阅读说明：本技术 催化脱氢方法 (Catalytic dehydrogenation process ) 是由 M·T·普雷茨 M·W·斯图尔特 于 2014-10-14 设计创作，主要内容包括：提供了一种改进的催化脱氢方法,所述方法包括在上流式流化反应器中在催化条件下使烷烃或烷基芳烃原料流与脱氢催化剂接触,其中所述流化反应器包括一个或多个反应器,所述催化条件包括范围从500℃到800℃的温度、范围从0.1到1000的重时空速、范围从0.1秒到10秒的气体停留时间,并且在流化反应器之后,通过使用旋风分离系统使夹带的催化剂与反应器的排出物分离,其中改进之处包括在上流式流化反应器和旋风分离系统之间插入冷却手段以大体上终止热反应,由此有效增加对于烯烃产物的总摩尔选择性。(An improved catalytic dehydrogenation process is provided comprising contacting an alkane or alkyl aromatic feedstream with a dehydrogenation catalyst under catalytic conditions in an upflow fluidized reactor, wherein the fluidized reactor comprises one or more reactors, the catalytic conditions comprising a temperature in the range of from 500 ℃ to 800 ℃, a weight hourly space velocity in the range of from 0.1 to 1000, a gas residence time in the range of from 0.1 seconds to 10 seconds, and separating the entrained catalyst from the reactor effluent after the fluidized reactor by using a cyclone separation system, wherein the improvement comprises inserting a cooling means between the upflow fluidized reactor and the cyclone separation system to substantially terminate the thermal reaction, thereby effectively increasing the overall molar selectivity to olefin products.)

1. A catalytic dehydrogenation process, the process comprising:

contacting an alkane or alkylaromatic feed stream with a dehydrogenation catalyst comprising gallium and platinum and supported by an alumina support or an alumina silica support under catalytic conditions in an upflow fluidized reactor, wherein the catalytic conditions include a temperature ranging from 500 ℃ to 800 ℃ ranging from 0.1hr^-1To 1000hr^-1And a gas residence time ranging from 0.1 to 10 seconds, wherein the upflow fluidized reactor comprises:

a first upflow reactor comprising one or more reactors selected from the group consisting of a bubble bed reactor, a turbulent bed reactor, a fast fluidized reactor, and a riser reactor;

a second upflow reactor comprising a riser reactor; and

a frustum disposed between the first upflow reactor and the second upflow reactor;

separating the entrained catalyst from the reactor effluent in a cyclone system downstream of the second upflow reactor; and

cooling the entrained catalyst and the reactor effluent prior to separating the entrained catalyst from the reactor effluent, wherein cooling the entrained catalyst and the reactor effluent substantially terminates thermal reaction, thereby effectively increasing overall molar selectivity to olefin products.

2. The catalytic dehydrogenation process of claim 1, comprising cooling the entrained catalyst with the reactor effluent prior to the cyclone system.

3. The catalytic dehydrogenation process of claim 1, wherein cooling the entrained catalyst and the reactor effluent comprises at least one of: (i) passing the entrained catalyst with the reactor effluent through a quench exchanger located in the first upflow reactor; and (ii) injecting a cooling medium into the frustum or second reactor.

4. The catalytic dehydrogenation process of claim 3, wherein the first upflow reactor comprises the quench exchanger, and cooling the entrained catalyst and the reactor effluent comprises passing the entrained catalyst and the reactor effluent through the quench exchanger within the first upflow reactor.

5. The catalytic dehydrogenation process of claim 3, wherein cooling the entrained catalyst with the reactor effluent comprises injecting a cooling medium into the frustum or second reactor, wherein the cooling medium comprises at least one of steam, liquid water, cold catalyst, liquid hydrocarbon, cooled product gas, fuel, and packing particles.

6. The catalytic dehydrogenation process of claim 5, wherein the cooling medium comprises at least one of steam and liquid water.

