Pyrolysis thermal

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

Pyrolysis. Vinyl chloride is more stable than saturated chloroalkanes to thermal pyrolysis, which is why nearly all vinyl chloride made commercially comes from thermal dehydrochlorination of EDC. When vinyl chloride is heated to 450°C, only small amounts of acetylene form. Litde conversion of vinyl chloride occurs, even at 525—575°C, and the main products are chloroprene [126-99-8] and acetylene. The presence of HCl lowers the amount of chloroprene formed. 

Ethylene Dichloride Pyrolysis to Vinyl Chloride. Thermal pyrolysis or cracking of EDC to vinyl chloride and HCl occurs as a homogenous, first-order, free-radical chain reaction. The accepted general mechanism involves the four steps shown in equations 10—13 ... 

Cracking temperatures are somewhat less than those observed with thermal pyrolysis. Most of these catalysts affect the initiation of pyrolysis reactions and increase the overall reaction rate of feed decomposition (85). AppHcabiUty of this process to ethane cracking is questionable since equiUbrium of ethane to ethylene and hydrogen is not altered by a catalyst, and hence selectivity to olefins at lower catalyst temperatures may be inferior to that of conventional thermal cracking. SuitabiUty of this process for heavy feeds like condensates and gas oils has yet to be demonstrated. 

The as-produced filaments were very strongly covered by amorphous carbon produced by thermal pyrolysis of acetylene. The amount of amorphous carbon varied with the reaction conditions. It increased with increasing reaction temperature and with the percentage of acetylene in the reaction mixture. Even in optimal conditions not less than 50% of the carbon was deposited in the form of amorphous carbon in accordance with [13]. 

This could be a result of dealumination of the catalysts in the presence of water formed in the thermal pyrolysis of woody biomass. 

Hydrogen production. Intensive R D is underway on the production of hydrogen from natural gas and biomass. Concerning biological hydrogen, a national co-operative platform has been formed with 11 institutes and universities. In addition, thermal (pyrolysis) and hydrothermal processes are being studied at multiple places. Other research areas include various thermal and hydrothermal processes (BTC, TNO, ECN), and hydrogen from electricity produce by renewables (solar, wind, and tidal power). 

Carbonized Resins. A special sorbent made by controlled thermal pyrolysis of polyvinylidene chloride (Dow developmental Adsorbent XF-4175L) (34) was shown to be three to five times more effective for the collection of highly volatile compounds, such as vinyl chloride (Figure 5) and methyl chloride, than the best available activated charcoal (31,36,37). Although this sorbent is not commercially available, Carbosive and Carbosive S show similar collection properties and they are available from gas chromatographic supply houses or may be obtained already packed in small collection tubes (SKC Inc., Eighty Four, PA). 

All fluorocarbenes are ground state singlets. For laboratory use there are some precursors which thermally generate difluorocarbene.42 Its identification is usually made by a subsequent chemical insertion reaction. A few industrially important processes proceed via difluorocarbene. The thermal pyrolysis of chlorodifluoromethane (CHF2C1) for the production of tetrafluoroethene and hexafluoropropene gives the intermediate CF2 which dimerizes to the alkene. 

Visbreaking is a mild thermal pyrolysis of heavy petroleum fractions whose object is to reduce fuel production in a refinery and to make some gasoline. 

Pyrolysis. Vinyl chloride is more stable than saturated ehloroalkanes to thermal pyrolysis. That is why nearly all vmyl chlonde made commercially comes from thermal clehydrochlorination of ethylene dichloride (EDC). When vinyl chloride is heated to 450°C, only small amounts of acetylene form. Decomposition of vinyl chlonde via a free-radical chain process begins at approximately 550°C, and increases with increasing temperature. Acetylene, HC1. chloropiene, and vinylacetylene are formed in about 35% total yield at 680°C. At higher temperatures, tar and soot formation becomes increasingly important. When dry and in contact with metals, vinyl chloride does not decompose below 450°C. However, if water is present, vinyl chloride can corrode iron, steel, and alum in 11m because ofthe presence of trace amounts of HC1. This HC1 may result from the hydrolysis of the peroxide formed between oxygen and vinyl chlonde. 

The initial pyrolysis reaction of SiH4 has been explored extensively (98), and the growing consensus is that the thermal decomposition of SiH4 involves the elimination of H2 to form silylene, as shown in equation 1 (98, 101). Possibly, thermal pyrolysis is controlled by heterogeneous reactions on hot surfaces (102, 103), but this hypothesis is controversial, and considerable experimental evidence for a gas decomposition mechanism exists (98). However, at low pressures and high temperatures, heterogeneous decomposition will likely be important in the overall mechanism (104). 

