Process for concentrating amine water at room temperature

Abstract

Process for concentrating amine water, coining from natural gas purification and / or combustion fumes decarbonization processes, including a direct osmosis process, carried out at a temperature comprised from 20 - 25 °C.

Description

[0001] Process for concentrating amine water at room temperature

[0002] Field of the invention

[0003] The present invention refers to a process for concentrating wastewater, containing nitrogenous organic compounds, coming from natural gas purification and / or combustion fume decarbonization processes, said waters also being known as "amine waters".

[0004] Background

[0005] The raw natural gas, after extraction from the field, must be treated, in order to remove the impurities contained in it, up to acceptable values, required by the end users. Natural gas impurities include, for example, acid gases, such as hydrogen sulphide (H2S) and carbon dioxide (CO2) . These gases, being acid, can cause damage, given their high corrosive capacity, to the transmission and conversion equipment thereof, to the environment and to people. The most widely used methods for removing acid gases from raw natural gas are washing with aqueous solutions of basic species, such as potassium carbonate and aliphatic amines.

[0006] In particular, the removal of H2S and CO2 in raw natural gas is usually carried out by washing the gas itself with aqueous solutions of alkanolamines, e.g., monoethanolamine (MEA) , diethanolamine (DEA) diisopropanolamine (DIPA) , triethanolamine (TEA) , N- methyldiethanolamine (MDEA) , 2- ( 2-aminoethoxy ) ethanol, as reported in R. Wagner, Fundamentals gas sweetening, Laurance Reid Gas Conditioning Conference, 26 February- 01 March 2006, Norman, Oklahoma.

[0007] The aqueous solutions of alkanolamines are also used in post-combustion processes of CO2 removal, as reported in Z. Liang et al., "Recent progress and new developments in post-combustion carbon-capture technology with amine based solvents", International Journal of Greenhouse Gas Control, 40, 2015, pp . 26-54. In this case, mixtures of alkanolamines containing for example monoethanolamine (MEA) , diethanolamine (DEA) , diisopropanolamine (DIPA) , or other tertiary amines such as for example triethanolamine (TEA) , N- methyldiethanolamine (MDEA) are also used. The oxidizing environment of the combustion fumes and the coexistence of nitrogen oxides (NOX) can lead to the formation of N- nitrosoamines and / or N-ni troamines , known as carcinogens, as reported in several studies, see for example X. Chen et al., "Emerging N-nitrosoamines and N- nitramines from amine based postcombustion CO2 capture", Chemical Engineering Journal, 335, 2018, pp . 921-935.

[0008] Using aqueous solutions of alkanolamines, at the end of the gas purification and / or combustion fume decarbonization process, aqueous solutions containing ammonium sulphides, ammonium carbonates and ammonium carbammates deriving from the salification reactions of the respective alkanolamines with H2S and CO2 will be obtained. Said compounds being thermolabile are subsequently thermally decomposed, to allow the reuse of the aqueous solutions of alkanolamines and at the same time the release of CO2 and H2S in the gas phase. Generally, the acid gases, released by this decomposition process, are also recovered. H2S, for example, is sent to an oxidation reactor, where it is transformed into elemental sulphur, producing energy, while CO2 is used either as an inert gas or for the production of dry ice.

[0009] Despite their reuse, aqueous solutions of alkanolamines must then be disposed of, since, due to the progressive deterioration of the same, which would lead to the decrease of their specific capacity in removing acid gases, their periodic replacement, partial or total, is required, as reported in R. Wagner, Fundamentals gas sweetening, Laurance Reid Gas Conditioning Conference, 26 February-01 March 2006, Norman, Oklahoma. Said deterioration is caused by the succession of natural gas washing cycles or CO2 removal cycles in the post-combustion processes and by the regeneration process of the aqueous solutions of alkanolamines themselves, which occurs at high temperatures .

[0010] The wastewater to be disposed of are therefore aqueous solutions having a basic pH, frequently greater than 8, containing residual alkanolamines, alkylammonium salts, ammonium carbamates, metal salts and many other products deriving from the degradation reactions of the alkanolamines, such as for example ammonia (NH3) , heterocyclic compounds as reported in "Solvent management: solvent stability and amine degradation in CO2 capture processes", Carbon Management, (2011) , 2:5, 551-566, or from the reaction of said alkanolamines with the oxidizing environment of the combustion fumes, which leads, as described above, to the formation of the nitro derivatives .

[0011] All the species mentioned above are potential aggressive chemicals, as also reported in several publications including I. Eide-Augmo et al., "Environmental impact of amines", Energy Procedia, 1, 2009, pp . 1297-1304, and in I. A. Henry et al., "Aerobic and anoxic biodegradability of amines applied in CO2 capture", International Journal of Greenhouse Gas Control, 58, 2017, 266-275.

