Method for preparation of methanol

Abstract

To provide a method for preparation of methanol using the recycle of unconverted gas for maximum use of synthesis gas used in methanol synthesis.SOLUTION: A method for the preparation of methanol comprises conversion of a mixture of fresh methanol synthesis gas and unconverted methanol synthesis separated from produced methanol in a low-pressure separator and recycled and admixed with the fresh synthesis gas upstream of the suction side of a make-up gas compressor.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to the production of methanol by conversion of synthesis gas to methanol. In particular, the present invention is a process for the production of methanol by conversion of a mixture of fresh methanol synthesis gas and unconverted methanol synthesis gas separated from the produced methanol in a low pressure separator, recycled and mixed with said fresh synthesis gas upstream of the discharge side of a make-up compressor.

[0002] The process of the present invention avoids valuable unconverted synthesis gas, which in known production processes is typically purged to the atmosphere or used as fuel. [Background technology]

[0003] Methanol syngas is any gas composition that contains hydrogen and carbon dioxide and / or carbon monoxide. Methanol syngas is typically described in terms of its modulus, i.e., M=(H2-CO2) / (CO+CO2). Syngas is balanced with respect to the methanol reaction when the modulus is equal to 2.

[0004] Heterogeneous methanol synthesis is carried out in today's practice by reacting carbon oxides with hydrogen in the presence of a copper-based catalyst according to the following equation: 3H2+CO2=CH3OH+H2O (1) 2H2+CO =CH3OH (2)

[0005] The methanol synthesis catalyst also has the ability to react with water gas shift (WGS) reactions, i.e. CO + H2O = CO2 + H2 (3) and the reverse water gas shift (RWGS) reaction, i.e. CO2+H2=CO +H2O (4) catalyzes. Summary of the Invention [Problem to be solved by the invention]

[0006] The synthesis gas used for methanol synthesis can be derived from natural gas by steam-methane reforming, optionally followed by an oxy-fuel secondary reformer, or by autothermal reforming alone. [Means for solving the problem]

[0007] To obtain maximum utilization of the synthesis gas produced, it is necessary to recycle a portion of the unconverted gas contained in the methanol reactor effluent, which is cooled and separated from the liquid methanol product in a high pressure separator prior to recycling.

[0008] Further separation of the unconverted synthesis gas from the produced methanol is achieved in a low pressure separator.

[0009] The standard solution is to deliver the gas from the synthesis section by passing it through a purge gas line from a low pressure separator. The pressure in the low pressure separator is typically around 4 bar g.

[0010] Usually, recycling the unconverted syngas from the low pressure separator is not as successful because the pressure of the separated gas is much lower than the pressure of the fresh syngas upstream of the make-up compressor, which is about 28 bar g.

[0011] If the pressure of the gas to the make-up gas compressor is low, i.e., lower than the pressure in the low pressure separator, gas from the low pressure separator can be recycled to the suction side of the make-up gas compressor and added to the existing make-up gas.

[0012] Accordingly, the present invention provides a method for producing methanol from a synthesis gas comprising hydrogen and carbon dioxide, comprising the following steps: (a) mixing fresh methanol synthesis gas with unconverted methanol synthesis gas recovered from a downstream low pressure separator, passing the synthesis gas mixture to the suction side of a make-up gas compressor, and pressurizing the synthesis gas mixture; (b) introducing the pressurized synthesis gas mixture into one or more methanol reaction stages for conversion in the presence of a methanol catalyst; (c) recovering a reaction effluent from step (b) comprising methanol and unconverted synthesis gas; (d) cooling the reaction effluent below the dew point of methanol; (e) separating a portion of the methanol from a portion of the unconverted synthesis gas in a high pressure separator, and recycling the portion of the unconverted synthesis gas through a recycle compressor to the discharge side of the makeup compressor; (f) separating a further portion of the methanol from a further portion of the unconverted synthesis gas in a low pressure separator; (g) recycling at least a portion of the unconverted synthesis gas from step (f) to step (a) upstream of the suction side of the make-up gas compressor; Including, The process wherein the pressure of the fresh synthesis gas in step (a) is lower than the pressure of the unconverted synthesis gas recovered from the low pressure separator in step (f).

[0013] In one embodiment of the invention, the synthesis gas mixture further comprises carbon monoxide.

[0014] In a further embodiment of the invention, a portion of the unconverted synthesis gas separated in the high pressure separator is passed to a purge gas scrubber and liquid from said purge gas scrubber is passed to a low pressure separator.

[0015] The advantages and effects of the present invention are: reducing the module M of the synthesis gas passed to the methanol synthesis stage, making said gas more optimal for methanol production; The aim is to conserve the produced methanol that would otherwise be lost in purging the gas separated in the low pressure separator.

[0016] This can be exploited in several ways, namely: Feed material flow conservation: Saving of feed material while maintaining power input and production output; Power Savings: Savings in compressed power input while maintaining feed material flow and production output. Increased Production: Obtain increased production output while maintaining feed material flows and power inputs.

Claims

1. 1. A method for producing methanol from a synthesis gas comprising hydrogen and carbon dioxide, comprising the steps of: (a) mixing fresh methanol synthesis gas with unconverted methanol synthesis gas recovered from the low pressure separator and passing the synthesis gas mixture to the suction side of a make-up gas compressor to pressurize the synthesis gas mixture; (b) introducing the pressurized synthesis gas mixture into one or more methanol reaction stages for conversion in the presence of a methanol catalyst; (c) recovering a reaction effluent from step (b) comprising methanol and unconverted synthesis gas; (d) cooling the reaction effluent below the dew point of methanol; (e) separating a portion of the methanol from a portion of the unconverted synthesis gas in a high pressure separator, and recycling the portion of the unconverted synthesis gas through a recycle compressor to the discharge side of the makeup compressor; (f) separating a further portion of the methanol from a further portion of the unconverted synthesis gas in a low pressure separator; (g) recycling at least a portion of the unconverted synthesis gas from step (f) to step (a) upstream of the suction side of the make-up gas compressor; Including, the pressure of the fresh synthesis gas in step (a) is lower than the pressure of the unconverted synthesis gas recovered from the low pressure separator in step (f); The method.

2. The method of claim 1 , wherein the synthesis gas mixture further comprises carbon monoxide.

3. 3. The process of claim 1 or 2, wherein a portion of the unconverted synthesis gas separated in the high pressure separator is passed to a purge gas scrubber and liquid from said purge gas scrubber is passed to a low pressure separator.