Dynamic hydrogen dispenser from LOHC

Abstract

A liquid organic hydrogen carrier (LOHC) dehydrogenation system is described that is capable of satisfying the hydrogen demand over time in short-term kinetics while ensuring high dehydrogenation throughout all operating conditions. The system includes one or more reactors including a LOHC vessel and a circulation loop including a recirculation pump, a preheater capable of supplying reaction heat as sensible heat, and a cartridge filled with a solid catalyst.

Description

[0001] This invention relates to a continuous liquid organic hydrogen storage carrier (LOHC) dehydrogenation system, comprising one or more reactant liquid containers having free space for containing the generated gas, and the containers being connected to an external solid dehydrogenation catalyst cartridge via a loop equipped with a pump for circulating the liquid phase. In particular, the dehydrogenation system further includes a heat exchanger suitable for preheating the liquid phase to provide heat of reaction. Background Technology

[0002] LOHC (Liquid Organic Hydrogen Carrier) technology has become one of the main methods for storing and transporting hydrogen. This technology offers many advantages compared to other technologies (high-pressure hydrogen, liquid hydrogen, and hydrogen stored in the form of metal hydrides). In particular, it avoids the use of high-pressure tanks, eliminates the need for expensive compression or liquefaction processes of hydrogen itself at very low temperatures, allows the use of the same infrastructure as hydrocarbons, and can be stored an unlimited number of times without progressive loss. The cycle of producing, storing, and releasing hydrogen on a suitable medium has been the subject of much research, as has the use of released hydrogen to generate heat or electricity. Studies have shown that the use of LOHC is also cost-effective, especially for long-distance transport.

[0003] The LOHC technology cycle essentially consists of four steps: hydrogenation of a medium or carrier at an average pressure of 10-50 bar to produce feed LOHC; transport of the feed LOHC in liquid form at ambient pressure and temperature, dehydrogenating the LOHC to release hydrogen and obtain waste LOHC; and recycling the waste LOHC back to the hydrogenation step. The first two steps and the last step are well-defined in terms of equipment and operating conditions. However, the dehydrogenation stage presents more challenges because its implementation depends heavily on the specific use of hydrogen, the location of the dehydrogenator (whether fixed or on a movable support), and the continuous demand for hydrogen from the system used. Furthermore, the process is complicated by the fact that the dehydrogenation reaction occurs at high temperatures ranging from 200°C to 350°C, depending on the type of LOHC used, and that the reaction is endothermic, requiring the provision of heat of reaction at these temperatures. Therefore, a structure that meets the following requirements must be determined: 1. Capable of supplying hydrogen at variable flow rates to quickly adapt to changes in the needs of the system used; 2. Energy independence, meaning that energy supply does not require external sources; 3. Ensure high dehydrogenation of the feed LOHC under all operating conditions.

[0004] Rapid adaptation to changes in demand means transitioning from one steady state to another within seconds or tens of seconds; high dehydrogenation means that the conversion rate of feed LOHC to dehydrogenated LOHC is greater than 50%, preferably 80%, under all operating conditions. It should also eliminate the need for a large storage buffer for the resulting hydrogen between the dehydrogenator and the system in use.

[0005] Several types of dehydrogenation reactors have been proposed in published and patent literature. Most studies are based on plug flow reactors (PFRs), which are divided into three zones: a heating zone that raises the temperature of the feed LOHC to the reaction temperature; a zone containing a solid catalyst for the reaction to take place; and a cooling zone that brings the temperature of the two-phase gas-liquid flow to a level compatible with the application requirements.

[0006] Patent US 11,383,974 describes different types of dehydrogenation reactors, namely fixed-bed and moving-bed reactors, but always of batch or plug-flow type. The patent also focuses on the use of reaction promoters, namely secondary or polyols, where the dehydrogenation reaction proceeds in two steps: the first step is hydrogen exchange between LOHC and the oxidized form of the promoter (i.e., the corresponding ketone), and the second step is the dehydrogenation of the resulting alcohol. The advantage of this solution is that it can provide the heat of reaction to the system at a lower temperature (approximately 200°C) than the temperature required for direct dehydrogenation via LOHC. The document does not mention possible dynamic applications.

[0007] US Patent 10,350,566 describes in detail a plug-flow reactor consisting of three zones, where the first zone is used for preheating the LOHC, the second zone is used for the reaction to occur, and the third zone is used for separating the gas stream from the liquid stream at the outlet. Similarly, this document does not mention dynamic behavior.

