Method for treating an effluent stream generated by a carbon capture system

Abstract

A method for treating an effluent stream generated by a carbon capture system comprises contacting a cyclic amine-containing solution and a gas stream in the carbon capture system to remove carbon dioxide from the gas stream, the carbon capture system generating an effluent stream discharged from the carbon capture system; and subjecting the effluent stream to advanced oxidation. The method allows for treating effluent streams comprising cyclic amines so as to efficiently decompose the cyclic amines.

Description

[0001] 241039W001 1

[0002] Method for Treating an Effluent Stream Generated by a Carbon Capture System

[0003] The present invention relates to a method for treating an effluent stream.

[0004] Many industrial processes generate gas streams comprising acid gases, in particular carbon dioxide (CO2). For example, the combustion of a fuel, such as coal, oil, peat or waste in a combustion plant, such as a power plant, generates a process gas stream known as a flue gas stream. In general, the flue gas stream contains particulates and gaseous contaminants such as CO2. Due to the negative environmental effects of releasing CO2 to the atmosphere, processes have been developed for removing or reducing the amount of CO2 from industrial gas streams.

[0005] Industrial carbon dioxide (CO2) capturing plants ("carbon capture systems”) typically include an absorber in which a flue gas stream is treated by being brought into countercurrent contact with a liquid absorbent. The liquid absorbent is typically an amine-containing solution which can efficiently remove CO2, as well as other contaminants, such as sulfur dioxide and hydrogen chloride, from a flue gas stream. Treatment of the flue gas stream with amine-containing solutions results in an effluent stream that may be regenerated and recirculated throughout the system.

[0006] Examples of amines commonly used in absorbents include alkanolamines such as monoethanolamine (MEA), 2-amino-2-methyl-1 -propanol (AMP), diethanolamine (DEA), 2-(2-tert-butylaminoethoxy)ethanol (TBAEE), 3-amino-1 -methylaminopropane (MAP A), N-methyldiethanolamine (MDEA) and triethanolamine (TEA), as well as cyclic diamines such as piperazine and triethylenediamine (TEDA, DABCO).

[0007] Using an amine-containing solution to remove CO2 from the gas stream typically results in the essentially unavoidable presence of the amine in various effluent streams obtained from the carbon capture system. The presence of the amines may prevent the efficient treatment of such streams, e.g., in municipal water facilities.

[0008] It has been described that amine-containing wastewater may be subjected to biological wastewater treatment and / or advanced oxidation pretreatment, i.e., a set of chemical treatment procedures designed to remove organic and inorganic contaminants from water and wastewater. Exemplary publications include: - Oh et al., "Advanced Oxidation Pretreatment for Biological Treatment of Reclaimer Wastewater Containing High Concentration N-methyldiethanolamine”, Appl. Sci. 2022, 12, 3960;

[0009] - Yin et al., "Handling of Amine-Based Wastewater Produced During Carbon Capture", Journal of Environmental Informatics Letters 2 (2), 57-69 (2019);

[0010] - Domingo et al., "Biological treatment of industrial wastewater from post-combustion carbon capture”, Chemical Engineering Science, 287 (2024) 119766;

[0011] - Dong et al., "Wastewater treatment in amine-based carbon capture”, Chemosphere 222 (2019) 742— 756; and

[0012] - Samnani et al., "Review on amine-rich carbon capture wastewater treatment processes”, Journal of Environmental Systems Engineering, 2023, 1-30 (Preprint). 241039W001 2

[0013] Biodegradability of amines, however, can vary greatly. While some amines have been shown to be biodegradable, it has now been found that cyclic amines may be highly stable under biodegradation conditions, showing little to no biodegradation, in particular cyclic amines comprising one or more tertiary amino groups. While the increased oxidative stability of such cyclic amines is advantageous during operation of the carbon capture system, it makes disposal of the effluents more difficult.

[0014] A known alternative to treating the effluent streams is incineration, which however typically requires prior concentration and water removal from the effluent stream so as to obtain a combustible feed. These steps require high amounts of energy and special equipment. Hence, for relatively dilute effluent streams, incineration is not readily feasible.

[0015] There is a need to provide a process for treating effluent streams comprising cyclic amines so as to efficiently decompose the cyclic amines.

[0016] Due to the unique properties of cyclic amines, it is not easy to predict the success of certain degradation processes. For example, it is known that triethylenediamine (1 ,4-diazabicyclo[2.2.2]octane, also known as TEDA or DABCO) forms relatively stable addition compounds with hydrogen peroxide, e.g., Oswald et al., "Organic Nitrogen Compounds I”, J. Org. Chem. 1963, 28 (3), 651-657, and Cookson et al., "The 1,4-diaza[2.2.2] Bicyclooctane-hydrogen peroxide complex as a source of anhydrous hydrogen peroxide: the preparation of bis(trialkylsilyl) peroxides”, Journal of Organometallic Chemistry, 99 (2), 1975, C31-C32. TEDA is also known to effectively quench singlet oxygen, see Quannes et al., "Quenching of singlet oxygen by tertiary aliphatic amines. Effect of DABCO”, J. Am. Chem. Soc. 1968, 90 (23), 6527-6528.

[0017] Thus, cyclic amines have been shown to behave unlike other amines in the presence of aggressive oxidative conditions. The skilled person would not readily assume that cyclic amines are susceptible to decomposition by, e.g., Advanced Oxidation Processes.

[0018] The invention provides a method for treating an effluent stream, the method comprising subjecting an effluent stream containing or suspected of containing a cyclic amine, to advanced oxidation.

[0019] The effluent stream may be generated in any industrial process which involves a cyclic amine, for example as a reactant or catalyst or other processing aid, e.g., in a carbon capture system, in an oil refinery or in polyurethane synthesis.

