PROCESS AND APPARATUS FOR REMOVAL OF METAL CARBONYLS FROM A GAS MIXTURE

Abstract

The invention relates to a process for removal of metal carbonyl from a gas mixture. The gas mixture is subjected to a gas scrubbing in an absorber with methanol as the physical scrubbing liquid to obtain the laden methanol. The metals of the metal carbonyls are at least partially precipitated from the laden methanol as metal sulfides to obtain a first suspension comprising metal sulfides and at least a proportion of the laden methanol. The first suspension is sent to a treatment vessel and therein brought into direct contact with water vapor in countercurrent to obtain a second suspension comprising at least water, methanol and metal sulfides and a gaseous product. The second suspension and the gaseous product are withdrawn from the treatment vessel as separate streams.

Claims

1.-19. (canceled)

20. A process for removal of metal carbonyls from a gas mixture in which the gas mixture is subjected to a gas scrubbing in an absorber with methanol as the physical scrubbing liquid to obtain laden methanol and in which the metals of the metal carbonyls are at least partially precipitated from the laden methanol as metal sulfides to obtain a first suspension which comprises the metal sulfides and at least a proportion of the laden methanol and the first suspension is sent to a treatment vessel, wherein the first suspension is brought into direct contact with water vapor in countercurrent in the treatment vessel to obtain a second suspension comprising at least water, methanol and metal sulfides and a gaseous product and the second suspension and the gaseous product are withdrawn from the treatment vessel as separate streams.

21. The process according to claim 20, wherein the first suspension comprising a proportion of the laden methanol is sent to the treatment vessel and the remainder of the laden methanol is sent to a regeneration.

22. The process according to claim 20, wherein the gaseous product comprises a mixture of hydrogen sulfide (H.sub.2S) and methanol vapor.

23. The process according to claim 22, wherein methanol is condensed out of the methanol vapor of the gaseous product and the remaining hydrogen sulfide (H.sub.2S) is sent to a Claus plant for further processing.

24. The process according to claim 20, wherein the gaseous product is withdrawn from a top region of the treatment vessel and/or the second suspension is withdrawn from a bottom region of the treatment vessel.

25. The process according to claim 20, wherein the second suspension is supplied to a distillation to obtain substantially pure methanol as the tops product and a mixture comprising substantially metal sulfides and water as the bottoms product.

26. The process according to claim 20, wherein the first suspension is supplied to the treatment vessel from at least one residence time vessel.

27. The process according to claim 20, wherein the first suspension is supplied to the treatment vessel from at least two separate residence time vessels.

28. The process according to claim 27, wherein the first suspension comprises substantially iron sulfides in a first of the at least two separate residence time vessels and the first suspension comprises substantially nickel sulfides in a second of the at least two separate residence time vessels.

29. The process according to claim 28, wherein a feed from the first residence time vessel to the treatment vessel is arranged above a feed from the second residence time vessel to the treatment vessel.

30. The process according to claim 20, wherein the precipitation of the metal sulfides from the metal carbonyls present in the laden methanol is brought about by desorption of carbon monoxide (CO) from the laden methanol and/or by temperature elevation of the laden methanol.

31. The process according to claim 30, wherein the desorption of the carbon monoxide (CO) is carried out in a decompression vessel by decompression (flashing) of the laden methanol.

32. The process according to claim 31 wherein after the decompression the laden methanol is supplied to the at least one residence time vessel to form the first suspension in the at least one residence time vessel.

33. The process according to claim 20, wherein the water vapor is supplied to the treatment vessel in a lower region of the treatment vessel.

34. The process according to claim 20, wherein the gas mixture comprises a synthesis gas, wherein the synthesis gas comprises as constituents at least hydrogen (H.sub.2), carbon monoxide (CO), carbon dioxide (CO.sub.2), hydrogen sulfide (H.sub.2S) and metal carbonyls.

