Catalyzed pyrolysis, rate

The condensed phase mechanism was explained taking into account the decrease of the pyrolysis rate of polypropylene BiCl3 could catalyze the condensation between chloroparaffin and polypropylene by addition to chain end double bonds (Equation 4.25) formed either in reaction (Equation 4.22) or in chain scission occurring during volatilization of polypropylene 31... 

Many of the reactions listed at the beginning of this section are acid catalyzed, although a number of basic catalysts are also employed. Esterifications are equilibrium reactions, and the reactions are often carried out at elevated temperatures for favorable rate and equilibrium constants and to shift the equilibrium in favor of the polymer by volatilization of the by-product molecules. An undesired feature of higher polymerization temperatures is the increased probability of side reactions such as the dehydration of the diol or the pyrolysis of the ester. Basic catalysts produce less of the undesirable side reactions. 

The response of the cotton fiber to heat is a function of temperature, time of heating, moisture content of the fiber and the relative humidity of the ambient atmosphere, presence or absence of oxygen in the ambient atmosphere, and presence or absence of any finish or other material that may catalyze or retard the degradative processes. Crystalline state and DP of the cotton cellulose also affect the course of thermal degradation, as does the physical condition of the fibers and method of heating (radiant heating, convection, or heated surface). Time, temperature, and content of additive catalytic materials are the major factors that affect the rate of degradation or pyrolysis. 

Thermal reactions of acetylene, butadiene, and benzene result in the production of coke, liquid products, and various gaseous products at temperatures varying from 4500 to 800°C. The relative ratios of these products and the conversions of the feed hydrocarbon were significantly affected in many cases by the materials of construction and by the past history of the tubular reactor used. Higher conversions of acetylene and benzene occurred in the Incoloy 800 reactor than in either the aluminized Incoloy 800 or the Vycor glass reactor. Butadiene conversions were similar in all reactors. The coke that formed on Incoloy 800 from acetylene catalyzed additional coke formation. Methods are suggested for decreasing the rates of coke production in commercial pyrolysis furnaces. 

The decomposition of methoxynaphthalene occurs by two parallel mechanisms hydrolysis predominates at SC water density while thermal pyrolysis is dominant at zero and subcrltlcal water densities. The hydrolysis is proven to be a proton catalyzed mechanism and is positively affected by dissolved NaCl, all in agreement with the secondary salt effect rate law. This rate law has traditionally been applied to liquid media but the current work has proven that the same rate law applies also for SC water. 

In many organic reactions such as hydrolysis or certain rearrangements, water is the solvent and catalyst via self-dissociation, and sometimes also a reactant [11, 12]. The advantage of the use of water is that the addition of acids and bases may be avoided. This means that cleaning the effluent is easier and less expensive. The ionic product of water increases with pressure (under supercritical conditions) therefore reaction rates e.g. of acid- or base-catalyzed reactions also increase. On the other hand, the reaction of free radicals, which are undesirable during pyrolysis, decreases with pressure (see Introduction), thus high selectivities can be achieved. 

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