DYNAMIC MEASUREMENT OF AQUEOUS AMINE CARBON DIOXIDE ABSORPTION

A system may comprise a heat spreader with a sample holder, an amine solution in the sample holder; a temperature sensor configured to measure a temperature of the amine solution; a heating and cooling device in the spreader, a gas flow valve connected to a gas inlet tube, wherein an end of the gas inlet tube sits below a surface level of the amine solution; and a CO2 (carbon dioxide) sensor connected to a gas outlet tube.

BACKGROUND

Aspects of the present disclosure relate to the dynamic measurement of aqueous amine carbon dioxide absorption kinetics parameters.

Carbon capture and sequestration is a central focus of efforts to reduce the rate of climate change due to greenhouse gas accumulation in the atmosphere.

Carbon capture relies on the ability to separate carbon dioxide (CO2) gas from other gasses at typically low concentrations (15% to 30%) and purify the gas to 90% or better.

One method of carbon capture involves the use of aqueous amine solutions to absorb CO2 from flue gas streams at low temperature and concentration. The solution is then heated, and the absorbed CO2 is released at high concentration suitable for subsequent liquefaction or downstream use.

BRIEF SUMMARY

The present disclosure provides a system and methods of dynamic measurement of aqueous amine carbon dioxide absorption kinetics parameters. In some embodiments, the system includes a heat spreader with a sample holder; an amine solution in the sample holder; a thermocouple configured to measure a temperature of the amine solution; a heating and cooling device in the spreader; a gas flow valve connected to a gas inlet tube, wherein an end of the gas inlet tube sits below a surface level of the amine solution; and a CO2 (carbon dioxide) sensor connected to a gas outlet tube.

Some embodiments of a method comprises placing an amine solution in a sample holder; placing the sample holder in a receptacle in a heat spreader; bringing a temperature of the amine solution to a desired temperature value; valving a specified gas volume with a CO2 concentration to the amine solution for a period of time sufficient to saturate the amine while monitoring a CO2 exhaust concentration using a CO2 sensor; thermal cycling the amine solution by alternately heating and cooling the amine solution for fixed time periods and a number of cycles; and monitoring the CO2 exhaust concentration.

Some embodiments of a method comprises determining, based on a result of a CO2 (carbon dioxide) absorption test, a capacity of an amine solution and an initial concentration of absorbed CO2; determining first order reaction kinetics parameters of the amine solution; determining a change in amine concentration verses time; and modifying a manufacturing process based on the first order reaction kinetics parameters of the amine solution and the change in amine concentration verses time.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to dynamic measurement of aqueous amine carbon dioxide absorption kinetics parameters. While the present disclosure is not necessarily limited to such applications, various aspects of the disclosure may be appreciated through a discussion of various examples using this context.

Carbon capture and sequestration is a central focus of efforts to reduce the rate of climate change due to greenhouse gas accumulation in the atmosphere. Carbon capture relies on the ability to separate carbon dioxide (CO2) gas from other gasses at relatively lower concentrations (e.g., 15% to 30%, 10% to 40%, etc.) and purify the gas to 90% or higher. In some instances, one method of carbon capture involves the use of aqueous amine solutions (referred to herein as amine solution, amine, or sample) to absorb CO2 from flue gas streams at low temperature and concentration. The solution is then heated, and the absorbed CO2 is released at high concentration suitable for subsequent liquefaction or downstream use. The solution is then cooled and the cycle repeated.

The temperature swing process referred to above expends significant amounts of energy to heat and cool the aqueous amine solution to capture and release the gas. There are many types of amines and each has different capacities and rates of reaction. These parameters impact the energy required to carry out the temperature swing process and the associated throughput of CO2. Therefore, in some embodiments, a method is presented to rapidly measure and analyze small quantities of an aqueous amine solution and compute the corresponding CO2 capture capacity and reaction kinetic parameters, thereby allowing CO2 processes to be efficiently and precisely tailored for an application.

In some embodiments, the system proposed rapidly cycles the sample amine solution through a user defined temperature trajectory while measuring absorbed and desorbed CO2 from a known gas stream (e.g., the composition of the gas stream is known) thereby providing the dynamic response data for the sample amine solution that allows the analysis and determination of the reaction kinetic parameters.

