- Kinetics of the NH3and CO2 solid-state reaction at low temperature
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Ammonia and carbon dioxide play an important role in both atmospheric and interstellar ice chemistries. This work presents a theoretical and experimental study of the kinetics of the low-temperature NH3 and CO2 solid-state reaction in ice films, the product of which is ammonium carbamate (NH4+NH2COO-). It is a first-order reaction with respect to CO2, with a temperature-dependent rate constant fitted to the Arrhenius law in the temperature range 70 K to 90 K, with an activation energy of 5.1 ± 1.6 kJ mol-1 and a pre-exponential factor of 0.09 +1.1-0.08 s-1. This work helps to determine the rate of removal of CO2 and NH3, via their conversion into ammonium carbamate, from atmospheric and interstellar ices. We also measure first-order desorption energies of 69.0 ± 0.2 kJ mol-1 and 76.1 ± 0.1 kJ mol-1, assuming a pre-exponential factor of 1013 s-1, for ammonium carbamate and carbamic acid, respectively.
- Noble,Theule,Duvernay,Danger,Chiavassa,Ghesquiere,Mineva,Talbi
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- Catalytic Urea Synthesis from Ammonium Carbamate Using a Copper(II) Complex: A Combined Experimental and Theoretical Study
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The synthesis of urea fertilizer is currently the largest CO2 conversion process by volume in the industry. In this process, ammonium carbamate is an intermediate en route to urea formation. We determined that the tetraammineaquacopper(II) sulfate complex, [Cu(NH3)4(OH2)]SO4, catalyzed the formation of urea from ammonium carbamate in an aqueous solution. A urea yield of up to 18 ± 6% was obtained at 120 °C after 15 h and in a high-pressure metal reactor. No significant urea formed without the catalyst. The urea product was characterized by Fourier transform infrared (FT-IR), powder X-ray diffraction (PXRD), and quantitative 1H{13C} NMR analyses. The [Cu(NH3)4(OH2)]SO4 catalyst was then recovered at the end of the reaction in a 29% recovery yield, as verified by FT-IR, PXRD, and quantitative UV-vis spectroscopy. A precipitation method using CO2 was developed to recover and reuse 66 ± 3% of Cu(II). The catalysis mechanism was investigated by the density functional theory at the B3LYP/6-31G*? level with an SMD continuum solvent model. We determined that the [Cu(NH3)4]2+ complex is likely an effective catalyst structure. The study of the catalysis mechanism suggests that the coordinated carbamate with [Cu(NH3)4]2+ is likely the starting point of the catalyzed reaction, and carbamic acid can be involved as a transient intermediate that facilitates the removal of an OH group. Our work has paved the way for the rational design of catalysts for urea synthesis from the greenhouse gas CO2.
- Dennis, Donovan,Ekmekci, Merve B.,Hanson, Danielle S.,Paripati, Amay,Wang, Yigui,Washburn, Erik,Xiao, Dequan,Zhou, Meng,Zhou, Xinrui
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- Carbamic acid: Molecular structure and IR spectra
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Infrared absorption spectra of mixed H2O, NH3 and 12CO2/13CO2 ices subjected to 1 MeV proton irradiation were investigated. The results of analyses of the spectra suggest formation of carbamic acid at low temperatures. The stability of this compound in the solid phase is attributed to intermolecular hydrogen bonding of the zwitter-ion (NH3+COO-) structure.
- Khanna,Moore
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- New attempt for CO2 utilization: One-pot catalytic syntheses of methyl, ethyl and n-butyl carbamates
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The direct production of methyl, ethyl and n-butyl carbamates (MC, EC and BC) from NH3, CO2 and alcohols could efficiently be catalyzed by V2O5, and ca. 11-25% yields with 98% selectivity for alkyl carbamates could be obtained. The catalyst could be recycled six times without obvious decrease in catalytic activity. XRD and XPS analysis showed that in-situ produced (NH4)2V 3O8 was the catalytically active species.
- Li, Jian,Qi, Xiujuan,Wang, Liguo,He, Yude,Deng, Youquan
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- First characterisation of two important postulated intermediates in the formation of a HydT DNA lesion, a thymidine oxidation product
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A number of environmental pollutants and endogenous oxidation agents form 1-(2-deoxy-β-d-ribofuranosyl)-5-hydroxy-5-methylhydantoin (HydT), an important DNA lesion resulting from thymidine oxidation. In this paper, two intermediates, postulated in the formation of HydT, have been characterised for the first time. The first, N1-formyl-N3-pyruvoylurea intermediate, was produced by the ozonolysis reaction of 2′,3′,5′-tri-O-acetylribo-, 3′,5′-di-O-TBS- and N3,O3′,O5-tribenzyl-protected thymidines and was shown to produce, upon decomposition and depending on the protecting group and the conditions, HydT alone, or together with protected-β-d-ribofuranosyl-N1-formylurea and formamide products. In addition, the second and long sought, open-chain-pyruvoylurea intermediate, was produced through de novo synthesis in protected β-d-ribofuranosyl-, 2-deoxy-β-d-ribofuranosyl- and 2-deoxy-β-d-ribopyranosyl systems. The conditions that induce the cyclization to the hydantoin ring of HydT have been determined. The chemistry utilised in the de novo synthesis is suitable for generating isotopically labelled HydT, as a reference in isotope-dilution-aided quantification of DNA damage.
