Ethylene manufacture

A large amount of BTX is obtained as a by-product of ethylene manufacture (see Ethylene). The amount produced strongly depends on the feed to the ethylene plant. This is illustrated in Table 3 for various feeds to a typical large scale plant producing 450,000 t/yr of ethylene (16). Note that only about 1—2% of the ethane/propane feeds end up as BTX and it is almost completely benzene and toluene. As the feed goes up in molecular weight, the yield of BTX increases from 4% with butane feed to about 10% with gas oils, and the BTX proportions go from 72 20 8 respectively, to 44 34 22 respectively. 

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. 

Whatever the fractionation scheme used, the fraction is removed as overhead from the debutanizer. References 45 and 46 give ethylene manufacturing process. 

The use of methane, ethane, ethylene, propylene, and propane pure light hydrocarbons as refrigerants is quite common, practical, and economical for many hydrocarbon processing plants. Examples include ethylene manufacture from cracking some feedstock, ethylene or other hydrocarbon recycle purification plants, gas-treating plants, and petroleum refineries. 

The one aspect of ethylene manufacture that sets it apart from most other petrochemicals is the wide range of alternate feedstocks that can be used. Most others are limited to one or a few commercial alternatives. Ethylene is a simple molecule, CH2=CH2, and if you thought that lots of hydrocarbons could be cracked to form it, you d be right, as you can see in Table 5—1-... 

So not much else is formed. Thats a contrast to ethylene manufacture, especially cracking the heavy liquids, where the by-products are abundant. 

Pyrolysis gasoline gasoline produced by thermal cracking as a byproduct of ethylene manufacture. It is used as a source of benzene by the hydrodealkylation process. 

Changes in technology and in the availability of optimum feedstocks have far-reaching effects on the entire product mix. For example, when the availability of LPG and ethane for ethylene manufacture has decreased, n-butane and the higher crude cuts have been used, and the proportion of by-product butadiene has increased. 

Major demand segments for NGLs indicate that around 35-40 percent of gas liquids, principally ethane and propane, are consumed as cracking feedstocks for ethylene manufacture. Some of the chemical derivatives obtained from ethane and propane are shown in Fig. 20.6. 

National Emission Standards for Closed Vent Systems, Control Devices, Recovery Devices and Routing to a Fuel Gas System or a Process National Emission Standards for Equipment Leaks—Control Level 1 National Emission Standards for Equipment Leaks—Control Level 2 Standards National Emission Standards for Oil-Water Separators and Organic-Water Separators National Emission Standards for Storage Vessels (Tanks)—Control Level 2 National Emission Standards for Ethylene Manufacturing Process Units Heat Exchange Systems and Waste Operations... 

In 1825, Faraday isolated benzene from a liquid condensed by compressing oil gas. Benzene was first synthesized by Mitscherlich in 1833 by distilling benzoic acid with lime. Benzene was first commercially recovered from light oil derived from coal tar in 1849 and from petroleum in 1941 (IARC 1982a). Several years after the end of World War II, the rapidly expanding chemical industry created an increased demand for benzene that the coal carbonization industry could not fulfill. To meet this demand, benzene was produced by the petroleum and petrochemical industries by recovery from reformat and liquid by-products of the ethylene manufacturing process (Purcell 1978). 

The appeal of an acetic acid process, based on ethane oxidation, lies mostly in the absence of the need for the energy demanding step for syngas production. On the other hand, it has to compete not only with the well established methanol carbonylation (Section 4.2), but also with the current utilization of ethane in steam crackers for ethylene manufacture. In fact, ethane feedstock becomes attractive for acetic acid production if it is locally abundant and can be supplied at minimal cost, e.g., in a petrochemical complex close to a large gas field. The construction of a semi-commercial plant of 30 kt/a in the Persian Gulf region has been announced. 

Although steam cracking was initially designed for ethylene manufacture, it is only economically justified if tbe different hydrocarbons which it produces are properiy upgraded as petrochemical intennediates. Hence although ethane only produces ethylene as an upgradable product, in the case of propane an attempt is made to profit from the sale of ethylene and propylene, and, in the case of the liquid petroleum fractions (naphtha... 

