OA20946A - Process for concentrating amine water. - Google Patents

Abstract

The present invention relates to a process for concentrating amine water by dehydrating it through membrane distillation at a temperature ranging from 30°C to 95°C and at a pressure ranging from 1.0 bar to 1.5 absolute bar.

Description

PROCESS FOR CONCENTRATING AMINE WATER

CROSS-REFERENCE TO RELATEE» APPLICATIONS

This Patent Application daims priority from Italian Patent Application No. 102019000009207 filed on June 17, 2019, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The présent invention is part of the treatment of wastewater produced by natural gas treatment plants and in particular produced by naturai gas washing plants.

The présent invention relates to a process for concentrating wastewater derîving from the partial or total replacement of aqueous solutions of Chemical compounds containing nitrogen used for the treatment of natural gas which in this text are also indicated with tire term amine water.

In the présent patent application, ail the operatîng conditions reported in the text must be understood as preferred conditions even if not expressly dedared.

For the purposes of the présent discussion the term to comprise or to include also comprises the term to consist in or essentially consisting of'.

For the purposes of the présent discussion the définitions of the ranges always comprise the extreme values unless otherwise specified.

For the purposes of the présent patent application polymer refers to a macromolecule consisting of several groups of atoms, répétitive units, the same or different (in the copolymers), joined in a chain by repeating the same type of bond.

BACKGROUND ART

The réduction of the hydrogen sulphide content in the raw natural gas is usually carried oui by washing with aqueous solutions of tertiary alkanolamines (typically MDEA, Nmethyldiethanolamîne), inducing the formation of the respective salts. The latter are subsequently thermally decomposed ailowing the recycling of the washing solutions and at the same time the release of gaseous hydrogen sulphide. The partial or total periodic replacement of aqueous solutions of tertiary alkanolamines is necessary due to their progressive détérioration foilowing the washing and régénération cycles (R. Wagner, Gas Sweetening Fundamentals, Laurance Reid Gas Conditiong Conférence, 26 February - 01 Mardi 2006, Norman, Oklahoma). The wastewater obtained, amine water, has a pH greater than 9.0 and high contents of organic and înorganic Chemical compounds.

Amine water is usuaily sent to pyrolysis or disposai (C.V. Simmons, Reclaiming Used Amine and Glycol Solutions, 04 March - 06 Match 1991, Norman, Oklahoma). This entails high costs especîally if it is necessary the transportation thereof, for example, by tankers.

The sending of amine water to a biodégradation process is not possible due to îts high toxicity (1. Eide Augmo et al., Environmental Impact of Amines, Energy Procedia 1 (2009) 1297- 1304).

One way to reduce transportation and disposai costs is to concentrate amine water.

Traditionally, the concentration by distillation of amine water requîtes operating conditions such as high températures, the vacuum and the use of equipment made of spécial materials capable of withstanding its Chemical aggressiveness.

EP 0918049 describes a process for purifying aqueous solutions containing alkanolamines by distillation carried out in film evaporators. The process takes place in two stages: déhydration is carried out in the first stage while purification is performed in the second stage.

The treated solutions contain from 10% to 90% weight of water, up to 20% weight of contaminants and dégradation products, the remaining part being alkanolamines and possibly a cosolvent. In the first stage it îs operated at températures in the range 130 - 180°C and pressures in the range 0.4 - 0.9 bar.

In the second stage it is operated at températures in the range 120 - 200°C and pressures in the range 0.02 - 0.1 bar.

The concentration of amine water by nanofiitration (NF) or reverse osmosis (RO) requires the application of high hydraulic pressures, typîcally in the range 5-150 bar and îs subject to phenomena of irréversible fouling of the membranes (fouling, scaîing). For this reason, said Systems are proposed downstream of pretreatment processes (S.S. Madaeni, The Application of Membrane Technology for Water Disinfection, Water Research 33 (2) (1999) 301 - 308; L.F. Greenlee et al., Reverse Osmosis Desalination: Water Sources, Technology, and Today’s Challenges, Water Research 43 (2009) 2317-2348).