[0020] US 2024 / 261722 A describes a process and system for removing heat stable amine salts from a contaminated amine absorption solution containing amine in salt form generated during an amine-based acid gas recovery operation. At least a portion of the heat stable amine salts is removed from the contaminated aqueous amine absorption solution in an amine reclamation unit using, e.g., ion exchange or electrodialysis reclamation technique, to produce a waste stream containing dissolved salts and / or acids, and a regenerated amine absorption solution containing a reduced amount of the heat stable amine salts. The waste stream is oxidized to obtain an oxidized product stream comprising carbon dioxide, water and nitrogen. The oxidized product stream may be directed to the acid gas recovery process. Oxidation is effected by combustion or waste water treatment using bleach, peroxide or air. 241039W001 3

[0021] The concentration of the cyclic amine in the effluent stream may vary in broad ranges, from dilute solutions to more concentrated solutions. Hence, the concentration of the cyclic amine in the effluent stream may range from 10 ppmw to 90 wt.-%, preferably 100 ppmw to 75 wt.-%, more preferably 500 ppmw to 50 wt.-%, based on the total weight of the effluent stream.

[0022] In particular, the invention provides a method for treating an effluent stream generated by a carbon capture system, the method comprising:

[0023] contacting a cyclic amine-containing solution and a gas stream in the carbon capture system to remove carbon dioxide from the gas stream, the carbon capture system generating an effluent stream discharged from the carbon capture system; and

[0024] subjecting the effluent stream to advanced oxidation.

[0025] In one embodiment, the invention provides a method for treating an effluent stream generated by a carbon capture system, the method comprising:

[0026] contacting a cyclic amine-containing solution and a gas stream in the carbon capture system to remove carbon dioxide from the gas stream, the carbon capture system generating an effluent stream discharged from the carbon capture system, cyclic amine being present in the effluent; and

[0027] subjecting the effluent stream to advanced oxidation.

[0028] Surprisingly, it was found that cyclic amines are susceptible to decomposition when subjected to advanced oxidation.

[0029] The cyclic amine-containing solution comprises a cyclic amine which is preferably selected from

[0030] I) cyclic amines comprising one or more secondary amino groups in the ring;

[0031] ii) cyclic amines comprising one or more tertiary amino groups in the ring; and / or

[0032] ill) cyclic amines comprising both at least one tertiary amino group and at least one secondary amino group.

[0033] It is understood that cyclic amines I), which comprise one or more secondary amino groups in the ring, comprise no amino groups in the ring which are not secondary. Further, cyclic amines ii), which comprise one or more tertiary amino groups in the ring, comprise no amino groups in the ring which are not tertiary.

[0034] In particular, the cyclic amine may be selected from

[0035] I) piperidine, 2-methylpiperidine, 4-methylpiperidine, 4-(2-hydroxyethyl)-piperidine,

[0036] 2,2,6,6-tetramethylpiperidine and derivatives thereof, piperazine and 2-methylpiperazine;

[0037] ii) 1-(2-hydroxyethyl)piperidine, 1 ,4-dimethylpiperazine, 1 ,4-bis(2-hydroxyethyl)piperazine, triethylenediamine, 2-hydroxymethyl triethylenediamine, and 1 -methyl-2-pyrrolidine ethanol; and / or ill) 1 -methylpiperazine and 1-(2-hydroxyethyl)piperazine. 241039W001 4

[0038] Derivatives of 2,2,6,6-tetramethylpiperidine are in particular substituted in the 4-position, such as 2, 2,6,6-tetramethyl-4-piperidinol.

[0039] When the cyclic amine comprises one or more secondary amino groups in the ring, the secondary amino groups are preferably sterically hindered secondary amino groups. A sterically hindered secondary amino group” is understood to have at least one secondary or tertiary carbon atom directly adjacent to the nitrogen atom.

[0040] Thus, in one embodiment, the cyclic amine is selected from

[0041] I) 2-methylpiperidine, 2,2,6,6-tetramethylpiperidine and derivatives thereof; and / or

[0042] ii) 1-(2-hydroxyethyl)piperidine, 1,4-dimethylpiperazine, 1 ,4-bis(2-hydroxyethyl)piperazine, triethylenediamine and 1-methyl-2-pyrrolidine ethanol.

[0043] In one embodiment, the cyclic amine does not comprise a ring nitrogen bearing a beta-hydroxyalkyl substituent, in particular hydroxyethyl. It is understood that nitrogen-adjacent carbon atom is designated as alpha and the carbon atom(s) adjacent to it as beta. It is believed that a hydroxy group at the beta-carbon, such as present in a hydroxyethyl moiety, mediates a nucleophilic attack resulting in replacement or substitution of the nitrogen atom. Thus, amines comprising a ring nitrogen bearing a beta-hydroxyalkyl substituent, in particular hydroxyethyl, are believed to be more susceptible to decomposition. The advantages of the present invention are especially applicable to cyclic amines which are resistant to decomposition.

[0044] In one embodiment, the cyclic amine is selected from

[0045] I) 2-methylpiperidine and 2,2,6,6-tetramethylpiperidine and derivatives thereof; and / or

[0046] ii) 1,4-dimethylpiperazine and triethylenediamine.

[0047] The concentration of the cyclic amine in the cyclic amine-containing solution is typically 10 to 70 wt.-%, based on the total weight of the cyclic amine-containing solution.

[0048] The cyclic amine-containing solution is preferably an aqueous solution.

[0049] In one embodiment, the cyclic amine-containing solution comprises at least one non-aqueous organic solvent. The non-aqueous solvent is preferably selected from:

[0050] C4-C10 alcohols such as n-butanol, n-pentanol and n-hexanol;

[0051] ketones such as cyclohexanone;

[0052] esters such as ethyl acetate and butyl acetate;

[0053] lactones such as y-butyrolactone, 5-valerolactone and E-caprolactone;

[0054] amides such as tertiary carboxamides, for example N,N-dimethylformamide; or N-formylmorpholine and N-acetylmorpholine;

[0055] lactams such as y-butyrolactam, 6-valerolactam and E-caprolactam and N-methyl-2-pyrrolidone (NMP); 241039W001 5

[0056] sulfones such as sulfolane;

[0057] sulfoxides such as dimethyl sulfoxide (DMSO);

[0058] glycols such as ethylene glycol (EG) and propylene glycol;

[0059] polyalkylene glycols such as diethylene glycol (DEG) and triethylene glycol (TEG);

[0060] di- or mono(Ci-C4-alkyl ether) glycols such as ethylene glycol monomethyl or dimethyl ether;

[0061] di- or mono(Ci-C4-alkyl ether) polyalkylene glycols such as diethylene glycol dimethyl ether, dipropylene glycol monomethyl ether and triethylene glycol dimethyl ether;

[0062] cyclic ureas such as N, N-dimethylimidazolidin-2-one and dimethylpropyleneurea (DMPU); thioalkanols such as ethylenedithioethanol, thiodiethylene glycol (thiodiglycol, TDG) and methylthioethanol; and mixtures thereof.