Propylene is usually produced as a byproduct of ethylene manufacture. An alternative process is catalytic dehydrogenation of propane, as described in U.S. 4,381,417 (to UOP). What is the cost of production of propylene by this route for a world-scale plant ... 

Sulfides find use (Table 3) in the refinery and petrochemical industries. " Some refiners use dimethyl sulfide as a sulfiding agent to convert the metal oxide hydrotreating catalysts to their sulfide form. In ethylene manufacture, ethane or other hydrocarbon liquid like naphtha is reacted at high temperatures with steam. The process would make an unacceptable amount of coke and produce too much carbon... 

Although utilized for chemical manufacture in some short-lived ventures prior to World War I and continuously since the early 192O s, ethylene manufacture and separation were the subjects of relatively few publications outside of patents before the end of World War II. Since that time numerous articles have been published on ethylene production by cracking C2-C3 gas fractions and selected oil fractions and on its separation by adsorption processes. Its production is the greatest of any of the hydrocarbons from petroleum, and much literature is available on its utilization. A selected list of references is given in the bibliography under Ethylene. 

Section, which appears every month. It also has a special section on Patents which lists new patents according to their classification. The Process Issue of the Petroleum Refiner is now carrying a special section on Petrochemical Processes. In the September 1952 issue for example, Extractive Distillation for Aromatic Recovery, Modified SO2 Extraction for Aromatic Recovery, Udex Extraction, Ethylene Manufacture by Cracking, Ethylene Production, Hypersorption, Hydrocol, Dehydrogenation (for butadiene), and Butadiene Process, were described. These descriptions include the main essentials of the process, simplified flow diagrams, and the name of the company offering it. Formerly these processes were described under the Process Section. 

Toluene. The sources of toluene lie primarily in the catalytic reforming of selected petroleum fractions rich in naphthenes or in the recovery of toluene contained in aromatic concentrate (pyrolysis gasoline) produced as a byproduct of ethylene manufacture—mostly from naphtha/gas oil cracking. U.S. production and pricing for benzene and the aromatics discussed in Sections... 

Benzene. Benzene is derived from several sources. A small amount is still recovered from coke oven by-product streams. However, the primary sources are from the catalytic refonning of petroleum fractions rich in naphthenes (see Section 6.2.1.7, above), recovery from aromatic concentrate (pyrolysis gasoline) produced as a by-product of ethylene manufacture, hydrodealkylation of... 

Shortages of prime feedstocks for ethylene manufacture have spawned numerous attempts to use alternate raw materials. Methane 1s one such raw material that 1s the most abundant component of natural gas, usually comprising up to 90 mole % of the hydrocarbon fraction. Thus, methane represents a considerably more abundant source for ethylene than ethane/propane, the two most widely used raw materials. 

The same relationship between plant complexity and loss in raw material value to fuel also exists in petrochemical processing. The three common raw materials for ethylene manufacture in the U.S.—ethane/propane, naphtha, and gas oil—exhibit similar trade-off relationships between processing complexity and fuel value loss (see Table I). 

The economic and therefore commercially suitable processes for obtaining propylene are as a by-product of catalytic cracking, as a byproduct of ethylene manufacture, and as a co-product of an isobutane cracker. 

We have seen that by 1973 catalytic cracking will only satisfy 2 to 4 billion lbs/year of a projected 11 billion lb/year propylene demand. Most of the balance will be produced as a by-product of ethylene manufacture. Shifting from ethane and propane to heavier stocks such as n-butane and gas oil will satisfy propylene needs. Some propylene will also be produced from isobutane steam crackers as an isobutylene co-product. 

Before considering the economics of this approach to ethylene manufacture, we discuss briefly some of the technical aspects of residue hydrocracking. 

Figure 5. Crude/naphtha price relationship for equal ethylene manufacturing...

Carlona n. Poly(ethylene), manufactured by Shell, The Netherlands. 

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