Chemistry of hydrocarbon compounds – Plural serial diverse syntheses – To produce unsaturate
Reexamination Certificate
2000-08-04
2002-05-28
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
To produce unsaturate
C585S648000, C585S653000, C585S658000
Reexamination Certificate
active
06395944
ABSTRACT:
The present invention relates in general to the production of mono-olefins by the oxidative dehydrogenation of gaseous paraffinic hydrocarbons having two or more carbon atoms and in particular to the production of mono-olefins by autothermal cracking, especially of ethane, propane, and butanes.
BACKGROUND OF THE INVENTION
A known commercial route to the production of olefins is via steam cracking of paraffinic hydrocarbons. Steam cracking involves pyrolysis of the hydrocarbons. Olefins can also be prepared by cracking a paraffinic feed wherein the heat required for pyrolysis is provided by the partial combustion of the feedstock and not by conventional tubular fired heaters as in the steam cracking. This process can be described as “autothermal cracking” and will be described as such hereinafter. Autothermal cracking may be accomplished in the absence of a catalyst, as described in for example, an article entitled “Autothermal Cracking for Ethylene Production” by R. M. Deanesly in Petrol. Refiner, 29 (September, 1950), 217 and GB-A-794,157, or in the presence of a catalyst capable of supporting combustion beyond the normal fuel rich limit of flammability as described in, for example, EP-A-0164864; EP-A-0178853; EP-B1-0332289; EP-B1-0529793; and EP-A-0709446.
EP-A-0164864 and EP-A-0178853 describe the production of olefins together with carbon monoxide and hydrogen from gaseous paraffinic hydrocarbons, including ethane, by partial oxidation in spouted or fluid bed reactors. EP-A-0178853, for example, discloses a process for the preparation of synthesis gas (carbon monoxide and hydrogen from a hydrocarbon feed wherein the saturated hydrocarbon and oxygen-containing gas are introduced in a ratio of 1.1 to 5 times the stoichiometric ratio of hydrocarbon to oxygen for complete combustion. This process does not require a catalyst for its operation.
EP-B1-0332289 provides a process for the production of a mono-olefin from a gaseous paraffinic hydrocarbon having at least two carbon atoms or a mixture thereof by partially combusting a mixture of the hydrocarbon(s) and a molecular oxygen-containing gas in a composition of from 5 to 9 times the stoichiometric ratio of hydrocarbon to molecular oxygen-containing gas for complete combustion to carbon dioxide water, in contact with a catalyst capable of supporting combustion beyond the normal fuel rich limit of flammability.
EP-B1-0529793 discloses a process for the production of mono-olefins from a paraffin-containing hydrocarbon feed having at least two carbon atoms, the process comprising
(A) a first step of partially combusting a mixture of the hydrocarbon feed and a molecular oxygen-containing gas in contact with a catalyst capable of supporting combustion beyond the normal fuel rich limits of flammability, said first step carried out under a total pressure of greater than 5 bar absolute and at a temperature of greater than 650° C., and
(B) a second step of cooling the mono-olefinic products to 600° C. or less within less than 50 milliseconds of formation.
Finally, EP-A-0709446 discloses a process for the conversion of a liquid paraffin-containing hydrocarbon which comprises the step of:
(a) partially combusting a mixture of the liquid hydrocarbon and a molecular oxygen-containing gas in a reaction chamber with a catalyst capable of supporting combustion beyond the normal fuel rich limit of flammability, the mixture having a stoichiometric ratio of hydrocarbon to oxygen of greater than the stoichiometric ratio required for complete combustion to carbon dioxide and water, to produce a product stream and a carbon deposit in the reaction chamber;
(b) periodically replacing the liquid hydrocarbon and molecular oxygen-containing gas mixture in step (a) with a fuel-rich carbon-containing stream for a period of time sufficient to effect substantial removal of the carbon deposit from the reaction chamber.
In addition to the valuable olefinic product(s) the autothermal cracking reaction produces both carbon monoxide and hydrogen, which in admixture is hereinafter to be referred to as “synthesis gas”. The resulting synthesis gas from autothermal cracking is usually used as a fuel. This is a problem because it represents a waste of a valuable resource and therefore imposes an economic penalty on the process. A solution to this problem is to recover the synthesis gas and convert it to higher value products.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for the production of a mono-olefin from a feedstock comprising a paraffinic hydrocarbon which process comprises the steps of:
(a) feeding the feedstock and a molecular oxygen-containing gas to an autothermal cracker, where they are reacted by oxidative dehydrogenation to form a product comprising one or more mono-olefin(s) and synthesis gas,
(b) separating the product from step (a) into a synthesis gas-containing stream and one or more olefins and recovering the one or more olefin(s),
(c) contacting synthesis gas-containing stream separated in step (b) with either:—
(i) a catalyst for the conversion of synthesis gas to methanol under conditions whereby synthesis gas is converted to methanol, and optionally thereafter or simultaneously contacting the methanol so-formed with a catalyst for the dehydration of methanol to ethylene, under conditions whereby methanol is converted to ethylene and recovering the ethylene, or optionally methanol or both; or
(ii) a catalyst for the water gas shift reaction under conditions whereby carbon monoxide in the synthesis gas is converted by reaction with water to hydrogen and carbon dioxide and thereafter recovering hydrogen; or
(iii) a catalyst for the conversion of synthesis gas to hydrocarbons under conditions whereby synthesis gas is converted to a hydrocarbon product and thereafter recovering at least a part of the hydrocarbon product.
The term “oxidative dehydrogenation” is not intended to be limiting in any way and broadly describes the chemistry involved. It is believed that both partial oxidation and cracking occur in the reaction.
The feedstock may be oxidatively dehydrogenated in the autothermal cracker in the presence of absence of a catalyst capable of supporting combustion beyond the normal fuel rich limit of flammability, preferably in the presence of such a catalyst. The principal role of the catalyst is to stabilise partial combustion of the gaseous mixture which may not otherwise be flammable. Suitably the catalyst is a supported platinum group metal. Preferably, the metal is either platinum or palladium, or a mixture thereof. Although a wide range of support material are available, it is preferred to use alumina as the support. The support material may be in the form of spheres, other granular shapes or ceramic foams. Preferably, the foam is a monolith which is a continuous multichannel ceramic structure, frequently of a honeycomb appearance. A preferred support for the catalytically active metals is a gamma alumina. The support is loaded with a mixture of platinum and palladium by conventional methods well known to those skilled in the art. The resulting compound is then heat treated to 1200° C. before use. Catalyst promoters may also be loaded onto the support. Suitable promoters include copper and tin.
The catalyst may be used as a fixed bed or as a solids recirculating bed, for example a fluid or spouted bed. Use of the catalyst in a fixed bed can avoid the problem of attrition, which is mainly associated with moving bed operations. Moreover, the use of a fixed bed also facilitates rapid quenching of the products as compared with the use of a fluid bed.
In the process for the production of a mono-olefin from a feedstock comprising a gaseous paraffinic hydrocarbon the paraffinic hydrocarbon may suitably be ethane, propane or butane. The paraffinic hydrocarbon may be substantially pure or may be in admixture with other hydrocarbons and optionally other materials, for example methane, nitrogen, carbon monoxide, carbon dioxide, steam or hydrogen. A paraffinic hydrocarbon-containing fraction such as naphtha, gas oil
Griffiths David Charles
Maunders Barry Martin
Woodfin William Terence
BP Chemicals Limited
Dang Thuan D.
Nixon & Vanderhye
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