[0063] More preferably, the non-aqueous solvent is selected from sulfones, lactams glycols and polyalkylene glycols. Most preferably, the non-aqueous solvent is selected from lactams, such as N-methy l-2-py rrol idone (NMP), and sulfones, such as sulfolane. A preferred non-aqueous solvent is sulfolane.

[0064] In one embodiment, the cyclic amine-containing solution comprises one or more non-cyclic amines.

[0065] In one embodiment, the non-cyclic amines is selected from a sterically unhindered primary amine and / or a sterically unhindered secondary amine. Suitable sterically unhindered primary or secondary amines include: alkanolamines such as monoethanolamine (MEA), diethanolamine (DEA), ethylaminoethanol, 1-amino-2-methylpropan-2-ol, 2-amino-1 -butanol, 2-(2-aminoethoxy)ethanol and 2-(2-aminoethoxy)ethanamine, and polyamines such as hexamethylenediamine, 1,4-diaminobutane, 1,3-diaminopropane, 3-(methylamino)propylamine (MAPA), N-(2-hydroxyethyl)ethylenediamine, 3-(dimethylamino)propylamine (DMAPA), 3-(diethylamino)propylamine, N,N'-bis(2-hydroxyethyl)ethylenediamine.

[0066] The cyclic amine-containing solution may further comprise additives such as anti-foam agents, buffers, metal salts and corrosion inhibitors.

[0067] The gas stream contacted with the cyclic amine-containing solution comprises carbon dioxide and, optionally, further acid gases such as hydrogen sulfide. The gas stream may comprise carbon dioxide in an amount of 1 to 40 vol.-%. Moreover, the gas stream may comprise hydrogen sulfide in an amount of 10 ppmv to 20 vol.-%.

[0068] In one embodiment, the gas stream is a flue gas stream. The flue gas stream may be obtained from the combustion of a fuel, such as coal, oil, peat or waste, for example from a combustion plant, such as a power plant.

[0069] The carbon capture system may be any system suitable for gas treatment as known to the skilled person. The conventional method of using a process involving absorption and stripping to remove CO2from gaseous streams is described, e.g., in US 4,384,875. 241039W001 6

[0070] In one embodiment, the effluent stream is generated by a carbon capture system comprising:

[0071] - an absorption column in which the flue gas stream to be treated is contacted with the cyclic amine- containing solution to remove carbon dioxide from the flue gas stream, wherein a CO2-depleted gas is withdrawn at the top of the absorption column, and wherein a CC>2-laden cyclic amine-containing solution is withdrawn from the bottom of the absorption column;

[0072] - optionally, a water wash unit in which CC>2-depleted gas is subjected to a water wash by contacting the CC>2-depleted gas with water;

[0073] - optionally, an acid wash unit in which the CO2-depleted gas is subjected to an acid wash by contacting the CC>2-depleted gas with a dilute aqueous acid, such as dilute sulfuric acid;

[0074] - a regeneration column in which the CC>2-laden cyclic amine-containing solution is stripped of CO2, preferably by countercurrent flow with steam which is generated by heating of regenerated cyclic amine- containing solution at the bottom of the regeneration column, and wherein steam vapors of the cyclic amine-containing solution are obtained at the top of the regeneration column;

[0075] - optionally, a reflux loop comprising a condenser system, wherein the steam vapors of the cyclic amine- containing solution are condensed and a partial stream of the condensed is returned as reflux to the regeneration column; and

[0076] - optionally, a reclaimer unit for treating the CO2-I aden cyclic amine-containing solution or the regenerated CC>2-laden cyclic amine-containing solution.

[0077] Typically, the carbon capture system comprises an absorption column, in which the flue gas stream to be treated is contacted with the cyclic amine-containing solution (in the following also referred to as "the absorbent”) under conditions of pressure and temperature such that the absorbent removes essentially all of the CO2Comprised in the gas stream. A CC>2-depleted gas is withdrawn at the top of the absorption column and typically released into the atmosphere, whereas a CC>2-laden absorbent is withdrawn from the bottom of the absorption column.

[0078] In one embodiment, the CC>2-depleted gas may be subjected to a water wash in a water wash unit by contacting the CC>2-depleted gas with water, preferably in countercourrent. This allows for reducing emissions of ammonia and amines before the CC>2-depleted gas is released into the atmosphere. The water wash unit is preferably integrated into the top of the absorption column. The water wash unit is typically configured to comprise a backwash loop, from which a backwash bleed stream is removed and into which fresh water is continually fed so as to avoid accumulation of contaminants. The backwash bleed stream may constitute or contribute to the effluent stream to be treated.

[0079] In one embodiment, the CC>2-depleted gas obtained from the absorption column is subjected to an acid wash in an acid wash unit. This allows for reducing emissions of ammonia and amines before the CC>2-depleted gas is released into the atmosphere. For this purpose, the CC>2-depleted gas is typically contacted with a dilute aqueous acid, such as dilute sulfuric acid, preferably in countercurrent. The acid is typically fed to a recycle loop to maintain a pH value of 3 to 6 in the dilute aqueous acid. A bleed stream of salt solution is removed so as to avoid accumulation of salts. The salt solution bleed stream may constitute or contribute to the effluent stream to be treated. In one embodiment, the CC>2-depleted gas is subjected to one or more stages of a water wash, and subsequently subjected to an acid wash in an acid wash unit. 241039W001 7

[0080] The CO2-laden absorbent is typically regenerated in a regeneration column, wherein the CO2-laden absorbent is stripped of CO2 by countercurrent flow with steam which is generated by heating of regenerated absorbent at the bottom of the regeneration column. The regenerated absorbent is withdrawn from the bottom of the regeneration column and is recycled into the absorber. A CO2-rich gas, mainly comprising steam and CO2, is withdrawn from the top of the regeneration column. The CO2-rich gas is treated further to remove water, and compressed before the CO2 is sent for deposition or other use.