35. An apparatus for removal of metal carbonyls from a gas mixture in which the gas mixture is subjected to a gas scrubbing with methanol as a physical scrubbing liquid and in which the metals of the metal carbonyls are at least partially precipitable from laden methanol as metal sulfides, comprising the following constituents in fluid communication with one another: a treatment vessel comprising a means for supplying steam to the treatment vessel and a means for supplying a first suspension comprising laden methanol and metal sulfides to the treatment vessel, wherein the means for supplying the steam and the means for supplying the first suspension are arranged such that the steam and the first suspension are movable with respect to one another in countercurrent and in direct contact with mass transfer inside the treatment vessel; a means for withdrawing a gaseous product from the treatment vessel; a means for withdrawing a second suspension comprising water, methanol and metal sulfides from the treatment vessel.

36. The apparatus according to claim 35, further comprising at least one residence time vessel in communication with the means for supplying the first suspension to the treatment vessel, wherein the residence time vessel comprises a reaction and settling zone for precipitating the metal sulfides from the metal carbonyls in which the first suspension is producible.

37. The apparatus according to claim 36, further comprising at least two separate residence time vessels and separate means for supplying the first suspension to the treatment vessel which are in communication with the respective residence time vessels, wherein a first suspension comprising substantially iron sulfides is producible in a first residence time vessel and a first suspension comprising substantially nickel sulfides is producible in a second residence time vessel, wherein the separate means for supplying the first suspension to the treatment vessel comprise a first and a second means for supplying the first suspension to the treatment vessel, wherein the first suspension comprising substantially iron sulfides is suppliable to the treatment vessel via the first means and the first suspension comprising substantially nickel sulfides is suppliable to the treatment vessel via the second means, wherein the first means for supplying the treatment vessel is arranged above the second means.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The invention is more particularly elucidated hereinbelow by way of examples without in any way limiting the subject matter of the invention. Further features, advantages and possible applications of the invention will be apparent from the following description of the working examples in connection with the drawings.

[0073] FIG. 1 shows a schematic diagram of a first exemplary embodiment of the process according to the invention/of the apparatus according to the invention,

[0074] FIG. 2 shows a schematic diagram of a second exemplary embodiment of the process according to the invention/of the apparatus according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0075] FIG. 1 is a schematic diagram of a process flow 1/an apparatus 1 for use in a plant for gas scrubbing of crude synthesis gases with methanol as the scrubbing medium according to a first working example of the invention.

[0076] Via conduit 100 an absorption column 101 is supplied at a pressure of 40 bar with a crude synthesis gas mixture containing at least the components hydrogen (H.sub.2) and carbon monoxide (CO) as desired components and metal carbonyls, hydrogen sulfide (H.sub.2S) and carbon dioxide (CO.sub.2) as components to be removed. In the top region of the absorption column 101 regenerated methanol is applied via the liquid distributor 102 and flows down the absorption column in finely divided form to absorb undesired constituents from the crude synthesis gas. The crude synthesis gas traverses the absorption column 101 from bottom to top to be depleted of undesired constituents such as H.sub.2S and CO.sub.2 by absorption in methanol. Purified synthesis gas exits the absorption column via conduit 114. In the bottom region 103 the methanol laden inter alia with H.sub.2S is withdrawn from the absorption column 101 via conduit 104, warmed in an indirect heat exchanger 105 and via conduit 106 and expansion valve 107 decompressed into the decompression vessel 108 to a pressure of 12 bar. The decompression gas released upward also contains CO and thus, on account of the equilibrium shift in the equilibrium reaction, metal carbonyls present in the laden methanol are converted into metal sulfides by the H.sub.2S present in the laden methanol. To amplify the stripping of CO nitrogen is supplied as a stripping gas via the conduit 109. The gases withdrawn via the conduit 110 are recompressed to 40 bar via the compressor 111, supplied via conduit 112 to the indirect heat exchanger 105 for cooling and subsequently as a recycle gas stream, via conduit 113, combined with the crude synthesis gas stream in conduit 100. The methanol at least partially freed of CO in the decompression vessel 108 is sent via conduit 115 to an indirect heat exchanger 116 and warmed before being sent via conduit 117 to the residence time vessel 118.

