DE4325513A1 - Process for producing a highly pure carbon monoxide product stream and a hydrogen product stream - Google Patents

Abstract

Process for producing a highly pure carbon monoxide product stream and a hydrogen product stream by fractionating a substantially dry and CO2-free H2/CO crude gas mixture by means of single-stage partial condensation and subsequent low-temperature fractionation of the CO-rich condensate formed in the partial condensation, the gaseous H2-enriched, CO-containing fraction formed in the partial condensation being separated in a membrane separation unit into a hydrogen product stream and a low-H2, CO-containing fraction and the low-H2, CO-containing fraction being fed to the low-temperature fractionation for the recovery of the carbon monoxide still contained therein.

Description

The invention relates to a method for obtaining a high pure carbon monoxide product stream and a hydrogen pro duct flow by dismantling a largely dry and CO₂-free H₂ / CO raw gas mixture using a single-stage par tial condensation and subsequent low temperature fraction nation of the formed during the partial condensation CO-rich condensate.

Due to increased purity requirements for the dismantling products, the growing importance of operating cost of a plant, as well as the constant improvement of the Available thermodynamic data, took place at H₂ / CO decomposition has been a constant tech in recent years African change.

As the main supplier of the H₂ / CO raw gas mixture is still before calling the steam reformer. But also the heavy oilers gassing with oxygen - i.e. partial oxidation -  a cheap oxygen source provided in the past Years of importance as an H₂ / CO supplier.

Most of the carbon monoxide so produced is used in the Formic and acetic acid production used. Another Customers can be found in polycarbonate chemistry, which as Raw material phosgene of high purity and this in turn coal highest purity monoxide required. The methane content of the Carbon monoxide must be less than 10 mol ppm, the Hydrogen content must be less than 1000 mol ppm. The generated one Hydrogen is used for a wide variety of hydrogenation purposes.

An overview of the processes in use Manufacture of carbon monoxide and hydrogen as a by-product give the articles by R. Fabian in LINDE reports from technology and Science No. 55, 1984, pages 38 to 42 and Dr. R. Ber ninger in LINDE reports from technology and science No. 62, 1988, pages 18 to 23.

When decomposing H₂ / CO gas mixtures, which consist of a par tial oxidation is to achieve a CO yield of over 90%, however, a cooling of the H₂ / CO gas mixture up to approx. 70 K necessary. The cold required for this is due to the low-temperature relaxation of the separator drive generated H₂-rich electricity. At a Such cold relaxation usually comes at least two expansion turbines are used. This ent voltage turbines are relatively expensive and prone to failure, which is why they are constantly monitored and serviced frequently have to. Since they also at temperatures below the liquefy pressure point operated by pressureless nitrogen (-196 ° C) some components of the separation system have to be complex be specially insulated.

The object of the present invention is to overcome the disadvantages of Avoid prior art, but in particular should  the investment and operating costs of an H₂ / CO separation plant be reduced.

This is achieved in that the at partial condensation formed gaseous H₂-enriched te, CO-containing fraction in a membrane separation unit in a hydrogen product stream and in a H₂-poor, CO-ent holding fraction separated and the H₂-poor, contain CO de Fraction of low temperature fractionation to obtain the carbon monoxide contained in it is supplied.

The method according to the invention can now be used do without expansion turbines. Instead, one Membrane separation unit used, which works without moving parts tet and is therefore neither prone to failure nor expensive maintenance needed. Membranes for the separation of hydrogen from water Substance-containing gas mixtures are sufficient for the person skilled in the art knows. In the method according to the invention is therefore already in the membrane separation unit a large part of the H₂ / CO raw gas Mix contained hydrogen discharged while this with conventional CO / H₂ separation processes only in the deep temperature fractionation happens.

The method according to the invention and further embodiments formulated in the claims are explained in more detail with reference to FIGS . 1 and 2. The same process steps or system parts have identical reference numerals.

Obtain all of the following quantities for process streams to mol%.