[0081] In particular, to effect the regeneration of the absorbent, the 002-laden absorbent withdrawn from the bottom of the absorber is typically introduced into the upper part of the regeneration column, and the CO2-laden absorbent is maintained at its boiling point under pressure in this column. The heat necessary for maintaining the boiling point may be provided by reboiling the absorbent solution contained in the stripping column. The reboiling process may be effectuated by indirect heat exchange between part of the solution to be regenerated located in the lower half of the stripping column and a hot fluid at appropriate temperature, generally saturated water vapor.

[0082] In the course of regeneration, the CO2 contained in the 002-laden solvent is released and stripped by the steam vapors of the absorbent. Steam containing the stripped CO2 emerges at the top of the regeneration column and is typically passed through a reflux loop comprising a condenser system. A partial stream of the condensed phase is typically returned as reflux to the regeneration column. A reflux bleed stream of the condensed phase is typically removed from the process so as to avoid accumulation of contaminants. The reflux bleed stream may constitute or contribute to the effluent stream to be treated.

[0083] At the bottom of the stripping column, the hot regenerated absorbent (also called "lean absorbent”) is drawn off and recycled to the absorption column after having used part of the heat content of the solution to heat, by indirect heat exchange, the rich solvent to be regenerated, before its introduction into the stripping column.

[0084] The 002-laden solvent is typically regenerated at a temperature in the range of 100 to 160 °C. The regeneration column is typically operated at a pressure in the range of 1 to 10 atm. The CO2-laden solvent feed may be preheated by heat exchange with hot regenerated solvent to within 5 to 30° C of the bottoms of the regeneration column.

[0085] In one embodiment, the carbon captures system comprises a reclaimer unit. A reclaimer unit may be used to treat absorbent, in order to separate amine compounds such as the cyclic amine from accumulated undesired compounds in the absorbent. The types of undesired compounds found in the amine-based solvent are a function of the impurities in the gaseous streams, the type of amine compounds present in the absorbent, and the operating conditions of the carbon capture system. A reclaimer unit may be used, for example, to remove high-boiling degradation products, ionic species, impurities, fine suspended solids from the absorbent, or any combination thereof.

[0086] General processes for reclaiming the amine compound from the amine-based solvent include: thermal reclaiming, ion-exchange, electrodialysis, mechanical filtration, and adsorption (e.g. using activated carbon). These general processes may be used to separate the amine compound from the degradation products, ionic species, impurities, fine suspended solids present in the amine-based solvent, or any combination 241039W001 8

[0087] thereof. In one embodiment, the carbon captures system comprises a reclaimer unit selected from an ionexchange reclaimer unit, a thermal reclaimer unit and an electrodialysis reclaimer unit, preferably an ionexchange reclaimer unit.

[0088] In an ion-exchange amine reclaimer unit, the anions in the absorbent are exchanged with hydroxyl groups attached to the exchanger resin, hence cationic species such as ammonium and protonated amine are neutralized so that the alkalinity function is restored. In one embodiment, the thus obtained ammonia may then be stripped off from the solution by vacuum stripping or a stripping medium such as air, while the remaining solution containing free amines can be routed back to the carbon capture system.

[0089] The exchanger resin is periodically regenerated by treatment with an alkaline solution such as sodium hydroxide and yields a reclaimer effluent stream which is usually relatively dilute. The reclaimer effluent stream may constitute or contribute to the effluent stream to be treated.

[0090] The CC>2-laden cyclic amine-containing solution may be treated in the reclaimer unit prior to being regenerated in a regeneration column. The reclaimer unit, for example an ion-exchange amine unit, at least partially removes carbon dioxide in the form of bicarbonate from the cyclic amine-containing solution. Preferably, however, the regenerated cyclic amine-containing solution obtained from the regeneration column is treated in the reclaimer unit.

[0091] Further potential sources of the effluent stream to be treated are leaks of the cyclic amine-containing solution and leaks or drainages during equipment maintenance, including planned shutdowns and emergency shutdowns.

[0092] As discussed above, effluent streams to be discharged from the carbon capture system may be generated at several points within the carbon capture system. The effluent streams can be discharged from the carbon capture system continuously or intermittently. It is understood that the effluent streams typically do not warrant further processing or work-up and are thus permanently discharged from the carbon capture system, i.e., neither the effluent stream nor components thereof are not recycled to the carbon capture system. In one embodiment, the carbon capture system comprises one or more of the following components, and the effluent stream is generated by one or more of said components:

[0093] - a reclaimer unit, in particular a reclaimer unit selected from an ion-exchange reclaimer, a thermal reclaimer and an electrodialysis reclaimer, preferably an ion-exchange reclaimer,

[0094] - a water wash unit for treating CC>2-depleted gas from the absorption column;

[0095] - an acid wash unit for treating CC>2-depleted gas from the absorption column; and

[0096] - a reflux loop comprising a condenser system, the reflux loop being in fluid connection with the regeneration column.

[0097] Two or more of the obtained effluent streams may be combined to form the effluent stream to be treated. 241039W001 9

[0098] The present invention is particularly useful when the carbon captures system comprises an ion-exchange reclaimer unit, which typically yields a relatively dilute effluent. Such dilute effluents typically cannot be efficiently subjected to incineration.