[0012] The only method, currently applied on a large scale, to dispose of amine waters is to send them to pyrolysis. Since there are not many incinerators authorized to treat this type of waste, as they must have the authorization for the disposal of special waste, it is necessary to transport the amine water to be disposed of, for example by tank trucks, towards the incinerators authorized for the treatment of special waste equipped with dedicated safety systems. Consequently, the transport and treatment costs are directly correlated to the volume of amine water to be treated.

[0013] Therefore, in order to reduce disposal costs, a concentration of the amine waters to be sent to pyrolysis is required.

[0014] The concentration methods currently used and described in the literature are different, and all have disadvantages .

[0015] EP 1027323 Bl by Shell Int. Research describes a method for treating amine water by conventional distillation (DC) . The method involves two steps: dehydration and purification of the alkanolamine used. In the experimental part, it is reported about the treatment of an amine water containing 42% by weight of diisopropanolamine (DIPA) and 55% by weight of water, working at a temperature comprised from 154-177°C under vacuum; and the treatment of the amine water containing 40% by weight of N-methyldiethanolamine (MDEA) , 29% by weight of water, 31% by weight of sulfolane, operating at a temperature comprised from 135-148°C under vacuum. The concentration of amine water by conventional distillation (DC) therefore requires working under vacuum at high temperatures using equipment made of special materials capable of withstanding high pH at the required operating temperatures. Furthermore, at said temperatures further degradation products of the alkanolamines, such as for example heterocyclic products, which are difficult to dispose of, can be formed during the distillation process.

[0016] US 9028654 B2 by Alstom Technology describes a method for treating amine water that involves two evaporative treatments and a reverse osmosis (RO) . At the end of the process, water with a purity higher than 95% is obtained. The concentration by conventional membrane systems such as nanofiltration (NF) , reverse osmosis (RO) , requires the application of high hydraulic pressures, comprised from 5-150 bar, at which the membranes used are more affected by chemical aggression and fouling as described in "The application of membrane technology for water disinfection", Water Research, 33 (2) , 1999, pp . 301-308, and in "Reverse osmosis desalination: Water sources, technology, and today's challenges", Water Research, 43 (9) , 2009, pp . 2317-2348.

[0017] Unconventional distillation systems have also been described such as membrane distillation (MD) , in which water vapour is passed as distillate through membrane contactors , and pervaporation ( PV) , in which selective membranes are used not in direct contact with amine water heated to a temperature lower than boiling temperature . However, the water selectivity towards alkanolamine of said systems is negatively af fected by the surfactant action of the alkanolamines themselves . In addition, these systems require a certain expenditure of thermal energy, leading to obtaining low distillate flows , as reported in "Advances in membrane distillation for water desalination and puri fication applications" , Water, 5 , 2013 , pages 94-196 .

[0018] US 2022242756 Al of the Applicant describes a process for concentrating an amine water containing 66000 mg / 1 of total nitrogen, by membrane distillation (MD) , obtaining a total nitrogen rej ection equal to 99% and distillate flows equal to 0 . 8-2 . 2 1 m-2h-1, operating at temperatures higher than room temperature , about 50- 70 ° C, and at atmospheric pressure .

[0019] US 5334314 A by Deutsche Carbone describes a method for treating amine water by pervaporation ( PV) , using membranes of acid-treated polyvinyl alcohol . The examples describe the dehydration of a mixture containing 70 % by weight of ethylamine and 30 % by weight of water, operating at 85 ° C and with a di stillate flow of 0 . 8 kg m-2h-1. In the experimental part , the dehydration of a mixture containing 40 % by weight o f pyridine and 60 % by weight of water operating at 95 ° C, and the dehydration of a mixture containing 70 % by weight of dimethylamine and 30 % by weight of water operating at 100 ° C are also exempli fied . In all the examples cited, it is presumably operated under vacuum . US 5051188 A by Basf AG describes a method for treating amine water by pervaporation (PV) , using polyvinyl alcohol membranes. In the experimental part the dehydration of a mixture containing 45% by weight of methylamine (as such or as carbamate) , 28% by weight of CO2, 27% by weight of water, operating at 80°C under vacuum is exemplified. A distillate flow of 0.5 kg m-2h_1is obtained.

[0020] US 5171499 A by Texaco describes a method for treating amine water by using pervaporation (PV) in which composite membranes consisting of a layer of dense polyvinyl alcohol, deposited on a porous alumina support, are employed. Said substrate is necessary to ensure resistance to chemical aggressiveness. The dehydration of mixtures containing 74-78% by weight of amine, working at 70°C under vacuum, is also exemplified. Fresh water selectivity in the distillate of 57-60% and distillate flows of 0.5 kg m-2h-1are obtained.

