The present invention relates to a method for manufacturing carbon membranes supported on a ceramic support, wherein the membranes are used for the separation of gases.

FIELD OF THE INVENTION

In recent years researchers intended to develop membrane-based separation technologies to acquire higher purities and less energy consumption compared to conventional methods such as cryogenic distillation and pressure swing adsorption. With membranes technology, high purity H ₂ could be achieved while CO ₂ is available at high purity for CCS or CCU purposes. Integration of membranes in a reactor, could shift the equilibrium limited reactions to increase the efficiency of the processes.

The necessity of mitigating CO ₂ emissions in recent decades for controlling the global warming caused by greenhouse gases is inevitable. Shifting from fossil-based fuels to green energy sources is a must for a sustainable future. Hydrogen as a potential solution for energy storage-carrier and consumption in chemicals synthesis such as fertilizers, mainly produced via steam reforming. H ₂ separation and purification from CO ₂ is considered one of the energy intensive processes.

H ₂ recovery from waste streams such as metal industries off gases, could decrease the demand for fresh H ₂ and as a result a decrease of the carbon footprint of metal industries. Currently due to limitations of the traditional technologies in H ₂ separation from waste streams, these gases are burned to recover the energy or just sent to flare system. CO ₂ separation and purification from industries flue gasses such as power plants or refineries are considered one of the main challenges in recent years.

While polymeric membranes are considered as a mature technology in areas such as water purification via reverse osmosis, in gas separation processes, still it is in early stages. Polymeric membranes for H ₂ /CO ₂ and CO ₂ /N ₂ separations suffer from sorption of CO ₂ , enlarging the polymer structure (swelling). The swelling phenomena decreases the selectivity of polymeric membranes and their final performance. Inorganic membranes do not swell and are considered as a potential technology for h /CC^ and CO ₂ /N ₂ separations.

Disadvantages of traditional methods such as absorption, in energy usage and solvent loss, are preventing from them to be widely accepted in the industries. Therefore, novel methods are required to eliminate these obstacles and make it possible for CO ₂ separation and purification to be implemented widely in industries processes.

In addition, polymeric membranes are limited in operational temperature and pressure ranges due to the CO ₂ sorption in the structure and swelling of the polymer for high temperature and pressure applications such as membrane reactors for H ₂ production.

Due to chemical limitations of polymeric membranes in terms of swelling and instability at high temperatures, the h /CC^ and CO ₂ /N ₂ separation carried out at lower temperatures and pressures. Crosslinking of polymers is a common method to decrease the swelling which has disadvantages such as decrease in permeability which would increase the required surface area of the membranes for the process.

Currently due to limitations of the membranes in gas separation processes, new high-performance membranes are required.

Palladium membranes in recent years are being studied intensively due to their H ₂ unique permeation mechanism. Palladium membranes could reach almost infinite selectivity and high permeability in H ₂ separation and purification processes. Palladium as a noble metal, has passed even gold price in recent years due to lack of supply and high demand in the market. Palladium membranes suffer from a phenomenon which is called embrittlement which happens in certain temperatures which can destroy the membrane. Also, hydrogen transport mechanism in palladium membranes will follow the square root of hydrogen concentration; this limits the enhance in hydrogen flow via increase in operational pressure difference between retentate and permeate streams to decrease the required surface area of the membrane for the separation process.

Carbon membranes as an inorganic membrane, are produced by carbonization of a thermosetting polymer in an inert atmosphere or vacuum. Carbon membranes with a molecular sieve and surface adsorption transport mechanisms could be considered as a potential gas separation solution in industries. Due to carbon structure and chemical stability, carbon membranes can perform at temperatures up to 500 °C and operational pressure difference, depending on the support, could be as high as 140 bar.

Due to physical limitations in self supported carbon membranes such as mechanical fragility, supported carbon membranes are used; producing an increase in physical stability of the membrane and enhances the permeation performance of membranes because of the possibility to decrease the thickness of the membrane to few micrometre ranges. The thickness of supported carbon membranes could be as low as 1 pm to enhance the flow through carbon membranes.

An object of the present invention is to provide membranes that demonstrate a high selectivity for H2/CO2 and H2 permeability, high selectivity for H2/N2 and H2 permeability and/or a high selectivity for CO2/N2 and CO2 permeability.

Another object of the present invention is to provide high temperature resistant membranes with performance test up to 470 °C.

Another object of the present invention is to provide tubular supported membranes capable of high operational pressures up to 70 bar pressure difference between retentate and permeate.