7. The catalytic dehydrogenation process of claim 5, wherein the cooling medium comprises a cold catalyst having a temperature at least 10 ℃ lower than the temperature of the entrained catalyst and reactor effluent.

8. The catalytic dehydrogenation process of claim 5, wherein the cooling medium comprises a cooled product gas having a temperature at least 50 ℃ lower than the temperature of the entrained catalyst and reactor effluent.

9. The catalytic dehydrogenation process of claim 1, wherein the cooling reduces the temperature of the entrained catalyst and reactor effluent by at least 5 ℃.

10. The catalytic dehydrogenation process of claim 1, wherein the thermal conversion does not exceed 20% of the total conversion at the reaction temperature.

11. The catalytic dehydrogenation process of claim 1, wherein the alkane and/or alkylaromatic hydrocarbon is selected from propane and/or ethylbenzene and the molar ratio of thermal reaction products to catalytic reaction products is greater than 0:1 to less than or equal to 0.1: 1.

12. The catalytic dehydrogenation process of claim 1, wherein the overall selectivity is improved by at least 0.5 mole percent as compared to a process having an equivalent overall conversion, but not including cooling of entrained catalyst and reactor effluent.

Technical Field

The present invention relates to an improved catalytic dehydrogenation process.

Background

In a fluidized reaction system for dehydrogenating paraffinic and/or alkylaromatic hydrocarbons to related olefins, the selectivity of the thermal (gas phase) reaction of a paraffinic and/or alkylaromatic hydrocarbon feedstock is sometimes significantly lower than the catalytic selectivity. For example, in the case of propane, the selectivity of thermal dehydrogenation to propylene is about 45 mole% to 50 mole%, while the selectivity of catalytic dehydrogenation to propylene is about 99 mole% or higher. Likewise, the selectivity of the thermal dehydrogenation of ethylbenzene to styrene is about 67 mole percent, while the selectivity of the catalytic dehydrogenation of ethylbenzene is about 99 mole percent or greater.

Upflow fluidized reactors are an economical means of dehydrogenating alkanes and alkylaromatics. In particular, a riser, a turbulent bed reactor, a bubble bed reactor or a fast fluidized reactor has the advantage of being able to carry out the dehydrogenation reaction with the shortest residence time. However, the delivery of product gas and solids to the catalyst separation system, as well as the separation system itself, increases the overall gas residence time. This additional gas residence time results in less selectivity for the reaction of the feedstock and less overall reactor selectivity to the desired product.

Disclosure of Invention

The present invention is an improved catalytic dehydrogenation process. In particular, the improved process increases the overall reactor selectivity to related olefins by using a quench means.

The invention comprises the following steps:

1. an improved catalytic dehydrogenation process comprising contacting an alkane or alkyl aromatic feedstream with a dehydrogenation catalyst comprising gallium and platinum and supported on an alumina support or an alumina silica support in an upflow fluidized reactor under catalytic conditions comprising a temperature ranging from 500 ℃ to 800 ℃, a weight hourly space velocity ranging from 0.1 to 1000, a gas residence time ranging from 0.1 to 10 seconds, and separating entrained catalyst from the reactor effluent by using a cyclone separation system after the fluidized reactor, wherein the improvement comprises inserting a cooling means between the upflow fluidized reactor and the cyclone separation system to substantially terminate thermal reactions, thereby effectively increasing the overall molar selectivity to olefin product.

2. The improved catalytic dehydrogenation process of clause 1, wherein the thermal conversion does not exceed 20% of the total conversion at the reaction temperature.

3. The improved catalytic dehydrogenation process of item 1, wherein the cooling means is selected from the group consisting of: (i) a quench exchanger located between the fluidized reactor and the cyclone separation system; and (ii) injecting a cooling medium into a region between the fluidized reactor and the cyclone system.