[0021] Therefore, an alternative solution is needed that allows the amine water to be concentrated while working under economic and optimal process conditions so as not to produce further toxic impurities, which are difficult to dispose of and harmful to both humans and the environment .

[0022] The Applicant has surprisingly found that by operating with a direct osmosis (FO) process, using membranes made of polyamide, polysulfone and / or polyester, the amine waters, coming from natural gas purification and / or combustion fumes decarbonization processes, can be concentrated working at room temperature and atmospheric pressure. In fact , to date there are still no applications in the art of the direct osmosis ( FO) technique alone to concentrate amine waters , containing alkanolamines , working under economic and optimal operating conditions , such as for example at room temperature and atmospheric pressure .

[0023] US 20190263685 Al by Chevron USA describes a method for diluting a saturated brine without the addition o f fresh water . Dilution is obtained by contacting the saturated brine with wastewater associated with the production of hydrocarbons by direct osmosis ( FO) . Said wastewater does not contain amines .

[0024] WO 2012106732 A2 by Hydration Systems LLC . describes a method for concentrating by direct osmosis ( FO) waters coming from a digester rich in ammonia (NH3) . The concentrate obtained is subsequently used for the concomitant production of biomethane and fertili zers . The method involves several steps : filtration of waters rich in NH3from the digester, correction of pH and concentration by FO .

[0025] US 20220204375 Al by Industrial Technology Research Institute describes a method for treating wastewater comprising several steps : a direct osmosis ( FO) and an electrodialysis (ED) . Wastewater is concentrated by FO up to 7-14 % . The concentrate obtained i s fed to the ED, whereby the conversion of salts into acids and bases i s obtained . The by-products from the ED are recycled to the FO until " zero discharge" is reached . The method for treating wastewater is claimed in the presence of compounds dissolved completely dissociated in ions , while there are no indications for the non-dissociated or poorly dissociated dissolved compounds such as, for example, the alkanolamines and the nitrogenous organic compounds deriving from their degradation.

[0026] M. Giagnorio et al., in "Hybrid forward osmosis nanofiltration for wastewater reuse: system design", Membranes, 9 (5) , 2019, 61, describe a method for the recovery of water around 85% from groundwater, contaminated by inorganic species and not by alkanolamines, like in the present invention. The method comprises several steps: a direct osmosis (FO) and a nanofiltration (NF) .

[0027] K.L. Hickenbottom et al., in "Forward osmosis treatment of drilling mud and fracturing wastewater from oil and gas operations", Desalination, 312, 2013, pp . 60-66, describe a method for the recovery of 80% water by FO from wastewater and drilling mud from hydrocarbon extraction. Even in the presence of a high content of organic and inorganic species, the presence of alkanolamines has not been reported either in wastewater or in the drilling mud used.

[0028] Objects of the invention

[0029] The Applicant has now found that it is possible to concentrate the amine water, coming from natural gas purification and / or combustion fumes decarbonization processes, by means of a process comprising a direct osmosis (FO) process, using semi-permeable membranes and working under economic and optimal operating conditions, such as for example operating at room temperature and atmospheric pressure.

[0030] A further aspect of the present invention concerns a process for concentrating amine waters, as described above, also comprising a step of regenerating the solution, used in the direct osmosis ( FO) process , as a drawing solution (DS ) .

[0031] Brief description of the drawings

[0032] Figure 1 : Non-limiting example of FO Sterlitech plant used to carry out the trial in question .

[0033] Detailed description of the invention

[0034] All terms used in this patent appl ication, unless otherwise indicated, are to be understood in their ordinary meaning, as known in the technical field in which they are applied .

[0035] For the purposes o f the present invention, in the following description and claims , the definitions of numerical ranges comprise the individual values within the range and its extremes , unless otherwise speci fied .

[0036] For the purposes o f the present invention, in the following description and claims , the terms "comprising" , " includes" are also inclusive of the terms "consisting essentially of" or "which consists of" .

[0037] For the purposes o f the present invention, "room temperature" means a temperature comprised from 20-25 ° C .