US 9,028,654 describes a process and a System for the treatment of a wastewater containing amines or the dérivatives thereof and water. The process provides for the wastewater to be subjected to évaporation, by means of at least two heat exchangers and one RO. From this process, water with a purity greater than 95% by weight based on the weight of the distillate obtained after évaporation is obtained.

The application of Systems based on membrane distillation (MD) and pervaporation (PV) hâve been proposed for the concentration of wastewater with a complexity comparable to that of amine water. Both provide for the heatîng of the feed in liquid phase, the perméation of the distîllate in vapour phase through a membrane (in both Systems it is not necessary to reach the boiling température of the feed) and the condensation of the latter to give a distîllate in liquid phase with a composition other than that of the feed. The distîllate is enriched by low boiling Chemical compounds while the concentrate is enriched by high boiling Chemical compounds. The flow of vapour from the feed sector to that of the distîllate can be promoted by keepîng the distîllate sector under vacuum (vacuum membrane distillation, VMD), in carrier gas flow (sweep gas membrane distillation, SGMD) or by condensing the vapour at a sufficiently low température by heat exchange with a cold fluid (aîr gap membrane distillation, AGMD; direct contact membrane distillation DCMD). The fundamental différence between MD and PV is in the rôle played by the membrane in the séparation. MD is based on porous hydrophobie membranes which only act as a support for the liquid - vapour interface. The presence of surfactants (for example amines and the salts thereof) in the feed reduces the effectiveness of the MD by promoting the passage of the feed in liquid phase as such in the distîllate sector (L.M. Camacho et al., Advances in Membrane Distillation for Water Desalination and Purification Applications, Water 5 (2013) 94 — 196). PV is based on dense membranes with high Chemical selectivity towards some feed components (Q. Wang et al., Desalination by Pervaporation: a Review, Desalination 387 (2016) 46-60).

US 9,039,900 describes an MD based on polymeric membranes containing carbon nano tubes. Carbon nanotubes improve permeability, selectivity and mass transport. The examples describe the déhydration of mixtures containing active ingrédients of drugs (ibuprofen, acetaminophenol, diphenhydramîne, dibucaine) that are solid or high boiling in water obtaining enrichments greater than 94% operating at températures in the range 80 90°C and applying the vacuum in the distîllate sector.

US 2011/0180479 describes a process for treating waters which comprises a first séparation stage to form a concentrate containing less than 7% by weight of dîssolved solid and a second MD stage based on a system containing a bundle of hollow fibers. By introducing an RO stage, it is possible to reduce wastewater to zéro discharge. The treatment also allows to recover water with a quality suitable for reuse or discharge into the environment.

US 7,837,877 describes a membrane system for the séparation of fluid mixtures. The membrane is used in the form of a porous septum and interposed between the two compartnients of a module between which a pressure différence is maintained. The system allows the séparation of the initial mixture in a permeate in liquid phase and a distîllate in gas phase, each of which has a composition different from the other one and from the feed. The ex amples describe the séparation of mixtures of water, carbon dioxide, hydro gen, C3 hydrocarbons, C3- alcohols. The effectiveness in lhe Ireatment of amine water is not exemplified.

US 5,171,449 describes a process for treating amine water by PV. The process is based on composite membranes made up of a dense polyvinyl alcohol layer deposited on a porous alumina support. The porous alumina support is necessary to ensure the résistance to the Chemical aggression of the amine. The examples describe the déhydration of mixtures 74 78% by weight of amine, the remaining part being water, operating at a température of 70°C and applying the vacuum in the distillate sector. Selectivity of the water in the distillate of 57 - 60% and distillate flow of 3.1 - 1.6 kg/(m²*h) are obtained. The membrane is stable for 22 days.

US 5,334,314 describes a process for dehydrating aqueous solutions containing amines by PV, in which the solution is put in contact with a membrane, on a first side, keepîng the Chemical potential of the water on the opposite side that is lower than that on the first side. The membrane used has a cross-linked polyvinyl alcohol layer characterized in that said layer has undergone treatment with acids.

