METHOD AND PLANT FOR PLASMA CATALYTIC CARBON DIOXIDE HYDRATION WITH IN-SITU WATER REMOVAL AND ADDITIONAL HYDROGEN PRODUCTION

Description

FIELD OF THE INVENTION

[0001] The present invention relates to the field of synthetic methane production with in-situ produced water / water vapour removal and additional hydrogen generation from it. In particular, the present invention relates to synergetic effect of a gliding arc discharge plasma (GADP) and catalytic carbon dioxide hydrogenation with subsequent produced water removal and additional hydrogen production at low temperatures and atmospheric to moderate-level pressures.BACKGROUND OF THE INVENTION

[0002] The exothermic Sabatier reaction produces methane and water during carbon dioxide and hydrogen reaction at stoichiometric ratio of 1:4, temperatures above 300-500 °C, and high pressures 1-10 MPa, and in the presence of a catalyst, usually Ni-based supported on aluminium oxide. The reaction is as follows: CO 2 + 4 H 2 ↔ CH 4 + 2 H 2 O , Δ H = − 165 kJ mol .

[0003] Beside Ni, other transition metals such as Ru, Rh, Pd and Pt are generally used as catalytic material for methanation in the form of metal nanoparticles (MNP) deposited on various supports (MNP / support). Also, new methanation catalyst support materials, such as metal oxides, modified oxides, metal-organic frameworks, zeolites, mesoporous silica, carbon materials, etc., have been widely investigated to increase its activity and stability. Reversible CO 2 hydrogenation reaction (Sabatier reaction) requires in-situ water removal to get higher methane yield and selectivity. Therefore, the introduction of water-selective materials (sorbents or membranes) have been widely studied. Among the different water-selective materials that have been proposed and tested in CO 2 hydrogenation literature, zeolite materials are the most widely used followed by silica, ceramics, etc. (Faria et al., 2018, https: / / doi.org / 10.1016 / j.jcou.2018.05.005). ASHOK JANGAM ET AL: "A review of recent catalyst advances in CO2 methanation processes",CATALYSIS TODAY, ELSEVIER, AMSTERDAM, NL, vol. 356, 29 July 2020 (2020-07-29), pages 471-489,discloses CO2 methanation processes. It states that the reaction can be performed using plasma including a gliding arc plasma and that Ni on a high surface area porous material is a suitable catalyst.

[0004] Exploration of novel catalysts and supports as well as demonstration of complete value chain and energy-efficient technology for carbon dioxide methanation has received much attention. Recently, plasma-assisted both catalytic and non-catalytic carbon dioxide hydrogenation has been applied to overcome the barriers of the traditional thermo-catalytic process. The use of plasma enables activation of molecules via excitation, dissociation and ionization, thus generating reactive species such as electrons, ions, radicals, exited species, etc. These reactive plasma species contribute to both the gas phase and surface reactions, undertaking new reaction pathways proceeding at ambient temperatures to 200 °C and atmospheric pressures to several bar.

[0005] Therefore, exists the need for synthetic methane production with in-situ water removal in which the process can be carried out at low temperatures and pressures, thus overcoming shortcomings typical for conventional thermal catalytic carbon dioxide hydrogenation process.SUMMARY OF THE INVENTION

[0006] The novelty of the present invention relates to a method performing the gliding arc plasma-catalytic carbon dioxide hydrogenation with in-situ water removal and additional hydrogen production from it via plasma-activated aluminium and water / water vapour reaction at low temperatures and atmospheric to moderate-level pressures of 1-5 bars.

