Chemistry of hydrocarbon compounds – Aromatic compound synthesis – Having alkenyl moiety – e.g. – styrene – etc.
Reexamination Certificate
2000-08-14
2002-07-16
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
Having alkenyl moiety, e.g., styrene, etc.
C585S435000, C585S436000, C585S319000
Reexamination Certificate
active
06420620
ABSTRACT:
The present invention relates to a process for the preparation of styrene or substituted styrenes from a feed containing 1-phenyl ethanol (also known as &agr;-phenyl ethanol or methyl phenyl carbinol) or substituted 1-phenyl ethanol, involving the conversion of bis(phenyl ethyl)ethers or substituted bis(phenyl ethyl)ethers into styrene or substituted styrenes. The present invention also relates to the conversion per se of bis(phenyl ethyl)ethers or substituted bis(phenyl ethyl)ethers into styrene or substituted styrenes.
A commonly known method for manufacturing styrene is the coproduction of propylene oxide and styrene starting from ethylbenzene. In general such process involves the steps of (i) reacting ethylbenzene with oxygen or air to form ethylbenzene hydroperoxide, (ii) reacting the ethylbenzene hydroperoxide thus obtained with propene in the presence of an epoxidation catalyst to yield propylene oxide and 1-phenyl ethanol, and (iii) converting the 1-phenyl ethanol into styrene by dehydration using a suitable dehydration catalyst. The present invention particularly focuses on the last step, i.e. the dehydration of 1-phenyl ethanol to yield styrene.
During the dehydration of 1-phenyl ethanol to styrene several by-products in addition to water are formed, such as polystyrenes including dimers and trimers of styrene and bis(phenyl ethyl)ethers. A major part of the bis(phenyl ethyl)ethers formed consists of bis(&agr;,&agr;-phenyl ethyl)ether, which is assumed to result from the reaction between two molecules of 1-phenyl ethanol. Another bis(phenyl ethyl)ether normally formed in a substantial amount is bis(&agr;,&bgr;-phenyl ethyl)ether. Bis(&bgr;,&bgr;-phenyl ethyl)ether is normally formed in minor amounts. The latter two bis(phenyl ethyl)ethers are assumed to result from the reaction between 1- and 2-phenyl ethanol and from the reaction between two molecules of 2-phenyl ethanol, respectively. The 2-phenyl ethanol is usually already present in small amounts in the feed to the dehydration treatment. This is predominantly the result of the preceding epoxidation step, wherein beside the main products propylene oxide and 1-phenyl ethanol also some 2-phenyl ethanol and methyl phenyl ketone are formed. Also in the oxidation step some 2-phenyl ethanol and methyl phenyl ketone is already formed. Since the boiling points of 1- and 2-phenyl ethanol and methyl phenyl ketone are all very close, a distillation treatment will not effect full separation.
The bis(phenyl ethyl)ethers together form a substantial part of the so called residual fraction or heavy ends, i.e. all components present in a stream having a boiling point which is higher than the boiling point of 1-phenyl ethanol. Normally the heavy ends will contain 5 to 50% by weight of bis(phenyl ethyl)ethers, suitably 10 to 40% by weight. As stated herein before, a substantial part of the bis(phenyl ethyl)ethers is composed of bis(&agr;,&agr;-phenyl ethyl)ether. The remaining part is composed of bis(&agr;,&bgr;-phenyl ethyl)ether with small amounts of bis(&bgr;,&bgr;-phenyl ethyl)ether being sometimes present as well. Other main components present in the heavy ends include 2-phenyl ethanol (0-40% by weight), 1-phenyl ethanol (0-20% by weight), methyl phenyl ketone (0-30% by weight) and polystyrenes (0-40% by weight). Small quantities of other ethers, such as the ether reaction product of 1-phenyl ethanol and phenol, may also be present. The exact quantities of each of these components is determined by the specific reaction conditions and catalyst employed in the dehydration step as well as by the product separation means applied after this dehydration step. Beside these main components the remainder of the heavy ends, up to 100% by weight, is formed by other compounds having a boiling point higher than that of 1-phenyl ethanol.