STATEMENTS OF THE INVENTION

The present invention thus provides in a first aspect a method for manufacturing a carbon membrane supported on a ceramic support from hydroquinone, the method comprising the following steps: a) synthesis of precursor oligomer by condensation of hydroquinone with formaldehyde in aqueous acidic media and heat; b) preparation of a dipping solution in an organic solvent; c) coating a ceramic support via dip coating solution made in step b); d) drying and polymerization of the coated support’s top layer in step c); e) carbonization of the polymerized construction of d), and f) post treatment of the carbonized construction of e), and optionally g) repetition of step c) to f) for multilayer carbon membranes.

The present invention thus relates to separation of H2 and CO2 from gas mixtures via carbon membranes synthesized from a thermosetting polyhydroquinone precursor. The membrane is supported on a ceramic porous material via coating method. The membrane could operate at extremely high temperatures and high pressures. H2/CO2, CO2/N2 and H2/N2 ideal selectivities and permeabilities passes well beyond performance of current organic membranes such as Robeson’s upper bound limit of polymeric membranes. High selectivity and permeability coupled with lower price compared to palladium membranes and high chemical and mechanical stability, will reduce the cost of H2 separation and purification in capital and operational costs.

In an example the dipping solution comprises the precursor oligomer and formaldehyde and possible other permeation enhancing components for initiation the polymerization and adding functional groups to the polymer.

In an example step b) further comprises synthesis of co-polymer with ethylene diamine or composite polymer with aluminum acetylacetonate.

In an example of the present method step f) of post treatment comprises humidification and oxidation of the membrane top layer with a diluted oxygen concentration in a stream which is used to enhance the permeance of the carbon membrane with opening the pores via oxidation.

In an example of the present method the carbonization temperature according to step e) is in a range of 500 - 1200 °C.

In an example of the present method several coating layers are applied on the ceramic support, wherein the number of layers is preferably in a range of 1-8, wherein the thickness of each layer is preferably in a range of 300 nm - 20 pm.

In an example of the present method the hydroquinone co-polymer is prepared from hydroquinone oligomer in an organic solvent with the addition of reagents such as ethylenediamine, aluminium acetylacetonate and formaldehyde , or combinations thereof.

In an example of the present method for the preparation of the dipping solution, hydroquinone oligomers are used as the main precursor and mixed with at least one component chosen from the group of polyvinyl butyral (PVB), aluminium acetylacetonate and ethylene diamine, or combinations thereof.

In an example of the present method the porous ceramic support is chosen from the group of AI2O3, ZrC>2, MgO, zeolites, T1O2, S1O2, CeC>2, YSZ , porous transition metal oxides tubes, or combinations thereof.

The present invention also relates in a second aspect to a membrane on a ceramic tubular support, wherein the membrane comprises at least one layer of a hydroquinone derived carbon membrane.

The present invention also relates in a third aspect to the use of a membrane as discussed above or to a membrane obtained according to a method as discussed above in separation of H2 and/or CO2 from gas mixtures. In an example the gas separation processes are chosen from the group of H2/CO2, CO2/N2 and H2/N2.

In an example the present membrane is used in H2 separation and purification in H2 production reactors.

In an example the present membrane is used in H2 recovery from waste streams such as metal industries blast furnace off gas treatment and fertilizer production purge gas streams.

In an example the present membrane is used in CO2 separation for carbon capture and storage (CCS) and/or in carbon capture and utilization (CCU) processes, such as separation of CO2 from post combustion gas streams or bio syngas purification.

The present invention is focused on supported carbon membranes for H2/CO2, H2/N2 and CO2/N2 separation processes. Hydroquinone derived membranes on ceramic tubular supports with few micrometre thicknesses fabricated and the permselectivities tests are performed from 45 °C up to 470 °C and pressures differences up to 30 bar between the retentate and permeate. Fabrication parameters are tailored to reach high performance in each gas separation process in terms of permselectivities. Hydroquinone oligomers are used as the main precursor for carbon membrane and they are copolymerized with ethylene diamine for CO2/N2 and mixed with poly vinyl butyral (PVB) for H2/CO2 separation processes respectively. Moreover, carbon membranes are synthesized with aluminium acetylacetonate and hydroquinone oligomers to result a composite structure carbon membrane for H2/N2 separation. All three membranes are supported on tubular ceramic supports with average pore size of 100nm for alpha alumina support and 120nm for zirconia supports.

The invention will now be described by the following non-limiting examples.

Figure 1 indicates the permeability of membrane at multiple temperatures.

Figure 2 represents the performance of membrane compared to literature upper bound limit for H2/N2 separation membranes.

Figure 3 represents the H2 permeability at different operational pressures and temperatures. 8 Examples

Table 1 summarizes the fabrication parameters in three developed membranes.

