Process for producing ammonia and urea
Disclosed is a process for the production of ammonia comprising a step wherein synthesis gas is formed by catalytic partial oxidation. Also disclosed is a process of producing urea, wherein ammonia is formed in a process involving a step of catalytic partial oxidation, and carbon dioxide formed in the same process is reacted with said ammonia so as to form urea.
1. A process for the production of urea, comprising the steps of
(a) providing a hydrocarbon material;
(b) subjecting the hydrocarbon material to catalytic partial oxidation (CPO) by reaction with an oxygen-containing gas stream in a CPO reactor so as to produce a synthesis gas comprising carbon monoxide, hydrogen and carbon dioxide;
wherein said catalytic partial oxidation is a short contact time catalytic partial oxidation, conducted under a space velocity of 100,000 to 250,000 hr −1 ;
(c) subjecting the synthesis gas to a water gas shift reaction so as to react carbon monoxide with water to form a gas mixture comprising hydrogen and carbon dioxide;
(d) recovering CO 2 from the gas mixture of (c), so as to obtain said recovered CO 2 and a gas mixture enriched in hydrogen;
(e) purifying hydrogen from said gas mixture enriched in hydrogen using a pressure swing absorber, to yield a pure hydrogen stream and a purge gas stream; and
(f) reacting the hydrogen of (e) with nitrogen under ammonia-forming conditions so as to produce ammonia; and
(g) combining the ammonia produced in (f) with the recovered CO 2 from (d) to produce urea; and
wherein air supplied to a single air separation unit provides the oxygen-containing gas stream used in the catalytic partial oxidation and the nitrogen used in the ammonia-forming reaction; and
wherein the entire purge gas stream is recycled to the CPO reactor.
2. A process according to claim 1 , wherein the space velocity is 100,000 to 200,000 hr −1 .
3. A process according to claim 1 , wherein the oxygen-containing gas stream in (b) comprises at least 40% v/v oxygen.
4. A process according to claim 1 , wherein the oxygen-containing gas stream in (b) comprises at least 90%-100% v/v oxygen.
5. A process according to claim 1 comprising further purifying hydrogen by methanation of CO and CO 2 .
6. A process according to claim 1 , wherein the hydrocarbon material is selected from the group consisting of natural gas, Liquefied Petroleum Gas (LPG), refinery gas, naphtha, and mixtures thereof.
7. A process according to claim 1 , wherein the oxygen to carbon ratio in the catalytic partial oxidation is between 0.3 and 0.7.
8. A process according to claim 1 , wherein the synthesis gas obtained from the catalytic partial oxidation has a temperature between about 900° C. and 1200° C.
9. The process of claim 3 wherein the oxygen-containing gas stream comprises at least 60% v/v oxygen.
10. The process of claim 1 , wherein the steam-to-carbon (S/C), oxygen-to-carbon (O 2 /C) ratio and preheating temperatures of the streams to the CPO reactor are adjusted so that the amount of CO 2 produced in the synthesis gas is sufficiently high to use all of the ammonia produced in (f) without any additional ammonia or excess ammonia to produce urea in step (g).
11. The process of claim 10 , wherein the S/C is 0.4-0.6, the O 2 /C is 0.5-0.7.