N-butane feedstock

In the process based on n-butane feedstock, vanadium phosphorous oxides (V-P-O) catalysts are mainly used.1010-1012 Processes for the oxidation of low-cost C4 fraction from naphtha cracker consisting mainly of butenes have also been developed.1013,1014 In contrast with benzene oxidation where two carbon atoms are lost in the form of ethylene no carbon is lost in the oxidation of C4 hydrocarbons ... 

Direct dehydroisomerisation (DHI) of n-butane into isobutene over bifunctional zeolite-based catalysts represents a potential new route for the generation of isobutene utilising cheap n-butane feedstock. Isobutene is used worldwide for production of methyl tert-butyl ether (MTBE) and polyisobutylene. It is currently obtained via extraction from refinery/cracker C4 streams or via conversions of isobutane (in one step) or n-butane (in two steps).1,2 Isobutene can also be produced via the isomerisation of n-butenes,3 although there is no evidence that this is practised commercially.2,3... 

Thus, an operation able to crack butane would be able to lift propylene yields if the increased amounts of isobutane were to be fed into the system. This could be by either isobutane purchases or isomerisation of n-butane feedstock. This gives a gas cracking operation some flexibility in altering the ethylene/propylene split which is otherwise difficult with gaseous feedstock. 

ExxonMobil produces MEK from catalytic dehydrogenation of sec-butanol feedstock. On the other hand, Celanese produces MEK as a byproduct from their acetic acid production from the controlled oxidation of n-butane feedstock. 

Butane is primarily used as a fuel gas within the LPG mixture. Like ethane and propane, the main chemical use of butane is as feedstock for steam cracking units for olefin production. Dehydrogenation of n-butane to butenes and to butadiene is an important route for the production of synthetic rubber. n-Butane is also a starting material for acetic acid and maleic anhydride production (Chapter 6). 

Light naphtha containing hydrocarbons in the C5-C7 range is the preferred feedstock in Europe for producing acetic acid by oxidation. Similar to the catalytic oxidation of n-butane, the oxidation of light naphtha is performed at approximately the same temperature and pressure ranges (170-200°C and =50 atmospheres) in the presence of manganese acetate catalyst. The yield of acetic acid is approximately 40 wt%. 

However, at least the high vinylidene PIB type may be produced using a concentrated feedstock with an isobutylene content of 90%. Non-reactive hydrocarbons, such as isobutane, n-butane or other lower alkanes commonly present in petroleum fractions, may also be included in the feedstock as diluents. Further, the feedstock... 

Acetic Acid. Although at the time of this writing Monsanto s Rh-catalyzed methanol carbonylation (see Section 7.2.4) is the predominant process in the manufacture of acetic acid, providing about 95% of the world s production, some acetic acid is still produced by the air oxidation of n-butane or light naphtha. n-Butane is used mainly in the United States, whereas light naphtha fractions from petroleum refining are the main feedstock in Europe. 

Maleic Anhydride. Gas-phase catalytic oxidation of benzene or n-butane is the principal process for the industrial production of maleic anhydride.973 996-999 Until the 1970s commercial production was based predominantly on benzene. Because of its more favorable economics, a switch to butane as an alternative feedstock has taken place since then.966,999-1002 At present almost all new facilities use n-butane as the starting material. Smaller quantities of maleic anhydride may be recovered as a byproduct of phthalic anhydride manufacture (about 5-6%).1003,1004... 

Table III gives a range of the possible feedstocks that can be used to produce ethylene and the kinds and amounts of by-products that can be made from them. For our purposes we have selected a constant basis of 1 billion lbs/year ethylene production. The feedstocks illustrated in Table III include ethane, propane, n-butane, a full range naphtha, a light gas oil, and a heavy gas oil. The yields reflect high severity conditions with recycle cracking of ethane in all cases. For propane feed, propane recycle cracking has been included as well.

Figure 6 shows that with the present level of premium valuation for by-products, a 1.1 /lb naphtha price would result in this feedstock having an advantage over ethane, propane or butane at 1 /lb. The cost for naphtha-based ethylene in this case would be only 1.94 /lb vs. 2.04, 2.36, and 2.47 /lb from n-butane, propane, and ethane, respectively. The breakeven prices for the light feedstocks that would correspond to the 1.1 /lb naphtha price would be 0.6, 0.82, and 0.95 /lb for ethane, pro-... 

Figure 6. Effect of feedstock price on U.S. ethylene production costs (1000 MM Ibs/yr ethylene production premium value by-products). Note by-proauct prices as given in Table V. However, for n-butane feed9 the butanes contained in the Ch by-product are valued the same as n-butane feed.

