Ethylene steam cracker

BULK ANALYSIS OF METALS IN COKE DEPOSITS FROM COMMERCIAL ETHYLENE STEAM CRACKER (IN ppm)... 

Figure 7. Laboratory-scale ethylene steam cracker.

Oxidation of an Ethylene Steam Cracker Pyrolysis Tube Deposit in Water Vapor and Its Enhancement by Inorganic Catalysts... 

Gasification of a carbonaceous deposit formed on a radiantly heated ethylene steam cracker pyrolysis tube, in water vapour, at 721-1056°C was chemically controlled. Oxidation rates were linear between 10-85% burn off and increased proportionally with water vapour partial pressure (38-362 mm Hg). The activation energy and pre-exponential factor were 57 Real mole-l and 3.6 x 10 mg cm min" respectively. Gasification was catalysed by inorganic impurities entrained in the deposit and was promoted by hydrogen and butane. 

A principal factor governing the operating cycle of ethylene steam crackers (ESC) is coke formation on the inside surfaces of the radiantly heated pyrolysis tubes. Steam is used as the carrier for the hydrocarbon feedstock as it is known empirically to minimise this coking. It is probable that the observed deposition is a net process representing the difference between formation and removal, primarily by thermal oxidation. A fundamental requirement of any detailed understanding of the overall processes involved, therefore, is knowledge of the oxidation behaviour of such deposits. Although several studies have been undertaken on various carbons considered to simulate ESC pyrolysis tube coke (e.g. ( )) no relevant information has been published for plant material. To provide these data, therefore, the oxidation behaviour of a coke formed on an ESC tube has now been examined in water vapour. 

Ethylene steam cracker furnace tubes up to 1100°C carburization/oxidation... 

Thermal Cracking. / -Butane is used in steam crackers as a part of the mainly ethane—propane feedstream. Roughly 0.333—0.4 kg ethylene is produced per kilogram / -butane. Primary bv-pioducts include propylene (50 57 kg/100 kg ethylene), butadiene (7-8.5 kg/100 kg), butylenes (5-20 kg/WO kg) and aromatics (6 kg/ToO kg). 

Production estimates for propylene can only be approximated. Refinery propylene may be diverted captively to fuel or gasoline uses whenever recovery is uneconomic. Steam-cracker propylene production varies with feedstock and operating conditions. Moreover, because propylene is a by-product, production rates depend on gasoline and ethylene demand. 

Since the bulk of butadiene is recovered from steam crackers, its economics is very sensitive to the selection of feedstocks, operating conditions, and demand patterns. Butadiene supply and, ultimately, its price are strongly influenced by the demand for ethylene, the primary product from steam cracking. Currently there is a worldwide surplus of butadiene. Announcements of a number of new ethylene plants will likely result in additional butadiene production, more than enough to meet worldwide demand for polymers and other chemicals. When butadiene is in excess supply, ethylene manufacturers can recycle the butadiene as a feedstock for ethylene manufacture. 

Significant products from a typical steam cracker are ethylene, propylene, butadiene, and pyrolysis gasoline. Typical wt % yields for butylenes from a steam cracker for different feedstocks are ethane, 0.3 propane, 1.2 50% ethane/50% propane mixture, 0.8 butane, 2.8 hill-range naphtha, 7.3 light gas oil, 4.3. A typical steam cracking plant cracks a mixture of feedstocks that results in butylenes yields of about 1% to 4%. These yields can be increased by almost 50% if cracking severity is lowered to maximize propylene production instead of ethylene. 

Many heterogeneous catalysts have been commercialized to dimerize ethylene to selectively yield 1-butene or 2-butene (66—70). Since ethylene is generally priced higher than butylenes, economics favor the production of butylenes from steam crackers, not from ethylene. An exceUent review on... 