[0099] Further provided is a method for producing a CC>2-depleted gas stream and CO2 in a carbon capture system, comprising:

[0100] - an absorption step in which a cyclic amine-containing solution and a gas stream comprising CO2 are brought into contact to remove CO2 from the gas stream to obtain a CC>2-depleted gas stream and an least partially CO2-laden cyclic amine-containing solution,

[0101] - a regeneration step in which the 002-laden cyclic amine-containing solution is regenerated by stripping off CO2, preferably by contacting the CO2-I aden cyclic amine solution in a countercurrent flow with steam which is generated by heating of cyclic amine-containing solution at the bottom of a regeneration column, to obtain CO2 and a regenerated cyclic amine-containing solution,

[0102] - a recycling step in which the regenerated cyclic amine containing solution is at least partially recycled to the absorption step,

[0103] - a treatment step in which

[0104] a) the cyclic amine-containing solution or a partial stream thereof

[0105] b) the CO2 obtained in the regeneration step; and / or

[0106] c) the CC>2-depleted gas obtained in the absorption step

[0107] is subjected to a treatment step which generates an effluent stream which is permanently discharged from the carbon capture system; and

[0108] - an advanced oxidation step, in which the effluent stream generated in the treatment step is subjected to advanced oxidation.

[0109] The treatment step may comprise treating the cyclic amine-containing solution or a partial stream thereof in a reclaimer unit, treating the CO2 obtained in the regeneration step in a reflux loop, and / or treating the CO2-depleted gas obtained in the absorption step in a water wash unit and / or an acid wash unit as described above.

[0110] The embodiments and preferred embodiments described above with regard to the carbon capture system and the cyclic amine containing solution likewise apply to the method for producing a CO2-depleted gas stream and CO2 in a carbon capture system.

[0111] The effluent stream is subjected to advanced oxidation. Advanced Oxidation Processes (AOPs) are a set of chemical treatment procedures designed to remove organic and inorganic contaminants from water and wastewater. These processes rely on the generation of highly reactive species that can effectively degrade and oxidize contaminants. Such highly reactive species are oxidative radicals which are preferably selected from chlorine radicals (*01), sulfate radicals (’SOr), periodate radicals ( Os) and hydroxyl radicals (’OH), in particular hydroxyl radicals. 241039W001 10

[0112] The ability of an oxidant to initiate chemical reactions is measured in terms of its oxidation potential. The end product of complete oxidation (mineralization) of organic compounds is carbon dioxide (CO2) and water (H2O). The oxidation potential of hydroxyl radicals at 2.8V is high relative to ozone at 2.1V and chlorine at 1.4V.

[0113] In a preferred embodiment, generation of the highly reactive species is effected by activating a radical precursor by an activation means.

[0114] The radical precursor is a substance that is capable of being transformed into the highly reactive radical species by activation by an activation means.

[0115] Preferred radical precursors are selected from compounds comprising an 0-0 single bond in their molecular structure, such as hydrogen peroxide (H2O2), ozone (O3), persulfate ions (S2O82) or peroxymonosulfate ions (HSO5 ). Other radical precursors that can be envisaged are water and hydroxide ions (OH-).

[0116] Most preferred radical precursors are selected from hydrogen peroxide (H2O2), ozone (O3), and water.

[0117] Activation means refers to any physical, such as energetic, or chemical means suitable to initiate the conversion of the radical precursor into the highly reactive radical species. The means provides sufficient activation energy and / or lowers the activation energy, thus enabling the homolytic cleavage of a chemical bond or inducing electron transfer in the radical precursor. The activation means is preferably selected from irradiation with electromagnetic radiation, ionizing radiation or acoustic energy; electrical energy such as electrical oxidation; and chemical activation, in particular using a catalytic material or a chemical activator.

[0118] Electromagnetic radiation is preferably UV radiation, more preferably UV-C radiation having a wavelength of 200 to 280 nm.

[0119] Ionizing radiation may be selected from gamma radiation, more preferably electron beam irradiation or x-ray irradiation.

[0120] Acoustic energy may be provided by ultrasonic irradiation, preferably at a frequency between 20 kHz and 100 kHz, and more preferably 20 to 40 kHz.

[0121] Electrical energy may be applied as an electrochemical potential at an anode surface, most preferably using boron-doped diamond or mixed metal oxide electrodes, optionally combined with pulsed current or plasma discharge.

[0122] The activation means can be a chemical activator. Chemical activators are substances which promote the formation of highly reactive radicals.

[0123] Preferably, the chemical activators are selected from catalyst materials and accelerators. In the context of Advanced Oxidation, an accelerator is a substance that enhances the activation of a radical precursor by lowering the energy barrier or increasing the reaction rate of radicals formation without itself being the 241039W001 11

[0124] primary radical precursor. Preferred accelerators are hydroxyl anions in a concentration sufficient to accelerate the decomposition of the radical precursor or hydrogen peroxide.

[0125] In another preferred embodiment, the activation means is a catalyst material. In the context of Advanced Oxidation, the catalyst material is a substance that participates in the activation of a radical precursor by providing an alternative reaction pathway with a lower activation energy, typically through surface sites or redox cycling, and remains chemically unchanged after the reaction, except for reversible oxidation state changes. Catalytic materials enable continuous radical generation without being consumed stoichiometrical ly. The catalytic material is preferably a transition metal catalyst selected from iron, cobalt or manganese salts, preferably ferrous ions (Fe2+). Another preferred class of catalytic materials are photocatalysts, preferably selected from titanium dioxide, zinc oxide, tungsten trioxide, iron oxides, graphitic carbon nitride, zirconium dioxide, cadmium sulfide, silver phosphate, silver halogenides or bismuth oxides. Most preferably the photocatalyst is titanium dioxide, optionally doped with noble metals.

[0126] The combination of the radical precursor and the activation means can be dependent on the nature of the radical and the activation energy required to convert the radical precursor into the highly activated radical, in particularly hydroxy radicals (’OH).

[0127] In particular, Advanced Oxidation includes processes where a compound comprising an 0-0 single bond in its molecular structure is subjected to irradiation with electromagnetic radiation, in particular UV radiation; and / or activation by a catalyst material.

[0128] Thus, if the precursor is ozone or hydrogen peroxide, the activation means is preferably selected from a catalyst material and / or electromagnetic irradiation.

[0129] If the precursor is water, higher energies may be required to transform the precursor into highly reactive radicals, so that the activation means is preferably selected from electrical energy or ionizing radiation.

