JP2023111315A - Method for producing urea - Google Patents
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- JP2023111315A JP2023111315A JP2022013115A JP2022013115A JP2023111315A JP 2023111315 A JP2023111315 A JP 2023111315A JP 2022013115 A JP2022013115 A JP 2022013115A JP 2022013115 A JP2022013115 A JP 2022013115A JP 2023111315 A JP2023111315 A JP 2023111315A
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- urea
- sulfur
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- carbon monoxide
- gas
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- 239000004202 carbamide Substances 0.000 title claims abstract description 116
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 title claims abstract description 115
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 79
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 83
- 238000006243 chemical reaction Methods 0.000 claims abstract description 83
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims abstract description 75
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims abstract description 72
- 229910002091 carbon monoxide Inorganic materials 0.000 claims abstract description 72
- 239000011593 sulfur Substances 0.000 claims abstract description 63
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 62
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 40
- 229910021529 ammonia Inorganic materials 0.000 claims abstract description 37
- 239000007789 gas Substances 0.000 claims description 68
- 239000007864 aqueous solution Substances 0.000 claims description 44
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 claims description 22
- 235000019270 ammonium chloride Nutrition 0.000 claims description 7
- HYHCSLBZRBJJCH-UHFFFAOYSA-M sodium hydrosulfide Chemical compound [Na+].[SH-] HYHCSLBZRBJJCH-UHFFFAOYSA-M 0.000 claims description 7
- 238000002156 mixing Methods 0.000 claims description 6
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Inorganic materials S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 claims description 4
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 abstract description 53
- 229910000037 hydrogen sulfide Inorganic materials 0.000 abstract description 50
- 238000000034 method Methods 0.000 abstract description 27
- 235000001508 sulfur Nutrition 0.000 description 57
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 54
- 239000005077 polysulfide Substances 0.000 description 53
- 229920001021 polysulfide Polymers 0.000 description 53
- 150000008117 polysulfides Polymers 0.000 description 53
- 150000002500 ions Chemical class 0.000 description 51
- JJWKPURADFRFRB-UHFFFAOYSA-N carbonyl sulfide Chemical compound O=C=S JJWKPURADFRFRB-UHFFFAOYSA-N 0.000 description 40
- 229910002092 carbon dioxide Inorganic materials 0.000 description 27
- 239000001569 carbon dioxide Substances 0.000 description 24
- 238000002474 experimental method Methods 0.000 description 15
- 230000015572 biosynthetic process Effects 0.000 description 14
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 12
- 238000004364 calculation method Methods 0.000 description 12
- 238000005755 formation reaction Methods 0.000 description 12
- 239000001307 helium Substances 0.000 description 11
- 229910052734 helium Inorganic materials 0.000 description 11
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 11
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 10
- 235000011114 ammonium hydroxide Nutrition 0.000 description 10
- 239000006227 byproduct Substances 0.000 description 10
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 9
- 238000007254 oxidation reaction Methods 0.000 description 8
- -1 alkali metal salt Chemical class 0.000 description 7
- 238000004458 analytical method Methods 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 6
- 238000011088 calibration curve Methods 0.000 description 6
- MTHSVFCYNBDYFN-UHFFFAOYSA-N diethylene glycol Chemical compound OCCOCCO MTHSVFCYNBDYFN-UHFFFAOYSA-N 0.000 description 6
- 229910052757 nitrogen Inorganic materials 0.000 description 6
- 230000003647 oxidation Effects 0.000 description 6
- 238000003786 synthesis reaction Methods 0.000 description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 5
- 239000003153 chemical reaction reagent Substances 0.000 description 5
- FSEUPUDHEBLWJY-HWKANZROSA-N diacetylmonoxime Chemical compound CC(=O)C(\C)=N\O FSEUPUDHEBLWJY-HWKANZROSA-N 0.000 description 5
- 239000011521 glass Substances 0.000 description 5
- 238000002360 preparation method Methods 0.000 description 5
- 239000002994 raw material Substances 0.000 description 5
- 239000002904 solvent Substances 0.000 description 5
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 4
- 239000012159 carrier gas Substances 0.000 description 4
- 239000007806 chemical reaction intermediate Substances 0.000 description 4
- 239000003337 fertilizer Substances 0.000 description 4
- BRWIZMBXBAOCCF-UHFFFAOYSA-N hydrazinecarbothioamide Chemical compound NNC(N)=S BRWIZMBXBAOCCF-UHFFFAOYSA-N 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 239000007787 solid Substances 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- 238000011282 treatment Methods 0.000 description 4
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 3
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 3
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 3
- 230000004913 activation Effects 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 229920005549 butyl rubber Polymers 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 239000002803 fossil fuel Substances 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000011261 inert gas Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000003960 organic solvent Substances 0.000 description 3
- 230000001590 oxidative effect Effects 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- 230000035939 shock Effects 0.000 description 3
- 241000894007 species Species 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 231100000331 toxic Toxicity 0.000 description 3
- 230000002588 toxic effect Effects 0.000 description 3
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 2
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 2
- 238000002835 absorbance Methods 0.000 description 2
- 229910052783 alkali metal Inorganic materials 0.000 description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 239000003054 catalyst Substances 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- FBAFATDZDUQKNH-UHFFFAOYSA-M iron chloride Chemical compound [Cl-].[Fe] FBAFATDZDUQKNH-UHFFFAOYSA-M 0.000 description 2
- 239000012046 mixed solvent Substances 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 239000000618 nitrogen fertilizer Substances 0.000 description 2
- 239000007800 oxidant agent Substances 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 238000001536 pulsed discharge helium ionisation detection Methods 0.000 description 2
- 238000006722 reduction reaction Methods 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000012453 solvate Substances 0.000 description 2
- BFSVOASYOCHEOV-UHFFFAOYSA-N 2-diethylaminoethanol Chemical compound CCN(CC)CCO BFSVOASYOCHEOV-UHFFFAOYSA-N 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 239000012901 Milli-Q water Substances 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- PFRUBEOIWWEFOL-UHFFFAOYSA-N [N].[S] Chemical compound [N].[S] PFRUBEOIWWEFOL-UHFFFAOYSA-N 0.000 description 1
- 238000000862 absorption spectrum Methods 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 150000003863 ammonium salts Chemical class 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 230000005587 bubbling Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000021615 conjugation Effects 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 239000010779 crude oil Substances 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011067 equilibration Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000004868 gas analysis Methods 0.000 description 1
- 238000004817 gas chromatography Methods 0.000 description 1
- 150000004677 hydrates Chemical class 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 239000005457 ice water Substances 0.000 description 1
- 239000000543 intermediate Substances 0.000 description 1
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 229910052976 metal sulfide Inorganic materials 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 description 1
- 235000019345 sodium thiosulphate Nutrition 0.000 description 1
- 229910052815 sulfur oxide Inorganic materials 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000002371 ultraviolet--visible spectrum Methods 0.000 description 1
- 150000003672 ureas Chemical class 0.000 description 1
Landscapes
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
Description
本発明は、尿素の製造方法に関する。 The present invention relates to a method for producing urea.
尿素は世界中で最も多く使用されている窒素肥料である。国際肥料協会（International Fertilizer Association）が公表する統計によると、２０１９年に全世界で消費された尿素肥料は計５２３８万トン（窒素量換算）に上り、これは全窒素肥料消費量（１０７７２万トン；窒素量換算）の約半分を占めている。今後も人口増加による食料需要の拡大に伴い、尿素市場は数十年に渡って成長を続けると予想される。 Urea is the most widely used nitrogen fertilizer worldwide. According to statistics published by the International Fertilizer Association, the total amount of urea fertilizer consumed worldwide in 2019 was 52.38 million tons (nitrogen equivalent), which is equivalent to the total nitrogen fertilizer consumption (107.72 million tons). ; equivalent to nitrogen). It is expected that the urea market will continue to grow for several decades in the future as the demand for food expands due to population growth.
尿素は、一般的な工業プロセスでは二酸化炭素とアンモニアとの反応により製造されている。この反応は定量的ではなく、また、高温高圧条件を必要とするため、エネルギー利用の効率化や未反応物の回収及び処理などについて、従来、改良が重ねられてきている。工業的に収率を上げるために多段階からなるサイクルシステムも用いられているが、エネルギー消費量が多く、大量の二酸化炭素を排出する。 Urea is produced by the reaction of carbon dioxide and ammonia in a common industrial process. Since this reaction is not quantitative and requires conditions of high temperature and high pressure, conventional efforts have been made to improve the efficiency of energy utilization and the recovery and disposal of unreacted substances. A multi-stage cycle system is also used to increase the industrial yield, but it consumes a lot of energy and emits a large amount of carbon dioxide.
尿素の製造のための別の方法として、特許文献１には、硫化カルボニルとアンモニアをメタノール中で混合し、０.１７～１.７ＭＰａ、４０～１４０℃で反応させる方法が開示されている。また、特許文献２では、アンモニア、一酸化炭素、及び硫黄を有機溶剤（メタノール、ジエチレングリコール、あるいはジエチルエタノールアミン）中で混合し、１.７～２．８ＭＰａ、９０～１１０℃で反応させ、尿素を製造する方法が開示されている。これらの方法は二酸化炭素とアンモニアを原料とする従来法と比較して、一回の反応で達成できる収率が高く、反応条件も穏やかでエネルギーコストが低い。 As another method for producing urea, Patent Document 1 discloses a method of mixing carbonyl sulfide and ammonia in methanol and reacting them at 0.17-1.7 MPa and 40-140°C. Further, in Patent Document 2, ammonia, carbon monoxide, and sulfur are mixed in an organic solvent (methanol, diethylene glycol, or diethylethanolamine), reacted at 1.7 to 2.8 MPa, 90 to 110 ° C., and urea is disclosed. Compared to conventional methods using carbon dioxide and ammonia as raw materials, these methods can achieve high yields in a single reaction, are mild in reaction conditions, and have low energy costs.
しかし、特許文献１又は特許文献２に記載の尿素の製造方法では、尿素と共に硫化水素が同モル量発生し、この方法の工業プロセスへの適用の妨げになっていた。
本発明の課題は、低コストかつ高収率で、作業工程が少なく、有害な副生成物の発生が抑えられた尿素の製造方法を提供することである。
However, in the method for producing urea described in Patent Document 1 or Patent Document 2, the same molar amount of hydrogen sulfide is generated together with urea, hindering the application of this method to industrial processes.
SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing urea at a low cost and in a high yield, in which the number of working steps is small and the generation of harmful by-products is suppressed.
本発明者らは、上記課題の解決のため鋭意検討し、アンモニア、一酸化炭素、及び硫黄の反応が、水中でも高収率かつ低コストで進行することを初めて見出した。そして、水中での反応により、有毒な硫化水素の発生を大幅に抑えることに成功し、さらに検討を重ねて、本発明を完成させた。
具体的には、本発明は以下のとおりである。
The present inventors made intensive studies to solve the above problems, and discovered for the first time that the reaction of ammonia, carbon monoxide, and sulfur proceeds in water at a high yield and at a low cost. They succeeded in significantly suppressing the generation of toxic hydrogen sulfide by a reaction in water, and completed the present invention after repeated studies.
Specifically, the present invention is as follows.
