DE102022103174A1 - Functionalized activated carbon as an adsorbent for the separation of CO2 from atmospheric air - Google Patents

Abstract

The invention relates to functionalized activated carbon suitable for separating CO2 from atmospheric air, its production and its use in a method for separating CO2 from atmospheric air.

Description

The invention relates to functionalized activated carbon suitable for separating carbon dioxide (CO ₂ ) from atmospheric air, its production and its use in a method for separating CO ₂ from atmospheric air.

The need to slow global climate change caused by greenhouse gas emissions is very urgent. Above all, the increase in atmospheric CO ₂ levels must be avoided in the long term. In addition to avoiding and reducing CO _{2 ,} technologies for adsorbing CO ₂ from the ambient air are known. In particular, "Direct Air Capture" (DAC) is suitable for reducing the proportion of CO ₂ in the atmospheric air through "negative carbon emissions". The development of suitable adsorption materials should enable efficient and energetically sensible CO ₂ separation.

A challenge is the development of efficient adsorption materials that have a high CO ₂ adsorption capacity and require little energy for desorption. In particular, the thermal properties of the adsorption materials represent an effective lever for the application of DAC technologies on an industrial scale.

From the US 2013/0095996 A1 , the US 2017/0239609 A1 and the CN104607073B1 adsorption materials are known. However, the solutions known from the prior art are still unsatisfactory.

Classical adsorption materials are known, which include, for example, the metal-organic frameworks (MOFs), the zeolites, amine-functionalized mesoporous materials and polymer-based adsorbers.

The object of the invention is now to provide materials that are specifically tailored to the requirements of industrial separation of CO ₂ from atmospheric air, in particular direct air capture technology (DAC technology), and in particular have a high adsorption capacity able to combine economic advantages.

This object is solved by the subject matter of the independent claims.

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 CO ₂ from the air.

Classic adsorption materials, such as Metal Organic Frameworks (MOFs), zeolites and polymers, have relatively low thermal conductivity. This circumstance requires significantly more time and energy for heating and cooling. Both have a negative impact on the efficiency of the adsorption materials, especially in the case of DAC technology.

In contrast, the amine-functionalized adsorbents described here offer an efficient way of combining high adsorption capacity with economic advantages. It has now been found in connection with the invention that this is made possible in particular by adapting the thermal conductivity. In order to make the separation of carbon dioxide from the air energetically efficient, it is important that the adsorption materials are chosen in such a way that the energy for the desorption and the associated heating and cooling phase is reduced to a minimum. The thermal properties of the adsorption materials also play a decisive role here. This is precisely what the present invention achieves.

Activated charcoal within the meaning of the present application is combustible and consists predominantly of carbon, the carbon content preferably being at least 90% by weight, in particular at least 95% by weight, preferably at least 98% by weight. The activated carbon has a porous structure, with the pores being open-pored and interconnected like a sponge. The inner surface is preferably between 300 and 2000 m ² /g coal. The density of the activated carbon is preferably in the range from 0.2 to 0.6 g/cm ³ .

In connection with the present invention, preference is given to a substance with a carbon content of at least 90%, an internal surface area of 300 and 2000 m ² /g and a density in a range from 0.2 to 0.6 g/cm ³ as “activated carbon”. " designated.

Activated charcoal can be obtained from a variety of sources. In most cases, this is made from plant, animal, mineral or petrochemical substances such as lignite or hard coal. Various types of activated carbon are known in the prior art. Such starting materials as wood, peat, coconut fiber and nut shells are also referred to as biochar. Activated charcoal made from animal material is called animal charcoal. Sugar charcoal is an activated charcoal that is made from glucose or another sugar as a starting material.

Gas activation and chemical activation should be mentioned for production and activation. In chemical activation manufacturing, a mixture of uncharred raw material is treated with chemicals. This is generally done by using dehydrating agents, especially 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 raw activated carbon obtained in this way is then activated by oxidation at 700 to 1000 °C with steam or carbon dioxide, sometimes also 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.

The activated carbon obtained can be used in particular for the production of the adsorbent according to the invention.