4. The improved catalytic dehydrogenation process of clause 3, wherein the alkane and/or alkylaromatic hydrocarbon is selected from propane and/or ethylbenzene and the molar ratio of the thermal reaction product to the catalytic reaction product is greater than 0 to less than or equal to 0.1: 1.

5. The improved catalytic dehydrogenation process of clause 1, wherein the cooling means is injecting a cooling medium into the zone between the reaction zone and the riser, wherein the cooling medium is one or more selected from the group consisting of steam and liquid water.

6. The improved catalytic dehydrogenation process of clause 2, wherein the overall selectivity is improved at an equal overall conversion by at least 0.5 mole percent over a process that does not utilize a cooling means.

7. The improved catalytic dehydrogenation process of clause 3, wherein the cooling medium is one or more selected from the group consisting of steam, water, cold catalyst, liquid hydrocarbon, cooled product gas, fuel, and filler particles.

Drawings

For the purpose of illustrating the invention, there is shown in the drawings forms that are exemplary; it should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

FIG. 1 is a schematic view of a first embodiment of the cyclone reactor system of the present invention wherein the cooling means comprises a quench exchanger interposed between the fluidized reactor and the disengaging system riser.

Detailed Description

An embodiment of the present invention provides an improved catalytic dehydrogenation process comprising contacting an alkane or alkylaromatic feed stream with a dehydrogenation catalyst comprising gallium and platinum and supported on an alumina or alumina silica support under catalytic conditions in an upflow fluidized reactor system, wherein the upflow fluidized reactor system comprises one or more reactors selected from the group consisting of a bubble bed reactor, a turbulent bed reactor, a fast fluidized reactor, and a riser reactor, the catalytic conditions comprising a temperature ranging from 500 ℃ to 800 ℃, a weight hourly space velocity ranging from 0.1 to 1000, a gas residence time ranging from 0.1 to 10 seconds, and separating the entrained catalyst from the effluent of the reactor after the fluidized reactor by using a cyclone separation system, wherein the improvement comprises inserting cooling means between the fluidized reactor and the cyclone separation system to substantially terminate thermal heat Thereby effectively increasing the overall molar selectivity to olefin products.

The improved process is useful under catalytic conditions including temperatures ranging from 500 ℃ to 800 ℃. All individual values and subranges from 500 ℃ to 800 ℃ are included herein and disclosed herein; for example, the catalytic reaction temperature may range from a lower limit of 500 ℃, 550 ℃, 600 ℃,650 ℃, 700 ℃ or 750 ℃ to an upper limit of 525 ℃, 575 ℃, 625 ℃, 675 ℃, 725 ℃ or 800 ℃. For example, the catalytic reaction temperature may range from 500 ℃ to 800 ℃, or alternatively, from 600 ℃ to 800 ℃, or alternatively, from 500 ℃ to 650 ℃, or alternatively, from 575 ℃ to 675 ℃.

The improved process includes a time period in the range of from 0.1 hour^-1To 1000 hours^-1Is useful under catalytic conditions of weight hourly space velocity (e.g., the ratio of the mass rate of the hydrocarbon feedstock in pounds per hour to the mass of catalyst in the catalytic reactor in pounds). From 0.1 hour^-1To 1000 hours^-1All individual values and subranges of (a) are included herein and disclosed herein; for example, the weight hourly space velocity of the catalytic reaction may range from 0.1 hour^-11 hour (h)^-110 hours, 10 hours^-1100 hours, 100 hours^-1Or 500 hours^-1Lower limit of (3) to 0.5 hour^-15 hours, 5 hours^-155 hours, 2^-1450 hours^-1Or 970 hours^-1The upper limit of (3). For example, the weight hourly space velocity of the catalytic reaction may range from 0.1 hour^-1To 1000 hours^-1Or alternatively from 0.1 hour^-1To 500 hours^-1Or alternatively from 400 hours^-1To 990 hours^-1Or alternatively from 250 hours^-1To 750 hours^-1。

