Olefins are traditionally produced from petroleum feedstocks 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 feedstocks. Ethylene and propylene are important commodity petrochemicals useful in a variety of processes for making plastics and other chemical compounds.
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 or 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. Other known syngas production processes include conventional steam reforming, autothermal reforming, or a combination thereof.
An alternate feed for the production of light olefins includes oxygenates, such as, for example, alcohols, particularly methanol and ethanol, dimethyl ether (DME), methyl ethyl ether, diethyl ether, dimethyl carbonate, and methyl formate. This conversion process is typically referred to as an oxygenate to olefins (OTO) reaction process. Many of these oxygenates may be produced by fermentation, or from synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials, including coal, recycled plastics, municipal wastes, or any organic material. Because of the wide variety of sources, alcohol, alcohol derivatives, and other oxygenates have promise as an economical, non-petroleum source for light olefin production.
When methanol is the oxygenate, the conversion process is typically referred to as a methanol to olefins (MTO) reaction process. Methanol 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 process for converting a feedstock containing methanol into one or more olefin(s), primarily ethylene and/or propylene, involves contacting the feedstock with a catalyst composition.
The catalysts used to promote the conversion of oxygenates to olefins are molecular sieve catalysts. Because ethylene and propylene are the most sought after products of such a reaction, research has focused on what catalysts are most selective to ethylene and/or propylene, and on methods for increasing the life and selectivity of the catalysts to ethylene and/or propylene.
Catalytic processes utilizing fluidized bed technology for conversion of hydrocarbon or oxygenates involving gas-solids contacting are widely used in industry for productions of petroleum-based fuels, chemical feed stocks and other industrial materials. The gaseous reactants are contacted with solid catalyst particles to provide gaseous products. Such processes often use continuous catalytic reactor unit operations, requiring catalyst regeneration at high temperature. FCC, OTO and other processes usually employ oxidative regeneration to remove coke or other carbonaceous deposits from spent or equilibrium catalysts. These operations often utilize combustion air to bum carbonaceous matter deposited on the catalyst during the conversion reactions. Ordinarily, this regeneration is carried out in a regeneration vessel separate from the main fluidized bed reactor. Attrition of the catalyst particles can occur during circulation of the catalyst into smaller particles of, less than about 100 microns, say, less than about 60 microns, in overall diameter, i.e., the largest particle dimension.
The waste flue gas or high temperature effluent from catalyst regeneration can be treated to remove entrained particles, such as catalyst fines carried from the process. Such removal is desirable inasmuch as these particles can cause erosion and plugging problems for downstream equipment, e.g., compressors, pumps, valves, exchangers and piping. Ultimately, the particles may be vented with gases to ambient atmosphere for disposal, e.g., through a cyclone used to separate solids from gases. Thus-disposed waste gases can have recoverable thermal value or environmentally objectionable properties resulting from particulate content, which renders such gases susceptible to further treatment. Accordingly, it would be desirable to provide a process, which ultimately recovers thermal value to the process from such high temperature effluent from catalyst regeneration.
U.S. Pat. No. 2,391,327 to Mekler teaches catalyst regeneration wherein flue gases from a regeneration zone are directed to a heat exchange unit such as a waste-heat boiler, steam superheater, hot gas turbine or the like.
U.S. Pat. No. 3,910,768 to Woebcke et al. relates to a high pressure cracking furnace whose flue gas is used to produce high pressure steam, cool cracked gas, preheat feed and drive a turbine.
U.S. Pat. No. 4,556,479 to Mauleon et al. and U.S. Pat. No. 5,002,915 to Harandi et al. disclose indirect cooling of catalyst regenerator flue gas with steam generation.
U.S. Pat. No. 4,956,509 to Harandi et al. discloses catalytic cracking of hydrocarbons wherein hot flue gas from a catalyst regenerator flows through a heat exchanger and is reduced from 650° to 510° C. (1200° to 950° F.) and is thence passed to a downstream heat recovery system, which may include steam generation, and reduced to 190° C. (375° F.) before release to the atmosphere.
U.S. Pat. No. 5,043,517 to Haddad et al. discloses two-stage heating of boiler feed water with hot reactor effluent.
U.S. Pat. No. 6,121,504 to Kuechler et al. discloses a process for converting oxygenates to olefins with direct product quenching for heat recovery and to improve heat integration.
All of the above references are incorporated herein by reference in their entirety.