Olefin plant yield

Basic Yield Data. This is a good place to start asking questions. If the process uses a catalytic reaction, do the yields represent new catalyst or catalyst regenerated a number of times For a thermal reaction like an olefin plant steam cracker, questions might be asked about on-stream time between decokings. Therefore, how much contingency is there in the specified number of crackers required ... 

Recycles are meticulously accounted for because they load equipment and draw utilities. An olefin plant sustaining relatively low conversion per pass often builds up large amounts of unreacted feed that is recycled to the steam crackers. With utilities charged to ultimate products, these recycles would seem to the model to be free. The model would likely opt for very low conversion, which usually gives high ultimate yield and saves feedstock. Assigning the utility costs to users causes the compressor to pay for the extra recycle and the model raises conversion to the true optimum value. 

With the percentages of the three xylenes from the various sources differing so much, it s not likely that a company, or the industry for that matter, will produce just the amount of the xylene isomer it wants. Para-xylene has the biggest demand and meta- the smallest, but none of the processes, cat reforming, olefins plants, or disproportionation, have commensurate yields. 

Ethane and propane produce a high yield of ethylene. Propane also gives a high yield of propylene. The earliest commercial olefin plants of any size were designed to use these two feeds, and they dominated U.S. plant designs in much of the 20th century. 

Despite the abundance of analysis in the technical journals on the subject, there really is only a moderate amount of flexibility to change the yields in olefin plants once they are built. The problem is that the yield of each of the coproducts moves in a different direction as the pressures and... 

The base-load supply of butadiene is from olefins plants simply because butadiene is coproduced with the other olefins. There s not much decision on whether or not to produce it. It just comes out, but in a small ratio compared CO ethylene and propylene. Cracking ethane yields one pound of butadiene for every 45 pounds of ethylene cracldng the heavy liquids, naphtha or gas oil, produces one pound of butadiene for every seven pounds of ethylene. Because of the increase in heavy liquids cracldng, about 75% of the butadiene produced in the United States is coproduced in olefin plants. 

A typical worldscale olefins plant producing a billion pounds a year of ethylene from heavy liquids can also yield up to 50 million pounds of styrene. Since the styrene is a coproduct, and the extraction costs are modest, the economics are very attractive compared to on-purpose styrene. 

Table 7 shows the yield distribution of the C4 isomers from different feedstocks with specific processing schemes. The largest yield of butylenes comes from the refineries processing middle distillates and from olefins plants cracking naphtha. The refinery product contains 35 to 65% butanes olefins plants, 3 to 5%. Catalyst type and operating severity determine the selectivity of the C4 isomer distribution (41) in the refinery process stream. Processes that parallel fluid catalytic cracking to produce butylenes and propylene from heavy cmde oil fractions are under development (42). 

Butylenes are four-carbon monoolefins that are produced by various hydrocarbon processes, principally catalytic cracking at refineries and steam cracking at olefins plants. These processes yield isomeric mixtures of 1-butene, cis- and tra s-butene-2, and isobutylene. Derivatives of butylenes range from polygas chemicals and methyl t-butyl ether, where crude butylenes streams may be used, to polybutene-1 and LLDPE, which require high-purity 1-butene. In 1997, the estimated consumption of butylenes (in billions of pounds) was alkylation, 32.0 MTBE, 12.0 other, including polygas and fuel uses, 0.5. 

Most olefins of petrochemical interest are produced by thermal cracking of naphtha feed stock, yielding about 12-14 million metric tons/year ethylene[l]. A Hungarian olefin plant, completed in 1975, is also operated on a naphtha feedstock. Yields and relative amounts of the main products greatly depend on the qualities of the naphtha feedstock pyrolyzed and the parameters of the cracking operation[2,3]. A detailed study of the pyrolysis is, therefore, of great industrial significance. 