The improved process is useful under catalytic conditions including gas residence times ranging from 0.1 seconds to 10 seconds. All individual values and subranges from 0.1 to 10 seconds are included herein and disclosed herein; for example, the gas residence time for the catalytic reaction can range from a lower limit of 0.1 seconds, 0.5 seconds, 1 second, 5 seconds, or 9 seconds to an upper limit of 0.4 seconds, 0.8 seconds, 3.5 seconds, 7.8 seconds, or 10 seconds. For example, the gas residence time for the catalytic reaction may range from 0.1 to 10 seconds, or alternatively, from 0.1 to 5 seconds, or alternatively, from 5 to 10 seconds, or alternatively, from 2.5 to 7.5 seconds.

In one embodiment of the invention, the improvement can be applied to catalytic paraffin dehydrogenation reactions where the thermal conversion does not exceed 20% of the total conversion at the reaction temperature based on the calculation method described herein. All individual values and subranges from no more than 20% of the total conversion are included herein and disclosed herein. For example, the thermal conversion at the reaction temperature may be 20% or less of the total conversion, or alternatively, the thermal conversion at the reaction temperature may be 16% or less of the total conversion, or alternatively, the thermal conversion at the reaction temperature may be 14% or less of the total conversion, or alternatively, the thermal conversion at the reaction temperature may be 12% or less of the total conversion.

The improvements of the invention can be applied to processes in which 70 mole% or more of the total reaction that takes place is dehydrogenation.

The improved process is useful in upflow fluidized reactors. The upflow fluidized reactor system includes one or more reactors selected from the group consisting of a bubble bed reactor, a turbulent bed reactor, a fast fluidized reactor, and a riser reactor. Such reactors are known in the art, and any one or more or combination of these types may be used in embodiments of the present invention.

The upflow fluidized reactor system also includes a cyclone separation system. Cyclonic separation systems are known in the art and in some cases include two or more stages of cyclonic separation. In the case where there is more than one cyclonic separating apparatus, the first separating apparatus into which the fluidised stream enters is referred to as the primary cyclonic separating apparatus. The fluidized effluent from the primary cyclone may enter the secondary cyclone. Primary cyclonic separating apparatus is known in the art and includes, for example, primary cyclones and under the names VSS, LD²And RS²A commercially available system. Primary cyclones are described, for example, in U.S. patent nos. 4,579,716; 5,190,650, respectively; and 5,275,641. In some known separation systems that utilize a primary cyclone as the primary cyclone means, one or more additional sets of cyclones are used, such as secondary cyclones and tertiary cyclones, to further separate the catalyst and product gases. It will be appreciated that any primary cyclonic separating apparatus may be used in embodiments of the invention.

Cooling means are interposed between the outlet of the upflow fluidized reactor and the inlet of the cyclonic separation system. In the case where two or more upflow reactors are used as shown in figure 1, the cooling means may be located after the first upflow reactor and in some cases before the second upflow reactor, but in all cases before the inlet to the cyclone system. In one embodiment, a heat exchanger or quench exchanger is used. Such exchangers are well known and exemplary exchangers include shell and tube exchangers that can heat steam, propane or product, or boilers capable of producing high pressure steam from liquid water, and shell and tube or conventional catalyst coolers using bayonet style tubes. Alternatively, coils may be used to superheat the vapor, or heat transfer regions may be provided to heat the liquid, which is then vaporized outside of the boiler vessel maintaining the liquid/vapor interface. In an alternative embodiment, the cooling medium is contacted with the fluidization stream exiting the upflow fluidization reactor. The cooling medium may be in any form, including liquid, solid, or gas. Exemplary cooling media include steam, liquid water, cold catalyst, liquid hydrocarbon, cooled product gas, fuel, and filler particles. The cooling medium may be a mixture of two or more cooling media. By "cold catalyst" used as a cooling medium is meant a dehydrogenation catalyst that is at least 10 ℃ lower than the temperature of the catalyst in the upflow fluidized reactor. The use of a catalyst cooler for the catalyst passing through the reactor at least once enables the production of such a cooler catalyst. "cooled product gas" as cooling medium means a dehydrogenation product gas which is at least 50 ℃ cooler than the fluidizing stream discharged from the upflowing fluidized reactor. "fuels" used as cooling media include, for example, hydrogen, methane gas, natural gas, and mixtures thereof. Although the use of a cooling medium is within the scope of the present invention, one advantage of using a heat exchanger is that additional gases or solids (i.e., cooling medium) that may be introduced need not be separated, which can result in a larger cyclone and containment vessel for the cyclone.

