Patent Application
20230405520
This relates to a process for CO2 capture, and in particular, a process using a membrane system.
A change in global or regional climate patterns, in particular a change apparent from the late 20th century onwards, has been attributed largely to the increased levels of atmospheric carbon dioxide (CO2) produced by the modern industrial activities. To reduce the levels of CO2 in the atmosphere, many technologies have been developed in past decades for carbon capture and sequestration (CCS), including electrochemical processes.
Currently, a broad range of electrochemical processes are used in industry for inorganic as well as organic compound production. One of the issues that had to be solved on the way from the conception and development of many electrochemical processes to their industrial use was the separation of the anolyte and the catholyte in addition to the energy efficiency and the purity of the products. This was mainly motivated by the need 1) to increase selectivity, and 2) to exclude the participation of precursors or intermediate products in undesired reactions at the electrode with opposite or even the same polarity. At present, different types of porous separators (diaphragms) and semi-permeable (ion-exchange or ion-selective) membranes are developed for this purpose. In the case of membranes, selectivity has become one of the key factors of industrial electromembrane processes with the focus on a high production capacity. Another important factor on the economic feasibility of an electromembrane process is the electrical energy requirements given in kWh/ton of product. This is directly connected to the membrane characteristics, the operating voltage, the electrical charge connected with the current efficiency of the process. The operating voltage is based on the thermodynamic cell potential, overpotential of the cathodic and anodic reaction, and potential loss caused by resistance of the electrolyte and the separator (the membranes) which relates to process and energy efficiency.
Historically, homogeneous polymeric membranes represent the type first implemented in industrial practice and are probably the most widespread type of ion-selective membranes up to the present day. Since 1940, high interest in industrial applications led to the first development of synthetic ion-selective membranes on the basis of phenol-formaldehyde polycondensation, and since then the electromembrane processes have become an important segment of electrochemical technologies in the industrial applications. This is primarily due to the advantages that electromembrane processes have over competing technologies, brought about by modifications to this process that allow them to require lower energy demands, reduced impact on the environment, and making possible a higher product purity and quality.
Most of the traditional membranes act on the principle of pore dimension or selective non-electrostatic interaction of transport species with the membrane materials.
Several gas separation technologies may be used for CO2 capturing from the various mixed gas, namely, membrane, absorption, adsorption and cryogenic. Conventional absorption technology using amine-based solvents has been in use on an industrial scale for decades, but the challenge is to recover the CO2 complex mixed gas with a minimum energy penalty and at an acceptable cost. The traditional amine-based and many other CCS systems have been estimated to consume approximately 30% of the power plant capacity, with corresponding coal fired power generation cost increasing by 50-90%. On the other hand, many cases demonstrated that membrane-based separation methods may be employed in a energy-efficient manner than the conventional and heat-driven separations. Membrane-based separation may use up to 90% less energy than its distillation counterpart. Thus, the membrane offers great advantages as a green technology due to its lower energy consumption, no chemical solvent usage, simple operation and maintenance, and high reliability. In addition, membrane systems can be modular, hence easy for expansion and scale up, and it have a compact module design which is crucial for industrial retrofit operation.
Among membrane technologies applied in industrial applications, polymers with intrinsic microporosity (PIM) have been successfully employed in gas selective membrane. Most traditional polymeric materials have a trade-off relationship according to the Robeson plot. The more flexible the polymer chains, the higher the permeability, since the chain dynamic can affect the transport properties and the separation performance, but this is usually coupled with robustness and durability issues.
Attempts to integrate functional inorganic material to improve the selectivity and permeability of polymeric membrane gains limited success in past decade. The key issues hindering separation performance are the compatibility between the inorganic and polymeric components and the partial blockage of the sieve micropores. Recent advances related to introducing mutually interactive functional groups to the polymer and the molecular sieve have led to significant improvement on both permeability and separation performance.
According to an aspect, there is provided an integrated membrane process and system that may be used to simultaneously capture CO2 from mixed gas and then convert CO2 into various carbon-negative industrial chemicals. The process and integrated system make use of three engineering technologies, namely, a Selective Ion Film (SIF) membrane apparatus (SMA), a Hybrid Nano-Fibre membrane (HNF) reactor system (CCC System), and an operating system.
