Petrochemical Processing pyrolysis

Pyrolysis of Ethane Pyrolysis of hydrocarbons such as C2H6 is important in the petrochemical process industry. The overall reaction can be written as... 

A number of petrochemical processes produce significant volumes of hydrogen as a by-product, including pyrolysis cracking. This can be used as a fuel oil substitute, but this greatly undervalues hydrogen, and alternative use in other chemical processes is the better option and generally pursued by successful operations. 

Serrano et al. [11] studied the use of a laboratory-scale screw kiln reactor to transform low-density polyethylene (LDPE) into petrochemical feedstock. In this process, pyrolysis was carried out at reaction temperatures of 400-550°C and screw speeds of 3-20 rpm (Figure 19.6). In this process the plastic feed is initially heated in a feed hopper until the feed is melted. The melted plastic is then fed into the screw conveyor where it is depolymerized into gas, liquid and solid. The hopper is equipped with a stirrer to mix the feed plastic. Nitrogen is also used to provide an inert medium for pyrolysis. 

The tenii petrochemicals refers to the basic chemicals that are derived from refinery petroleum cuts. They are produced by separation of the byproducts from the cracking (pyrolysis) of hydrocarbon streams. These streams range from natural gas to the heavy distillate (gas oil) cuts from a refinery primary fractionator. Some chemicals, such as the aromatics, are separated from various refinery streams. Figure 13.43 is simplified schematic of a petrochemical process. 

Xylenes. The main appHcation of xylene isomers, primarily p- and 0-xylenes, is in the manufacture of plasticizers and polyester fibers and resins. Demands for xylene isomers and other aromatics such as benzene have steadily been increasing over the last two decades. The major source of xylenes is the catalytic reforming of naphtha and the pyrolysis of naphtha and gas oils. A significant amount of toluene and Cg aromatics, which have lower petrochemical value, is also produced by these processes. More valuable p- or 0-xylene isomers can be manufactured from these low value aromatics in a process complex consisting of transalkylation, eg, the Tatoray process and Mobil s toluene disproportionation (M lDP) and selective toluene disproportionation (MSTDP) processes isomerization, eg, the UOP Isomar process (88) and Mobil s high temperature isomerization (MHTI), low pressure isomerization (MLPI), and vapor-phase isomerization (MVPI) processes (89) and xylene isomer separation, eg, the UOP Parex process (90). 

The pattern of commercial production of 1,3-butadiene parallels the overall development of the petrochemical industry. Since its discovery via pyrolysis of various organic materials, butadiene has been manufactured from acetylene as weU as ethanol, both via butanediols (1,3- and 1,4-) as intermediates (see Acetylene-DERIVED chemicals). On a global basis, the importance of these processes has decreased substantially because of the increasing production of butadiene from petroleum sources. China and India stiU convert ethanol to butadiene using the two-step process while Poland and the former USSR use a one-step process (229,230). In the past butadiene also was produced by the dehydrogenation of / -butane and oxydehydrogenation of / -butenes. However, butadiene is now primarily produced as a by-product in the steam cracking of hydrocarbon streams to produce ethylene. Except under market dislocation situations, butadiene is almost exclusively manufactured by this process in the United States, Western Europe, and Japan. 

Vegetable oils have the potential to substitute a fraction of petroleum distillates and petroleum-based petrochemicals in the near future. Possible acceptable converting processes of vegetable oils into reusable products are transesterification, solvent extraction, cracking and pyrolysis. Pyrolysis has received a significant amount of interest as this gives products of better quality compared to any other thermochemical process. The liquid fuel produced from vegetable oil pyrolysis has similar chemical components to conventional petroleum diesel fuel. 

Table 8.1 shows the stochastic model solution for the petrochemical system. The solution indicated the selection of 22 processes with a slightly different configuration and production capacities from the deterministic case, Table 4.2 in Chapter 4. For example, acetic acid was produced by direct oxidation of n-butylenes instead of the air oxidation of acetaldehyde. Furthermore, ethylene was produced by pyrolysis of ethane instead of steam cracking of ethane-propane (50-50 wt%). These changes, as well as the different production capacities obtained, illustrate the effect of the uncertainty in process yield, raw material and product prices, and lower product... 

In all examples of the palladium-catalyzed telomerization discussed up till now, the nucleophile (telogen) can be considered renewable. The taxogens used (butadiene, isoprene), however, are still obtained from petrochemical resources, although butadiene could, in principle, also be obtained from renewable resources via the Lebedev process that converts (bio)-ethanol into 1,3-butadiene. Limited attention has been given in this respect to the great family of terpenes, as they provide direct access to renewable dienes for telomerization. In particular, those terpenes industrially available, which are derived mostly from turpentine, form an attractive group of substrates. Behr et al. recently used the renewable 1,3-diene myrcene in the telomerization with diethylamine, for instance [18]. The monoterpene myrcene is easily obtained from (3-pinene, sourced from the crude resin of pines, by pyrolysis, and is currently already used in many different applications. 

Application An aromatics process based on extractive distillation, GT-BTX efficiently recovers benzene, toluene and xylenes from refinery or petrochemical aromatics streams, such as catalytic reformate or pyrolysis gasoline. 

Application A UOP aromatics complex is a combination of process units which are used to convert petroleum naphtha and pyrolysis gasoline into the basic petrochemical intermediates benzene, toluene, paraxylene and/or ortho-xylene. 

Olefins are not present in naphtha made from crude oil. However, some types of naphtha produced as refinery intermediates by thermal or catalytic cracking processes can contain high levels of olefins. Olefins tend to lead to high fouling rates in pyrolysis crackers and are usually avoided as petrochemical feedstock. 

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