The cooling means lowers the temperature of the fluidization stream. In an alternative embodiment, the instant invention provides an improved catalytic dehydrogenation process in accordance with any of the embodiments disclosed herein, except that the cooling means reduces the temperature of the fluidized stream by at least 5 ℃. All individual values and subranges from at least 5 ℃ are included herein and disclosed herein. For example, the reduction in temperature may be at least 5 ℃, or alternatively, the reduction in temperature may be at least 7 ℃, or alternatively, the reduction in temperature may be at least 9 ℃, or alternatively, the reduction in temperature may be at least 11 ℃, or alternatively, the reduction in temperature may be at least 13 ℃.

In an alternative embodiment, the instant invention provides an improved catalytic dehydrogenation process in accordance with any of the embodiments disclosed herein, except that the alkane is propane and the molar ratio of hot reaction products to catalytic reaction products exiting the reaction system is from greater than 0:1 to less than or equal to 0.1:1 (where the reaction system is defined as the process zone in which the feed and products are at the reaction temperature). In an alternative embodiment, the instant invention provides an improved catalytic dehydrogenation process in accordance with any of the embodiments disclosed herein, except that the alkylaromatic hydrocarbon is ethylbenzene and the molar ratio of the thermal reaction product to the catalytic reaction product is greater than 0:1 to less than or equal to 0.1: 1. In both cases of propane and ethylbenzene feedstocks, all individual values and subranges from 0:1 to 0.1:1 are included herein and disclosed herein. For example, the molar ratio of thermal reaction products to catalytic reaction products can be from a lower limit of 0:1, 0.001:1, 0.005:1, 0.01:1, 0.05:1, or 0.08:1 to an upper limit of 0.003:1, 0.008:1, 0.02:1, 0.05:1, 0.08:1, or 0.1: 1. The molar ratio of the thermal reaction products to the catalytic reaction products may be from 0 to 0.1:1, or alternatively, from 0.05:1 to 0.1:1, or alternatively, from 0:1 to 0.05:1, or alternatively, from 0.01:1 to 0.08: 1.

In an alternative embodiment, the instant invention provides an improved catalytic dehydrogenation process according to any of the embodiments disclosed herein, except that the overall selectivity is improved by at least 0.5 mole percent compared to a process without cooling means at an equivalent overall conversion. All individual values and subranges from at least 0.5 mole percent are included herein and disclosed herein. For example, the overall selectivity is improved by at least 0.5 mole%, or alternatively, by at least 1 mole%, or alternatively, by at least 1.5 mole%, or alternatively, by at least 2 mole%, at an equal overall conversion as compared to a process that does not employ cooling means.