[0008] Patent DE 10 2021 203 887 describes a plug-flow reactor in which vibrations occur in the solid catalyst bed, facilitating the separation of hydrogen produced by the catalyst pores. While the document does not mention dynamic behavior, it interestingly demonstrates the importance of the fluid dynamics mechanism underlying the dehydrogenation reaction.

[0009] US 2022 / 0305469 describes a plug flow reactor containing a solid catalyst structured in a bundle of channels that allow for good liquid-solid contact through the rapid escape of gases released from these channels. It also states that the system should be subjected to vibration to reduce the size of hydrogen bubbles and promote their exit from the channels.

[0010] US Patent 10,840,529 describes a system consisting of one or more dehydrogenation reactors that supplies hydrogen to a fuel cell. This operates under controlled anoxic conditions, such that unconverted hydrogen leaving the cell is used to provide the reaction heat required for dehydrogenation. Variations in hydrogen flow rate are achieved by operating all or only a portion of the dehydrogenation reactors in parallel.

[0011] US 2016 / 0214858 describes a sequence of one or more stirred reactors for releasing hydrogen from a LOHC (in the examples, perhydro-N-ethylcarbazole), each operating under different temperature, pressure, and catalyst conditions. To meet purity and flow rate requirements, a hydrogen accumulator is provided downstream of the reactors, based on storing hydrogen itself as a metal hydride, allowing for the accumulation or release of hydrogen as needed through temperature and pressure variations. The reported flow rate change time is approximately several hundred minutes, which is too high for dynamic system behavior.

[0012] Patent US 10,260,680 claims protection for the use of a dehydrogenation reactor in hydrogen vehicle refueling stations, noting the need to ensure rapid refueling times of several tens of minutes. To achieve this, the document suggests inserting a hydrogen storage device between the hydrogenation reactor and the refueling pump, at a pressure higher than the vehicle's own storage pressure, typically in the range of 300 to 700 bar. However, this solution implies a fairly large pressurized hydrogen tank, which poses risks, especially in busy areas such as service stations. The patent does not specify the reactor design or the response time to demand, which is highly variable, ranging from zero flow rate when there are no customers to 0.6 kg / min during refueling. Even if this application is based on a stationary reactor rather than a mobile carrier, a highly dynamic dispenser is still required.

[0013] Patent CN115520834 describes a loop in which an heat exchanger and a fixed-bed reactor are inserted into a circulation loop located between a vessel containing LOHC (loose hydrogen hydrate) and the top of the reactor. The heat exchanger has the function of condensing LOHC vapor contained in the gaseous hydrogen stream, and the inlet flow of the feed LOHC also promotes condensation.

[0014] In contrast, patent CN115285936 describes different dehydrogenation strategies based on the hydrogen-dimethyl carbonate reaction cycle.

[0015] Several articles in the published literature describe LOHC dehydrogenation reactors. They mainly focus on catalyst morphology with the aim of maximizing solid-liquid contact and heat exchange on the reactor walls. From this perspective, thin-film reactors in which the catalyst is spread onto the surface supplying the heat of reaction have been proposed (Journal of Catalysis 181, 113-123 (1999)), structured reactors using metal foam, ceramic substrates, or various forms of metal mesh as substrates (Materials 2020, 13, 277), and conventional tubular reactors filled with particulate catalysts have also been proposed.

[0016] The reactor types reported in the published literature for LOHC dehydrogenation include fixed-bed reactors, membrane reactors, spray and pulse reactors, thin-film liquid reactors, heat exchange reactors, and microstructured reactors (Aki Braunschweiler, Catalytic Dehydrogenation of Liquid Organic Hydrogen Carriers, Aalto Energy School of Chemical Engineering Thesis, 2018). Reactor structures were analyzed in all cases, but the reactor operation mode was consistently plug flow, where the reactor's fluid dynamics and efficiency are influenced by residence time. Therefore, no available dehydrogenation system layout ensures reactor fluid dynamics independent of operating conditions, especially the LOHC feed rate, thus providing efficiency independent of both the feed rate and ultimately the instantaneous hydrogen production required. Invention Details

[0018] It has now been found that liquid organic hydrogen carrier (LOHC) dehydrogenation systems can meet time-varying hydrogen demands with short-term kinetics while consistently ensuring high dehydrogenation levels under all operating conditions.

[0019] like Figure 1 As shown, the liquid organic hydrogen carrier (LOHC) continuous dehydrogenation system of the present invention includes one or more reactors in series, such as CSTR (continuous flow stirred tank reactor) type reactors. The characteristic of each reactor is that each reactor includes a container (hereinafter also referred to as a container) containing the reactant LOHC and a cylinder containing a solid catalyst. The liquid LOHC is circulated through the cylinder via a recirculation pump at a flow rate independent of the residence time of LOHC in the reactant complex, while the released hydrogen gas is sent for use after purification from the LOHC vapor.