[0130] In an Advanced Oxidation Process, highly accelerated oxidation reactions occur when the hydroxyl radicals react with organic contaminants to initiate a series of oxidative degradation reactions. However, hydroxyl radicals inevitably react with all kinds of organic and inorganic constituents in water, which results in decreasing the efficiency of hydroxyl radicals for degrading the contaminant of interest. Dissolved iron oxidation uses the hydroxyl radical before the oxidation of organics. It is also known that high alkalinity reduces the hydroxyl radical concentration, in particular by generation of carbonate ions. Advanced Oxidation Processes thus face the challenge of increasing the hydroxyl radical production yield and directing the reaction pathway where major reactions between hydroxyl radicals and the contaminants of interest occur.

[0131] In one embodiment, advanced oxidation includes one or more of the following processes to generate hydroxyl radicals:

[0132] 1) ozonation (O3): utilizes ozone gas. Ozonation is a special case where ozone itself is the radical precursor but also acts as a chemical accelerator. In a most preferred embodiment of ozonation, a further chemical accelerator is added, most preferably hydroxyl anions. Acceleration of ozone 241039W001 12

[0133] decomposition is most preferably effected at high pH-values, preferably in the range of 8 and more, and most preferably in the range of 8 to 10.

[0134] 2) Fenton's reaction: reaction of hydrogen peroxide (H2O2) with ferrous iron (Fe2+), i.e., Fenton's reagent.

[0135] In this embodiment, hydrogen peroxide is the radical precursor and Fenton's reagent is catalytic material used as the activation means.

[0136] 3) photocatalysis: uses a semiconductor material such as titanium dioxide (TIO2) and ultraviolet light. In this embodiment water is the radical precursor and the photocatalyst is the activation means. Photocatalysts act as activation means because they usually absorb light energy and create electronhole pairs that drive oxidation reactions. The photogenerated holes on the catalyst surface oxidize adsorbed water molecules or hydroxide ions, so that water constitutes the radical precursor that is converted into hydroxyl radicals. This mechanism enables radical generation without adding external oxidants, using only light and water.

[0137] 4) UV / H2O2: combines ultraviolet light and hydrogen peroxide. In this embodiment H2O2 is the radical precursor and UV irradiation is the activation means.

[0138] 5) UV / O3: combines ultraviolet light and ozone gas. In this embodiment ozone is the radical precursor and UV irradiation is the activation means.

[0139] 6) peroxone process (O3 / H2O2): combines ozone gas and hydrogen peroxide. In this embodiment, O3 can be considered to be the radical precursor and H2O2 has a dual function of being a radical precursor and a chemical accelerator acting as an activation agent.

[0140] 7) electrochemical oxidation: uses electrical currents to generate oxidizing agents, including hydroxyl radicals, directly from water. In this embodiment water is the radical precursor and electrical energy in the form of an electrochemical potential at an anode surface, most preferably using boron-doped diamond or mixed metal oxide electrodes, is the activation means.

[0141] 8) Photo-Fenton process: combines Fenton's reagent and ultraviolet light. In this embodiment, hydrogen peroxide is the radical precursor and a transition metal catalyst, preferably selected from iron, cobalt or manganese salts, and most preferably ferrous ions (Fe2+) is the catalytic material acting as an activation means.

[0142] Advanced oxidation preferably includes one or more of the following processes to generate hydroxyl radicals:

[0143] 2) Fenton's reaction: reaction of hydrogen peroxide (H2O2) with ferrous iron (Fe2+), i.e., Fenton's reagent 4) UV / H2O2: combines ultraviolet light and hydrogen peroxide

[0144] 6) peroxone process (O3 / H2O2): combines ozone gas and hydrogen peroxide

[0145] 7) electrochemical oxidation, most preferably in the presence of a boron-doped diamond or mixed metal oxide electrode: uses electrical currents to generate oxidizing agents, including hydroxyl radicals, directly from water

[0146] 8) Photo-Fenton process: combines Fenton's reagent and ultraviolet light

[0147] The effluent stream may be subjected to advanced oxidation in accordance with any of the methods known to the skilled person to be suitable for the treatment of amine-containing wastewater, such as those 241039W001 13

[0148] described in Ullmann's Encyclopedia of Industrial Chemistry, H. Lutze, "Water, 6. Treatment by Oxidation Processes” (2016), doi.org / 10.1002 / 14356007.o28_o17.pub2.

[0149] Specifically, in an embodiment, treatment of the effluent stream with a radical precursor or a radical precursor having an 0-0 single bond in its molecular structure without an activation means is not considered an advanced oxidation in the sense of the invention and hence excluded from the invention. It is rather considered a conventional oxidation because oxidation does not rely on hydroxyl radical formation, but rather on direct electron transfer oxidation. As a further example, ozonation without the presence of a further activation means, such as UV-radiation, hydrogen peroxide acting as a chemical accelerator or hydroxyl anions present in water with a pH of 8 or more acting as a chemical accelerator shall also be excluded from the scope of this invention.

[0150] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. Further, it is explicitly noted that the following set of embodiments provided below is not the set of claims determining the extent of protection, but represents a suitably structured part of the description directed to general and preferred aspects of the present invention.

[0151] 1. A method for treating an effluent stream generated by a carbon capture system, the method comprising:

[0152] contacting a cyclic amine-containing solution and a gas stream in the carbon capture system to remove carbon dioxide from the gas stream, the carbon capture system generating an effluent stream discharged from the carbon capture system; and

[0153] subjecting the effluent stream to advanced oxidation.

[0154] 2. The method of embodiment 1 , wherein the cyclic amine is selected from

[0155] I) cyclic amines comprising one or more secondary amino groups in the ring;

[0156] ii) cyclic amines comprising one or more tertiary amino groups in the ring; and / or

[0157] ill) cyclic amines comprising both at least one tertiary amino group and at least one secondary amino group.

[0158] 3. The method of embodiment 2, wherein the cyclic amine is selected from

[0159] I) piperidine, 2-methylpiperidine, 4-methylpiperidine, 4-(2-hydroxyethyl)-piperidine, 2, 2,6,6- tetramethylpiperidine and derivatives thereof, piperazine and 2-methy Ipiperazine;

[0160] ii) 1-(2-hydroxyethyl)piperidine, 1 ,4-dimethylpiperazine, 1 ,4-bis(2-hydroxyethyl)piperazine, triethylenediamine, 2-hydroxymethyl triethylenediamine, 1-methyl-2-pyrrolidine ethanol; and / or ill) 1 -methylpiperazine and 1-(2-hydroxyethyl)piperazine.

