Feedstock vaporization

One such catalytic system has been pilot planted by Toyo Engineering Company (7 ). It utilizes a combination catalyst and specially designed feedstock vaporization system to process hydrocarbons as heavy as crude oil to obtain reasonable conversions to hydrogen and carbon monoxide. Another process announced by Grand Paroise uses a fluidized bed of catalyst for the reforming step (8). Heat required is introduced into the fluidized catalyst by burning fuel inside of tubes immersed in the bed. Both of these systems have been extensively tested in large pilot installations and could be included in commerical installations in the near future if justified by economic considerations. 

The oil furnace process is the most common method of production today and is the source of over 95% of the total output of carbon black globally. In this process, a heavy aromatic fraction of petroleum distillate is atomized and sprayed into a furnace preheated to 1200-1900°C. The feedstock vaporizes and decomposes to form carbon black and combustion gases that are immediately cooled with a series of water sprays and heat exchangers to terminate the carbon black reaction and cool the carbon black product stream. The carbon black is separated from the combustion gases in bag filters and is conveyed for further densification either in pelletization processes or in agitator tanks (from which powdered, fluffy black is collected). 

As feedstock vaporizes and cracks during its sec-onds-long journey through the riser pipe, feedstock vapors are separated from the catalyst at cyclones at the top of the reactor and fed into a fractionator. There, different fractions condense and are extracted as separate products. The catalyst becomes inactive as coke builds on its surface. Spent catalyst is collected and fed into the regenerator, where coke deposits are burned off. The regenerated catalyst is recycled into the reactor at temperatures of 650 to 815 degrees Celsius. 

The first fractionating column was introduced in 1917. In the "still upon a still design, as the heated crude oil flowed into the column, a fraction of the feedstock vaporized and rose up through the upper stills. The heavier components flowed through the lower stills to the bottom of the column. 

A simple one-stage membrane system fitted with silicone rubber membranes that preferentially permeate the valuable feedstock vapor and reject the inert gas contaminants is shown in Figure 21.4. The permeate gas, enriched in the vapor components, is compressed and sent back to the reactor the residue gas, containing only the inert components, is purged. Feedstock losses can be essentially eliminated with such a design. 

Because of this parallel with liquid-vapor equilibrium, copolymers for which ri = l/r2 are said to be ideal. For those nonideal cases in which the copolymer and feedstock happen to have the same composition, the reaction is called an azeotropic polymerization. Just as in the case of azeotropic distillation, the composition of the reaction mixture does not change as copolymer is formed if the composition corresponds to the azeotrope. The proportion of the two monomers at this point is given by Eq. (7.19). 

The feedstocks used ia the production of petroleum resias are obtaiaed mainly from the low pressure vapor-phase cracking (steam cracking) and subsequent fractionation of petroleum distillates ranging from light naphthas to gas oil fractions, which typically boil ia the 20—450°C range (16). Obtaiaed from this process are feedstreams composed of atiphatic, aromatic, and cycloatiphatic olefins and diolefins, which are subsequently polymerized to yield resias of various compositioas and physical properties. Typically, feedstocks are divided iato atiphatic, cycloatiphatic, and aromatic streams. Table 2 illustrates the predominant olefinic hydrocarbons obtained from steam cracking processes for petroleum resia synthesis (18). 

Process Technology Evolution. Maleic anhydride was first commercially produced in the early 1930s by the vapor-phase oxidation of benzene [71-43-2]. The use of benzene as a feedstock for the production of maleic anhydride was dominant in the world market well into the 1980s. Several processes have been used for the production of maleic anhydride from benzene with the most common one from Scientific Design. Small amounts of maleic acid are produced as a by-product in production of phthaHc anhydride [85-44-9]. This can be converted to either maleic anhydride or fumaric acid. Benzene, although easily oxidized to maleic anhydride with high selectivity, is an inherently inefficient feedstock since two excess carbon atoms are present in the raw material. Various compounds have been evaluated as raw material substitutes for benzene in production of maleic anhydride. Fixed- and fluid-bed processes for production of maleic anhydride from the butenes present in mixed streams have been practiced commercially. None of these... 

Ethjlben ne Synthesis. The synthesis of ethylbenzene for styrene production is another process in which ZSM-5 catalysts are employed. Although some ethylbenzene is obtained direcdy from petroleum, about 90% is synthetic. In earlier processes, benzene was alkylated with high purity ethylene in liquid-phase slurry reactors with promoted AlCl catalysts or the vapor-phase reaction of benzene with a dilute ethylene-containing feedstock with a BF catalyst supported on alumina. Both of these catalysts are corrosive and their handling presents problems. 

Oxidation. Naphthalene may be oxidized direcdy to 1-naphthalenol (1-naphthol [90-15-3]) and 1,4-naphthoquinone, but yields are not good. Further oxidation beyond 1,4-naphthoquinone [130-15-4] results in the formation of ortho- h. h5 ic acid [88-99-3], which can be dehydrated to form phthaUc anhydride [85-44-9]. The vapor-phase reaction of naphthalene over a catalyst based on vanadium pentoxide is the commercial route used throughout the world. In the United States, the one phthaUc anhydride plant currently operating on naphthalene feedstock utilizes a fixed catalyst bed. The fiuid-bed process plants have all been shut down, and the preferred route used in the world is the fixed-bed process. 

