Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including heat exchanger for reaction chamber or reactants...
Reexamination Certificate
2000-06-19
2003-09-23
Johnson, Jerry D. (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including heat exchanger for reaction chamber or reactants...
C422S186220, C422S198000, C422S198000, C422S198000, C422S199000, C422S211000, C422S198000, C422S218000, C422S222000, C585S440000
Reexamination Certificate
active
06623707
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to catalytic reactors for carrying out dehydrogenation reactions, and has particular application to reactors for the dehydrogenation of ethylbenzene to produce styrene.
A well-known process for the commercial production of styrene via the dehydrogenation of ethylbenzene involves combining ethylbenzene with steam to form a diluted feed stream which is then further heated to a suitable reaction temperature (e.g., 500-700° C.) in a preheating furnace. The pre-heated feed stream is then fed at low pressure into a catalytic reactor typically containing a bed of iron oxide-based catalyst pellets. The dehydrogenation reaction to produce styrene is endothermic, with styrene yields being favored at relatively high temperatures and low pressures.
The complex product of the dehydrogenation reaction generally comprises a vaporized mixture of styrene and unreacted ethylbenzene together with water vapor, H
2
, CO, CO
2
, light hydrocarbons, benzene, toluene, and heavier components such as polymerized by-products. The vapor mixture is cooled to condense and separate the liquid phase from the gas phase, and the separated liquid is processed through a series of distillation columns to recover the styrene and recycle the unreacted ethylbenzene.
Commercial styrene production typically involves processing the ethylbenzene through two or more catalytic reactor stages operating in series, with the feed stream being reheated between stages to compensate for the heat lost during the endothermic process. U.S. Pat. No. 4,347,396 discloses a processing system incorporating a series of reactors for this purpose.
Since the equilibrium constant for ethylbenzene-to-styrene conversion depends inversely on reactor pressure, pressure drops within commercial reactors are kept as low as possible. A high catalyst surface area:volume ratio increases mass transfer efficiency and suppresses undesirable by-product formation. Catalyst utilization and efficiency can be improved somewhat by using tightly packed beds of relatively small catalyst beads or pellets, but such use increases reactor pressure drop, tending to negate the expected improvements in catalytic conversion rate and styrene selectivity.
One way to address the pressure drop problem is to deploy the packed pellet beds in a radial flow reactor. One example of such a reactor is disclosed in U.S. Pat. No. 5,358,698. Compared to the pressure drops developed by unidirectional feed stream flows across conventional packed catalyst beds, radial flow reactors significantly reduce pressure drop by dispersing the catalyst beads around a large cylindrical volume encircling the feed stream inlet. At the same time, the gas linear velocity through the distributed pellet bed is reduced.
Unfortunately, however, several drawbacks associated with radial flow reactors remain. Among these are the fact that the gas distribution and collection chambers for these reactors take up a large fraction (30~60%) of the overall volume of the reactor. Thus, the space utilization efficiency of radial reactors is low.
In addition, radial reactor designs require that the feed stream change flow direction at least twice between the gas inlet and gas outlet of the reactor. This kind of flow pattern can cause poor gas distribution over the packed bed along the reactor axis that can reduce catalyst efficiency, and can increase catalyst attrition along the edges of the cylindrical beds. Extra catalyst bed support structures and screening are also required, increasing the capital cost of the reactor and introducing operating reliability issues.
Finally, it is more difficult and expensive to introduce heat uniformly into the middle of the catalyst bed in these reactors. Thus larger temperature gradients tend to develop within the catalyst bed that negatively affect conversion, selectivity, and catalyst stability.
Honeycomb monolithic catalysts such as disclosed in U.S. Pat. No. 4,711,930 have been considered for use in dehydrogenation reactions but have found little use in commercial chemical processing systems. In principle, these catalysts should offer reduced feed stream pressure drops and improved heat/mass transfer efficiency when compared with pelletized catalysts. However, the art has not yet developed dehydrogenation reactor designs that effectively exploit the performance characteristics of these catalysts.
SUMMARY OF THE INVENTION
The present invention provides axial flow reactor designs offering efficiencies higher than those of existing pellet bed and radial flow reactors, while at the same time maintaining or reducing reactor size and capital cost. The designs can be employed in standalone systems, or they can be used for retrofit or supplemental reactors that can significantly improve the efficiency of existing series reactor systems.
The improved reactor designs of the invention include an improved axial flow dehydrogenation reactor that effectively exploits the advantages of honeycomb catalyst packing (hereinafter also referred to as monolithic packing). The reactor assembly includes a reaction chamber having an inlet and an outlet and containing two or more beds of monolithic catalyst disposed therewithin. The catalyst beds include an upstream bed and a downstream bed disposed in series along the reactant flowpath, the latter generally following a flow axis traversing the chamber from an upstream to a downstream direction between the chamber inlet and outlet.
Each of the catalyst beds in the chamber is formed of one or more monolithic dehydrogenation catalysts, each of which is a honeycomb catalyst incorporating a plurality of open-ended honeycomb channels traversing the catalyst from the upstream to the downstream direction on the reactant flowpath. These channels provide catalytically active channel wall surfaces for treating a heated vapor stream containing a hydrogen-containing reactant passing through the catalyst bed, at least partially converting the reactant to a dehydrogenated product in an efficient manner and at low pressure drops.
Also disposed within the chamber, and situated between the upstream and downstream catalyst beds to separate them from one another, are heating means for re-heating the vapor stream after traversal of the upstream catalyst bed. The heating means, which are preferably also designed to operate a low pressure drop, provide an effective and space-efficient way to restore heat energy to the reactant stream prior to its traversal of the downstream reactor bed.
Reactors of the described type may be utilized alone or in series to carry out a variety of endothermic dehydrogenation reactions at conversion rates equivalent or better than achievable in packed bed reactor systems. However, an alternative and preferred use of such a reactor is in combination with a radial flow reactor in a multiple-stage dehydrogenation reactor systems for the conversion of ethylbenzene to styrene. By a multiple-stage reactor system is meant a reactor system incorporating two or more dehydrogenation reactors in series, each reactor constituting a stage in the dehydrogenation process.
In another aspect the invention includes a multiple-stage dehydrogenation reactor system comprising at least two reactors in series. The system includes an axial flow reactor stage connected with a second reactor stage, the second stage being a second axial flow reactor stage or, more typically, a radial flow reactor stage.
The axial-flow reactor stage comprises a first reaction chamber having a first inlet and a first outlet and containing at least one monolithic catalyst bed of the kind above described, i.e., incorporating one or more monolithic honeycomb catalysts, each of which has honeycomb channels disposed along the flow axis within the chamber. More preferably, the axial flow stage will include at least two monolithic catalyst beds separated by heating means as above described, the upstream bed and downstream bed again being disposed in series along the flow axis and the heating means operating to add heat to reactant stream un
Addiego William P.
Campbell Stephen A.
Liu Wei
Odinak Mitchell E.
Corning Incorporated
Doroshenk Alexa J.
Johnson Jerry D.
Sterre Kees van der
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