[0020] like Figure 2 As shown, a heat exchanger can be advantageously inserted into the circulation loop to preheat the circulating liquid to a temperature above the reaction temperature, and is sufficient to maintain the temperature of the liquid contained in the container at the desired level by compensating for the heat demand of the reaction and dissipating heat outwards.

[0021] Preferably, such as Figure 1 and Figure 2 As shown, liquid LOHC (referred to as "feed LOHC" in the figure) is added to a container containing the reactant LOHC. Specifically, the so-called feed LOHC undergoes a dehydrogenation process within the container, thereby allowing the release of hydrogen gas and yielding waste LOHC, preferably in the liquid phase.

[0022] Preferably, the waste LOHC is circulated in a loop via at least one recirculation pump, thereby enabling its reuse.

[0023] More preferably, such as Figures 2 to 4 As shown, in this loop, the waste LOHC is preheated via at least one heat exchanger.

[0024] Preferably, such as Figures 2 to 4 As shown, the heat exchanger is located upstream of the outer cylinder containing the dehydrogenation catalyst in the circuit. Specifically, downstream of the heat exchanger, the waste LOHC encounters the cylinder outside the container containing the reactant LOHC, which in turn contains a solid catalyst, where a reaction occurs to obtain the extracted LOHC, i.e., partially dehydrogenated LOHC, and hydrogen gas generated in the gas phase.

[0025] Subsequently, as Figure 2 As shown, the mixture is fed into a LOHC reactor, which again allows for the removal of hydrogen and the recovery of waste LOHC.

[0026] In other words, the reactant LOHC from the outer cylinder is mixed with the feed LOHC, and the resulting mixture is recycled back to the outer cylinder containing the catalyst.

[0027] The volume of liquid in the container can be controlled by a liquid level controller.

[0028] The circulation rate of the reactant liquid is adjusted according to the required liquid temperature in the container, while the LOHC flow rate fed into the system is adjusted according to the required hydrogen extraction rate. The hydrogen pressure is regulated by a valve used to remove the released hydrogen.

[0029] The preferred liquid feed for LOHC is hydrogenated dibenzyltoluene.

[0030] The liquid temperature in this container is in the range of 250°C to 350°C, preferably in the range of 280°C to 320°C. In fact, this container is suitable for containing liquids at this temperature.

[0031] The total residence time depends on the ratio of the total volume of LOHC contained in the container and circulation loop (including the catalyst cartridge) to the flow rate of the feed LOHC:

[0032] The circulation flow rate is an arbitrary parameter used to optimize the liquid-solid contact in the cylinder and promote the release of hydrogen from the catalyst itself.

[0033] The circulating flow velocity R is greater than the flow velocity F LOHC Furthermore, this allows for a significantly lower volume ratio between the instantaneous gas and liquid flow rates within the catalyst container compared to the overall volume ratio between the gas and liquid flow rates at the system outlet. Placing the catalyst in a separate container from the liquid LOHC also enables the achievement of formal concentrations of solid catalyst within the system, unaffected by the stirring limits of conventional solid-liquid stirred reactors, which are practically less than 100-200 g / L, thus resulting in low liquid volume and high catalyst quantity. The maximum achievable catalyst concentration equals the apparent density of the catalyst (grams of catalyst per unit apparent volume), typically even exceeding 500 g / L.

[0034] The higher the circulation flow rate, the smaller the temperature difference between the inlet and outlet of the LOHC used for circulation in the cylinder, thus avoiding localized overheating of the liquid. In fact, it is known that LOHC produces decomposition products at high temperatures.

[0035] In another embodiment of the invention, the gas-liquid stream exiting the solid catalyst cartridge can be sent to a gas-liquid separation unit, which sends the gas phase to extract gaseous hydrogen and the liquid phase to an LOHC container, such as... Figure 3 As shown.

[0036] By using several reactors in series, each configured as described, higher conversion rates can be achieved with the same total amount of catalyst, or the same LOHC conversion rates can be achieved with a smaller amount of catalyst. Figure 4 The sequence of the three reactors is described.

[0037] Preferably, such as Figure 4 As shown, the system includes at least two reactors connected in series. Specifically, waste LOHC from the first reactor is fed into the second reactor located after the first reactor.

[0038] In this way, hydrogen is released and waste LOHC is obtained through the above configuration.

