PATENT
United States Patent Application 20120059206
Inventors:
Butler, James R. (Spicewood, TX, US)
Pelati, Joseph E. (Houston, TX, US)
Application Number: 13/290211
Publication Date: 03/08/2012
Assignee: FINA TECHNOLOGY, INC. (Houston, TX, US)
Abstract:
1. Field of the Invention
This invention relates generally to a process for the production of ethylbenzene and styrene.
2. Description of the Related Art
Styrene is an important monomer used in the manufacture of many of todays plastics. Styrene is commonly produced by making ethylbenzene, which is then dehydrogenated to produce styrene. Ethylbenzene is typically formed by one or more aromatic conversion processes involving the alkylation of benzene.
Aromatic conversion processes, which are typically carried out utilizing a molecular sieve type catalyst, are well known in the chemical processing industry. Such aromatic conversion processes include the alkylation of aromatic compounds such as benzene with ethylene to produce alkyl aromatics such as ethylbenzene. Typically an alkylation reactor, which can produce a mixture of monoalkyl and polyalkyl benzenes, will be coupled with a transalkylation reactor for the conversion of polyalkyl benzenes to monoalkyl benzenes. The transalkylation process is operated under conditions to cause disproportionation of the polyalkylated aromatic fraction, which can produce a product having an enhanced ethylbenzene content and a reduced polyalkylated content. When both alkylation and transalkylation processes are used, two separate reactors, each with its own catalyst, can be employed for each of the processes. The alkylation and transalkylation conversion processes can be carried out in the liquid phase, in the vapor phase, or under conditions in which both liquid and vapor phases are present, and combinations thereof.
In the formation of ethylbenzene from alkylation reactions of ethylene and benzene, impurities and undesirable side products may be formed in addition to the desired ethylbenzene. These undesirable products can include such compounds as xylene, cumene, n-propylbenzene and butylbenzene, as well as polyethylbenzenes, and high boiling point alkyl aromatic components, sometimes referred to as “heavies,” having a boiling point at or above 185° C. As can be expected, reduction of these impurities and side products is important. This is especially true in the case of xylene, particularly the meta and para xylenes, which have boiling points that are close to that of ethylbenzene and can make product separation and purification difficult.
Ethylene is obtained predominantly from the thermal cracking of hydrocarbons, such as ethane, propane, butane, or naphtha. Ethylene can also be produced and recovered from various refinery processes. Ethylene from these sources can include a variety of undesired products, including diolefins and acetylene, which can act to reduce the effectiveness of alkylation catalysts and can be costly to separate from the ethylene. Separation methods can include, for example, extractive distillation and selective hydrogenation of the acetylene back to ethylene. Thermal cracking and separation technologies for the production of relatively pure ethylene can account for a significant portion of the total ethylbenzene production costs.
Benzene can be obtained from the hydrodealkylation of toluene which involves heating a mixture of toluene with excess hydrogen to elevated temperatures (for example 500° C. to 600° C.) in the presence of a catalyst. Under these conditions, toluene can undergo dealkylation according to the chemical equation: C6H5CH3+H2→C6H6+CH4 This reaction requires energy input and as can be seen from the above equation, produces methane as a byproduct, which is typically separated and may used as heating fuel for the process.
In view of the above, it would be desirable to have a process of producing ethylbenzene, and styrene, which does not rely on thermal crackers and expensive separation technologies as a source of ethylene. It would also be desirable if the process was not dependent upon ethylene from refinery streams that contain impurities which can lower the effectiveness and can contaminate the alkylation catalyst. It would further be desirable to avoid the process of converting toluene to benzene with its inherent expense and loss of a carbon atom to form methane.
SUMMARY
One embodiment of the present invention is a process for making ethylbenzene which involves reacting toluene and methane in one or more reactors to form a first product stream comprising ethylbenzene and/or styrene and then further processing at least a portion of the components of the first product stream in at least a portion of an existing styrene production facility. The first product stream may also contain one or more of benzene, toluene, or methane. The process may comprise at least one separation apparatus for at least partial separation of the components from the first product stream. The reactors can include a reaction zone capable of dissipating heat to maintain the reaction zone within a desired temperature range for reacting toluene and methane to form ethylbenzene and/or styrene.
Methane may be separated from the first product stream creating a second product stream having reduced methane content. The methane may be recycled back to the reactors or may be utilized as heating fuel within the process. Toluene may also be separated from the first product stream and recycled to the reactors. At least a portion of the components of the first product stream can be further processed in a styrene production process. The styrene production process can include an alkylation reactor to form ethylbenzene by reacting benzene and ethylene, and a dehydrogenation reactor to form styrene by dehydrogenating ethylbenzene.
Yet another embodiment of the present invention is a process for making ethylbenzene and/or styrene which includes reacting toluene and methane in one or more reactors to form a first product stream comprising one or more of ethylbenzene, styrene, benzene, toluene, and methane; removing at least a portion of any methane from the first product stream to form a second product stream with reduced methane content; separation of at least a portion of the benzene from the first or second product stream; reacting at least a portion of the separated benzene in an alkylation reactor to form ethylbenzene; and dehydrogenating the ethylbenzene in one or more dehydration reactors to form styrene. At least a portion of one or more of the separation, alkylation, and dehydrogenation processes are performed utilizing the facilities of an existing styrene production facility. The one or more reactors may have one or more reaction zones and be capable of dissipating heat to maintain one or more of the reaction zones within the desired temperature range(s) to promote the reaction of toluene and methane to form ethylbenzene.
A further embodiment of the invention is a method for revamping an existing styrene production facility by adding a process for reacting toluene with methane to produce a new product stream containing ethylbenzene and styrene. The new product stream containing ethylbenzene and styrene may then be sent to the existing styrene production facility for further processing to form additional styrene. The existing styrene production facility can include a separation apparatus to remove at least a portion of any benzene and toluene from the new product stream, an alkylation reactor to form ethylbenzene by reacting the benzene and ethylene, and a dehydrogenation reactor to form styrene by dehydrogenating ethylbenzene.
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