＜１＞一酸化炭素、アンモニア、及び硫黄を反応させることを含む尿素の製造方法であって、上記反応を水中で進行させる製造方法。
＜２＞硫黄の一酸化炭素に対するモル比（Ｓ0／ＣＯ）が５以上である＜１＞に記載の製造方法。
＜３＞上記反応が常圧で行なわれる＜１＞又は＜２＞に記載の製造方法。
＜４＞アンモニアが溶解した水溶液、硫黄、及び一酸化炭素ガスを混合することを含む＜１＞～＜３＞のいずれかに記載の製造方法。
＜５＞上記水溶液のｐＨが９.０～１１.０である＜４＞に記載の製造方法。
＜６＞上記水溶液が塩化アンモニウムを含む＜４＞又は＜５＞に記載の製造方法。
＜７＞上記水溶液が硫化水素ナトリウムを含む＜４＞～＜６＞のいずれかに記載の製造方法。
<1> A method for producing urea, which comprises reacting carbon monoxide, ammonia, and sulfur, wherein the above reaction proceeds in water.
<2> The production method according to <1>, wherein the molar ratio of sulfur to carbon monoxide (S 0 /CO) is 5 or more.
<3> The production method according to <1> or <2>, wherein the reaction is carried out at normal pressure.
<4> The production method according to any one of <1> to <3>, including mixing an aqueous solution in which ammonia is dissolved, sulfur, and carbon monoxide gas.
<5> The production method according to <4>, wherein the aqueous solution has a pH of 9.0 to 11.0.
<6> The production method according to <4> or <5>, wherein the aqueous solution contains ammonium chloride.
<7> The production method according to any one of <4> to <6>, wherein the aqueous solution contains sodium hydrogen sulfide.
本発明により、新規の尿素の製造方法が提供される。本発明の尿素の製造方法は、作業工程が少なく、高収率であるとともに、有害レベルの硫化水素を発生しない。 The present invention provides a novel method for producing urea. The method for producing urea of the present invention has fewer steps, a higher yield, and does not generate harmful levels of hydrogen sulfide.
以下、本発明を詳細に説明する。以下に記載する構成要件の説明は、代表的な実施形態や具体例に基づいてなされることがあるが、本発明はそのような実施形態に限定されるものではない。
本明細書において「～」を用いて表される数値範囲は「～」前後に記載される数値を下限値及び上限値として含む範囲を意味する。
The present invention will be described in detail below. Although the constituent elements described below may be described based on representative embodiments and specific examples, the present invention is not limited to such embodiments.
In this specification, the numerical range represented by "to" means a range including the numerical values described before and after "to" as lower and upper limits.
本発明の尿素製造方法は、一酸化炭素、アンモニア、及び硫黄を反応させることを含み、この反応を水中で進行させる製造方法である。この尿素製造方法では、二酸化炭素とアンモニアを原料とする従来法で取り入れられているような高温高圧条件を必要とせず、エネルギーコストを抑えることができる。また、二酸化炭素排出量を抑えることができる。 The urea production method of the present invention is a production method in which carbon monoxide, ammonia, and sulfur are reacted, and this reaction proceeds in water. This urea production method does not require the high temperature and high pressure conditions adopted in conventional methods using carbon dioxide and ammonia as raw materials, and can reduce energy costs. In addition, carbon dioxide emissions can be suppressed.
一酸化炭素（ＣＯ）及びアンモニア（ＮＨ3）からの尿素（（ＮＨ2）2ＣＯ）の生成は酸化反応であり、進行には酸化剤を要する。
ＣＯ＋２ＮＨ3→（ＮＨ2）2ＣＯ＋２Ｈ+＋２ｅ-
The formation of urea ((NH 2 ) 2 CO) from carbon monoxide (CO) and ammonia (NH 3 ) is an oxidation reaction and requires an oxidant to proceed.
CO+ 2NH3 →( NH2 ) 2CO +2H ++ 2e-
硫黄（Ｓ0）は、多硫化物イオン（Ｓn
2-（ｎ＝２～８））へと還元することで酸化剤として機能し、尿素生成を駆動する。
ｎＳ0＋２ｅ-→Ｓn
2-（ｎ＝２～８）
すなわち、反応全体としては以下の式で表される。
ＣＯ＋２ＮＨ3＋Ｓ0→（ＮＨ2）2ＣＯ＋Ｓn
2-＋２Ｈ+
Sulfur (S 0 ) functions as an oxidant by reduction to polysulfide ions (S n 2− (n=2-8)) and drives urea production.
nS 0 +2e − →S n 2− (n=2 to 8)
That is, the reaction as a whole is represented by the following formula.
CO+ 2NH3 + S0 → ( NH2 ) 2CO + Sn2- +2H +
本明細書において、多硫化物イオンは一般式Ｓn 2-（ｎ＝２～８）で表される二価陰イオンを意味する。多硫化物イオンは、ｎが単一の数値で表される１種類の化合物からなっていてもよく、ｎが異なる数値で表される２種以上の化合物の混合物であってもよい。平衡状態においては、例えば２５℃、ｐＨ１０．５の水中では、多硫化物イオンはｎ＝５の状態で最も多く存在し、次いで多いｎ＝４、ｎ＝６の成分と合わせた存在比率は８０～９０％程度となる。本発明の尿素製造方法では、これらの比率を調整する必要はない。 As used herein, a polysulfide ion means a divalent anion represented by the general formula S n 2- (n=2-8). The polysulfide ion may consist of one type of compound where n is represented by a single numerical value, or may be a mixture of two or more types of compounds where n is represented by different numerical values. In the equilibrium state, for example, in water at 25° C. and pH 10.5, polysulfide ions are present most abundantly when n=5, and the abundance ratio of polysulfide ions together with those of n=4 and n=6 is 80. ~90%. It is not necessary to adjust these ratios in the urea production method of the present invention.
本発明において、多硫化物というときは、多硫化物イオンに加えて、多硫化物イオンの塩及びその溶媒和物等も含む意味である。塩はアルカリ金属塩が好ましく、アルカリ金属としてはナトリウム、カリウム又はリチウムが好ましい。溶媒和物としては水和物が挙げられる。 In the present invention, the term polysulfide is meant to include not only polysulfide ions but also salts of polysulfide ions and solvates thereof. The salt is preferably an alkali metal salt, and the alkali metal is preferably sodium, potassium or lithium. Solvates include hydrates.
本発明の尿素製造方法では、特許文献１及び特許文献２で開示された方法と比較して、有毒な硫化水素の発生を大幅に抑えることができる。これは、硫化水素は水中で速やかに硫黄と反応し、多硫化物イオンを生じるためである。
（ｎ－１）Ｓ0＋ＨＳ-→Ｓn
2-＋Ｈ+
In the method for producing urea of the present invention, generation of toxic hydrogen sulfide can be greatly suppressed as compared with the methods disclosed in Patent Documents 1 and 2. This is because hydrogen sulfide rapidly reacts with sulfur in water to produce polysulfide ions.
(n−1) S 0 +HS − →S n 2− +H +
本反応の進行には、アルカリ性ｐＨが好ましい。実施例でも示すように、ｐＨを１０.３以上に調整することにより、硫化水素ガスの発生濃度を５ｐｐｍ未満に抑えることができる（２５℃での測定結果）。硫化水素ガス濃度は任意の温度・ｐＨ条件において、熱力学計算から予測することができる。 An alkaline pH is preferred for the progress of this reaction. As shown in the examples, by adjusting the pH to 10.3 or more, the concentration of hydrogen sulfide gas generated can be suppressed to less than 5 ppm (measurement results at 25°C). Hydrogen sulfide gas concentration can be predicted from thermodynamic calculations under arbitrary temperature and pH conditions.
多硫化物イオンは腐食作用を有する（国際公開第２０１４／０２５５３３号等）。したがって、本発明の尿素の製造方法を工業的に実施する場合においては、反応容器の腐食の問題も生じ難い。また、多硫化物イオンは酸化処理により容易に元素硫黄又は硫黄酸化物に変換できる。例えば、多硫化物の酸素による元素硫黄への酸化は、硫化水素から元素硫黄への酸化と比較しても迅速である（Steudel, 1986; Kleinjan et al., 2005）。このような酸化処理により最終的に得られる硫酸イオンは、肥料成分として尿素と共に使用することも考えられる。 Polysulfide ions have a corrosive effect (WO 2014/025533, etc.). Therefore, when the method for producing urea of the present invention is applied industrially, the problem of corrosion of the reaction vessel is less likely to occur. Also, polysulfide ions can be easily converted to elemental sulfur or sulfur oxides by an oxidation treatment. For example, the oxidation of polysulfides by oxygen to elemental sulfur is rapid compared to the oxidation of hydrogen sulfide to elemental sulfur (Steudel, 1986; Kleinjan et al., 2005). It is also conceivable to use the sulfate ions finally obtained by such oxidation treatment together with urea as a fertilizer component.
本発明の尿素の製造方法により生じた多硫化物イオンは、酸化処理により元素硫黄に変換し、本発明の尿素の製造方法に再利用することもできる。 The polysulfide ions generated by the method for producing urea of the present invention can be converted to elemental sulfur by oxidation treatment and reused in the method for producing urea of the present invention.
本発明の尿素の製造方法において、重要な反応中間体は硫化カルボニル（ＯＣＳ）であり、一酸化炭素と多硫化イオンとの以下の反応から生成する。
ＣＯ＋Ｓn
2-→ＯＣＳ＋Ｓn-1
2-
生成した硫化カルボニルがアンモニアと反応することで、尿素が生じる。
上記の硫化カルボニル生成反応は、尿素生成反応全体の進行速度を律速する段階でもある。結果として、尿素の生成速度は、一酸化炭素と多硫化物イオンの濃度に比例する。
In the method for producing urea of the present invention, an important reaction intermediate is carbonyl sulfide (OCS), which is produced from the following reaction between carbon monoxide and polysulfide ions.
CO + S n 2- →OCS + S n-1 2-
The produced carbonyl sulfide reacts with ammonia to produce urea.
The carbonyl sulfide formation reaction described above is also a stage that determines the rate of progress of the entire urea formation reaction. As a result, the rate of urea production is proportional to the concentrations of carbon monoxide and polysulfide ions.
本発明の尿素の製造方法において、尿素の生成速度は以下の反応速度式で表される：
ｄ［（ＮＨ2）2ＣＯ］／ｄｔ＝ｋ［ＣＯ］［Ｓn
2-］
［（ＮＨ2）2ＣＯ］、［ＣＯ］、［Ｓn
2-］は、各成分の水中濃度（ｍｏｌ／Ｌ）を表す。ｋは速度定数であり、活性化エネルギー（Ｅa＝５８．５ｋJ／ｍｏｌ）及び頻度因子（Ａ＝６．７×１０7）を用いて以下のアレニウスの式から求められる：
ｋ＝Ａeｘｐ（－Ｅa／ＲＴ）
Ｒは気体定数、Ｔは絶対温度である。
In the urea production method of the present invention, the urea production rate is represented by the following reaction rate formula:
d [ ( NH2 ) 2CO ]/dt=k[CO][ Sn2- ]
[(NH 2 ) 2 CO], [CO], and [S n 2- ] represent the water concentration (mol/L) of each component. k is the rate constant and is determined from the following Arrhenius equation using the activation energy (E=58.5 kJ/mol) and frequency factor (A=6.7×10 7 ):
k=Aexp(-Ea/RT)
R is the gas constant and T is the absolute temperature.
なお、反応全体の式（ＣＯ＋２ＮＨ3＋Ｓ0→（ＮＨ2）2ＣＯ＋Ｓn 2-＋２Ｈ+）が示すように、反応進行に伴う一酸化炭素の減少量、及び多硫化物イオンの増加量は、尿素の生成量と同量である。このため、一酸化炭素及び多硫化物イオンの濃度を経時観測しなくても尿素の生成速度を計算することができる。反応開始時における一酸化炭素・多硫化物イオンの量、及び上記のアレニウスの式から得られる速度定数ｋを用いることで、任意の温度条件下における尿素生成速度を予測することができる。 As shown by the overall reaction formula (CO+2NH 3 +S 0 →(NH 2 ) 2 CO+S n 2− +2H + ), the amount of carbon monoxide decreased and the amount of polysulfide ions increased as the reaction progressed. The amount is the same as the amount of urea produced. Therefore, the production rate of urea can be calculated without monitoring the concentrations of carbon monoxide and polysulfide ions over time. Using the amount of carbon monoxide/polysulfide ions at the start of the reaction and the rate constant k obtained from the above Arrhenius equation, the urea production rate under arbitrary temperature conditions can be predicted.