Currently in the United States, ethylene cost is lower via production from the light feedstocks regardless of the type of by-product valuation applicable. Of these, n-butane appears most interesting if premium prices for by-products can be applied. Ethane is best for limited by-product outlets. 

Butadiene (> 98%w/w) 20 ooo longtons Catalytic dehydrogenation of n-butenes feedstock of liquid mixed hydrocarbon stream containing 80.5 mol % n-butenes, 11.5 mol % n-butane, and 1 mol % of higher hydrocarbons. 

This relationship will vary with the aromatic content of the feedstock. With a highly aromatic feed, the catalyst with the higher hydrogenation activity may give a higher isobutane/n-butane ratio, although with the pentanes and hexanes the effect is reversed. 

Feedstocks for various industrial pyrolysis units are natural gas liquids (ethane, propane, and n-butane) and heavier petroleum materials such as naphthas, gas oils, or even whole crude oils. In the United States, ethane and propane are the favored feedstocks due, in large part, to the availability of relatively cheap natural gas in Canada and the Arctic regions of North America this natural gas contains significant amounts of ethane and propane. Europe has lesser amounts of ethane and propane naphthas obtained from petroleum crude oil are favored in much of Europe. The prices of natural gas and crude oil influence the choice of the feedstock, operating conditions, and selection of a specific pyrolysis system. 

Furnace Flexibility. In this example, the flexibility of an operating propane furnace in handling alternate feedstocks was examined. Specifically, the maximum loading of the furnace subjected to various process and physical constraints is to be determined. The alternate feedstocks are ethane, n-butane and a naphtha. The following physical and process limits are observed. 

FEEDSTOCK PROPANE (BASE) ETHANE N-BUTANE NAPHTHA... 

The second term in each summation is CO converted to C02 in the pollution control device the third is due to unconverted feedstock. These screening calculations verify that the n-butane route emits approximately Vi the C02 compared to the benzene pathway. Based on the economic and environmental screening, the benzene route would be excluded from further consideration. More detailed calculations based on optimized flowsheets confirm these screening calculations are accurate.72... 

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. 

Ethylene. The largest potential chemical market for n-butane is in steam cracking to ethylene and coproducts. n-Butane is a supplemental feedstock for olefin plants and has accounted for 1-4 percent of total ethylene production for most years since 1970. ft can be used at up to 10-15 percent of the total feed in... 

The liquid-phase oxidation (LPO) of light saturated hydrocarbons yields acetic acid and a spectrum of coproduct acids, ketones, and esters. Although propane and pentanes have been used, n-butane is the most common feedstock because it can ideally yield two moles of acetic acid. The catalytic LPO process consumes more than 500 million lb of n-butane to produce about 500 million lb of acetic acid, 70 million lb of methyl ethyl ketone, and smaller amounts of vinyl acetate and formic acid. The process employs a liquid-phase, high-pressure (850 psi), 160-180°C oxidation, using acetic acid as a diluent and a cobalt or manganese acetate catalyst. 

Maleic Anhydride. Prior to 1975, benzene was the feedstock of choice for maleic anhydride manufacture. By the early 1980s, for economic reasons, many producers had switched to the n-butane process described in the section n-Butane Derivatives . By 1988, all of the maleic anhydride produced in the United States came from that process. However, about half of the maleic anhydride produced abroad still comes from benzene oxidation, with a small amount being recovered as a coproduct in phthalic anhydride manufacture. 

The various components of LPG streams are used in a variety of processes. Propane, butane and isobutane are used as cracker feedstock for the production of olefins which is discussed in later chapters. In addition n-butane is used for the production of 1,3-butadiene. This compound can also be extracted from the C4 cracked gases by extensive distillation coupled with a selective absorption process. 

Research has been carried out to investigate the changes observed during the activation process. This takes the form of heating a catalyst precursor up to the reaction temperature in an n-butane/air feedstock, and leaving it on-line for varying times (the standard times that have been adopted are 0.1 hour, 8 hours, 84 hours and 132 hours). The samples are then taken off-line and characterized as fully as possible. 

Feedstocks. Propane and n-butane, 99.9+% (Matheson Co., E. Rutherford, NY), were used without further purification. Impurities included very small amounts of methane, ethane, isobutane, and traces of higher paraffins, n-Hexane (Phillips) was 99+%. 

Feedstock composition, mol per cent n-butane = 2, butene-1 =31, butene-2 = 18, isobutene = 49. 

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