Fig. 1 shows schematically a method for obtaining a high-purity carbon monoxide product stream and a hydrogen product stream by decomposing a CO₂-free H₂ / CO raw gas mixture from a steam reforming process. Such a procedure makes sense for "small plants", ie with a production of less than 3000 Nm³ / h CO. Such a process delivers a carbon monoxide product stream with a so-called polycarbonate purity, that is less than 1 ppm CH₄ and less than 10 ppmH₂.

The CO₂-free H₂ / CO raw gas mixture is fed via line 1 to an adsorption stage A and dried in it. At closing the dried raw gas is fed via line 1 'through the heat exchangers E1 and E2 and via line 1 ''to the separator D1. It is cooled in the heat exchanger E1, while in the heat exchanger E2, which the raw gas leaves at a temperature of 88.4 K, CH₄ and CO are condensed out and separated in the separator D1. The gaseous H₂-enriched, CO-containing fraction formed in the partial condensation is heated in the heat exchangers E1 and E2 and fed to the membrane separation unit M. This is separated into a hydrogen product stream (permeate), which is discharged via line 3 , and into a low-H₂, CO-containing fraction (retentate). The latter is fed via line 4 through the heat exchangers E1 and E3 and via line 4 'to the separator D2. It is cooled in the heat exchanger E1 and partially condensed in the heat exchanger E3.

At the head of the separator D2, an H₂-rich, CO-containing, gaseous fraction is drawn off via line 10 , expanded in valve c and beige 6 to be described line mixes. The CO-rich condensate obtained in the separator D1 is released after relaxation in the valve a via line 5 to the top of the separation column T1. The separation column T1 works at a pressure of 6.5 bar, the top temperature being -185 ° C and the bottom temperature -168 ° C. In addition, the CO-rich condensate from the separator D2, which is supplied via line 11 after expansion in the valve b, is fed into the center of the separating column T1. The CO-rich condensate from separator D2 is lower in CH₄ than the CO-rich condensate from separator D1. By feeding the CO-rich condensate from the separator D2 via line 11 into the separation column T1, even more CO can be backwashed and recovered in this. At the top of the separation column T1, an H₂-rich gaseous fraction is drawn off via line 6 , the pressure in valve d is relaxed and the hydrogen product stream in line 3 is mixed with process streams to be cooled in the heat exchangers E2 and E1 after prior heating in indirect heat exchange. The bottom of the separation column T1 is divided. A first part is partially evaporated via line 7 'in the heat exchanger E2 and given as a heater in the separation column T1. A second part is relaxed in the valve e and fed via line 7 of the CO / CH₄ separation column T2 as an intermediate reflux. A third part is expanded in the valve f, completely evaporated in the heat exchanger E2 and passed via line 7 '' as an intermediate heater to the CO / CH₄ separation column T2. The separation column T2 works at a pressure of 3.1 bar, the head temperature being -180 ° C and the bottom temperature -157 ° C. From the separation column T2, CO with product purity is drawn off at the top via line 9 , heated in the heat exchangers E3 and E1 and fed to the compressor C2. The bottom product of the separation column T2, a CH₄-rich fraction, is added to line 6 via line 8 and expansion valve g. Part of the bottom product of the separation column T2 will give up after partial evaporation in the heat exchanger E3 via line 8 'of the separation column T2 as a heater.

With this procedure, an additional CO cycle is required for cooling. For this purpose, a partial stream is drawn off from the carbon monoxide product in line 12 on the pressure side of the compressor C2 via line 13 and cooled in the heat exchanger E1. This partial flow is now again divided into a first flow (line 14 ), which relaxes in the turbine X in a cold-performing manner and is then fed again via lines 14 'and 16 to the first stage of the compressor C1. A second stream is fed via line 15 into the heat exchanger E2, cooled in it and again divided into two partial streams. One of the partial streams is expanded in valve i and fed as a return via line 17 of the CO / CH₄ separation column T2. The other partial flow of the CO-rich product partial flow introduced via line 15 is expanded to approximately 1.8 bar in valve h and thus forms the peak cold for the process. It is fed to the heat exchangers E2 and E1 after its relaxation via line 16 , thereby evaporating in the heat exchanger E2 and heated in the heat exchanger E1, and then fed to the lowest compression stage C1.