The déhydration of a mixture containing 70% by weight of ethylamine is exemplified, the remaining part being water, operating at a température of 85°C a distillate flow of 0.750 kg/m²*h is obtained. The examples describe the déhydration of a mixture containing 40% by weight of pyridine, 60% by weight of water operating at 95°C; then they describe the déhydration of a mixture containing 70% by weight of dimethylamine, the remaining part being water, operating at 100°C; the membrane stabîlity at températures close to 10û°C and high amine concentrations. In ail the examples cited, it is presumed that the vacuum is applied in the distillate sector.

US 5,051,188 describes a process for treating amine water by PV, for example using a water-selective membrane. The patent describes the use of membranes which hâve an active layer based on polyvinyl alcohol or the dérivatives thereof.

The patent describes in particular the déhydration of a mixture containing 45% by weight of me thy lamine (as such or as carbamate), 28% by weight of carbon dioxide, the remaining part being water. It is operated at a température of 80°C applying the vacuum in the distillate sector and obtaining a distillate flow of 0,500 kg/m²*h.

US 4,311,594 describes a process for treating waters containing neutral organic compounds C4+ by means of PV. Non-porous hydrophobie polymeric membranes are used. The latter may consist of polyolefins and their copolyniers, polyolefins containing fluorine and their copolymers, polysiloxanes, or polyuréthanes. It is operated at températures in the range 20 C - 70°C, applying the vacuum in the distillate sector.

US 3,750,735 describes a process for treating waters containing formaldéhyde using organic polymeric membranes characterized by the presence of anionic groups derived from strong acids, for example polymers of acrylonitrîle and styrene sulfonate whose porosity is not specified. It is operated at températures in the range 25°C - 70°C, applying the vacuum in the distillate sector.

Amine water is toxic and caustic. It is traditîonally sent for pyrolysis or disposai. This entails high costs especially if the transportation thereof is necessary.

One of the ways to reduce the transportation and disposai costs of amine water is to concentrate it by déhydration.

DISCLOSURE OF INVENTION

Therefore, the subject of the présent patent application is a process for concentrating the amine water by dehydrating it through membrane distillation (MD) conducted by maintaining the pressure between 1 bar and 1.5 absolute bar, defmable as atmospheric pressure, and the température in the range 30 - 95°C, preferably 40 - 90°C, more preferably at 70°C.

The amine water treated according to the described and claimed process can preferably be an amine water which comprises water and Chemical compounds containing nitrogen, characterized in that the concentration of total nitrogen varies in the range of between 10000 mg/L and 100000 mg/L. Said amine water can preferably further comprise sulfur sulfïde whose concentration of sulfur sulphîde ranges from 1000 mg/L to 10000 mg/L. Said amine water can preferably hâve a Chemical oxygen demand which ranges from 100000 mg/L to 1000000 mg/L. Said amine water can preferably hâve an electrical conductivîty that ranges from 500 pS/cm to 150000 pS/cm. Said amine water, moreover, can preferably hâve a boron content with a concentration which ranges from 10 mg/L to 1000 mg/L.

Advantageously, the process described and claimed allows to operate under milder conditions than those described in the prior art (lower températures, pressure 1-1.5 absolute bai’ instead of vacuum) through MD. The Systems involved do not require spécial materials capable of withstanding the Chemical aggressiveness of the amine water.

In this way it is possible to reduce the quantity of wastewater to be sent for pyrolysis or disposai and to recover water with a quality suitable for reuse or discharge into the environment.

The teachings traceable in the State of the art underline the critical issues related to the presence in the feed of Chemical compounds capable of acting as surfactants.

The latter are capable of modifying the surface properties of the membranes used in MD, in particular of reducing their hydrophobicity, an essential prerequisite to ensure the passage of the distillate in vapour phase (enriched by water) but not of the feed in liquid phase through the membranes themselves (L.M. Camacho et al., Advances in Membrane Distillation for Water Desalination and Purification Applications, Water 5 (2013) 94 - 196).