[0007] The present disclosure also relates to a system suitable for performing the process according to the present invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. 1 represents a scheme of a gliding arc discharge plasma (GADP) catalytic reactor for CO 2 hydrogenation. Fig. 2 represents a multi-point BET plot of a high specific surface area of 1012.6 m 2< / g Fig. 3 shows X-ray diffraction (XRD) patterns of Ni / PCH catalyst. Fig. 4 represents a scheme of reaction chamber for in-situ water / water vapour removal and additional hydrogen production. Fig. 5 represents a plot related to additional hydrogen production via activated aluminium and water reaction during GADP catalytic CO 2 methanation process. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention relates to a method and a system for performing the following Sabatier reaction (R1) using the synergetic effect of a gliding arc discharge plasma (GADP) and a catalyst with subsequent in-situ water removal and additional hydrogen production via water and plasma-activated aluminium reaction (R2) at low temperatures and atmospheric to moderate-level pressures:         CO 2 + 4H 2 ↔ CH 4 + 2H 2 O     (R1)         3H 2 O + 2Al → 3H 2 + Al 2 O 3      (R2)

[0010] The method characterised in that: said catalyst is based on the combination of a high specific surface area porous clay heterostructure (PCH) support and nickel - Ni / PCH catalyst; and said a mixture of CO 2 and H 2 gases and a catalyst are activated by a gliding arc discharge plasma (GADP); and said produced water / water vapour is removed via reaction with plasma-activated aluminium (R2); and said additional hydrogen is produced to react with carbon dioxide thus minimizing the initial amount of hydrogen needed for the process.

[0011] The support of Ni-based catalyst is made of a porous high specific surface area (S BET ) and pore volumes clay heterostructure formed by chemical method.

[0012] The support of the Ni / PCH catalyst has a high specific surface area S BET of 1000 to 1100 m 2< / g, total pore volume of 1.15 cm 3< / g, good dispersion of Ni nanoparticles D avg 18 nm. The multi-point BET specific surface area of the catalyst support was measured using the gas sorption (physisorption / chemisorption) system: the Quantachrome Autosorb iQ instrument and Quantachrome's ASiQwin Software. Nitrogen N 2 was used as the adsorbent gas. The total pore volume is derived from the amount of N 2 vapor adsorbed at a relative pressure P / P 0 close to unity, by assuming that the pores are then filled with liquid N 2 adsorbate. The high specific surface area of support encourages a better dispersion of Ni nanoparticles, improves the formation of active centres, and has good availability of gaseous reactants and higher conversion as well as catalytic activity. Fig. 2 shows the multi-point BET plot of a high specific surface area of 1012.6 m 2< / g porous clay heterostructure support used for Ni catalyst. Fig. 3 shows XRD pattern of the distribution on Ni nanoparticples on the PCH support. The average diameter of the Ni nanoparticles was measured using the X-ray diffraction method, TOPAS 4.1 software and the Scherrer equation.

[0013] The Ni loading varies from 5 to 30 wt% on the PCH catalyst support. Preferably, the higher the Ni loading, the better performance of the Ni / PCH catalyst is achieved. Table 1 shows evaluation of Ni / PCH catalyst efficiency increasing the Ni loading from 5 to 30 wt%. Table 1No.Ni loading wt%Conversion (X CO2 ), %Selectivity (S CH4 ), %Yield (Y CH4 ), %1518.618.63.4421028.692.026.432080.075.060.343094.094.088.6

[0014] Process conditions: fixed-bed tube reactor, stoichiometric H 2 :CO 2 ratio 4:1, 10 bars pressure, average temperature 400 °C, and gas hourly space velocity (GHSV) 756 1 / h.

[0015] The average size of the Ni / PCH catalyst is 3 mm in diameter and 4-5 mm in length. The Ni / PCH catalyst during conventional thermo-catalytic carbon dioxide methanation process is characterized by CO 2 conversion of 94%, synthetic CH 4 yield of 88.6% and selectivity of 94%, respectively. Process conditions: fixed-bed tube reactor, stoichiometric H 2 :CO 2 ratio 4:1, 10 bars pressure, average 400 °C temperature, and gas hourly space velocity (GHSV) of 756 1 / h.