In some aspects, a specially engineered SMA may be used that includes sodium selective membranes with SIF technology and enhanced PTFE formula to improve the sodium ion (Na+) flux and selectivity. Such a SIF may possess strong hydrophobic characteristics and dense ion interactive pathways, which provide the high flux for sodium ion and minimizes the anions such as chloride from diffusing across.
In some aspects, the operating system may include a Membrane Operation (MO) unit, a Chemical Technology (CT) unit, a System Engineering and Operation (sEO) unit and an Expert AI Module (eAi), which may be linked to an Engineering Process & Operation Database such as by using 5G Tech. MO and CT modules operate the membrane systems under the designed operation conditions, while sEO and eAi modules function as engineering experts with self learning capability to continue the optimization of the system using the operation process database.
In some aspects, the CCC system may include a feed conditioner, first and second HNF selective membrane reactor systems (SMR A and SMR B), the operating system, and an off-gas recycling system. The feed conditioner is used to condition and store the CO2 capturing agent from SMA, which may improve the efficiency, minimize the fouling of the membranes, extend the membrane life and reduce the operation cost.
In some aspects, the SMRs may include modular membrane cassettes, a membrane cleaning system, a Trans-Membrane Pressure (TMP) monitoring and operating system, a CO2 gas analyzer and a pH/temperature analyzer. Inside the membrane cassette, the CO2-selective HNF membranes separate CO2 from the nitrogen dominant mixed gas. HNF technology utilizes a PVDF (polyvinylidene difluoride) formula enhanced with nano-technologies and a formulation process that forms an Asymmetric structure with intrinsic microporosity. The formula and engineering process described herein form structures of the membranes that may have improved selectivity while increasing the permeability of CO2 gas in CO2/N2/O2 gas mixture.
The CCC system may achieve a 99.9% carbon (CO2) capture rate, while simultaneously producing carbon negative chemicals such as NaHCO3, Na2CO3 etc. The CCC system may be operated in an effective temperature in the range of 5 to 50° C. and a pressure in the range of 35 to 350 kPa.
According to an aspect, there is provided a carbon capture system comprising a SIF apparatus and an operating system used to capture CO2 from various mixed gas that may contain N2, O2, CH4, H2 in different combinations and with the CO2 concentration varying from 5 to 70 wt % in the mixed gas. Various NaCl containing brine or sea water may be used as the raw material for manufacturing the CO2 capturing agent. A selective ion film may be incorporated into the SIF membrane with a PTFE formula that allow for a desired level of selectivity and flux, and a suitable tolerance to concentrations of alkaline solution and chlorine gas oxidation.
According to an aspect, a SMA is provided with an electromembrane process and 3D structured surface electrodes that work with the SIF membranes to produce a CO2 capturing agent while simultaneously producing other products, such as Cl2, chloroacetic acid, CaCl2, H2, etc. The SMA may operate at a cell voltage of up to 3.8 V and a current density of up to 7000 A/m2, which may be controlled and optimized by the operating system to improve current efficiency. The CO2 capturing agent generated by the SMA may have 99.9% purity or more and may have an effective concentration in the range of 1.3 wt % to 4.2 wt %. A suitable purity and concentration may have an effect on the efficiency and life expectancy of the membrane in the CCC system.
The membrane may have an effective selectivity range of between 57 and 109 of CO2 relative to N2, and a flux in the range of 328 to 394 GPU in addition to high resistance to various chemicals, aging, and plasticization. The membrane may have an optimal flux around 350 GPU at the selectivity about 102 when the operation pressure is around 20 psi while the critical operation pressure ranges from 15 to 25 psi.
The operating system may include four or five modules and may communicate over a wired or wireless link (such as 5G functional link) and serves as the center of operation, optimization and remote control. The control system may be expanded as needed due to its modular structure design. The control system (OS) may be used to optimize the operation of one membrane train or any number of trains within a desired set of criteria and may be used to rotate the membrane trains to balance the membrane operation life. This allows the system to be scaled up depending on the requirements of the industrial application. The operating system may allow the remote operation and diagnosis of the process and system by experts nationally or globally.
