Photochemical modification of hydrogen vectors

Abstract

A method for producing hydrogen from a low molecular weight hydrogen vector, wherein the low molecular weight hydrogen vector is modified under light in the presence of a light-absorbing carbon enabler.

Description

[Technical Field]

[0001] The present invention relates to a method for producing hydrogen from hydrocarbons having saturated CH bonds, and more particularly to a method for modifying one or more members of low molecular weight hydrogen vectors, such as gaseous alkanes and water vapor, in the presence of a light-absorbing carbon enabler in order to generate hydrogen and value-added co-products. [Background technology]

[0002] Hydrogen is a clean, flammable, and non-toxic fuel well-suited for a sustainable future. The combustion of hydrogen only produces water as a by-product. However, transporting and storing hydrogen in both gaseous and liquid forms presents safety challenges. This difficulty can be circumvented by using more stable and abundant low-molecular-weight hydrogen vectors as hydrogen sources, such as, but not limited to, CH4 and H2O.

[0003] Conventional methods for reforming these small molecules into hydrogen require either some form of non-renewable energy or renewable energy enabled by heat, electricity, or light.

[0004] Natural gas is a major source of methane and one of the most abundant fossil fuels currently available on Earth. In addition to its use as a fuel, natural gas is an important source of methane and light alkanes that can be processed to produce various chemical products, including hydrogen and unsaturated hydrocarbons. These alkanes can be processed, for example, by thermally powered catalytic dehydrogenation to produce alkenes and hydrogen. However, these processes typically require extreme temperatures, usually achieved by burning fossil fuels, resulting in significant greenhouse gas emissions.

[0005] The direct conversion of methane under mild reaction conditions to produce carbon and hydrogen requires high energy (434 kJ mol) mainly to break the CH bond. -1 Therefore, it is the "holy grail" of chemistry. [Overview of the initiative]

[0006] The present invention provides an alternative to the use of conventional high-energy consumption methods for producing hydrogen by reforming hydrogen vectors. In the process or method of the present invention, one or more low molecular weight hydrogen vectors are introduced into a reactor containing a light-absorbing carbon enabler. When the low molecular weight hydrogen vectors are brought into contact with the light-absorbing carbon enabler, and the light-absorbing carbon enabler is simultaneously exposed to a light source, which may be xenon or an LED light source, hydrogen and value-added co-products are generated from the low molecular weight hydrogen vectors.

[0007] The artificial lighting used in the process or method of the present invention may be powered by renewable energy. The intensity of the light may be adjusted by optical or electronic means, such as by using lenses or by adjusting the power of xenon or LED lighting. Compared to conventional thermal strategies, using artificial light generated from solar or renewable energy to initiate the reforming of hydrogen vectors breaks the limits of thermodynamics, allows access to the reaction under milder conditions, and reduces greenhouse gas emissions.

[0008] The light-absorbing carbon enablers of the present invention are, for example, coal, biochar, charcoal, carbon black, and biomass. These carbon enablers react with a hydrogen vector, thereby consuming both carbon and the hydrogen vector in the process according to the following reaction equation. C+CH4+light → 2C+2H2 C+H2O+light → CO+H2 [Brief explanation of the drawing]

[0009] The drawings below are merely illustrative of specific embodiments of the disclosure and should not be considered as limitations on its scope. They may be used to understand the processes disclosed herein and the results of experimental studies described later.

