Ethylene coke from

Miyazawa et al. (92) related rates of decrease of aliphatic hydrogen protons during pyrolysis of ethylene tar pitch to formation of mesophase. Yokono et al, (93) used the model compound anthracene to monitor the availability of transferable hydrogen. Co-carboniza-tions of pitches with anthracene suggested that extents of formation of 9,10-dihydroanthracene could be correlated with size of optical texture. The method was then applied to the carbonization behaviour of hydrogenated ethylene tar pitch (94). This pitch, hydrogenated at 573 K, had a pronounced proton donor ability and produced, on carbonization, a coke of flow-type anisotropy compared with the coarse-grained mosaics (<10 ym dia) of coke from untreated pitch. 

Thermal cracking of ethane, propane, butane, naphthas, gas oils, and/or vacuum gas oils is the main process employed for the production of ethylene and propylene butadiene and benzene, toluene, and xylenes (BTX) are also produced. Thermal cracking of these hydrocarbons is also called pyrolysis of hydrocarbons. Ethylene is the organic chemical produced worldwide in the largest amoimts and has been called keystone to the petrochemical industry. This technology is well documented in the literature. Somewhat similar thermal cracking processes are used to produce vinyl chloride monomer (VCM) from ethylene dichloride (EDQ, styrene from ethylbenzene, and allyl chloride from propylene dichloride (PDC). Production of charcoal and coke from wood and coal is actually a pyrolysis process, but it is not discussed here. 

Somorjai80 studied the formation of irreversible coke from 14C ethylene on Pt (111) from 50 to 400°C and found that 75% was irreversible at the point where the H/C decreases to 0.2. This leads to graphitisation of the coke, and its inability to desorb and migrate. 

Figure 5.36 Coking from ethylene. TGA measurements [405]. Flows (mol/h) C2H4=0.2, H20=0.16, N2=0.1, H2S=10 ). Tube diameter 18 mm, basket diameter 10 mm, 0.85 g catalyst (Zr02, 0.5% K). Reproduced with the permission of Elsevier.

Chemical Uses. In Europe, products such as ethylene, acetaldehyde, acetic acid, acetone, butadiene, and isoprene have been manufactured from acetylene at one time. Wartime shortages or raw material restrictions were the basis for the choice of process. Coking coal was readily available in Europe and acetylene was easily accessible via calcium carbide. 

In general, when the product is a fraction from cmde oil that includes a large number of individual hydrocarbons, the fraction is classified as a refined product. Examples of refined products are gasoline, diesel fuel, heating oils, lubricants, waxes, asphalt, and coke. In contrast, when the product is limited to, perhaps, one or two specific hydrocarbons of high purity, the fraction is classified as a petrochemical product. Examples of petrochemicals are ethylene (qv), propylene (qv), benzene (qv), toluene, and xylene (see Btx processing). 

The principal sources of feedstocks in the United States are the decant oils from petroleum refining operations. These are clarified heavy distillates from the catalytic cracking of gas oils. About 95% of U.S. feedstock use is decant oil. Another source of feedstock is ethylene process tars obtained as the heavy byproducts from the production of ethylene by steam cracking of alkanes, naphthas, and gas oils. There is a wide use of these feedstocks in European production. European and Asian operations also use significant quantities of coal tars, creosote oils, and anthracene oils, the distillates from the high temperature coking of coal. European feedstock sources are 50% decant oils and 50% ethylene tars and creosote oils. 

Why start out with benzene The obvious answer is that benzene is one of the handRil of basic building blocks in the petrochemicals industry along with ethylene, propylene, and a few others. The more subde reason is that benzene, more than any of those other chemicals, comes from a broader b e- steel mill coking, petroleum refining, and olefins plants. For that reason, the benzene network, the sources and the uses, is more complex than any of the others. 

Chen and co-workers have studied the role of coke deposition in the conversion of methanol to olefins over SAPO-34 [111]. They found that the coke formed from oxygenates promoted olefin formation while the coke formed from olefins had only a deactivating effect The yield of olefins during the MTO reaction was found to go through a maximum as a function of both time and amount of coke. Coke was found to reduce the DME dilfusivity, which enhances the formation of olefins, particularly ethylene. The ethylene to propylene ratio increased with intracrystal-line coke content, regardless of the nature of the coke. 

In Figure 7 the selectivity to methane, ethane, ethylene, gases, gasoline (210°C), diesel (310°C), and coke at 65% level of conversion have been plotted for HYUS zeolites with 28, 21, 12, and 2 Al per unit cell for cracking gas-oil. It is apparent from the figures that thO selectivity to and C products decreases with a decreasing number of aluminum, up to 10- 0 Al per unit cell. With further dealumination the selectivity to and products... 

The dry gas prodnced from the DCC process contains approximately 50% ethylene. The cracking reactions are endothermic, and compared to FCC, a higher coke make is required to satisfy the heat balance. 

Ethylene was formerly procured from alcohol (itself produced from raw material which was actually or potentially a foodstuff) by warming with sulfuric acid, by passing the vapors over heated coke impregnated with phosphoric acid, or by comparable methods. Ethylene combines with bromine to give ethylene dibromide,... 

Steam cracking (Fig. 2), consists of a furnace in which the cracking takes place is at 815 to 870°C (1500 to 1600°F). As many as 6 to 20 furnaces are in parallel to increase ethylene production. Steam is used as a diluent to inhibit coking in the tubes and to increase the percentage of ethylene formed. The amount of steam changes with the molecular weight of the hydrocarbon feedstock and varies from 0.3 kg steam/kg ethane to 0.9... 

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