SEPARATION OF HYDROGEN FROM HYDROCARBONS UTILIZING ZEOLITIC IMIDAZOLATE FRAMEWORK MATERIALS

CATEGORY: HYDROGEN
PATENT
SEPARATION OF HYDROGEN FROM HYDROCARBONS UTILIZING ZEOLITIC IMIDAZOLATE FRAMEWORK MATERIALS
European Patent EP2259861
Inventors:
NI, Zheng (11 School StreetApt. 49, Clinton, NJ 08809, US)
Paur, Charanjit S. (225 Main Street, Apt. 112South Bound Brook, New Jersey 08880, US)
Kortunov, Pavel (155 Broad StreetApt. 25, Flemington, NJ 08822, US)
Zengel, John (40 Overlook Drive, Clinton, NJ 08809, US)
Deckman, Harry W. (2 Woods Edge Court, Clinton, NJ 08809, US)
Application Number:
EP20090713131
Publication Date:
02/08/2012
Assignee:
ExxonMobil Research and Engineering Company (1545 Route 22 East P.O. Box 900, Annandale, NJ 08801-0900, US)
Abstract
The present invention relates to the selective separation of hydrogen (“H2”) hydrocarbons in streams containing both hydrogen and hydrocarbons (e.g. methane, ethylene, ethane, propylene, propane, etc.) utilizing a zeolitic imidazolate framework (“ZIF”) material. Preferably, the stream to be separated is fed to the present process in a substantially gaseous phase. In preferred embodiments, the current invention is utilized in either a pressure swing adsorption process, a temperature swing adsorption process, or a membrane separations process to separate hydrogen from hydrocarbons present in hydrogen production streams or petrochemical/petroleum refining product streams and intermediate streams.
FIELD OF THE INVENTION
The present invention relates to the selective separation of hydrogen from hydrocarbons in streams containing both hydrogen and hydrocarbons utilizing a zeolitic imidazolate framework material. Preferably, the stream to be separated is fed to the present process in a substantially gaseous phase. In preferred embodiments herein, the zeolitic imidazolate framework material is incorporated into a Swing Adsorption unit, more preferably a Pressure Swing Adsorption unit or a Temperature Swing Adsorption unit from Which a hydrogenrich stream is produced from a feedstream containing both hydrogen and hydrocarbon compounds.
BACKGROUND OF THE INVENTION
Gas separation is an important process utilized in various industries, particularly in the production of fuels, chemicals, petrochemicals and specialty products. A gas separation can be accomplished by a variety of methods that, assisted by heat, solids, or other means, generally exploits the differences in physical and/ or chemical properties of the components to be separated. For example, gas separation can be achieved by partial liquefaction or by utilizing a solid adsorbent material that preferentially retains or adsorbs a more readily adsorbed component relative to a less readily adsorbed component of the gas mixture, or by several other gas separation techniques known in the industry. One such commercially practiced gas separation process is pressure swing adsorption (“PSA”). PSA processes, When operated under certain conditions, allow a selective component or components in a gas mixture to be preferentially adsorbed Within the pore structure of porous adsorbent materials relative to a second component or components in the gas mixture. The total amount adsorbed of each component in the material (i.e., the adsorption capacity) and the selectivity of the adsorption for a specific component over another component may often be improved by operating the process under specific pressure and temperature conditions since both pressure and temperature influence the adsorption loading of the components to a different extent. The efliciency of the PSA process may be further improved by the implementation of processing steps, such as the use of purge stream(s) that have optimally chosen composition, pressures and temperatures. However, relatively few adsorbent materials have separation selectivities, adsorption capacities and other beneficial properties (such as chemical and physical inertness and durability) so as to be able to function as commercially viable and cost-efficient adsorbents in a PSA process.
Some adsorbent materials are able to adsorb a greater amount of one component than another component under certain conditions. Certain components may not be selectively adsorbed or may not be adsorbed to an acceptable level that would lead to an economically viable process. However, if sizable differences in adsorption properties exist for selective components in an adsorbent material, PSA processes can be used to effectively separate certain component gases from a mixture. For example, if a gas mixture such as air is passed at some pressure and temperature through a vessel containing an adsorbent material that selectively adsorbs more oxygen than nitrogen, at least a portion of the oxygen contained in the feedstream Will stay in the adsorbent and the gas coming out of the vessel Will be enriched in nitrogen. When the bed reaches a selected fraction of its total capacity to adsorb oxygen, it can be regenerated by various pressure swing techniques, thereby releasing the adsorbed oxygen (and any other associated gas components), which can then be captured and isolated as a separate product stream. The adsorbent material which has now been “desorbed” of the oxygen can then be reutilized and the various steps of the PSA process cycle are repeated so as to allow a continuous operation.
