Carbonates thermal decomposition

Delayed coke (Table 16.1) is produced during the delayed coking process—a batch process—from vacuum residua (Chapter 2) (Speight and Ozum, 2002). The carbonization (thermal decomposition) reactions involve dehydrogenation, rearrangement, and condensation. Two of the common feedstocks are vacuum residues and aromatic oils. 

On the other hand, if the halogen is y to a fully alkylated nitrogen and on a fully alkylated carbon, thermal decomposition (Scheme 10.17) can intrude (the Hofmann-Loffler-Freytag reaction) with (after hydrolysis) formation of a ketone and an alkene. 

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

Uranium can be prepared by reducing uranium halides with alkali or alkaline earth metals or by reducing uranium oxides by calcium, aluminum, or carbon at high temperatures. The metal can also be produced by electrolysis of KUF5 or UF4, dissolved in a molten mixture of CaCl2 and NaCl. High-purity uranium can be prepared by the thermal decomposition of uranium halides on a hot filament. 

The evidence obtained in compaction experiments is of particular interest in the present context. Figure 3.22 shows the results obtained by Avery and Ramsay for the isotherms of nitrogen on compacts of silica powder. The hysteresis loop moved progressively to the left as the compacting pressure increased, but the lower closure point did not fall below a relative pressure of 0-40. Similar results were obtained in the compaction of zirconia powder both by Avery and Ramsay (cf. Fig. 4.5), and by Gregg and Langford, where the lower closure point moved down to 0-42-0-45p° but not below. With a mesoporous magnesia (prepared by thermal decomposition of the hydrated carbonate) the position of the closure point... 

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,... 

Pyrolysis. Pyrolysis, eg, retorting, destmctive distillation, carbonization, is the thermal decomposition of an organic material ia the absence of... 

Carbonization. Next to combustion, carbonization represents one of the largest uses of coal (2,24—26). Carbonization is essentially a process for the production of a carbonaceous residue by thermal decomposition, accompanied by simultaneous removal of distillate, of organic substances. 

Chemistry. Coal gasification iavolves the thermal decomposition of coal and the reaction of the carbon ia the coal, and other pyrolysis products with oxygen, water, and hydrogen to produce fuel gases such as methane by internal hydrogen shifts... 

There are three essential factors in the thermal decomposition of limestone (/) the stone must be heated to the dissociation temperature of the carbonates (2) this minimum temperature (but in practice a higher temperature) must be maintained for a certain duration and (J) the carbon dioxide evolved must be removed rapidly. 

Lithium Oxide. Lithium oxide [12057-24-8], Li20, can be prepared by heating very pure lithium hydroxide to about 800°C under vacuum or by thermal decomposition of the peroxide (67). Lithium oxide is very reactive with carbon dioxide or water. It has been considered as a potential high temperature neutron target for tritium production (68). 

Decomposition and Decarboxylation. Maleic anhydride undergoes anaerobic thermal decomposition in the gas phase in a homogeneous unimolecular reaction to give carbon monoxide, carbon dioxide, and acetylene [74-86-2] in equimolar amounts. The endothermic... 

Thermal decomposition of dihydroperoxides results in initial homolysis of an oxygen—oxygen bond foUowed by carbon—oxygen and carbon—carbon bond cleavages to yield mixtures of carbonyl compounds (ketones, aldehydes), esters, carboxyHc acids, hydrocarbons, and hydrogen peroxide. 

Thermal decomposition of hydroxyalkyl hydroperoxyalkyl peroxides produces mixtures of starting carbonyl compounds, mono- and dicarboxyHc acids, cycHc diperoxides, carbon dioxide, and water. One specific hydroxyalkyl hydroperoxyalkyl peroxide from cyclohexanone (2, X = OH, Y = OOH) is a soHd that is produced commercially as a free-radical initiator and bleaching agent (see Table 5). On controlled decomposition, it forms 1,12-dodecanedioic acid (150). 

Two processes, partial oxidation and thermal decomposition, are used for the production of carbon blacks. The partial oxidation process can be represented by the foUowiag reaction ... 

Thermal decomposition of hydrocarbons is carried out ia the absence of oxygen and at a high temperature required to break the carbon—hydrogen... 