[0016] The Ni / PCH catalyst is reduced under hydrogen flow at 480 °C for 2 hours. The reduced Ni / PCH catalyst is then placed over the surface of the electrodes 2 of the gliding arc discharge plasma (GADP) in the reactor (Fig. 1). The distance between the electrodes 2 and the catalyst bed 4 is in the range of 1-2 cm. The catalyst is not directly immersed into the GADP due to too high thermal load, potential physical damage and deactivation.

[0017] A mixture of gases CO 2 and H 2 3 is activated, i.e. ionized by a GADP then passes through the placed catalyst 4 thus initiating adsorption-desorption catalyst-gas phase interaction reactions.

[0018] Gliding arc discharge plasma is used to operate as the main discharge source as it shares both properties typical for thermal and non-thermal plasmas and is suitable for CO 2 conversion.

[0019] No external heating is used in the process. GADP is a source of heat. Preferably, the process is carried out at atmospheric to moderate-level up to 5 bars, absolute up to 6 bars pressure.

[0020] Synergy of the GADP activating CO 2 and H 2 gases via vibrational excitation (different activation mechanism compared to a direct barrier discharge (DBD)) and later activated gas mixture interaction with catalyst via heterogeneous adsorption / desorption reactions to produce ultimate desired product synthetic methane is one of the key novelty of the present invention.

[0021] No other gases, except CO 2 and H 2 , are used to form plasma.

[0022] A reactor suitable for carrying out plasma-assisted catalytic carbon dioxide hydrogenation process according to the present invention is disclosed in Fig. 1. The reactor according to Fig. 1, which is used only with illustrative purposes, comprises the following parts: i. A cylindrical quartz tube 1, which is the reactor wall. The external part of the tube 1 is covered by a 2 mm thick perforated stainless steel tube to protect the reactor from fracture while working at moderate-level pressures. ii. At the bottom of the quartz tube 1, two electrodes 2, made of stainless steel, are placed to generate plasma. The distance between the electrodes 2 can vary from 1-2 mm. The length of the electrodes 2 is 20 mm and the width is 10 mm. The electrodes have the shape of sails. The electrodes are insulated by a Teflon ring. iii. Plasma-forming feed gas (CO 2 and H 2 ) is supplied via a 2 mm diameter tube 3 installed at the very bottom of the reactor. iv. The catalyst bed 4 is placed over the electrodes 2 at the distance from 1-2 cm. v. A K-type thermocouple temperature profile probe 5 is placed axially the reactor length in the centre to measure temperature profile every 10 mm at six different points. vi. A condenser 6 is used to condense reaction by-product water. vii. A stainless steel water removal reaction chamber 7, containing plasma-activated aluminium, is used to remove reaction water and produce additional hydrogen via plasma-activated aluminium and water reaction. viii. A rotameter 8 is used to measure the flow rate of gaseous reaction products. ix. A pressure control valve 9. x. Gas chromatograph (GC) and gas analyser 10.

[0023] The high voltage electrodes 2 can be supplied by an AC or DC or pulsed current with a voltage of 10 kV (1.5-3.0 kV, 30-50 mA, current conditions). The power injected in these conditions is in the range of 100-140 W.

[0024] The ratio of feed gas H 2 and CO 2 is 1.66, i.e. 10 l / min H 2 and 6 l / min CO 2 . The total flow of 16 l / min is used as a plasma-forming gas and a reaction gas.

[0025] Gaseous products composition is measured by gas chromatography and gas analysis methods.