Advantageously, the obtainable distillate has chemical-physical characteristics which indicate contamination at least 99% lower than the feed, for example, electrical conductivity, the Chemical oxygen demand, the respective contents of different heteroelements.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aims and advantages of the présent invention will appear more clearly from the following description and from the accompanying figures, given purely by way of a nonlimiting example, which represent preferred embodiments of the présent invention.

Figure 1 schematically illustrâtes a module for the concentration of amine water according to the process described and claimed in the présent patent application.

In the Figure the feed (1), i.e. the amine water, is heated (2), for example in a heat exchanger, before being fed to the MD membrane distillation unit in a first sector at atmospheric pressure, for example between 1 bar and 1.5 absolute bar (3). From here the distillate in vapour phase permeates through a polymeric membrane (10), leaving the concentrate (7) in the first sector. On the opposite side with respect to the first atmospheric pressure sector there is a second atmospheric pressure sector (4) in which carrier gas (5) flows which drags the distillate in vapour phase becoming saturated. Said saturated gaseous stream of distillate in vapour phase is cooled (6), for example in a heat exchanger, forming a distillate in liquid phase (8) and a gaseous stream containing the carrier gas and any noncondensable (9).

Figure 2 is similar to Figure 1 where however the carrier gas (5) is static.

BEST MODE FOR CARRYING OUT THE INVENTION

The Applicant now describes in detail the process for concentrating amine water subject of the présent patent application, also referring to Figure 1.

The amine water is concentrated by dehydrating it through membrane distillation (MD) conducted by maîntaining the pressure between 1 bar and 1.5 absolute bar, definable as atmospheric pressure, and the température in the range 30 - 95°C.

The amine water can preferably be an amine water which comprises water and Chemical compounds containing nitrogen, characterized in that the concentration of total nitrogen varies in the range of between 10000 mg/L and 100000 mg/L.

Preferably the concentration of total nitrogen in the amine water can vary in the range between 20000 mg/L and 100000 mg/L, more preferably in the range between 30000 mg/L and 100000 mg/L, still more preferably it is equal to 66000 mg/L.

Preferably the process described and claimed in the présent patent application allows to concentrate amine water in which the nitrogen-containing Chemical compounds are the amines, more preferably an alkanolamine, stîll more preferably N-methyldiethano lamine.

The amine water (1) is heated to températures in the range from 30°C to 95 ° C, preferably 5 from 40°C to 90°C, more preferably to 70°C.

For this purpose, heat exchangers external to the MD System or internai to the same System can be used, for example selected from coils, plates, or tube bundle exchangers.

Once heated, the amine water is fed to one or more MD units, each comprising one or more sectors maintaîned at a pressure that varies in the range 1-1.5 absolute bar, definable as 10 atmospheric pressure (3), adjacent to a polymeric membrane (10), which in turn is adjacent to one or more sectors (4) maintaîned at a pressure that varies in the range 1-1.5 absolute bar (atmospheric pressure).

A carrier gas (5) can be fed to said MD unit in a dedicated sector maintaîned at a pressure which varies in the range 1-1.5 absolute bar (atmospheric pressure), distinct from that in 15 which the amine water is fed.

The carrier gas can be fed at an initial température which preferably varies in the range of between 10°C and 95°C.

The carrier gas can be selected from nitrogen, oxygen, carbon dioxide, methane, or mixtures thereof.

The polymeric membranes used for the purposes of the présent patent application are hydrophobie and porous. The tenu hydrophobie membrane refers to membranes characterized by a contact angle wîth water greater than or equal to 70°, preferably in the range between 70° and 180°, more preferably in the range between 100° and 150°. The term porous membranes means membranes characterized by pores with a nominal diameter that 25 varies in the range between 0.1 and 5.0 gm.

Said hydrophobie and porous polymeric membranes allow to obtain a vapour saturated carrier gas (distilled in vapour phase, enriched by water) and a concentrate (7). Amine water can preferably circulate wîth a linear speed in the range 0.3 - 3.0 m/s. The carrier gas can preferably circulate with a linear speed in the range 0.0 - 7.0 m/s, preferably between 0.1 30 7.0 m/s.

