Hydrocarbon unconverted

Although the selectivity of isopropyl alcohol to acetone via vapor-phase dehydrogenation is high, there are a number of by-products that must be removed from the acetone. The hot reactor effluent contains acetone, unconverted isopropyl alcohol, and hydrogen, and may also contain propylene, polypropylene, mesityl oxide, diisopropyl ether, acetaldehyde, propionaldehyde, and many other hydrocarbons and carbon oxides (25,28). 

Secondary alcohols (C q—for surfactant iatermediates are produced by hydrolysis of secondary alkyl borate or boroxiae esters formed when paraffin hydrocarbons are air-oxidized ia the presence of boric acid [10043-35-3] (19,20). Union Carbide Corporation operated a plant ia the United States from 1964 until 1977. A plant built by Nippon Shokubai (Japan Catalytic Chemical) ia 1972 ia Kawasaki, Japan was expanded to 30,000 t/yr capacity ia 1980 (20). The process has been operated iadustriaHy ia the USSR siace 1959 (21). Also, predominantiy primary alcohols are produced ia large volumes ia the USSR by reduction of fatty acids, or their methyl esters, from permanganate-catalyzed air oxidation of paraffin hydrocarbons (22). The paraffin oxidation is carried out ia the temperature range 150—180°C at a paraffin conversion generally below 20% to a mixture of trialkyl borate, (RO)2B, and trialkyl boroxiae, (ROBO). Unconverted paraffin is separated from the product mixture by flash distillation. After hydrolysis of residual borate esters, the boric acid is recovered for recycle and the alcohols are purified by washing and distillation (19,20). 

By-products from EDC pyrolysis typically include acetjiene, ethylene, methyl chloride, ethyl chloride, 1,3-butadiene, vinylacetylene, benzene, chloroprene, vinyUdene chloride, 1,1-dichloroethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane [71-55-6] and other chlorinated hydrocarbons (78). Most of these impurities remain with the unconverted EDC, and are subsequendy removed in EDC purification as light and heavy ends. The lightest compounds, ethylene and acetylene, are taken off with the HCl and end up in the oxychlorination reactor feed. The acetylene can be selectively hydrogenated to ethylene. The compounds that have boiling points near that of vinyl chloride, ie, methyl chloride and 1,3-butadiene, will codistiU with the vinyl chloride product. Chlorine or carbon tetrachloride addition to the pyrolysis reactor feed has been used to suppress methyl chloride formation, whereas 1,3-butadiene, which interferes with PVC polymerization, can be removed by treatment with chlorine or HCl, or by selective hydrogenation. 

The solvent is then evaporated, and the unconverted sterol is recovered by precipitation from an appropriate solvent, eg, alcohol. The recovered sterol is reused in subsequent irradiations. The solvent is then evaporated to yield vitamin D resin. The resin is a pale yeUow-to-amber oil that flows freely when hot and becomes a brittie glass when cold the activity of commercial resin is 20 30 x 10 lU/g. The resin is formulated without further purification for use in animal feeds. Vitamin D can be crystallized to give the USP product from a mixture of hydrocarbon solvent and ahphatic nitrile, eg, benzene and acetonitrile, or from methyl formate (100,101). Chemical complexation has also been used for purification. 

Several other changes that are supposed to slow down the reaction can cause runaway. In the case of ethylene oxidation, chlorinated hydrocarbons are used as inhibitors. These slow down both the total and the epoxidation, although the latter somewhat less. When the reaction is running too high and the inhibitor feed is suddenly increased in an attempt to control it, a runaway may occur. The reason is similar to that for the feed temperature cut situation. Here the inhibitor that is in the ppm region reacts with the front of the catalytic bed and slowly moves down stream. The unconverted reactants reach the hotter zone before the increased inhibitor concentration does. 

The reaction takes place at low temperature (40-60 °C), without any solvent, in two (or more, up to four) well-mixed reactors in series. The pressure is sufficient to maintain the reactants in the liquid phase (no gas phase). Mixing and heat removal are ensured by an external circulation loop. The two components of the catalytic system are injected separately into this reaction loop with precise flow control. The residence time could be between 5 and 10 hours. At the output of the reaction section, the effluent containing the catalyst is chemically neutralized and the catalyst residue is separated from the products by aqueous washing. The catalyst components are not recycled. Unconverted olefin and inert hydrocarbons are separated from the octenes by distillation columns. The catalytic system is sensitive to impurities that can coordinate strongly to the nickel metal center or can react with the alkylaluminium derivative (polyunsaturated hydrocarbons and polar compounds such as water). 

Another process for silicon carbide fibers, developed by Verbeek and Winter of Bayer AG [45], also is based on polymeric precursors which contain [SiCH2] units, although linear polysilmethylenes are not involved. The pyrolysis of tetramethylsilane at 700°C, with provision for recycling of unconverted (CHg Si and lower boiling products, gave a polycarbosilane resin, yellow to red-brown in color, which was soluble in aromatic and in chlorinated hydrocarbons. Such resins could be melt-spun but required a cure-step to render them infusible before they were pyrolyzed to ceramic... 

The unconverted reactants and the reaction products leaving the reactor were sent first to a hot vessel heated at 110°C for the collection of the waxes, followed by a second cold vessel cooled at 0°C for the separation of liquid aqueous and organic products. All the transfer lines between the reactor and the hot trap were kept at 150°C to prevent the solidification of the waxes and the condensation of gasoline and diesel range hydrocarbon products outside of the proper traps. 

