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  Method and reactor system for converting oxygenate contaminants in an mto reactor system product effluent to hydrocarbonsUSPTO Application #: 20060135828Title: Method and reactor system for converting oxygenate contaminants in an mto reactor system product effluent to hydrocarbons Abstract: Disclosed is a method and reactor system for converting oxygenate and/or olefin contaminants in a methanol to olefin reactor system product effluent to hydrocarbons, including paraffin compounds, preferably over a sulphided catalyst of the type Nickel or Cobalt combined with Molybdenum or Tungsten. In one embodiment, the oxygenate-containing stream to be hydrogenated comprises one or more of the following streams, alone or in combination: a quench tower bottoms stream, a water absorption unit bottoms stream, a C4+ stream, and/or a C5+ stream. (end of abstract) Agent: Exxonmobil Chemical Company - Baytown, TX, US Inventor: John Richard Shutt USPTO Applicaton #: 20060135828 - Class: 585250000 (USPTO) Related Patent Categories: Chemistry Of Hydrocarbon Compounds, Adding Hydrogen To Unsaturated Bond Of Hydrocarbon, I.e., Hydrogenation The Patent Description & Claims data below is from USPTO Patent Application 20060135828. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention is to an apparatus and reactor system for converting oxygenate contaminants in a methanol to olefin reactor system product effluent to hydrocarbons. More particularly, the invention is to converting oxygenate contaminants in a C.sub.4+ or C.sub.5+ fraction, a quench tower bottoms, and/or a water absorption unit bottoms to paraffin hydrocarbons preferably over a sulphided catalyst of the type Nickel or Cobalt combined with Molybdenum or Tungsten. BACKGROUND [0002] Olefins have been traditionally produced from petroleum feedstock by catalytic or steam cracking processes. These cracking processes, especially steam cracking, produce light olefin(s) such as ethylene and/or propylene from a variety of hydrocarbon feedstock. Ethylene and propylene are important commodity petrochemicals useful in a variety of processes for making plastics and other chemical compounds. Ethylene is used to make various polyethylene plastics, and in making other chemicals such as vinyl chloride, ethylene oxide, ethylbenzene and alcohol. Propylene is used to make various polypropylene plastics, and in making other chemicals such as acrylonitrile and propylene oxide. [0003] The petrochemical industry has known for some time that oxygenates, especially alcohols, are convertible into light olefin(s). There are numerous technologies available for producing oxygenates including fermentation or reaction of synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials including coal, recycled plastics, municipal waste or any other organic material. Generally, the production of synthesis gas involves a combustion reaction of natural gas, mostly methane, and an oxygen source into hydrogen, carbon monoxide and/or carbon dioxide. Syngas production processes are well known, and include conventional steam reforming, autothermal reforming, or a combination thereof. [0004] Methanol, the preferred alcohol for light olefin production, is typically synthesized from the catalytic reaction of hydrogen, carbon monoxide and/or carbon dioxide in a methanol reactor in the presence of a heterogeneous catalyst. For example, in one synthesis process methanol is produced using a copper/zinc oxide catalyst in a water-cooled tubular methanol reactor. The preferred methanol conversion process is generally referred to as a methanol-to-olefin(s) (MTO) process, where methanol is converted to primarily ethylene and/or propylene in the presence of a molecular sieve catalyst. [0005] Undesirable C.sub.4+ or C.sub.5+ olefins (heavy olefins) can be formed as byproducts of the MTO process. U.S. Pat. No. 5,714,662 to Vora et al. provides a practical use for a C.sub.3 and C.sub.4 olefin stream separated from an MTO product effluent and for water byproduct formed in the MTO process. More specifically, the Vora et al. patent is directed to a process for producing light olefins from crude methanol. The patent discloses that propylene and butylene fractions from the MTO product effluent can be converted to high octane ether and other high value products. Optionally, butylene from the MTO process can be dimerized and hydrogenated to produce a C.sub.8 alkylate having a high octane for use in blending motor gasoline. [0006] Undesirable