- Psykarakis, Emmanuel E.,Chatzopoulou, Elli,Gimisis, Thanasis
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p. 2289 - 2300
(2018/04/05)
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- Direct NHC-catalysed redox amidation using CO2 for traceless masking of amine nucleophiles
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The N-heterocyclic carbene (NHC)-catalysed redox amidation reaction is poorly developed and usually requires catalytic co-additives for electron-rich amine nucleophiles. We report a masking strategy (using CO2) that couples release of the free amine nucleophile to catalytic turnover, and in doing so, enables direct catalytic redox amidation of electron-rich amines.
- Davidson, Robert W. M.,Fuchter, Matthew J.
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supporting information
p. 11638 - 11641
(2016/10/04)
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- HIGH-YIELD PROCESS FOR THE SYNTHESIS OF UREA
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A process for the direct synthesis of urea from ammonia and carbon dioxide at high pressures and temperatures, with the formation of ammonium carbamate as intermediate, comprising a decomposition step of the ammonium carbamate and stripping of the gases formed, operating substantially at the same pressure as the synthesis step, wherein the recycled liquid streams are fed, at least partially, to the same decomposition and stripping step after being preheated by heat exchange with a stream included in the high-pressure synthesis cycle.
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Paragraph 0086-0127
(2014/04/03)
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- A process for synthesis of urea and a related arrangement for a reaction section of a urea plant
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A process for synthesis of urea and a related reaction section of a urea plant, where: ammonia and carbon dioxide are reacted in a liquid phase in a first reaction zone (S1) and heat (Q1) is withdrawn from said first reaction zone to promote the formation of ammonium carbamate, the liquid product (103) from said first reaction zone is then passed to a second reaction zone (S2) distinguished from said first reaction zone, and heat (Q2) is added to said second reaction zone to promote the decomposition of ammonium carbamate into urea and water, where the liquid phase in at least one of said first reaction zone and second reaction zone is kept in a stirred condition.
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Paragraph 0079
(2013/06/27)
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- N-(4-Substituted-benzoyl)-N′-(β-d-glucopyranosyl)ureas as inhibitors of glycogen phosphorylase: Synthesis and evaluation by kinetic, crystallographic, and molecular modelling methods
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N-(4-Substituted-benzoyl)-N′-(β-d-glucopyranosyl) ureas (substituents: Me, Ph, Cl, OH, OMe, NO2, NH2, COOH, and COOMe) were synthesised by ZnCl2 catalysed acylation of O-peracetylated β-d-glucopyranosyl urea as well as in reactions of O-peracetylated or O-unprotected glucopyranosylamines and acyl-isocyanates. O-deprotections were carried out by base or acid catalysed transesterifications where necessary. Kinetic studies revealed that most of these compounds were low micromolar inhibitors of rabbit muscle glycogen phosphorylase b (RMGPb). The best inhibitor was the 4-methylbenzoyl compound (Ki = 2.3 μM). Crystallographic analyses of complexes of several of the compounds with RMGPb showed that the analogues exploited, together with water molecules, the available space at the β-pocket subsite and induced a more extended shift of the 280s loop compared to RMGPb in complex with the unsubstituted benzoyl urea. The results suggest the key role of the water molecules in ligand binding and structure-based ligand design. Molecular docking study of selected inhibitors was done to show the ability of the binding affinity prediction. The binding affinity of the highest scored docked poses was calculated and correlated with experimentally measured Ki values. Results show that correlation is high with the R-squared (R2) coefficient over 0.9.
- Nagy, Veronika,Felfoeldi, Nora,Konya, Balint,Praly, Jean-Pierre,Docsa, Tibor,Gergely, Pal,Chrysina, Evangelia D.,Tiraidis, Costas,Kosmopoulou, Magda N.,Alexacou, Kyra-Melinda,Konstantakaki, Maria,Leonidas, Demetres D.,Zographos, Spyros E.,Oikonomakos, Nikos G.,Kozmon, Stanislav,Tvaroska, Igor,Somsak, Laszlo
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supporting information; experimental part
p. 1801 - 1816
(2012/04/10)
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- 5′-Uridyl derivatives of N-glycosyl allophanic acid and biuret
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(2′,3′-O-Isopropylidene-5′-uridyl) 4-(2,3,4,6-tetra-O-acetyl-β-d-glycopyranosyl)allophanates were obtained in the reactions of 2′,3′-O-isopropylidene-uridine and O-peracetylated β-d-gluco-, galacto- and xylopyranosylamines, and OCNCOCl. 2,3,4,6-Tetra-O-acetyl-β-d-glucopyranosyl isocyanate and N-(2′,3′-O-isopropylidene-5′-uridyl)urea gave 1-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-5-(2′,3′-O-isopropylidene-5′-uridyl)biuret. Deprotection of the β-d-gluco configured allophanate and biuret was carried out by standard methods.