[0010] [Figure 1] Figure 1 is a bar graph detailing the hydrogen evolution activity of the tested carbon material from methane under various surface temperatures, simulated light, dark conditions, and natural light, with and without external heating. [Figure 2] Figure 2 details the Raman spectra of the carbon material before and after the reaction with methane. [Figure 3] Figure 3 details the rates at which carbon monoxide and hydrogen gas are produced from the photoreformation of carbon materials and water at light intensities of 15.8, 23.6, and 35.4 W cm⁻² using a Xe lamp used to simulate sunlight at 40-60°C. [Modes for carrying out the invention]

[0011] The present invention provides a method for modifying hydrogen vectors to produce hydrogen and useful co-products (or co-manufactures). The hydrogen vectors of the present invention include methane, gaseous alkanes, other saturated hydrocarbons having CH bonds similar to the CH bonds of methane, and low molecular weight molecules such as water. When using the present invention, the high temperature and associated high energy requirements of the prior art methods can be avoided by using a light-absorbing carbon enabler in the presence of light to modify these hydrogen vectors to produce (manufacture) hydrogen and useful co-products.

[0012] In the process or method of the present invention, one or more low molecular weight hydrogen vectors are introduced into a reactor. This reactor may be a batch reactor or a continuous flow reactor, and may contain a light-absorbing carbon enabler. The low molecular weight hydrogen vectors are brought into contact with the light-absorbing carbon enabler, and at the same time, the light-absorbing carbon enabler is exposed to a light source.

[0013] The light source may be sunlight, a xenon or light-emitting diode light source, or another artificial light source. The intensity of the light source is approximately 0.1 W cm². -2 From approximately 300 W cm -2 It may be in the range of, preferably about 10 to about 60 W cm -2 The light intensity may be adjusted by optical or electronic means, such as by using lenses or by adjusting the power of the xenon, LED, or other artificial lighting used. The use of light, along with the use of one or more light-absorbing carbon enablers, enables the generation of hydrogen and value-added co-products from the low molecular weight hydrogen vector at temperatures lower than those required in the prior art, and consequently with lower energy consumption.

[0014] The artificial lighting used in the process or method of the present invention may be powered by renewable energy. This renewable energy may be generated concurrently with its use, or it may be stored in a battery or other energy storage means until needed. Compared to conventional thermal methods, using artificial light generated from solar or renewable energy to initiate the reforming of hydrogen vectors breaks thermodynamic limits, allows for the use of the reaction under milder conditions, and reduces greenhouse gas emissions.

[0015] The light-absorbing carbon enabler of the present invention is, for example, coal, biochar, carbon, carbon black, and biomass, but is not limited thereto. These carbon enablers react with the hydrogen vector, whereby both the carbon and the hydrogen vector are consumed in the process or method of the present invention according to the following exemplary reaction equations. C + CH4 + light → 2C + 2H2 C + H2O + light → CO + H2

[0016] The hydrogen production rate can increase as the temperature in the reactor increases, but the process or method of the present invention may be carried out at a temperature as low as 20 degrees Celsius. Nevertheless, by using light and the light-absorbing carbon enabler, hydrogen generation is possible at a temperature substantially lower than that of the prior art.

[0017] The process or method of the present invention may be carried out in a batch or flow process or method at a pressure of approximately atmospheric pressure to 30 psi, or at other pressures within the skill and knowledge of those skilled in the art.

[0018] The present invention enables replacing an energetically inefficient thermochemical steam gasification process with a more efficient photochemical process that operates under ambient conditions using renewable sunlight with a low activation energy in the range of E a = 2 - 7 kJ mol -1

[0019] The hydrogen generation described in this book results in a zero-carbon footprint, uses environmentally friendly renewable precursors such as coal, biochar, charcoal, carbon black, biomass, etc., but is not limited to these, and is easily scalable using fixed or fluidized bed photoreactor technology. Furthermore, by solar cells and light-emitting diodes, the process can be continuously driven and the intermittency of sunlight can be avoided. Using one of the products of the process or method of the present invention, namely syngas, a mixture of H2 / CO, hundreds of thousands of chemical products can be manufactured.

[0020] As described in more detail in the following examples, in order to demonstrate / judge the usefulness of the process or method of the present invention in reforming low-molecular hydrogen vectors, one or more low-molecular hydrogen vectors were introduced into the reactor in which the photoabsorbing carbon enabler was present.