However, finding suitable materials that specifically discriminate between diflicult to separate gases in both an eflicient and effective manner (that is that they have both good separation selectivity and a high adsorption capacity) are not easily found. Additionally, many adsorbent materials known in the art do not hold up well to the additional components in the streams or are unable to sustain the severe pressure and/or temperature conditions, including cyclic conditions, required by the processes. Therefore, commercially suitable, and more importantly, commercially valuable adsorbent materials are not very readily available. Researchers in the industry continually look for improved adsorbent materials, process configurations and operating conditions to make these separation processes economically viable.
An early teaching of a PSA process having a multi-bed system is found in U.S. Pat. No. 3,430,418 wherein a system having at least four beds is described. This ’418 patent describes a cyclic PSA processing sequence that includes in each bed: (1) higher pressure adsorption With release of product eflTuent from the product end of the bed; (2) co-current depressurization to intermediate pres sure With release of void space gas from the product end thereof; (3) countercurrent depressurization to a lower pressure; (4) purge; and (5) repressurization. The void space gas released during the cocurrent depressurization step is commonly employed for pressure equalization purposes to provide purge gas to a bed at its lower desorption pressure. Another conventional PSA processes using three sorbent beds is disclosed in U.S. Pat. No. 3,738,087.
Another industrially important gas separation process is temperature swing adsorption (“TSA”). TSA processes, when operated under certain pressure and temperature conditions, allow some components to be selectively adsorbed over others within the pore structure of an adsorbent material. In this process, a stream containing components to be separated flows through an adsorbent material wherein one or more of the components are selectively adsorbed over another component or components. An effluent stream, reduced in concentration of the selectively adsorbed component(s) is obtained during this adsorption “stage” or “step” of the TSA process. In this process, after the adsorbent material has adsorbed a certain amount of the desired component(s), the temperature of the adsorbent is increased, and the selectively adsorbed component(s) is released, or desorbed from the adsorbent materials and can be collected separate from the eflTuent stream in this step of the overall TSA process cycle. By cyclically swinging the temperature of adsorbent beds, TSA processes can be used to separate components in a mixture when used With an adsorbent that selectively adsorbs one or more of the stream components in the feed mixture relative to one or more different stream components comprising the feed mixture.
PSA and TSA processes do not need to be mutually exclusive. A combined PSA/TSA process may be utilized, for example, by increasing the temperature of the adsorbent materials during the loWer pressure purge step of a conventional PSA process to improve the desorption of the selectively adsorbed component(s) in the process. The bed temperature can then be reduced (or alloWed to be reduced) during the adsorption portion of the PSA cycle to improve the adsorption characteristics and/or adsorption capacity of the material.
Besides using pressure and temperature to regenerate the adsorption bed, the adsorbent can be regenerated With a purge that is floWed through the adsorbent bed in a manner that displaces adsorbed molecules from the adsorbent. Processes that are conducted With this type of adsorbent regeneration technique are often called partial pressure purge displacement processes (“PPSA”). Processes such as PSA, TSA, purge displacement, and combination thereof are referred to herein as sWing adsorption processes. These sWing adsorption processes can be conducted With rapid cycles (i.e., cycles of short duration) in Which case they are referred to as rapid cycle thermal sWing adsorption (RCTSA), rapid cycle pressure sWing adsorption (RCPSA), and rapid cycle partial pressure sWing or displacement purge adsorption (RCPPSA) technologies.
Additionally, membrane separation processes can be used for the separation of gas components in a mixture. In a membrane separation process, one or more components of the mixed stream contact one side of a membrane material and a portion of the mixed stream permeates through the membrane and is retrieved from the other side of the membrane material as a “permeate” stream. In this process, the permeate stream has a higher concentration (in mole %, Weight %, or volume % as defined by the process) of a select component than the mixed stream that initially contacts the membrane. A “retentate” stream is also obtained from the first side of the membrane Which has a loWer concentration (in mole %, Weight %, or volume % as defined by the process) of a select component than the mixed stream that initially contacts the membrane. In this manner, a separation of components is made resulting in a higher value for the tWo separated streams (i .e., the retentate and the permeate streams) than the original mixed stream that is fed to the membrane separations process. The physical conditions on the permeate side of the membrane (for example pressure, temperature, and purge conditions) are chosen so that there is a gradient of chemical potential across the membrane that is favorable to drive the select component from the feed side to the permeate side of the membrane.