As previously said, a MD unit comprises one or more sectors maintaîned at a pressure which varies in the range 1-1.5 absolute bar (atmospheric pressure) adjacent to a polymeric membrane, said membrane being in turn adjacent to one or more sectors maintaîned at pressure varying in the range 1-1.5 absolute bar.

The sectors can be in the press filter type configuration, in the case of membranes in the form of sheets, or in the tube bundle type exchanger configuration, in the case of membranes in the form of hollow fibres.

The carrier gas saturated with vapour distillate is cooled b y heat exchange (6) with a fluid which îs at an initial température which varies in the range from 0°C to 25°C (9) so as to obtain a distillate in liquid phase (8).

For this purpose, heat exchangers external to the MD system or internai to the same system can be used, for example selected from coils, plates, or tube bundle exchangers.

The saturated gas of vapour distillate can also be cooled by direct contact with a fluid at an initial température which varies in the range 0 - 25°C. Said fluid can be selected from water, nitrogen, oxygen, carbon dioxide, pure ormixed methane.

The distillate in liquid phase, enriched by water, can be sent to subséquent treatments until reaching a quality suitable for reuse or discharge into the environment.

Said treatments can include a further membrane distillation operation.

Furthermore, the process described and claimed can comprise a stage in which the concentrate (7) (enriched by the high-boiling Chemical compounds including methyldietylamine (MDEA) is sent to pyrolysïs or disposai.

Furthermore, the gas enriched by non-condensable (9) can be sent to subséquent treatments until reaching a quality suitable for reuse or discharge into the environment.

The technical solution object of the present patent application allows the concentration by déhydration of the amine water under milder conditions than those described in the prior art, lower températures and atinospheric pressure instead of the vacuum, through MD.

Faillite to use the vacuum unexpectedly allows to maximize its effectiveness.

In the present patent application, hydrophobie and porous membranes comprising inorganic or organic polymers and copolymers or combinations thereof, preferably organic polymers and copolymers or combinations thereof, more preferably organic polymers containing halogens and their copolymers, or combinations thereof, can be used; or organic polymers not containing halogens and their copolymers or combinations thereof can be used. still more preferably the hydrophobie and porous membranes can be organic polymers containing fluorine and their copolymers, or combinations thereof; or organic polymers not containing fluorine and their copolymers, or combinations thereof. still more preferably said membranes can be selected from oxides, sulphides, zeolîtes, metal-organic materîals, such as for example metal-organic frameworks; carbonaceous materîals, such as for example graphene; polysilanes and their copolymers; polysiloxanes and their copolymers; polysulfones and their copolymers; polyacrylates and their copolymers; polycarbonates and their copolymers;

proteins, polyamides and their copolymers; polyuréthanes and their copolymers; polyketones and their copolymers; polyesters and their copolymers; polysaccharides, polyelhers and their copolymers; polyaromatics and their copolymers; polyolefms and their copolymers; or combinations thereof, Polyolefms containing fluorine, polyolefms not containing fluorine, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, or combinations thereof are preferred; among them the most preferred is polypropylene.

The Chemical compounds listed above can be used in the préparation of the membranes as single Chemical compounds or the combinations thereof, that is, as mixtures of the same or as successive layers of the same.

Polyolefms not containing fluorine are less expensive and less problematic from an environmental point of view (both during production and disposai) than those containing fluorine used in similar processes (E. Corsini et al,, Perfluorinatcd Compounds Emerging Persistent Organic Pollutants with Potential Immunotoxicity, Toxicology Letters 230 (2) 2014 263 -270),

The membranes used maintain their performance unaltered for at least 300 hours of service without being affected by the Chemical aggressiveness of the amine water.

Preferably the process described and claimed in the présent patent application allows to concentrate amine water which further comprises sulfur sulfide whose concentration varies in the range between 1000 mg/L and 10000 mg/L, preferably in the range between 2000 mg/L and 10000 mg/L, more preferably in the range between 3000 mg/L and 10000 mg/L, stili more preferably equal to 3950 mg/L.