[0038] For the purposes of the present invention, "amine water" means wastewater, containing nitrogenous organic compounds , coming from natural gas puri fication and / or combustion fumes decarboni zation processes . The nitrogenous organic compounds contained in the amine water of the present invention consist of carbon atoms bonded to hydrogen atoms , to one or more nitrogen atoms and may also contain other heteroatoms in addition to nitrogen, such as for example oxygen . Said nitrogenous organic compounds may be present as such and / or in salt form and generally comprise linear, branched, cyclic, aromatic aliphatic amines and the salts thereof ; alkanolamines and the salts thereof ; aromatic and aliphatic heterocycles ; ammonium carbamates and mixtures thereof . Said nitrogenous organic compounds preferably consist of alkanolamines , salts thereof , degradation products thereof , and mixtures thereof . By degradation products of alkanolamines in the present invention are meant organic compounds , such as for example aromatic and aliphatic heterocyclics , aliphatic and aromatic amines and / or the salts thereof , ammonium carbamates .

[0039] Ammonia, another degradation product o f alkanolamines and organic compounds containing nitrogen, since it is not an organic compound is not included in the nitrogenous organic compounds , but is counted, like all the inorganic compounds containing nitrogen, when expressing the amount o f total nitrogen in mg / 1 present in the amine water to be treated, the measurement being linked to the total nitrogen content present in solution, whether it is present in organic or inorganic compounds .

[0040] Therefore , the main obj ect of the present invention is a process for concentrating amine water, coming from natural gas puri fication and / or combustion fumes decarboni zation processes , including a direct osmosis process , carried out at a temperature comprised from 20- 25 ° C, which includes the following steps :

[0041] ( a ) contacting a feed solution (AA) , consisting o f amine water, comprising nitrogenous organic compounds , and an initial drawing solution ( DS ) , comprising a solute dissolved in water , through a cell , interposed between the two solutions and containing a semi-permeable membrane, said membrane being selective to the passage of water;

[0042] (b) diluting the initial drawing solution (DS) by a spontaneous flow of water, said permeate, passing through the semi-permeable membrane from the feed solution (AA) to the drawing solution (DS) , obtaining a final drawing solution (DS' ) having a solute concentration lower than that of the initial drawing solution (DS) .

[0043] The amine water to be concentrated is generally directly withdrawn from the wastewater of natural gas purification and / or combustion fumes decarbonization processes. Said amine water can be used as such withdrawn or preferably pre-treated, using techniques known in the art, such as for example filtration, clarification, oil elimination and degassing, to make it homogeneous and reduce the potential causes of damage (e.g., fouling, abrasion, corrosion) of the semi-permeable membrane.

[0044] In a preferred embodiment the amine water has a total nitrogen content comprised from 3,000 to 90, 000 mg / 1, preferably from 8,000 to 70,000 mg / 1, said content being determined by means of a Shimadzu analyzer TOC V CPH™ equipped with Shimadzu TMN 1™ detectors for total nitrogen .

[0045] The total nitrogen content of the amine water of the present invention is linked both to the nitrogen content present in the nitrogenous organic compounds and to the inorganic nitrogen present therein, for example coming from compounds such as ammonia, obtained from decomposition processes of the same nitrogenous organic compounds .

[0046] In a particularly preferred embodiment , the nitrogenous organic compounds contained in the amine water comprise amines having a total number of carbon atoms comprised from 1 to 12 .

[0047] The amines contained in the amine water may also be cyclic and contain more than one nitrogen atom, such as for example piperidine , pyrrolidine , piperazine and the corresponding tertiary amines having a total carbon number of less than or equal to 12 . A non-limiting example consists of the following amines : N- methylpiperidine , N-ethylpiperidine , N- methylpyrrolidine , N-ethylpyrrolidine , N- methylpiperazine , N-ethylpiperazine . Some of these amines , such as for example morpholine , may also contain other heteroatoms in addition to the nitrogen atom .

[0048] In an advantageously preferred embodiment , the amines contained in the amine water have nitrogen atom and number of oxygen atoms comprised from 1 to 3 .

[0049] In a further advantageously preferred embodiment , the amines contained in the amine water are alkanolamines having a nitrogen atom, a total number of carbon atoms comprised from 3 to 9 and a number of oxygen atoms comprised from 1 to 3 .

[0050] The alkanolamines contained in the amine water are advantageously selected from the group formed by monoethanolamine (MEA) , diethanolamine ( DEA) diisopropanolamine ( DIPA) , triethanolamine ( TEA) , N- methyldiethanolamine (MDEA) , 2- ( 2-aminoethoxy ) ethanol and mixtures thereof . Below are reported the structure formulas of the listed amines .

[0051] In a further advantageously preferred embodiment , the alkanolamines present in the amine water to be concentrated are monoethanolamine (MEA) , methyldiethanolamine (MDEA) and triethanolamine ( TEA) , and mixtures thereof , preferably N-methyldiethanolamine (MDEA) .

[0052] In a preferred embodiment the pH of the feed solution (AA) is comprised from 7 to 13 , preferably from 9 to 12 . In a further preferred embodiment, the osmotic pressure of the feed solution (AA) is comprised from 5 to 160 bar, preferably from 14 to 121 bar.