[0026] The condensable products, mainly water vapour, are collected in a chamber 7 for in situ water removal and additional hydrogen production to be used again as a reactant in the Sabatier process. Whereas oxygen is captured in the reaction by-products. This is the second key novelty of the present invention minimizing the need of hydrogen for CO 2 methanation process: I. Aluminium scrap is activated in a glow discharge plasma in the presence of 3-10 Pa of hydrogen with purity not less than 99.00%, or argon with purity not less than 99.00%, or hydrogen and argon mixtures with the best Ar:H 2 proportion 70:30 as residual gasses for 10-60 min treatment in plasma with the DC power density up to 10-30 W / cm 2< . Temperature is 60-110 0< C during the plasma process. II. 30 g of plasma-activated hydrophilic aluminium 11 is placed in a chamber 7 (Fig. 4) in a layered structure between the layers of NaOH particles 13 (Fig. 4). The proportion of layers thickness between the layers of NaOH particles 13, acting as a reaction promoter between plasma-activated aluminium and water molecules, and activated aluminium layer 11 is 1:5 by volume. A stainless steel mesh 14 with pores diameters of 1 mm and glass wool 12 were used at the inlet and outlet of reaction molecules to prevent aluminium and reaction by-products Bayerite - Al(OH) 3 , thermonatrite - Na 2 CO 3 •H 2 O migration from the reaction chamber 7. III. In case a water condensation equipment 6 is present (Fig. 1), H 2 O molecules enter the chamber 7 were reaction between activated aluminium 11 and condensed water molecules (R2 reaction) takes place and pure H 2 gas and reaction by-products Bayerite - Al(OH) 3 , thermonatrite - Na 2 CO 3 •H 2 O are produced. The other gases, such as CH 4 , CO 2 unreacted and H 2 unreacted , also entering the chamber 7, have no impact on reaction between activated aluminium and water. They just leave the chamber and go for analysis. EXAMPLES

[0027] The present invention is further disclosed by way of examples which only intend to illustrate the present invention and by no means are limiting the scope thereof.Example 1

[0028] A typical reactor operation and procedure as disclosed in the present invention is as follows: 1. With 25 g of Ni / PCH catalyst with 30 wt% Ni loading corresponding to an GHSV of 7700 1 / h, the reactor, shown in Fig. 1, is supplied with a mixture of CO 2 and H 2 with a flow rate of 6 l / min and 10 l / min, respectively, at atmospheric to 4 bars absolute pressure and at temperature of 20 °C. Distance from the GADP electrodes 2 to the catalyst bed 4 is 1 cm. The parameters of the plasma generator: current - 1.5 A, voltage - 300 V, frequency - 250 kHz. The parameters of the GADP: current 40-50 mA, voltage 2.5-3.5 kV. 2. Without the GADP and presence of Ni / PCH catalyst at atmospheric and increased pressure to 4 bars, no change in the composition of outlet gases is observed. When the GADP is switched on, the temperature increases slowly and after 2 minutes the production of methane and water vapour is obtained at around 60-80 °C and atmospheric pressure, which is impossible to obtain in conventional thermo-catalytic Sabatier reaction. 3. With the GADP switched on and absence of Ni / PCH catalyst, no methane is obtained. Plasma activates and converts only CO 2 to CO and H 2 to H. 4. The steady state conditions producing methane are reached after around 7 minutes. 5. The temperature in the reactor is not controlled, i.e. the reactor is not cooled, and therefore the temperature profile measured by the K-type thermocouple in the reaction zone at six different places 5 (Fig. 1), starting from the hottest zone close to the GADP electrodes 2 and the coolest zone at the outlet of the reactor, settles down at 550°C, 380 °C, 310 °C, 240 °C, 150 °C, and 110°C, respectively. 6. Such a high temperature is reached due to exothermal nature of the catalytic R1 reaction. 7. The temperature profile in the reactor measured without the catalyst and the GADP switched on at the same experimental conditions is as follows: 315 °C, 280 °C, 260 °C, 240 °C, 220 °C, and 180 °C, respectively. 8. The efficiency of the GADP catalytic process for CO 2 methanation is summarized in Table 2. Table 2Pressure in reactor, barNi / PCH catalyst with 30 wt% Ni loadingXco2, %X H2 , %CH 4 , vol%CH 4 T< , vol%S CH4 , %Y CH4 , %CB 1< , %SER 2< , kWh / m 3< SER, kJ / mol122.2948.016.421.918.994.2388.983.06246.21226.4152.878.322.020.215.3487.342.43195.30326.0755.0111.522.028.037.3189.771.77142.66427.0954.0113.322.033.279.0289.011.26101.16 T< CH 4 - methane concentration at thermodynamic equilibrium 1< CB - carbon balance 2< SER - specific energy requirements 9. In all cases the production of methane starts after 2 minutes at 60-80 °C temperature. The GADP activates both CO2 and H2 gases via vibrational excitation as well as minimizes the activation barrier of Ni / PCH catalyst thus making adsorption / desorption of gases on its surface possible at such low temperature. 10. Pressure has a positive impact on higher conversion of CO2 and CH4 selectivity and yield. However, the reaction in the present invention proceeds at atmospheric pressure and low temperature as conventional CO2 methanation (Sabatier) reaction is limited to such conditions. 11. The specific energy requirements (SER) are in the range of 3.46 to 8.42 kWh / m3, or 278.19 to 677.07 kJ / mol. This is mostly depended on a higher CO2 and H2 conversion and CH4 concentration at increased pressure. 12. High value of carbon balance around 89% show that carbon deposition is minimal to clog catalyst pores thus reducing its efficiency. No solid carbon deposition on catalyst surface is observed.Example 2