Figure 1 illustrates a schematic view of a first embodiment of the cyclone reactor system 1 of the present invention wherein the cooling means comprises a quench exchanger interposed between the fluidized reactor and the separation system riser. The system includes an upflow fluidized reactor 40 in which the dehydrogenation catalyst is fluidized in a flow of an alkane or alkylaromatic feedstock with the dehydrogenation product and hydrogen. The fluidized stream exits the reactor 40 and passes through the quench exchanger 30 where the temperature of the fluidized stream is reduced. The fluidization flow then flows upward through the frustum 20 into the transport riser 10 and then into the secondary cyclonic separation system. The cyclone separation system also includes a primary cyclone 50 that initially separates the solid catalyst from the fluidized stream, with the separated catalyst exiting the primary cyclone via dipleg 52. The effluent of the primary cyclone, which contains the gas phase dehydrogenation product, hydrogen, unreacted feedstock and remaining catalyst, exits the primary cyclone 50 and enters the secondary cyclone 60. Additional catalyst separation occurs in the secondary cyclone 60 and the separated catalyst is discharged through dipleg 62. The effluent of the secondary cyclone 60 enters the separator plenum 70.

In an alternative embodiment, the fluidized flow effluent of the upflow fluidized reactor 40 may enter a tube, vessel, or frustum 20 where the effluent is contacted with a cooling medium. The cooling medium is injected into the bottom of the transport riser 10 or into the top of the frustum 20, in the region indicated by the bracket 15 shown in fig. 1. In yet another embodiment, the fluidized stream effluent may flow through the quench exchanger 30 and contact the cooling medium.

In an alternative embodiment, an improved catalytic dehydrogenation process comprising contacting an alkane or alkyl aromatic feedstream with a dehydrogenation catalyst comprising gallium and platinum and supported on an alumina support or an alumina silica support in an upflow fluidized reactor under catalytic conditions comprising a temperature ranging from 500 ℃ to 800 ℃, a weight hourly space velocity ranging from 0.1 to 1000, a gas residence time ranging from 0.1 seconds to 10 seconds, and separating entrained catalyst from the reactor effluent by using a cyclone separation system after the fluidized reactor, wherein the improvement consists essentially of interposing cooling means between the upflow fluidized reactor and the cyclone separation system, thereby substantially terminating the thermal reaction and thereby effectively increasing the overall molar selectivity to olefin products.

Examples of the invention

The following examples illustrate the invention but are not intended to limit the scope of the invention.

Comparative example 1 is a model of the upflow fluidized reactor system and cyclone separation system disclosed in U.S. published application 20120123177, which dehydrogenates propane to propylene with a selectivity of 91 mole% to 94 mole%.

Inventive example 1 is a model of an upflow fluidized reactor system as in comparative example 1, further comprising a quench exchanger located between the upflow fluidized reactor and the cyclone separation system.

A model was used to illustrate the possible propylene selectivity obtained with the present invention.

Highly active and highly selective paraffin dehydrogenation catalysts are known. As an example, in PCT publication No. PCT/US2012/046188, table 1 shows that the propane conversion is about 37.6% and the catalytic selectivity is 99.3 mole%. The experiments illustrated in table 1 of PCT/US2012/046188 were carried out at 600 ℃, which is the temperature that exhibits a very low gas phase reaction. PCT/US2012/046188, table 6, reproduced below in table 1, represents catalytic selectivity, which is expected to produce a very active and highly selective catalyst.

TABLE 1

Cyclic numbering	C3H8Conversion (%)	C3H6Selectivity (%)
			1	41.8	99.4
2	38.1	99.3
			5	37.9	99.3
8	37.6	99.2
			10	37.6	99.3

Alternatively, PCT/US2012/046188, table 9, reproduced in part as table 2 below, showed a propane conversion of 46.1% and a selectivity of propane to propylene of 96.4% at 625 ℃ using the same catalyst. At 625 ℃, propane showed significantly more gas phase reaction, which reduced the total measured selectivity in the experiment. To show this, a simple model was developed as described in table 3.