Fig. 2 shows schematically a method for obtaining a high-purity carbon monoxide product stream and a hydrogen product stream by decomposing a CO₂-free H₂ / CO raw gas mixture from a partial oxidation process. Such a procedure makes sense for systems with a daily production of more than 5000 Nm³ / h CO. Such a process provides a carbon monoxide product stream with a so-called acetic acid unit, i.e. with at least 98.5% CO.

In contrast to the process described in FIG. 1, this embodiment of the process according to the invention has an additional separation column T3. The T3 separation column works at a pressure of 10.0 bar, the top temperature being -184 ° C and the bottom temperature being -164 ° C. The separating columns T1 and T2 work at pressures of 8.0 and 3.0 bar, the head temperatures being -185 ° C and -180 ° C and the bottom temperatures being -167 ° C and -163 ° C. The separation column T3 is the CO-rich condensate of the separator D2 via line 11 and Ent voltage valve b fed as a return. The H₂-rich fraction obtained at the top of the separation column T3 is relaxed in the valve k and added via line 18 to the H₂-rich fraction in line 6 . At the bottom of the separation column T3, a CO product is drawn off (line) via line 19 , expanded in valve 1 and, after evaporation and heating in the heat exchangers E2 and E1, leads to the lowest stage of the compressor C1 train. Part of the bottom fraction of the separation column T3 is partially evaporated in the heat exchanger E3 and given via line 19 'as a heater in the separation column T3. The cooling required for this process management is covered by line 21 be provided liquid nitrogen, which is heated and evaporated in the heat exchangers E2 and E1 in indirect heat exchange with processes to be cooled and evaporated.

The two tables 1 and 2 below give examples of temperatures, pressures and compositions of the gas mixtures in the lines with the reference numerals in FIGS. 1 and 2.

Table 1 ( Fig. 1)

Table 2 ( Fig. 2)

Claims (6)

1. A process for the production of a high-purity carbon monoxide product stream and a hydrogen product stream by decomposing a largely dry and CO₂-free H₂ / CO raw gas mixture by means of one-stage partial condensation and subsequent low-temperature fractionation of the CO-rich condensate formed in the partial condensation, thereby characterized in that the gaseous H₂-enriched, CO-containing fraction formed in the partial condensation is separated in a membrane separation unit into a hydrogen product stream and into a H₂-poor, CO-containing fraction and the H₂-poor, CO-containing fraction the cryogenic fractionation is fed to recover the carbon monoxide still contained in it. 2. The method according to claim 1, characterized in that the gaseous gases formed in the partial condensation H₂-enriched, CO-containing fraction before being fed into the membrane separation unit in indirect heat exchange with process streams to be cooled is heated.   3. The method according to claims 1 or 2, characterized records that the membrane separation unit cascaded out sets is. 4. The method according to any one of claims 1 to 3, characterized records that from the membrane separation unit in the deep temperature fractionation, low-H₂, CO-containing Partial condensing fraction, which in the partial Condensation formed gaseous H₂-enriched Frak tion removed from the process, the CO-rich condensate this partial condensation together with the CO-rich Condensate upstream of the membrane separation unit partial condensation in a first separation column from Hydrogen and in a second column of methane freed and a highly pure from the head of the second column Carbon monoxide product stream is withdrawn. 5. The method according to any one of claims 1 to 3, characterized records that from the membrane separation unit in the deep temperature fractionation, low-H₂, CO-containing Partial condensing fraction, which in the partial Condensation formed gaseous H₂-enriched Frak tion removed from the process, the CO-rich condensate this partial condensation in a separation column from It frees hydrogen and that from the top of this column deducted high-purity carbon monoxide fraction in the Cryogenic fractionation obtained high purity Carbon monoxide product stream is added. 6. The method according to any one of claims 4 or 5, characterized ge indicates that the or in the low-temperature fracture tionation obtained carbon monoxide product streams before their Delivery in indirect heat exchange with process to be cooled flow heated and / or one or more stages be sealed.