FIG.1depicts a system100for testing the CO2 absorption parameters for an amine solution. In exemplaryFIG.1, a gas mixture containing a known percentage of CO2 and other gases (for example, 10% CO2in N2) is valved from tank101to a mass flow controller105which is set to a specific flow rate. For example, the flow rate may be 15 sccm (Standard Cubic Centimeters per Minute), other flow rates are possible and considered by this disclosure. In some instances, time variable flow profiles are also possible. For example, the flow rate may range from 10 sccm to 20 sccm. In some embodiments, multiple gas tanks and regulators are used to allow gas mixtures to be created. In this case the exit flows from each mass flow controller are joined to the single line prior to a flow meter106.

In some embodiments, the gas may flow through a pressure regulator102, a valve103, and a filter104. In some instances, the pressure regulator102is a device that is used on a gas line to regulate the pressure of the gas being delivered to an appliance or system.

In some instances, the tank101may be at a high pressure, but the system may require a lower pressure to operate safely and efficiently. In some instances pressure regulator102reduces the pressure of the gas coming from the gas line to a lower, more manageable level before it enters the rest of the system100.

In some embodiments, the gas stream flows through flow meter106, pressure meter107, and temperature sensor108to a test cell113containing an amine solution111to be tested. In some instances, temperature sensors can be based on a variety of technologies, including thermistors, RTDs (resistance temperature detectors), and thermocouples. For example, the amine solution size may be 100 to 200 uL (microliters). In some embodiments, a thermocouple sensor109is placed in test cell113to monitor the temperature of the solution during a test. In some embodiments, the gas stream is bubbled through amine solution111through a thin gas inlet tube110. As depicted, an end of the gas inlet tube110may sit below the surface of the amine solution111. For example, the end of the gas inlet tube110may be situated below the surface of the amine solution111or a bubbling device may be attached to the end of gas inlet tube110and the bubbling device may be situated below the surface of amine solution111.

In some instances, a flow meter for gas is a device that measures the flow rate of gas moving through a pipeline or system. The flow rate is typically measured in volume per unit time, such as cubic feet per hour (CFH), standard cubic centimeters per minute (SCCM), or cubic meters per hour (CMH). In some instances, a pressure meter for gas is a device used to measure the pressure of gas within a pipeline or system. Gas pressure meters can be mechanical or electronic and are designed to measure the pressure in one or more different units, such as pounds per square inch (PSI) or bar.

In some instances, valve103may be used to shut off or turn on gas flow completely from tank101. In some instances, filter104may remove particulates or other contaminants from the gas coming from tank101.

In some embodiments, the gas then flows through a thin gas outlet tube112downstream to a CO2 sensor114, a relative humidity116sensor, and a temperature sensor118. For example, the CO2 sensor114types include but are not limited to Nondispersive Infrared Sensor (NDIR), thermal, and photoacoustic sensors.

FIG.2illustrates an example thermal cycling sub system200. In some embodiments, sub-system200is designed to fit around sample cell113. Although the sample cell is depicted as a cylinder, other shapes are contemplated.

In some embodiments, during operation, the glass sample cell113is placed in a cylindrical receptacle202in a heat spreader205with an appropriate thermal interface grease. In practice, vacuum grease, or other suitable material (not shown) may be used to assure good thermal contact between the sample cell and the heat spreader205. For example, the sample size may be 100 uL to 200 uL, but other sample sizes may be used.

In some embodiments, during operation, cartridge heaters201and thermo-electric (Peltier) modules204are used to heat and cool the amine solution (e.g., the sample) in sample holder202through the heat spreader205(e.g., a copper heat spreader or a thermal spreader). Waste heat (e.g., heat removed during the cooling phase) is removed or dissipated from the system using fan sinks206and transferred (i.e., dissipated outside the system) by cooling duct208. In embodiments without the cooling duct208, the fan sinks206simply transfer the heated air to the ambient environment. In some embodiments, the thermal cycling is partially actuated by a thermo-electric module and partially actuated by another heating system such as cartridge heaters201. In some embodiments, the thermal cycling will have alternating cooling and heating phases.

In some instances, an ultrasonic liner203lining sample holder202may be used to produce ultrasonic vibration. For example, PVDF (polyvinylidene fluoride) liner is a material used in ultrasound imaging applications as a thin film or coating on the surface of transducers. The primary function of the PVDF liner is to act as a piezoelectric material, which generates and receives ultrasound waves. Ultrasound waves are generated by applying an electrical voltage to the PVDF liner, which causes it to vibrate and produce sound waves. The sound waves are transmitted through the sample, and when they bounce back, the PVDF liner receives the waves and converts them into electrical signals. These electrical signals are then processed to observe the sample under test with respect to whether it is changing behavior (e.g., change in state, viscosity, density, flow rate, composition, etc.). In alternate embodiments, the ultrasonic liner is used to agitate the sample under test.