There is a need in the art for improved sWing adsorption and/ or membrane processes utilizing adsorbent materials for the selective separation of hydrocarbon components. In particular, there is a need in the art for improved sWing adsorption and/ or membrane processes utilizing adsorbent materials for the selective separation and removal of hydrogen from streams containing hydrogen and hydrocarbons. Preferably the streams are associated With a petroleum or petrochemical process and/or associated products.
United States Patent Publication No. US2007/020203 8A1 discloses a family of materials Which shall be referred to herein as zeolitic imidazolate frameWorks (or “ZIF”s) materials. This publication describes in detail the synthesis and structural and pore volume characterization of various ZIF materials. It includes the loW temperature physisorption characterization (N2 and H2 at 77K andAr at 87K) of selected ZIF structures but it does not disclose adsorption properties of these materials at pressure and temperature conditions that
Would be relevant to separation processes of gases and hydrocarbons of interest in industrial applications.
SUMMARY OF THE INVENTION
The present invention is a separation process utilizing ZIPcontaining materials to effectively separate hydrogen from hydrocarbons in process feedstreams comprised of both components. Preferably the process feedstream is associated With a petroleum orpetrochemical process and/ or associated products. As utilized herein, the term “hydrogen” (or equivalent term “H2”) is defined as molecular hydrogen With the chemical composition H2. As utilized herein, the term “hydrocarbon(s)” (or “HC”) is defined herein as any molecular compound containing at least one carbon atom and at least one hydrogen atom.
In accordance With one embodiment of the present invention there is provided a process for separating H2 from a process feedstream, comprising:
a) contacting an adsorbent material comprised of a zeolitic imidazolate frameWork material With a process feedstream comprising H2 and at least one hydrocarbon compound at a first pressure and first temperature;
b) adsorbing at least a portion of the hydrocarbon compound in the adsorbent material;
c) producing a H2-rich product stream, Wherein the H2-rich product stream has a higher concentration of H2 by mol % than the process feedstream; and
d) producing a H2-lean product stream at a second pressure and second temperature, Wherein the H2-lean product stream has a loWer concentration of H2 by mol % than the process feedstream;
Wherein the zeolitic imidazolate frameWork material has a frameWork structure Wherein each vertex of the frameWork structure is comprised of a single metal ion and each pair of connected adjacent vertices of the frameWork structure is linked by nitrogen atoms of an imidazolate anion or its derivative, and Wherein the zeolitic imidazolate frameWork material has an adsorptive loading ratio for the hydrocarbon compound over H2 of at least 5.
In a more preferred embodiment of the present invention the zeolitic imidazolate frameWork material is selected from ZIF-1, ZIF-7, ZIF-8, ZIF-9, and ZIF-1 1.
In another preferred embodiment, the C2+ hydrocarbon compound is selected from CH4 (methane), C2H4 (ethylene), C2H6 (ethane), C3H6 (propylene), C3H8 (propane), C4H8 (1-butene), and C4H 10 (n-butane).
In accordance With one embodiment of the present invention there is provided a process for separating H2 from a process feedstream, comprising:
a) contacting a first side of a membrane comprised of a zeolitic imidazolate frameWork material With a process feedstream comprising H2 and at least one hydrocarbon compound at a first pressure and first temperature;
b) retrieving a first permeate stream from a second side of the membrane at a second pressure and second temperature, Wherein the first permeate stream consists of components that selectively permeate through the membrane and the first permeate stream has a loWer concentration of H2 by mol % than the process feedstream; and
c) retrieving a first retentate stream;
Wherein the zeolitic imidazolate frameWork material has a frameWork structure Wherein each vertex of the frameWork structure is comprised of a single metal ion and each pair of connected adjacent vertices of the frameWork structure is linked by nitrogen atoms of an imida
zolate anion or its derivative, and wherein the zeolitic imidazolate framework material has an adsorptive loading ratio for the hydrocarbon compound over H2 of at least 5.
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