Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – With means applying electromagnetic wave energy or...
Reexamination Certificate
2002-11-19
2004-11-09
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
With means applying electromagnetic wave energy or...
C422S139000, C422S140000, C422S145000, C422S147000, C422S198000
Reexamination Certificate
active
06814943
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the alkylation of hydrocarbons such as aromatics and paraffins to produce useful chemicals and motor fuel. This invention specifically relates to a method and apparatus for alkylation using a transport reactor.
BACKGROUND OF THE INVENTION
Hydrocarbon alkylation is widely used in the petroleum refining and petrochemical industries to produce a variety of useful acyclic and cyclic hydrocarbon products which are consumed in motor fuel, plastics, detergent precursors, and petrochemical feedstocks. Alkylation processes generally involve the alkylation of an alkylation substrate with an alkylating agent. The alkylation substrate is an aromatic hydrocarbon such as benzene if the process produces ethylbenzene, cumene, or linear alkyl benzenes. If the process produces motor fuels such as gasoline, the alkylation substrate may be a branched paraffinic hydrocarbon having from 4 to 6 carbon atoms. The alkylating agent is typically an olefinic hydrocarbon containing from 2 to about 20 carbon atoms, depending on the desired product of the process.
Much of the installed base of alkylation capacity uses liquid phase hydrofluoric acid, generally referred to as HF, as the catalyst. The use of HF in these applications has a long record of highly dependable and safe operation. However, the potential damage from an unintentional release of any sizable quantity of HF and the need to safely dispose of some byproducts produced in the process has led to an increasing demand for alkylation process technology which does not employ liquid phase HF as the catalyst.
Numerous solid alkylation catalysts have been described in the open literature. However, these catalysts appear to suffer from unacceptably high deactivation rates when employed at commercially feasible conditions. While some catalysts have a sufficiently useful lifetime to allow the performance of alkylation, the rapid change in activity results in a change in product composition and also requires the periodic regeneration of the catalyst with the accompanying removal of the reaction zone from operation. It is very desirable to provide a continuous process for alkylation which is not subjected to periodic reaction zone stoppages or variation in the product stream composition.
Transport reactors are commonly used in hydrocarbon processing. In a transport reactor, the catalyst bed as a whole moves. Thus, a transport reactor can be contrasted with a fixed bed catalytic reactor and with an ebullated bed catalytic reactor. In a fixed bed reactor the catalyst particles do not move, and in an ebullated bed reactor the catalyst particles are suspended in a fluid but the settling velocity of the catalyst particles balances the fluid upflow velocity so that the catalyst bed as a whole does not move. Although it is generally the case that the direction of catalyst flow through a transport reactor is upward, the direction may also be downward, horizontal, a direction that is intermediate between vertical and horizontal, or a combination of these directions.
When the direction of catalyst flow through a transport reactor is upward, the transport reactor is often called a riser-reactor. Riser-reactors are commonly used in hydrocarbon processing, such as fluidized catalytic cracking and more recently in fluidized solid bed motor fuel alkylation. In a common arrangement, a fluid hydrocarbon reactant engages a solid hydrocarbon conversion catalyst at the bottom of a riser-reactor and transports the catalyst in a fluidized state up the riser-reactor. During the ascent through the riser-reactor, the catalyst promotes certain desired conversion reactions among the reactants in order to produce desired products. A stream of catalyst and hydrocarbon products, by-products, and unreacted reactants if any discharges from the top of the riser-reactor into a separation zone. The hydrocarbons and the catalyst disengage in the separation zone, with the hydrocarbons being withdrawn overhead for recovery and the catalyst dropping by gravity to the bottom of the separation zone. Despite some deactivation that may have occurred to the catalyst in the riser-reactor, some of the catalyst that collects at the bottom of the separation zone usually has enough residual activity that it can be reused in the riser-reactor without first being withdrawn from the separation zone for regeneration. Such still-active catalyst is recirculated through a recirculation conduit from the bottom of the separation zone to the bottom of the riser-reactor, where the catalyst contacts reactants again.
Several methods are used for controlling the introduction of reactants and for controlling the recirculation of catalyst to the bottom of the riser-reactor. For example, one method is shown in a motor fuel alkylation process in U.S. Pat. No. 5,489,732 (Zhang et al.). Isoparaffins and olefins are introduced into the bottom of the riser-reactor, and the flow of catalyst through a single recirculation conduit to the bottom of the riser-reactor is controlled by several means including slide valves, other types of valves, lock hoppers, fluid flow control (reverse flow of liquid), screw conveyors, and L-valves. This patent also teaches that one reactant, isobutane, can also be introduced into the recirculation conduit for the purpose of flushing by-product hydrogen from the recirculating catalyst. This method, however, is not suitable for withdrawing catalyst symmetrically or uniformly from the bottom of the separation zone, if the bed of catalyst in the bottom of the separation zone is not totally fluidized in the axial direction, i.e., it is a moving packed bed or a bed that is merely at incipient fluidization. In these types of beds, catalyst that is below the angle of repose from the opening to the recirculation pipe remains stagnant, which leads to inefficient use of the separation zone. Areas of stagnant catalyst can lead to operational difficulties if, because of an upset or disruption, the stagnant catalyst breaks loose, enters the recirculation pipe, and enters the riser-reactor. Another method that uses a spout-fluid bed with a draft tube is shown in the article by H. Littman et al. entitled “Fluid Flow Pattern and Solids Circulation Rate in a Liquid Phase Spout-Fluid Bed with Draft Tube,”
The Canadian Journal of Chemical Engineering
, Vol. 70, October 1992, pp. 895-904. This method provides poor control of the fraction of the total flow rate of reactants to the bottom of the draft tube that would flow through the draft tube compared to that fraction which would flow in reverse flow through the annular bed around the draft tube and would effectively bypass the draft tube. Moreover, this method provides poor control of the catalyst flow rate to the bottom of the draft tube, once the geometry around the bottom of the draft tube is fixed.
Accordingly, there is a need for a method and an apparatus that is suitable for use in a transport reactor process that uniformly or symmetrically withdraws catalyst from the separation zone which separates the transport reactor effluent, that uniformly or symmetrically controls the flow of reactants to the bottom of the transport reactor, and that controls the flow of catalyst from the separation zone to the transport reactor.
SUMMARY OF THE INVENTION
This invention is a novel method and apparatus for alkylating an alkylation substrate with an alkylating agent using solid catalyst particles in a fluidized transport reactor. The effluent of the transport reactor passes to a separation zone, which separates the product alkylate from the solid catalyst particles. The solid catalyst particles recirculate from the separation zone to the transport reactor through two or more recirculation conduits. The recirculation rate of catalyst particles, through each recirculation conduit is regulated by a fluid-controlled valve that uses the alkylation substrate as the regulating fluid. Each fluid-controlled valve discharges catalyst through a conduit into the transport reactor, so that a single, common transport reactor is fed by a
Anderson Paul
Gosling Christopher D.
Kiel Wesley L.
Radcliffe William H.
Sechrist Paul A.
Moore Michael A.
Tolomei John G.
Tran Hien
UOP LLC
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