oxygenate compounds such as alcohols, aldehydes, ketones, esters, acids and ethers in the C.sub.1 to C.sub.6 range as well as trace quantities of aromatic compounds can also be formed in MTO reactors or in effluent processing. Additionally, a small amount of oxygenate from the feedstock, e.g., methanol or dimethyl ether ("DME"), can pass through the MTO reactor with the product effluent without being converted to desired product. As a result of oxygenate synthesis and/or oxygenate "pass through" in an MTO reactor system, the effluent from an MTO reactor can contain undesirably high concentrations of oxygenate compounds. [0007] Oxygenate and heavy olefin compounds contained in an MTO product effluent can be undesirable for several reasons. For example, in order for an olefin-containing effluent to be suitable for polymerization the effluent should contain, at most, a relatively small amount of oxygenates. Thus, oxygenate separation from the desired light olefins can be required in order to provide an olefin product stream of a sufficient purity for polymerization. Increased investment is required to separate and recover the oxygenates from the desired light olefins. [0008] Additionally, although the relative concentrations of oxygenates and heavy olefins in the product effluent are generally quite low, the total amount of oxygenates and heavy olefins in the effluent on an industrial scale can be enormous. A need exists for providing a use for the oxygenate and heavy olefin compounds which have been separated from the product effluent. That is, it is desirable to provide a practical use for the recovered oxygenate and heavy olefin contaminants so that commercial value can be realized from the oxygenate and heavy olefin contaminants separated from the product effluent. SUMMARY OF THE INVENTION [0009] The present invention provides a practical use for oxygenate and olefin contaminants in a methanol-to-olefin (MTO) reactor system product effluent. As used herein, "oxygenate" means one or more oxygenated hydrocarbons having at least one oxygen atom and at least one carbon atom. The invention is directed to a method and reactor system for converting oxygenate and/or olefin contaminants in a methanol to olefin reactor system product effluent to hydrocarbons, including mostly paraffins, preferably over a sulphided catalyst of the type Nickel or Cobalt combined with Molybdenum or Tungsten. In one embodiment, the oxygenate-containing stream to be hydrogenated comprises one or more of the following streams, alone or in combination: a quench tower bottoms stream, a water absorption unit bottoms stream, a C.sub.4+ stream, and/or a C.sub.5+ stream. The resulting C.sub.4+ and/or C.sub.5+ paraffin compounds can be used in blending motor gasoline, or as a solvent, or as steam cracking feed. Preferably, the oxygenates are concentrated or in admix with a C.sub.4+ and/or a C.sub.5+ hydrocarbons derived as co-products from an MTO conversion process. [0010] One embodiment of the invention is a method for hydrogenating oxygenate compounds including providing an effluent stream from an oxygenate to olefin reactor system. The effluent stream comprises one or more oxygenates, at least a portion of which are hydrogenated. Optionally, the hydrogenation includes contacting the oxygenates with hydrogen and a catalyst under conditions effective to convert at least a portion of the oxygenates to paraffins. [0011] Another embodiment is directed to a reactor system for converting oxygenate contaminants in an MTO product effluent to paraffins. The reactor system includes a reactor which converts an oxygenate-containing feedstock to an olefin-containing effluent, and a separation system in fluid communication with the reactor. The separation system separates light olefins in the olefin-containing effluent from oxygenate contaminants in the olefin-containing effluent. Optionally, the separation system includes a quench tower, a water absorption unit and/or a distillation unit, each of which forms a overhead stream comprising at least a portion of the light olefins, and a bottoms stream comprising at least a portion of the oxygenate contaminants. The reactor system also includes a hydrogenation unit which receives the oxygenate contaminants from the separation system and converts the oxygenate contaminants to paraffins. [0012] Another embodiment of the present invention is a method for hydrogenating oxygenates, including contacting in a hydrogenation unit an oxygenate in an oxygenate-containing