Table 1 : fabrication parameters of hydroquinone derived tubular supported carbon membranes.

Membrane for H2/CO2 H2/N2 CO2/N2

Support material AI2O3 ZrC>2 ZrC>2

Support average pore 100 nm 120 nm 120 nm size

Precursor (s) Hydroquinone, Hydroquinone Hydroquinone

Polyvinyl butyral oligomer, Aluminium oligomer, acetylacetonate ethylene diamine

Number of selective 3 2 2 layers (dippings)

Carbonization 500 °C 600 °C 500 °C temperature

Carbonization Ar N ₂ N ₂ atmosphere

Selective layer thickness 4.3 pm 6.7 pm 3.8 pm

An elemental analysis has been performed on the membranes. Results are summarized at Table 2.

Table 2: elemental analysis of hydroquinone derived carbon membranes wt%.

Membrane H2/CO2 H2/N2 CO2/N2

N 0 0- I .77

C 85.48 93.56 80.23

H 5.23 2.34 6.14

O 9.29 4.1 I I .86

Example 1 : H2/CO2 selective membrane

H2/CO2 high selectivity required in steam reforming reactors to firstly shift the equilibrium to the product side by removing one of the products according to Le- Chatelier's principle and secondly to produce high purity H2 at the permeate. Hydroquinone oligomer is used as a main precursor for synthesis of H2/CO2 selective membrane. Membrane consist of 3 ultra-thin layers, each one of the layers are optimized with fabrication parameters to have high selectivity and preserving high permeability while they stack up onto each other.

Results of permselectivities tests for H2/CO2 membrane are compared to upper bound limits of polymeric membranes. Most cited upper bound limit (Robeson, 2008) and three upper bounds according to operational temperatures (35, 100, 150 and 200 °C) from literature at 2020 indicating the superior performance of H2/CO2 selective hydroquinone derived membrane over the organic membranes in terms of both ideal selectivity and H2 permeability at operational temperatures from 45 °C to 470 °C and operational pressures from 1 to 6 barg.

Hydroquinone membrane reached maximum ideal H2/CO2 selectivity of 43 at 1 bar and 350 °C with H2 permeability of 12455 Barrer. Membrane chemical and physical stability were tested at 350 °C for a period of 380 hr. at 1 bar operational pressure.

Example 2: CO2/N2 selective membrane

CO2 separation from flue gas in industrial scale requires a minimum CO2/N2 selectivity of 70 and a minimum permeance of 3.3 ^c 10 ^~7 mol/(m ² s Pa) for being an economically feasible. In case of CO2/N2 selective hydroquinone derived carbon membrane, the requirement is validated, and the application of this membrane could have a critical role in industries for separation of CO2 from flue gas streams such as in metals manufacturing, power plants, and bio refineries.

Membrane is fabricated on a tubular porous zirconia support with an average pore size of 120 nm. Two ultra-thin selective carbon layers are utilized to reach the desired permselectivities performances. This carbon membrane consist of two selective layers on each other. Upper layer with bigger pore sizes acts as adsorption sites while second layer with smaller average pore size prevents from diffusion of N2 molecules.

Transport mechanism in the membrane follows surface diffusion mainly for CO2. Membrane fabrication is based on condensation polymerization of the oligomer and carbonization at inert atmosphere. Figure 1 indicates the permeability of membrane at multiple temperatures.

Figure 1 indicates the higher performance of CO2/N2 selective hydroquinone derived carbon membrane compared to polymeric membranes in operating pressures from 1 to 6 barg and operational temperatures from 45 °C to 470 °C.

CO2/N2 selective hydroquinone derived carbon membrane reached the maximum ideal selectivity of 680 at 150 °C and 2 bar pressure difference between permeate and retentate with CO2 permeability of 1471 Barrer.

Example 3: H2/N2 selective membrane

Hydrogen recovery from waste streams in industries such as metal, bio refineries, fertilizers production etc. could increase the efficiency of the processes and reduce the consumption of fresh hydrogen which is mostly produced from fossil fuels and it contributed to greenhouse gas emissions.

H2/N2 selective hydroquinone derived carbon membrane with 2-layer structure is fabricated on a zirconia porous support with average pore size of 120 nm. Performance of the membrane is tested in temperatures from 45 °C to 470 °C and pressures from 1 bar to 6 bar. Membrane is carbonized at 600 °C in N2 atmosphere. Figure 2 represents the performance of membrane compared to literature upper bound limit for H2/N2 separation membranes.

H2/N2 selective membrane reached maximum ideal selectivity of 302 at 2 bar and 150 °C with hydrogen permeability of 1314 Barrer. Figure 3 represents the H2 permeability at different operational pressures and temperatures.