- Tóth, Marietta,Somsák, László
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experimental part
p. 163 - 167
(2011/02/26)
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- Process for the production of urea from ammonia and carbon dioxide
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Process for the production of urea from ammonia and carbon dioxide in a urea plant containing a high-pressure synthesis section comprising at least one reactor section, a stripper and a condenser wherein all the high-pressure equipment is placed in a low position, wherein the height of the high-pressure section is less than 35 m from ground level and at least one of the reactor sections comprises means for the separate distribution of ammonia in the bottom of the reactor section.
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Page/Page column 4
(2009/12/07)
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- Process for the production of urea from ammonia and carbon dioxide
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Process for the production of urea from ammonia and carbon dioxide in a urea plant containing a high-pressure synthesis section comprising two reactor sections, a stripper and a condenser, and a recovery section, wherein in the first reactor section a first synthesis solution is formed that is fed to the second reactor section; fresh carbon dioxide is fed to the second reactor section and in the second reactor section a second synthesis solution is formed that is fed to the stripper, wherein the second synthesis solution is stripped with the use of carbon dioxide as stripping gas and the mixed gas stream obtained in the stripper is sent to the condenser together with fresh ammonia and a carbamate stream, whereafter the condensate that is formed in the condenser is fed to the first reactor section and the urea stream that is obtained in the stripper is further purified in the recovery section, wherein the flow of the first synthesis solution from the first reactor section to the second reactor section, the flow of the second synthesis solution from the second reactor section to the stripper, the flow of the mixed gas stream from the stripper to the condenser and of the condensate from the condenser to the first reactor section is a gravity flow.
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(2009/12/07)
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- PROCESS FOR THE PREPARATION OF UREA
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Process for the preparation of urea from ammonia and carbon dioxide in a urea production process comprising, in a high-pressure synthesis section, a. a reactor, wherein ammonia and carbon dioxide react to form a urea-comprising synthesis solution, b. a stripper, wherein the urea-comprising synthesis solution is heated and stripped, optionally in counter-current with a stripping agent, c. a submerged condenser, wherein the gas leaving the top of the stripper is, at least partially, condensed to form a condensate solution and d. an ejector, in the line connecting the submerged condenser and the reactor, supporting the transport of the condensate solution from the submerged condenser to the reactor, wherein a gas stream leaving the top of the submerged condenser is controlled by one or more controlling elements.
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Page/Page column 3; 6-9
(2008/12/06)
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- APPARATUS FOR UREA SYNTHESIS
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In an apparatus for synthesizing urea, it is avoided to pass downward a urea synthesis solution, which is a two-phase gas-liquid stream, and the stream is stabilized as such (i.e., as being the two-phase gas-liquid stream) to enable smoother operation, thereby lessening the flow resistance and reduce energy loss. Namely, an apparatus for synthesizing urea which comprises: a synthesis tube wherein NH3 is reacted with CO2 to give a urea synthesis solution containing urea, the unreacted NH3, the unreacted CO2 and water; a stripper whereby the urea synthesis solution is stripped by using at least a portion of the starting CO2 to thereby separate a gas mixture containing the unreacted NH3 and the unreacted CO2; a vertical submerge condenser which has a shell-and-tube structure and by which the above-described gas mixture is condensed into an absorption medium in the shell side under cooling with a cooling medium passing through the tube side; and a circulation means for circulating the liquid obtained from the condenser into the synthesis tube; wherein the synthesis tube is in the horizontal type and the pipe for feeding the urea synthesis solution from the synthesis tube to the stripper is located substantially horizontally and/or upward.
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Page/Page column 16-18; 1/3-3/3
(2008/06/13)
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- METHOD AND APPARATUS FOR SYNTHESIZING UREA
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In a process and an apparatus for synthesizing urea which synthesize urea from ammonia and carbon dioxide, the operating condition can be grasped easily and with good accuracy. A process for synthesizing urea which includes: a reaction step of obtaining a urea synthesis solution which contains urea, unreacted ammonia, unreacted carbon dioxide and water by causing ammonia and carbon dioxide to react with each other; a stripping step of separating a gas mixture containing the unreacted ammonia and the unreacted carbon dioxide by stripping the urea synthesis solution by using at least a portion of raw material carbon dioxide; a condensing step of obtaining a condensed liquid by condensing the gas mixture in an absorbing medium while cooling the gas mixture; a recycling step of recycling the condensed liquid to the reaction step; and a step of measuring the density of the condensed liquid online. An apparatus for carrying out this process is provided.