The CCC system may use the operating system and the integrated process that may be engineered to reliably use either HNF membranes or other similar types of membranes. The CCC system may employ a compact modular engineering design of the membrane elements and membrane trains and may be engineered to have up to sixteen (16) trains. The CCC system may be engineered into different sizes and scales with an affordable and competitive industrial system. The compact modular engineering design and system flexibility may facilitate a retrofit application. With a suitably-designed membrane, the operation pressure of the CCC system may be varied from 5 to 50 PSI and the flux and selectivity may be optimized using the operating system enabling the CCC system to handle different peaking conditions while keeping the desired CO2 capturing rate and optimal energy efficiency. Specifically, the CCC system may be sufficiently flexible to continue treatment with as little as 5% of the designed capacity, and as much as twice the designed capacity under peaking conditions.
The CCC system may be designed to capture and convert CO2 in various gas mixtures including, but not limited to, a typical coal-fired flue gas, such as a gas stream with the following composition:
In some examples, a CO2 recovery rate of 99.9% may be achieved while producing about 1.9 tonne NaHCO3/tonne CO2 captured by the CCC system.
The two-stage design of the CCC system may be used to achieve a CO2 recovery rate of 99.9% or more with a relatively high tolerance on the variation of CO2 concentration of the feed gas stream, such as in the range of 5 to 70%.
The CCC system may use different raw materials, such as sea water and various types of brines such as Na2SO4, NaNO3, NH4Cl, etc. to effectively capture CO2 from various mixed gas, and the final products can be various valuable carbon negative industrial chemicals such as, but not limited to, NaHCO3, Na2CO3, (NH4)2CO3, (NH4)HCO3, Cl2 gas, Chloroacetic acid, CaCl2, H2 or liquid H2, etc. In some examples, the brine may be based on Na, NH4, or other components that are able to produce a carbon capturing agent. This flexibility may be enhanced using the operating system and SMA. In some examples, NaHCO3 solutions in concentrations ranging from 50% to 99.5% saturated solution may be obtained as the final product to meet various industrial requirements. The NaHCO3 in the saturated solution may be crystalized into solid NaHCO3 or Na2CO3 products that meet the standard of membrane grade quality.
These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purposes of illustration only and are not intended to be in any way limiting, wherein:
There will now be described a process and integrated membrane system, identified generally by reference number 10, that captures CO2 and converts some or all of the CO2 into various carbon-negative industrial chemicals.
Referring to
Referring to
As noted above, the components are mixed together in first conditioner 108 to form a conditioned feed solution 112. The mixing time may be about 1 to 3 minutes of continuous mixing prior to adding conditioned feed solution 112 into an SMA tank 114 or other suitable container using a pump 116. When an appropriate current is applied to electrodes 118, sodium and hydrogen pass through a membrane 120 in SMA tank 114, while chlorine and other components do not. A capturing agent or capturing agent precursor 30 is produced for use in Carbon Capture and Conversion (CCC) System 200 depicted in
SMA system 100 may include a system of asymmetric SIF membranes and electrodes that is controlled with the operating system 14. As SIF membranes may be relatively thin and fragile, they may be reinforced with polytetrafluoroethylene (PTFE) to increase their mechanical strength for wide industrial applications. In a traditional electromembrane process, the voltage efficiency of the process is mainly caused by activation overpotential of the anode reaction and ohmic drop on the membrane. Using such an SIF membrane, the current efficiency loss mainly accounts for the transport of hydroxyl ions from the cathode to the anode compartment due to joint diffusion and migration. When enhanced with PTFE, the SIF technologies may form a strong ion charged surface film on top of the PTFE, thus reducing the flow of hydroxyl and chloride ions, improving the energy efficiency while producing a CO2 capturing agent with relatively high purity.
The SIF membranes with dense ion surface may be used to provide a selective pathway for sodium (Na+) ions, minimize anions such as chloride (CI−) or other anions from diffusing across SIF and decrease in hydroxyl ion flow back to the anode inside the cathode chamber, and decrease the membrane resistivity; in other words, the SIF membrane may be designed to keep the OH− and Cl− ions away from the membrane surface to reduce the potential polarization on the SIF surface, and enhance the flux of sodium (Na+) ion selectivity that increases the purity and concentration of the capturing agent in an energy-efficient manner.