In some instances, the thermo-electric module204, for example a Peltier module, is an electronic component that can be used to generate a temperature difference between its two sides when a current is passed through it. It works on the principle of the Peltier effect, which is the phenomenon that occurs when an electrical current is passed through a junction of two different metals or semiconductors, causing heat to be transferred from one side to the other. For example, a Peltier module is typically made up of two thin ceramic plates, each of which has a number of semiconductor elements sandwiched between them. When an electric current is passed through the module, heat is transferred from one ceramic plate to the other, creating a temperature difference between the two sides. This effect can be used for both heating and cooling applications, depending on the direction of the current flow.

In some instances, gas supply heat exchange duct207is a component of a heating system that is used to pre-heat the input gases.

In some embodiments, a computer (e.g., computing environment900) is used to control the power to the system elements and to read the sensors.

FIG.3depicts a graph300of data taken for aqueous amine carbon dioxide absorption kinetics parameters taken during presoak and thermal cycling using the system depicted inFIG.1andFIG.2, the flow of CO2 was constant and assured using mass flow controller105(although it may be varied as described above). In some instances, presoaking is leaving the amine at a constant temperature to saturate the amine with CO2 for a the given temperature, given CO2 concentration of the gas, and given gas flow rate. A flow value of 15 SCCM was used. The inlet CO2 gas concentration was assured by precision mix in tank101. In this example, there was a 10% volume concentration of CO2.FIG.3shows the CO2 output concentration during presoak time period301and thermal cycling periods302. In this test, sensor data and system state variables were recorded at approximately one second intervals or less. The outlet concentration of CO2 is depicted with solid line303and the sample temperature is depicted with the dashed line304. In some instances, graph demonstrates the ability of an amine solution to absorb and release CO2 with thermal cycling. For example, line303n(CO2 concentration) fluctuates with line304(temperature) because the amine solution absorb or release CO2 depending on the temperature of the amine solution.

FIG.4depicts an example method400for dynamic measurement of aqueous amine carbon dioxide absorption kinetics parameters. Operations of method400may be enacted by one or more computer systems, such as the system described inFIG.9below.

Method400begins with operation405of preparing a sample by loading a quantity of amine solution in the glass sample holder.

Method400continues with operation410of placing the sample holder in the receptacle in a heat spreader (e.g., a copper spreader block or heat spreader205).

Operation415includes bringing the temperature of the sample to a desired temperature value by appropriate heating or cooling using a thermocouple (e.g., thermocouple109) as a reference.

Operation420includes valving a specified CO2 gas volume and concentration to the sample for a period of time sufficient to saturate the amine with CO2 while monitoring the CO2 exhaust concentration using CO2 sensor (e.g., sensor114) to detect when saturation has been achieved. Herein, operation420may be referred to as a “pre-soak.” In some instances, pre-soaking saturation levels may depend on the concentration of CO2 for incoming gas, temperature of the amine, and humidity of the gas. In some embodiments, the amine solution may be saturated when the concentration of CO2 of gas leaving the amine solution has reached a constant value.

Method400continues with operation425of thermal cycling the sample by alternately heating and cooling the sample for pre-determined time periods and number of cycles while monitoring the CO2 exhaust concentration, temperature, pressure, and relative humidity. For example, see the results depicted inFIG.3. In some instances, after reaching a presoaking, heating and cooling the amine may case the amine to respectively absorb and release CO2. Thus, CO2 may be extracted from an incoming gas by heating the amine solution and later be released for collection by cooling the amine solution.

Method400may end with operation430of disposing of the sample. In some embodiments, the sample may be cooled to room temperature before disposal.

FIG.5depicts an example method500for predicting the behavior of the amine solution under varying conditions to improve use parameters and cost of operations. In some instances, method500may be predicted for actual use situations and plant models Operations of method500may be enacted by one or more computer systems such as the system described inFIG.9below.

Method500may begin with operation505of computing the capacity of the amine solution and initial concentration of absorbed CO2.

In some embodiments, given a known input flow volume CO2 and a concentration of a gas before and after passing through the amine solution; the net molar amount of CO2 absorbed in the sample can be computed by the difference of the2concentrations (before and after). Integrating this quantity over the presoak period results in the amount of CO2 absorbed in the sample. For example,FIG.6depicts graph600illustrating the results of a test determining the cumulative CO2 absorbed during presoak. In graph600, the number of moles of amine present in the sample solution is computed from the known sample volume and the percentage of amine by weight.