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Page/Page column 4; 10-11
(2008/06/13)
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- APPARATUS FOR UREA SYNTHESIS AND METHOD OF IMPROVING THE SAME
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In an apparatus for synthesizing urea and a method of improving the same, it becomes possible to provide a heavy condenser at a relatively low position and, further, it becomes possible to overcome the problems caused by passing a process fluid from the condenser in a tube. Namely, an apparatus for synthesizing urea which comprises: a synthesis tube wherein NH3 is reacted with CO2 to give a synthesis solution containing urea, the unreacted NH3, the unreacted CO2 and water; a stripper whereby the synthesis solution is stripped by using at least a portion of the starting CO2 to thereby separate a gas containing the unreacted NH3 and CO2; a vertical submerge condenser which has a shell-and-tube structure and by which the above-described gas is condensed into an absorption medium in the shell side under cooling with a cooling medium passing through the tube side; and a circulation means for circulating the liquid obtained from the condenser into the synthesis tube; wherein the condenser is located below the synthesis tube. A method of improving an apparatus for synthesizing urea having a synthesis tube which comprises providing the stripper, vertical submerge condenser and circulation means as described above and locating the condenser below the synthesis tube.
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Page/Page column 19-21; 1/6-6/6
(2008/06/13)
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- PROCESS FOR THE PREPARATION OF UREA
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The invention relates to a process for the preparation of urea from ammonia and carbon dioxide in a urea plant that contains a high-pressure synthesis section and one or more recovery section(s) at a lower pressure, the high-pressure synthesis section comprising a reactor, a stripper and a condenser, with gases leaving the high-pressure synthesis section being condensed in a medium-pressure condenser at 0.5-12 MPa to which also a carbamate stream from one of the recovery sections is supplied, afteer which at least a part of the formed condensate is supplied to the high-pressure condenser.
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Page/Page column 3; 4; 10
(2008/06/13)
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- Process for making dialkyl carbonates
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A process for the production of dialkyl carbonates from the reaction of alcohol, for example C1-C3 alcohols, with urea is disclosed wherein the water and ammonium carbamates impurities in the feed are removed in a prereactor. The water is reacted with urea in the feed to produce ammonium carbamate which is decomposed along with the ammonium carbamates originally in the feed to ammonia and carbon dioxide. In addition some of the urea is reacted with the alcohol in the first reactor to produce alkyl carbamate which is a precursor to dialkyl carbonate. Dialkyl carbonates are produced in the second reaction zone. The undesired by-product N-alkyl alkyl carbamates are continuously distilled off from the second reaction zone along with ammonia, alcohol and dialkyl carbonates under the steady state reactor operation. N-alkyl alkyl carbamates can be converted to heterocyclic compounds in a third reaction zone to remove as solids from the system.
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Page/Page column 3
(2008/06/13)
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- Process for the preparation of urea
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The invention relates to a process for the preparation of urea from ammonia and carbon dioxide in which the low-pressure carbamate stream formed in the further upgrading of the urea synthesis solution is stripped in a CO2-carbamate stripper in countercurrent contact with CO2, which results in the formation of a gas mixture consisting substantially of ammonia and carbon dioxide. This gas mixture is preferably subsequently condensed in a high-pressure carbamate condenser and then returned to the synthesis zone.
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- Urease-catalyzed Hydrolysis of Urea Differential vs. Integration Kinetic Methods
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The kinetics of urease-catalyzed hydrolysis of urea was studied with differential and integration kinetic methods.The values of Michaelis constant KM and of maximum reaction rate vmax equal to 19.9 mM and 0.178 mM urea/min mg protein, and 12.3 mM and 0.157 mM urea/min mg protein were obtained by differential and integration methods, respectively.Enzyme activity retention in the initial short period of the reaction was found responsible for the observed discrepancy between the obtained results. - Key words: urease; urea hydrolysis; differential and integration kinetic methods
- Leszko, Maciej,Zaborska, Wieslawa,Krajewska, Barbara
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p. 129 - 138
(2007/10/03)
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- INFLUENCE OF EXCESS CARBON DIOXIDE ON EQUILIBRIUM IN THE BAZAROV REACTION.
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Results of an investigation are presented of the effect of excess of CO//2 in the ammonia-carbon dioxide system on the equilibrium during synthesis of urea. It is shown that the degree of conversion of ammonia into urea increases with increase of the amount of excess CO//2.
- Gorlovskii,Koshcherenkov,Kucheryavyi
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p. 2780 - 2783
(2007/11/12)
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