Ureas from carbon dioxide

The assay used to quantify blood urea nitrogen relies on coupling the production of ammonia and carbon dioxide from urea to the transamination of a-ketoglutarate to glutamate and the subsequent oxidation of NADH ( 340) (Fig. 16-2). 

An aqueous solution of amitrole can decompose in the following free radical systems Fenton s reagent, UV irradiation, and riboflavin-sensitized photodecomposition (Plimmer et al, 1967). Amitrole-5- C reacted with Fenton s reagent to give radiolabeled carbon dioxide, unlabeled urea, and unlabeled cyanamide. Significant degradation of amitrole was observed when an aqueous solution was irradiated by a sunlamp (L = 280-310 nm). In addition to ring compounds, it was postulated that other products may have formed from the polymerization of amitrole free radicals (Plimmer et al., 1967). 

Indirect calorimetry This approach is so indirect that it does not involve measuring heat at all All the energy expended by a person arises from the oxidation of carbohydrates, fats and/or proteins, which use oxygen and produce carbon dioxide (and urea), all of which can be measured. 

Daicel Chemical Industries in Japan patented a promising phosgene-free process involving the reaction of an aliphatic diamine with dimethyl carbonate (DMC) to produce carbamate esters, which are then thermally converted to the corresponding aliphatic diisocyanates [38] (Scheme 5.4). It is noteworthy that this process could be a total phosgene-free process since the reactant, DMC, can be made directly from methanol and carbon dioxide (or urea) and eliminates the use of phosgene [39]. 

Because urea is made from ammonia and carbon dioxide, all urea plants are located adjacent to or in close proximity to an ammonia plant. Figure 22.21111 shows an example of an ammonia plant and a urea plant that are part of the same complex. 

GREENOX A process for purifying carbon dioxide from combustion gases, so that it may be used in greenhouses for enhancing plant growth. Nitric oxide is removed by the SCR process, using urea as the reductant. Carbon monoxide and ethylene are catalytically oxidized to carbon dioxide. Developed by Haldor Topsoe in 1997. 

Two umbilical arteries from the foetus carry blood to the placenta and a single umbilical vein returns blood from the placenta back to the foetus. The functions of the placenta in pregnancy are to supply oxygen and nutrients from the maternal circulation to the foetus and to remove waste materials, such as urea and carbon dioxide, from foetal blood. 

Guanidine is a soluble, crystalline compound and acts as a very strong base, as would be expected from the fact that it contains three ammonia residues, one of which, as an imino group, is in place of a carbonyl oxygen in urea or in carbonic acid. It readily absorbs carbon dioxide from the air. It is decomposed by barium hydroxide into urea and ammonia. 

In the partial-recycle process, part of the off-gas ammonia and carbon dioxide from the carbamate strippers is recycled to the urea reactor. Recycling is accomplished by absorbing the stripper gases in a recycle stream of partially stripped urea effluent, in process-steam condensate, or in mother liquor from a crystallization finishing process. In this manner, the amount of NH3 in off-gas is reduced. Any proportion of the unreacted ammonia can be recycled typically, the amount of ammonia that must be used in some other process is reduced to about 15% of that from a comparable once-through unit. 

Due to the incomplete second reaction, the reactor outlet mixture contains significant amounts of ammonium carbamate in addition to urea and water. The ammonium carbamate is usually removed by decomposing into its constituents ammonia and carbon dioxide (reverse reaction of Eq. (3.15)) via increasing temperature and decreasing pressure [12]. Stripping using ammonia or carbon dioxide also supports ammonia carbamate decomposition [12] (see also process description in Section 3.3.2) and, in addition, removes the formed ammonia and carbon dioxide from the hquid phase. 

An economic study comparing the Fluor Solvent process with the activated hot potassium carbonate process for the removal of carbon dioxide from synthesis gas for the production of ammonia and urea has been reported by Cook and Tennyson (1969). The authors concluded that the process is more economical than activated hot potassium carbonate in all cases stud-... 

The ammonia process can be combined with a urea process, and some operating and investment efficiencies can be realized." The synthesis gas generated by conventional means is mixed with liquid ammonia before the carbon dioxide is removed. This mixture of ammonia and carbon dioxide is synthesized to urea, and the off-gas from this operation is used for ammonia synthesis. The carbon dioxide-removal step thus is eliminated, and the compression of carbon dioxide for urea is avoided. 

Case a above corresponds to Eq. (17). It is seen that in this case, which is based on the use of pure methane as feed, on 100% conversion of the feed and 100% yield of ammonia from hydrogen and nitrogen and of carbon dioxide from carbon and oxygen, there is a deficit of carbon dioxide of 13% compared to the amount required for full conversion of ammonia to urea. 