Preferably, the process described and claimed in the présent patent application allows to concentrate amine water further characterized by a Chemical oxygen demand which varies in the range between 100000 mg/L and 1000000 mg/L, more preferably between 200000 mg/L and 1000000 mg/L, still more preferably between 300000 mg/L and 1000000 mg/L, still more preferably equal to 711000 mg/L.

Preferably, the process described and claimed in the présent patent application allows to concentrate amine water further characterized by an electrical conductivity which varies in the range between 500 pS/cm and 150000 pS/cm, more preferably that varies in the range between 5000 pS/cm and 150000 pS/cm, still more preferably between 10000 pS/cm and 150000 pS/cm, still more preferably it is 10180 pS/cm.

Preferably the process described and claimed in the présent patent application allows to concentrate amine water which further comprises a boron concentration which varies in the range between 10 mg/L and 1000 mg/L, preferably in the range between 50 mg/L and 1000 mg/L, more preferably in the range between 100 mg/L and 1000 mg/L, more preferably equal to 358 mg/L.

In a preferred form, the process described and claimed in the présent patent application allows to concentrate amine water comprising nitrogen-containing Chemical compounds, characterized in that the concentration of total nitrogen can vary in the range between 10000 mg/L and 100000 mg/L, preferably between 20000 mg/L and 100000 mg/L, more preferably between 30000 mg/L and 100000 mg/L; further comprising sulfur sulfide whose concentration varies in the range between 1000 mg/L and 10000 mg/L, preferably in the range between 2000 mg/L and 10000 mg/L, more preferably in the range between 3000 mg/L and 10000 mg/L.

In a preferred form, the process described and claimed in the présent patent application allows to concentrate amine water comprising nitrogen-containing Chemical compounds, characterized in that the concentration of total nitrogen can vary in the range between 10000 mg/L and 100000 mg/L, preferably between 20000 mg/L and 100000 mg/L, more preferably between 30000 mg/L and 100000 mg/L; further comprising sulfur sulfide whose concentration varies in the range between 1000 mg/L and 10000 mg/L, preferably in the range between 2000 mg/L and 10000 mg/L, more preferably in the range between 3000 mg/L and 10000 mg/L; said amine water also having a Chemical oxygen demand which varies in the range between 100000 mg/L and 1000000 mg/L, more preferably between 200000 mg/L and 1000000 mg/L, still more preferably between 300000 mg/L and 1000000.

In a preferred form, the process described and claimed in the présent patent application allows to concentrate amine water comprising nitrogen-containing Chemical compounds, characterized in that the concentration of total nitrogen can vary in the range between 10000 mg/L and 100000 mg/L, preferably between 20000 mg/L and 100000 mg/L, more preferably between 30000 mg/L and 100000 mg/L; further comprising sulfur sulfide whose concentration varies in the range between 1000 mg/L and 10000 mg/L, preferably in the range between 2000 mg/L and 10000 mg/L, more preferably in the range between 3000 mg/L and 10000 mg/L; said amine water also having a Chemical oxygen demand that varies in the range between 100000 mg/L and 1000000 mg/L, more preferably between 200000 mg/L and 1000000 mg/L, still more preferably between 300000 mg/L and 1000000; said amine water also having electrical conductivity which varies in the range between 500 pS/cm and 150000 pS/cm, more preferably which varies in the range between 5000 pS/cm and 150000 pS/cm, still more preferably between 10000 pS/cm and 150000 pS/cm.

