Integrated process for the production of formaldehyde-stabilised urea

Patent metadata

Field	Value
Publication number	US-10550076-B2
Application number	US-201616062748-A
Country	US
Kind code	B2
Filing date	Nov 28, 2016
Priority date	Dec 18, 2015
Publication date	Feb 4, 2020
Grant date	Feb 4, 2020

Abstract

A process for producing formaldehyde-stabilised urea is described comprising generating a synthesis gas, subjecting the synthesis gas to water-gas shift to form a shifted gas; recovering carbon dioxide from the shifted gas; synthesising methanol from the carbon dioxide-depleted synthesis gas; subjecting recovered methanol to oxidation; subjecting the methanol synthesis off-gas to methanation; synthesising ammonia from the ammonia synthesis gas and recovering the ammonia; reacting ammonia and recovered carbon dioxide stream to form a urea stream; and stabilising the urea by mixing the urea stream and a stabiliser prepared using the recovered formaldehyde, wherein a portion of the synthesis gas by-passes either the one or more of the water-gas shift reactors, carbon dioxide removal unit, or water-gas shift reactors and the carbon dioxide removal unit used in the process.

First claim

The invention claimed is:

1. A process for producing formaldehyde-stabilised urea comprising the steps of:
(A) generating a synthesis gas comprising hydrogen, nitrogen, carbon monoxide, carbon dioxide and steam in a synthesis gas generation unit;
(B) subjecting the synthesis gas to one or more stages of water-gas shift in one or more water-gas shift reactors to form a shifted gas;
(C) recovering carbon dioxide from the shifted gas in a carbon dioxide removal unit to form a carbon dioxide-depleted synthesis gas;
(D) passing the carbon dioxide-depleted synthesis gas through a methanol synthesis unit to synthesize a crude methanol and recovering the crude methanol and a methanol synthesis off-gas stream comprising nitrogen, hydrogen and residual carbon monoxide;
(E) oxidizing at least a portion of the recovered crude methanol with air in a formaldehyde production unit to produce an oxidised gas containing formaldehyde and a formaldehyde vent gas, the crude methanol having been adjusted to have a water content in a range of from 5 wt % to 20 wt %;
(F) methanating the methanol synthesis off-gas in a methanation reactor containing a methanation catalyst to form an ammonia synthesis gas;
(G) synthesising ammonia from the ammonia synthesis gas in an ammonia production unit and recovering the ammonia;
(H) reacting a portion of the ammonia and at least a portion of the recovered carbon dioxide in a urea production unit to form a urea stream; and
(I) stabilising the urea by mixing the urea stream and a stabiliser prepared using formaldehyde recovered from the formaldehyde production unit,
wherein:
(i) a portion of the synthesis gas generated by the synthesis gas generation unit by-passes
(a) one or more water-gas shift reactors; or
(b) one or more water-gas shift reactors and the carbon dioxide removal unit; or

(ii) a portion of the shifted gas by-passes the carbon dioxide removal unit; and
wherein the crude methanol recovered from step (D) is fed to oxidizing step (E).

2. The process according to claim 1 wherein the synthesis gas is generated by steam reforming a hydrocarbon or gasifying a carbonaceous feedstock.

3. The process according to claim 1 , wherein the synthesis gas is generated from a hydrocarbon by adiabatic pre-reforming, primary reforming in a fired or gas-heated steam reformer and secondary or autothermal reforming with air or oxygen-enriched air, or a combination thereof.

4. The process according to claim 3 , wherein a portion of the hydrocarbon by-passes the primary fired or gas-heated steam reformer.

5. The process according to claim 1 , further comprising compressing and dividing a source of air into a first portion that is provided to the formaldehyde production unit of step (E) for oxidizing methanol and a second portion that is further compressed and provided to the synthesis gas generation unit of step (A).

6. The process according to claim 1 , wherein the one or more stages of water-gas shift of step (B) comprise one or more stages of high temperature shift, low temperature shift, medium temperature shift, isothermal shift, or sour shift.

7. The process according to claim 1 , wherein the one or more stages of water-gas shift in step (B) consists of a high temperature shift reactor and a low temperature shift reactor and the portion of the synthesis gas by-passes either the high temperature shift reactor, or both the high temperature shift reactor and the low temperature shift reactor, or a portion of a high-temperature shifted gas by-passes the low temperature shift reactor.

8. The process according to claim 1 , wherein carbon dioxide is removed in step (C) using absorption or adsorption.

9. The process according to claim 1 , wherein the methanol synthesis of step (D) is performed on a once-through basis, or on a recycle basis wherein unreacted gases, after methanol condensate removal, are returned to the methanol synthesis unit.

10. The process according to claim 1 , wherein the methanol synthesis unit of step (D) is operated in a single stage at an inlet temperature in the range of from 200-320° C.

11. The process according to claim 1 , wherein the formaldehyde production unit of step (E) comprises an oxidation reactor containing a bed of oxidation catalyst.

12. The process according to claim 1 , wherein the formaldehyde production unit of step (E) generates a formaldehyde vent gas which is directly recycled or recycled after one or more stages of vent gas treatment in a vent-gas treatment unit.

13. The process according to claim 12 , wherein the vent gas treatment unit comprises a gas-liquid separator that separates a nitrogen-rich off-gas from liquid methanol.

14. The process according to claim 12 , wherein the formaldehyde vent gas is recycled to the methanol synthesis step (D) either directly without treatment or indirectly after first passing to an emission control unit comprising a catalytic combustor to convert the vent stream into carbon dioxide, nitrogen and steam.

15. The process according to claim 12 , wherein the formaldehyde vent gas is recycled to the carbon dioxide removal step (C) either directly without treatment or indirectly after first passing to an emission control unit comprising a catalytic combustor to convert the vent stream into carbon dioxide, nitrogen and steam.

16. The process according to claim 12 , wherein the formaldehyde vent gas is recycled to the urea synthesis stage after it has first passed to an emission control unit comprising a catalytic combustor to convert the vent stream into carbon dioxide, nitrogen and steam.

17. The process according to claim 12 , wherein the formaldehyde vent gas is recycled directly to a synthesis gas generation unit comprising the synthesis gas.

18. The process according to claim 1 , wherein the one or more stages of water-gas shift of step (B) comprise a single stage of high temperature shift, a combination of high temperature shift and low temperature shift, a single stage of medium temperature shift, or a combination of medium temperature shift and low temperature shift.

19. The process according to claim 1 , wherein (i) a portion of the synthesis gas generated by the synthesis gas generation unit by-passes (a) one or more water-gas shift reactors.

20. The process according to claim 1 , wherein (i) a portion of the synthesis gas generated by the synthesis gas generation unit by-passes (b) one or more water-gas shift reactors and the carbon dioxide removal unit.

21. The process according to claim 1 , wherein (ii) a portion of the shifted gas by-passes the carbon dioxide removal unit.

Assignees

• Johnson Matthey Plc

Inventors

• Erlandsson Ola
• Magnusson Andreas Erik Johan
• Mcfarlane Kate
• Pach John David
• Sheldon Daniel Thomas
• Ward Darren

Classifications

• C07C273/04 Primary

  from carbon dioxide and ammonia · CPC title

• C01C1/0405

  from N2 and H2 in presence of a catalyst · CPC title

• C07C273/14 Primary

  Separation; Purification; Stabilisation; Use of additives · CPC title

• C07C1/0405

  Apparatus · CPC title

• C07C29/1516

  Multisteps · CPC title