本発明の尿素製造方法では、全ての反応は水中で進行する。本発明では、多硫化物イオンの生成、硫化カルボニルの生成、硫化カルボニルとアンモニアとの反応などの上記の複数の工程が、水中で連続的に進行することを初めて見出した。そして、上述のように有毒な硫化水素の発生を大幅に抑えることに成功した。 In the urea production method of the present invention, all reactions proceed in water. In the present invention, it was found for the first time that the above-described multiple processes such as the formation of polysulfide ions, the formation of carbonyl sulfide, and the reaction between carbonyl sulfide and ammonia proceed continuously in water. And, as described above, we succeeded in greatly suppressing the generation of toxic hydrogen sulfide.
特許文献２に記載の、アンモニア、一酸化炭素、及び硫黄を原料とする尿素合成方法は、有機溶剤の使用によりコストが高く、また環境負荷の問題もあった。同文献では溶剤を用いない尿素製造方法も開示されているが、反応進行には高濃度のアンモニア、一酸化炭素、及び硫黄が必要であり（１．８Ｌ容器中にそれぞれ８．５、３．９、３．１ｍｏＬ）、尿素収率も低かった（６１％）。反応を水中で進行させる本発明の方法により、低コスト、環境調和的かつ高収率な尿素の製造が可能になる。 The method for synthesizing urea using ammonia, carbon monoxide, and sulfur as raw materials described in Patent Document 2 is expensive due to the use of organic solvents, and also has the problem of environmental load. The document also discloses a urea production method that does not use a solvent, but the reaction requires high concentrations of ammonia, carbon monoxide, and sulfur (8.5, 3.5 in a 1.8 L vessel, respectively). 9, 3.1 mol) and the urea yield was also low (61%). The method of the present invention, in which the reaction proceeds in water, enables the production of urea at low cost, in an environmentally friendly manner, and in high yield.
本明細書において、「水中」というとき、水の中のみでなく、水とガス相の界面も含む意味である。また、「水中」というとき、主に水を含む溶媒中との意味であり、他の媒体や成分を含む溶媒中を除く意味ではない。したがって、反応は、水中に加えて、水と水に混和可能な媒体との混合溶媒中で進行させてもよい。水に混和可能な媒体の例としては、メタノール、エタノール、アセトン、Ｎ，Ｎ－ジメチルホルムアミド、Ｎ－メチル－２－ピロリドン、テトラヒドロフラン、エチレングリコール、ジエチレングリコール等が挙げられる。混合溶媒は水を７０質量％以上含有することが好ましく、８０質量％以上含有することが好ましく、９０質量％以上含有することが好ましい。 As used herein, the term "in water" is meant to include not only water, but also the interface between water and gas phases. Also, the term "in water" means in a solvent containing mainly water, and does not mean excluding in a solvent containing other media or components. Therefore, the reaction may proceed in water as well as in a mixed solvent of water and a water-miscible medium. Examples of water-miscible media include methanol, ethanol, acetone, N,N-dimethylformamide, N-methyl-2-pyrrolidone, tetrahydrofuran, ethylene glycol, diethylene glycol, and the like. The mixed solvent preferably contains water in an amount of 70% by mass or more, preferably 80% by mass or more, and preferably 90% by mass or more.
本発明の尿素の製造方法において、一酸化炭素は気体として反応水溶液に接触させればよい。反応水溶液と接触させる一酸化炭素を含むガス相中には、一酸化炭素以外に窒素などの不活性ガスや微量の二酸化炭素が含まれていてもよい。一酸化炭素は、ガス相中に存在する他の気体の総モル量より多いモル量でガス相に含まれていることが好ましく、例えば、他の気体の総モル量の２倍以上、４倍以上、５倍以上、又は１０倍以上であることが好ましい。反応開始時における一酸化炭素の分圧は、０．０５～３０ＭＰａとなる範囲内であることが好ましく、０．０８～１０ＭＰａとなる範囲内であることがより好ましく、０．１～５ＭＰａとなる範囲内であることがさらに好ましい。反応開始時における一酸化炭素の分圧は、実施例で示すように、常圧（０．１ＭＰａ）でも高い尿素収率をもたらすことができる（最大で略１００％）。反応時における反応容器内の一酸化炭素の分圧が好ましい範囲内で維持されるように、反応により消費された一酸化炭素を補いながら行ってもよい。 In the method for producing urea of the present invention, carbon monoxide may be brought into contact with the aqueous reaction solution as a gas. The gas phase containing carbon monoxide to be brought into contact with the aqueous reaction solution may contain an inert gas such as nitrogen or a trace amount of carbon dioxide in addition to carbon monoxide. Carbon monoxide is preferably contained in the gas phase in a molar amount greater than the total molar amount of the other gases present in the gas phase, for example, 2 times or more, 4 times the total molar amount of the other gases It is preferably 5 times or more, or 10 times or more. The partial pressure of carbon monoxide at the start of the reaction is preferably in the range of 0.05 to 30 MPa, more preferably in the range of 0.08 to 10 MPa, and 0.1 to 5 MPa. It is more preferable to be within the range. As shown in Examples, the partial pressure of carbon monoxide at the start of the reaction can bring about a high yield of urea (up to approximately 100%) even at normal pressure (0.1 MPa). Carbon monoxide consumed by the reaction may be compensated for so that the partial pressure of carbon monoxide in the reaction vessel during the reaction is maintained within a preferred range.
本発明の尿素の製造方法において、アンモニアは水中に溶解したアンモニア水溶液として反応に用いることが好ましい。アンモニアは、アンモニウムイオンとの平衡を通じて水溶液ｐＨの緩衝材としても働くことから（ＮＨ3＋Ｈ+⇔ＮＨ4
+）、一酸化炭素に対して当量以上で用いることが好ましく、過剰量であってもよい。
アンモニア水溶液に硫黄を懸濁又は分散させて一酸化炭素を含むガス相と接触させることが好ましい。
In the method for producing urea of the present invention, ammonia is preferably dissolved in water and used for the reaction as an aqueous solution of ammonia. Ammonia also acts as a buffer for the pH of an aqueous solution through equilibrium with ammonium ions (NH 3 +H + ⇔ NH 4 + ). good.
Preferably, sulfur is suspended or dispersed in an aqueous ammonia solution and brought into contact with the gas phase containing carbon monoxide.
硫黄は天然物であっても合成製品であっても、これらの組み合わせであってもよい。硫黄は化石燃料の精製プロセスから大量に生じている安価な材料である。近年では、硫黄精製技術の向上や硫黄を多く含む原油の採掘などにより、世界全体の硫黄の供給量は増加傾向にある。需要量を超過した硫黄は世界各地で山積みに放置されており、中長期的な環境への悪影響が懸念されている（Wagenfeld et al., 2019）。本発明の尿素の製造方法は、硫黄の有効な活用法として、このような問題の解決にも資すると考えられる。 Sulfur can be natural or synthetic products, or combinations thereof. Sulfur is a cheap material that originates in large quantities from fossil fuel refining processes. In recent years, due to improvements in sulfur refining technology and extraction of sulfur-rich crude oil, the world supply of sulfur is on the rise. Sulfur in excess of demand is left in piles around the world, raising concerns about its medium- to long-term adverse environmental impacts (Wagenfeld et al., 2019). The method for producing urea of the present invention is considered to contribute to solving such problems as an effective utilization of sulfur.
本発明の製造方法で使用される硫黄は、単体硫黄若しくはその同素体又はそれらの混合物であってもよい。硫黄は、固体であっても液体であってもよいが、固体であることが好ましい。固体は、アモルファスであっても結晶であってもよい。硫黄としては例えば単体硫黄や固体の６～２０の硫黄を含む環状硫黄［例えば八員環Ｓ８を単位とする斜方昌系硫黄（α硫黄）や六員環Ｓ６の菱面体構造の硫黄など］を挙げることができる。硫黄は粉末状で用いることが好ましい。 Sulfur used in the production method of the present invention may be elemental sulfur, an allotrope thereof, or a mixture thereof. The sulfur may be solid or liquid, preferably solid. A solid may be amorphous or crystalline. Examples of sulfur include elemental sulfur and solid cyclic sulfur containing 6 to 20 sulfurs [for example, rhombohedral sulfur having an eight-membered ring S8 as a unit and rhombohedral sulfur having a six-membered ring S6]. can be mentioned. Sulfur is preferably used in powder form.
十分な尿素の収率を得るため、硫黄は一酸化炭素に対するモル比（Ｓ0／ＣＯ比）が２.０以上で用いられることが好ましく、２.４以上で用いられることがより好ましく、５以上で用いられることがより好ましい。実施例で示すように、Ｓ0／ＣＯ比を５以上とすることにより、一酸化炭素に対する尿素の収率を略１００％とすることができる。また、Ｓ0／ＣＯ比を５以上とすることにより、副産物として生じる硫化水素の大部分を硫黄と反応させ、多硫化物イオンに変換することができる。すなわち、尿素製造過程における硫化水素ガスの発生量を抑えることができる。Ｓ0／ＣＯ比の上限は特にないが、硫黄が過剰であることにより反応水溶液の撹拌が困難となる場合等において、１０程度としておけばよい。一酸化炭素、アンモニア、又は両方を順次供給しながら反応を進行させる場合は、反応時に、常にＳ0／ＣＯが５以上に保持されるように、硫黄を過剰量で用いることが好ましい。 In order to obtain a sufficient yield of urea, the molar ratio of sulfur to carbon monoxide (S 0 /CO ratio) is preferably 2.0 or more, more preferably 2.4 or more. It is more preferable to use the above. As shown in the examples, by setting the S 0 /CO ratio to 5 or more, the yield of urea to carbon monoxide can be made approximately 100%. Further, by setting the S 0 /CO ratio to 5 or more, most of the hydrogen sulfide produced as a by-product can be reacted with sulfur and converted into polysulfide ions. That is, the amount of hydrogen sulfide gas generated in the urea production process can be suppressed. Although there is no particular upper limit for the S 0 /CO ratio, it may be set to about 10 in cases such as when stirring of the reaction aqueous solution becomes difficult due to excess sulfur. When the reaction proceeds while supplying carbon monoxide, ammonia, or both in sequence, it is preferable to use an excessive amount of sulfur so that S 0 /CO is always maintained at 5 or more during the reaction.
本発明の尿素製造方法において、反応水溶液はアンモニアが溶解していることにより、通常アルカリ性である。上述のように、アルカリ性では硫化水素ガスの発生が抑えられると共に、多硫化物イオンの溶解度が増すことによって、尿素生成速度が上昇する。一方、強いアルカリ性条件下では、反応中間体である硫化カルボニルが加水分解し、尿素収率が低下する。これらのことから、ｐＨは９．０～１１．０であることが好ましく、１０．３～１０．５であることが特に好ましい。反応水溶液のｐＨは、実施例で示すように、塩化アンモニウム等のアンモニウム塩を添加して調整することができる。 In the method for producing urea of the present invention, the aqueous reaction solution is usually alkaline due to dissolved ammonia. As described above, alkalinity suppresses the generation of hydrogen sulfide gas and increases the solubility of polysulfide ions, thereby increasing the rate of urea production. On the other hand, under strongly alkaline conditions, carbonyl sulfide, which is a reaction intermediate, is hydrolyzed, resulting in a decrease in urea yield. For these reasons, the pH is preferably 9.0 to 11.0, particularly preferably 10.3 to 10.5. The pH of the reaction aqueous solution can be adjusted by adding an ammonium salt such as ammonium chloride, as shown in Examples.
