Naphtha economics

Naphtha at one time was a more popular feed, and alkah-promoted catalysts were developed specifically for use with it. As of 1994 the price of naphtha in most Western countries is too high for a reformer feed, and natural gas represents the best economical feedstock. However, where natural gas is not available, propane, butane, or naphtha is preferentially selected over fuel oil or coal. 

Anhydrous stannous chloride, a water-soluble white soHd, is the most economical source of stannous tin and is especially important in redox and plating reactions. Preparation of the anhydrous salt may be by direct reaction of chlorine and molten tin, heating tin in hydrogen chloride gas, or reducing stannic chloride solution with tin metal, followed by dehydration. It is soluble in a number of organic solvents (g/100 g solvent at 23°C) acetone 42.7, ethyl alcohol 54.4, methyl isobutyl carbinol 10.45, isopropyl alcohol 9.61, methyl ethyl ketone 9.43 isoamyl acetate 3.76, diethyl ether 0.49, and mineral spirits 0.03 it is insoluble in petroleum naphtha and xylene (2). 

Table 6 shows the effect of varying coil oudet pressure and steam-to-oil ratio for a typical naphtha feed on the product distribution. Although in these tables, the severity is defined as maximum, in a reaUstic sense they are not maximum. It is theoretically possible that one can further increase the severity and thus increase the ethylene yield. Based on experience, however, increasing the severity above these practical values produces significantly more fuel oil and methane with a severe reduction in propylene yield. The mn length of the heater is also significantly reduced. Therefore, this is an arbitrary maximum, and if economic conditions justify, one can operate the commercial coils above the so-called maximum severity. However, after a certain severity level, the ethylene yield drops further, and it is not advisable to operate near or beyond this point because of extremely severe coking. 

Methanol dehydrogenation to ethylene and propylene. In some remote ioca-tions, transportation costs become very important. Moving ethane is almost out of the question. Hauling propane for feed or ethylene itself in pressurized or supercooled vessels is expensive. Moving naphtha or gas oil as feed requires that an expensive olefins plant with unwanted by-products be built. So what s a company to do if they need an olefins-based industry at a remote site One solution that has been commercialized is the dehydrogenation of methanol to ethylene and propylene. While it may seem like paddling upstream, the transportation costs to get the feeds to the remote sites plus the capital costs of the plant make the economics of ethylene and its derivatives okay. 

More toluene is formed than is needed in the catalytic reforming of naphtha. Benzene is always in tight supply. Table 8.7 shows the catalytic reformate production percentages of benzene, toluene, and xylene vs. the U.S. chemical demand. When the price is right it is economical to hydrodealkylate (add hydrogen, lose the methyl) toluene to benzene. This is best done on pure toluene, where the yield can be as high as 98.5%. The reaction can be promoted thermally or catalytically. As much as 30-50% of all benzene is made this way. 

The economics of thermal reforming and hydroforming of sweet and sour heavy straight-run naphthas have been compared recently by McLaurin, McIntosh, and Kaufman (15). They concluded that the relative economics of the two processes were virtually the same for both feed stocks. 

In view of these considerations, a large amount of effort is reported in the scientific press on the development of a process to produce benzene from n-hexane by combined cyclization and dehydrogenation. w-Hexane has a low Research octane number of only 24.8 and can be separated in fair purities from virgin naphthas by simple distillation. Recently, an announcement was made of a process in the laboratory stage for aromatiza-tion of n-hexane (16). The process utilizes a chromia-alumina catalyst at 900° F., atmospheric pressure, and a liquid space velocity of about one volume of liquid per volume of catalyst per hour. The liquid product contains about 36% benzene with 64% of hexane plus olefin. The catalyst was shown to be regenerable with a mixture of air and nitrogen. The tests were made on a unit of the fixed-bed type, but it was indicated that the fluid technique probably could be used. If commercial application of this or similar processes can be achieved economically, it could be of immense help in relieving the benzene short-age. 

Because of their ready availability, natural-gas liquids (mixtures of mainly ethane, propane, and butanes) are used in the manufacture of ethylene and propylene in the United States.140 141 In Europe and Japan the main feedstock is naphtha. Changing economic conditions have led to the development of processes using heavy oil for olefin production.138 142... 

Cracked Gas Drying. Ethylene and propylene are two of the most important petrochemical raw materials today. They are manufactured by a thermal cracking of ethane, propane, or naphtha. One of the important separation-purification steps in the production of ethylene and propylene is removal of water before low temperature separation. Although alumina has been the most commonly used desiccant in drying cracked gas in the past, 3A molecular sieve adsorbents have an overall economic advantage 32), and many cracked gas plants are using the 3A molecular sieves today. 

The U.S. ethylene industry has been based primarily on the cracking of ethane and propane derived from natural gas. The quantities and liquid contents of U.S. natural gases have been such as to permit substantial quantities of these light hydrocarbons to be recovered for use as economically attractive ethylene feedstocks. In Europe and Japan, however, naphthas have been generally the available and preferred feeds to pyrolysis. 

The light hydrocarbons produce only minor amounts of by-products, while naphtha and heavier feeds produce substantial quantities of propylene, butadiene, and aromatics. Thus, while in the United States these products are obtained generally from other routes at present, in Europe and Japan ethylene production serves as a major source of these chemicals. As discussed in greater detail later, by-product outlet considerations can play an important role in feedstock selection, and by-product realizations can have a major effect on the ethylene production economics. 

In the past, coal or heavy hydrocarbon feedstock ammonia plants were not economically competitive with plants where the feedstocks were light hydrocarbons (natural gas to naphtha). Because of changing economics, however, plants that can handle heavy hydrocarbon feedstock are now attracting increasing attention- In addition, the continuous development and improvement of partial oxidation processes at higher pressure have allowed reductions in equipment size and cost. Therefore, the alternate feedback ammonia plants based on a partial oxidation process may become economically competitive in the near future. 

Synthesis gas is prepared by the steam reforming or partial oxidation of a liquid or gaseous hydrocarbon feedstock, or by direct combination of carbon dioxide wilh purified hydrogcn-ricli gases. Economic considerations usually favor the steam-re form mg route for a naphtha or natural gas... 

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