Catalyst bed system for an endothermic catalytic dehydrogenation process and an endothermic dehydrogenation process

Abstract

A catalyst bed system, and a dehydrogenation process using the same, including a horizontal catalyst bed having a mixture of at least one catalytic material and at least one first inert material, a predetermined volume of at least one second inert material arranged upstream of the catalyst bed, wherein the volume of the reactor above the catalyst bed system is not filled by any solid material (empty space). The volume of the second inert material and the volume of the reactor above the second inert material (empty space) is between 0.04 and 0.73, preferably between 0.06 and 0.3, most preferably between 0.09 and 0.2.

Claims

1. An endothermic catalytic dehydrogenation process comprising: providing a catalyst bed system in a reactor, wherein the catalyst bed system comprises (1) a horizontal catalyst bed comprising a catalytic material and a first inert material, and (2) a layer of a second inert material of a predetermined volume arranged upstream of the horizontal catalyst bed, wherein the volume of the reactor above the second inert material is not filled by any solid material, wherein the ratio of volume of the second inert material to the volume of the reactor above the second inert material is between 0.04 and 0.73, and wherein the second inert material is selected from: (i) an oxide of a main group II element, an oxide of a main group III element, an oxide of a transition group III element, an oxide of a transition group IV element, an oxide of a transition group V element, and mixtures thereof, (ii) a nitride of a main group III element, a nitride of a main group IV element, and mixtures thereof, and (iii) a carbide of a main group III element, a carbide of a main group IV element, and mixtures thereof; optionally contacting the catalytic material with a reduction gas to reduce the catalytic material; passing a heat stream having a first temperature T1 through the volume of the second inert material and the horizontal catalyst bed, thereby heating the second inert material and the horizontal catalyst bed and regenerating the catalytic material; and subsequent to passing the heat stream through the volume of the second inert material, passing a hydrocarbon stream having a second temperature T2 through the volume of the second inert material and the horizontal catalyst bed, thereby dehydrogenating the hydrocarbon stream in the horizontal catalyst bed, wherein: (i) the second inert material is upstream of the horizontal catalyst bed for both the heat stream and the hydrocarbon stream, (ii) T1 is between 700 and 1000 C. and T2 is between 400 and 650 C., and (iii) T1>T3>T2, wherein T3 is a temperature at the interface of the second inert material and the horizontal catalyst bed which fluctuates by about 10 to 100 C.

2. The process according to claim 1, wherein the temperature T1 of the heat stream is between 725 and 810 C.

3. The process according to claim 1, wherein the temperature T2 of the hydrocarbon stream is between 550 and 650 C.

4. The process according to claim 1, wherein the temperature T3 is between 500 and 800 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is further explained in more detail based on the following examples in conjunction with the Figures.

(2) FIG. 1 shows a schematic view of a first embodiment of the catalyst bed system according to the invention.

(3) FIG. 2 shows a schematic view of a second embodiment of the catalyst bed system according to the invention.

(4) FIG. 3 shows a first diagram showing the temperature profile of a conventional catalytic bed and process.

(5) FIG. 4 shows a second diagram showing the temperature profile of an embodiment of the catalytic bed and process according to the invention.

DETAILED DESCRIPTION

(6) FIG. 1 shows schematically a first embodiment of a set up of the catalytic bed. Here a reactor 1 for conducting a dehydrogenation process having a catalyst bed 3 and a layer of inert material 2 arranged thereon is illustrated.

(7) In propane dehydrogenation (PDH) the horizontal catalyst bed 3 is a mixture of inert material and catalytic material with 50 vol % of each. The catalytic material is the active phase catalyzing the dehydrogenation while the inert phase stores the heat that it releases during the endothermic dehydrogenation reaction. Typically, a reaction cycle is a sequence of 7-15 min of hot regeneration air to heat up the catalyst bed and combust some coke and 7-15 min of propane dehydrogenation including with some side reactions like coke formation.

(8) According to the present catalyst bed system the extra layer 2 of second inert material is arranged on top of the existing catalyst/inert material mixture. This extra layer 2 of inert material has a thickness of about 20 to 40 cm.

(9) The heat stream 4 consisting of hot air and an injection fuel gas is fed to the catalyst bed system 2, 3 in order to heat and regenerate the catalyst system. Subsequently, a hydrocarbon feed in form of a propane feed 5 enters the reactor 1. By flowing through the catalyst bed system 2 and 3 propane is dehydrogenated and the thus formed propene stream 6 leaves the reactor for further work up.

(10) FIG. 2 shows schematically a second embodiment of an arrangement of the catalytic bed system according to the invention. Here a layer of inert material 2 is arranged in a separated vessel 7. Downstream of said vessel 7 the reactor 1 for conducting a dehydrogenation process having a catalyst bed 3 is arranged.

(11) The amount of inert material in vessel 7 is 30 to 72 tons.