反応水溶液には硫化水素塩を添加してもよい。硫化水素塩の添加により、硫化水素イオンと硫黄との以下の反応から多硫化物イオンを得ることができる：
（ｎ－１）Ｓ0＋ＨＳ-→Ｓn
2-＋Ｈ+
多硫化物イオンは、一酸化炭素、アンモニア及び硫黄の反応で生じるが（ＣＯ＋２ＮＨ3＋Ｓ0→（ＮＨ2）2ＣＯ＋Ｓn
2-＋２Ｈ+）、硫化水素塩の添加により予め反応水溶液に存在させておくことで、反応開始直後から高い反応速度で尿素の製造を進めることができる。
A hydrogen sulfide salt may be added to the aqueous reaction solution. Addition of hydrogen sulfide salts allows polysulfide ions to be obtained from the following reactions of hydrogen sulfide ions with sulfur:
(n−1) S 0 +HS − →S n 2− +H +
Polysulfide ions, which are formed in the reaction of carbon monoxide, ammonia and sulfur (CO+ 2NH3 + S0 →( NH2 ) 2CO + Sn2- +2H + ), are pre-existed in the aqueous reaction solution by the addition of hydrogen sulfide salts. In this way, the production of urea can proceed at a high reaction rate immediately after the start of the reaction.
硫化水素塩の例としては、硫化水素ナトリウムが挙げられる。硫化水素塩の添加量が多すぎると、尿素製造後に残存する硫化水素の濃度が高まり、尿素収率の低下にもつながる。したがって、硫化水素塩は一酸化炭素に対して５％～２０％程度のモル比を目安として用いることが好ましい。 Examples of hydrogen sulfide salts include sodium hydrogen sulfide. If the amount of hydrogen sulfide added is too large, the concentration of hydrogen sulfide remaining after urea production increases, leading to a decrease in urea yield. Therefore, it is preferable to use hydrogen sulfide at a molar ratio of about 5% to 20% with respect to carbon monoxide.
本発明の尿素製造方法における反応温度は、３５℃～１００℃が好ましく、５０℃～９０℃がより好ましく、５０℃～８０℃がさらに好ましい。実施例で示すように、３５℃条件と６５℃条件とでは最終的に得られる尿素の収率には大きな差は見られないが、高温ほどより早い反応速度を得ることができる。一方、高温では生成した尿素が加水分解するため、これを抑えるためには反応温度は１００℃以下であることが好ましい。反応は常圧（０．１ＭＰａ）で行なうことが可能であるが、反応速度を上げるため、例えば０．０５～３０ＭＰａ、好ましくは０．１～５ＭＰａの範囲で行なってもよい。 The reaction temperature in the method for producing urea of the present invention is preferably 35°C to 100°C, more preferably 50°C to 90°C, even more preferably 50°C to 80°C. As shown in Examples, there is no significant difference in the yield of urea finally obtained between the 35° C. condition and the 65° C. condition, but the higher the temperature, the faster the reaction rate can be obtained. On the other hand, since the urea produced hydrolyzes at high temperatures, the reaction temperature is preferably 100° C. or lower in order to suppress this. The reaction can be carried out at normal pressure (0.1 MPa), but in order to increase the reaction rate, it may be carried out at, for example, 0.05 to 30 MPa, preferably 0.1 to 5 MPa.
本発明の尿素製造方法は、一酸化炭素、アンモニア、及び硫黄が水中で反応できる限りどのような容器又は装置を用いて行なわれてもよい。典型的には、アンモニア水溶液、硫黄粉末、及び一酸化炭素ガスを混合及び撹拌して反応を進行させる。 The urea production method of the present invention may be carried out using any vessel or apparatus as long as carbon monoxide, ammonia and sulfur can react in water. Typically, an aqueous ammonia solution, sulfur powder, and carbon monoxide gas are mixed and stirred to allow the reaction to proceed.
混合及び撹拌方法の一例として、アンモニア水溶液、硫黄粉末、及び一酸化炭素ガスを気密性の反応容器中で振盪、撹拌する方法が挙げられる。例えば、反応容器内に、アンモニア水溶液及び硫黄粉末を仕込んだ後、反応容器内に一酸化炭素ガスを注入して振盪する。又は反応容器内に、硫黄粉末を仕込んだ後、アンモニア水溶液及び一酸化炭素ガスを注入してもよい。反応容器は一酸化炭素ガスの注入前に不活性ガスで満たし、この不活性ガスを一酸化炭素ガスに置き換えてもよく、一酸化炭素ガスの注入前に反応容器内の気体を真空ポンプ等で吸引していてもよい。 An example of a mixing and stirring method includes shaking and stirring an aqueous ammonia solution, sulfur powder, and carbon monoxide gas in an airtight reaction vessel. For example, after charging an aqueous ammonia solution and sulfur powder into a reaction vessel, carbon monoxide gas is injected into the reaction vessel and shaken. Alternatively, an aqueous ammonia solution and carbon monoxide gas may be injected into the reactor after charging sulfur powder. The reaction vessel may be filled with an inert gas before injecting the carbon monoxide gas, and the inert gas may be replaced with the carbon monoxide gas. You may be sucking.
混合及び撹拌は、硫黄を懸濁させているアンモニア水溶液中に一酸化炭素ガスをバブリングする等の方法でも行うことができる。 Mixing and stirring can also be performed by a method such as bubbling carbon monoxide gas into an aqueous ammonia solution in which sulfur is suspended.
本発明の尿素製造方法にかける反応時間は、原料の濃度、温度等の条件に応じて、目標の収率が得られる時間に設定すればよい。上述のように、尿素収率の経時変化は、反応開始時における一酸化炭素・多硫化物イオンの濃度、及び速度定数ｋを用いた速度論的計算によって予測できる。例えば尿素収率８０％は６５℃では1日程度で達成することができ、より高温ではさらに短時間で達成できる（例えば８０℃では８～９時間、１００℃では２～３時間；実施例を参照）。 The reaction time for the method for producing urea of the present invention may be set to a time that allows the target yield to be obtained, depending on the conditions such as the concentration and temperature of the raw materials. As described above, the change in urea yield over time can be predicted by kinetic calculation using the concentration of carbon monoxide/polysulfide ions at the start of the reaction and the rate constant k. For example, a urea yield of 80% can be achieved in about one day at 65°C, and can be achieved in a shorter time at higher temperatures (eg, 8-9 hours at 80°C, 2-3 hours at 100°C; reference).
尿素製造後の反応水溶液中には、尿素のほか、多硫化物イオンや残存する原料（アンモニア等）が含まれる。尿素はこの水溶液から、浸透膜を用いた選別や（Ray et al., 2019; 2021）、吸着材への濃集（Urbanczyk et al., 2016）、有機溶剤（エタノール等）への溶解・再沈殿による集積（Marepula et al., 2021）など、様々な方法で精製・単離することができる。尿素は、反応水溶液から必要に応じて他の成分を処理した後、水溶液として利用することもできる。例えば多硫化物イオンは、酸素により速やかに硫黄へと酸化できる（Steudel, 1986; Kleinjan et al., 2005）。この酸化反応では、副産物としてチオ硫酸イオン（S2O4 2-）も生じると予想されるが、チオ硫酸イオンは硫化金属触媒（CuS等；Lara et al., 2019）や紫外線（Ahmad et al., 2015）等の利用により、硫酸イオン（SO4 2-）へと容易に変換できる。これら酸化処理により得られる尿素及び硫酸イオンを含む水溶液は、窒素及び硫黄含有肥料としての使用も考えられる。 In addition to urea, the reaction aqueous solution after urea production contains polysulfide ions and residual raw materials (ammonia, etc.). From this aqueous solution, urea is sorted using a permeable membrane (Ray et al., 2019; 2021), concentrated on an adsorbent (Urbanczyk et al., 2016), dissolved in an organic solvent (e.g. ethanol), and recycled. It can be purified and isolated by various methods, including accumulation by precipitation (Marepula et al., 2021). Urea can also be used as an aqueous solution after treating other components from the reaction aqueous solution as necessary. For example, polysulfide ions can be rapidly oxidized to sulfur by oxygen (Steudel, 1986; Kleinjan et al., 2005). This oxidation reaction is also expected to produce thiosulfate ions (S 2 O 4 2- ) as a by-product, which are generated by metal sulfide catalysts (CuS et al.; Lara et al., 2019) and ultraviolet light (Ahmad et al., 2019). ., 2015), it can be easily converted to sulfate ion (SO 4 2- ). Aqueous solutions containing urea and sulfate ions obtained by these oxidation treatments can also be used as nitrogen- and sulfur-containing fertilizers.
本発明の尿素製造方法に必要な硫黄は、化石燃料の精製プロセスから大量に生じている安価な材料である。また、アンモニアの製造工程においても、化石燃料の利用を通して、硫黄は副産物として大量に得られている。一方、一酸化炭素は、高い製造効率を実現する電気化学触媒が複数開発されており（例えばSatanowski and Bar-Even, 2020）、また、アンモニア製造に関わる工業プロセスからも副産物として大量に得ることができる。このため、本発明は従来プロセスを補完する、低コストで環境調和的な新規尿素製造方法として、持続可能社会への貢献が期待される。 The sulfur required for the urea production process of the present invention is an inexpensive material that originates in large quantities from fossil fuel refining processes. Also in the ammonia production process, a large amount of sulfur is obtained as a by-product through the use of fossil fuels. On the other hand, carbon monoxide has been developed with several electrochemical catalysts that achieve high production efficiency (e.g., Satanowski and Bar-Even, 2020), and it can also be obtained in large quantities as a by-product from industrial processes related to ammonia production. can. Therefore, the present invention is expected to contribute to a sustainable society as a new low-cost, environmentally friendly method for producing urea that complements conventional processes.
以下に実施例を挙げて本発明をさらに具体的に説明する。以下の実施例に示す材料、試薬、物質量とその割合、操作等は本発明の趣旨から逸脱しない限り適宜変更することができる。従って、本発明の範囲は以下の実施例に限定されるものではない。 EXAMPLES The present invention will be described more specifically with reference to examples below. The materials, reagents, amounts and ratios of substances, operations, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Accordingly, the scope of the invention is not limited to the following examples.
１－１．尿素合成手順
内容量１３ｍｌのガラスバイアル瓶に硫黄粉末（コロイド状）を２．５～２００ｍｇ計り入れ、ブチルゴム栓及びアルミキャップを取り付けた。瓶内の気体を油回転真空ポンプ（ＧＣＤ－１３６Ｘ、アルバック）で吸引し、一酸化炭素ガス８ｍＬ（０．１ＭＰａ（１気圧））及びアンモニア水溶液５ｍＬをそれぞれシリンジで注入した。アンモニア水溶液は、１０％アンモニア水試薬を直接、あるいは純水で５％に希釈したものを用いた。水溶液ｐＨは、塩化アンモニウムをアンモニアに対して１／１０の割合（モル比）で混合することで調整した。これにより、実験後のｐＨは１０．３～１０．５となった（塩化アンモニウムを加えない場合は１０．７～１０．８）。水溶液にはさらに、１５％硫化水素ナトリウム試薬を、硫化水素ナトリウム濃度が６．５ｍＭとなるよう加えた。この添加量は、ＣＯ量に対して１／１０（モル比）に相当する。
1-1. Urea Synthesis Procedure 2.5 to 200 mg of sulfur powder (colloidal) was weighed into a 13 ml glass vial, and a butyl rubber stopper and an aluminum cap were attached. The gas in the bottle was sucked with an oil rotary vacuum pump (GCD-136X, Ulvac), and 8 mL of carbon monoxide gas (0.1 MPa (1 atm)) and 5 mL of an aqueous ammonia solution were each injected with a syringe. As the aqueous ammonia solution, a 10% aqueous ammonia reagent was directly used, or a reagent diluted to 5% with pure water was used. The pH of the aqueous solution was adjusted by mixing ammonium chloride with ammonia at a ratio (molar ratio) of 1/10. This resulted in a pH of 10.3-10.5 after the experiment (10.7-10.8 when no ammonium chloride was added). Further, 15% sodium hydrogen sulfide reagent was added to the aqueous solution so that the sodium hydrogen sulfide concentration was 6.5 mM. This added amount corresponds to 1/10 (molar ratio) of the CO amount.