[0161] 4. The method according to any one of the preceding embodiments, wherein the cyclic amine does not comprise a ring nitrogen bearing a beta-hydroxyalkyl substituent, in particular hydroxyethyl. 241039W001 14

[0162] 5. The method according to any one of the preceding embodiments, wherein the cyclic amine- containing solution is an aqueous solution.

[0163] 6. The method according to any one of the preceding embodiments, wherein the tertiary amine- containing solution further comprises a non-cyclic amine.

[0164] 7. The method according to any one of the preceding embodiments, wherein the gas stream is a flue gas stream.

[0165] 8. The method according to any one of the preceding embodiments, wherein the effluent stream is an aqueous effluent stream.

[0166] 9. The method according to any one of the preceding embodiments, wherein the effluent stream is generated by a carbon capture system comprising:

[0167] - an absorption column in which the flue gas stream to be treated is contacted with the cyclic amine-containing solution to remove carbon dioxide from the flue gas stream, wherein a CO2- depleted gas is withdrawn at the top of the absorption column, and wherein a CO2-laden cyclic amine-containing solution is withdrawn from the bottom of the absorption column; and - a regeneration column in which the CC>2-laden cyclic amine-containing solution is stripped of CO2, preferably by countercurrent flow with steam which is generated by heating of regenerated cyclic amine-containing solution at the bottom of the regeneration column.

[0168] 10. The method according to embodiment 9, wherein the carbon capture system comprises one or more of the following components, and the effluent stream is generated by one or more of said components:

[0169] - a reclaimer unit;

[0170] - a water wash unit;

[0171] - an acid wash unit; and

[0172] - a reflux loop comprising a condenser system, the reflux loop being in fluid connection with the regeneration column.

[0173] 11. The method of embodiment 10, wherein the effluent stream is at least partially generated by a reclaimer.

[0174] 12. The method of embodiment 11, wherein the reclaimer is selected from an ion-exchange reclaimer, a thermal reclaimer and an electrodialysis reclaimer.

[0175] 13. The method of embodiment 12, wherein the reclaimer is an ion-exchange reclaimer.

[0176] 14. The method of any one of the preceding embodiments, wherein advanced oxidation includes one or more of the following processes: 241039W001 15

[0177] 1) ozonation

[0178] 2) Fenton's reaction

[0179] 3) photocatalysis

[0180] 4) UV / H2O2

[0181] 5) UV / ozonation

[0182] 6) peroxone process

[0183] 7) electrochemical oxidation

[0184] 8) Photo-Fenton process.

[0185] 15. A method for producing a CC>2-depleted gas stream and CO2 in a carbon capture system, comprising:

[0186] - an absorption step in which a cyclic amine-containing solution and a gas stream comprising CO2 are brought into contact to remove CO2 from the gas stream to obtain a CC>2-depleted gas stream and an at least partially CC>2-laden cyclic amine-containing solution,

[0187] - a regeneration step in which the CC>2-laden cyclic amine-containing solution is regenerated by stripping off CO2, preferably by contacting the CO2-I aden cyclic amine solution in a countercurrent flow with steam which is generated by heating of cyclic amine-containing solution at the bottom of a regeneration column, to obtain CO2 and a regenerated cyclic amine- containing solution,

[0188] - a recycling step in which the regenerated cyclic amine containing solution is at least partially recycled to the absorption step,

[0189] - a treatment step in which

[0190] a) the cyclic amine-containing solution or a partial stream thereof

[0191] b) the CO2 obtained in the regeneration step; and / or

[0192] c) the CC>2-depleted gas obtained in the absorption step

[0193] is subjected to a treatment step which generates an effluent stream which is permanently discharged from the carbon capture system; and

[0194] - an advanced oxidation step, in which the effluent stream generated in the treatment step is subjected to advanced oxidation.

[0195] 16. The method according of any one of the preceding embodiments, wherein advanced oxidation causes oxidative radicals to be present in the effluent stream.

[0196] 17. The method according to embodiment 16, wherein the oxidative radicals are selected from chlorine radicals (’Cl), sulfate radicals (’SOr), periodate radicals (dOs) and hydroxyl radicals (’OH), in particular hydroxyl radicals.

[0197] 18. The method according to embodiment 16 or 17, wherein advanced oxidation involves subjecting a radical precursor to an activation means to generate oxidative radicals. 241039W001 16

[0198] 19. A method according to embodiment 18, where the radical precursor is selected from hydrogen peroxide (H2O2), ozone (O3), persulfate ions (S2O82), peroxymonosulfate ions (HSO5 ), water, and hydroxide ions (OH ).

[0199] 20. A method according to any one of the preceding embodiments where the activation means is selected from irradiation with electromagnetic radiation, ionizing radiation or acoustic energy; electrical energy such as electrical oxidation; and chemical activation, in particular using a catalytic material or a chemical activator.

[0200] 21. A method according to any one of the preceding embodiments, wherein the radical precursor and the activation means are selected from the following combinations:

[0201] - ozone / hydrogen peroxide (peroxone),

[0202] - ozone / UV-irradiation,

[0203] - hydrogen peroxide / transition metal catalyst, in particularly ferrous ions (Fe2+), and optionally UV- irradiation (Fenton and Photo-Fenton),

[0204] - hydrogen peroxide / hydroxyl groups in a concentration sufficient to yield a pH of 8 or more, - water / photocatalysts and irradiation, in particularly titanium dioxide,

[0205] - water / electrical energy, preferably applied as an electrochemical potential at an anode surface, in particular using boron-doped diamond or mixed metal oxide electrodes.

[0206] 22. A method according to any one of the preceding embodiments excluding oxidation with hydrogen peroxide or ozone without an additional activation means, in particular the activation means listed in embodiment 20.

[0207] The invention is further illustrated by the following examples.