In some embodiments, the capacity of the amine to absorb CO2 is computed by dividing the moles of CO2 absorbed divided by the moles of amine in the sample. The capacity of CO2 absorption can be compared in many cases with the known values for particular amines in the literature and serves as an initial condition for subsequent calculations.

Referring back toFIG.5, the method500continues with operation510of computing the first order reaction kinetics parameters of the amine solution for the Arrhenius or Eyring form of reversable nth order reaction kinetics appropriate to the amine sample. Given the concentrations and temperatures shown above for the thermal cycling period302, the system may be determined by computing the CO2 absorption of the sample versus time.

Method500may continue with operation515of computing the change in amine concentration vs. time and carbamate concentration. In some instances, since carbamate is formed in the forward reaction (absorption) and continuity, it is possible to compute the change in amine concentration vs time and the associated changes in carbamate concentration etc. In some instances, continuity refers to the principle of mass conservation, which states that the total mass of a closed system remains constant over time, barring any external inputs or outputs. The initial concentrations of carbamate and amine are known from operation505.

In some instances, the Arrhenius equation and the Eyring equation are two different formulations used to describe the kinetics of reversible nth order reactions. Both the Arrhenius equation and the Eyring equation relate the rate constant (k) of a reaction to the temperature (T) and other relevant physical constants.

The Arrhenius equation is given by:

k=A*exp⁡(-Ea/RT)where A is the pre-exponential factor, Ea is the activation energy for the reaction, R is the universal gas constant, and T is the temperature (e.g., in kelvin). This equation relates the (k) rate constant to the activation energy required to overcome the energy barrier for the reaction to occur. As the temperature increases, the rate constant increases due to the increased kinetic energy of the reactants, which allows more collisions to occur and thus more successful reactions. This equation is commonly used for simple reactions involving a single transition state.

The Eyring equation is given by:

k=(k_b*Th)*exp⁡(-Δ⁢G‡/RT)where kb is the Boltzmann constant, h is Planck's constant, ΔG‡ is the Gibbs free energy of activation, and R and T have the same meanings as in the Arrhenius equation. This equation is used for more complex reactions involving multiple transition states. It relates the rate constant to the free energy of activation required to overcome the energy barrier for the reaction to occur. The Eyring equation takes into account the entropy and enthalpy changes that occur during the reaction.

In some embodiments, the method solves for the parameters A1, E1, A2, E2 given the constraining data [AMINE], [CARB] and [CO2] and equations:

In the case of the Arrhenius form, the method includes solving for the Arrhenius constants for k (forward and reverse).

A variety of methods exist to solve for the4parameters given the arrays of data resulting from observation. In some embodiments, a statistical modeling software package that allows users to fit complex mathematical models to data may be used to determine one or more functions that fit the gathered data. In some instances, the Eyring form may also be computed with a model. In some instances, after running a test, the fully known set of equations and associated constants may comprise a complete model for the behavior of the amine that allows the prediction of the behavior of the amine solution under varying conditions in practical situations and plant models to estimate the optimal use parameters and cost of operations.

In some embodiments, method500continues with operation520of applying the results of operation515to modify a manufacturing process. For example, given a manufacturing process producing a gas with a particular concentration of waste CO2, the results of one or more rounds of testing may be used to select an amine solution and temperature for a process. For example, given the temperature swing parameters for a given manufacturing processs, the kinetics model can be used to simulate the performance of a given amine solution in the plant. Using these simulations to calculate the amount of CO2 captured for a given energy input, an amine with the highest performance may be selected for further testing.

Using the method described above, multiple amine solutions were examined and the results of the examination were used to compute the corresponding first order reaction constants. These are shown inFIG.7andFIG.8.FIG.7depicts graph700illustrating the estimated forward and reverse activation energies for CO2 absorption in various aqueous amine solutions.FIG.8depicts graph800illustrating the estimated forward and reverse pre-exponential factors (rate of the process) for CO2 absorption in various aqueous amine solutions. The4constants depicted for each amine solution, when plugged into the equations above, create a model for the performance of the amine that can then be applied to compute the performance of the amine usage in a given plant. The ability to model performance allows for fine tuning industrial processes without experimentation on the process itself. For example, tear down and setup on an industrial process to change CO2 capture methods in order to improve the methods may be cost prohibitive. However, by using an experimental process, as described herein, the CO2 capture methods for the industrial process may be improved without testing on the industrial setup itself. In some embodiments, Ef and Er refer to the forward and reverse reaction kinetics model constants, where E corresponds to energy. In some embodiments, Af and Ar refer to the forward and reverse reaction kinetics model constants where A is a pre-exponential constant.