MTO reactor effluent with hydrogen and a hydrogenation catalyst under conditions effective to convert the oxygenate to one or more paraffin compounds. [0013] Optionally, the oxygenate-containing MTO reactor effluent of the inventive method or reactor system includes C.sub.4+ and/or C.sub.5+ olefin. The C.sub.4+ or C.sub.5+ olefin contacts hydrogen and the hydrogenation catalyst in the hydrogenation unit under conditions effective to convert the C.sub.4+ or C.sub.5+ olefin to one or more paraffin compounds. BRIEF DESCRIPTION OF THE FIGURES [0014] Various embodiments of the overall invention are shown by way of example in the attached Figures, wherein: [0015] FIG. 1 is a flow diagram showing a process for reacting methanol to form an olefin, with the olefin being separated into a first fraction containing ethylene and propylene and a second fraction containing dimethyl ether and C.sub.4+ hydrocarbon components; and [0016] FIG. 2 is a flow diagram showing a process for removing water from an oxygenate-containing stream and separating the light oxygenates from the heavy oxygenates, and hydrogenating the heavy oxygenates to form hydrocarbons. DETAILED DESCRIPTION [0017] The present invention provides a practical use for oxygenate contaminants and/or heavy olefin contaminants in a product effluent. Specifically, the invention is a new method and reactor system for converting C.sub.4+ or C.sub.5+ oxygenate contaminants and/or C.sub.4+ or C.sub.5+ olefins (heavy olefins) separated from a product effluent to commercially useful hydrocarbons, e.g., paraffins. The invention is particularly well-suited for implementation in an oxygenate-to-olefin (OTO) reactor system such as an methanol-to-olefin (MTO) reactor system. Heavier oxygenates and/or heavy olefins preferably are separated from the product effluent through a bottoms stream of a quench tower. Additionally or alternatively, at least a portion of the lighter oxygenates and/or heavy olefins in the overhead stream of the quench tower are removed from the product effluent through a water absorption unit bottoms stream and/or by a separation unit, e.g., distillation unit, which optionally is downstream of the quench tower and the water absorption unit. The oxygenates and/or heavy olefins from the bottoms stream of the quench tower and/or from the water absorption unit and/or from the separation unit, e.g., distillation unit, preferably are directed, alone or in combination, to one or more hydrogenation units wherein the oxygenates and/or heavy olefins are hydrogenated over a catalyst, preferably a sulphided catalyst of the type Nickel or Cobalt combined with Molybdenum or Tungsten. Through hydrogenation, at least a portion of the oxygenates and/or heavy olefins are converted to hydrocarbons such as paraffins, which can be used in a variety of commercially viable applications. For example, the C.sub.5+ paraffins can be used in blending motor fuels or as solvents or as steam cracking feed. C.sub.4 and lower paraffins can be used as steam cracker feed or fuel, e.g., as LPG. [0018] The product effluent from an MTO reactor contains many oxygenates. For example, an MTO product effluent can include one or more of the following oxygenates: Dimethyl Ether (DME), Methyl Ethyl Ether, Methyl Isopropyl Ether, Acetaldehyde, Methyl Sec-Butyl Ether, n-Propanal, 2-Propenal, 2-Methyl-2-Propenal, iso-Butanal, Butanal, Acetic Acid, Methyl Ester, Methanol, Acetone, 2-Methyl Butanal, Propanoic Acid, Methyl Ester, 3-Buten-2-one, Ethanol, 2-Butanone, iso-Propanol, 3-Methyl-3-Buten-2-one, Pentanal, 2-Methyl Pentanal, 3-Methyl Pentanal, 3-Methyl-2-Butanone, 3-Pentanone, 2-Methyl-1-Penten-3-one, 2-Pentanone, 2-Methyl-3-Pentanone, 3-Methyl-2-Pentanone, 4-Methyl-2-Pentanone, Formic Acid, Acetic Acid, Propanoic Acid, and Butyric Acid. [0019] Additionally, an MTO product effluent can include one or more olefins. For example, an MTO product effluent can include one or more of the following olefins: acetylene, ethylene, propylene, 1-butene, 2-butene, isobutene, butadiene, C.sub.5 olefins, C.sub.5 diolefins, C.sub.6 olefins, and C.sub.7+ olefins. In accordance with the present invention, one or more of these oxygenates and/or olefins are converted in a hydrogenation unit to one or more paraffin compounds. Preferably, the catalyst used in the hydrogenation unit is a sulfided catalyst, however, any hydrogenation catalyst could be implemented in accordance with the present invention. Continue reading... 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