Method of cooling a synthesis gas in a catalytic reactor

Abstract: Method of direct cooling synthesis gas in a catalytic reactor with one or more catalyst beds of a metal oxide catalyst being loaded on gas permeable partitions with distribution means, which method comprises admixing the synthesis gas during its passage through the reactor with a cooling gas being introduced into a mixing zone beneath each partition, wherein the mixing zones are obtained by passing a reducing gas through the catalyst bed, so that the catalyst volume shrinks during reduction of the catalyst particles, and, thereby, providing necessary cavities for the mixing zones beneath each partition.

Description: The present invention relates to a method of cooling a synthesis gas in catalytic reactions. In particular, the invention is concerned with cooling of synthesis gas in exothermic conversion processes by a cooling gas, which is added to the synthesis gas during its passage through the reactor. Catalytic processes are usually carried out in a reactor with one or more beds of catalyst particles. A large number of those processes proceed exothermically with considerable heat generation. It is necessary to remove heat evolving during the catalytic reactions at least from parts of the catalyst bed in order to maintain a desired conversion rate and to avoid destruction of the catalyst. This is conventionally carried out by indirect cooling of the reacting synthesis gas through heat exchange with a cooling medium or by direct cooling with introduction of a cooling gas, usually fresh synthesis gas, into the catalyst bed through distribution aggregates. In many reactors, the catalyst is arranged as a continuous bed in the reactor, and cooling gas is distributed within the catalyst bed. The known methods of direct cooling of reacting synthesis gas disadvantageously demand expensive reaction volume to provide necessary space for distributing or admixing cooling gas and synthesis gas between or within the catalyst beds. When introducing cooling gas directly within the catalyst bed, the stream of cooling gas is poorly distributed within the bed resulting in local flow variations and varying mixing ratios of cooling gas and synthesis gas. Further drawback of conventional designed reactors is poor utilization of the expensive pressure shell, high pressure drop, and formation of by-products because of disintegration of the catalyst particles and insufficient cooling of parts of the catalyst bed. It is, therefore, often desired to revamp conventional designed reactors employing direct cooling of synthesis gas, to avoid the above problems and to obtain higher production capacity. It has been found that the problems and disadvantages of conventionally cooled reactors may be avoided when utilizing shrinkage of the catalyst volume occurring during activation of many catalyst types, leading to cavities formed in the activated catalyst. Those cavities may conventionally be utilized for introduction and admixing of cooling gas in the residual gas stream without wasting expensive reactor volume. Shrinkage of the catalyst volume occurs when reducing metal oxide components in the catalyst particles by contact with reducing gas, which is passed through the reactor during activation of the catalyst. This invention provides a method of direct cooling of synthesis gas in a catalytic reactor with one or more catalyst beds of a metal oxide catalyst, characterized by the steps of (a) passing a reducing gas being rich in hydrogen and/or carbon monoxide through the metal oxide catalyst beds, wherein the catalyst being loaded between gas permeable partitions without a space between the beds, thereby reducing the metal oxide catalyst to its metallic form, the metallic form having a smaller volume than the metal oxide, whereby the total volume of each catalyst bed between the partitions shrinks, leaving a void volume beneath each partition, said volume constituting a mixing zone; and (b) admixing the synthesis gas during its passage through the reactor with a cooling gas, the cooling gas being introduced into the mixing zone beneath each partition. In practice, the invention is carried out by arranging within a reactor one or more partitions connected or provided with gas distribution and mixing aggregates, and loading the space between the partitions with non-activated catalyst particles. After the catalyst particles are loaded, reducing gas of e.g. mixtures of hydrogen and nitrogen is passed through the catalyst beds. Thereby, metal oxides in the catalyst are reduced to their metallic form, which causes the catalyst volume to shrink. The invention is particularly useful in the performance of cooled exothermic processes, being catalyzed by the above catalyst types, and, in particular, catalytic synthesis of methanol by exothermic conversion of carbon oxides and hydrogen in contact with a metal oxide catalyst usually consisting of zinc oxide, copper oxide, chromium oxide and aluminium oxide. These metal oxides shrink up to 20 volume per cent during activation of the catalyst by reduction of the metal oxides. The invention may further be used with catalysts, which show no or only minor shrinkage during activation as described above. Those catalysts are mixed with or provided with separately arranged particles, which shrink or otherwise being removed from the catalyst bed during activation without being catalytic active in the subsequent synthesis process.

Claims: Method of direct cooling of synthesis gas in a catalytic reactor with one or more catalyst beds of a metal oxide catalyst, characterized by the steps of (a) passing a reducing gas being rich in hydrogen and/or carbon monoxide through the metal oxide catalyst beds, wherein the catalyst being loaded between gas permeable partitions without a space between the beds, thereby reducing the metal oxide catalyst to its metallic form, the metallic form having a smaller volume than the metal oxide, whereby the total volume of each catalyst bed between the partitions shrinks, leaving a void volume beneath each partition, said volume constituting a mixing zone; and (b) admixing the synthesis gas during its passage through the reactor with a cooling gas, the cooling gas being introduced into the mixing zone beneath each partition. The method of claim 1, wherein the cooling gas is fresh synthesis gas. The method of claim 1 and 2, wherein the synthesis gas comprises carbon oxides and hydrogen for use in preparation of methanol. The method of claim 1, wherein the mixing zones being provided by including particles in the catalyst beds, which particles shrink or being removed during passage of the reducing gas through the catalyst beds. Method of providing mixing zones for a cooling gas and synthesis gas in a gas cooled catalytic reactor having one or more catalyst beds of a metal oxide catalyst loaded between gaspermeable partitions being equipped with means for distribution of the cooling gas into the mixing zones, which method comprises, passing a reducing gas being rich in hydrogen and/or carbonmonoxide through the catalyst beds prior to passage of the synthesis gas and cooling gas, reducing the metal oxide catalyst to its metallic form having a minor volume than the metal oxide, so that the total volume of each catalyst bed between the partition shrinks leaving void volume for the mixing zone downstream each partition.

Inventors: TOPSOE HALDOR FREDERIK AXEL, TOPSOE, HALDOR FREDERIK AXEL
Applicants: TOPSOE HALDOR AS, HALDOR TOPSOE A/S
Application year: 1993
Main classification: B01J8
IPC codes: C07B61, C07C31, B01J37, B01J8, C07C29