PROCESS FOR METHANOL PRODUCTION

Abstract

A process for the synthesis of methanol from an input stream of synthesis gas, comprising the following steps: subjecting a portion of said input stream as feed stream to an adiabatic reactive step, providing an effluent containing methanol and unreacted synthesis gas; quenching of said effluent with a further portion of said input stream, providing a quenched stream; subjecting said quenched stream to an isothermal reactive step, providing a methanol-containing product stream.

Claims

1. A process for the synthesis of methanol from an input stream of synthesis gas, comprising the following steps: subjecting a portion of said input stream as feed stream to an adiabatic reactive step, providing an effluent containing methanol and unreacted synthesis gas; quenching of said effluent with a further portion of said input stream, providing a quenched stream; subjecting said quenched stream to an isothermal reactive step, providing a methanol-containing product stream.

2. The process according to claim 1, wherein the feed stream to said adiabatic reactive step comprises a fraction of said input stream which has been pre-heated by acting as a cooling medium of said isothermal reactive step, thus forming a pre-heated stream.

3. The process according to claim 2, wherein said pre-heated stream mixes with a further fraction of said input stream to form the feed stream to said adiabatic reactive step, said further fraction being directly sent to said adiabatic reactive step.

4. The process according to claim 2, wherein said isothermal reactive step is carried out in a catalytic bed comprising heat exchange bodies and said fraction acting as a cooling medium traverses said heat exchange bodies.

5. The process according to claim 1, wherein said input stream is obtained by pre-heating at least a portion of a stream of synthesis gas by indirect heat exchange with said methanol-containing product stream.

6. The process according to claim 1, which is suitable to be performed on a small scale.

7. A reactor system for the synthesis of methanol from an input stream of synthesis gas, comprising: an adiabatic catalytic zone, receiving a portion of said input stream as feed stream, and providing an effluent containing methanol and unreacted synthesis gas; a quench line of a further portion of said input stream which mixes with said effluent, providing a quenched stream; an isothermal catalytic zone, receiving said quenched stream and providing a methanol-containing product stream.

8. The reactor system according to claim 7, said isothermal catalytic zone comprising a catalytic bed and heat exchange bodies immersed in the catalytic bed, said bodies being preferably plates.

9. The reactor system according to claim 8, wherein said feed stream to the adiabatic catalytic zone comprises a stream of pre-heated synthesis gas and said reactor system comprises a line for feeding a fraction of said input stream into said heat exchange bodies to act as a cooling medium, thus providing said stream of pre-heated synthesis gas.

10. The reactor system according to claim 9, wherein said feed stream to the adiabatic catalytic zone comprises a further fraction of synthesis gas which is directly sent to the adiabatic zone and said reactor system comprises a line for mixing said further fraction with said stream of pre-heated synthesis gas.

11. The reactor system according to claim 7, wherein said input stream is obtained by pre-heating at least a portion of a stream of synthesis gas and said reactor system comprises a heat exchanger receiving the methanol-containing product stream as heating medium to pre-heat said at least a portion of said stream of synthesis gas and provide said input stream.

12. The Process reactor according to claim 7, wherein said adiabatic zone comprises a single catalytic bed.

13. The reactor system according to claim 7, wherein said adiabatic zone and said isothermal zone are comprised in separate reaction vessels.

14. The reactor system according to claim 13, wherein the quench line of said further portion of the input stream is injected into the effluent of the adiabatic catalytic zone outside said separate vessels.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG. 1 illustrates a simplified scheme of a reactor system according to a first embodiment of the invention.

[0049] FIG. 2 illustrates a simplified scheme of a reactor system according to a second embodiment of the invention.

[0050] FIG. 3 illustrates a simplified scheme of a reactor system according to a third embodiment of the invention.

DETAILED DESCRIPTION

[0051] FIG. 1 shows a reactor system 100 for the synthesis of methanol from an input stream 1 of synthesis gas. Said input stream 1 is the effluent of a front-end section (not shown).

[0052] Said system 100 comprises a first adiabatic reactor 101 and a second isothermal reactor 102. Said first and second reactors are placed in two separate vessels. Said isothermal reactor 102 contains heat exchange plates 104 immersed in a catalytic bed 105.

[0053] Said input stream 1 of synthesis gas is split into two portions, namely a first portion 1a and a second portion 1b. Said portions 1a and 1b have the same composition, but may have different flow rates.

[0054] Said second portion 1b is used as cooling medium in the heat exchange plates 104 of the isothermal reactor 102, thus removing heat from the catalytic bed 105 and providing a stream 2 of preheated synthesis gas.