次に、バイアル瓶を恒温振盪機（ＢＲ－２３ＦＨ、タイテック）内に固定し、一定温度（３５、５０、又は６５℃）で１５０ｒｐｍにて振盪させた。一定時間経過後、バイアル瓶を振盪機から取り出し、瓶内のガス成分を室温下にてガスクロマトグラフィーで分析した。その後、窒素・水素混合ガス（９６：４）を満たした嫌気性グローブボックス（ＶＧ－８００；サンプラテック）内にてバイアル瓶を開封し、水溶液サンプルを孔径０．２２μｍのろ紙（ポリテトラフルオロエチレン製）でろ過し、ガラス容器に保管した。 The vials were then fixed in a thermostatic shaker (BR-23FH, Taitec) and shaken at 150 rpm at constant temperature (35, 50, or 65° C.). After a certain period of time, the vial was taken out from the shaker, and the gas components in the bottle were analyzed by gas chromatography at room temperature. After that, the vial bottle was opened in an anaerobic glove box (VG-800; Sunplatek) filled with a nitrogen/hydrogen mixed gas (96:4), and the aqueous solution sample was filtered with a filter paper (made of polytetrafluoroethylene) having a pore size of 0.22 μm. ) and stored in a glass container.
実験で用いた全ての試薬は、硫黄粉末（ナカライテスク）を除いて、富士フイルム和光純薬から購入した。水溶液の調製にはＭｉｌｌｉ－Ｑ水（１８．２ＭΩ・ｃｍ）を溶媒として用いた。一酸化炭素ガス（純度９９．９％）はＧＬサイエンスより購入した。 All reagents used in the experiments were purchased from FUJIFILM Wako Pure Chemical Industries, Ltd., except sulfur powder (Nacalai Tesque). Milli-Q water (18.2 MΩ·cm) was used as a solvent for the preparation of aqueous solutions. Carbon monoxide gas (purity 99.9%) was purchased from GL Science.
１－２．尿素定量手順
反応水溶液中の尿素濃度はジアセチルモノオキシム（ＤＡＭＯ）法（Rahmatullah and Boyde, 1980）に則り定量した。まず、以下の水溶液をそれぞれ用意した。
３．４ｇ ＤＡＭＯを純水に溶かし１００ｍｌに調整した水溶液
０．１９ｇ チオセミカルバジド（ＴＳＣ）を純水に溶かし２０ｍｌに調整した水溶液
９７％ 硫酸 ５６．０１ｍｌに純水を加え１００ｍｌに調整した水溶液
０．１５ｇ塩化鉄（ＦｅＣｌ3）を純水に溶かし１０ｍｌに調整した水溶液
1-2. Urea Determination Procedure The urea concentration in the aqueous reaction solution was determined according to the diacetyl monoxime (DAMO) method (Rahmatullah and Boyde, 1980). First, the following aqueous solutions were prepared.
3.4 g Aqueous solution adjusted to 100 ml by dissolving DAMO in pure water 0.19 g Aqueous solution adjusted to 20 ml by dissolving thiosemicarbazide (TSC) in pure water Aqueous solution adjusted to 100 ml by adding pure water to 56.01 ml of 97% sulfuric acid An aqueous solution prepared by dissolving 15 g of iron chloride (FeCl 3 ) in pure water and adjusting the volume to 10 ml.
ＤＡＭＯ水溶液とＴＳＣ水溶液は体積比９．６１５：０．３８５にて、硫酸水溶液と塩化鉄水溶液は体積比３２：０．００９にてそれぞれ混合し、得られた２種の混合液は体積比１０：３２．００９（すなわちＤＡＭＯ＆ＴＳＣ：硫酸＆塩化鉄＝１０：３２．００９）にて混合した。一方、サンプル水溶液は純水で５０００倍に希釈し、ポリプロピレン容器に移した。ここに上記の混合液を体積比１．２：４（混合液：サンプル）で加え、よく振った後、７０℃、１５０ｒｐｍに設定した恒温振盪機（ＢＲ－２３ＦＨ、タイテック）内に固定した。７５分後、容器を氷水で冷却し、得られた水溶液の波長３５０～８００ｎｍにおける吸光スペクトルを紫外可視分光器（Ｖ－６５０、日本分光）にて計測した。５２５ｎｍ及び６２５ｎｍにおける吸光度の差から尿素濃度を定量した（図１）。得られた結果の再現性は、サンプル準備から分析までの一連の手順を複数の条件下にて繰り返し行い調査した。同一条件にて得られた尿素生成量の相違は５％未満であった。 The DAMO aqueous solution and the TSC aqueous solution were mixed at a volume ratio of 9.615:0.385, and the sulfuric acid aqueous solution and the iron chloride aqueous solution were mixed at a volume ratio of 32:0.009. : 32.009 (i.e. DAMO & TSC: sulfuric acid & iron chloride = 10:32.009). On the other hand, the sample aqueous solution was diluted 5000 times with pure water and transferred to a polypropylene container. The above mixture was added thereto at a volume ratio of 1.2:4 (mixture:sample), shaken well, and fixed in a constant temperature shaker (BR-23FH, Taitec) set at 70° C. and 150 rpm. After 75 minutes, the container was cooled with ice water, and the absorbance spectrum of the resulting aqueous solution was measured at a wavelength of 350 to 800 nm with an ultraviolet-visible spectroscope (V-650, JASCO Corporation). Urea concentration was quantified from the difference in absorbance at 525 nm and 625 nm (Fig. 1). The reproducibility of the obtained results was investigated by repeating a series of procedures from sample preparation to analysis under multiple conditions. Differences in urea production obtained under identical conditions were less than 5%.
１－３．一酸化炭素残量定量手順
尿素合成実験後のバイアル瓶中の一酸化炭素残量はアジレント社製ガスクロマトグラフ（７８９０Ｂ）にて定量した。検出器はパルス放電ヘリウムイオン化（ＰＤＨＩＤ）検出器を、カラムはＭＩＣＲＯＰＡＣＫＥＤ－ＳＴ（信和化工）を、キャリアガスは高純度ヘリウム（純度＞９９．９９９９５％）を使用した。ヘリウムガスの流圧は０．３１ＭＰａ（４５ｐｓｉ）で一定とした。カラム温度は３５℃で１分間保持した後、１０℃／ｍｉｎで６５℃へと昇温し、４分間保持後に２０℃／ｍｉｎで１８５℃へと昇温した。この測定条件により得られた一酸化炭素標準ガスのクロマトグラム及び検量線を図２に示す。ガスサンプルは、ヘリウム（純度＞９９．９９９９５％）を満たした内容量６ｍｌのガラスバイアル瓶に任意量を移し、希釈した後に測定を行った。反応水溶液中の溶存一酸化炭素量は、ガス分析から得られた一酸化炭素分圧及び、文献に記された一酸化炭素のヘンリー定数（９．７×１０-6ｍｏｌ ｍ-3 Ｐａ-1；Sander, 2015）から計算した。得られた結果の再現性は、サンプル準備から分析までの一連の手順を、複数の条件下にて繰り返し行い調査した。同一条件にて得られた一酸化炭素残量の相違は１０％未満であった。
1-3. Procedure for Quantifying Remaining Carbon Monoxide The amount of carbon monoxide remaining in the vial after the urea synthesis experiment was quantified using a gas chromatograph (7890B) manufactured by Agilent. A pulse discharge helium ionization (PDHID) detector was used as a detector, a MICROPACKED-ST (Shinwa Kako) column was used, and high-purity helium (purity>99.99995%) was used as a carrier gas. The helium gas flow pressure was kept constant at 0.31 MPa (45 psi). After maintaining the column temperature at 35°C for 1 minute, the temperature was increased to 65°C at a rate of 10°C/min, and after maintaining the temperature for 4 minutes, the temperature was increased to 185°C at a rate of 20°C/min. FIG. 2 shows the chromatogram and calibration curve of the carbon monoxide standard gas obtained under these measurement conditions. An arbitrary amount of the gas sample was transferred to a 6-ml glass vial bottle filled with helium (purity >99.99995%), diluted, and then measured. The amount of dissolved carbon monoxide in the reaction aqueous solution was calculated using the carbon monoxide partial pressure obtained from gas analysis and Henry's constant of carbon monoxide described in the literature (9.7×10 −6 mol m −3 Pa −1 ; Sander, 2015). The reproducibility of the obtained results was investigated by repeating a series of procedures from sample preparation to analysis under multiple conditions. The difference in carbon monoxide remaining amount obtained under the same conditions was less than 10%.
１－４．二酸化炭素発生量定量手順
尿素生成過程に副産物として生じる二酸化炭素は、水溶液がアルカリ性のため、ほぼ全てが炭酸イオン（ＣＯ3
2-）及び重炭酸イオン（ＨＣＯ3
-）として溶存していると予想される。これらを定量するため、窒素・水素混合ガス（９６：４）を満たした嫌気性グローブボックス内にて、実験後の反応水溶液１００μＬをガラスバイアル瓶（内容量６ｍｌ）に移し、ブチルゴム栓及びアルミキャップを取り付けた。ここに、純水で２倍に希釈した８５％リン酸水溶液１００μＬをシリンジで注入し、発生した二酸化炭素ガスをアジレント社製ガスクロマトグラフ（７８９０Ｂ）にて定量した。検出器はパルス放電ヘリウムイオン化（ＰＤＨＩＤ）検出器を、カラムはＭＩＣＲＯＰＡＣＫＥＤ－ＳＴ（信和化工）を、キャリアガスは高純度ヘリウム（純度＞９９．９９９９５％）を使用した。ヘリウムガスの流圧は０．３１ＭＰａ（４５ｐｓｉ）で一定とした。カラム温度は１５０℃で５分間保持した後、２０℃／ｍｉｎで２３０℃へと昇温した。この測定条件により得られた二酸化炭素標準ガスのクロマトグラムを図３に示す。なお、実験に用いたアンモニア水には、元々わずかながら二酸化炭素が含まれている。これを定量し、実験後の二酸化炭素濃度から差し引くことで、実験中に発生した二酸化炭素量を算出した。得られた結果の再現性は、サンプル準備から分析までの一連の手順を、複数の条件下にて繰り返し行い調査した。同一条件にて得られた二酸化炭素量の相違は１０％未満であった。
1-4. Quantitative procedure for the amount of carbon dioxide generated Carbon dioxide, which is produced as a by-product in the urea production process, is expected to be dissolved almost entirely as carbonate ions (CO 3 2- ) and bicarbonate ions (HCO 3 - ) because the aqueous solution is alkaline. be done. In order to quantify these, in an anaerobic glove box filled with nitrogen / hydrogen mixed gas (96: 4), 100 μL of the reaction aqueous solution after the experiment was transferred to a glass vial bottle (contents 6 ml), and a butyl rubber stopper and an aluminum cap were transferred. attached. 100 μL of an 85% aqueous solution of phosphoric acid diluted twice with pure water was injected with a syringe, and the carbon dioxide gas generated was quantified using a gas chromatograph (7890B) manufactured by Agilent. A pulse discharge helium ionization (PDHID) detector was used as a detector, a MICROPACKED-ST (Shinwa Kako) column was used, and high-purity helium (purity>99.99995%) was used as a carrier gas. The helium gas flow pressure was kept constant at 0.31 MPa (45 psi). After maintaining the column temperature at 150°C for 5 minutes, the temperature was raised to 230°C at a rate of 20°C/min. A chromatogram of carbon dioxide standard gas obtained under these measurement conditions is shown in FIG. Ammonia water used in the experiment originally contains a small amount of carbon dioxide. By quantifying this and subtracting it from the carbon dioxide concentration after the experiment, the amount of carbon dioxide generated during the experiment was calculated. The reproducibility of the obtained results was investigated by repeating a series of procedures from sample preparation to analysis under multiple conditions. The difference in the amount of carbon dioxide obtained under identical conditions was less than 10%.