In the United States alone, there are 23 production plants yielding about 22 billion pounds per year in 2010. The largest producers include ExxonMobil, Dow Chemical, Basell USA, Formosa Plastics, Huntsman, INEOS Olefins and Polymers, Phillips Sumika, Sunoco, and Total Petrochemicals. 

Ethylene. The largest potential chemical market for n-butanc is in steam cracking to ethylene and coproducts. n-Butane is a supplemental feedstock for olefin plants and has accounted for 1 to 4 percent of total ethylene production for most years since 1970. It can be used at up to 10 to 15 percent of the total feed in ethane/propane crackers with no major modifications. n-Butane also can be used as a supplemental feed at as high as 20 to 30 percent in hea y naphtha crackers. The consumption of C s has fluctuated considerably from year to year since 1970, depending on the relative price of butane and other feedstocks. The yield of ethylene is only 36 to 40 percent, with the other products including methane, propylene, ethane, butadiene, acetylene, and butylenes. About 1 to 2 billion lb of butane are consumed annually to produce ethylene. 

By adding up to 36% ethylene glycol to the aqueous catalyst phase, the space-time yield could be boosted up to approx. 3 mt m-3 h-1 for propene hydroformylation, a factor of 20 in comparison to the conventional two-phase process without changing the reaction conditions. Because of this surprising speed-up, higher alpha-olefins up to 1-octene are converted with high to acceptable space-time yield (Fig. 22). Up to date this process is not commercialized, but has been tested in a continuous pilot plant. 

Figure 5. Comparison of olefin yield obtained in micro fluid-bed and large pilot plant...

During the history of a half century from the first discovery of the reaction (/) and 35 years after the industrialization (2-4), these catalytic reactions, so-called allylic oxidations of lower olefins (Table I), have been improved year by year. Drastic changes have been introduced to the catalyst composition and preparation as well as to the reaction process. As a result, the total yield of acrylic acid from propylene reaches more than 90% under industrial conditions and the single pass yield of acrylonitrile also exceeds 80% in the commercial plants. The practical catalysts employed in the commercial plants consist of complicated multicomponent metal oxide systems including bismuth molybdate or iron antimonate as the main component. These modern catalyst systems show much higher activity and selectivity... 

Hikino et al. [153] have investigated by enzymatic means the stereospecific epoxidation reactions of olefinic double bonds in the plant Curcuma zedoaria Roscoe. They studied the bioconversion of germacrone (207), a constituent of C. zedoaria, by microorganisms in the hope of obtaining stereoselective epoxidation as in the case of the plant. Cuminghamella blakesleeana yielded three major products (208 - 210) from germacrone, Fig. (42). 

Styrene, one of the world s major organic chemicals, is derived from ethylene via ethylbenzene. Several recent developments have occurred with respect to this use for ethylene. One is the production of styrene as a co-product of the propylene oxide process developed by Halcon International (12). In this process, benzene is alkylated with ethylene to ethylbenzene, and the latter is oxidized to ethylbenzene hydroperoxide. This hydroperoxide, in the presence of suitable catalysts, can convert a broad range of olefins to their corresponding oxirane compounds, of which propylene oxide presently has the greatest industrial importance. The ethylbenzene hydroperoxide is converted simultaneously to methylphenyl-carbinol which, upon dehydration, yields styrene. Commercial application of this new development in the use of ethylene will be demonstrated in a plant in Spain in the near future. 

Yield Pattern. Table XI presents a feed/product summary for a naphtha based billion lb/yr ethylene plant at various severities of 23, 25, and 27 wt % ethylene (once-through basis). The naphtha feed is the same one as referred to earlier (see Table III). It is immediately apparent that feed requirements are increased at lower severities for a given ethylene production rate. Also, production of olefin by-products increases as severity decreases. Note especially the 36% increase in propylene production as severity is dropped from 27% ethylene to 23% ethylene. Butadiene production goes up somewhat, while butylenes production jumps by over 100% going from 27 to 23% ethylene. 

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