Ethylene from propane cracking

Chemicals directly based on propane are few, although as mentioned, propane and LPG are important feedstocks for the production of olefins. Chapter 6 discusses a new process recently developed for the dehydrogenation of propane to propylene for petrochemical use. Propylene has always been obtained as a coproduct with ethylene from steam cracking processes. Chapter 6 also discusses the production of aromatics from LPG through the Cyclar process. ... 

The production of ethylene by gas crackers, mostly from C2, C3, and some C4 feeds, amounts to about 40% of the world ethylene capacity. This results in a small coproduction of benzene compared to benzene co-produced in naphtha and gas oil crackers, which account for 60% of the world s ethylene production capacity. A typical overall benzene yield from ethane cracking is on the order of only 0.6% of the ethane feed, and the yield of benzene from propane cracking is on the order of 3% of the propane feed. In contrast, the... 

The most common method of producing ethylene commercially is high temperature coil cracking of propane or of a mixture of ethane and propane. Recovery of ethylene from the cracked gases is often accomplished by low temperature, high pressure straight fractionation. Another customary manufac-... 

As a general rule difficult or expensive separations should be performed last, since by that time less total material will be involved. Consider Table 4-1, which gives the product mix obtained in a cracking furnace of an ethylene plant and the normal boiling points of the compounds. Suppose it is desired to separate the six groups listed in the table using distillation. The separation of ethylene from ethane and propylene from propane will be the most difficult because they have the smallest boiling-point differences. Therefore, these steps should be performed last. 

Besides methane and hydrogen, other products observed were mainly ethane, ethylene (probably due to propane cracking), propene which are shown in figure 3. Minor amounts of benzene and toluene were also found but these products could not be quantified because their slow desorption from the zeolite s channels. 

Wyandotte A process for making a mixture of ethylene and propylene glycols, for use as antifreeze, from propane. The propane is cracked to a mixture of ethylene and propylene, which are not separated but converted to the corresponding glycols by chlorohydrination. Developed by the Wyandotte Chemicals Corporation. 

When naphtha or gas oil is cracked, imagine the limitless combinations possible. Naphthas are made up of molecules in the C5 to Cio range gas oils from Cio to perhaps C30 or C40. The structures include everything from simple paraffins (aliphacics) to complex polynuclear aromatics, so a-much wider range of possible molecules can form. Ethylene yields.froin..cracking naphtha or gas oil are much smaller than those from ethane or propane, as you can see from Table 5-1- But to compensate the plant operator, a full range of other hydrocarbons is produced as by-products also. 

Referring to the hardware in Figure 5—4, there are much larger facilities required for heavier liquids cracking than for ethane or propane. As you saw in Table 5—1, the yield of ethylene from the heavier feeds is much lower than from ethane. That means that to produce the same amount of ethylene on a daily basis, the gas-oil furnaces have to handle nearly five times as much feed as ethane furnaces. As the design engineer scales up these volumes, he or she has to worry about the size of the cubes necessary to heat up that much feed, the residence times best for each kind of feed, and the best pressure/temper-ature/steam mixture conditions. 

Feed stock for the first sulfuric acid alkylation units consisted mainly of butylenes and isobutane obtained originally from thermal cracking and later from catalytic cracking processes. Isobutane was derived from refinery sources and from natural gasoline processing. Isomerization of normal butane to make isobutane was also quite prevalent. Later the olefinic part of the feed stock was expanded to include propylene and amylenes in some cases. When ethylene was required in large quantities for the production of ethylbenzene, propane and butanes were cracked, and later naphtha and gas oils were cracked. This was especially practiced in European countries where the cracking of propane has not been economic. 

The methyl-acetylene and propadiene in the C3 cut are hydrogenated to propylene in a liquid-phase reactor. Polymer-grade propylene is separated from propane in a C3- splitter. The residual propane is either recycled for further cracking, or exported. C4s and hght gasoline are separated in a debutanizer. Gas expansion (heat recovery) and external cascade using ethylene and propylene systems supply refrigeration. 

The model includes several reactions which account for cocracking effects. Examples of this type of reaction include the reverse reactions of R-l and R-4 and the reaction R-17. R-17 predicts more ethylene and less heavier products from cocracking ethane and propane than from separate cracking. 

The techniques of preparation and of separation of hydrocarbons were improved. New construction materials led to cracking being conducted under more severe conditions, to increase the amount of olefins produced.. This also permitted a change from propane to ethane as the raw material for ethylene synthesis. Aromatics became available from petroleum naphthenes. Diolefins and acetylene were also manufactured from petroleum sources. 

In Western Europe, approximately 95% of ethylene is produced from steam-cracking naphtha. In the United States, ethylene manufactured from ethane accounts for approximately 70% of ethylene production, while steam-cracking naphtha accoxmts for 30% of ethylene production [11]. In the future, ethane will almost certainly be used for the vast majority of ethylene manufactured. In the Middle East, ethylene production is based on ethane (or ethane/propane mixtures) derived from natural gas or extracted from crude oil. In addition, energy costs in the Middle East are about five times lower than in Europe. 

Almost all ethylene produced in the world comes from steam cracking of hydrocarbon feedstocks, which can be natural gas (ethane, propane, and butane) or naphtha and gas oils. The feedstocks actually used depend on (1) what is available and (2) what specific demands there are for certain coproducts. 

Olefins are produced primarily by thermal cracking of a hydrocarbon feedstock which takes place at low residence time in the presence of steam in the tubes of a furnace. In the United States, natural gas Hquids derived from natural gas processing, primarily ethane [74-84-0] and propane [74-98-6] have been the dominant feedstock for olefins plants, accounting for about 50 to 70% of ethylene production. Most of the remainder has been based on cracking naphtha or gas oil hydrocarbon streams which are derived from cmde oil. Naphtha is a hydrocarbon fraction boiling between 40 and 170°C, whereas the gas oil fraction bods between about 310 and 490°C. These feedstocks, which have been used primarily by producers with refinery affiliations, account for most of the remainder of olefins production. In addition a substantial amount of propylene and a small amount of ethylene ate recovered from waste gases produced in petroleum refineries. 

The most important commercial use of ethane and propane is in the production of ethylene (qv) by way of high temperature (ca 1000 K) thermal cracking. In the United States, ca 60% of the ethylene is produced by thermal cracking of ethane or ethane/propane mixtures. Large ethylene plants have been built in Saudi Arabia, Iran, and England based on ethane recovery from natural gas in these locations. Ethane cracking units have been installed in AustraHa, Qatar, Romania, and Erance, among others. 

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. 

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