[0077] Formation of metal sulfides from the metal carbonyls is favored by stripping of CO in the decompression vessel 108 and additional warming of the laden methanol in the indirect heat exchanger 116. The residence time vessel 118 has a reaction zone and a settling zone. The laden methanol is passed through the reaction zone for as long as required for complete precipitation of the metal sulfides. The precipitated metal sulfides then pass into the settling zone which as illustrated in the example of the residence time vessel 118 is configured as a conical bottom in which the metal sulfides and a proportion of the laden methanol accumulate as the first suspension. The larger part of the laden methanol, i.e. the supernatant containing only a small proportion of sulfides, if any, is withdrawn from the residence time vessel via conduit 119 and sent to column 120 for hot regeneration. The sulfide sludge, the first suspension containing the smaller part of the laden methanol and metal sulfides, is supplied via conduit 121 to treatment vessel 122 at a pressure of 10 bar and a temperature of 90° C. The first suspension traverses the treatment vessel 122 from top to bottom after application via port 123. Treatment vessel 122 is simultaneously supplied via conduit 124 with water vapor at a pressure of 8 bar and a temperature of 283° C. Water vapor traverses treatment vessel 122 from bottom to top so that the first suspension and the water vapor are in direct contact in countercurrent, thus allowing mass transfer and heat exchange between the water vapor and the first suspension. Due to the mass transfer and heat exchange between the first suspension and the water vapor the metal sulfides pass into the aqueous phase, i.e. are “transprecipitated” into the aqueous phase and therein form larger agglomerates which have a stronger sedimentation propensity than metal sulfides of the methanolic suspension (first suspension). Water vapor from conduit 124 is used to strip hydrogen sulfide from the laden methanol supplied via conduit 121. The stripped hydrogen sulfide exits treatment vessel 122 via conduit 125 as a gaseous product.

[0078] The internals in vessel 122 and column 129 indicated in the figure are to be understood as being merely schematic. Based on their knowledge of the art or based on routine experiments those skilled in the art will be able to select internals which not only ensure satisfactory mass transfer between the phases involved but also enable passage of a suspension without an excessive propensity for blockage.

[0079] In addition to hydrogen sulfide the gaseous product in conduit 125 also contains vaporous methanol obtained on account of the heat transfer of the water vapor to the laden methanol of the first suspension. Gaseous product in conduit 125 which has a pressure of 6.5 bar and a temperature of 129° C. is subsequently subjected to a multistage process for removal by condensation of the vaporous methanol (not shown). The obtained product comprising primarily hydrogen sulfide, also referred to as Claus gas, is subsequently sent to a Claus plant for production of sulfur.

[0080] At a pressure of 7 bar and a temperature of 143° C. the second suspension comprising water, methanol and metal sulfides is sent from the bottom region 126 of the treatment vessel 122 via conduit 127 to a rectification column 129 using pump 128. A thermal removal of the methanol from the second suspension is carried out in rectification column 129. Obtained as the bottoms product is a sulfide sludge composed of metal sulfides and water which is withdrawn via conduit 130 and sent for disposal. Withdrawn at the top of the rectification column 129 is methanol which is sent via conduit 131 to the column 120 for hot regeneration. The gases obtained in the hot regeneration are withdrawn via conduit 133 and worked up similarly to the gaseous product withdrawn in conduit 125. Hot regenerated methanol exits column 120 via conduit 131 and after cooling in the indirect heat exchanger 132 is sent to the absorption column 101 for reabsorption of undesired constituents of the crude synthesis gas FIG. 2 is a schematic diagram of a process flow 2/an apparatus 2 for use in a plant for gas scrubbing of crude synthesis gases with methanol as the scrubbing medium according to a second working example of the invention.

