Pyrolysis, also

Pyrolysis of scrap tires was studied by several mbber, oil, and carbon black industries [14]. Pyrolysis, also known as thermal cracking is a process in which polymer molecules are heated in partial or total absence of air, until they fragment into several smaller, dissimilar, random-sized molecules of alcohols, hydrocarbons, and others. The pyrolysis temperature used is in the range of 500°C-700°C. Moreover, maintenance of partial vacuum during pyrolysis in reactors lowered the economy of the process. Several patents were issued for the pyrolysis of worn out tires to yield cmde oil, monomers, and carbon black in economic ways [15-18]. The major drawback of chemical recycling is that the value of the output is normally low and the mixed oils, gases, and carbon black obtained by pyrolysis cannot compete with similar products from natural oil. Pyrolyzing plant produces toxic wastewater as a by-product of the operation [19]. 

Slow pyrolysis, also called carbonization, is characterized by a high charcoal yield and is not considered for hydrogen production processes. The slow pyrolysis of wood (24 h typical residence time) was a common industrial technology to produce charcoal, acetic acid, methanol, and ethanol from wood until the early 1900s. 

Ester Pyrolysis also obeys this preference, and the Hofmann Rule is generally followed whenever a reaction passes through a cyclic transition state. 

Higher silicon hydrides with Ge, e.g. Si2H5GeH3 and other compounds produced in these pyrolysis reactions, have also been obtained by hydrolysis of Mg or Ca germanide-silicides446, 475, 636 and have been separated by gas chromatography446, 447. P and As derivatives produced by pyrolysis also be obtained in coupling reactions ... 

Hoechst HTP [High Temperature Pyrolysis] Also called Hoechst-Uhde. A two-stage process for making a mixture of acetylene and ethylene by cracking higher hydrocarbons. In the first stage, a... 

Pyrolysis, also termed thermolysis (Greek pur = fire thermos = warm luo = loosen), is a process of chemical and thermal decomposition, generally leading to smaller molecules. Semantically, the term thermolysis is more appropriate than pyrolysis, since fire implies the presence of oxygen and hence of reactive and oxygen-bearing intermediates. In most pyrolysis processes, however, air is excluded, for reasons of safety, product quality, and yield. 

Preceramic Polymer Pyrolysis. Chemical options also are available for the pyrolysis step. Certainly, the rate of pyrolysis, that is, the time-temperature profile of pyrolysis, is extremely important. However, the gas stream used in pyrolysis also is of great importance. Inert- or reactive-gas pyrolysis can be carried out. 

Using equations (3) and (4), equations (2a-2c) can be written as depending on only one variable. This variable should be easily monitored experimentally. Such a variable is the mass fraction of the gas G or the mass fraction of the solid residue (1 - G). The three equations (2a-2c) can be initially used to calculate the values for k-, k2 and a-). This can be done using a best-fit technique for experimental data that are assumed to be described by equations (2) in isothermal conditions. Once the values for k-, k2 and a- are known, the kinetics equations can be integrated and solved for any time t. This model has been successfully applied, for example, to describe the pyrolysis of cellulose and of pine needles [8]. In anal ical pyrolysis this model can be used to determine the amount of gas generated during pyrolysis. Also, analytical pyrolysis data can be used to fit the kinetics model for use in other practical applications. 

The mechanical problems related to the rapid solid sample introduction or related to the introduction of solid samples with no air leak makes this type of pyrolyser more appropriate for liquid or even gas sample pyrolysis. Also, it being possible to build large furnace pyrolysers, this type is successfully used when larger amounts of sample are necessary to be pyrolysed. This is a common case for the pyrolysis of non-homogeneous samples when a few mg of sample do not represent well the average sample composition. 

A problem with lasers is the difficulty of knowing precisely the equivalent temperature of pyrolysis. Also, due to some inherent characteristics of laser pyrolysis, its reproducibility is not always good. Several studies [e.g. 25] showed variability in the total mass of material pyrolysed and difficulties in the control of the pyrolysis temperature. The secondary reactions with the radicals from the plume (although catalytic reactions are probably absent) also make this technique less reproducible. 

The walls of the expansion chamber as well as those of the RF region must be inert (glass or gold-coated), and the expansion chamber should be heated (at moderate temperatures 150-200° C) to reduce condensation. Common problems for this type of pyrolyser are condensations on the cool portion of the system. On the other hand, heating the walls of the sample region (with resistors) may generate decomposition of the sample before pyrolysis. Also, the expansion chamber extends the time for the sample to be introduced in the mass spectrometer ion source and therefore the time... 

Besides formic acid and acetaldehyde, the oxidative pyrolysis also generates ethanol, ethyl formate, ethane, CO2, CO, etc. 

Pyrolysis also has been used to evaluate the efficiency of removal of proteins from plant materials using enzymes [21],... 

Pyrolysis also has been utilized for the determination of the structure of unique natural polymers in certain lacquers such as those produced by Rhus vernicifera and Rhus succedanea [2] and utilized as surface coating for wood, porcelain, etc. in Japan. The pyrolysis products of the two lacquer films at 400° C contain respectively laccol and urushiol, and each also contains alkenes, alkanes, alkenylphenols, and alkylphenols. From these results it was possible to assign the following structure for laccol polymer ... 

Commonly, analytical pyrolysis is performed as flash pyrolysis. This is carried out with a fast rate of temperature increase, of the order of 10,000° C/s, targeting isothermal conditions at a temperature where the sample is completely pyrolyzed. After the final pyrolysis temperature is attained, the temperature is maintained essentially constant (isothermal pyrolysis). Special types of analytical pyrolysis also are known. One example is fractionated pyrolysis, in which the same sample is pyrolyzed at different temperatures for different times in order to study special fractions of the sample. 

Analytical pyrolysis is used frequently in practice for qualitative identification and for obtaining quantitative or semiquantitative information on samples containing polymers, either synthetic or natural. However, most of this work remains unreported in peer reviewed literature but is rather common in industrial laboratories. Since the objects made from plastic or elastomers are typically insoluble or not easily analyzed by other techniques, analytical pyrolysis is very successful in this type of analysis [11]. The very small amount of material necessary for pyrolysis also allows in many cases performance of the analysis without the destruction of the object to be investigated. Qualitative and quantitative work includes applications for the identification of unknown samples and also for quality control purposes, evaluation of starting materials, evaluation of finished products, reverse engineering and competitor s product analysis, etc. [1]. Among other applications, Py-GC/MS can be used to quantitatively differentiate between natural and synthetic organic materials [12]. 

The pyrolysis products of acrylic acid indicate that only about 25% of monomer is generated during pyrolysis. A significant amount of decarboxylation takes place during pyrolysis. Also, water is present in the pyrolysate (about 15%). The elimination of CO2 may take place as a simple reaction at the side chain of the polymer as shown below ... 

The first unit operation in the production of waste or biomass derived activated carbon is pyrolysis, also known as baking or charring. In this process the material is heated in an essentially oxygen-free atmosphere to drive off the free moisture and volatiles. The material that remains is called char or fixed carbon. The char yield is dependent upon heating rate and in a study performed by Roberts et al. (1978) on the production of municipal solid waste derived activated carbon, the following... 

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