Patent Publication Number: US-2020299212-A1

Title: Processes for catalytic paraffin dehydrogenation and catalyst recovery

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Provisional Patent Application No. 62/821,672 filed Mar. 21, 2019, which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a process for dehydrogenation of paraffins by reacting a paraffin stream with metal oxide catalyst(s) to produce light olefins, such as propylene, and a process for the recovery of metal oxide catalyst fines from the reactor effluent stream using a wash fluid and filtration. 
     BACKGROUND 
     The abundance of alkanes and paraffins from shale and stranded gas has spurned the development of more cost-effective ways to produce light olefins, the demand for which has increased significantly in recent years. Steam cracker units using lighter shale condensates as feedstock have been used to meet to the increase in the demand for light olefins, like ethylene. However, these units have been found to be deficient for propylene production due to the low propylene/ethylene ratio and low propylene yield. As a result, finding routes for the targeted production of propylene have received considerable interest. 
     It has been shown that catalytic dehydrogenation provides the possibility of high selectivity to a single olefin product. Current alkane dehydrogenation processes for the production of propylene and other light olefins employ the use of platinum-based and chromium-based catalysts. Given the expense associated with platinum and the carcinogenic properties of chromium, there is a need for developing less expensive, less toxic metal oxide catalysts that can is capable of good alkene selectivity during the dehydrogenation process and a correspondingly high yield. 
     A potential deficiency in processes for alkane or paraffin dehydrogenation employing a riser or fluidized-bed type reactor is the amount of catalyst fines in the effluent streams leaving the dehydrogenation reactor. With regard to the reactor effluent stream, a water quench tower is used to cool the reactor effluent and condense the water therein, particularly if dilution steam is used to lower the partial pressure of the alkane or paraffin. The catalyst fines contained in the reactor effluent stream cannot easily be separated from quench water, leading to excessive fouling in the equipment and consequential high maintenance costs. Thus, there is also a need for improved recovery of catalyst fines found in the effluent stream from the dehydrogenation reactor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The  FIG. 1  is a schematic illustration of a process for catalytic paraffin dehydrogenation and catalyst recovery of the kind described herein. 
       SUMMARY 
       There is provided, in one form, a process for dehydrogenating paraffins by contacting a metal oxide catalyst with a paraffin having 2-8 carbon atoms in a riser, fluidized bed, or fixed-bed swing reactor for a reaction period ranging from about 0.05 seconds to about 10 minutes. In one embodiment, the metal oxide catalyst is selected from group consisting of oxides of zinc, titanium, copper, iron, manganese, aluminum, silicon, zirconium, cerium, dysprosium, erbium, europium, gadolinium, lanthanum, neodymium, praseodymium, samarium, terbium, ytterbium, yttrium, niobium, and combinations thereof, wherein the metal oxide catalyst is substantially free of platinum and chromium. 
       There is further provided in another form, a process for recovering catalyst fines from the reactor effluent stream of a catalytic paraffin dehydrogenation reaction in a riser or fluidized-bed type reactor, the process comprising: contacting a metal oxide catalyst with a paraffin having 2-8 carbon atoms; generating a reactor effluent stream comprising metal oxide catalyst fines after contacting the metal oxide catalyst with the paraffin; and contacting the reactor effluent stream with a wash fluid to transfer the metal oxide catalyst fines from the reactor effluent stream into the wash fluid and form a cooled catalyst effluent stream and a substantially catalyst-free product stream. 
     
    
    
