Functionalized activated charcoal as adsorbent for removing cofrom atmospheric air

Abstract

The invention relates to functionalized activated charcoal which is suitable for removing CO2 from atmospheric air, to the production thereof, and to its use in a method for removing CO2 from air. The activated charcoal is functionalized with an aminopropyltrialkoxysilane.

Description

[0001] Description

[0002] Functionalized activated carbon as an adsorbent for the capture of CO2 from atmospheric air

[0003] The invention relates to functionalized activated carbon suitable for the separation of carbon dioxide (CO2) from atmospheric air, its production, and its use in a process for the separation of CO2 from atmospheric air.

[0004] The need to slow global climate change caused by greenhouse gas emissions is very urgent. Above all, the increase in atmospheric CO2 concentrations must be sustainably prevented. In addition to CO2 prevention and reduction, technologies for adsorbing CO2 from the ambient air are known. Direct air capture (DAC) is particularly suitable for reducing the proportion of CO2 in the atmosphere through "negative carbon emissions." The development of suitable adsorption materials should enable efficient and energetically viable CO2 capture.

[0005] One challenge is the development of efficient adsorption materials that exhibit high CC>2 adsorption capacity and require low energy for desorption. Thermal properties of the adsorption materials, in particular, represent an effective lever for the application of DAC technologies on an industrial scale.

[0006] Adsorption materials are known from US 2013 / 0095996 A1, US 2017 / 0239609 A1, and CN 104607073 B1. However, the solutions known from the state of the art are still unsatisfactory.

[0007] Classic adsorption materials are known, such as metal organic frameworks (MOFs), zeolites, amine-functionalized mesoporous materials and polymer-based adsorbers.

[0008] The invention is based on the object of providing materials that are specifically tailored to the requirements of the industrial capture of CO2 from atmospheric air, in particular the Direct Air Capture technology (DAC technology), and in particular are able to combine high adsorption capacity with economic advantages.

[0009] This problem is solved by the subject matter of the independent claims.

[0010] According to a first aspect of the invention, an adsorbent made of activated carbon is described which has been functionalized with an aminotrialkoxysilane and is suitable for separating CO2 from the air.

[0011] Conventional adsorption materials, such as metal-organic frameworks (MOFs), zeolites, and polymers, exhibit relatively low thermal conductivity. This requires significantly more time and energy for heating and cooling. Both factors negatively impact the efficiency of the adsorption materials, especially in the case of DAC technology.

[0012] The amine-functionalized adsorbents described here, in contrast, offer an efficient way to combine high adsorption capacity with economic advantages. It has now been discovered in connection with the invention that this is made possible, in particular, by adjusting the thermal conductivity. To make the removal of carbon dioxide from the air energetically efficient, it is important that the adsorption materials are selected so that the energy required for desorption and the associated heating and cooling phases is reduced to a minimum. The thermal properties of the adsorption materials also play a crucial role in this process. This is precisely what is achieved by the present invention.

[0013] Activated carbon in the sense of the present application is combustible and consists predominantly of carbon, with the carbon content preferably being at least 90 wt.%, in particular at least 95 wt.%, preferably at least 98 wt.%. The activated carbon has a porous structure, with the pores being open-pored and interconnected like a sponge. The internal surface area is preferably between 300 and 2000 m². 2 / g coal. The density of activated carbon is preferably in the range of 0.2 to 0.6 g / cm 3 .

[0014] In the context of the present invention, a material having a carbon content of at least 90%, an internal surface area of ​​300 and 2000 m 2 / g and a density in the range of 0.2 to 0.6 g / cm 3Activated carbon can be obtained from various sources. It is usually made from plant, animal, mineral, or petrochemical materials such as lignite and hard coal. Various types of activated carbon are known in the art. Source materials such as wood, peat, coconut fiber, and nutshells are also referred to as biochar. Animal charcoal refers to activated carbon made from animal material. Sugar charcoal refers to activated carbon made from glucose or another sugar as the starting material.

[0015] Gas activation and chemical activation are two methods of production and activation. In chemical activation, a mixture of uncarbonized raw material is treated with chemicals. This is generally achieved using dehydrating agents, particularly zinc chloride or phosphoric acid, preferably at 500 to 900 °C. Another process is dry distillation, also known as coking, in which the material is heated in an oxygen-free atmosphere and volatile components are driven off at temperatures around 800 °C. The resulting raw activated carbon is then oxidatively activated at 700 to 1000 °C with steam or carbon dioxide, and sometimes with air. During this activation, part of the carbon is converted into carbon monoxide using the water-gas process, which creates additional pores and increases the surface area of ​​the carbon.