[0039] More preferably, such as Figure 4 As shown, the waste LOHC obtained from the first reactor is fed into a container containing the reactant LOHC located in the second reactor for reuse and conversion.

[0040] like Figure 4As shown, in the case of three reactors connected in series, waste LOHC from the first reactor is fed into the second reactor; similarly, waste LOHC from the second reactor is fed into the corresponding LOHC container in the third reactor. Brief description of the attached diagram

[0042] Figure 1 This is a flowchart of the reactor unit of the present invention; Figure 2 A flowchart illustrating the reactor unit of the present invention, which includes a heat exchanger for preheating the circulating liquid; Figure 3 A flowchart illustrating the reactor unit of the present invention is provided, which includes a gas-liquid separation unit located at the outlet of a cylinder containing a catalyst. Figure 4 The structure of the dehydrogenation system is shown, which includes three reactor units connected in series. Figure 5 This represents the response time calculated using a dynamic model that instantaneously changes the supply flow rate from the steady-state value of Example 1 to one-tenth of it; Figure 6 The display shows the outlet pressure and flow rate calculated by a dynamic model transitioning from the final conditions of Example 3 to the final conditions of Example 1. Invention Details

[0044] The operation of the above-described reaction system is explained in detail in the following examples. These are derived from published literature (Dürr S. et al., International Journal of Hydrogen Energy) International Journal of Hydrogen Energy (Volume 46, Issue 64, 2021, pp. 32583-32594); and Jorschick H., Preuster P. et al., Hydrogen Storage Using Shift Reactors, Energy and Environmental Sciences ( Energy Environ. Sci). The mathematical modeling of the system, based on kinetic and thermodynamic data obtained in [Article Title 2017, 10, 1652-1659], involved the fully hydrogenated dibenzyltoluene (DBTH) as a LOHC. Both articles reported results obtained using platinum supported on alumina as a catalyst. DBTH is well known to be the most advantageous LOHC due to its energy density (=7479 kJ / kg DBTH), the commercial availability of the precursor dibenzyltoluene (DBT), its physical and chemical properties (melting point = -50 °C, boiling point = 371 °C), and its compatibility with transportation and storage systems for heavy hydrocarbons such as gasoline and diesel. Platinum catalysts supported on alumina are generally considered the most efficient for the DBTH dehydrogenation reaction.

[0045] The reaction pathway used consists of three consecutive dehydrogenation stages, as shown in the following reaction equations:

[0046] The equilibrium constants for the three reactions reported in the cited references at 291 °C and the kinetic parameters reproducing the trend of hydrogenation degree over time at 291 °C were determined. A steady-state model of the CSTR was constructed using these values, which calculates the hydrogen production as a function of residence time and catalyst content in the reactor.

[0047] A dynamic model was also established, which starts from the static operating conditions obtained from the CSTR model and calculates the time required to reach different static operating conditions, characterized by higher or lower hydrogen production.

[0048] These models yielded the results shown in the following embodiments.

[0049] Example 1: Setting up a CSTR reactor to produce 150 kW of hot hydrogen.

[0050] The heat of combustion for the formation of water from hydrogen is -241.8 kJ / mol, therefore, 2233 mol / h is required to obtain 150 kW. For operation in a CSTR reactor at 291 °C and 1 bar hydrogen pressure with 6000 g of Pt / Al₂O₃ catalyst at a grammatical concentration of 200 g / L, 305.3 mol / h of DBTH with a degree of hydrogenation of 100% must be added. Under these conditions, the degree of dehydrogenation of the effluent DBT is 18.7%. Table 1 below summarizes the reactor parameters: Table 1

[0051] Example 2: Setting up three CSTR reactors in series

[0052] Using a series of three CSTR reactors, almost identical results to those of Example 1 can be obtained, wherein 100% hydrogenated DBTH feed is added to the first reactor at the same flow rate as in Example 1, and the effluent from the previous reactor is added to the other two reactors. The amount of catalyst from Example 1 is divided equally among the three reactors, with the liquid volume in each reactor being 1 / 3 of that in Example 1. Table 2 below summarizes the reactor parameters: Table 2

[0053] Dividing the same amount of catalyst as used in Example 1 into three reactors allowed for more efficient use of the available hydrogen content and increased the energy produced by 15%.

[0054] Example 3: Calculate the response time of the CSTR reactor to instantaneous changes in the feed rate.