Computing environment900contains an example of an environment for the execution of at least some of the computer code involved in performing the inventive methods, such as and application for predicting the behavior of the amine solution under varying conditions to improve use parameters and cost of operations in example method400. In addition to example method400, computing environment900includes, for example, computer901, wide area network (WAN)902, end user device (EUD)903, remote server904, public cloud905, and private cloud906. In this embodiment, computer901includes processor set910(including processing circuitry920and cache921), communication fabric911, volatile memory912, persistent storage913(including operating system922and example method400, as identified above), peripheral device set914(including user interface (UI), device set923, storage924, and Internet of Things (IoT) sensor set925), and network module915. Remote server904includes remote database930. Public cloud905includes gateway940, cloud orchestration module941, host physical machine set942, virtual machine set943, and container set944.

PROCESSOR SET910includes one, or more, computer processors of any type now known or to be developed in the future. Processing circuitry920may be distributed over multiple packages, for example, multiple, coordinated integrated circuit chips. Processing circuitry920may implement multiple processor threads and/or multiple processor cores. Cache921is memory that is located in the processor chip package(s) and is typically used for data or code that should be available for rapid access by the threads or cores running on processor set910. Cache memories are typically organized into multiple levels depending upon relative proximity to the processing circuitry. Alternatively, some, or all, of the cache for the processor set may be located “off chip.” In some computing environments, processor set910may be designed for working with qubits and performing quantum computing.

Computer readable program instructions are typically loaded onto computer901to cause a series of operational steps to be performed by processor set910of computer901and thereby effect a computer-implemented method, such that the instructions thus executed will instantiate the methods specified in flowcharts and/or narrative descriptions of computer-implemented methods included in this document (collectively referred to as “the inventive methods”). These computer readable program instructions are stored in various types of computer readable storage media, such as cache921and the other storage media discussed below. The program instructions, and associated data, are accessed by processor set910to control and direct performance of the inventive methods. In computing environment900, at least some of the instructions for performing the inventive methods may be stored in example method400in persistent storage913.

VOLATILE MEMORY912is any type of volatile memory now known or to be developed in the future. Examples include dynamic type random access memory (RAM) or static type RAM. Typically, the volatile memory is characterized by random access, but this is not required unless affirmatively indicated. In computer901, the volatile memory912is located in a single package and is internal to computer901, but, alternatively or additionally, the volatile memory may be distributed over multiple packages and/or located externally with respect to computer901.

END USER DEVICE (EUD)903is any computer system that is used and controlled by an end user (for example, a customer of an enterprise that operates computer901), and may take any of the forms discussed above in connection with computer901. EUD903typically receives helpful and useful data from the operations of computer901. For example, in a hypothetical case where computer901is designed to provide a recommendation to an end user, this recommendation would typically be communicated from network module915of computer901through WAN902to EUD903. In this way, EUD903can display, or otherwise present, the recommendation to an end user. In some embodiments, EUD903may be a client device, such as thin client, heavy client, mainframe computer, desktop computer and so on.

REMOTE SERVER904is any computer system that serves at least some data and/or functionality to computer901. Remote server904may be controlled and used by the same entity that operates computer901. Remote server904represents the machine(s) that collect and store helpful and useful data for use by other computers, such as computer901. For example, in a hypothetical case where computer901is designed and programmed to provide a recommendation based on historical data, then this historical data may be provided to computer901from remote database930of remote server904.

PRIVATE CLOUD906is similar to public cloud905, except that the computing resources are only available for use by a single enterprise. While private cloud906is depicted as being in communication with WAN902, in other embodiments a private cloud may be disconnected from the internet entirely and only accessible through a local/private network. A hybrid cloud is a composition of multiple clouds of different types (for example, private, community or public cloud types), often respectively implemented by different vendors. Each of the multiple clouds remains a separate and discrete entity, but the larger hybrid cloud architecture is bound together by standardized or proprietary technology that enables orchestration, management, and/or data/application portability between the multiple constituent clouds. In this embodiment, public cloud905and private cloud906are both part of a larger hybrid cloud.