[0053] The drawing solution (DS) of the present invention consists of a solute dissolved in water.

[0054] The solute of the initial drawing solution (DS) can be selected from organic or inorganic compounds, preferably in the solid state at room temperature and pressure .

[0055] Non-limiting examples of solutes consisting of organic compounds in accordance with the present invention are sugars, such as sucrose or glucose, or organic salt compounds deriving from carboxylic acid salts or from amines, such as for example the propionates or the quaternary ammonium salts.

[0056] Non-limiting examples of solutes consisting of inorganic compounds, in accordance with the present invention, are represented by inorganic salts having metal cations belonging to group I, II of the periodic table, such as for example NaCl, NaBr, NaNO3, Na2SO4, KC1, KBr, KNO3, K2SO4, MgCl2, MgBr2, Mg (NO3)2, MgSO4, CaCl2, CaBr2, Ca(NO3)2. If the nitrates (NaNO3, KNO3, Mg(NO3)2, Ca(NO3)2) are used as solutes, the final drawing solutions can be used in agriculture as fertilizers.

[0057] In a preferred embodiment, the drawing solution has an initial solute concentration (ci) such as to produce an initial osmotic pressure value comprised from 20 to 250 bar, preferably from 40 to 160 bar.

[0058] It is known that the solute concentration is directly correlated to the osmotic pressure, measured in bar, by the Van' t Hoff equation (I) , reported below: II = i Rg T c (I) wherein :

[0059] Rg is the universal gas constant: 0.083144 1 bar Kt 1 mol-1;

[0060] T is the temperature of the solution expressed in

[0061] K; c is the concentration of the solute in the solution in mol I-1; i is Van' t Hoff coefficient, which defines the number of molecules and / or ions, present in solution .

[0062] In a particularly preferred embodiment the solute of the initial drawing solution (DS) is an inorganic salt selected from NaCl, KC1, MgC12, CaC12, KNO3 or mixtures thereof containing NaCl .

[0063] In a particularly preferred embodiment, the salt of the initial salt drawing solution (DS) is NaCl.

[0064] A non-limiting example of initial drawing solution (DS) preparation is reported in the experimental part.

[0065] The two solutions AA and DS are subsequently placed in two thermostatted tanks in such a way as to work throughout the process at a stable temperature value comprised from 20-25°C. Said tanks are connected to a cell interposed between them and containing a semi- permeable membrane. Said semi-permeable membrane is selective for the passage of water from one solution to another .

[0066] In a preferred embodiment, the semi-permeable membrane, used in the present invention, is characterized by having a water permeability coefficient comprised from 0.5 to 6 1 nr2tr1bar-1and a sodium chloride permeability coefficient comprised from 0.1 to 2 1 nr2tr1, said coefficients being calculated using sodium chloride, as a solute in the drawing solution, and deionized water, as a feed solution, operating at a temperature comprised from 20-25°C, as reported in A. Tiraferri et al., "A method for the simultaneous determination of transport and structural parameters of forward osmosis membranes", Journal of Membrane Science, 444, 2013, pp. 523-538.

[0067] In a particularly preferred embodiment, the semi- permeable membrane is made of polyamide, polysulfone and / or polyester.

[0068] A non-limiting example in accordance with the present invention consists of a thin-film composite (TFC) membrane composed of a polyamide selective layer, called active layer, and of a polysulfone and / or polyester support layer, characterized by reduced concentration polarization. This composition allows the membrane to be highly water-selective, especially when treating highly contaminated amine waters. These types of membranes are economical and maintain their performance unaltered without being affected by the chemical aggressiveness of the amine water with which they come into contact, operating at temperatures comprised from 20-25°C. Under these operating conditions, the use time of said membrane is around 2-4 years .

[0069] In a further particularly preferred embodiment said membrane has a thickness comprised from 50-300 pm. Before each experiment , the membrane is immersed into distilled water for 15 min, so as to condition it and wash any impurities present on it . Subsequently said membrane is inserted in a cell placed between the AA and DS solution so that the active layer faces the AA, while the support layer faces the DS . Then, the AA and DS solutions are added to the respective tanks , as previously reported . Several experiments were carried out both by using the same feed solution (AA) and varying the value of the osmotic pressure and / or the ratio o f the input flow rates o f DS versus AA and using di f ferent feed solutions .

