Butane process

Thermal Cracking. Heavy petroleum fractions such as resid are thermally cracked in delayed cokers or flexicokers (44,56,57). The main products from the process are petroleum coke and off-gas which contain light olefins and butylenes. This stream also contains a considerable amount of butane. Process conditions for the flexicoker are more severe than for the delayed coker, about 550°C versus 450°C. Both are operated at low pressures, around 300—600 kPa (43—87 psi). Flexicokers produce much more linear butenes, particularly 2-butene, than delayed cokers and about half the amount of isobutylene (Table 7). This is attributed to high severity of operation for the flexicoker (43). 

Pentane Isomerization. Pentane isomerization, although carried out on a much smaller scale, increased the critical supply of aviation gasolines toward the end of the war. Two pentane processes—one developed by Shell and one by Standard (Indiana) —were commercialized before the end of the war. The principal differences between the butane and pentane processes are the use in pentane isomerization of somewhat milder conditions and the use of an inhibitor to suppress side reactions, principally disproportionation. In general, the problems of the butane processes are inherent also in pentane isomerization, but the quality of the feed stocks is less important. Catalyst life is much... 

The other commercialized pentane isomerization process is that of the Standard Oil Co. (Indiana) (20). This process differs from the Indiana-Texas butane process in that the aluminum chloride is introduced as a slurry directly to the reactor and that about 0.5% by volume of benzene is added continuously in the feed to suppress side reactions. Temperature, catalyst composition, space velocity, and hydrogen chloride concentration are generally similar to those in the corresponding butane process, but the reactor pressure is about 100 pounds lower. The Pan American Refining Co. operated the Indiana pentane isomerization process commercially during the last nine months of the war and produced about 400 barrels of isopentane per calendar day. 

Based on the process description above, Table 6.11 can be generated which contains the total emission of each pollutant. Emissions are converted to impact indicators using the environmental fate and impact assessment tool EFRAT.79 A comparison of environmental indicators for MA production from either benzene or n-butane is shown in Table 6.12. All of the environmental indices in the n-butane process are less than or equal... 

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. 

In the first commercial process, introduced in 1933, maleic anhydride was produced by the catalytic oxidation of benzene with air. Although its appeal declined after the 1970s the benzene process is still operated, particularly where -butane is not available. The catalyst is a mixed oxide (70% V2O5 30% M0O3) deposited on a low surface area carrier to limit side reactions. Atom efficiency is inherently low, as implied by the stoichiometry of the oxidation in which two carbon atoms out of six are lost as CO2 (Equation B4). Molar yields however can be relatively high ca. 73%) and are generally higher than those in the -butane processes. 

The other commercialized pentane process is that of the Standard Oil Company (Indiana) (8,26). This process differs from the Standard (Indiana)—Texas butane process in that 0.5% benzene is added to inhibit disproportionation and the make-up aluminum chloride is added directly to the reactor as a slurry. 

Temperature, catalyst composition, space velocity, and hydrogen chloride concentration are generally similar to those in the corresponding butane process, but the reactor pressure is about 100 pounds lower. The detailed operating conditions are given in Table V. 

There have been notable shifts in raw materials for the manufacture of maleic anhydride and phenol. Made for many years by the oxidation of benzene, maleic anhydride now is made by a catalytic process from butane. The butane process was found to result in lower costs of operation as well as reduced environmental, safety, and health hazards. Another example is the manufacture of phenol, initially made from benzene or chlorobenzene. Subsequently, however, with large supplies of cumene from the catalytic reaction of benzene and propylene, production came to be dominated by cumene-derived phenol, which, requires a lower capital investment and offers reduced operating expenses as well as reduced environmental and safety problems. A novel... 

The modified process is based on the oxidation of butane (see Fig. 9.32). A major advantage of C4 over benzene is that no carbon is lost in the reaction. The yield from butane process is 30% greater than that from the benzene process. Also, C4 is much cheaper than benzene. Benzene is a known carcinogen. So, the fixed bed process with n-butane as the raw material has been the only MA route used commercially since 1985 in the United States. In the fixed bed process, a low concentration of butane is passed over the catalyst at 400 80°C and 0.3-0.4MPa. The process generates more water than the benzene process. Unsupported vanadium phosphorus oxide (VPO) catalysts with promoters such as lithium, zinc, and molybdenum are commonly used. 

In the second butane process, the Phillips process, dehydrogenation is carried out in two steps. In the first step, butane is passed over a catalyst containing aluminium, chromium and sodium oxides at about 600°C and atmospheric pressure n-butenes are isolated from the product gas. In the second step, the butenes are mixed with steam and passed over a catalyst containing ferric and... 

At the moment, selective oxidation of -butane to MA is the only catalytic oxidation process employing a light alkane as the feedstock which has been fully established at an industrial level. It must be indicated that surprisingly the results from the -butane process (MA yield around 80%, with selectivity of 60%) are better than those obtained from butenes. This fact has encouraged the scientific community to study similar catalytic reactions with other alkanes. Thus, other successful processes could be developed by using the appropriate catalyst, optimal reaction conditions, and an improved reactor technology. 

Replacement of the latter by -butane considerably reduces the number of byproducts, particularly in comparison to the heavy by-products obtained (i.e. phthahc anhydride and benzoquinone) from the benzene process. Moreover, the -butane process avoids the toxicity associated with the employment of benzene as the raw material (carcinogen) and becomes important in saving raw material costs (around 64%). It is also important to emphasize that the -butane process drastically decreases the formation of carbon oxides (atomic economy). Thus, whereas benzene has six carbon atoms, MA has four, and as a result, two CO2 molecules for each MA molecule are obtained. Accordingly, under optimal conditions, 100 kg of benzene generate 129 kg of maleic anhydride and 113 kg of CO2, whereas 100 kg of -butane generate 170 kg of maleic anhydride. 

Currently, the industrial single-step process from n-butane is carried out with an active phase based on vanadyl pyrophosphate, (VO)2P207, commonly named as a VPO catalyst. Yields to MA of around 60% obtained from alkane are lower than those from benzene (near 73%), but important cost savings on the final product (higher than 40%) are achieved through the n-butane process. ... 

On the other hand, yields to MA similar to those from -butane can be reached from processes using butenes, but the number of by-products obtained is also higher than from the -butane process. Indeed, the formation of small amounts of furan, acetaldehyde, crotonaldehyde, or methyl-vinyl-ketone are observed from n-butene, which makes the process more expensive due to the need for a purification step. During the selective oxidation of -butane (a cheaper raw material) these products are not formed, but the main by-products are CO and CO2. Indeed, both parallel and consecutive reactions of total combustion must be taken into account in the process from n-butane since they are mainly responsible for the limited yield to MA. In this way, -butane conversion lower than 75-80% has been reported to be adequate in order to avoid further oxidation of MA, an important factor in the decrease of the process selectivity. 

In spite of the potential advantages of a fluid bed, all benzene-based processes still rely heavily on the fixed-bed, tubular reactors.It is also believed to be the case with the Amoco butane process. The main reason for this overwhelming preference is the difficulty in producing catalysts with low attrition rates. 

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