remove the benzene and its higher homologues.

The gas mixture emerging from the tower 3 has because of the washing with kerosene a changed ethylene-ethane ratio, so that subsequently in the fractionator a liquid containing ethylene condenses, which is richer in ethylene and poorer in it Ethane is as it is commonly received.

The gas mixture then becomes the reversible adsorption apparatus5 and 6, which are charged with activated carbon and silica gel and which do the cleaning with regard to the remaining heavy impurities such as water, benzene, its higher homologues and the like, further improve and also hold back the kerosene fumes, which has absorbed the gas mixture in the tower 3 during the washing.

That from the adsorption apparatus 5 and 6, the tower 3, which latter the plant 12, 22 is assigned, and the regeneration column 15 existing unit forms the new part in the method according to the invention.

After leaving the adsorption apparatus, the gas mixture becomes the Heat exchangers 7, 8 and the apparatus 10 supplied from the known per se Fractionator exists.

In the heat exchanger 7, in which, as usual, the temperature to about -100 to -110 "C is lowered, no clogging and no solid deposits occur because of the treatment of the gas mixture in tower3 and in the adsorption apparatus 5, 6 the heavy impurities have been excreted, which otherwise the aforementioned Would cause disadvantages.

In the heat exchanger8, in which the temperature is around - 145 to -160 "C is reduced, the condensation of the ethylene-containing liquid occurs, which moves from top to bottom in countercurrent to the gaseous mixture. Because of the Washing with kerosene, which the ethylene-containing liquid has experienced in tower 3, if it is richer in ethylene and poorer in ethane, so that, as explained in the introduction, has a higher cleaning efficiency than usual and still exists Remnants of impurities, especially acetylene, due to their solubility completely removed, leaving solid deposits of such impurities both in the pressure circuit as well as in the expansion circuits of the ethylene-containing liquid be avoided by yourself.

This ethylene-containing liquid formed in the heat exchanger 8 is collected in the usual way in a container 9 and from this to the fractionation apparatus 10 passed, in which they in a known manner, taking advantage of their low temperature is brought to expansion.

If necessary, some of the obtained ethylene-containing Fraction returned to the coke oven gas cycle to increase the concentration of ethylene, after being in the apparatus 11 of a large part of their Content of acetylene, sulfur compounds, nitrogen oxides, etc. have been freed and after the ethylene-ethane ratio is improved by a treatment with kerosene has been what in the example described here in the one described below Apparatus 12, 22 happens.

This apparatus is shown schematically in the drawing, though it is a known measure which does not form part of the invention.

This apparatus is used in the process according to the invention used because it has the advantage that the ethylene from the ethane, both in the Kerosene are solved, can be separated in such a way that the former is used can be fed back into the cycle and the latter diverted will.

As is known, this apparatus can also be operated under pressure, although in the present example it is operated at atmospheric pressure.

The kerosene is as it comes from the tower3, i. H. with a temperature of 450, C and containing, among other things, ethane and ethylene absorbed, in suitable Introduced height into the column 12, at the bottom of a coil 13 a heating causes a flow of gaseous ethane that rectifies the kerosene, which descends from above, whereby this is freed from its ethylene content.

As is known, the operation of the column 12 is that the gaseous ethylene rises to the top, while the ethylene freed from the bottom and all the ethane as well as the other heavy, separated from the gas mixture in tower 3 Kerosene containing impurities is removed.

Instead of arranging a snake 13 at the bottom of the column, the same can the ethylene gas part flowing from the apparatus 10 and appropriately cleaned in the apparatus 11 be supplied for the above-mentioned purpose, to win ethane therefrom and in the Cycle the coke oven gas with an ethylene gas with a suitable ethylene-ethane ratio traced back.

The other impurities of a heavy nature, which in Tower 3 were separated from the mixture, are from the kerosene together with the Ethane excreted in the heat regeneration column 15, in a known manner a suitable heat exchanger 14, a heating coil 16, a reflux coil 17 and a capacitor 18 is assigned.

The kerosene purified in this way is sucked off by a pump 19, cooled in 20 and 14, in the ammonia cooler 21 to a temperature of 450 C (operating temperature of columns 22 and 12) and introduced into the upper end of the small column 22, in which it is with the diverted from the upper end of the column 12 gaseous Ethylene saturates.

At the lower end of the small column 22 is saturated with ethylene Kerosene is suitably separated into two parts, one of which is used as a reflux serves for irrigation in the upper part of the column 12, while the other part in a container 23 is collected, in which it is once again through an ammonia coil 24 and from which it is cooled by a pump 25 to the top of the absorption tower 3 is funded.

The gaseous ethylene not absorbed in the small column 22 is fed back into the coke oven gas cycle.

Claims (1)

PATENT CLAIM: Process for removing substances such as acetylene and its homologues, mercaptans, COS, C S2, nitrogen oxides, cyclopentadiene, butadiene and styrene from gases produced by fractional liquefaction by means of pressure and cold cleaned, characterized in that the combination per se known process steps are carried out in the specified order, namely: 1. The gas is released after CO2, H2S, benzene and its homologues have been eliminated washed with kerosene at 12 atm and -40'C, which mainly removes ethane, 2. The gas washed according to 1 becomes porous at 10 to 12 atmospheres and -35 to -50 "C Adsorbents such as activated carbon, silica gel or aluminum oxide, whereby In addition to the vaporous kerosene, most of the resin formers are retained, and 3. the gas so obtained is introduced into the fractionator and here cooled down to the dew point of the ethylene, whereby the liquid ethylene fraction, which essentially consist of ethy- len accompanied by ethane, methane, acetylene and washes the remaining contaminants out of the gas. Documents considered: German Auslegeschrift No. t 012 940; French patent specification No. 662 383.