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Ammonium Carbamate

Single crystals for two polymorphs of the ammonium carbamate self-derivative salt of prolinamide have been successfully obtained and characterized. Decarbonation of the carbamate salts was monitored by calorimetry, confirming stabilization of the reactive carbonated adducts in the solid state. Sublimation of the salts afforded crystals of prolinamide, leading to the first crystal structure of this otherwise common molecule. Reactivity of the ammonium carbamate self-derivative salt is further illustrated by the observation of a series of derived products, including dehydroprolinamide, a methylene-bridged prolinamide, and a bicyclic derivative. Crystal structures of these products display distinct amidic and/or non-amidic hydrogen bonding. This study emphasizes the reactivity of carbonated amines stabilized in the solid and opens perspectives for a systematic study of (solid-state) reactions involving these trapped reactive species.

ammonium carbamate


(a) Ammonium carbonate ((NH4)2CO3, CAS Reg. No. 8000-73-5) is a mixture of ammonium bicarbonate (NH4HCO3) and ammonium carbamate (NH2COONH4). It is prepared by the sublimation of a mixture of ammonium sulfate and calcium carbonate and occurs as a white powder or a hard, white or translucent mass.

Ammonium carbamate is a salt formed by the reaction of ammonia with carbon dioxide or carbamic acid. Ammonium carbamate can play a key role in the formation of carbamoyl phosphate, which is necessary for both the urea cycle and the production of pyrimidines. In this enzyme-catalyzed reaction, ATP and ammonium carbamate are converted to ADP and carbamoyl phosphate. Ammonium carbamate is used as an inert ingredient in aluminum phosphide pesticide formulations functioning to make the phosphine less flammable by freeing ammonia and carbon dioxide to dilute hydrogen phosphide formed by a hydrolysis reaction. It can also be used as a good ammoniating agent, but not nearly as strong an ammoniating agent as ammonia. Ammonium carbamate has also been used in Glycoblotting, a high throughput method for N-glycan enrichment, proven to be feasible for selective enrichment analysis of O-glycans of common (mucin) glycoproteins.

Addition of water to NH3:CO2 ice on grains slowed the reaction down. At the H2O:CO2 ratio of 5:1, the reaction was not detected on the experimental timescale. This result calls into question the thermal formation of ammonium carbamate in dense molecular clouds and outer regions of protostellar and protoplanetary environments with dominating water ice mantle chemistry. However, it can still happen in inner regions of protostellar and protoplanetary environments in crystalline ices.

The specific energy storage capacities of phase change materials (PCMs) increase with temperature, leading to a lack of thermal management (TM) systems capable of handling high heat fluxes in the temperature range from 20C to 100C. State of the art PCMs in this temperature range are usually paraffin waxes with energy densities on the order of a few hundred kJ/kg or ice slurries with energy densities of the same magnitude. However, for applications where system weight and size are limited, it is necessary to improve this energy density by at least an order of magnitude. The compound ammonium carbamate (AC), [NH4 ][H2NCOO], is a solid formed from the reaction of ammonia and carbon dioxide which endothermically decomposes back to ammonia and carbon dioxide in the temperature range of 20C to 100C with an enthalpy of decomposition of 2,010 kJ/kg. Various methods to use this material for TM of low-grade, high-flux heat have been evaluated including: bare powder, thermally conductive carbon foams, thermally conductive metal foams, hydrocarbon based slurries, and a slurry in ethylene glycol or propylene glycol. A slurry in glycol is a promising system medium for enhancing heat and mass transfer for TM. Small-scale system level characterizations of AC in glycol have been performed and results indicate that AC is indeed a promising material for TM of low-grade heat. It has been shown that pressures on the order of 200 torr will achieve rapid decomposition and thermal powers of over 300 W at 60C have been found, demonstrating the capability of AC.

Schmidt, Joel Edward, "The use of ammonium carbamate as a high specific thermal energy density material for thermal management of low grade heat" (2011). Graduate Theses and Dissertations. 352. _theses/352

Ammonium carbamate is produced by reacting ammonia and carbon dioxide at high pressures (up to 200 bar) in a special reactor. The urea reactor is a reactor vessel inside a protective shell. Should there be a leak in the reactor, the shell can contain the chemicals released long enough for an orderly plant shutdown. The space between the reactor skin and the shell is most often empty and employs various methods of detecting a leak ranging from conductivity measurements to infrared analysis.

Duplex steels though are not completely impervious to an attack by ammonium carbamate. There are two circumstances where a different material, zirconium, is needed. Zirconium is the best material for ammonium carbamate but is expensive, hard-to-work-with, etc., so using zirconium, as a standard material of construction is not feasible. There are two instances in urea plants though where zirconium is the prudent choice.