Bitumen is a hydrogen-deficient oil that is upgraded by carbon removal (coking) or hydrogen addition (hydrocrackiag) (2,4). There are two methods by which bitumen conversion can be achieved by direct heating of mined tar sand and by thermal decomposition of separated bitumen. The latter is the method used commercially, but the former has potential for commercialisation (see Fuels, SYNTHETIC). 

Cyclopentadienyltitanium Compounds with Other Carbon Titanium Links. Cyclopentadienyltitanium trichloride and, particularly, CpgTiClg react with RLi or with RAl compounds to form one or more R—Ti bonds. As noted, the Cp groups stabilize the Ti—R bond considerably against thermal decomposition, although the sensitivity to air and moisture remains. Depending on the temperature, mole ratio, and stmcture of R, reduction of Ti(IV) may be a serious side reaction, which often has preparative value for Cp Ti(Ill) compounds (268,274,275). 

Polyurethanes. These polymers can be considered safe for human use. However, exposure to dust, generated in finishing operations, should be avoided. Ventilation, dust masks, and eye protection are recommended in foam fabrication operations. Polyurethane or polyisocyanurate dust may present an explosion risk under certain conditions. Airborne concentrations of 25—30 g/m are required before an explosion occurs. Inhalation of thermal decomposition products of polyurethanes should be avoided because carbon monoxide and hydrogen cyanide are among the many products present. 

Solutions of these fire retardant formulations are impregnated into wood under fliU cell pressure treatment to obtain dry chemical retentions of 65 to 95 kg/m this type of treatment greatly reduces flame-spread and afterglow. These effects are the result of changed thermal decomposition reactions that favor production of carbon dioxide and water (vapor) as opposed to more flammable components (55). Char oxidation (glowing or smoldering) is also inhibited. 

The heavy metal salts, ia contrast to the alkah metal salts, have lower melting points and are more soluble ia organic solvents, eg, methylene chloride, chloroform, tetrahydrofiiran, and benzene. They are slightly soluble ia water, alcohol, ahphatic hydrocarbons, and ethyl ether (18). Their thermal decompositions have been extensively studied by dta and tga (thermal gravimetric analysis) methods. They decompose to the metal sulfides and gaseous products, which are primarily carbonyl sulfide and carbon disulfide ia varying ratios. In some cases, the dialkyl xanthate forms. Solvent extraction studies of a large number of elements as their xanthate salts have been reported (19). 

Barium nitrite [13465-94-6] Ba(N02)2, crystallines from aqueous solution as barium nitrite monohydrate [7787-38-4], Ba(N02)2 H2O, which has yellowish hexagonal crystals, sp gr 3.173, solubihty 54.8 g Ba(NO2)2/100 g H2O at 0°C, 319 g at 100°C. The monohydrate loses its water of crystallization at 116°C. Anhydrous barium nitrite, sp gr 3.234, melts at 267°C and decomposes at 270 °C into BaO, NO, and N2. Barium nitrite may be prepared by crystallization from a solution of equivalent quantities of barium chloride and sodium nitrite, by thermal decomposition of barium nitrate in an atmosphere of NO, or by treating barium hydroxide or barium carbonate with the gaseous oxidiation products of ammonia. It has been used in diazotization reactions. 

Beryllium Oxalate. BeryUium oxalate trihydrate [15771 -43-4], BeC204 -3H20, is obtained by evaporating a solution of beryUium hydroxide or oxide carbonate in a slight excess of oxaHc acid. The compound is very soluble in water. Beryllium oxalate is important for the preparation of ultrapure beryllium hydroxide by thermal decomposition above 320°C. The latter is frequentiy used as a standard for spectrographic analysis of beryUium compounds. 

Bismuth trioxide may be prepared by the following methods (/) the oxidation of bismuth metal by oxygen at temperatures between 750 and 800°C (2) the thermal decomposition of compounds such as the basic carbonate, the carbonate, or the nitrate (700—800°C) (J) precipitation of hydrated bismuth trioxide upon addition of an alkah metal hydroxide to a solution of a bismuth salt and removal of the water by ignition. The gelatinous precipitate initially formed becomes crystalline on standing it has been represented by the formula Bi(OH)2 and called bismuth hydroxide [10361 -43-0]. However, no definite compound has been isolated. 

---