Process and a plant for the production of methanol

Abstract

A process for the production of methanol from synthesis gas via an equilibrium reaction is conducted in a methanol pre-converter within a certain operational window, said operational window being defined by the area below an approximately linear curve of the partial pressure of carbon monoxide vs. the boiling water temperature for water temperatures between 210 and 270° C. Methanol of different product grades may be obtained by operating in specific areas of the operational window.

Claims

1. A process for the production of methanol from synthesis gas via an equilibrium reaction proceeding at elevated temperatures under elevated pressure according to the synthesis reactions
CO+2H.sub.2.Math.CH.sub.3OH+heat  (1)
CO.sub.2+3H.sub.2.Math.CH.sub.3OH+H.sub.2O+heat  (2)
CO+H.sub.2O.Math.CO.sub.2+H.sub.2+heat  (3) in the presence of a catalyst, said process being conducted in a methanol pre-converter within an operational window, said operational window being defined by the area below an approximately linear curve of the partial pressure of carbon monoxide vs. the boiling water temperature for water temperatures from 210 to 270° C., where the partial pressure of carbon monoxide increases from 20 kg/cm.sup.2 at 210° C. to 32.5 kg/cm.sup.2 at 270° C., and divided into two areas by an estimated by-product curve of the partial pressure of carbon monoxide vs. the boiling water temperature, said areas leading to the production of methanol of different product qualities.

2. Process according to claim 1, which is conducted in an area within the operational window to the left of and below the by-product curve, which indicates the upper limit for obtaining grade AA methanol or methanol of similar quality.

3. Process according to claim 1, which is conducted in an area within the operational window to the right of and above the by-product curve, where the methanol product is a more byproduct-containing methanol product which is still pure enough to be a fuel grade or methanol-to-olefins (MTO) grade methanol.

4. Process according to claim 1, wherein the catalyst is a Cu/ZnO-based catalyst.

5. A plant for the production of methanol by the process according to claim 1, said plant comprising a make-up gas compressor and a synthesis reactor in a methanol loop, wherein a once-through pre-converter is installed between the make-up gas compressor and the methanol loop, said pre-converter operating within the operational window defined by the area below the approximately linear, dashed curve of the partial pressure of carbon monoxide vs. the boiling water temperature for water temperatures from 210 to 270° C., where the partial pressure of carbon monoxide increases from 20 kg/cm.sup.2 at 210° C. to 32.5 kg/cm.sup.2 at 270° C.

6. A plant for the production of methanol by the process according to claim 2, said plant comprising a make-up gas compressor and a synthesis reactor in a methanol loop, wherein a once-through pre-converter is installed between the make-up gas compressor and the methanol loop, said pre-converter operating within the operational window defined by the area below the approximately linear, dashed curve of the partial pressure of carbon monoxide vs. the boiling water temperature for water temperatures from 210 to 270° C., where the partial pressure of carbon monoxide increases from 20 kg/cm.sup.2 at 210° C. to 32.5 kg/cm.sup.2 at 270° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in more detail with reference to the figures, where

(2) FIG. 1 shows the operational window to be used in the process according to the invention,

(3) FIG. 2 shows an embodiment of the pre-converter concept according to the invention, and

(4) FIG. 3 shows an alternative embodiment of the pre-converter concept according to the invention.

DETAILED DESCRIPTION

(5) In FIG. 1, the operational window to be used in the process according to the invention is defined by the area below the approximately linear, dashed curve (the deactivation curve) of the partial pressure of carbon monoxide vs. the boiling water temperature for water temperatures from 210 to 270° C., where the partial pressure of carbon monoxide increases from 20 kg/cm.sup.2 at 210° C. to 32.5 kg/cm.sup.2 at 270° C.

(6) As already mentioned, it is possible to obtain different methanol grades within the operational window depending on the combination of partial pressure of CO and boiling water temperature. In FIG. 1, the solid curve (the byproduct curve) indicates the upper limit for obtaining grade AA methanol or methanol of similar high quality. Operating above the curve will move the methanol product into a more byproduct-containing methanol product which is, however, pure enough to be counted as fuel grade or methanol-to-olefins (MTO) grade methanol.

(7) Furthermore, the dashed deactivation curve depicts the limit for catalyst deactivation. Operating above the curve will lead to a fast deactivation of the catalyst.

(8) In FIG. 2, compressed make-up synthesis gas 1 (compressor not shown) is heated in the feed/effluent heat exchanger (hex1) before it enters the pre-converter (A). After being passed through the pre-converter, the gas 2 is cooled in the feed/effluent heat exchanger (hex1) and sent to a condenser c1, optionally sent to another condenser c2 as stream 9. As much as possible of the methanol is condensed in condenser c1 before the two-phase flow is separated in a first separator (s1). The gas 3 from the separator (s1) is then mixed with the gas 4 from a second separator (s2) or optionally sent directly downstream the recirculator (R) as stream 5.

(9) After mixing, the gas is compressed in said recirculator (R). The resulting feed gas 6 to the reactor (B) is pre-heated in the feed/effluent heat exchanger (hex2) before it enters the reactor (B).

(10) The outgoing gas 7 is cooled in the feed/effluent heat exchanger (hex2) prior to being cooled as much as possible in condenser c2 in order to condense as much methanol as possible. Then the two-phase flow is separated in the second separator (s2).

(11) A small amount 8 of the gas from the separator (s2) is sent to purge to avoid build-up of inert constituents. The rest of the gas flow from the separator (s2) is mixed with the gas from the separator (s1). Finally, the liquids from the two separators (s1) and (s2) are mixed, and the mixture is sent to a low pressure separator before being sent out of the methanol section.

(12) FIG. 3 shows another embodiment, different from the one shown in FIG. 2. Here, the make-up synthesis gas (1′) is compressed (compressor not shown), and the compressed gas is mixed with part of the recycled gas from the recirculator R′ and heated in the feed/effluent heat exchanger (hex1′) before it enters the pre-converter (A′). After passing through the pre-converter, the gas 2′ is cooled in the feed/effluent heat exchanger (hex1′). Then the cooled gas from the pre-converter (A′) is mixed with cooled gas from the reactor (B′). After the mixing, the two-phase flow is cooled further in condenser c1′ to condense as much methanol as possible.

(13) When the gas has cooled as much as possible, the two-phase flow is separated in a separator (s1′). Some of the outgoing gas from the separator is sent to purge to avoid build-up of inert constituents. The rest of the gas is sent to the recirculator R′ and used as feed gas to the reactor (B′). The feed gas to reactor (B′) is heated in the feed/effluent heat exchanger (hex2′) before it enters the reactor. After reactor (B′), the gas is cooled in the feed/effluent heat exchanger (hex2′) and mixed with cooled gas from the pre-converter (A′).

(14) Optionally, the cooled gas from the pre-converter (A′) is fed to another condenser c2′ to condense as much methanol as possible. After the gas has cooled, the two-phase flow is separated in another separator (s2′), from where the gas phase is sent to the inlet of the recirculator R′, while the liquid phase is mixed with the liquid phase from separator s1′.

(15) The fresh make-up gas is very reactive towards formation of by-products. A lower catalyst temperature compared to the existing reactor can therefore be foreseen; hence the additional cooling system.