In a preferred form, the process described and claimed in the présent patent application allows to concentrate amine water comprising nitrogen-containing Chemical compounds, characterized in that the concentration of total nitrogen can vary in the range between 10000

I ] mg/L and 100000 mg/L, preferably between 20000 mg/L and 100000 mg/L, more preferably between 30000 mg/L and lOüOOü mg/L; further comprising sulfur sulfide whose concentration varies in the range between 10Ü0 mg/L and 10000 mg/L, preferably in the range between 2000 mg/L and 10000 mg/L, more preferably in the range between 300Ü mg/L and 10000 mg/L; said amine water also characterized by a Chemical oxygen demand which varies in the range between 100000 mg/L and 1000000 mg/L, more preferably between 200000 mg/L and 1000000 mg/L, still more preferably between 300000 mg/L and 100000Û; said amine water also characterized by an electrical conductivîty that varies in the range between 500 pS/cm and 150000 pS/cm, more preferably that varies in the range between 5000 pS/cm and 150000 pS/cm, still more preferably between 10000 pS/cm and 150000 pS/cm; said amine water which further comprises a boron concentration which varies in the range between 10 mg/L and 1000 mg/L, preferably in the range between 50 mg/L and 1000 mg/L, more preferably in the range between 100 mg/L and 1000 mg/L.

In ail the preferred forms accordîng to the présent patent application, the nitrogen concentration, the sulfur sulfide, the Chemical oxygen demand, the electrical conductivîty and the boron concentration can vary in the preferred ranges previously listed.

The data shown in the examples show that the quality of the distillaie in liquid phase obtainable through MD conducted by applying vacuum in the distiilate sector is lower than that obtainable through MD conducted by maintaining the distiilate sector at atmospheric pressure.

The MD conducted by maintaining the distiilate sector at atmospheric pressure is therefore the most effective system for concentrating amine water.

Some application examples of the présent invention are now described, which hâve a purely descriptive and non-limîting purpose and which represent preferred embodiments.

EXAMPLES

The MD tests were carried out by means of a system equipped with a tubular module made of AISI 316 L stainless Steel with an internai diameter of 25 mm and a length of 300 mm. A beam of polypropylene capillary membranes AccurelS S 6/2™ membrane, with an internai diameter of 1.8 mm, was housed inside the module; wall thickness of 0.45 mm; total area of 131 cm²; pore diameter of 0.2 pm; contact angle with water of 120° measured with a Biolin Scientific Attension T200™ angle meter.

It was operated by completely recycling the distiilate and the concentrate to the 2L feed tank. The latter was placed on a DLab MS-H280-Pro™ stining-heating magnetic plate with integrated température probe to maintain the system température at the value defîned for each test.

The feed was sent to the module by means of a Plastomec P051^1M polypropylene magnetic drive pump in order to hâve a linear speed tangential to the external surface of the capillary membranes of 2.6 m/s. The System has been prepared so that the lumen of each capillary membrane can be maintained in the flow of carrier gas or altematively under vacuum.

The distillate in vapour phase was condensed by means of a straight barre 1 liebig glass réfrigérant maintained at 0°C by means of a Lauda RC6™ thermo-cryostat with external circulation of the mixture of water and Petronas ParafluBlu™ 1/1 v./v. The distillate in liquid phase was collected in a glass flask connected to the réfrigérant. Amine water containing MDEA having the foilowing chemical-physîcal characteristics was used as a feed:

• pH of 12.7 measured by the Eutech PH510™ instrument with Hanna HI1230™ probe;

• electrical conductivity (EC) of 10180 pS/cm measured by the Hanna EC215™ instrument with Hanna HI76303™ probe;

• Chemical oxygen demand (COD) of 711000 mg/L;

• total nitrogen content (N) of 66000 mg/L;

• sulfur sulfide content (S) of 3950 mg/L;

• boron content (B) of 358 mg/L.

The measurements of COD, N, S, B, respectively, were carried out with a test tube kit using the Merck Spectroquant Pharo 300™ ultraviolet - visible spectrophotometer equipped with the Merck Spectroquant TR320™ reactor.

Boron was introduced as boric acid (Sigma Aldrich ACS - grade™, purity greater than 99.5% weight) as a tracer. Measurements of the distillate flow rate were carried out in liquid phase every 15 min from which it was possible to trace the flow and 50 mL samples of the same to measure its chemical-physical properties, in this text also generically indîcated with the term G .

The respective retentions R hâve been calculated from the chemical-physical characteristics of the feed and the distillate according to the équation:

R(G) % = [(G) Feed - (G) Distillate] * 100 / (G) Feed.