In the conventional processes for manufacturing styrene the heavy ends formed in the course of the process are disposed of as fuel and are burnt in a boiler house. In this way relatively valuable products are lost. It would be beneficial if the amount of valuable products present in the heavy ends could be reduced.
The present invention aims to provide an effective process for converting components present in the heavy ends into styrene, thus increasing the overall yield of styrene while lowering the amount of heavy ends.
In U.S. Pat. No. 4,375,570 a process for the recovery of aromatic hydrocarbons from dehydration residues obtained in the preparation of styrene from 1-phenyl ethanol is disclosed. The process involves subjecting the dehydration residues to a thermal cracking treatment at a temperature in the range of 325 to 475° C. and at an elevated pressure of about 5 to 21 bar, withdrawing the cracked effluent from the reaction zone and recovering liquid aromatic hydrocarbons from this cracked effluent. The dehydration residue generally is the residual fraction obtained after removal of the crude styrene from the dehydration product stream. It was found that by carrying out the thermal cracking at elevated pressure, the C
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aromatic hydrocarbons formed were composed predominantly of ethylbenzene and contained low amounts (usually less than 3% by weight) of styrene monomer. The ethylbenzene can be recycled to the oxidation step where ethylbenzene hydroperoxide is formed, which is a precursor of 1-phenyl ethanol from which styrene is formed. Thus, the overall styrene selectivity of the process is increased and the amount of heavy ends eventually obtained is decreased. The thermal cracking treatment, however, requires rather severe conditions, as a result of which tar-like products are formed which in return result in fouling of the equipment. Furthermore, these severe conditions are less desired for reasons of process control and necessitate the use of more expensive equipment. Moreover, the improvement of overall styrene selectivity and yield is obtained indirectly, i.e. via the production of ethylbenzene. During the conversion of ethylbenzene into styrene additional losses again occur.
The present invention has the advantage that it provides a process wherein the improvement of styrene selectivity and styrene yield is obtained more directly. Furthermore, the process of the present invention does not involve any thermal cracking treatment requiring rather severe process conditions, but makes use of a less severe treatment to enhance styrene selectivity and overall styrene yield.
Accordingly, the present invention relates to a process for the preparation of styrene or substituted styrenes comprising the steps of:
(a) subjecting a feed containing 1-phenyl ethanol or substituted 1-phenyl ethanol to a dehydration treatment in the presence of a suitable dehydration catalyst,
(b) subjecting the resulting product stream to a separation treatment, thus obtaining a stream containing styrene or substituted styrene and a residual fraction containing heavy ends, and
(c) converting at least part of these heavy ends to styrene or substituted styrenes by subjecting a stream containing these heavy ends to a cracking treatment in the presence of an acidic cracking catalyst.
Within the further context of the present application the term “styrene” also embraces substituted styrenes, by which are meant styrenes containing one or more substituents bonded to the aromatic ring or to the vinyl group. Such substituents typically include alkyl groups, such as methyl or ethyl groups. Similarly, the terms “bis(phenyl ethyl)ethers” and “1-phenyl ethanol” also embrace respectively substituted bis(phenyl ethyl)ethers and substituted 1-phenyl ethanols having the same substituents as the corresponding substituted styrenes.
The production of styrene by dehydrating 1-phenyl ethanol is well known in the art. It can be carried out both in the gas phase and in the liquid phase. Suitable dehydration catalysts include for instance acidic materials like alumina, alkali alumina, aluminium silicates and H-type synthetic zeolites. Dehydration conditions are also well known and usually include reaction temperatures of 100-200° C. for liquid phase
De Bie Johan Hendrik
Dirkzwager Hendrik
Overtoom Robertus Raymundus Maria
Van Zwienen Marinus
Griffin Walter D.
Shell Oil Company
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