１－５．硫化水素ガス定量手順
尿素合成実験後のバイアル瓶中硫化水素ガス量はアジレント社製ガスクロマトグラフ（７８９０Ｂ）にて定量した。検出器は化学発光硫黄（ＳＣＤ）検出器を、カラムはＤＢ－Ｓｕｌｆｕｒ ＳＣＤ（アジレント）を、キャリアガスは高純度ヘリウム（純度＞９９．９９９９５％）を使用した。ヘリウムガスの流速は３ｍｌ／ｍｉｎで一定とした。カラム温度は３５℃で５分間保持した後、６０℃／ｍｉｎで１２５℃へと昇温した。この測定条件により得られた硫化水素標準ガスのクロマトグラム及び検量線を図４に示す。得られた結果の再現性は、サンプル準備から分析までの一連の手順を、複数の条件下にて繰り返し行い調査した。同一条件にて得られた硫化水素量の相違は１０％未満であった。
1-5. Hydrogen Sulfide Gas Quantitative Procedure The amount of hydrogen sulfide gas in the vial after the urea synthesis experiment was quantified using a gas chromatograph (7890B) manufactured by Agilent. A sulfur chemiluminescence (SCD) detector was used as a detector, a DB-Sulfur SCD (Agilent) was used as a column, and high-purity helium (purity >99.99995%) was used as a carrier gas. The helium gas flow rate was constant at 3 ml/min. After maintaining the column temperature at 35°C for 5 minutes, the temperature was raised to 125°C at a rate of 60°C/min. FIG. 4 shows the chromatogram and calibration curve of the hydrogen sulfide standard gas obtained under these measurement conditions. The reproducibility of the obtained results was investigated by repeating a series of procedures from sample preparation to analysis under multiple conditions. The difference in the amount of hydrogen sulfide obtained under the same conditions was less than 10%.
１－６．多硫化物イオン定量手順
多硫化物イオンは、アルカリ性である反応水溶液中には安定して溶存しているが、ｐＨを酸性に調整することで、硫黄と硫化水素に変換できる（Ｓn
2-＋２Ｈ+→（ｎ－１）Ｓ0＋Ｈ2Ｓ；図８a）。ここで発生した硫化水素を定量すれば、多硫化物イオン量を求めることができる。
窒素・水素混合ガス（９６：４）を満たした嫌気性グローブボックス内にて、実験後の水溶液サンプル５０μＬをガラスバイアル瓶（内容量２０ｍｌ）に移し、ブチルゴム栓及びアルミキャップを取り付けた。ここに、純水で２倍に希釈した８５％リン酸水溶液１００μＬをシリンジで注入し、発生した硫化水素ガスをアジレント社製ガスクロマトグラフ（７８９０Ｂ）にて定量した。ガスクロマトグラフによる分析方法は、１－５．硫化水素ガス定量手順と同様である。
1-6. Polysulfide ion determination procedure Polysulfide ions are stably dissolved in the alkaline reaction aqueous solution, but can be converted to sulfur and hydrogen sulfide by adjusting the pH to acidic (S n 2- +2H + →(n−1)S 0 +H 2 S; FIG. 8a). By quantifying the hydrogen sulfide generated here, the amount of polysulfide ions can be obtained.
In an anaerobic glove box filled with a nitrogen/hydrogen mixed gas (96:4), 50 μL of the aqueous solution sample after the experiment was transferred to a glass vial bottle (capacity: 20 ml) and attached with a butyl rubber stopper and an aluminum cap. 100 μL of an 85% aqueous solution of phosphoric acid diluted twice with pure water was injected with a syringe, and the generated hydrogen sulfide gas was quantified using a gas chromatograph (7890B) manufactured by Agilent. The analysis method by gas chromatograph is 1-5. It is the same as the hydrogen sulfide gas quantitative procedure.
１－７．硫化カルボニル検出手順
尿素生成反応の中間体として生じる硫化カルボニルは、四重極質量分析計（ＪＭＳ－Ｑ１５００ＧＣ；日本電子）を備えたガスクロマトグラフ（７８９０Ｂ；アジレント）にて検出した。カラムはＤＢ－Ｓｕｌｆｕｒ ＳＣＤ（アジレント）を、キャリアガスは高純度ヘリウム（純度＞９９．９９９９５％）を使用した。ヘリウムガスの流速は２．８ｍｌ／ｍｉｎで一定とした。カラム温度は３５℃で３．５分間保持した後、２０℃／ｍｉｎで２４５℃へと昇温した。ｍ／ｚ＝２５～２００の範囲において分析を行った。実験条件は、アンモニア濃度を５％、ＣＯ分圧を０．１ＭＰａ、硫黄量を１００ｍｇ、反応温度を５０℃、反応期間を１日間とした。
1-7. Carbonyl Sulfide Detection Procedure Carbonyl sulfide produced as an intermediate in the urea production reaction was detected with a gas chromatograph (7890B; Agilent) equipped with a quadrupole mass spectrometer (JMS-Q1500GC; JEOL Ltd.). DB-Sulfur SCD (Agilent) was used as the column, and high-purity helium (purity>99.99995%) was used as the carrier gas. The helium gas flow rate was constant at 2.8 ml/min. After maintaining the column temperature at 35°C for 3.5 minutes, the temperature was raised to 245°C at a rate of 20°C/min. Analysis was performed in the range of m/z=25-200. The experimental conditions were ammonia concentration of 5%, CO partial pressure of 0.1 MPa, sulfur content of 100 mg, reaction temperature of 50° C., and reaction period of 1 day.
２．結果
図５に、３５、５０、６５℃における尿素収率（ＣＯ使用量換算）の経時変化を示す。アンモニア濃度は５質量％（図５ａ）或いは１０質量％（図５ｂ）とした。反応開始時のＣＯ分圧は０．１ＭＰａ（０．３３ｍｍｏＬ、８ｍＬ）、硫黄量は３．１ｍｍｏＬ（１００ｍｇ）とした。尿素生成速度は高温ほど速く、収率８０％には６５℃では１日で、５０℃では２日で、３５℃では６日程度で到達した。収率はその後もさらに上昇し、例えばアンモニア濃度５％、反応温度５０℃及び６５℃の条件では、９８±５％の尿素収率が３日間で達成された（図５ａ）。アンモニア濃度を１０％とした場合も、誤差の範囲（±５％）で同様の傾向が見られた（図５ｂ）。副産物としては二酸化炭素が観測されたが、収率は全ての条件において０．８％未満であった。二酸化炭素は、反応中間体である硫化カルボニルが加水分解することで生じたと予想される（ＯＣＳ＋Ｈ2Ｏ→ＣＯ2＋Ｈ2Ｓ）。
2. Results FIG. 5 shows changes over time in urea yield (in terms of CO usage) at 35, 50 and 65°C. The ammonia concentration was set to 5% by weight (Fig. 5a) or 10% by weight (Fig. 5b). The CO partial pressure at the start of the reaction was 0.1 MPa (0.33 mmoL, 8 mL), and the amount of sulfur was 3.1 mmoL (100 mg). The higher the temperature, the faster the urea production rate, and the yield of 80% was reached in one day at 65°C, in two days at 50°C, and in about six days at 35°C. The yield further increased after that, for example, under the conditions of ammonia concentration of 5% and reaction temperatures of 50° C. and 65° C., a urea yield of 98±5% was achieved in 3 days (FIG. 5a). When the ammonia concentration was 10%, a similar trend was observed within the margin of error (±5%) (Fig. 5b). Carbon dioxide was observed as a by-product, but yields were less than 0.8% under all conditions. Carbon dioxide is expected to be produced by hydrolysis of the reaction intermediate carbonyl sulfide (OCS+ H2O → CO2 + H2S ).
なお、塩化アンモニウムを除いた条件では、塩化アンモニウムを含む場合に比べて尿素収率がわずかに低下し、ＣＯ2の収率が増加した。例えばアンモニア濃度５％・反応温度５０℃とした場合、反応５日後の尿素及び二酸化炭素の収率はそれぞれ９６±５％、２±０．２％となった。一方、アンモニア又は硫黄粉末のいずれかを除いた条件では、尿素の生成は観測されなかった。一酸化炭素ガスを二酸化炭素ガスに置き換えた場合も、尿素は生じなかった。また、硫化水素ナトリウムを除いた条件（図５ａの「ＮaＨＳ無し」）では、尿素生成は初期（０～１日目）にはほとんど見られなかったものの、その後（１～３日目）加速度的に進行し、５日目には収率９０％を超える結果となった（図５ａ）。 It should be noted that under the conditions without ammonium chloride, the yield of urea slightly decreased and the yield of CO 2 increased compared to the case of containing ammonium chloride. For example, when the ammonia concentration was 5% and the reaction temperature was 50° C., the yields of urea and carbon dioxide after 5 days of reaction were 96±5% and 2±0.2%, respectively. On the other hand, no urea formation was observed under conditions where either ammonia or sulfur powder was excluded. No urea was produced when carbon monoxide gas was replaced with carbon dioxide gas. In addition, under the conditions excluding sodium hydrogen sulfide (“no NaHS” in Fig. 5a), urea formation was hardly observed in the initial stage (days 0 to 1), but accelerated thereafter (days 1 to 3). , resulting in a yield of over 90% on day 5 (Fig. 5a).
さらに、硫黄使用量は、尿素の収率のみならず、副産物として生じる硫化水素の濃度にも大きく影響することが確認された。図６に、硫黄使用量に応じた硫化水素ガスの濃度変化（上）を、尿素収率及びＣＯ残量の変化（下）と共に示す。本図の横軸は、硫黄と一酸化炭素の使用量のモル比（Ｓ0／ＣＯ）とした。全ての条件において、ＣＯ使用量は一定（０．３３ｍｍｏＬ（８ｍＬ、０．１ＭＰａ））であり、硫黄使用量を０．０８～６．２ｍｍｏＬ（２．５～２００ｍｇ）の範囲で調整した。アンモニア濃度は５％、反応温度は５０℃、反応期間は５日間とした。
硫化水素ガス濃度は、Ｓ0／ＣＯ比が０から２の範囲において次第に増加し、Ｓ0／ＣＯ＝２付近で最大値（約６０ｐｐｍ）を示した。その後は減少に転じ、Ｓ0／ＣＯ＝５付近で下げ止まり、最終的に２ｐｐｍで落ち着いた。一方、尿素収率はＳ0／ＣＯ＝０～２にかけて大きく増加し、Ｓ0／ＣＯ＝２付近で９０％を超えた後はわずかずつ増加し、Ｓ0／ＣＯ＝５程度以上において９８±５％に達した。
Furthermore, it was confirmed that the amount of sulfur used greatly affects not only the yield of urea but also the concentration of hydrogen sulfide produced as a by-product. FIG. 6 shows changes in the concentration of hydrogen sulfide gas (upper) depending on the amount of sulfur used, together with changes in urea yield and remaining amount of CO (lower). The horizontal axis of the figure represents the molar ratio (S 0 /CO) of the amounts of sulfur and carbon monoxide used. In all conditions, CO usage was constant (0.33 mmoL (8 mL, 0.1 MPa)) and sulfur usage was adjusted in the range of 0.08-6.2 mmoL (2.5-200 mg). The ammonia concentration was 5%, the reaction temperature was 50°C, and the reaction period was 5 days.