Thermal pyrolysis for upgrading plastic wastes is one of the better methods for recycling plastics in terms of its perspectives for industrial implementation. The conical spouted bed reactor proposed in this paper may be a solution to the problems arising in fluidized beds handling sticky solids, as particle agglomeration phenomena, which can cause defluidization. In order to avoid defluidization, experiments have been carried out in batch mode in the temperature range of 450-600 °C. A good performance of the reactor is proven under the conditions of maximum particle stickiness. 

The treatment methods for remediation of energetic materials from soils are divided on in situ and ex situ biological (bioremediation, phytoremediation, composting), in situ and ex situ physico-chemical (adsorption, oxidation, electrokinetic separation, extraction, solidification, reduction, soil washing), in situ and ex situ thermal (pyrolysis, desorption) [1]. Among the above described... 

In recent years, we have seen an explosive interest in nanomaterials, in particular in nanofibers, nanofilaments, and nanotubes of the very different chemical composition. The interest arises from the specific mechanical and physicochemical properties of these nano objects, which allow them to be used, for example, as specific adsorbents, catalyst supports, reinforcing components of composite materials, and so on. The most cited generic types of nanomaterials are carbon nanofilaments and nanotubes. Numerous methods for preparing these carbon materials are known. However, the simplest method seems to be thermal pyrolysis of various carbon contain ing precursors (e.g., carbon monoxide, saturated and unsaturated hydro carbons, etc.) in the presence of special catalysts that are typically nanosized particles of nickel, cobalt, iron metals, or their alloys with different metals. 

Ethylene is produced in large quantities in many countries by the thermal pyrolysis of ethane with the generalised stoichiometry ... 

The thermal pyrolysis of hydrocarbons proceeds by free radical chain reaction processes. These processes are exceedingly complex and this overview concentrates on the details as it impacts on the technology and economics of olefin production. 

Dry methods and postcalcination methods The industrial micron sized R2O3 powder is commonly made by thermal pyrolysis of rare earth carbonates or oxalates at a temperature of 600-1000 °C. The dry methods usually result in fine powders with a relatively wide size distribution. After the sintering, the surface OH and other solvent related species are generally removed, therefore, the powder may exhibit better luminescence efficiency and longer decay time. Nano-sized rare earth oxide products could be obtained from finely selected precursors like hydroxides gels, premade nanostructures, through heat treatment, spray pyrolysis, combustion, and sol-gel processes. 

High-temperatnre pyrolysis and cracking of waste thermoplastic polymers, such as polyethylene, polypropylene and polystyrene is an environmentally acceptable method of recycling. These type of processes embrace both thermal pyrolysis and cracking, catalytic cracking and hydrocracking in the presence of hydrogen. Mainly polyethylene, polypropylene and polystyrene are used as the feedstock for pyrolysis since they have no heteroatom content and the liquid products are theoretically free of sulfur. 

According to this concept, Masuda et al. [75] studied the catalytic cracking of the oil coming from a previous thermal pyrolysis step of polyethylene at 450°C in the bench-scale fixed-bed reactor shown in Figure 3.11. The catalysts employed were different zeolite types REY (rare earth exchanged zeolite Y), Ni-REY (nickel and rare earth... 

In the series described thus far, it was found that the degradation of waste plastics proceeds efficiently by both thermal pyrolysis and hydrolysis in a steam atmosphere. A wax and carbonaceous residue produced by the hydrolysis of PET are decomposed by reaction with steam over an FeOOH catalyst, the activity of which remains stable in a steam atmosphere. However, the liquid product from generated from the process mentioned above contains a large amount of heavy oil, as shown in Figure 6.10. Both catalysts and chemical processes are required for efficiently upgrading the quality of the heavy oil. 

In particular, as far as the plastic catalytic degradation is concerned, there are various possible scenarios. In large urban areas the best approach probably is to build a plastic waste pyrolysis plant in an acceptable near area at not to great distance, in order to minimize transport cost of the plastic waste. In that case, safety and environmental concerns of such a new plant should first be denied with satisfactorily before the new plant can get the go-ahead. Near refineries however, the best approach might be to co-feed plastic waste with oil fractions into refinery crackers, or even have a unit of pure thermal pyrolysis first with the produced wax-type fraction to be upstaged in another reactive refinery process. In the first case of co-feeding, a lot of research has to be carried out, addressing aspects of defluidization mainly, before an alteration of a process of the scale of FCC units can go ahead. 

Table 9.4 Some laboratory experiments of thermal pyrolysis...

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