     DETAILED DESCRIPTION 
     It has been discovered that contacting one or more metal oxide catalysts with a paraffin having 2-8 carbon atoms in a dehydrogenation reaction for a period ranging from about 0.05 seconds to about 10 minutes in a reactor may lead to better selectively for the production of certain olefins, such as propylene and ethylene. It has also been discovered that metal oxide catalyst fines, generated because of attrition in a riser or fluidized-bed type reactor, are contained within the reactor effluent stream. These catalyst fines may be recovered by contacting the effluent stream of the reactor with a wash fluid, typically oil or water, to form a cooled catalyst effluent stream and a substantially catalyst-free product stream and then filtering the cooled catalyst effluent stream with a set of filters to capture the catalyst fines for potential reuse. 
     In one embodiment, the paraffin to be contacted with the metal oxide catalyst(s) may be propane, ethane, n-butane, isobutane, and combinations thereof. In another embodiment, the paraffin may be introduced to the reactor with or without an inert diluent or steam. 
     The metal oxide catalysts useful in dehydrogenating the paraffin to produce a light olefin product gas may be made up of one or more of the following oxides: zinc, titanium, copper, iron, manganese, aluminum, silicon, zirconium, cerium, dysprosium, erbium, europium, gadolinium, lanthanum, neodymium, praseodymium, samarium, terbium, ytterbium, yttrium, or niobium. In a non-limiting embodiment, the metal oxide catalyst(s) used are substantially free of platinum and chromium. 
     The dehydrogenation of the paraffin using metal oxide catalysts of the kinds described above and recovery of catalyst fines in the reactor effluent stream may be accomplished, in one non-limiting embodiment, by the process depicted in the  FIG. 1  in which a paraffin feedstock 10 comprising paraffins having 2-8 carbons is contacted with one or more metal oxide catalysts in a riser or fluidized bed reactor under dehydrogenation conditions. This process may be performed at a reaction temperature of 500-800° C., a space velocity of 0.1-1 h −1 , and a pressure of 0.01-0.2 MPa. In one embodiment, the reaction period may range from about 0.05 seconds to about 10 minutes. In other non-limiting embodiments, the dehydrogenation reaction between the paraffin and the metal oxide catalyst(s) may also be carried out in a fixed-bed swing or riser or fluidized-bed reactor from which a reactor outlet stream  20  is formed. The reactor outlet stream  20 , in one non-restrictive embodiment, is then sent to a cyclone or disengager to separate catalyst from the reactor outlet stream and form an overhead reactor effluent stream  30 . 
     In a non-limiting embodiment, the reactor effluent stream  30  contains light olefins, such as, without limitation, propylene and/or ethylene. The bulk of the catalyst is retained within the reactor or recovered in the cyclone/disengager and then sent as a separated catalyst stream  40  to a regenerator, which uses combustion air 50 to produce a flue gas stream  60  and a regenerated catalyst stream  70  that is returned to the reactor. 
     However, some catalyst fines, formed due to attrition in reactor types like riser or fluidized-bed reactors, may be contained in the reactor effluent stream  30 . These metal oxide catalyst fines may be recovered in a process in which the reactor effluent stream  30  is contacted in a quench tower with a wash fluid  90 , typically oil or water, to transfer the metal oxide catalyst fines from the reactor outlet stream into the wash fluid and form a cooled catalyst effluent stream  100  and a substantially catalyst-free product stream  80 . In one non-restrictive embodiment, the reactor effluent stream  30  is contacted with the wash fluid in a quench tower that contains vapor-liquid contacting elements, such as, without limitation, packing or trays. The quench tower, in another embodiment, may also have a recirculation loop for continuously recirculating a wash fluid to the contacting elements. 
     In another non-restrictive embodiment, the cooled catalyst effluent stream  100  may subsequently be converted into a slurry and then directed to one or more filters to separate the metal oxide catalyst fines. In one embodiment, the slurry is continuously passed through a first filter in a filtration mode to separate the metal oxide catalyst fines therefrom while a second filter in parallel with the first filter is in backflushing mode to remove the separated metal oxide catalyst fines therefrom. The filtration of the slurry may comprise periodically alternating the first and the second filters between filtration and backflushing mode. After filtration, the separated metal oxide catalyst fines may be collected and accumulated in a catalyst accumulator. The catalyst fines may then be prepared for reuse in the dehydrogenation reaction. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. However, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, paraffins, metal oxide catalysts, dehydrogenation reaction conditions and equipment, and catalyst fine recovery conditions and equipment falling within the claimed or disclosed parameters, but not specifically identified or tried in a particular example, are expected to be within the scope of this invention. 
     The present invention may be practiced in the absence of an element not disclosed. In addition, the present invention may suitably comprise, consist or consist essentially of the elements disclosed. For instance, the process may comprise, consist of, or consist essentially of: contacting a metal oxide catalyst with a paraffin having 2-8 carbon atoms in a reactor for a reaction period ranging from about 0.05 seconds to about 10 minutes. 
     Alternatively, the recovery of the catalyst fines from a reactor effluent stream may comprise, consist of, or consist essentially of: contacting a metal oxide catalyst with a paraffin having 2-8 carbon atoms, generating a reactor effluent stream comprising metal oxide catalyst fines after contacting the metal oxide catalyst with the paraffin, and contacting the reactor effluent stream with a wash fluid to transfer the metal oxide catalyst fines from the reactor effluent stream into the wash fluid and form a cooled catalyst effluent stream and a substantially catalyst-free product stream. 
     The words “comprising” and “comprises” as used throughout the claims, are to be interpreted to mean “including but not limited to” and “includes but not limited to”, respectively. 
     As used herein, the word “substantially” shall mean “being largely but not wholly that which is specified.” 
     As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     As used herein, the term “about” in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the given parameter). 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.