[0055] Figure 5The display shows the response time calculated by a dynamic model for an instantaneous change in the feed rate from the steady-state value of Example 1 to one-tenth of that value. In addition to the liquid volume, a gas volume of 10 liters was also distributed to the reactor. The initial conditions were the steady-state conditions of Example 1. Figure 5 and Figure 6 The chart shows the trends in hydrogen production rate and pressure over time.

[0056] The adaptation to the new conditions occurs within seconds, during which excess hydrogen relative to the extracted hydrogen is stored in the reactor's gas volume, leading to an increase in pressure. This increase slows the rate of the direct dehydrogenation reaction and increases the rate of the reverse reaction, allowing the system to rapidly reach its new operating conditions.

[0057] The increase in H2 demand takes a relatively long time because the amount by which this demand exceeds productivity cannot be greater than the amount that would cause the system pressure to drop below the operating pressure limit (1 atmosphere in the given example). In fact, initially, the required hydrogen is supplied by the gas contained in the reactor's free volume and the gas produced from the dehydrogenation reaction, which takes several minutes to reach near-final steady-state levels. Therefore, the demand must be increased gradually while simultaneously maintaining the pressure above 1 atmosphere during the transient period. The required H2 flow rate is used in the diagram, which increases according to the following formula:

[0058] in u max It is the required steady-state flow rate. u ° is the initial flow velocity. Parameter a is adaptive.

[0059] Figure 6 The charts in the figure show the outlet pressure and flow rate calculated by a dynamic model for the transition from the final conditions of Example 3 to the final conditions of Example 1.

[0060] This change in conditions also requires tens of seconds to achieve the required flow rate.

[0061] Therefore, it has been demonstrated that the LOHC dehydrogenation system can meet time-varying hydrogen demand with short-term kinetics while still ensuring high dehydrogenation efficiency under all operating conditions.

[0062] In particular, a layout for the dehydrogenation system has been provided that ensures reactor fluid dynamics independent of operating conditions, especially independent of the LOHC feed rate, thereby providing efficiency independent of the feed rate and ultimately independent of the instantaneous hydrogen production required.

Claims

1. A continuous liquid organic hydrogen carrier (LOHC) dehydrogenation system, comprising one or more reactors connected in series, characterized in that... Each reactor includes a container containing the reactant LOHC and an outer cylinder containing the dehydrogenation catalyst, equipped with at least one pump for circulating the liquid phase from the container to the cylinder and a circuit for a heat exchanger suitable for preheating the liquid phase, wherein the container has a free volume for the generated gas.

2. The dehydrogenation system of claim 1, wherein the heat exchanger is adapted to preheat the liquid circulating in the loop to a temperature above the reaction temperature and sufficient to maintain the temperature of the liquid contained in the container at a level necessary to compensate for the heat requirements of the reaction and for outward heat dissipation.

3. The dehydrogenation system according to claim 1 or 2, wherein the container includes a level controller for the volume of liquid present.

4. The dehydrogenation system according to one or more of claims 1-3, wherein the circulation rate of the reactant liquid is adjusted according to the desired temperature of the liquid in the container.

5. The dehydrogenation system according to one or more of claims 1-4, wherein the container includes a hydrogen extraction valve for regulating hydrogen pressure.

6. The dehydrogenation system according to one or more of claims 1-5, wherein the LOHC flow rate added to the system is adjusted according to the desired hydrogen extraction rate.

7. The dehydrogenation system according to one or more of claims 1-6, wherein the LOHC feed is hydrogenated dibenzyltoluene.

8. The dehydrogenation system according to one or more of claims 1-7, wherein the container is suitable for containing liquid at a temperature in the range of 250°C to 350°C, preferably 280°C to 320°C.

9. The dehydrogenation system according to one or more of claims 1-8, wherein the gas-liquid separation unit is inserted between the outlet of the solid catalyst cartridge and the return container.

10. The dehydrogenation system according to one or more of claims 1-9, comprising three or more reactors connected in series.

11. The dehydrogenation system according to one or more of the preceding claims, wherein partially dehydrogenated LOHC and hydrogen generated in the gas phase are present at the outlet of the outer cylinder.

12. The dehydrogenation system according to one or more of the preceding claims, wherein the heat exchanger is located upstream of the outer cylinder containing the dehydrogenation catalyst in the circuit.

13. A dehydrogenation system according to one or more of the preceding claims, wherein the reactant LOHC from the outer cylinder is mixed with the feed LOHC, and the resulting mixture is recycled back to the outer cylinder.

14. A dehydrogenation system according to one or more of the preceding claims, comprising at least two reactors connected in series, and wherein waste LOHC from a first reactor is added to a second reactor located after the first reactor.

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