Cracking n-hutane is also similar to ethane and propane, hut the yield of ethylene is even lower. It has been noted that cracking either propane or butanes at nearly similar severity produced approximately equal liquid yields. Mixtures of propane and butane LPG are becoming important steam cracker feedstocks for C2-C4 olefin production. It has been forecasted that world LPG markets will grow from 114.7 million metric tons/day in 1988 to 136.9 MMtpd in the year 2000, and the largest portion of growth will be in the chemicals field. 

The liquefied plastic fraction is heated to over 400 °C. This leads to cracking of the plastic into components of different chain lengths. Gases count for 20%-30% and oils for 60%-70% they are separated by distillation. Any naphtha produced is treated in a steam cracker, resulting in monomers like ethylene and propylene that are recovered. Such monomers can be used to produce plastics again. The heavy fractions can be processed into synthesis gas or conversion coke and then be transferred for further use. At most 5% of the input is converted into a mineral fraction. It is likely that this consists mainly of the inorganic additives in plastics. 

Manufacture Some of the butadiene produced is recovered from steam crackers along with ethylene and propylene. However, most of it is now produced by the dehydrogenation of butene. CH3 CH-CH-CH3 CH2-CH-CH-CH2 + H2... 

Traditional olefin plants have more than one alias. One is even fraudulent. They are variously called ethylene plants after their primary product steam crackers because the feed is usiuilly mixed with steam before it is cracked or whatever aacker, where whatever is the name of the feed (ethane cracker, gas oil cracker, etc.). Olefin plants are sometimes referred to as ethylene crackers, biit only those who don t know any better, use that misnomer. Ethylene is not cracked but rather is the product of cracking. 

Name four alternatives to the steam cracker to make ethylene and/or propylene. 

Steam crackers provide the traditional cost-effective approach for olefins production from lighter feed stocks such ethane, propane, naphtha, and AGO. However, these options typically provide higher E/P ratio. To meet the increasing demands of ethylene and particularly propylene, refiners and petrochemical producers are planning integrated facilities. The objectives are ... 

A major current refinery-petrochemical project is under construction for Saudi Aramco-Sumitomo Chemical at their Rabigh, KSA site. In conjunction with our JGC partner we have linked the upstream refinery expansion to a combined mega-DCC unit and mega-ethane steam cracker. Corresponding production rates are 1500 kta ethylene/950 kta propylene. The corresponding integrated layout is shown below in Figure 8.2. 

The principal source of toluene is catalytic reforming of refinery streams. This source accounts for ca 79% of the total toluene produced. An additional 16% is separated from pyrolysis gasoline produced in steam crackers during the manufacture of ethylene and propylene. The reactions taking place in catalytic reforming to yield aromatics are dehydrogenation or aromatization of cyclohexanes, dehydroisomerization of substituted cyclopentanes, and the cyclodehydrogenation of paraffins. The formation of toluene by these reactions is shown. 

A plant contains all production units required to produce a certain intermediate or finished product. The relationship between a site s plants varies between two extremes. At integrated sites (Verbundstandorte) the plants cover certain steps of the overall production process and are closely linked by material flows. This can be seen as a "plant within a plant" concept based on a process focus. Integrated sites are especially common in production of commodity chemicals. For example, the new integrated site built by BASF in Nanjing, China, consists of a steam cracker producing among others ethylene and propylene. Nine other plants further process the substances. The overall investment to build the site was U.S. 2.9 billion.10... 

The best hope for olefin/paraffin facilitated membrane separations seems to be the solid polymer electrolyte membranes discussed earlier, the results of which are shown in Figures 11.21 and 11.22. If stable membranes with these properties can be produced on an industrial scale, significant applications could develop in treating gases from steam crackers that manufacture ethylene and from polyolefin plants. 

Steam cracker tar (SCT) is a by-product from the steam cracking of naphtha or gas oils to produce ethylene. The characteristics and yield of SCT is dependent on the feed characteristics, the plant design and severity of cracking,... 

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