[0029] Another GADP catalytic reactor operation and procedure as disclosed in the present invention is as follows: 1. With 25 g of Ni / PCH catalyst with 30 wt% Ni loading corresponding to an GHSV of 7700 1 / h, the reactor is supplied with a mixture of CO 2 and H 2 with a flow rate of 6 l / min and 10 l / min, respectively, at atmospheric to 4 bars absolute pressure at temperature of 20 °C. Distance from the GADP electrodes 2 to the catalyst bed 4 is 1 cm. The parameters of the plasma generator: current - 1.5 A, voltage - 300 V, frequency - 250 kHz. The parameters of the GADP: current 40-50 mA, voltage 2.5-3.5 kV. 30 g of plasma-activated hydrophilic aluminium is placed in the developed innovative chamber to react with condensed water. 2. In situ water removal with subsequent additional hydrogen production via R2 reaction is carried out. Fig. 4 shows how the water is removed and additional hydrogen is produced during plasma-catalytic carbon dioxide hydrogenation (15 - reaction gases: CO 2 + H 2 , 16 - GADP catalytic reactor (or traditional Sabatier reactor), 17 - product gases: CH 4 + H 2 O, plus unreacted CO 2 and H 2 , 18 - condenser, 19 - product gases without water: CH4, plus unreacted CO 2 and H 2 , 20 - condensed water, 7 - chamber, 14 - stainless steel mesh, 12 - glass wool, 13 - NaOH, 11 - plasma-activated hydrophilic aluminium, 21 - additional hydrogen production). A mixture of gases (CH 4 produced , CO 2 and H 2 unreacted ), in case of entering the chamber 7, has no direct impact on additional hydrogen production. They simply leave the chamber having no direct impact on condensed water and activated aluminium reaction to produce additional hydrogen. 3. Fig. 5 shows additional H 2 production according to R2 reaction. Additional H 2 production starts after 47 minutes and ends after 60 minutes of the continuous operation of the process producing methane. The concentration of product gases is measured by a gas analyser. 4. During this process, beside the reaction between condensed water and activated aluminium (R2 reaction), a reversible water-gas shift (RWGS) reaction also dominates. According to RWGS the concentration of H 2 and CO 2 should decrease, and the one of CO and H 2 O should increase. However, H 2 concentration increased up to 5-6 vol% (CO 2 decreased up to 5 vol%, CO increased up to 2-3%) implying the presence of the R2 reaction. 5. Produced additional hydrogen could be used as a reactant in CO 2 methanation process, thus minimizing the need of green hydrogen needed for the reaction.