[0070] During each experiment , the pushing force was the only di f ference in the osmotic pressures on the two sides of the membrane . In fact , by ef fect only of the di f ference in osmotic pressure , which is created between the feeding solution (AA) , consisting of the amine water, and the drawing solution ( DS ) , the water passes from the former to the latter, thus decreasing the volume of the amine water and consequently increasing the concentration (mg / 1 ) of total nitrogen present therein . Alkanolamines and other organic or salt compounds are rej ected by the membrane . During the direct osmosis ( FO) process some solute particles can permeate the membrane thereby decreasing both the pushing force and the solute concentration in the DS and increasing the solute concentration in the AA. However, this reverse flow i s usually negligible compared to the loss of pushing force due to the dilution o f the DS and the concentration o f the AA following water permeation . During the direct osmosis (FO) process the AA solution is progressively concentrated, while the drawing solution (DS) is diluted.

[0071] The diluted drawing solution, which is obtained at the end of the process, called DS' , was analysed by determining the total organic carbon and total nitrogen content, as reported in the experimental part. Said solution DS' generally has a total organic carbon content comprised from 10 to 2500 mg I-1, preferably from 20 to 1500 mg I-1and a total nitrogen content comprised from 5-250 mg I-1, preferably from 10-60 mg I-1, said contents being determined by means of a Shimadzu analyzer TOC V CPH™ equipped with Shimadzu TMN 1™ detectors for total nitrogen and Shimadzu NDIR™ for carbon.

[0072] A non-limiting example of apparatus used to carry out the trial is the FO Sterlitech plant, schematized in Figure 1. Said plant consists of two tanks with a capacity of 7 1 each (5, 6) , one used respectively for the AA being fed, the other for the drawing solution (DS) . The feed tank is kept under magnetic stirring (4) , Velp Scientifica, to ensure the homogeneity of the AA, while the tank for the DS is positioned on a Kern Instruments digital scale (2) , connected to a data acquisition system (1) , to record the distillate flow. In the plant there is a cell (12) , which has the following dimensions: 146 mm long, 94.5 mm wide and 1.5 mm deep. The semi-permeable membrane (11) is placed in the cell and has a total active area of 140 cm2. In the apparatus there are also two pumps (7, 8) , Cole Parmer, with variable speed, used to guarantee the tangential flow rate of 1.8 1 min-1for both the AA and the DS . Two flow meters (9, 10) , ASA, are positioned respectively, to adjust the flow rates of the AA and of the DS. The apparatus is kept at a constant temperature by using a Julabo Corio thermostat CD BC26 ™ capable of keeping the temperature of the water bath (3) at 21 ± 1°C, said temperature being measured by means of a thermometer probe Hanna Instruments HI 985089 ™. Finally, there is also a data acquisition system (1) .

[0073] The apparatus described above has an equi-current configuration .

[0074] It is also possible to work counter-currently obtaining results comparable or sometimes higher than the experiments carried out in equi-current in terms of total recovery of water from the initial AA solution.

[0075] In a preferred embodiment by working with an initial osmotic pressure value of the drawing solution comprised from 40 to 160 bar and a ratio between the inlet flow rates of DS versus AA comprised from 2.2 to 2.6, preferably from 2.3 to 2.5 recoveries of water higher than 30% by volume, preferably higher than 40% with respect to the total volume of the initial amine water are obtained. A dilute drawing solution is thus obtained with chemical-physical characteristics indicative of contamination (i.e., TOC, TN) at least 99.0% lower than those of the amine water being fed.

[0076] Furthermore, by working with these flows, dilute and regenerable final drawing solutions (DS' ) can be obtained by methods known in the art, such as for example reverse osmosis (RO) processes, operating at a maximum hydraulic pressure of 70 bar.

[0077] In Example 1 by working with a ratio of inlet flow rates DS versus AA equal to 2.4, there is a total recovery of water from the AA equal to 44% with respect to the initial volume, while in Example 2, using the same feed solution AA1 of Example 1 and working with a ratio of inlet flow rates DS versus AA equal to 1.5, there is a total recovery of water greater than and equal to 52%. However, the final drawing solution DS' of Example 1 contains less contaminants and a lower amount of chlorides than that of Example 2.

[0078] This allows a reverse osmosis (RO) process to be applied to regenerate the DS' and use it again as a drawing solution, improving process economy and avoiding further waste disposal.

[0079] A further object of the present invention is therefore, a process for concentrating amine water, coming from natural gas purification and / or combustion fume decarbonization processes, comprising a direct osmosis process (FO) , carried out at a temperature comprised from 20-25°C including the steps described above and a reverse osmosis process (RO) to regenerate the final drawing solution (DS' ) , the direct osmosis process (FO) being characterized by an initial osmotic pressure value of the drawing solution (DS) comprised from 40 to 160 bar and a ratio of inlet flow rates DS versus AA comprised from 2.2 and 2.6, preferably from 2.3 to 2.5, advantageously equal to 2.4.