[0021] The reactor was composed of a stainless-steel reactor body having one or more quartz glass windows arranged around it and a valve for controlling the inflow and outflow of gas (gas) to and from the reactor body. The quartz glass window of the reactor irradiates light, which may be sunlight, or LED lighting or xenon lighting simulating sunlight, onto the surface of the photoabsorbing carbon enabler arranged in the reactor and enables the generation of hydrogen in the reactor. The reactor may be heated, for example, by a heating cartridge arranged inside or outside the reactor body. The reactor is easily scalable using fixed or fluidized bed photoreactor technology to create a reactor suitable for commercial use.

[0022] For the reaction, one of the following was used as the light source: sunlight amplified by optical lenses (solar power), xenon illumination, or four combined or separated LED lights (ultraviolet (UV), blue, green, and red). The light intensity was changed by manually adjusting the power to the xenon or LED lights. An Omega temperature controller was attached to a heating cartridge inserted into the copper block, along with thermocouples inserted into the reactor to measure and control the temperature inside the reactor. The reaction gas containing low molecular weight hydrogen vectors was introduced into the reactor at a flow rate controlled by a mass flow controller. The surface area of ​​the light-irradiated carbon enabler could be controlled by optical lenses. A new sample was used for each test condition. Exhaust gases were periodically collected and analyzed.

[0023] In all of these embodiments, carbon and light are facilitators necessary to enable these photochemical modification reactions. In this process, the carbon is consumed or transformed, and the light provides energy for the conversion of the hydrogen vector into a co-product of hydrogen and value-added carbon or carbon monoxide. The process or method of the present invention is unique in that the carbon enabler is not a catalyst, but is transformed or consumed during the generation of hydrogen.

[0024] [Example 1] Carbon-enabled photoreforming of alkanes to green hydrogen under ambient conditions. To confirm the usefulness of replacing the thermochemical methane pyrolysis process, which is typically carried out in the temperature range of 800-1100°C, with a photochemical process driven by sunlight under ambient conditions, methane was passed through the laboratory-scale reactor described above. The same carbon enabler was used for each test. Four tests were conducted under "dark" conditions at the reactor temperatures shown in Figure 1. The four tests were conducted under 300 watts of xenon light at 10 W cm². -2at the light intensity and at the temperature shown in FIG. 1. Each test under sunlight and under xenon illumination was carried out at 54.8 and 35 W cm -2 of light intensity without additional heating. The spot size of the illumination was adjusted as shown in FIG. 1.

[0025] Regarding the generation of hydrogen, it was detected and measured with a gas chromatograph equipped with both a thermal conductivity detector (TCD) and flame ionization detectors (FID).

[0026] The activation energy shown in FIG. 1 was measured by an Arrhenius plot. Note that k = Ae (-Ea / T) is

[0027] [Example 2] Changes in the form of the carbon material before and after the photoreforming reaction of CH4 to produce H2 and C Raman analysis of the carbon material used in Example 1 was carried out for both before and after the reaction for the carbon enabler to confirm the changes in its form and chemical structure during the reaction. The results are shown in FIG. 2.

[0028] The Raman spectrum of the carbon material was collected at 1 mW using a red laser (532 nm) with a Bruker SENTERRA Raman microscope. The results are shown in FIG. 2. The difference in the ratio between the D band and the G band (visible as the left bulge at a wavenumber of 1350 and the right bulge at a wavenumber of 1600) and the height of the band signal change with the form of the carbon material. The increase in the height of the D band in the second spectrum indicates a change in the form of the carbon from a more ordered state to a less ordered state.

[0029] [Example 3] Photoreforming of carbon utilization of water to green syngas under ambient conditions The usefulness of the process or method of the present invention in reforming steam with hydrogen and carbon monoxide (CO) was demonstrated as follows: Steam was passed through the above-described laboratory-scale reactor. The same carbon enabler was used for each test. Four tests were conducted under 300 watts of xenon light at 15.8 W cm². -2 The tests were conducted at light intensities ranging from 40°C to 60°C, as shown in Figure 1. One test was performed under xenon illumination at 23.6 W cm². -2 Light intensity and 35.4 W cm -2 The tests were performed at different light intensities, each at 60°C.