Claims

1. A method for performing the reactions (R1), (R2) with catalyst and in-situ water / water vapour removal and additional hydrogen production:         CO2 + 4H2 ↔ CH4 + 2H2O     (R1)         3H2O + 2Al → 3H2 + Al2O3     (R2) the method characterised in that: - the catalyst is based on the combination of a high specific surface area of 1000 to 1100 m2 / g, measured by a gas sorption method with N2 gas as adsorbent, porous clay heterostructure (PCH) support and nickel - Ni / PCH catalyst; and - a mixture of CO2 and H2 gases and a catalyst is activated by a gliding arc discharge plasma (GADP) ) to further perform (R1); and - the produced reaction by-product water / water vapour is in-situ removed via reaction with plasma-activated aluminium (R2); and - as the result of the R2 reaction, the additional hydrogen is produced to react with carbon dioxide, thus minimizing the initial amount of hydrogen needed for the process.

2. The method according to claim 1, characterized in that the catalyst is based on the combination of nickel and a high specific surface area porous clay heterostructure (PCH) as a support formed by a chemical method.

3. The method according to claim 1, characterized in that the Ni / PCH catalyst comprises nickel of 5 to 30 wt%, most preferably 30 wt%, and a PCH support of specific surface area of 1000 to 1100 m2 / g, and total pore volume up to 1.15 cm3 / g, measured by a gas sorption method with N2 adsorbent, and dispersion of Ni nanoparticles (Davg 18 nm) defined using the X-ray diffraction method.

4. The method according to claim 1, characterized in that the Ni / PCH catalyst during the conventional thermo-catalytic carbon dioxide methanation process in a fixed-bed tube reactor at the H2:CO2 ratio of 4:1, reactor pressure of 10 bars, average temperature of 400 °C, GHSV of 756 l / h, and Ni loading 30 wt.%, is characterized by CO2 conversion of 94.0%, CH4 yield of 88.6%, and selectivity of 94%, respectively.

5. The method according to claim 1, characterized in that the gliding arc discharge plasma (GADP) is used to activate carbon dioxide and hydrogen via vibrational excitation pathway and active sites of Ni / PCH catalyst at atmospheric to moderate pressures up to 5 bars and low temperatures to produce synthetic methane.

6. The method according to claim 1 or 5, characterized in that no other gases, except CO2 and H2, are used to form plasma and active medium of gas mixture to interact with catalyst via heterogeneous adsorption / desorption reactions to produce synthetic methane and water.

7. The method according to any of claims 1 to 6, characterized in that the hydrogen and carbon dioxide are provided in an H2 / CO2 ratio of 1.66, i.e. 10 l / min H2 and 6 l / min CO2.

8. The method according to claim 1 to 7, characterized in that the synthetic methane production, according to R1 reaction, starts preferably at 60 to 80 °C temperature, most preferably at 60 °C temperature, and atmospheric to moderate-level pressure up to 5 bars, most preferably atmospheric pressure, and after two minutes of plasma ignition.

9. The method according to claim 1 to 8, characterized in that the water molecules, produced after R1 reaction, react with activated aluminium (R2 reaction) instantly after entering the reaction zone and are converted to pure hydrogen, and oxygen is captured in reaction by-products Bayerite - Al(OH)3 and Na2CO3•H2O thermonatrite.

10. A system for producing synthetic methane from carbon dioxide and hydrogen with in-situ water removal and additional hydrogen production characterised by comprising a gliding arc discharge (GAD) device arranged to generate plasma; a catalyst comprising nickel on a support comprising porous clay heterostructure with a high specific surface area of 1000 to 1100 m2 / g measured by a gas sorption method with N2 adsorbent; a reaction chamber, containing plasma-activated aluminium, for in-situ water / water vapour removal and additional hydrogen production.