TABLE 2

Examples of the invention	C3H8Conversion (%)	C3H6Selectivity (%)
			6	46.1	96.4

TABLE 3 catalytic and gas phase propane → propylene selectivity model

	Thermodynamic mechanism	Unit of	Catalytic reactor laboratory
				In(a)	33.18
Ea/R	-33769.5
					Residual propane	Mol% of	100
	Average reaction temperature	℃	625
					Residence time	Second of	2
	Catalytic conversion rate	％	44
					Catalytic selectivity	Mol% of	99.3
	Heat rate, k	Mole/second	0.01197
					Heat conversion rate	％	2.4
	Conversion of heat	％	2.4
					Thermal selectivity	Mol% of	45
	Overall conversion	％	46.4
					Total selectivity	Mol% of	96.5

The catalytic selectivity, taken from table 1, showed a selectivity of 99.3 mole%. The Thermal selectivity of propane is taken from the Industrial Engineering chemical Process design and Development of fromentt (Thermal Cracking of propane, kinetics and Product distribution) at page 440. The Thermal reaction rate was calculated using the Laider coefficient described by Fromert in Thermal Cracking of propane, kinetics and product distributions, using the Arrenhius equation shown below in Eqn. (1),

(1)

the application of the Arrenhius equation was taken from the rearrangement of Eqn. (1) as shown in Eqn (2) below. This enables the calculation of the molar reaction rate, k, per second.

(2)

The thermal reaction rate was then calculated for propane and was obtained at 45 mole% selectivity. The catalytic performance is resolved to obtain the measured total conversion. The resulting overall selectivity should then be close to the value measured in the experiment. In this case, the model showed 96.5 mol% selectivity, compared to 96.4 mol%.

The method described above was used to model the present invention by combining the expected catalytic performance in a catalytic reactor with the associated gas phase reaction kinetics.

Reactor sizing guidelines

Upper conveying lifting pipe

The height of the transport section is based on the physical layout of the device. Because the plant is physically comprised of a hydrocarbon stripper and a two-stage cyclone separation system, there is a minimum distance between the fast fluidized/turbulent bed reactor and the cyclone. This increases the gas residence time, leading to thermal cracking of the propane and degradation of the products.

The diameter of this upper section is set on the basis of a maximum of about 35 to 80ft/s so that catalyst and gas are quickly delivered to the cyclone without causing unnecessary equipment corrosion or catalyst consumption.

Fast fluidized/turbulent bed reactor

The diameter and height of the lower reactor are set based on the desired catalyst loading to achieve the desired catalytic conversion with the shortest possible gas residence time. The above model was applied to comparative example 1. In comparative example 1, the catalytic conversion in the lower reactor was considered to be 37.58% and in the transport riser 3.31% at the desired catalytic selectivity. After the catalytic reaction in each of the reactor, transport riser and cyclone zones, the remaining propane in each zone undergoes a thermal reaction. This is a rough estimate of selectivity since thermal and catalytic reactions will occur simultaneously. As a result, the reaction system achieved a conversion of 45.5% with an overall selectivity of 93.8 mole%, as shown in table 4.

Alternatively, the model may also be applied to reactor type B. The model was applied to inventive example 1, shown in table 5. In inventive example 1, a quench exchanger or direct quench introduction can be applied directly after the fast fluidized/turbulent bed reactor. By immediately quenching the catalyst and gas, the overall conversion was reduced from 45.5% to 43.3% and the selectivity increased from 93.8% to 96.2%. This is an improvement of as much as 2.5 mole% over reactor type a. In fact, the incremental selectivity of the additional 2.2% conversion is only 45 mole%, which is extremely poor and undesirable.

In addition to improving the overall selectivity of the process alone, the gas residence time in the catalytic reactor can be increased to raise the level of overall conversion to the same level as shown for reactor type a. If the conversion is increased, the results can be found in Table 6. In this example, a 45.5% conversion of propane was achieved with an overall selectivity of 96.1 mole%.

The use of a quench exchanger or direct quench into the riser can increase selectivity to the desired olefin product. Alternatively, the reaction temperature may be increased to achieve higher conversion at a similar selectivity as in the case where no quench exchanger is used.

TABLE 4

TABLE 5

TABLE 6

The present invention may be embodied in other forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.