[0080] The chemical-physical characterizations of the samples, respectively, of AA, DS and DS' were carried out with the processes reported in the experimental part.

[0081] The following embodiment examples are provided merely to illustrate the present invention and should not be construed in a sense that would limit the scope of protection defined by the claims.

[0082] Experimental section

[0083] CARBON AND NITROGEN CONTENT ANALYSIS

[0084] Total nitrogen (TN) and total carbon (TC) , the latter in turn distinguished into organic carbon (TOC) and inorganic carbon (IC) , were quantified by means of a Shimadzu analyzer TOC V CRH™ equipped with Shimadzu detectors TMN 1™ for total nitrogen and Shimadzu NDIR™ for carbon. DETERMINATION OF THE CHLORIDES

[0085] The determination of the chlorides, Cl~, was performed by means of ion chromatography, IC, with an instrument Thermo Fisher Scientific Dionex ICS 6000TM, using a Thermo Fisher Scientific Dionex lonpac AG11-HCTM pre-column, a Thermo Fisher Scientific Dionex lonpac AS11-HCTM column and a conductimetric detector. Potassium hydroxide, KOH, was used as the eluent produced by the Thermo Fisher Scientific Dionex EGC IIITM generator . PREPARATION OF THE DRAWING SOLUTIONS

[0086] The following reagents were used for the preparation of the drawing solutions (DS) :

[0087] - Sodium chloride, NaCl, purity > 99.8%, Carlo Erba.

[0088] - Deionized water (DW) from a Millipore Mill! Q™ system, used in all preparations.

[0089] In a 1 L calibrated flask, a NaCl stock solution (3 mol I-1) was prepared by dissolving 175.52 g of NaCl in 1 L of DW. The stock solution obtained was used for the preparation of the drawing solutions , DS . The initial concentration ( ci ) in mol I-1of solute , in each drawing solution, was converted to osmotic pressure , in bar, by the Van' t Hof f equation ( I ) .

[0090] FEED SOLUTION AA

[0091] Feed solutions thereof called AA1 and AA2 , respectively, were used .

[0092] The feed solution AA1 was withdrawn directly from the wastewater of natural gas puri fication processes and pre-treated, using techniques known in the art such as for example filtration, clari fication, oil elimination and degassing to make it homogeneous and reduce the potential causes of membrane damage . The total nitrogen content present in the AA1 solution is 11760 mg I-1, while the total organic carbon content is 50420 mg I-1.

[0093] The feed solution AA2 was withdrawn directly from the decarboni zation wastewater of the post-combustion processes and pre-treated, using techniques known in the art such as for example filtration, clari fication, oil elimination and degassing to make it homogeneous and reduce the potential causes of membrane damage . The total nitrogen content present in the AA2 solution is 50500 mg I-1, while the total organic carbon content is 216420 mg I-1.

[0094] EXAMPLE 1 :

[0095] Example 1 was carried out at a temperature of 21 ° C , using as feed solution AA1 and a DS with an initial osmotic pressure equal to 80 bar .

[0096] The ratio of inlet flow rates DS vs . AA is 2 . 4 .

[0097] By operating under the conditions reported above , an average permeate flow of 3 . 5 1 m-2h-1was obtained, with a total water recovery of 44% (amine solution concentration factor of 1.79 and solution volume decrease of 44%) .

[0098] Table 1 reports the final percentage retention observed (R %) , referred to TOC and TN, and the concentration of chlorides (Cl-) in the final drawing solution (DS' ) , said retention being calculated with the following equation (IT)

[0099] RG% — ( 1_C G, final DS / C G, initial AA) *100 (IT) where G refers to the values obtained respectively from TOC or TN expressed in mg I-1.

[0100] Table 1

[0101] EXAMPLE 2 :

[0102] This experiment was carried out at a temperature of 21 °C using as feed solution AA1 and a DS having an initial osmotic pressure equal to 140 bar and a ratio of inlet flow rates of DS vs. AA equal to 1.4.

[0103] By operating under these conditions, an average permeate flow of 3.8 1 m-2h-1was obtained, with a total water recovery of 52% (amino solution concentration factor of 2.08 and solution volume decrease of 52%) . With a 9% higher flow and 18% higher recovery compared to Example 1, using a 75% greater initial osmotic pressure, lower retentions are obtained, as well as a very high chloride concentration in the final DS (DS' ) and hardly manageable as a feed to an RO as indicated in Table 2.

[0104] Table 2

[0105] EXAMPLE 3:

[0106] This experiment was carried out at a temperature of 21 °C using as feed solution AA2 and a DS having an initial osmotic pressure equal to 219 bar and a ratio of inlet flow rates of DS vs. AA equal to 2.4.