(12) The heat stream 4 consisting of hot air and an injection fuel gas is fed at first to the vessel 7 passing the inert material layer 2 and subsequently to the catalyst bed 3 in order to heat and regenerate the catalyst system. Subsequently, a hydrocarbon feed in the form of a propane feed 5 enters vessel 7 and subsequently reactor 1. By flowing through the catalyst bed 3, propane is dehydrogenated and the thus formed propene/propylene stream 6 leaves the reactor for further work up.

(13) FIG. 3 presents a temperature profile of a conventional process according to WO 95/23123 A1 not using an extra layer of inert material as the present process. Shown are the temperature profiles at the start of the hydrocarbon cycle and the end of the hydrocarbon cycle. The regeneration cycle restores the temperatures of the catalytic bed material. The temperature in the upper layers of the catalyst bed decreases sharply during the dehydrogenation cycle, as clearly can be seen from this temperature profile. This sharp temperature change can however be avoided when the reactor is operated with the second inert material as shown below.

Example 1: First Operational ModeAdditional Heat Input

(14) According to the first operational mode using an arrangement according to FIG. 1 the injection gas flow is increased in order to provide extra heat.

(15) Simulations of temperatures in the inert layer indicate that the outlet temperature at the bottom (outlet) of that layer can be almost constant and propane is heated to higher temperature than T2 during the dehydrogenation cycle.

(16) In FIG. 4 a temperature profile of the catalytic bed for a first operational mode is shown. Here the gas outlet or interface temperature T3 (solid line) and gas inlet (dotted line) temperature T1, T2 of the inert layer, which has in this case a thickness of 40 cm, are presented over time. The inlet temperature of the inert layerthis means the temperature at the top of the layerclearly reflects the sequential dehydrogenation (lower temperature T2) and regeneration phases (higher temperature T1) of a typical PDH unit operation in between regeneration and dehydrogenation.

(17) The dehydrogenation phase is characterized by the propane feed at the lower temperature T2 and the regeneration phase is characterized by the heat feed at the higher temperature T1 representing the combined temperature of air and injection gas combustion (dotted line). In between the two phases, there is also a steam purge and reduction phase at lower temperatures. During the dehydrogenation cycle the top of the catalyst cools only down by 38 C. thus ensuring a relatively high overall temperature for the dehydrogenation cycle and an overall high conversion rate.

(18) An increased heat input with the inert layer on top does not expose the catalytic material catalyst to temperatures higher than the maximum exposure temperature. In the embodiment as described here this maximum exposure temperature T3 of the catalytic material is between 550 and 700 C. It is however in general possible to apply other maximum exposure temperatures depending on the catalytic material.

(19) The thickness of the extra layer of inert material has also an influence on the production rate.

(20) In general, the propylene production increases using an extra layer of inert material upstream of the catalytic bed.

(21) Conversion and selectivity data (not shown) indicate that the increase of propylene production is related to an increase in conversion rather than to a higher selectivity.

(22) Furthermore, the coke production is also lower than in conventional batches (not shown).

(23) There is furthermore no indication of a significant increase in cracking in the catalyst bed i.e. first inert material and/or catalyst material, when increasing the injection gas flow. This strongly indicates that at PDH operating temperatures thermal cracking is significantly lower than catalytic cracking.

(24) In summary it is to be said that due to the arrangement of an extra layer of a second inert material on top of the conventional catalyst bed the propylene production can be increased significantly by adding extra heat for instance in form of extra injection gas. It is possible to add extra heat without exposing the catalyst to higher temperatures. This has a positive effect on selectivity and conversion.

Example 2: Second Operational ModeSame Operating Conditions

(25) The applicability of the present catalyst bed system using the same operating conditions i.e. no increased heat stream was also tested.

(26) Propylene production in the present case and when using the conventional batch having the same heat input is higher in the first case using the extra layer of inert material on top of the catalyst bed. The production is increased.

(27) When comparing the selectivity and conversion rate it interestingly can be stated that the conversion for both cases is similar. The higher production rate using the catalyst bed of the invention is rather due to an increased selectivity.

(28) Higher selectivity is also confirmed by the lower coke production (not shown).

(29) The inert layer is the main contributor for the higher selectivity in propylene production. It creates lower peak temperatures in the catalyst bed and that has a large effect on selectivity.

(30) The average catalyst temperatures on the other hand do not differ much. In the batch using the catalytic system according to the invention the catalyst temperature seems to be a little bit lower because of the endothermic character of the dehydrogenation reaction. A higher production thus causes a lower average temperature.

(31) In summary it can be said that when operating with the same process parameters, the extra inert layer provides a selectivity advantage resulting in extra propylene production.

(32) Maximum temperature exposure of the catalyst bed is lower than in previous batches and the selectivity higher.

(33) If an inert layer is combined with normal process conditions, the total average propylene production is increased and the catalyst is exposed to lower temperatures mainly in the upper part of the catalyst bed.