[0081] Via the conduit 200 an absorption column 201 is supplied at a pressure of 40 bar with a crude synthesis gas mixture containing at least the components hydrogen (H.sub.2) and carbon monoxide (CO) as desired components and metal carbonyls, hydrogen sulfide (H.sub.2S) and carbon dioxide (CO.sub.2) as components to be removed. In the top region of the absorption column 201 regenerated methanol is applied via conduit 244 and liquid distributor 202 and falls down the absorption column 201 in finely divided form to absorb undesired constituents from the crude synthesis gas. The crude synthesis gas traverses the absorption column 201 from bottom to top. Purified synthesis gas exits the absorption column via conduit 203.

[0082] Absorption column 201 comprises at least a so-called prewash region and a region for desulfurization. The lower prewash region serves primarily for removal of hydrogen cyanide (HCN), further trace constituents such as carbonyl sulfide (COS) and hydrogen sulfide (H.sub.2S). The upper region serves primarily for desulfurization, i.e. removal of hydrogen sulfide (H.sub.2S), and removal of carbon dioxide (CO.sub.2). Both regions are separated from one another by a gas-permeable chimney tray 214.

[0083] Withdrawn from the lower prewash region via conduit 204 is methanol laden primarily with H.sub.2S and HCN which on account of the metal carbonyl-specific better solubility of iron carbonyls compared to nickel carbonyls in methanol contains primarily iron carbonyls. The methanol laden primarily with H.sub.2S, HCN and iron carbonyls is warmed in the indirect heat exchanger 205 and via conduit 206 and expansion valve 207 decompressed into the decompression vessel 208 to a pressure of 12 bar. The decompression gas released also contains CO and thus, on account of the equilibrium shift of the equilibrium reaction, iron carbonyls present in the laden methanol are converted into iron sulfides by the H.sub.2S present in the laden methanol. To amplify the stripping of CO nitrogen is supplied as a stripping gas via the conduit 209. The gases withdrawn via conduit 210 are recompressed to 40 bar via compressor 211, supplied via conduit 212 to the indirect heat exchanger 205 for cooling and subsequently as a recycle gas stream, via conduit 213, combined with the crude synthesis gas stream in conduit 200. The methanol at least partially freed of CO in the decompression vessel 208 is sent via conduit 215 to an indirect heat exchanger 216, warmed in heat exchanger 216 and then sent via conduit 217 to the residence time vessel 218.

[0084] Withdrawn from the upper region of the absorption column 201 serving for desulfurization via conduit 219 is a methanol laden with H.sub.2S and CO.sub.2 which on account of the metal carbonyl-specific poorer solubility in methanol of nickel carbonyls compared to iron carbonyls contains primarily nickel carbonyls. The methanol laden primarily with H.sub.2S, CO.sub.2 and nickel carbonyls is warmed in the indirect heat exchanger 220 and via conduit 221 and expansion valve 222 decompressed into the decompression vessel 223 to a pressure of 12 bar. The decompression gas released also contains CO and thus, on account of the equilibrium shift, nickel carbonyls present in the laden methanol are converted into nickel sulfides by the H.sub.2S present in the laden methanol. To amplify the stripping of CO nitrogen is supplied as a stripping gas via conduit 224. The gases withdrawn via the conduit 225 are recompressed to 40 bar via compressor 226, supplied via conduit 227 to the indirect heat exchanger 220 for cooling and subsequently as a recycle gas stream, via conduit 228, combined with the crude synthesis gas stream in conduit 200. The methanol at least partially freed of CO in decompression vessel 223 is sent via conduit 229 to an indirect heat exchanger 230, warmed in heat exchanger 230 and then sent via conduit 231 to the residence time vessel 232.

