An Integrated Oxidative Alkane Dehydrogenation and Hydrogen Generation Process

Abstract

The present invention relates to an integrated oxidative alkane dehydrogenation and hydrogen generation process, wherein carbon dioxide from Pressure Swing Adsorption (PSA) off gas stream of Hydrogen Generation Unit (HGU), and alkane from any known source are sent to oxidative dehydrogenation (ODH) unit for producing high value olefins, such as ethylene, propylene and butenes. Products formed from ODH reactor are separated and the stream comprising of hydrogen, carbon monoxide and methane are recycled to Shift reactor of HGU unit for enhanced production of hydrogen at PSA.

Claims

An integrated process for catalytic oxidative dehydrogenation (ODH) of alkane(s) and for generation of hydrogen, the process comprising:a) feeding a fresh hydrocarbon alkane feed (1) along with a carbon dioxide rich stream (2) to an ODH reactor (A) comprising a dehydrogenation catalyst, where the alkane feed gets converted into alkenes, and producing an effluent gas comprising of hydrogen, methane, carbon monoxide, carbon dioxide, water and unreacted alkanes;b) separating an ODH effluent gas (5) from the ODH reactor (A) in a Gas Separation system, wherein the Gas Separation system consists of a De-Propanizer section (B), a De-Butanizer and C4 Splitter section (C), a C3 Splitter section (D), a De-Methanizer section (E), and a C2 Splitter section (F);c) separating the ODH effluent gases (5) into (i) C4+ stream (6) consisting of C4 alkanes, C4 olefins and higher hydrocarbons; (ii) C3 stream (7) consisting of propane and propylene; and (iii) Off gas stream (8) consisting of hydrogen, methane, ethane, ethylene, carbon monoxide and carbon dioxide in the De-Propanizer section (B);d) separating butanes (3), butene (9) and heavy hydrocarbons (10) from C4+ stream (6) in the De-Butanizer and C4 Splitter section (C) and recycling back the butane (3) to the ODH reactor (A) for further conversion;e) separating the C3 stream (7) into petrochemical grade propylene (11) and propane rich stream (4) in the C3 Splitter section (D) and recycling back propane rich stream (4) to the ODH reactor (A) for further conversion;f) routing the Off gas stream (8) from the De-Propanizer section (B) to the De-Methanizer section (E), wherein the Off gas stream (8) gets separated into two streams: (i) a stream consisting of ethane, ethylene and carbon dioxide (12) and (ii) a stream consisting of hydrogen, methane and carbon monoxide (13);g) routing the stream consisting of ethane, ethylene and carbon dioxide (12) to the C2-Splitter section (F), wherein the stream (12) is separated into petrochemical grade ethylene (15) and a stream rich in ethane and carbon dioxide (14);h) routing the stream rich in ethane and carbon dioxide (14) back to the ODH reactor (A) for recycling of ethane and carbon dioxide;i) routing the stream (13) coming from the De-Methanizer section (E) consisting of hydrogen, methane and carbon monoxide to Hydrogen Generation Unit (HGU) Shift Reactor(G) and mixing the stream (13) with effluent gases (17) coming from Hydrogen Generation Unit (HGU) Reformer Reactor (H),wherein the HGU Reformer reactor (H) is fed with methane, naphtha or other suitable hydrocarbon feed and steam (16), wherein the hydrocarbon feed and steam (16) undergo a reforming reaction at elevated temperatures of 750-850⁰C and produces effluent gas (17) comprising of hydrogen, carbon monoxide, carbon dioxide and un-reacted methane and steam and traces of nitrogen;j) converting the carbon monoxide from the effluent gases (17) and from the stream (13) into hydrogen and carbon dioxide in presence of steam in the HGU Shift reactor (G);k) routing product gases (18) from the HGU Shift reactor (G) consisting of hydrogen, carbon dioxide and rest carbon monoxide, methane, steam and nitrogen to Pressure Swing Adsorption (PSA) section (I) of HGU to separate pure hydrogen (19);l) routing a portion of off gases from PSA (20) having a composition of carbon dioxide 80-95 wt%, carbon monoxide 0.1-5wt%, methane 0.1-10wt%, hydrogen 0.1-5wt% and traces of steam and nitrogen to a furnace of the HGU reformer reactor (H) as fuel (21); andm) routing remaining portion of the PSA Off gas (20) to the ODH reactor (A) as a carbon dioxide source to supplement the recycle carbon dioxide rich stream (14) coming from the C2 Splitter section (F).The process as claimed in claim 1, wherein the fresh hydrocarbon alkane feed (1) is selected from the group consisting of ethane, propane, n-butane, iso-butane, or any mixture thereof.The process as claimed in claim 1, wherein the carbon dioxide rich stream (2) is a PSA off gas stream (22).The process as claimed in claims 1 or 2, wherein conversion of the propane to propylene is 20-40 wt% and selectivity of the propylene is 85-95 wt%.The process as claimed in claim 1, wherein the ODH reactor (A) is a fixed bed tubular reactor, a fluidized bed reactor, a moving bed reactor, or any combination thereof.The process as claimed in claim 1, wherein the dehydrogenation catalyst comprises of metal oxides, and wherein metals in the metal oxides are selected from the group consisting of VB, VIB, VIII, and alkali metals group.The process as claimed in claim 1, wherein a molar ratio of the fresh hydrocarbon alkane feed (1) to the carbon dioxide fed to the ODH reactor in step a) is in a range of 0.3-0.8.The process as claimed in claim 1, wherein gas hourly space velocity (GHSV) of a mixture of the fresh hydrocarbon alkane feed (1) and the carbon dioxide rich stream (2) in step a) is 200-2500 h-1.The process as claimed in claim 1, wherein diluent (N2) concentration in a mixture of the fresh hydrocarbon alkane feed (1) and the carbon dioxide rich stream (2) in step a) is 0.01-30 vol%.

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