Urea synthesis

Claim 2

The process of claim 1, wherein the amount of a NH3 reactor feed stream substantially free of ammonium carbamate and which is usually charged to the reactor separately from the carbamate recycle stream, is such that the molar ratio of said ammonia reactor feed stream to the net amount of urea formed in said reactor, is lower than the molar ratio of the total ammonia present in said reactor as ammonium carbamate, as net amount of urea formed and as ammonia, to the total C02 present in said reactor as ammonium carbamate, as C02 and as the net amount of urea formed.

Claim 3

The process of claim 1, wherein said urea reactor is operated at a temperature of from about 320* to about 430* F. and at a pressure of from about 1,500 psig to about 4,500 psig.

Claim 4

separating said urea from said gaseous product formed in (2),

Claim 5

charging fresh C02 feed and urea to said gaseous product separated in (3) and causing the resulting mixture to react to form an aqueous ammonium carbamate solution, the amount of said C02 charged to said gaseous product as a fresh feed being such that said solution contains from about 2.1 to about 3.6 molar proportions of NH3 as ammonium carbamate and free NH3 per molar proportion of C02 as ammonium carbamate and free C02 therein, and the amount of urea charged to said gaseous product being such that said solution contains from about 0.1 to about 10 parts by weight of urea, per part by weight of total C02 as ammonium carbamate and free C02, the pressure of (2) and (4) being from about 10 psia to about 670 psia, and

Claim 6

The process for forming urea, which comprises:

Claim 7

recycling said solution formed in (4) to said reactor.

Claim 8

The process of claim 4, wherein urea is charged to the first mixture in the form of an aqueous urea solution containing NH3 and ammonium carbamate.

Claim 9

The process of claim 4, wherein the heat of reaction of said C02 and NH3 to form ammonium carbamate is removed by indirect heat exchange with a urea reactor feed stream.

Claim 10

The process of claim 4, wherein the heat of reaction of said C02 and NH3 to form ammonium carbamate is removed by indirect heat exchange with an aqueous urea solution (i) containing ammonium carbamate and ammonia, whereby the latter ammonium carbamate is decomposed to NH3 and C02, NH3 and water are vaporized to gas, and the resulting gaseous phase (ii) is removed from the residual liquid phase comprising an aqueous urea solution (iii).

Claim 11

The process of claim 7, wherein the resulting gaseous phase (ii) constitutes said first mixture.

Claim 12

The process of claim 7, wherein the pressure of said first mixture is substantially equal to the pressure of said aqueous urea solution (i).

Claim 13

The process of claim 4, wherein the heat of reaction of said C02 and NH3 to form ammonium carbamate is removed by indirect heat exchange with an aqueous urea solution, said urea solution being concentrated by evaporation of water thereof.

Claim 14

The process of claim 4, wherein said gaseous mixture is condensed to a liquid and said fresh C02 feed and urea are charged thereto in (4).