[0085] Formation of iron or nickel sulfide from the respective metal carbonyls is favored by stripping of CO in the decompression vessels 208 and 223 and additional warming of the respective laden methanol in the indirect heat exchangers 216 and 230. Residence time vessels 218 and 232 each have a reaction zone and a settling zone. Laden methanol is passed through the reaction zone for as long as required for largely complete precipitation of the respective metal sulfide. The residence time is about 4 hours in the case of iron sulfide and about 50 minutes in the case of nickel sulfide. The precipitated metal sulfides then pass into the respective settling zones of the residence time vessels 218 and 232 which as shown in the example of FIG. 2 are configured as conical bottoms in which the respective metal sulfides and a proportion of the laden methanol accumulate as the first suspension. The larger part of the laden methanol, i.e. the supernatant containing only a very small proportion of metal sulfides, if any, is withdrawn from the residence time vessels 218, 232 via the conduits 233 and 234 and sent to a column for hot regeneration (not shown).

[0086] The sulfide sludge from the residence time vessel 218, i.e. the first suspension containing part of the laden methanol and in this case primarily iron sulfide, is supplied via conduit 235 to treatment vessel 240 at a pressure of 10 bar and a temperature of 90° C. The first suspension from residence time vessel 218 traverses the treatment vessel from top to bottom after application via port 241. The sulfide sludge from the residence time vessel 232, the first suspension containing part of the methanol and in this case primarily nickel sulfide, is simultaneously supplied via conduit 236 to treatment vessel 240 at a pressure of 10 bar and a temperature of 90° C.

[0087] The feed of the conduit 235 from the residence time vessel 218 to the treatment vessel 240 is arranged above the feed of the conduit 236 from the residence time vessel 232 to the treatment vessel 240. Based on the total amount of metal sulfides in the residence time vessel 218 the first suspension from residence time vessel 218 contains substantially iron sulfides. Based on the total amount of metal sulfides in the residence time vessel 232 the first suspension from residence time vessel 232 contains substantially nickel sulfides.

[0088] In addition to the supply of the first suspensions from the residence time vessels 218 and 232 treatment vessel 240 is supplied via conduit 237 with water vapor at a pressure of 8 bar and a temperature of 283° C. Water vapor traverses the treatment vessel from bottom to top so that the first suspensions from the residence time vessels 218, 232 and the water vapor are in direct contact in countercurrent, thus allowing mass transfer and heat exchange between the water vapor and the first suspensions.

[0089] Due to the mass transfer and heat exchange between the first suspensions and the water vapor the metal sulfides pass into the aqueous phase, i.e. are transprecipitated into the aqueous phase and therein form larger agglomerates which have a stronger sedimentation propensity than metal sulfides in methanolic suspension (first suspension).

[0090] The feed ports 241, 242 of the conduits 235 and 236 to the treatment vessel 240 are arranged such that the first suspension comprising substantially iron sulfide from residence time vessel 218 is in direct contact with water vapor from conduit 237 for longer than is the case for the first suspension comprising substantially nickel sulfide from residence time vessel 232. In the example shown the feed port of the conduit 235 is for this reason arranged above the feed port of the conduit 236 so that the port 241 is likewise arranged above the port 242. In terms of height arrangement the ports 241, 242 are the same level as the respective feeds of the conduits 235, 236.

[0091] Water vapor from conduit 237 is used to strip hydrogen sulfide from the laden methanol. Stripped hydrogen sulfide exits treatment vessel 240 via conduit 238. In addition to hydrogen sulfide the gaseous product in conduit 238 also contains vaporous methanol obtained on account of the heat transfer of the water vapor to the laden methanol of the first suspension. Gaseous product in conduit 238 which has a pressure of 6.5 bar and a temperature of 129° C. is subsequently subjected to a multistage process for removal by condensation of the vaporous methanol (not shown). The obtained product comprising primarily hydrogen sulfide, also referred to as Claus gas, may subsequently be sent to a Claus plant for production of sulfur.

