Pyrolysis light hydrocarbon

Under the assumptions of naphtha price and aromatics value stated above, naphtha pyrolysis clearly would be superior to light hydrocarbon pyrolysis at their current feed prices. A similar analysis can probably be made also for gas oil. Thus, if the possible developments discussed above do materialize, the heavier feeds could probably dominate almost all new U.S. ethylene plant construction in the future. 

Traditionally, olefins in the United States have been produced from light hydrocarbon pyrolysis. Earlier publications on computer simulation and control of pyrolysis reactors were addressed primarily to pyrolysis furnaces using ethane, propane and butane as feedstocks (1,2,3). 

Table III. Gases and Light Hydrocarbon Pyrolysis Products ...

Burning a portion of a combustible reactant with a small additive of air or oxygen. Such oxidative pyrolysis of light hydrocarbons to acetylene is done in a special burner, at 0.001 to 0.01 s reaction time, peak at 1,400°C (2,552°F), followed by rapid quenching with oil or water. 

The U.S. ethylene industry has been based primarily on the cracking of ethane and propane derived from natural gas. The quantities and liquid contents of U.S. natural gases have been such as to permit substantial quantities of these light hydrocarbons to be recovered for use as economically attractive ethylene feedstocks. In Europe and Japan, however, naphthas have been generally the available and preferred feeds to pyrolysis. 

United States. The U.S. ethylene industry has been based mainly on pyrolysis of light hydrocarbons, predominately ethane and propane recovered from natural gas. Essentially all the ethane recovered is used as pyrolysis feed, whereas only about one quarter of the propane is used for this purpose. The remainder is mostly consumed in the LPG market. 

Other sources of benzene include processes for steam cracking heavy naphtha or light hydrocarbons such as propane or butane to produce a liquid product (pyrolysis gasoline) rich in aromatics that contains up to about 65 percent aromatics, about 50 percent of which is benzene. Benzene can be recovered by solvent extraction and subsequent distillation. 

Olefin production is achieved by pyrolysis of various feedstocks, ranging from light hydrocarbons (ethane, propane) to naphthas, gas oils and even crude oils. The variety of and change in the nature of available feedstocks due to new sources (e.g. off-gas from the North Sea) or to political problems, and the marked variation in prices and... 

Temperature is one of the most important factors that affect the process of plastics pyrolysis. The required temperature varies with different types of plastics and the desired composition of products. At a temperature above 600°C, the products are mainly composed of mixed fuel gases such as H2, CH4 and light hydrocarbons At 400-600°C, wax and liquid fuel are produced. The liquid fuel products consist mainly of naphtha, heavy... 

Catalysts tend to be deactivated in the process of plastics pyrolysis because of coke deposition on their surface. The deactivation of HZSM-5, HY, H-zeolite and silica-alumina was compared by Uemichi et al. [86]. In the case of PE pyrolysis and HZSM-5 added as catalyst, no deactivation occurred due to the low coke deposit, and high yields of light hydrocarbons (mainly branched hydrocarbons and aromatics) were achieved. In the case of PS, however, coke production increased dramatically, so HZSM-5 was deactivated very quickly. Silica-alumina catalyst was deactivated gradually and slowly with the increase of cracking gas, while HY- and H-zeolite molecule sieve catalysts were deactivated very quickly. Walendziewski et al. [87] studied the catalytic cracking of waste... 

Computer modeling of hydrocarbon pyrolysis is discussed with respect to industrial applications. Pyrolysis models are classified into four groups mechanistic, stoichiometric, semi-kinetic, and empirical. Selection of modeling schemes to meet minimum development cost must be consistent with constraints imposed by factors such as data quality, kinetic knowledge, and time limitations. Stoichiometric and semi-kinetic modelings are further illustrated by two examples, one for light hydrocarbon feedstocks and the other for naphthas. The applicability of these modeling schemes to olefins production is evidenced by successful prediction of commercial plant data. 

The focus of this chapter is to provide an overview of pyrolysismodeling techniques, with emphasis on industrial applications. Examples are outlined for the case light hydrocarbon and naphtha pyrolysis. 

Starting with the pioneering work of Myers and Watson (9) on propane pyrolysis, this approach has been successfully applied to virtually all light hydrocarbons (10,11,12,13,14) and extended up to C8 normal and branched paraffins (15,16). Fewer studies have been reported on mixture pyrolysis (17,18,19), especially for heavier feedstocks (20). This type of modeling will be illustrated later with an example. 

Successful stoichiometric modeling is demonstrated for industrial pyrolysis of light hydrocarbon and their mixtures. A semikinetic approach is more appropriate for naphtha pyrolysis. Although the final form of such a model is simple, its development generally requires more innovations. Applicability of the naphtha model to olefins production is evidenced by the successful prediction of commercial plant performances. 

Typ es of Coke Formed During the Pyrolysis of Light Hydrocarbons... 

Pyrolysis reactions are undoubtedly occurring after combustion, and chemi-ionization may be occurring in addition to charge exchange reactions between primary ions, such as CsHs, and light hydrocarbons. Hence, the chemi-ion profile would not decay necessarily as it does in leaner combustion, where recombination begins to dominate ion formation. Instead, a different sequence of chemi-ion reactions may become important, with the precursor being C2, rather than CH. 

Under idealized conditions, the primary products of biomass gasification by pyrolysis, partial oxidation, or reforming are essentially the same The carbon oxides and hydrogen are formed. Methane and light hydrocarbon gases are also formed under certain conditions. Using cellulose as a representative feedstock, examples of some stoichiometries are illustrated by these equations ... 

The results obtained can be explained by considering the reactions involved in the processes. We can assume that the main reactions in catalytic pyrolysis are catalytic cracking of tars and light hydrocarbons, which will explain the increase in gas yields when the catalyst is present in the reaction bed (18). Steam reforming of tars (reac. 1), methane (reac. 2) and Cj (reac. 3), and the water-gas shift reaction (reac. 4) can explain the final gas composition generated in catalytic steam gasification. 

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