Carbon reforming

The most effective method of SNG production with an HTGR is the stcam-carbon reforming process in which superheated steam reacts with pulverized coal to form methane-rich SNG. A system for accomplishing this process is shown in Fig. 24. In this system, an intermediate heat exchanger (1HX) has been used to isolate the nuclear heat source from the process steam, thus allowing the use of conventional equipment for... 

In a basic solution, hydroxide ion removes a proton from the a-carbon of the keto tautomer. The anion that is formed has two resonance contributors a carbanion and an enolate ion. The enolate ion contributes more to the resonance hybrid because the negative charge is better accommodated by oxygen than by carbon. Protonation on oxygen forms the enol tautomer, whereas protonation on the a-carbon reforms the keto tautomer. 

Steam may be fed to the gasifier in some cases to provide a reaction environment that will promote fixed-carbon reforming and minimize the production... 

Allyl NN-dialkylcarbamates (155) can be converted into the masked y-keto-esters (156) by a sequence of anion formation (LDA), condensation with dimethyl carbonate, reformation of an anion, and finally, alkylation. The reactions are largely regiospecific and efficient but have only been tried using simple substrates i.e., R = H or Me E = Me or PhCH2). 

Carbon suboxide, C3O2, OCCCO. M.p. — 107 C, b.p. 6-8°C. A toxic gas (malonic acid plus P2O5) which polymerizes at room temperature. Reforms malonic acid with water. 

Some of ihe carbon monoxide and hydrogen produced in ihe steam-naphtha reforming process react to form methane ... 

In addition, a catalytic version of Tt-allylpalladium chemistry has been devel-oped[6,7]. Formation of the Tr-allylpalladium complexes by the oxidative addition of various allylic compounds to Pd(0) and subsequent reaction of the complex with soft carbon nucleophiles are the basis of catalytic allylation. After the reaction, Pd(0) is reformed, and undergoes oxidative addition to the allylic compounds again, making the reaction catalytic.-In addition to the soft carbon nucleophiles, hard carbon nucleophiles of organometallic compounds of main group metals are allylated with 7r-allylpalladium complexes. The reaction proceeds via transmetallation. These catalytic reactions are treated in this chapter. 

Synthesis gas is obtained either from methane reforming or from coal gasification (see Coal conversion processes). Telescoping the methanol carbonylation into an esterification scheme furnishes methyl acetate directly. Thermal decomposition of methyl acetate yields carbon and acetic anhydride,... 

Synthesis Gas Chemicals. Hydrocarbons are used to generate synthesis gas, a mixture of carbon monoxide and hydrogen, for conversion to other chemicals. The primary chemical made from synthesis gas is methanol, though acetic acid and acetic anhydride are also made by this route. Carbon monoxide (qv) is produced by partial oxidation of hydrocarbons or by the catalytic steam reforming of natural gas. About 96% of synthesis gas is made by steam reforming, followed by the water gas shift reaction to give the desired H2 /CO ratio. 

Methane. The largest use of methane is for synthesis gas, a mixture of hydrogen and carbon monoxide. Synthesis gas, in turn, is the primary feed for the production of ammonia (qv) and methanol (qv). Synthesis gas is produced by steam reforming of methane over a nickel catalyst. 

Fig. 1. Hydrogen production flow sheet, showing steam reforming, shift, hot potassium carbonate CO2 removal, and methanation.

Naphtha desulfurization is conducted in the vapor phase as described for natural gas. Raw naphtha is preheated and vaporized in a separate furnace. If the sulfur content of the naphtha is very high, after Co—Mo hydrotreating, the naphtha is condensed, H2S is stripped out, and the residual H2S is adsorbed on ZnO. The primary reformer operates at conditions similar to those used with natural gas feed. The nickel catalyst, however, requires a promoter such as potassium in order to avoid carbon deposition at the practical levels of steam-to-carbon ratios of 3.5—5.0. Deposition of carbon from hydrocarbons cracking on the particles of the catalyst reduces the activity of the catalyst for the reforming and results in local uneven heating of the reformer tubes because the firing heat is not removed by the reforming reaction. 

After the steam reforming step, the product gas stream contains a considerable quantity of carbon monoxide which may undergo reaction with additional steam, thereby increasing the hydrogen yield ... 

Reactions. Heating an aqueous solution of malonic acid above 70°C results in its decomposition to acetic acid and carbon dioxide. Malonic acid is a useful tool for synthesizing a-unsaturated carboxyUc acids because of its abiUty to undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic acids are formed from the reaction of malonic acid and benzaldehyde derivatives (1). If aUphatic aldehydes are used acryhc acids result (2). Similarly this facile decarboxylation combined with the condensation with an activated double bond yields a-substituted acetic acid derivatives. For example, 4-thiazohdine acetic acids (2) are readily prepared from 2,5-dihydro-l,3-thiazoles (3). A further feature of malonic acid is that it does not form an anhydride when heated with phosphorous pentoxide [1314-56-3] but rather carbon suboxide [504-64-3] [0=C=C=0], a toxic gas that reacts with water to reform malonic acid. 

Because the synthesis reactions are exothermic with a net decrease in molar volume, equiUbrium conversions of the carbon oxides to methanol by reactions 1 and 2 are favored by high pressure and low temperature, as shown for the indicated reformed natural gas composition in Figure 1. The mechanism of methanol synthesis on the copper—zinc—alumina catalyst was elucidated as recentiy as 1990 (7). For a pure H2—CO mixture, carbon monoxide is adsorbed on the copper surface where it is hydrogenated to methanol. When CO2 is added to the reacting mixture, the copper surface becomes partially covered by adsorbed oxygen by the reaction C02 CO + O (ads). This results in a change in mechanism where CO reacts with the adsorbed oxygen to form CO2, which becomes the primary source of carbon for methanol. 

Fig. 1. Fquilihrium conversion of carbon oxides to methanol based on reformed natural gas composition of 73% H2, 15% CO, 9% CO2, and 3% CH ...

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

This excess hydrogen is normally carried forward to be compressed into the synthesis loop, from which it is ultimately purged as fuel. Addition of by-product CO2 where available may be advantageous in that it serves to adjust the reformed gas to a more stoichiometric composition gas for methanol production, which results in a decrease in natural gas consumption (8). Carbon-rich off-gases from other sources, such as acetylene units, can also be used to provide supplemental synthesis gas. Alternatively, the hydrogen-rich purge gas can be an attractive feedstock for ammonia production (9). 

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