The hydrogen sulfide gas concentration gradually increased in the range of the S 0 /CO ratio from 0 to 2, and showed a maximum value (about 60 ppm) near S 0 /CO=2. After that, it started to decrease, stopped falling around S 0 /CO=5, and finally stabilized at 2 ppm. On the other hand, the urea yield increases greatly from S 0 /CO = 0 to 2, increases slightly after exceeding 90% near S 0 /CO = 2, and reaches 98 ± 1 at S 0 /CO = 5 or more. reached 5%.
反応後の水溶液は多硫化物イオン特有の黄色を示し、その濃さは尿素生成量に比例して増加した。また、図５ａに示す尿素合成実験で消費された一酸化炭素量と生成した多硫化物イオン量とを比較したところ、ほぼ一対一の関係が見られた（図７）。これらの結果は、一酸化炭素から尿素（及び二酸化炭素）の生成反応が、硫黄の多硫化物イオンへの還元反応と共役して進行していることを意味している。これらの共役は、以下の反応式で表される。
ＣＯ＋２ＮＨ3＋ｎＳ0→（ＮＨ2）2ＣＯ＋Ｓn
2-＋２Ｈ+
ＣＯ＋Ｈ2Ｏ＋ｎＳ0→ＣＯ2＋Ｓn
2-＋２Ｈ+
The aqueous solution after the reaction showed a yellow color peculiar to polysulfide ions, and its concentration increased in proportion to the amount of urea produced. Also, when the amount of carbon monoxide consumed and the amount of polysulfide ions produced were compared in the urea synthesis experiment shown in FIG. 5a, a nearly one-to-one relationship was observed (FIG. 7). These results imply that the formation reaction of urea (and carbon dioxide) from carbon monoxide proceeds in conjunction with the reduction reaction of sulfur to polysulfide ions. These conjugations are represented by the following reaction schemes.
CO+ 2NH3 + nS0 → ( NH2 ) 2CO + Sn2- +2H +
CO + H2O + nS0 → CO2 + Sn2- +2H +
３．熱力学的計算による解析
水中における多硫化物イオン及び硫化水素の濃度分布は熱力学計算から予想できる。図８に熱力学計算を行なった結果を示す。本計算では、水溶液及びガスの容量は上記の尿素合成実験と同じ設定とした（それぞれ５ｍＬ、８ｍＬ）。また、尿素（及び二酸化炭素）生成反応が完全に進行した場合、すなわち、一酸化炭素全量（０．３３ｍｍｏｌ）に相当する硫黄が多硫化物イオンへと還元された場合を想定した。硫黄量は平衡後も残存することとした。硫黄が多硫化物イオンではなく、硫化水素へと還元された場合の硫化水素ガス濃度の計算も行なった（図８ｂ：多硫化物イオン無し）。
3. Analysis by Thermodynamic Calculations The concentration distribution of polysulfide ions and hydrogen sulfide in water can be predicted from thermodynamic calculations. FIG. 8 shows the results of thermodynamic calculations. In this calculation, the volumes of aqueous solution and gas were set the same as in the above urea synthesis experiment (5 mL and 8 mL, respectively). In addition, it was assumed that the urea (and carbon dioxide) formation reaction proceeded completely, that is, sulfur corresponding to the total amount of carbon monoxide (0.33 mmol) was reduced to polysulfide ions. The amount of sulfur was assumed to remain after equilibration. Hydrogen sulfide gas concentrations were also calculated when sulfur was reduced to hydrogen sulfide rather than to polysulfide ions (Fig. 8b: no polysulfide ions).
図８ａに、硫黄粉末が十分に存在する場合における、溶存硫黄成分の濃度分布をｐＨの関数として示す（温度２５℃）。硫化水素成分（Ｈ2Ｓ及びＨＳ-）は、硫黄及び多硫化物イオンとの間の平衡から生じるが、本実験を行ったｐＨ（１０．３～１０．５）においては０．７～１ｍＭで推移すると計算された。この濃度は多硫化物イオンに比べてわずかであり、溶存硫黄成分に占める割合は１～１．５％に過ぎない。結果として、水溶液と平衡にあるガス中の硫化水素濃度は１～３ｐｐｍに抑えられる（図８ｂ）。一方、硫黄が多硫化物イオンではなく、硫化水素へと還元されると仮定した場合、硫化水素ガスの予想濃度は１３０～２１０ｐｐｍと大きく増加した（図８ｂ）。多硫化物イオンの平均長は５．０であることから、Ｓ0／ＣＯが５以上であれば、硫化水素ガスの発生量は十分に低減できると予想される。一方、硫黄量が少なければ（例えばＳ0／ＣＯ＝２）、還元された硫黄種（Ｓ2-）を多硫化物イオンとして取り込みきることができず、実験でも見られたような（図６）、ガス相への硫化水素の発散をもたらすこととなる。このように、多硫化物イオンを考慮した熱力学計算は、本実験結果をうまく説明できる。反応を行った温度である３５、５０、６５℃においては、最終的に到達する硫化水素ガス濃度は、それぞれ３～８ｐｐｍ、１４～３０ｐｐｍ、４７～９８ｐｐｍと予想された。 Figure 8a shows the concentration distribution of dissolved sulfur components as a function of pH in the presence of sufficient sulfur powder (temperature 25°C). Hydrogen sulfide components (H 2 S and HS − ), which arise from the equilibrium between sulfur and polysulfide ions, range from 0.7 to 1 mM at the pH (10.3-10.5) where this experiment was performed. It was calculated that the transition at . This concentration is very small compared to polysulfide ions, and accounts for only 1 to 1.5% of the dissolved sulfur component. As a result, the hydrogen sulfide concentration in the gas in equilibrium with the aqueous solution is suppressed to 1-3 ppm (Fig. 8b). On the other hand, assuming that sulfur is reduced to hydrogen sulfide rather than polysulfide ions, the expected concentration of hydrogen sulfide gas increased significantly from 130 to 210 ppm (Fig. 8b). Since the average length of polysulfide ions is 5.0, it is expected that if S 0 /CO is 5 or more, the amount of hydrogen sulfide gas generated can be sufficiently reduced. On the other hand, if the amount of sulfur is small (for example, S 0 /CO=2), the reduced sulfur species (S 2- ) cannot be taken in as polysulfide ions, as was observed in the experiment (Fig. 6). ), resulting in the evolution of hydrogen sulfide into the gas phase. Thus, thermodynamic calculations considering polysulfide ions can well explain the results of this experiment. At the reaction temperatures of 35, 50 and 65° C., the final hydrogen sulfide gas concentrations were expected to be 3-8 ppm, 14-30 ppm and 47-98 ppm, respectively.
なお、上記の計算に用いた熱力学パラメータは、多硫化物イオンについてはKamyshny et al. (2007)から、ＨＳ-についてはShock et al. (1997)から、溶存Ｈ2ＳについてはShock et al. （1989）から、Ｈ2ＳガスについてはRobie and Hemingway (1995)から、それぞれ得た。 The thermodynamic parameters used in the above calculations are from Kamyshny et al. (2007) for polysulfide ions, from Shock et al. ( 1997 ) for HS − , and from Shock et al. (1989) and for H 2 S gas from Robie and Hemingway (1995), respectively.
水中において、多硫化イオンは一酸化炭素と反応し、硫化カルボニルを生じることが知られている（Kamyshny et al., 2003)。
ＣＯ＋Ｓn
2-→ＯＣＳ＋Ｓn-1
2-
In water, polysulfide ions are known to react with carbon monoxide to produce carbonyl sulfide (Kamyshny et al., 2003).
CO + S n 2- →OCS + S n-1 2-
硫化カルボニルは、米国特許第２６８１９３０号明細書が示すように、尿素製造における重要な反応中間体となる。本実施例においても、硫化カルボニルはバイアル瓶中のガス相から、硫化水素と共に微量に検出された（図９）。硫化カルボニルの生成速度は、一酸化炭素及び多硫化イオンの濃度に比例する（Kamyshny et al., 2003)。一方、硫化カルボニルは、水中では二酸化炭素及び硫化水素へと速やかに加水分解することが知られている。
ＯＣＳ＋Ｈ2Ｏ→ＣＯ2＋Ｈ2Ｓ
Carbonyl sulfide is an important reaction intermediate in urea production, as shown in US Pat. No. 2,681,930. Also in this example, a trace amount of carbonyl sulfide was detected together with hydrogen sulfide from the gas phase in the vial bottle (Fig. 9). The rate of carbonyl sulfide formation is proportional to the concentrations of carbon monoxide and polysulfide ions (Kamyshny et al., 2003). On the other hand, carbonyl sulfide is known to rapidly hydrolyze to carbon dioxide and hydrogen sulfide in water.
OCS+ H2O → CO2 + H2S
この半減期は、例えば５０℃、ｐＨ１０においては１８秒であり（Kamyshny et al., 2003)、実施例で見られた尿素生成プロセス（図５）に比べてはるかに短い時間スケールで進行する。しかし、実施例では二酸化炭素はあまり生じなかったことから（収率０．８％未満）、硫化カルボニルは生成後直ちにアンモニアと反応し、尿素へと変化したと考えられる。 This half-life is, for example, 18 seconds at 50° C. and pH 10 (Kamyshny et al., 2003), which proceeds on a much shorter timescale than the urea production process seen in the examples (FIG. 5). However, since very little carbon dioxide was produced in the examples (yield less than 0.8%), it is considered that carbonyl sulfide reacted with ammonia immediately after production and changed to urea.
すなわち、尿素生成反応全体の速度は、硫化カルボニルの生成が律速している可能性が考えられる。実際、図５ａに示す３５、５０、６５℃における尿素収率の経時変化は、一酸化炭素及び多硫化物イオンの濃度を用いた以下の単純な一次反応式でうまく再現できた（図１０）。
ｄ［（ＮＨ2）2ＣＯ］／ｄｔ＝ｋ［ＣＯ］［Ｓn
2-］
［（ＮＨ2）2ＣＯ］、［ＣＯ］、［Ｓn
2-］は、各成分の水中濃度（ｍｏｌ／Ｌ）を、ｋは速度定数を表す。
That is, it is conceivable that the rate of the overall urea production reaction is controlled by the production of carbonyl sulfide. In fact, the time course of urea yield at 35, 50 and 65° C. shown in FIG. 5a was successfully reproduced by the following simple first-order equation using concentrations of carbon monoxide and polysulfide ions (FIG. 10) .
d [ ( NH2 ) 2CO ]/dt=k[CO][ Sn2- ]
[(NH 2 ) 2 CO], [CO], and [S n 2- ] represent the concentration in water (mol/L) of each component, and k represents the rate constant.
図１０に示す、尿素収率及び一酸化炭素残量の実験結果（プロット）の反応速度式による再現（曲線）から、３５、５０、６５℃における速度定数ｋ（１／ｍｏｌＬＳ）は、それぞれ０．００７２、０．０３、０．０５４と予想された。 From the reproduction (curves) of the experimental results (plots) of urea yield and residual carbon monoxide shown in FIG. expected 0.0072, 0.03, 0.054.