Synthetic chemical approaches to the preparation of carbon-14 labeled materials iavolve a number of basic building blocks prepared from barium [ CJ-carbonate (2). These are carbon [ C]-dioxide [ CJ-acetjlene [U— C]-ben2ene, where U = uniformly labeled [1- and 2- C]-sodium acetate, [ C]-methyl iodide, [ C]-methanol, sodium [ C]-cyanide, and [ CJ-urea. Many compHcated radiotracers are synthesized from these materials. Some examples are [l- C]-8,ll,14-eicosatrienoic acid [3435-80-1] inoxn. [ CJ-carbon dioxide, [ting-U— C]-phenyhsothiocyanate [77590-93-3] ftom [ " CJ-acetjlene, [7- " C]-norepinephrine [18155-53-8] from [l- " C]-acetic acid, [4- " C]-cholesterol [1976-77-8] from [ " CJ-methyl iodide, [l- " C]-glucose [4005-41-8] from sodium [ " C]-cyanide, and [2- " C]-uracil [626-07-3] [27017-27-2] from [ " C]-urea. All syntheses of the basic radioactive building blocks have been described (4). 

Some of the chemicals mentioned above and others, such as chlorinated mbber or paraffin, antimony trioxide, calcium carbonate, calcium borate, pentaerythrithol, alumina trihydrate, titanium dioxide, and urea—melamine—formaldehyde resin, may be used to formulate fire retardant coatings. Many of these coatings are formulated in such a way that the films intumesce (expand) when exposed to fire, thus insulating the wood surface from further thermal exposure. Fire retardant coatings are mostly used for existing constmction. 

This ammonia is recycled to the reactor via a compressor and a heater. Liquid ammonia is used as reflux on the top of the absorber. The net amount of carbon dioxide formed in the reactor is removed as bottom product from the absorber in the form of a weak ammonium carbamate solution, which is concentrated in a desorber-washing column system. The bottom product of this washing column is a concentrated ammonium carbamate solution which is reprocessed in a urea plant. The top product, pure ammonia, is Hquefted and used as reflux together with Hquid makeup ammonia. The desorber bottom product, practically pure water, is used in the quench system in addition to the recycled mother Hquor. 

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

The carbon dioxide removed in synthesis gas preparation can be reacted with ammonia, to lonn urea CO(NH2)2- This is an excellent fertilizer, highly concentrated in nitrogen (46.6%) and also useful as an additive in animal feed to provide the nitrogen for formation of meat protein. Urea is also an important source of resins and plastics by reacting it with formaldehyde from methanol. 

Reaction of the glycol, 70, affords an oxazolidinone rather than the expected carbamate (71) on fusion with urea. It has been postulated that the urea is in fact the first product formed. This compound then undergoes 0 to N migration with loss of carbon dioxide reaction of the amino alcohol with the isocyanic acid known to result from thermal decomposition of urea affords the observed product, mephenoxolone (74) this compound shows activity quite similar to that of the carbamate. An analogous reaction on the glyceryl ether, 75, affords metaxa-lone (76). 

Sodium (9.6 parts) was dissolved in butanol (192 parts) and di-n-butyl ethyl 1 -methyl-n-butylmalonate (62,B parts) and urea (14.4 parts) were added to the warm solution with agitation. The mixture was then heated to reflux temperature in three quarters of an hour and maintained for 2 hours. The reaction mass was kept, water (150 parts) added, the aqueous portion separated, and the butanol layer extracted with water (3 x 50 parts). The combined aqueous extracts were then given 3 small extractions with benzene, the aqueous liquors separated, charcoaled,filtered and precipitated with concentrated hydrochloric acid (acid to congo-paper). The solid was collected, washed with water, dissolved in N-sodium hydroxide and reprecipitated with carbon dioxide. On recrystallization, from aqueous alcohol, the pentobarbitone was obtained. 

Synthesis gas is a major source of hydrogen, which is used for producing ammonia. Ammonia is the host of many chemicals such as urea, ammonium nitrate, and hydrazine. Carbon dioxide, a by-product from synthesis gas, reacts with ammonia to produce urea. 

Exit gases from the shift conversion are treated to remove carbon dioxide. This may be done by absorbing carbon dioxide in a physical or chemical absorption solvent or by adsorbing it using a special type of molecular sieves. Carbon dioxide, recovered from the treatment agent as a byproduct, is mainly used with ammonia to produce urea. The product is a pure hydrogen gas containing small amounts of carbon monoxide and carbon dioxide, which are further removed by methanation. 

Where ammonia is employed to raise the condensate pH, several reactions take place, but none of the reaction products are particularly stable. Essentially, white ammonium carbamate is formed from the reaction of ammonia and carbon dioxide, and these damp feathery crystals may cause blockages in cold areas of the condensate system. The salt is unstable and, if heated, the ammonium carbamate forms urea [CCKNH ], which then hydrolyzes back to ammonia and carbon dioxide ... 

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