The adsorbent preferably has an activated carbon content of at least 80% by weight, in particular at least 85% by weight, based on the mass of the entire adsorbent. More preferably, the adsorbent consists of activated carbon and differs from substrates coated only with activated carbon.

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

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.

In an even more preferred embodiment, the aminotrialkoxysilane is a (3-aminopropyl)triethoxysilane.

Furthermore, according to a preferred embodiment, the adsorption material is described, wherein the activated charcoal is designed as an essentially microporous activated charcoal.

The porosity is a physically relevant parameter for description. The porosity, or pore fraction, is a measure of the pores, and thus the free spaces, in a material. It is the fraction of the volume of the pores over the total volume and takes values between 0 and 1 or as a percentage between 0% and 100%. Empirical measurements of porosity typically determine “accessible void space”, the total void space accessible from the surface.

According to a preferred embodiment, the porosity refers to the entire cavity of the activated carbon. According to a further preferred embodiment, the porosity relates to the cavity accessible to gases, in particular CO ₂ . The measurement of the inner surface can be determined here by gas binding, in particular by adsorption of CO ₂ .

With regard to the porosity, according to their average diameter, a classification is made: micropores of no more than 2 nm, mesopores from 2 to 50 nm and macropores of more than 50 nm.

In this context, the mean diameter of the pores is based on the diameter of a pore, ie the average diametral distance between two points at the pore entrance.

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

The activated carbon preferably has an essentially mesoporous structure. In connection with the present invention, “essentially mesoporous” refers to activated carbon with a proportion of mesoporous pores, based on the total number of pores, of at least 50%, more preferably at least 70%.

Such an essentially microporous structure has been shown to be particularly easy to functionalize and enables the efficient adsorption of CO ₂ . In particular, aminotrialkoxysilane was well suited for the functionalization of the microporous structure, as this essentially preserved it.

According to another aspect, there is a method of making the adsorbent, the method comprising functionalizing activated carbon with aminotrialkoxysilane in a solvent.

According to a preferred embodiment, the method for producing the adsorbent is described, with an alcohol being used as the solvent. According to a further preferred embodiment, the method for producing the adsorbent is described, with methanol being used as the solvent.

A process is preferably described in which an acidic or basic pretreatment takes place before the functionalization with the aminotrialkoxysilane. As a result, the advantages of functionalization can be used even better. Functionalization and pre-treatment are thus coordinated with one another.

Such an essentially microporous structure has been shown to be particularly easy to functionalize and enables the efficient adsorption of CO ₂ . In particular, the method described is suitable for functionalizing activated carbon with an essentially microporous structure. Preserving the microporous structure of the activated carbon is particularly important for efficient use in the DAC process. This is achieved by the procedure described here, in particular the use of the aminotrialkoxysilane in a methanol solvent. Other functionalization procedures reduce or destroy the microporous structure of the activated carbon.

According to a further preferred embodiment, the method for producing the adsorbent is described, the aminotrialkoxysilane being present in an amount of less than 2% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, based on the amount of solvent used.

Under the further process conditions, such an amount of aminotrialkoxysilane is found to be optimal for the required functionalization.

According to a further aspect, a method for separating CO ₂ from air using the adsorbent is described, wherein the adsorbent is brought into contact with atmospheric air in an adsorption step.

According to a preferred embodiment, the method for separating CO ₂ from the air using the adsorbent is described, the adsorbent being released in a desorption step.

According to a preferred embodiment, the method for separating CO ₂ from the air using the adsorbent is described, the method being designed as a DAC method.

The CO ₂ obtained can now be reused. The use of renewable raw materials is an effective lever for improving the overall CO ₂ balance of vehicles. In this context, sustainable polymer solutions are becoming increasingly important in the automotive industry based on the life cycle analysis of motor vehicles.

The CO ₂ obtained using the functionalized adsorption material by means of the DAC process can be used in particular for synthesis purposes. Thermoplastic polymers based on bound CO ₂ 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 CO ₂ balance over the product life cycle.

Further preferred configurations of the invention result from the remaining features mentioned in the dependent claims.

Unless stated otherwise in the individual case, the various embodiments of the invention mentioned in this application can advantageously be combined with one another.