The conditioned solution from conditioner 108 is then fed into an anode chamber 122 inside the SMA tank 114. To avoid concentration polarization around an anode 124, conditioned solution 112 may be uniformly distributed around anode 124 in anode chamber 122. The ionic contact between the SIF membrane 120 and the electrode results in the formation of a three-dimensional active layer, providing a contacting surface and ionically conductive pathways among the electrodes 118, SIF membrane 120 and the electrolyte. This may improve the electric efficiency and life of anode 124.
Depending on the requirements and operation from the down stream process, the voltage applied to electrodes 118 may vary, such as from 1.5V to 3.8V, and which may be continuously optimized with an operating system 14 during the operations. As a result, the Cl− ion in anode chamber 122 is converted into Cl2 gas 126 and collected from the top of Anode chamber 122. The quality of chlorine gas 126 may be sufficient to be liquified as liquid chlorine product. If desired, chlorine gas 126 may also be converted into various carbon negative chemicals, such as hypochloric acid, chloroacetic acid, or dissolved into a CaO solution to form CaCl2. Any residue from anode chamber 122 may be continuously removed and properly disposed of. Carbon negative compounds (or chemicals) include those compounds that are produced from carbon dioxide and stable under normal temperature and pressure conditions.
A cathode compartment 130 inside SMA container 114 may be initially fed with a 0.1% wt water solution of sodium hydroxide, with a pH of about 14. Under the applied voltage, the water solution is initially reduced to gaseous hydrogen and hydroxyl ions simultaneously at a cathode 132:
2H2O+2e−=H22OH−EO(H2O/H2)=−0.828 V
Hydrogen gas 134 generated in the Cathode chamber 130 may be collected from the top of cathode chamber 130, then compressed or liquified for industrial use. In some examples, the purity of hydrogen gas 134 may exceed 99.95%.
With the applied voltage, the Na+ ion in anode chamber 122 is pulled to SIF membrane 120, driven through SIF membrane 120 and into cathode chamber 130, where the Na+ ion is reacted with OH− ions in the conditioned agent to form CO2 capturing agent 30. An optimum concentration of capturing agent 30 in cathode chamber 103 may be controlled by operating system 14, depending on the requirements from the CCC system 200 operation. Inside SMA tank 114, an appropriate design of SIF 120 helps produce a high quality of CO2 capturing agent 30 in an energy efficient manner.
The sEO and eAi systems 20 and 22 may also enable the SMA 100 and the CCC system 200 to be operated remotely, which may allow the operator to remotely diagnose the system problems and fine tune the operation to improve the operation efficiency and reliability.
With the optimization from operating system 14, the energy efficiency of SMA system 100 may be improved relative to electrolysis with a conventional process such as a porous diaphragm. Safety improvement in SMA system 100 represents an additional important aspect.
In the depicted example, CO2 capturing agent 30 from first stage 12 is conditioned with a second conditioning agent 44 in feed conditioner 32, and then fed into first SMR 34, while the mixed CO2 gas from second SMR 36 with the lowered CO2 concentration flows through the membrane in first SMR 34 along the membrane's internal channel (not shown). Second conditioning agent 44 may be based on sodium and hydroxide ions or related compounds obtained from SMA 100. Second conditioning agent 44 may also include other additives that improve stability, improve efficiency, or improve the life expectancy of the membrane. In some examples, NaHCO3 may be included as a seeding compound. Water may be added as needed. While the number of reactors may vary, the depicted example includes first and second SMRs 34 and 36 separated by a baffle 50, and a weir 52 adjacent to the outlet of second SMR 36. Baffle 50 and weir 52 may be provided to control the fluid flow and therefore the reaction as the mixed capturing agent from first SMR 34 flows into second SMR 36 at the bottom by the gravity. As the CO2 exits membrane 46, it reacts with the capturing agent to produce a recoverable compound, such as NaHCO3. The membrane maintenance and recovery cleaning systems 40 may be automatically operated and controlled by the operating system. The number of SMR stages may be increased or decreased, depending on the materials available and the desired results. It will also be recognized that, if an alternative carbon capturing agent is obtained, CCC system 200 may be operated without SMA 100.