[0030] Under each of these conditions, the production rates of hydrogen and carbon monoxide were measured by periodic sampling of effluent gases using GC-FID and GC-TCD. The results are shown in Figure 3, demonstrating that the use of light- and light-absorbing carbon materials enables the production of hydrogen and carbon monoxide at ambient temperature or slightly above ambient temperature, which is considerably lower than the temperature range of 800-1000°C required by conventional processes.

[0031] The activation energies of H2 and CO, i.e., 7.0 and 2.2 kJ / mol. -1 This is the 180-240 kJ mol required by conventional processes. -1 It was considerably lower than that.

[0032] While embodiments of this disclosure are described in detail, it should be understood that, unless otherwise specified, this disclosure is not limited to specific materials, reactants, processes, or methods, and can be modified. It should also be understood that the techniques used in this document are intended to describe specific embodiments only, and are not intended to limit them. Furthermore, in this disclosure, steps can be performed in different sequences where logically possible.

Claims

1. A method for modifying a low molecular weight hydrogen vector for producing hydrogen and one or more co-products, a. Introducing the low molecular weight hydrogen vector into a reaction apparatus containing a light-absorbing carbon enabler; b. The light-absorbing carbon enabler in the reactor is at least about 0.1 W cm －２ Exposure to a light source having an intensity of; and c. Optionally, separate hydrogen from one or more co-products of the reaction. Includes, A method for modifying a low molecular weight hydrogen vector, characterized in that at least a portion of the light-absorbing carbon enabler is consumed during the reaction.

2. A method for photochemically modifying a hydrogen vector in a reaction apparatus containing a light-absorbing carbon enabler, a. Introducing the low molecular weight hydrogen vector into the reaction apparatus; b. The light-absorbing carbon enabler in the reactor is at least about 0.1 W cm －２ Exposure to a light source having an intensity of; and c. Optionally, separate hydrogen from one or more co-products of the reaction. Includes, The carbon is consumed or altered in the method described above. A photochemical modification method for hydrogen vectors characterized by the following.

3. The method according to 1 or 2, characterized in that the low molecular weight hydrogen vector is selected from the group consisting of gaseous alkanes, methane, and water.

4. The method according to 1 or 2, characterized in that the low molecular weight hydrogen vector is selected from the group consisting of methane and water.

5. The method according to any one of claims 1 to 4, characterized in that the light-absorbing carbon enabler is one or more coals, biochar, charcoal, carbon black, or biomass.

6. The intensity of the aforementioned light source is approximately 0.1 W cm². －２ The method according to any one of 1 to 5, characterized in that it is greater than

7. The light source intensity is approximately 2 W cm². －２ The method according to any one of 1 to 5, characterized in that it is greater than

8. The intensity of the aforementioned light source is approximately 0.1 W cm². －２ From approximately 300 W cm －２ The method according to any one of 1 to 5, characterized in that it is the same.

9. The intensity of the aforementioned light source is approximately 2 W cm². －２ From approximately 60 W cm －２ The method according to any one of 1 to 5, characterized in that it is the same.

10. The intensity of the light source is about 10 W / cm －２ to about 60 W / cm －２ The method according to any one of claims 1 to 5, characterized in that it is as such.

11. The method according to any one of 1 to 5, characterized in that the co-product of the above reaction is carbon or carbon monoxide (CO).

12. The method according to any one of claims 1 to 5, characterized in that the reaction is driven by sunlight or artificial light.

13. The method according to any one of 1 to 5, characterized in that the reaction occurs under ambient conditions.

14. The method according to any one of 1 to 5, characterized in that the reaction occurs at a temperature of 20 to 60 degrees Celsius.

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