なお、反応全体の式（ＣＯ＋２ＮＨ3＋Ｓ0→（ＮＨ2）2ＣＯ＋Ｓn
2-＋２Ｈ+）が示すように、反応進行に伴う一酸化炭素の減少量、及び多硫化物イオンの増加量は、尿素の生成量と同量となる。このため、尿素の生成速度の計算には、一酸化炭素及び多硫化物イオンの濃度を経時観測する必要は無い。実際、上記の一次反応式は、反応開始時における一酸化炭素量（［ＣＯ］0（ｍｏｌ））、多硫化物イオン量（［Ｓn
2-］0（ｍｏｌ））、水溶液量（ＶL（Ｌ））及びガス体積（Ｖg（Ｌ））をパラメータとして、以下のように表すことができる。
ｄ［（ＮＨ2）2ＣＯ］／ｄｔ＝ｋ（（［ＣＯ］0－［（ＮＨ2）2ＣＯ］ＶL）／（（Ｖg／ＲＴＨ）＋ＶL）（［（ＮＨ2）2ＣＯ］＋［Ｓn
2-］0／ＶL）
Ｒは気体定数、Ｔは絶対温度、ＨはＣＯのヘンリー定数である。
As shown by the overall reaction formula (CO+2NH 3 +S 0 →(NH 2 ) 2 CO+S n 2− +2H + ), the amount of carbon monoxide decreased and the amount of polysulfide ions increased as the reaction progressed. The amount is the same as the amount of urea produced. Therefore, the calculation of the urea production rate does not require monitoring the concentration of carbon monoxide and polysulfide ions over time. In fact, the above first-order reaction formula is based on the amount of carbon monoxide ([CO] 0 (mol)), the amount of polysulfide ions ([S n 2- ] 0 (mol)), and the amount of aqueous solution ( VL (L)) and the gas volume (V g (L)) can be expressed as follows.
d[( NH2 ) 2CO ]/dt=k(([CO] 0 -[( NH2 ) 2CO ] VL )/(( Vg /RTH)+ VL )([( NH2 ) 2CO ] + [S n 2- ] 0 /V L )
R is the gas constant, T is the absolute temperature, and H is the Henry's constant of CO.
実験結果の反応速度式による再現（図１０）から得られた速度定数は、アレニウスプロットにおいて直線性を示した（図１１）。直線を外挿して予想される温度と速度定数の関係は、先行研究で報告された一酸化炭素と多硫化物イオンからの硫化カルボニルの生成速度定数（◆）（Kamyshny et al., 2003)と大まかには調和的となった。 The rate constants obtained from the kinetic equation reproduction of the experimental results (Fig. 10) showed linearity in the Arrhenius plot (Fig. 11). The relationship between temperature and the rate constant predicted by extrapolating the straight line is similar to the rate constant of carbonyl sulfide formation from carbon monoxide and polysulfide ions reported in a previous study (◆) (Kamyshny et al., 2003). generally harmonious.
アレニウスプロットから得られる活性化エネルギー（Ｅa＝５８．５ｋJ／ｍｏｌ）及び頻度因子（Ａ＝６．７×１０7）は、以下の式に代入することで、任意の温度における尿素生成速度の予測に利用できる：
ｋ＝Ａeｘｐ（－Ｅa／ＲＴ）
Ｒは気体定数、Ｔは絶対温度である。例えば反応温度８０℃では、尿素収率８０％は８～９時間、９０％は９～１０時間で達成できると予想された（図１２）。
The activation energy (E=58.5 kJ/mol) and frequency factor (A=6.7×10 7 ) obtained from the Arrhenius plot are substituted into the following equation to predict the urea production rate at any temperature: Available for:
k=Aexp(-Ea/RT)
R is the gas constant and T is the absolute temperature. For example, at a reaction temperature of 80° C., it was expected that a urea yield of 80% could be achieved in 8-9 hours and 90% in 9-10 hours (FIG. 12).
以上のように、本発明の水を溶媒とする尿素の製造方法は、作業工程が少なく、有害レベルの硫化水素の発生を伴わないと共に、高収率な尿素の製造を可能とする。尿素生成速度や副産物である硫化水素のガス濃度は、反応速度式及び熱力学計算により、定量的に予測できる。 As described above, the method for producing urea using water as a solvent according to the present invention has fewer work steps, does not generate harmful levels of hydrogen sulfide, and enables the production of urea at a high yield. The rate of urea production and the gas concentration of hydrogen sulfide, which is a by-product, can be quantitatively predicted by reaction rate equations and thermodynamic calculations.
参考文献
Ahmad N., Ahmad F., Khan I. and Khan A.D. (2015) Studies on the oxidative remova l of sodium thiosulfate from aqueous solution. Arabian Journal for Science and Engineering 40, 289-293.
Kamyshny, Jr. A., Goifman, A., Rizkov D. and Lev O. (2003) Formation of carbonyl sulfide by the reaction of carbon monoxide and inorganic polysulfides. Enviro nmental Science & Technology 37, 1865-1872.
Kamyshny, Jr. A., Gun J., Rizkov D., Voitsekovski T. and Lev O. (2007) Equilibri um distribution of polysulfide ions in aqueous solutions at different temperat ures by rapid single phase derivatization. Environmental Science & Technology 41, 2395-2400.
Kleinjan W.E., de Keizer A. and Janssen A.J.H. (2005) Kinetics of the chemical o xidation of polysulfide anions in aqueous solution. Water Research 39, 4093-41 00.
Lara J.M.G., Cardona F.P., Vallmajor A.R. and Cadevall M.C. (2019) Oxidation of thiosulfate with oxygen using copper(II) at a catalyst. Metals 9, 387.
Marepula H., Courtney C.E. and Randall D.G. (2021) Urea recovery from stabilized urine using a novel ethanol evaporation and recrystallization process. Chemic al Engineering Journal Advances 8, 100174.
Rahmatullah M. and Boyde T.R.C. (1980) Improvements in the determination of urea using diacetylmonoxime; methods with and without deprotonation. Clinica Chimi ca Acta 107, 3-9.
Ray H., Perreault F. and Boyer T.H. (2019) Urea recovery from fresh human urine by forward osmosis and membrane distillation (FO-MD). Environmental Science Wa ter Research & Technology 5, 1993-2003.
Ray H., Perreault F. and Boyer T.H. (2020) Ammonia recovery from hydrolyzed huma n urine by forward osmosis with acidified draw solution. Environmental Science & Technology 54, 11556-11565.
Robie R.A., Hemingway B.S. (1995) Thermodynamic Properties Of Minerals And Relat ed Substances At 298.15 K And 1 Bar (105 Pascals) Pressure And At Higher Tem peratures. U.S. Geological Survey Bulletin 2131, U.S. Geological Survey.
Sander R. (2015) Compilation of Henry's law constants (version 4.0) for water as solvent. Atmospheric Chemistry and Physics 15, 4399-4981.
Shock E.L., Sassani D.C., Willis M. and Sverjensky D.A. (1997) Inorganic species in geological fluids: Correlations among standard molal thermodynamic propert ies of aqueous ions and hydroxide complexes. Geochimica et Cosmochimica Acta 6 1, 907-950.
Shock E.L., Helgeson H.C. and Sverjensky D.A. (1989) Calculation of the thermody namic and transport properties of aqueous species at high pressure and tempera tures: Standard partial molal properties of inorganic neutral species. Geochim ica et Cosmochimica Acta 53, 2157-2183.
Satanowski A. and Bar-Even A. (2020) A one-carbon path for fixing CO2. EMBO rep orts 21, e50273.
Steudel R. (1986) Mechanism for the formation of elemental sulfur from aqueous s ulfide in chemical and microbiological desulfurization processes. Industrial & Engineering Chemistry Research 35, 1417-1423.
Urbanczyk E., Sowa M. and Simka W. (2016) Urea removal from aqueous solutions - a review. Journal of Applied Electrochemistry 46, 1011-1029.
Wagenfeld J.G., Al-Ali K., Almheiri S., Slavens, A.F. and Calvet N. (2019) Susta inable applications utilizing sulfur, a by-product from oil and gas industry: A state-of-the-art review. Waste Managements 95, 78-89.
References
Ahmad N., Ahmad F., Khan I. and Khan AD (2015) Studies on the oxidative removal of sodium thiosulfate from aqueous solution. Arabian Journal for Science and Engineering 40, 289-293.
Kamyshny, Jr. A., Goifman, A., Rizkov D. and Lev O. (2003) Formation of carbonyl sulfide by the reaction of carbon monoxide and inorganic polysulfides. Environmental Science & Technology 37, 1865-1872.
Kamyshny, Jr. A., Gun J., Rizkov D., Voitsekovski T. and Lev O. (2007) Equilibrium distribution of polysulfide ions in aqueous solutions at different tempera- tures by rapid single phase derivatization. Environmental Science & Technology 41, 2395-2400.
Kleinjan WE, de Keizer A. and Janssen AJH (2005) Kinetics of the chemical oxidation of polysulfide anions in aqueous solution. Water Research 39, 4093-41 00.
Lara JMG, Cardona FP, Vallmajor AR and Cadevall MC (2019) Oxidation of thiosulfate with oxygen using copper(II) at a catalyst. Metals 9, 387.
Marepula H., Courtney CE and Randall DG (2021) Urea recovery from stabilized urine using a novel ethanol evaporation and recrystallization process. Chemical Engineering Journal Advances 8, 100174.
Rahmatullah M. and Boyde TRC (1980) Improvements in the determination of urea using diacetylmonoxime; methods with and without deprotonation. Clinica Chimi ca Acta 107, 3-9.
Ray H., Perreault F. and Boyer TH (2019) Urea recovery from fresh human urine by forward osmosis and membrane distillation (FO-MD). Environmental Science Water Research & Technology 5, 1993-2003.
Ray H., Perreault F. and Boyer TH (2020) Ammonia recovery from hydrolyzed huma n urine by forward osmosis with acidified draw solution. Environmental Science & Technology 54, 11556-11565.
Robie RA, Hemingway BS (1995) Thermodynamic Properties Of Minerals And Relat ed Substances At 298.15 K And 1 Bar (10 5 Pascals) Pressure And At Higher Tem peratures. US Geological Survey Bulletin 2131, US Geological Survey.
Sander R. (2015) Compilation of Henry's law constants (version 4.0) for water as solvent. Atmospheric Chemistry and Physics 15, 4399-4981.
Shock EL, Sassani DC, Willis M. and Sverjensky DA (1997) Inorganic species in geological fluids: Correlations among standard molal thermodynamic properties of aqueous ions and hydroxide complexes. Geochimica et Cosmochimica Acta 6 1, 907-950.
Shock EL, Helgeson HC and Sverjensky DA (1989) Calculation of the thermodynamic and transport properties of aqueous species at high pressure and tempera tures: Standard partial molal properties of inorganic neutral species. Geochim ica et Cosmochimica Acta 53, 2157-2183.
Satanowski A. and Bar-Even A. (2020) A one-carbon path for fixing CO 2 . EMBO reports 21, e50273.
Steudel R. (1986) Mechanism for the formation of elemental sulfur from aqueous s ulfide in chemical and microbiological desulfurization processes. Industrial & Engineering Chemistry Research 35, 1417-1423.
Urbanczyk E., Sowa M. and Simka W. (2016) Urea removal from aqueous solutions - a review. Journal of Applied Electrochemistry 46, 1011-1029.
Wagenfeld JG, Al-Ali K., Almheiri S., Slavens, AF and Calvet N. (2019) Susta inable applications utilizing sulfur, a by-product from oil and gas industry: A state-of-the-art review. Managements 95, 78-89.
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