Depending on the overall operation, the concentration of CO2 in the mixed gas from second SMR B may vary from 1 to 18.5%. In case of the flue gas from a power plant, an example of a typical composition of the raw flue gas may be as follows:
With the CO2 concentration varying from 8.5% to 13.8% in the raw mixed gas, the feeding CO2 concentration to SMR A may vary from 3.1 to 6.9% and the recovery rate may be greater than 99.9%. this may be achieved through optimization of the operating parameters, and/or by recycling the mixed gas, such as from first SMR 34 back to second SMR 36.
When the CO2 mixed gas flows through the internal channel of the membranes of SMRs 34 and 36, the CO2 is selectively permeated through the membranes from the inside to the outside surface of the membranes. The CO2 at the surface of the membranes reacts rapidly with the high concentration of the fresh CO2 capturing agent. The large reacting surface provided by the membranes and fast chemical reactions may allow the capturing agent to capture more than 99.9% CO2 permeated through the membrane. Under the control of the operating system 14 (as shown in
The partially-used CO2 capturing agent 30 from first SMR 34 flows into second SMR 36 at the bottom by the gravity and continues to capture CO2 at the surface of the membranes inside second SMR 36 while the raw CO2 mixed gas such as the flue gas from the power plant flows through the membranes from second SMR 36 to first SMR 34.
SMR uses HNF membranes, which are hybrid nano-fibre membranes containing specially engineered nano-particles and employing an asymmetric structure formed with an advanced polymeric formula. Compared to many traditional polymeric membranes, the specially engineered nano-particles, the enhanced compatible polymeric formula, and advanced engineering process allows novel structures to be formed that have better selectivity and increased permeability for CO2 in a CO2/N2/O2 gas mixture, while maintaining the advantages of mechanical stability of PVDF polymeric membranes and the possibility of large-scale production.
Depending on the composition of the raw mixed gas and operation conditions, the ratio of membranes in second SMR 36 to that in first SMR 34 may be engineered to vary from 0.8 to 3.8 based on final process requirements. The membranes in SMRs 34 and 36 may be functionalized to enhance the separation of CO2 from the mixed gas using the nano-particles with specific functional groups, such as the functional groups shown in
The selective membrane reactors 34 and 36 in CCC system 200 may contain membrane modules, cassettes with 24 to 64 modules, any may be connected to, or include, online analyzing and monitoring systems, and integrated maintenance and recovery systems 40 that may be controlled and operated by the operating system 14. The membrane cassettes (not shown) may be designed as a basic modular element, and engineered into an independent train. In some examples, between 2 and 16 independent trains may be used in CCC system 200 depending on the mass flow of a CO2 mixed gas. Therefore, the modular engineering design may be easily applied for various industrial scales. Furthermore, using a modular engineering design and the operating system, CCC system 200 allows rapid startup and each train may be easily isolated from the system for troubleshooting and repairing. In some examples, CCC system 200 engineering may allow various membranes besides the HNF membranes to be utilized for CO2 capturing and conversion.
The membranes used in SMRs 34 and 36 may be manufactured with an enhanced thick PVDF layer that support the strength and rigidity of the membrane. Nano particles may be embedded into the matrix with the intrinsic micropores forming a flexible polymeric structure that may be regulated with operational pressure and other operational parameters. The pores of the membrane may also be referred to as void volumes, and may be functionalized with nano-particles. This approach may be used to increase the amount of the free volume in the membrane matrix. As a result, the CO2 gas flux is increased and may be regulated according to the operation and feeding mass flow of CO2 mixed gas.
As shown in
The two-stages of CCC system 200 discussed herein may be used to effectively capture CO2 from various gas mixtures that may then be converted into carbon negative chemicals for various industrial applications. CCC system 200 may include one or more of the following aspects.
In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the elements is present, unless the context requires that there be one and only one of the elements.
The scope of the following claims should not be limited by the preferred embodiments set forth in the examples above and in the drawings but should be given the broadest interpretation consistent with the description as a whole.
| Number | Date | Country | |
|---|---|---|---|
| 63352367 | Jun 2022 | US |