The process of oxidation recommended by the inventor of the above-described apparatus, for the removal of unaltered phosphorus from tbe amorphous modification, is very unsatisfactory. A far better method, and one more quickly and more easily executed, is the application of an appropriate solvent, as bisulphide of carbon, oil of turpentine, or some other liquid hydrocarbon, by which the whole of the adhering unconverted phosphorus is readily and completely removed. This means of purification is also advantageous, inasmuch as the whole of the unaltered phosphorus obtained in. solution may be recovered by simple distillation of the solvent, whilo in the process of oxidation the phosphorus, being converted into phosphorous and phosphoric Acids, is lost, the acids being dissolved and removed by the subsequent washing. 

Gasification by low-temperature steam-reforming reactions, the heart of die MRG process, is carried out between liquid hydrocarbons and steam over catalyst to fonn methane, hydrogen, and carbon oxides. In order to increase the calonfic value of product gas to the values similar to natural gas, methanation reactions are required. Hydrogen in product gas is reacted with C02 and CO to form methane, with only a small portion unconverted. Methanation reactions are ... 

Figure 9.5 illustrates a simplified scheme of the Mitsubishi process. The process includes the recycle of unconverted propane, and the BOC-PSA technology for rejection of N2 the latter is present in the feed, which contains oxygen-enriched air, and is also generated in the reactor by ammonia combustion. The unconverted hydrocarbon is recovered and recycled to the reactor [23fig], One Mitsubishi patent claims the differentiation of ammonia along the catalytic bed [23d], This might... 

Complete Methanol Conversion - The major products of the MTG conversion are hydrocarbons and water. Consequently, any unconverted methanol will dissolve into the water phase and be lost unless a distillation step to process the very dilute water phase is added to the process. Thus, essentially complete conversion of methanol is highly preferred. 

H-Coal hydroclone underflow was supplied by Hydrocarbon Research, Inc. It contained 9.09% ash and required filtration. Because of the relatively high viscosity of the stock, filtration was difficult, and only a limited amount of hydrotreater feed was prepared. Inspections are given in Table V. Thermal and atmospheric exposure during filtration downgraded the stock. The benzene and heptane insolubles in the product were substantially higher than those in the feed, when corrected to an ash plus unconverted coal free basis. The filtrate still contained 0.12% ash. 

MTBE separation in practice, this section has only one distillation column, operating under pressure so as to use a water-cooled condenser. It separates MTBE at the bottom, and methanol and unconverted C4. at the top. This is because the azeotropes formed by these hydrocarbons with alcohol have boil ing points lower than that of the azeotrope formed by methanol and ether. The latter has a boiling point of 51.6 C at 0.1 10 Pa. Its weight composition for each of its components is 14 and 86 per cent (30 to 70 at 0.8.10 Pa). Raffinate treatment this section comprises two-step water scnibltiag of the raffinate to remove the methanol, followed by fractionation of the water/methanol mixture. The alcohol recovered is recycled to the reactor. 

To provide an illustration, the flow sheet of the IFP process shown in Fig. 3.12 comprises two possible variants. The simpler corresponds to the direct use of the etherified solution in the gasoline pool, without separating e excess methanol contained. Operations are conducted with two reactors in series the first with an upflow stream and expanded bed with recycle of part of the previously cooled effluent for better control of the temperature rise, and the second with a downflow stream and a fixed bed. The more complex involves the recovery of excess methanol, first by azeotropic distillation in a depentanizer with part of the unconverted hydrocarbons, and then by water washing of this raffinate. The hydrocarbon phase is added to the bottom of the depentanizer. The water/methanol mixture is distilled to recover and recycle the alcohol to the etherification staee. 

The separator produces a water phase, a hydrocarbon liquid phase (which can be regarded as a synthetic crude oil) and a recycle gas. Part of the synthesis gas is purged to stop the build up of inert materials such as nitrogen. The recycle gas contains light hydrocarbon gases, unconverted synthesis gas and carbon dioxide produced in the process. This is sent to a gas treatment plant for recovery of synthesis gas. This operation may be integrated into the gas clean-up operation of the fresh synthesis gas from the gasifier. 

Early attempts to convert methanol into olefins were based on the zeolite ZSM-5. The Mobil MTO process was based on the fluidised bed version of the MTG technology. Conversion took place at about 500°C allegedly producing almost complete methanol conversion. However, careful reading of the patent Uterature indicates that complete methanol conversion may not have been achieved by this means. Because of incomplete conversion, there would be a necessity to strip methanol and dimethyl ether from water and hydrocarbon products in order to recycle unconverted methanol. In this variant, the total olefin yield is less than 20% of the products of which ethylene is a minor but not insignificant product. The major product is gasoUne. Ethylene is difficult to process and has to be treated specially. Claims that it is possible that ethylene can be recycled to extinction conflict with the known behaviour of ethylene in zeolite catalyst systems and have to be viewed with some suspicion. 

Figure 4. FIMS spectra of the unconverted material after hydrocracking treated VGO over (a) all-amorphous, and (b) all-zeolitic catalysts (two-stage operation), Z indicates the hydrocarbon stoichiometry, C H2w+z, (poly)naphthenes occur for Z < 0, and aromatics are possible at Z < —4 (Reproduced with permission from reference 35. Copyright 1994 T. Huizinga.)...

---