[0092] At a pressure of 7 bar and a temperature of 143° C. the second suspension comprising water, methanol and metal sulfides is sent from the bottom region 243 of the treatment vessel 240 via conduit 239 to a rectification column (not shown) analogously to the example from FIG. 1. Analogously to the example according to FIG. 1 a thermal separation of the methanol from the second suspension is carried out in the rectification column. Obtained as the bottoms product is a sulfide sludge composed of metal sulfides and water which is withdrawn from the rectification column and sent for disposal. Workup of the tops product from the rectification is carried out analogously to the example according to FIG. 1. Hot regenerated methanol is finally supplied to the absorption column 201 via conduit 244 and liquid distributor 202 and reused for absorption of undesired constituents from crude synthesis gas.

[0093] Embodiments of the invention are described with reference to different types of subject matter. In particular, certain embodiments are described with reference to process claims while other embodiments are described with reference to apparatus claims. However, it will be apparent to a person skilled in the art from the description hereinabove and hereinbelow that unless otherwise stated in addition to any combination of features belonging to a type of subject matter any combination of features relating to different types of subject matter may also be contemplated. All features may be combined to achieve synergistic effects which go beyond simple summation of the technical features.

[0094] While the invention was represented and described in detail in the drawings and the preceding description, such representation and description shall be considered elucidatory or exemplary and non-limiting. The invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments may be understood and carried out by those skilled in the art of the field of the claimed invention through study of the drawings, the disclosure and the dependent claims.

[0095] In the claims the word “comprising” does not exclude further elements or steps and the indefinite article “a” does not exclude a plurality. Reference numerals in the claims should not be interpreted as limiting the scope of the claims.

LIST OF REFERENCE NUMERALS

[0096] 1, 2 Inventive process or apparatus [0097] 100 Conduit [0098] 101 Absorption column [0099] 102 Liquid distributor [0100] 103 Bottom region of the absorption column [0101] 104 Conduit [0102] 105 Indirect heat exchanger [0103] 106 Conduit [0104] 107 Expansion valve [0105] 108 Decompression vessel [0106] 109 Conduit [0107] 110 Conduit [0108] 111 Compressor [0109] 112 Conduit [0110] 113 Conduit [0111] 114 Conduit [0112] 115 Conduit [0113] 116 Indirect heat exchanger [0114] 117 Conduit [0115] 118 Residence time vessel [0116] 119 Conduit [0117] 120 Column for hot regeneration [0118] 121 Conduit [0119] 122 Treatment vessel [0120] 123 Port [0121] 124 Conduit [0122] 125 Conduit [0123] 126 Bottom region of treatment vessel [0124] 127 Conduit [0125] 128 Pump [0126] 129 Rectification column [0127] 130 Conduit [0128] 131 Conduit [0129] 132 Indirect heat exchanger [0130] 133 Conduit [0131] 200 Conduit [0132] 201 Absorption column [0133] 202 Liquid distributor [0134] 203 Conduit [0135] 204 Conduit [0136] 205 Indirect heat exchanger [0137] 206 Conduit [0138] 207 Expansion valve [0139] 208 Decompression vessel [0140] 209 Conduit [0141] 210 Conduit [0142] 211 Compressor [0143] 212 Conduit [0144] 213 Conduit [0145] 214 Chimney tray [0146] 215 Conduit [0147] 216 Indirect heat exchanger [0148] 217 Conduit [0149] 218 Residence time vessel [0150] 219 Conduit [0151] 220 Indirect heat exchanger [0152] 221 Conduit [0153] 222 Expansion valve [0154] 223 Decompression vessel [0155] 224 Conduit [0156] 225 Conduit [0157] 226 Compressor [0158] 227 Conduit [0159] 228 Conduit [0160] 229 Conduit [0161] 230 Indirect heat exchanger [0162] 231 Conduit [0163] 232 Residence time vessel [0164] 233 Conduit [0165] 234 Conduit [0166] 235 Conduit [0167] 236 Conduit [0168] 237 Conduit [0169] 238 Conduit [0170] 239 Conduit [0171] 240 Treatment vessel [0172] 241 Port [0173] 242 Port [0174] 243 Bottom region of treatment vessel [0175] 244 Conduit