• 1 Schematische Darstellung einer Ausführungsform des DAC-Verfahrens zur Abscheidung von CO₂ aus der Atmosphärenluft mittels Adsoption an dem erfindungsgemäßen Adsoprtionsmittel

The invention is explained below in exemplary embodiments with reference to the associated drawings. It shows:

• 1 Schematic representation of an embodiment of the DAC process for separating CO ₂ from the atmospheric air by means of adsorption on the adsorption agent according to the invention

1 shows a schematic representation of a DAC process for separating CO ₂ from atmospheric air.

Here, the DAC device is configured as a single unit comprising the activated carbon adsorbent of the invention functionalized with an aminotrialkoxysilane. The adsorption (10) and desorption or regeneration (20) can take place one after the other.

With adsorption 10, the system is opened in the first step and atmospheric air flows in without any further aids or with the help of fans. At ambient temperature, CO ₂ chemically binds to the CO ₂ -depleted air and exits the system 11. This step is complete when the sorbent of the invention is fully saturated with CO ₂ . In the next step, the fans are switched off, the inlet valve is closed and the residual air is guided out of the system either through a pressure drop 4 by suction or the introduction of steam.

The regeneration 20 then takes place, in that the system is heated to a certain temperature xysilane has been functionalized now effectively releases the CO ₂ . The released CO ₂ is collected and transported out of the system for cleaning, compression or recycling. To start another cycle, the system should be cooled to ambient conditions.

Both during adsorption 10 and during desorption 20, electrical energy is fed in to operate the system 2, 5.

• Es wird eine 0,25 Gew.-% Lösung von Aminotrialkoxysilan (APTM) in Methanol hergestellt. Anschließend wird so viel aktivierte Aktivkohle hinzugegeben, dass diese gerade noch vollständig mit Lösung bedeckt ist. Anschließend wird die Lösung gerührt, solange bis das Methanol vollständig verdampft ist.

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

• A 0.25% by weight solution of aminotrialkoxysilane (APTM) in methanol is prepared. Then enough activated carbon is added that it is just completely covered with solution. The solution is then stirred until the methanol has completely evaporated.

Such an essentially microporous structure has been shown to be particularly easy to functionalize and enables the efficient adsorption of CO ₂ . In particular, the method described is suitable for functionalizing activated carbon with an essentially microporous structure. Preserving the microporous structure of the activated carbon is particularly important for efficient use in the DAC process. This is achieved by the procedure described here, in particular the use of the aminotrialkoxysilane in a methanol solvent. Other functionalization procedures reduce or destroy the microporous structure of the activated carbon.

Reference List

1

atmospheric air

2

Electricity entry adsorption

3

heat input

4

pressure drop

5

Electricity input regeneration

10

adsorption phase

11

Discharge of CO ₂ depleted air

12

Discharge of pure CO ₂

13

water discharge

20

regeneration phase

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US 2013/0095996 A1 [0004]
• US 2017/0239609 A1 [0004]
• CN 104607073 B1 [0004]

Claims (10)

Activated carbon adsorbent functionalized with an aminotrialkoxysilane for the removal of CO ₂ from air. Adsorption material according to claim 1 wherein the aminotrialkoxysilane is a (3-aminopropyl)triethoxysilane. Adsorption material according to claim 1 or 2 , wherein the activated carbon is formed as a substantially microporous activated carbon. Process for producing the adsorbent according to any one of the preceding Claims 1 until 3 , the method comprising the functionalization of activated carbon with aminotrialkoxysilane in a solvent. procedure according to claim 4 , with an acidic or basic pretreatment taking place before the functionalization with the aminotrialkoxysilane. Process for producing the adsorbent according to the foregoing claim 4 or 5 , An alcohol, preferably methanol, being used as the solvent. Process for producing the adsorbent according to any one of the preceding Claims 4 until 6 , wherein the aminotrialkoxysilane is used in an amount of less than 2% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, based on the amount of solvent. A method for separating CO ₂ from air using the adsorbent according to any one of the preceding Claims 1 until 3 wherein the adsorbent is contacted with atmospheric air in an adsorption step (10). A method according to the preceding claim, wherein the adsorbent is released in a desorption step (20). Method according to either of the preceding two Claims 8 or 9 , the method being designed as a DAC method.

Images