# US 2017/0283372 A1 · Process for producing high-purity aqueous urea solution in urea production process > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0283372 A1 - Document ID: US20170283372A1 - Status: Published application - Kind: A1 - Application number: 15/508,994 - Filed: 2015-08-27 - Published: 2017-10-05 - Earliest claimed: 2014-09-22 - Assignees: Toyo Engineering Corporation - Applicants: Toyo Engineering Corporation - Inventors: Haruyuki MORIKAWA; Shuhei NAKAMURA; Keishi SATO - Web page: https://patentgrep.com/patent/US20170283372A1 ## CPC - C07C 273/16: Separation; Purification - C07C 273/04: from carbon dioxide and ammonia - C07C 275/00: Derivatives of urea, i.e. compounds containing any of the groups [IMAGE cpc-sch-C07C-0967.gif], the nitrogen atoms not being part of nitro or nitroso groups - C07B 2200/13: Crystalline forms, e.g. polymorphs - C07C: ACYCLIC OR CARBOCYCLIC COMPOUNDS - C07B: GENERAL METHODS OF ORGANIC CHEMISTRY; APPARATUS THEREFOR (preparation of carboxylic acid esters by telomerisation C07C67/47; telomerisation C08F) ## Abstract The present invention relates to a method for producing a high-purity aqueous urea solution, utilizing a urea production process at least including a urea synthesis step of synthesizing urea from a raw material feed to produce a urea synthesis liquid, and a urea purification step of purifying the urea synthesis liquid to produce an aqueous urea solution with high urea concentration. The present invention includes a urea crystallization step of separating a part of the urea synthesis liquid and/or a part of the aqueous urea solution and crystallizing urea contained in the separated urea synthesis liquid and/or aqueous urea solution to produce solid crystal urea, and a mixing step of mixing the crystal urea with water to produce a high-purity aqueous urea solution. A high-purity aqueous urea solution to be produced is an aqueous urea solution with high purity suitable as a reducing agent for SCR. ## Claims ### Claim 1 A method for producing a high-purity aqueous urea solution in a urea production process, the process comprising at least a urea synthesis step for synthesizing urea from a raw material feed to produce a urea synthesis liquid and a urea purification step for purifying the urea synthesis liquid to produce an aqueous urea solution having high urea concentration, wherein the method further comprises: a urea crystallization step of separating a part of the urea synthesis liquid and/or a part of the aqueous urea solution, and crystallizing urea contained in a separated urea synthesis liquid and/or aqueous urea solution to produce crystal urea being a solid; and a mixing step of mixing the crystal urea with water to produce a high-purity aqueous urea solution. ### Claim 2 (depends on 1) The method for producing a high-purity aqueous urea solution according to claim 1, wherein the urea crystallization step comprises the steps of: crystallizing urea contained in the separated urea synthesis liquid and/or aqueous urea solution to produce slurry containing crystal urea; subjecting the slurry to solid-liquid separation into crystal urea and a mother liquid; and further optionally sending back a part of the mother liquid after the solid-liquid separation to the urea synthesis step. ### Claim 3 (depends on 1) The method for producing a high-purity aqueous urea solution according to claim 1, wherein conditions for concentrating the aqueous urea solution to generate the crystal urea in the urea crystallization step are 60 to 80 mmHg (abs.) in pressure and 50 to 80° C. in temperature. ### Claim 4 (depends on 1) The method for producing a high-purity aqueous urea solution according to claim 1, wherein: the urea production process further comprises a urea concentrating step of concentrating the aqueous urea solution produced in the urea purification step to increase urea concentration in the aqueous urea solution; and the urea crystallization step separates and crystallizes a part of an aqueous urea solution between the urea purification step and the urea concentrating step and/or a part of an aqueous urea solution in the urea concentrating step. ### Claim 5 (depends on 1) The method for producing a high-purity aqueous urea solution according to claim 1, wherein the urea production process comprises a finishing step of producing solid granular urea from a concentrated aqueous urea solution. ### Claim 6 (depends on 2) The method for producing a high-purity aqueous urea solution according to claim 2, wherein conditions for concentrating the aqueous urea solution to generate the crystal urea in the urea crystallization step are 60 to 80 mmHg (abs.) in pressure and 50 to 80° C. in temperature. ### Claim 7 (depends on 2) The method for producing a high-purity aqueous urea solution according to claim 2, wherein: the urea production process further comprises a urea concentrating step of concentrating the aqueous urea solution produced in the urea purification step to increase urea concentration in the aqueous urea solution; and the urea crystallization step separates and crystallizes a part of an aqueous urea solution between the urea purification step and the urea concentrating step and/or a part of an aqueous urea solution in the urea concentrating step. ### Claim 8 (depends on 3) The method for producing a high-purity aqueous urea solution according to claim 3, wherein: the urea production process further comprises a urea concentrating step of concentrating the aqueous urea solution produced in the urea purification step to increase urea concentration in the aqueous urea solution; and the urea crystallization step separates and crystallizes a part of an aqueous urea solution between the urea purification step and the urea concentrating step and/or a part of an aqueous urea solution in the urea concentrating step. ### Claim 9 (depends on 2) The method for producing a high-purity aqueous urea solution according to claim 2, wherein the urea production process comprises a finishing step of producing solid granular urea from a concentrated aqueous urea solution. ### Claim 10 (depends on 3) The method for producing a high-purity aqueous urea solution according to claim 3, wherein the urea production process comprises a finishing step of producing solid granular urea from a concentrated aqueous urea solution. ### Claim 11 (depends on 4) The method for producing a high-purity aqueous urea solution according to claim 4, wherein the urea production process comprises a finishing step of producing solid granular urea from a concentrated aqueous urea solution.