[0055] Said stream 2 of preheated synthesis gas is fed into the first adiabatic reactor 101, where partially reacts to provide an effluent stream 3 of partially reacted gas, containing methanol and unreacted synthesis gas. In said reactor 101, the temperature raises and the reaction equilibrium is rapidly reached.

[0056] Said effluent stream 3, after leaving the reactor 101, mixes with the first portion 1a of synthesis gas. Said portion 1a of synthesis gas has a lower temperature than the effluent stream 3, thus providing a stream 4 with decreased temperature and increased concentration of synthesis gas, which results in a shift of the reaction equilibrium towards rights in the subsequent isothermal reactor 102. Said first portion 1a of synthesis gas is also referred to as quench stream.

[0057] Said input stream 4 enters said isothermal reactor 102, wherein synthesis gas is further converted to methanol providing a methanol-containing product stream 5. As already described above, the heat generated during the isothermal reactive step is directly removed by the second portion 1b of synthesis gas traversing the heat exchange plates 104 immersed in the catalytic bed 105.

[0058] According to the embodiment shown in FIG. 2, the reactor system 100 comprises a heat exchanger 103, besides said first adiabatic reactor 101 and said second isothermal reactor 102.

[0059] Preferably, said input stream 1 is obtained by partially heating the effluent 10 of the front-end section (not shown). In greater detail, a portion 10a of the effluent 10 is heated in said heat exchanger 103 by heat-exchange with the methanol-containing stream 5 leaving the isothermal reactor 102 providing a pre-heated stream 10c, while the remaining portion 10b bypasses the heat exchanger 103 and merges with said pre-heated portion 10c forming the input stream 1 of synthesis gas.

[0060] Said input stream 1 of synthesis gas is split into a first portion 1a, as in the above embodiment of FIG. 1, and a second portion 1c.

[0061] Said second portion 1c forms the input stream to the first adiabatic reactor 101, where partially reacts to provide the effluent stream 3 containing methanol and unreacted synthesis gas. Said effluent stream 3 is subsequently mixed with the first portion 1a of synthesis gas having lower temperature, resulting in an input stream 4 to the isothermal reactor 102. Said input stream 4 enters the isothermal reactor 102, wherein synthesis gas is further converted to methanol forming a methanol-containing product stream 5, which is used as heating medium in the heat exchanger 103 providing a methanol-containing stream 6 with decreased temperature. Said stream 6 is subsequently subjected to purification in a suitable purification section (not shown).

[0062] According to this embodiment, the heat generated in the catalytic bed 105 of the isothermal reactor 102 is directly removed by a suitable cooling medium 7, e.g. water, traversing the heat exchange plates 104 immersed in the catalytic bed 105.

[0063] FIG. 3 illustrates an embodiment which is a combination of FIGS. 1 and 2, wherein the input stream 1 of synthesis gas is divided into three fractions, namely a first fraction 1a, a second fraction 1b and a third fraction 1c.

[0064] Said second fraction 1b is used as cooling medium in the heat exchange plates 104 of the isothermal reactor 102, thus removing heat from the catalytic bed 105 and providing a stream 2 of preheated synthesis gas.

[0065] Said stream 2 of preheated synthesis gas is mixed with the third fraction 1c of synthesis gas to form the input stream 8 to the adiabatic reactor 101. The third fraction 1c has lower temperature than the stream 2 and their mixing allows to finely regulate the inlet temperature to the adiabatic reactor 101. Said third fraction 1c is also referred to as cold-shot stream.

[0066] Said input stream 8 partially reacts in said adiabatic reactor 101 to provide an output stream 3 containing methanol and unreacted synthesis gas.

[0067] Said effluent stream 3 is subsequently mixed with the first fraction 1a of synthesis gas having lower temperature, resulting in an input stream 4 to the isothermal reactor 102. As a consequence, said stream 4 has a decreased temperature and an increased concentration of synthesis gas, resulting in a shift of the reaction equilibrium towards rights. Said first fraction la is also referred to as quench stream.

[0068] Said input stream 4 enters said isothermal reactor 102, wherein synthesis gas is further converted to methanol providing the methanol-containing stream 5. As already described above, the heat generated is directly removed by the second fraction 1b of synthesis gas traversing the heat exchange plates 104 immersed in the catalytic bed 105.

[0069] As in the embodiment of FIG. 2, the output stream 5 of the isothermal reactor 102 is used to pre-heat the portion 10a of the effluent 10 of the front-end section in the above mentioned heat exchanger 103, while the remaining portion 10b bypasses the heat exchanger 103 and merges with said pre-heated portion 10c forming the input stream 1 of synthesis gas.

[0070] The presence of said heat exchanger 103 is advantageous because allows to modulate the temperatures of the fractions 1a, 1b, 1c of synthesis gas.