[0107] By operating under these conditions, an average permeate flow of 2.9 1 m-2h-1was obtained, with a total water recovery of 20% (amino solution concentration factor of 1.25 and solution volume decrease of 23%) .

[0108] Table 3 reports the final percentage retention observed (R %) , referred to TOC and TN, and the concentration of chlorides (Cl-) in the final DS (DS' ) Table 3.

[0109] Table 3

Claims

CLAIMS1. Process for concentrating amine water, coming from natural gas purification and / or combustion fumes decarbonization processes, including a direct osmosis process, carried out at a temperature comprised from 20-25°C, which includes the following steps :(a) contacting a feed solution (AA) , consisting of amine water, comprising nitrogenous organic compounds, and an initial drawing solution (DS) , comprising a solute dissolved in water, through a cell, interposed between the two solutions and containing a semi-permeable membrane, said membrane being selective to the passage of water;(b) diluting the initial drawing solution (DS) by a spontaneous flow of water passing through the semi-permeable membrane from the feed solution (AA) to the drawing solution (DS) , obtaining a final drawing solution (DS' ) having a solute concentration lower than the initial drawing solution (DS ) .

2. Process according to claim 1, wherein the amine water has a total nitrogen content comprised from 3,000 to 90,000 mg / 1, preferably from 8,000 to 70,000 mg / 1, said content being determined by meansof a Shimadzu analyzer TOC V CPH™ equipped with Shimadzu TMN 1™ detectors for total nitrogen .3 . Process according to any one of claims 1 to 2 , wherein the nitrogenous organic compounds contained in the amine water comprise amines having a total number of carbon atoms comprised from 1 to 12 .4 . Process according to claim 3 , wherein the amines have a nitrogen atom and a number of oxygen atoms comprised from 1 to 3 .5 . Process according to claim 4 , wherein the amines are alkanolamines having a nitrogen atom, a total number of carbon atoms comprised from 3 to 9 and a number of oxygen atoms comprised from 1 to 3 .6 . Process according to claim 5 , wherein the alkanolamines are selected from the group formed by monoethanolamine (MEA) , diethanolamine ( DEA) , diisopropanoloamine ( DIPA) , triethanolamine ( TEA) , N-methyldiethanolamine (MDEA) , 2- ( 2- aminoethoxy) ethanol and mixtures thereof .7 . Process according to claim 6 , wherein the alkanolamines are monoethanolamine (MEA) , methyldiethanolamine (MDEA) and triethanolamine ( TEA) and mixtures thereof , preferably N- monoethanolamine (MDEA) .8 . Process according to any one of claims 1 to 7 , wherein the pH of the feed solution (AA) is comprised from 7 to 13 , preferably from 9 to 12 .9 . Process according to any one of claims 1 to 8 , wherein the osmotic pressure of the feed solution(AA) is comprised from 5 to 160 bar, preferably from 14 to 121 bar.

10. Process according to any one of claims 1 to 9, wherein the solute of the initial drawing solution (DS) is selected from organic or inorganic compounds .

11. Process according to claim 10, wherein the solute is an inorganic compound selected from NaCl, KC1, MgC12, CaC12, KNO3 or mixtures thereof containing NaCl .

12. Process according to any one of claims 1 to 11, wherein the drawing solution (DS) has an initial osmotic pressure value comprised from 20 to 250 bar, preferably from 40 to 160 bar.

13. Process according to any one of claims 1 to 12, wherein the semi-permeable membrane has a water permeability coefficient comprised from 0.5 to 6 1 nr2hr1bar-1and a sodium chloride permeability coefficient comprised from 0.1 to 2 1 1m2hr1, said coefficient being calculated using said membrane in a direct osmosis process having sodium chloride as solute in the drawing solution (DS) and deionized water as feed solution (AA) , operating at a temperature comprised from 20-25°C.

14. Process according to any one of claims 1 to 13, wherein the semi-permeable membrane is made of polyamide, polysulfone and / or polyester.

15. Process according to claim 14, wherein the semi- permeable membrane has a thickness comprised from 50-300 pm .

16. Process for concentrating amine water, coming from natural gas purification and / or combustion fume decarbonization processes, comprising a direct osmosis process, carried out at a temperature comprised from 20-25°C, according to the previous claims from 1 to 15, and a reverse osmosis process to regenerate the final drawing solution (DS' ) , the direct osmosis process being characterized by an initial osmotic pressure value of the drawing solution (DS) comprised from 40 to 160 bar and a ratio of inlet flow rates DS versus AA comprised from 2.2 and 2.6, preferably from 2.3 to 2.5, advantageously equal to 2.4.

Images