PROCESS AND APPARATUS FOR REACTING FEED WITH A FLUIDIZED CATALYST WITH A REDUCTION IN CATALYST LOSS DURING STARTUP

Abstract

A fluidized catalytic reactor connected to a start-up heater is provided. The start-up heater provides sufficient heat to a catalyst containing stream to gradually increase the feed temperature. This allows for a critical volumetric flow rate to be achieved so that catalyst can be recovered from product instead of being entrained in product.

Claims

1. A reactor system comprising a reactor for contacting a reactant stream with a catalyst, said system comprising a. a reactor and b. a start up heater having lines for the reactor feed stream to be sent to said reactor.

2. The reactor system of claim 1 wherein said start-up heater is located downstream from a feed-effluent heat exchanger.

3. The reactor system of claim 1 wherein said start-up heater is upstream from said reactor.

4. The reactor system of claim 1 wherein the start-up heater is a fired heater, heat exchanger or a hot oil heater.

5. The process of claim 5 wherein said feed is at a volumetric flow rate at least 50% of a design flow rate for said reactor.

6. A process of start-up of a reactor comprising circulating a portion of a feed through a start-up heater to heat said feed to a temperature of at least 240 C.

7. The process of claim 5 wherein said feed is at a volumetric flow rate at least 85% of a design flow rate for said reactor.

8. The process of claim 5 wherein until said catalyst containing stream is at least at said temperature of at least 240° C. a heated catalyst feed is not sent from a regeneration unit to said reactor.

9. The process of claim 5 wherein said start-up heater heats said reactor feed stream until an exit temperature from said reactor for a feed effluent exceeds a predetermined temperature.

10. The process of claim 5 wherein said start-up heater provides sufficient heat to fluidize said catalyst containing stream sufficiently to allow for at least a 3 ft/sec.

11. The process of claim 5 wherein said start-up heater provides sufficient heat to fluidize said catalyst containing stream sufficiently to allow for at least a 5 ft/sec.

12. The process of claim 5 wherein said reactor is a fluidized bed paraffin dehydrogenation reactor.

13. The process of claim 5 wherein said heater is a fired heater, heat exchanger or a hot oil heater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic drawing of a process and apparatus of the present disclosure;

[0011] FIG. 2 is a graphical depiction of reaction flow velocity against time showing catalyst loss over time.

DETAILED DESCRIPTION

[0012] A process and apparatus have been developed that uses a start-up heater to increase the temperature of the feed vapor to maintain a critical volumetric flow rate through the reactor required for gas-solid separation that prevents loss of catalyst. The critical volumetric flow rate is generally at or above 50% of the design flow rate for the reactor during normal operation. Circulation of feed through the reactor at or above this critical flow rate is achieved by heating the feed to a minimum of 240° C. before introducing hot catalyst from the regenerator into the reactor. As the reactor heats up, the temperature of the feed exiting the feed heater is increased until the desired feed inlet temperature is achieved. The feed heater is located downstream of a feed-effluent heat exchanger so that as the exit temperature of the reactor increases, the heat input from the feed heater decreases as additional heat is transferred to the feed via the feed-effluent heat exchanger. A number of different heaters may be used including fired heaters, heat exchangers or hot oil heaters. In addition to providing enough flow to enable the cyclones to operate, the feed heater also maintains the necessary degree of fluidization for catalyst transport to enable circulation of catalyst from the reactor to the regenerator. In this situation the volumetric flow rate of the catalyst needs to be sufficient to achieve a minimum of 3 ft/s in the primary feed-contacting zone and preferentially a minimum of 5 ft/s in the primary feed-catalyst contacting zone and at least 60% of the normal reactor cyclone inlet velocity.

[0013] The PDH catalyst is used in a dehydrogenation reaction process to catalyze the dehydrogenation of paraffins, such as ethane, propane, iso-butane, and n-butane, to olefins, such as ethylene, propylene, isobutene and n-butenes, respectively. The PDH process will be described exemplarily to illustrate the disclosed apparatus and process.

