Method for methanol synthesis

Abstract

In a process for methanol production from synthesis gas, which comprises the steps of providing a make-up gas containing hydrogen and carbon monoxide, in which the content of carbon dioxide is less than 0.1 mole %, mixing the make-up gas with a hydrogen-rich recycle gas and passing the gas mixture to a methanol synthesis reactor, optionally via a sulfur guard, and subjecting the effluent from the synthesis reactor to a separation step, thereby providing crude methanol and the hydrogen-rich recycle gas, the customary addition of carbon dioxide to the make-up gas is replaced by addition of water in an amount of 0.1 to 5 mole %. This way, a CO.sub.2 compressor is saved, and the amount of poisonous sulfur in the make-up gas is markedly reduced.

Claims

1. A process for methanol production from synthesis gas, said process comprising the following steps: providing a make-up gas containing hydrogen and carbon monoxide, in which the content of carbon dioxide is less than 0.1 mole %, mixing the make-up gas with a hydrogen-rich recycle gas and passing the gas mixture to a methanol synthesis reactor, optionally via a sulfur guard, and subjecting the effluent from the synthesis reactor to a separation step, thereby providing crude methanol and the hydrogen-rich recycle gas, wherein the customary addition of carbon dioxide to the make-up gas is replaced by addition of water to the make-up gas in an amount to obtain a water content of 0.1 to 5 mole % in the make-up gas which is mixed with the hydrogen-rich recycle gas and passed to the methanol synthesis reactor.

2. Process according to claim 1, wherein the amount of added water corresponds to a content of 0.5 to 2.5 mole % in the make-up gas.

3. Process according to claim 2, wherein the amount of added water corresponds to a content of 0.8 to 1.2 mole % in the make-up gas.

Description

EXAMPLE 1

(1) This example shows the impact of the MUG composition on the synthesis loop performance in the base case: 29% CO, 67% H.sub.2, 3% N.sub.2 and 1% CH.sub.4; no CO.sub.2 and no H.sub.2O in the MUG.

(2) The following results were found:

(3) TABLE-US-00001 Recycle ratio 2.799 Steam production 3.535 kg/h BWR MeOH production 272.795 MTPD LPS MeOH production 163.873 MTPD HPS MeOH production 178.042 MTPD Water content in crude MeOH 0.82 wt % Carbon loop efficiency 11.33% Carbon BWR reactor efficiency 5.07% MUG 1.454 Nm.sup.3/h Recycle 4.069 Nm.sup.3/h Flash 80.410 Nm.sup.3/h Purge 1.281 Nm.sup.3/h Total purge 1.282 Nm.sup.3/h

(4) Gas compositions, measured as recycle gas composition (RGC), converter inlet gas composition (CIGC) and converter outlet gas composition (COGC) were as follows:

(5) TABLE-US-00002 RGC CIGC COGC H.sub.2, mole % 66.69 66.77 66.06 CO, mole % 28.04 28.29 27.78 CO.sub.2, mole % 0.126 0.093 0.13 N.sub.2, mole % 3.400 3.295 3.37 CH.sub.4, mole % 1.132 1.097 1.12

(6) Data for the boiling water reactor (BWR):

(7) TABLE-US-00003 Space-time yield, kg MeOH/kg catalyst/h 0.210 BWR inlet bed pressure, kg/cm.sup.2 .Math. g 81.475 BWR outlet bed pressure, kg/cm.sup.2 .Math. g 79.475 Pressure drop, kg/cm.sup.2 2.00 Number of tubes 4405 Total catalyst mass, kg 5.412 Duty of BWR, MW 2.449

(8) Temperatures:

(9) TABLE-US-00004 BWR temperature, ? C. 230 Approach temperature to MeOH equilibrium, ? C. 179.35 BWR inlet temperature, ? C. 208.00 BWR outlet temperature, ? C. 233.55 Maximum catalyst temperature (hot spot) , ? C. 233.91

EXAMPLE 2

(10) This example shows the impact of the MUG composition on the synthesis loop performance in case 2: 1 mole % CO.sub.2 and no H.sub.2O in the MUG.

(11) The following results were found:

(12) TABLE-US-00005 Recycle ratio 2.987 Steam production 6.123 kg/h BWR MeOH production 1.479 MTPD LPS MeOH production 1.383 MTPD HPS MeOH production 1.426 MTPD Water content in crude MeOH 1.525 wt % Carbon loop efficiency 95.58% Carbon BWR reactor efficiency 62.62% MUG 1.454 Nm.sup.3/h Recycle 4.342 Nm.sup.3/h Flash 654.137 Nm.sup.3/h Purge 2.176 Nm.sup.3/h Total purge 2.241 Nm.sup.3/h

(13) Gas compositions, measured as RGC, CIGC and COGC were as follows:

(14) TABLE-US-00006 RGC CIGC COGC H.sub.2, mole % 67.86 67.65 62.16 CO, mole % 4.952 10.73 4.54 CO.sub.2, mole % 1.191 1.143 1.12 N.sub.2, mole % 19.334 15.237 17.72 CH.sub.4, mole % 6.044 4.779 5.56