- a recycling section (SE-RI), for separating urea from an aqueous solution (SC) of unreacted products leaving the reactor (R2), comprising a stripper (S) for stripping a great part of carbamate and part of the free ammonia included in a urea solution coming out of said reactor (R2),

Claim 1 of the third auxiliary request differed from Claim 1 of the second auxiliary request in that the expression "via a carbamate condenser" was added after "means for recycling the stripped carbamate and free ammonia to said reactor (R2)" and the expression "via said carbamate condenser" was added after the expression "providing means for recycling the flash vapours (VF) to said reactor (R2) of the pre-existing plant" (step d).

A feed of ammonia (1) and carbon dioxide (2) in a molar ratio NH3:CO2 between 4 and 10 is passed in an autoclave (3) to achieve high conversion to urea (cf. column 3, lines 10 to 20). The resulting urea-containing stream is passed to an excess ammonia separation vessel (7) for removing excess ammonia which is condensed and recycled or stored (column 3, lines 26 to 30; lines 57 to 60). The residual effluent stream (17) is removed and passed into ammonium carbamate decomposer (18). An additional urea synthesis effluent stream (19), also containing ammonium carbamate, is passed into ammonium decomposer (18) together with stream (17)(cf. column 3, lines 61 to 66). This stream (19) comes from the second urea synthesis autoclave (55) which receives an aqueous ammonium carbamate solution (54) (see below) and additional ammonia (56) and carbon dioxide (57) and which operates with a relatively low proportion of excess ammonia, and achieves a lower percent conversion than the autoclave (3) (cf. column 2, lines 47 to 50; column 4, lines 63 to 75). The mixed gas-liquid stream removed from ammonium carbamate decomposer (18) is passed into decomposer separator vessel (23) to separate via (24) a mixed off-gas (cf. column 4, lines 1 to 2) and via (25) a liquid consisting primarily of an aqueous urea solution with a slight amount of residual ammonium carbamate and free ammonia (cf. column 4, lines 6 to 9). The mixed off-gases from separator (23) are passed into the condenser stripper (43) to be scrubbed to remove bulk of carbon dioxide so that a final ammonia stream free of carbon dioxide is removed via (47) and condensed to liquid ammonia stream (49) suitable for direct recycle (cf. column 4 lines 46 to 62). An aqueous ammonium carbamate solution is also withdrawn from unit (43) and passed into the second urea autoclave (55) (column 4, lines 63 to 67).

2.3. Thus, the resulting plant disclosed in document (2) comprises the same technical features as the resulting plant obtained by the claimed method. Indeed, the reactor (R2) corresponds to the reactor (55), the recovery section (SE-RI) corresponds to the system comprising the decomposer (18), the separator vessel (23) and the condenser stripper (43). The reactor (R1) corresponds to the reactor (3) also connected to the said system (18), (23) and (43) and to fresh ammonia and carbon dioxide. The said system is also connected to reactor (55), i.e. reactor (R2), for recycling carbamate solution (unreacted products). Furthermore, since the pure ammonia removed from the condenser (43) is recycled, one of the alternatives which emerges unambiguously for the skilled reader from the disclosure of document (2) is that the ammonia is recycled to the reactor (3), i.e. reactor (R1).

2.6. Document (6) is the Snamprogetti process as described in the patent in suit (cf. column 1, lines 18 to 52 and Figure 1). This description is not a prior art disclosure since it was part of the application as filed and, moreover, does not refer to any source of information made available to the public which could have confirmed the content of this description. It is, therefore, not admissible from a legal point of view to consider such a description as prior art. This finding has nevertheless no consequence on the issue to be decided since the parties agreed to rely in lieu thereof on the disclosure of document (22) which discloses the said Snamprogetti process with recycling of the carbamate solution to the reactor. However, document (22) cannot be the closest prior art since it does not address the same objective as the claimed invention, namely a method of retrofitting a pre-existing plant.

"Two synthesis autoclaves are employed in the process. The first autoclave receives feed streams of ammonia and carbon dioxide, with a high excess of ammonia being employed, and achieves a very high percent conversion to urea. The effluent from the first reactor is combined (emphasis added by the Board) with the effluent from the second reactor, and the resulting stream is processed to yield product urea solution, pure ammonia, and aqueous ammonium carbamate solution. The aqueous ammonium carbamate solution is then recycled to the second reactor, together with additional ammonia and carbon dioxide. This second reactor is operated with a relatively low proportion of excess ammonia, and achieves a lower percent conversion than the first reactor" (cf. column 2, lines 35 to 50). 041b061a72


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