[0014] The conditions in the dehydrogenation reactor may include a temperature of about 500 to about 800° C., a pressure of about 40 to about 310 kPa and a circulated catalyst to reactor feed ratio of about 5 to about 100. The dehydrogenation reaction may be conducted in a fluidized manner such that gas, which may comprise the reactant paraffins with or without a fluidizing inert gas, is distributed to the reactor in a way that lifts the dehydrogenation catalyst in the reactor vessel while catalyzing the dehydrogenation of paraffins. During the catalytic dehydrogenation reaction, coke is deposited on the dehydrogenation catalyst leading to reduction of the activity of the catalyst. The dehydrogenation catalyst must then be regenerated.

[0015] An example of the process is shown in FIG. 1 that shows the start-up heater 30 that is used to gradually increase the temperatures within the reactor until they reach about 240° C. A stream 10 comprising propane or butane, but other paraffins such as ethane may be present in the reactant stream in conjunction with or to the exclusion of other paraffins is passed through heat exchanger 15 with a stream 20 sent towards a valve 28. During start-up, all or a portion of stream 20 is sent in stream 25 to start-up heater 30. Then heated stream 35 is sent to be combined with the other portion of stream 20 to become stream 40 entering the bottom of reactor 45. Catalyst is sent through line 65 to be regenerated in regeneration unit 55 and regenerated catalyst is returned to the reactor through line 60.

[0016] In FIG. 2 it is shown the effect of the use of the start-up heater over the prior art where a start-up heater is not used. In FIG. 2, is seen reactor space velocity on the y-axis and temperature on the X-axis. There are high catalyst losses until the temperature in the reactor reaches about 210-225 C. As the velocity increases in the reactor, the catalyst losses are diminished. Between about 220 C to 400 C there are transitional catalyst losses that are lower than at the lower temperatures but still higher than desired. Above about 400 C to 650 C temperatures, the catalyst loss is minimized. On the right-hand y-axis is shown the cyclone inlet velocity in feet per second. When the reactor is at low temperatures there are also low pressures as well as low velocities. At such conditions much more catalyst is lost. However, by addition of the heater, the time period when the reactor is at low temperatures and catalyst losses are high is minimized and then the catalysts are retained in the reactor.

[0017] The dehydrogenation catalyst may be of any of a variety of catalysts suitable for a fluidized bed dehydrogenation unit. The dehydrogenation catalyst selected should minimize cracking reactions and favor dehydrogenation reactions. Suitable catalysts for use herein include an active metal which may be dispersed in a porous inorganic carrier material such as silica, alumina, silica alumina, zirconia, or clay. An exemplary embodiment of a catalyst includes alumina or silica-alumina containing gallium, a noble metal, and an alkali or alkaline earth metal. In most cases, the catalyst contains gallium.

[0018] The catalyst support comprises a carrier material, a binder and an optional filler material to provide physical strength and integrity. The carrier material may include alumina or silica-alumina. Silica sol or alumina sol may be used as the binder. The alumina or silica-alumina generally contains alumina of gamma, theta and/or delta phases. The majority of the catalyst support particles may have a nominal diameter of about 20 to about 200 micrometers with the average diameter of about 50 to about 150 micrometers. There are some particles as small as 1 micron although there are normally less than 5% of the particles smaller than 1 micron. The surface area of the catalyst support is 85-140 m2/g.

[0019] The dehydrogenation catalyst may support a dehydrogenation metal. The dehydrogenation metal may be a one or a combination of transition metals. A noble metal may be a preferred dehydrogenation metal such as platinum or palladium. Gallium is an effective supporting metal for paraffin dehydrogenation. Metals may be deposited on the catalyst support by impregnation or other suitable methods or included in the carrier material or binder during catalyst preparation.

[0020] The acid function of the catalyst should be minimized to prevent cracking and favor dehydrogenation. Alkali metals and alkaline earth metals may also be included in the catalyst to attenuate the acidity of the catalyst. Rare earth metals may be included in the catalyst to control the activity of the catalyst. Concentrations of 0.001% to 10 wt % metals may be incorporated into the catalyst. In the case of the noble metals, it is preferred to use about 10 parts per million (ppm) by weight to about 600 ppm by weight noble metal. More preferably it is preferred to use 10-100 ppm by weight noble metal. The preferred noble metal is platinum. Gallium should be present in the range of 0.3 wt % to about 3 wt %, preferably about 0.5 wt % to about 2 wt %. Alkali and alkaline earth metals are present in the range of about 0.05 wt % to about 1 wt %.