[0016] The activated carbon obtained can be used in particular for producing the adsorbent according to the invention.

[0017] The adsorbent preferably has an activated carbon content of at least 80 wt.%, in particular at least 85 wt.%, based on the mass of the total adsorbent. More preferably, the adsorbent consists of activated carbon and differs from substrates coated only with activated carbon.

[0018] According to a preferred embodiment, the adsorption material is described, wherein the aminotrialkoxysilane is a (3-aminoalkyl)trialkoxysilane.

[0019] According to a further preferred embodiment, the aminotrialkoxysilane is a (3-aminoalkyl)triethoxysilane. According to a further preferred embodiment, the aminotrialkoxysilane is a (3-aminopropyl)trialkoxysilane.

[0020] According to a further preferred embodiment, the aminotrialkoxysilane is a (3-aminopropyl)triethoxysilane.

[0021] Furthermore, according to a preferred embodiment, the adsorption material is described, wherein the activated carbon is formed as substantially microporous activated carbon.

[0022] Porosity is a physically relevant parameter for description. Porosity, or void fraction, is a measure of the pores, and thus the free spaces, in a material. It is the fraction of the volume of pores over the total volume and takes values ​​between 0 and 1, or as a percentage between 0% and 100%. Empirical measurements of porosity usually determine the "accessible void," the total void space accessible from the surface.

[0023] According to a preferred embodiment, the porosity refers to the entire cavity of the activated carbon. According to a further preferred embodiment, the porosity refers to the cavity accessible to gases, in particular CO2. The measurement of the inner surface can be determined here by gas binding, in particular by adsorption of CO2.

[0024] Regarding porosity, according to their average diameter, a classification is made into classes: micropores of not more than 2 nm, mesopores of 2 to 50 nm and macropores of more than 50 nm.

[0025] In this context, the mean diameter of the pores is defined as the diameter of a pore, i.e. the average diametrical distance between two points at the pore entrance.

[0026] Mesopores are the access routes for gases or liquids into the interior of the coal and are significantly involved in diffusion and mass transport processes into deeper areas of the grain.

[0027] The activated carbon preferably has a substantially mesoporous structure. In the context of the present invention, "substantially mesoporous" refers to activated carbon with a proportion of mesoporous pores, based on the total number of pores, of at least 50%, more preferably of at least 70%.

[0028] Such an essentially microporous structure has proven particularly well-suited for functionalization and enables the efficient adsorption of CO2. Aminotrialkoxysilane was particularly well-suited for functionalizing the microporous structure, as it essentially retained its original shape.

[0029] According to a further aspect, there is provided a process for preparing the adsorbent, the process comprising functionalizing activated carbon with aminotrialkoxysilane in a solvent.

[0030] According to a preferred embodiment, the process for producing the adsorbent is described, wherein an alcohol is used as the solvent. According to a further preferred embodiment, the process for producing the adsorbent is described, wherein methanol is used as the solvent.

[0031] A preferred method is described in which an acidic or basic pretreatment takes place before functionalization with the aminotrialkoxysilane. This allows the advantages of functionalization to be utilized even more effectively. Functionalization and pretreatment are thus coordinated.

[0032] Such an essentially microporous structure has proven particularly well-suited for functionalization and enables the efficient adsorption of CO2. The described process is particularly suitable for functionalizing activated carbon with an essentially microporous structure. Maintaining the microporous structure of the activated carbon is particularly important for efficient use in the DAC process. This is achieved by the process described here, in particular the use of the aminotrialkoxysilane in a methanol solvent. Other functionalization processes reduce or destroy the microporous structure of the activated carbon.

[0033] According to a further preferred embodiment, the process for producing the adsorbent is described, wherein the aminotrialkoxysilane is used in an amount of less than 2 wt.%, preferably less than 1 wt.%, more preferably less than 0.5 wt.%, based on the amount of solvent. Such an amount of aminotrialkoxysilane proves to be optimal for the required functionalization under the further process conditions.

[0034] According to a further aspect, a method for separating CC^ from the air using the adsorbent is described, wherein the adsorbent is brought into contact with atmospheric air in an adsorption step.

[0035] According to a preferred embodiment, the method for separating CO2 from the air using the adsorbent is described, wherein the adsorbent is released in a desorption step.

[0036] According to a preferred embodiment, the method for separating CO2 from the air using the adsorbent is described, wherein the method is designed as a DAC method.