(15) Data for the boiling water reactor (BWR):

(16) TABLE-US-00007 Space-time yield, kg MeOH/kg catalyst/h 1.139 BWR inlet bed pressure, kg/cm.sup.2 .Math. g 81.475 BWR outlet bed pressure, kg/cm.sup.2 .Math. g 79.475 Pressure drop, kg/cm.sup.2 2.00 Number of tubes 4405 Total catalyst mass, kg 5.412 Duty of BWR, MW 42.449

(17) Temperatures:

(18) TABLE-US-00008 BWR temperature, ? C. 230 Approach temperature to MeOH equilibrium, ? C. 49.67 BWR inlet temperature, ? C. 208.00 BWR outlet temperature, ? C. 240.95 Maximum catalyst temperature (hot spot) , ? C. 247.85

EXAMPLE 3

(19) This example shows the impact of the MUG composition on the synthesis loop performance in case 3: No CO.sub.2 and 1 mole % H.sub.2O in the MUG.

(20) The following results were found:

(21) TABLE-US-00009 Recycle ratio 3.175 Steam production 5.886 kg/h BWR MeOH production 1.429 MTPD LPS MeOH production 1.326 MTPD HPS MeOH production 1.366 MTPD Water content in crude MeOH 1.606 wt % Carbon loop efficiency 94.96% Carbon BWR reactor efficiency 61.69% MUG 1.454 Nm.sup.3/h Recycle 4.617 Nm.sup.3/h Flash 594.468 Nm.sup.3/h Purge 2.677 Nm.sup.3/h Total purge 2.737 Nm.sup.3/h

(22) Gas compositions, measured as RGC, CIGC and COGC were as follows:

(23) TABLE-US-00010 RGC CIGC COGC H.sub.2, mole % 72.71 71.35 67.20 CO, mole % 4.815 10.37 4.45 CO.sub.2, mole % 0.996 0.757 0.94 N.sub.2, mole % 15.838 12.763 14.64 CH.sub.4, mole % 5.019 4.057 4.65

(24) Data for the boiling water reactor (BWR):

(25) TABLE-US-00011 Space-time yield, kg MeOH/kg catalyst/h 1.101 BWR inlet bed pressure, kg/cm.sup.2 .Math. g 81.475 BWR outlet bed pressure, kg/cm.sup.2 .Math. g 79.475 Pressure drop, kg/cm.sup.2 2.00 Number of tubes 4405 Total catalyst mass, kg 5.412 Duty of BWR, MW 40.778

(26) Temperatures:

(27) TABLE-US-00012 BWR temperature, ? C. 230 Approach temperature to MeOH equilibrium, ? C. 58.97 BWR inlet temperature, ? C. 208.00 BWR outlet temperature, ? C. 240.70 Maximum catalyst temperature (hot spot), ? C. 245.90

EXAMPLE 4

(28) This example shows the impact of the MUG composition on the synthesis loop performance in case 4: No CO.sub.2 and 2 mole % H.sub.2O in the MUG.

(29) The following results were found:

(30) TABLE-US-00013 Recycle ratio 3.339 Steam production 5.813 kg/h BWR MeOH production 1.408 MTPD LPS MeOH production 1.303 MTPD HPS MeOH production 1.365 MTPD Water content in crude MeOH 3.523 wt % Carbon loop efficiency 96.75% Carbon BWR reactor efficiency 74.78% MUG 1.454 Nm.sup.3/h Recycle 4.854 Nm.sup.3/h Flash 538.024 Nm.sup.3/h Purge 2.773 Nm.sup.3/h Total purge 2.827 Nm.sup.3/h

(31) Gas compositions, measured as RGC, CIGC and COGC were as follows:

(32) TABLE-US-00014 RGC CIGC COGC H.sub.2, mole % 75.94 73.88 70.36 CO, mole % 2.098 7.84 1.95 CO.sub.2, mole % 1.121 0.863 1.06 N.sub.2, mole % 15.341 12.497 14.22 CH.sub.4, mole % 4.894 3.997 4.55

(33) Data for the boiling water reactor (BWR):

(34) TABLE-US-00015 Space-time yield, kg MeOH/kg catalyst/h 1.084 BWR inlet bed pressure, kg/cm.sup.2 .Math. g 81.475 BWR outlet bed pressure, kg/cm.sup.2 .Math. g 79.475 Pressure drop, kg/cm.sup.2 2.00 Number of tubes 4405 Total catalyst mass, kg 5.412 Duty of BWR, MW 40.270

(35) Temperatures:

(36) TABLE-US-00016 BWR temperature, ? C. 230 Approach temperature to MeOH equilibrium, ? C. 44.05 BWR inlet temperature, ? C. 208.00 BWR outlet temperature, ? C. 237.36 Maximum catalyst temperature (hot spot), ? C. 246.67