[0208] Example 1

[0209] An aqueous sample containing triethylenediamine (0.3 wt.-%) and sodium hydroxide (0.3 wt.-%) was subjected to electrochemical oxidation in an undivided cell with a current density of 100 mA / cm2. The cell formed part of a circuit, and the sample was pumped through cell and circuit during the electrochemical oxidation. A boron doped diamond electrode with a surface area of 63.6 cm2was used, having a boron doped diamond layer on a niobium substrate, as both anode and cathode. The gap between the electrodes was 3 mm.

[0210] The total organic carbon (TOC) value of the sample was determined to be 1926 ppm before the electrochemical oxidation. After 6 h, the TOC value was found to be decreased to 32 ppm. After 12 h, the TOC was found to be below the detection limit of 5 ppm. The TOC value was determined in accordance with DIN EN 1484 (H3). 241039W001 17

[0211] Example 2

[0212] An aqueous sample containing piperazine (0.3 wt%) and sodium hydroxide (0.3 wt%) was subjected to electrochemical oxidation in an undivided cell with a current density of 100 mA / cm2. The cell formed part of a circuit, and the sample was pumped through cell and circuit during the electrochemical oxidation. A boron doped diamond electrode with a surface area of 63.6 cm2was used, having a boron doped diamond layer on a niobium substrate, as both anode and cathode. The gap between the electrodes was 3 mm.

[0213] The total organic carbon (TOC) value of the sample was determined to be 1700 ppm before the electrochemical oxidation. After 6 h, the TOC value was found to be decreased to 130 ppm. After 12 h, the TOC was found to be decreased to 55 ppm. The TOC value was determined in accordance with DIN EN 1484 (H3).

Claims

241039W001 18Claims1. A method for treating an effluent stream generated by a carbon capture system, the method comprising:contacting a cyclic amine-containing solution and a gas stream in the carbon capture system to remove carbon dioxide from the gas stream, the carbon capture system generating an effluent stream discharged from the carbon capture system, cyclic amine being present in the effluent stream; andsubjecting the effluent stream to advanced oxidation.

2. The method of claim 1 , wherein the cyclic amine is selected fromI) cyclic amines comprising one or more secondary amino groups in the ring;ii) cyclic amines comprising one or more tertiary amino groups in the ring; and / orill) cyclic amines comprising both at least one tertiary amino group and at least one secondary amino group.

3. The method of claim 2, wherein the cyclic amine is selected fromI) piperidine, 2-methylpiperidine, 4-methylpiperidine, 4-(2-hydroxyethyl)-piperidine, 2, 2,6,6- tetramethylpiperidine and derivatives thereof, piperazine and 2-methy Ipiperazine;ii) 1-(2-hydroxyethyl)piperidine, 1 ,4-dimethylpiperazine, 1 ,4-bis(2-hydroxyethyl)piperazine, triethylenediamine, 2-hydroxymethyl triethylenediamine, 1-methyl-2-pyrrolidine ethanol; and / or ill) 1 -methylpiperazine and 1-(2-hydroxyethyl)piperazine.

4. The method according to any one of the preceding claims, wherein the cyclic amine does not comprise a ring nitrogen bearing a beta-hydroxyalkyl substituent, in particular hydroxyethyl.

5. The method according to any one of the preceding claims, wherein the cyclic amine-containing solution is an aqueous solution.

6. The method according to any one of the preceding claims, wherein the tertiary amine-containing solution further comprises a non-cyclic amine.

7. The method according to any one of the preceding claims, wherein the gas stream is a flue gas stream.

8. The method according to any one of the preceding claims, wherein the effluent stream is an aqueous effluent stream.241039W001 199. The method according to any one of the preceding claims, wherein the effluent stream is generated by a carbon capture system comprising:- an absorption column in which the flue gas stream to be treated is contacted with the cyclic amine-containing solution to remove carbon dioxide from the flue gas stream, wherein a CO2- depleted gas is withdrawn at the top of the absorption column, and wherein a CO2-laden cyclic amine-containing solution is withdrawn from the bottom of the absorption column; and - a regeneration column in which the CC>2-laden cyclic amine-containing solution is stripped of CO2, preferably by countercurrent flow with steam which is generated by heating of regenerated cyclic amine-containing solution at the bottom of the regeneration column.

10. The method according to claim 9, wherein the carbon capture system comprises one or more of the following components, and the effluent stream is generated by one or more of said components: - a reclaimer unit;- a water wash unit;- an acid wash unit; and- a reflux loop comprising a condenser system, the reflux loop being in fluid connection with the regeneration column.

11. The method of claim 10, wherein the effluent stream is at least partially generated by a reclaimer.

12. The method of claim 11, wherein the reclaimer is selected from an ion-exchange reclaimer, a thermal reclaimer and an electrodialysis reclaimer.

13. The method of claim 12, wherein the reclaimer is an ion-exchange reclaimer.

14. The method of any one of the preceding claims, wherein advanced oxidation includes one or more of the following processes:9) ozonation10) Fenton's reaction11) photocatalysis12) UV / H2O213) UV / ozonation14) peroxone process15) electrochemical oxidation16) Photo-Fenton process.241039W001 2015. A method for producing a CC>2-depleted gas stream and CO2 in a carbon capture system, comprising:- an absorption step in which a cyclic amine-containing solution and a gas stream comprising CO2 are brought into contact to remove CO2 from the gas stream to obtain a CC>2-depleted gas stream and an at least partially CC>2-laden cyclic amine-containing solution,- a regeneration step in which the CC>2-laden cyclic amine-containing solution is regenerated by stripping off CO2, preferably by contacting the CO2-I aden cyclic amine solution in a countercurrent flow with steam which is generated by heating of cyclic amine-containing solution at the bottom of a regeneration column, to obtain CO2 and a regenerated cyclic amine- containing solution,- a recycling step in which the regenerated cyclic amine containing solution is at least partially recycled to the absorption step,- a treatment step in whicha) the cyclic amine-containing solution or a partial stream thereofb) the CO2 obtained in the regeneration step; and / orc) the CC>2-depleted gas obtained in the absorption stepis subjected to a treatment step which generates an effluent stream which is permanently discharged from the carbon capture system, cyclic amine being present in the effluent stream; and- an advanced oxidation step, in which the effluent stream generated in the treatment step is subjected to advanced oxidation.