[0037] The captured CO2 can then be reused. The use of renewable raw materials is an effective lever for improving the overall CO2 footprint of vehicles. Sustainable polymer solutions are becoming increasingly important in the automotive industry, based on vehicle life cycle analyses.

[0038] The CO2 obtained using the functionalized adsorption material by means of the DAC process can be used in particular for synthesis purposes.

[0039] Thermoplastic polymers based on bound CO2 not only have the properties of easy processing in the form of forming processes, but also a property profile specified for the respective application and have a negative CO2 balance over the product life cycle.

[0040] Further preferred embodiments of the invention emerge from the remaining features mentioned in the subclaims.

[0041] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0042] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Figure 1 shows a schematic representation of an embodiment of the DAC method for

[0043] Separation of CC^ from atmospheric air by adsorption on the adsorption agent according to the invention

[0044] Figure 1 shows a schematic representation of a DAC process for the capture of CO2 from atmospheric air.

[0045] The DAC device is designed here as a single unit comprising the inventive adsorbent made of activated carbon functionalized with an aminotrialkoxysilane. Adsorption (10) and desorption or regeneration (20) can take place sequentially.

[0046] During adsorption 10, the system is opened in the first step, and atmospheric air flows in without any additional aids or with the aid of fans. At ambient temperature, CO2 chemically binds to the CO2-depleted air and leaves the system 11. This step is completed when the sorbent according to the invention is completely saturated with CO2. In the next step, the fans are switched off, the inlet valve is closed, and the residual air is removed from the system either through a pressure drop 4 by suction or by introducing steam.

[0047] Regeneration 20 then takes place by heating the system to a specific temperature 3. The inventive adsorbent, made of activated carbon functionalized with an aminotrialkoxysilane, now effectively releases the CO2. The released CO2 is collected and transported out of the system for purification, compression, or recycling. To start another cycle, the system should be cooled to ambient conditions.

[0048] During both adsorption 10 and desorption 20, electrical energy is fed in to operate the plant 2, 5.

[0049] The functionalized activated carbon used in the DAC process described above is obtained as follows:

[0050] A 0.25 wt% solution of aminotrialkoxysilane (APTM) in methanol is prepared. Enough activated carbon is then added to ensure it is just completely covered by the solution. The solution is then stirred until the methanol has completely evaporated.

[0051] Such an essentially microporous structure has proven particularly well-suited for functionalization and enables the efficient adsorption of CO2. The described process is particularly suitable for functionalizing activated carbon with an essentially microporous structure. Maintaining the microporous structure of the activated carbon is particularly important for efficient use in the DAC process. This is achieved by the process described here, in particular the use of the aminotrialkoxysilane in a methanol solvent. Other functionalization processes reduce or destroy the microporous structure of the activated carbon.

[0052] List of reference symbols

[0053] atmospheric air

[0054] Electricity input adsorption

[0055] Heat input

[0056] pressure drop

[0057] Electricity input regeneration

[0058] Adsorption phase

[0059] Removal of CO2-depleted air

[0060] Discharge of pure CO2

[0061] Water discharge

[0062] Regeneration phase

Claims

Claims: Adsorbent material made of activated carbon functionalized with an aminotrialkoxysilane for the removal of carbon dioxide (CC) from the air. Adsorbent material according to claim 1, wherein the aminotrialkoxysilane is a (3-aminopropyl)triethoxysilane. Adsorbent material according to claim 1 or 2, wherein the activated carbon is formed as substantially microporous activated carbon. Method for producing the adsorbent according to any one of the preceding claims 1 to 3, wherein the method comprises the functionalization of activated carbon with aminotrialkoxysilane in a solvent. Method according to claim 4, wherein an acidic or basic pretreatment takes place prior to functionalization with the aminotrialkoxysilane. Method for producing the adsorbent according to the preceding claim 4 or 5, wherein an alcohol, preferably methanol, is used as the solvent.A process for producing the adsorbent according to any one of the preceding claims 4 to 6, wherein the aminotrialkoxysilane is used in an amount of less than 2 wt%, preferably less than 1 wt%, more preferably less than 0.5 wt% based on the amount of solvent. A process for separating CO2 from the air using the adsorbent according to any one of the preceding claims 1 to 3, wherein the adsorbent is brought into contact with atmospheric air in an adsorption step (10). A process according to the preceding claim, wherein the adsorbent is released in a desorption step (20).

10. Method according to one of the preceding two claims 8 or 9, wherein the method is designed as a DAC method.

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