The naphthalene is vaporized, mixed with air, and fed to the top of the reactor. This process also allows for mixtures of ortho- s.yXen.e [95-47-6] to be mixed with the naphthalene and air, which permits the use of dual feedstocks. Both feedstocks are oxidized to phthaUc anhydride. The typical range of reactor temperature is 340—380°C. The reactor temperatures are controlled by an external molten salt. 

The vapor-phase process of SocifitH Chemique de la Grande Paroisse for production of nitroparaffins employs propane, nitrogen dioxide, and air as feedstocks (34). The yields of nitroparaffins based on both propane and nitrogen dioxide are relatively high. Nitric oxide produced during nitration is oxidized to nitrogen dioxide, which is adsorbed in nitric acid. Next, the nitric dioxide is stripped from the acid and recirculated. 

Thermal polymerization is not as effective as catalytic polymerization but has the advantage that it can be used to polymerize saturated materials that caimot be induced to react by catalysts. The process consists of the vapor-phase cracking of, for example, propane and butane, followed by prolonged periods at high temperature (510—595°C) for the reactions to proceed to near completion. Olefins can also be conveniendy polymerized by means of an acid catalyst. Thus, the treated olefin-rich feed stream is contacted with a catalyst, such as sulfuric acid, copper pyrophosphate, or phosphoric acid, at 150—220°C and 1035—8275 kPa (150—1200 psi), depending on feedstock and product requirement. 

Manufacture and Processing. Until World War II, phthaUc acid and, later, phthaUc anhydride, were manufactured primarily by Hquid-phase oxidation of suitable feedstocks. The favored method was BASF s oxidation of naphthalene [91-20-3] by sulfuric acid ia the presence of mercury salts to form the anhydride. This process was patented ia 1896. During World War I, a process to make phthaUc anhydride by the oxidation of naphthalene ia the vapor phase over a vanadium and molybdenum oxide catalyst was developed ia the United States (5). Essentially the same process was developed iadependendy ia Germany, with U.S. patents being granted ia 1930 and 1934 (6,7). 

The Tatoray process, which was developed by Toray Industries, Inc., and is available for Hcense through UOP, can be appHed to the production of xylenes and benzene from feedstock that consists typically of toluene [108-88-3] either alone or blended with aromatics (particularly trimethylbenzenes and ethyl-toluenes). The main reactions are transalkylation (or disproportionation) of toluene to xylene and benzene or of toluene and trimethylbenzenes to xylenes in the vapor phase over a highly selective fixed-bed catalyst in a hydrogen atmosphere at 350—500°C and 1—5 MPa (10—50 atm). Ethyl groups are... 

Synthesis Gas Preparation Processes. Synthesis gas for ammonia production consists of hydrogen and nitrogen in about a three to one mole ratio, residual methane, argon introduced with the process air, and traces of carbon oxides. There are several processes available for synthesis gas generation and each is characterized by the specific feedstock used. A typical synthesis gas composition by volume is hydrogen, 73.65% nitrogen, 24.55% methane, <1 ppm-0.8% argon, 100 ppm—0.34% carbon oxides, 2—10 ppm and water vapor, 0.1 ppm. 

The Rectisol process is more readily appHcable for acid gas removal from synthesis gas made by partial oxidation of heavy feedstocks. The solvents used in Purisol, Fluor Solvent, and Selexol processes have low vapor pressures and hence solution losses are minimal. Absorption systems are generally corrosion-free. 

Conrad Industries, Inc. (CentraUa, Washington) and Clean Air Products Company (Pordand, Oregon) have jointiy built a tire pyrolysis demonstration machine which allows recovery of combustible gases, oils, and other by-products. The equipment can also handle other carbonaceous material. It is designed to process 0.9 t/h of tires the entire system is estimated to cost about 2.3 x 10 . The feedstock consists of 5-cm tires chips which produce pyrolytic filler, a vapor gas yielding 11.5 kj/m (1000 Btu/ft ), and medium and light oils yielding about 42 MJ/kg (18,000 Btu/lb) (32). 

Process Description. Reactors used in the vapor-phase synthesis of thiophene and aLkylthiophenes are all multitubular, fixed-bed catalytic reactors operating at atmospheric pressure, or up to 10 kPa and with hot-air circulation on the shell, or salt bath heating, maintaining reaction temperatures in the range of 400—500°C. The feedstocks, in the appropriate molar ratio, are vaporized and passed through the catalyst bed. Condensation gives the cmde product mixture noncondensable vapors are vented to the incinerator. 

Carbon Blacks. Carbon blacks are occasionally used as components in mixes to make various types of carbon products. Carbon blacks are generally prepared by deposition from the vapor phase using petroleum distillate or gaseous hydrocarbon feedstocks (see Carbon, carbon black). 

The hydrocarbon gas feedstock and Hquid sulfur are separately preheated in an externally fired tubular heater. When the gas reaches 480—650°C, it joins the vaporized sulfur. A special venturi nozzle can be used for mixing the two streams (81). The mixed stream flows through a radiantly-heated pipe cod, where some reaction takes place, before entering an adiabatic catalytic reactor. In the adiabatic reactor, the reaction goes to over 90% completion at a temperature of 580—635°C and a pressure of approximately 250—500 kPa (2.5—5.0 atm). Heater tubes are constmcted from high alloy stainless steel and reportedly must be replaced every 2—3 years (79,82—84). Furnaces are generally fired with natural gas or refinery gas, and heat transfer to the tube coil occurs primarily by radiation with no direct contact of the flames on the tubes. Design of the furnace is critical to achieve uniform heat around the tubes to avoid rapid corrosion at "hot spots."... 

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