EXAMPLE 1: Test at 50°C (distillate sector at atmospheric pressure).

The lumen of each capillary membrane was maintained in the carrier air flow (Air Liquide Alphagaz 1™, purity greater than 99.999%) in order to hâve a linear speed of 4 m/s. An average distillate flow of 0.75 L/m²*h was obtained. Table 1 shows the pH of the distillate and the retentions referring to the Chemical - physical characteristics that indicate contamination after different service times (N.D. if not determined). The data shown show the membrane stabilily for at least 300 h of service.

Table L

t	pH	R(EC)	R(COD)	R(N)	R(S)	R(B)
[h]	H	[%]	[%]	[%]	[%]	[%]
50	8.5	99.48	99.97	99.97	N.D.	99.98
150	8.7	99.45	99.96	99.97	99.88	99.97
300	9.4	99.55	99.95	99.96	99.95	99.98

EXAMPLE 2: Test at 70 °C (distillate sector at atmospheric pressure).

The MD test described in Example 1 was repeated by operating at 70°C.

An average distillate flow of 2.20 L/m²*h was obtained. Table 2 shows the pH of the distillate and the retentions referring to the Chemical - physical characteristics that îndicate contamination after different service times. The data shown show the membrane stability for at least 300 h of service.

Table 2.

t	pH	R(EC)	R(COD)	R(N)	R(S)	R(B)
[h]	H	l%]	[%]	[%]	[%]	[%]
100	8.5	99.50	99.90	99.96	99.90	99.95
300	9.4	99.60	99.93	99.96	99.95	99.95

COMPARATIVE EXAMPLE 1: Test at 50°C (distillate sector under vacuum).

The lumen of each capillary membrane was maintaîned under a 20-mbar vacuum by connecting a water jet pump to a slot on the line downstream of the condenser. An average distillate flow of 5.0 L/m²*h was obtained. Table 3 shows the pH of the distillate and the retentions referring to the Chemical - physical characteristics that indicate contamination (N.D. if not determined). The data reported show that the MD conducted by maintaining the distillate sector at atmospheric pressure is the most effective system for concentrating amine water, allowing greater retentions referring to the chemical-physical characteristics indicating contamination and therefore the production of best quality water.

This cannot be deduced from the teachings found in the State of the art.

Table 3.

(	pH	R(EC)	R(COD)	R(N)	R(S)	R(B)
[h]	[-]	[%]	[%]	[%]	[%]	[%]
50	8.3	95.60	96.10	96.11	N.D.	96.13
200	8.3	95.50	95.80	96.01	96.00	96.10

Claims (19)

1. ] .Process for concentratîng amine water. said amine water being wastewater deriving from the partial or total replacement of aqueous solutions of Chemical compounds containing nitrogen used for the treatment of natural gas and comprising water and nitrogen-containing Chemical compounds and having a concentration of total nitrogen ranging between 10000 mg/L and 100000 mg/L, by dehydrating said amine water through membrane distillation at a température ranging from 30°C to 95°C and at a pressure ranging from 1 bar to 1.5 absolute bar; wherein the amine water is heated and fed to a membrane distillation unit in a first sector at atmospheric pressure, adjacent to a polymeric membrane, said membrane being in turn adjacent to a second sector at atmospheric pressure; both sectors being maintained at atmospheric pressure between 1 and 1.5 absolute bar; and wherein a distillate in vapour phase permeates through the polymeric membrane, leaving a concentrate in the first sector; and wherein in the second atmospheric pressure sector a carrier gas flows which drags the distillate in vapour phase becoming saturated.
2. 2 .Process according to claim 1 wherein the température varies from 40°C to 90°C.
3. 3 .Process according to claim 1 or 2 wherein the nitrogen-containing Chemical compounds are amines.
4. 4 .Process according to claim 3 wherein the amine is an alkanolamine.
5. 5 .Process according to claim 4 wherein the alkanolamine is N-methyldiethanolamine.
6. 6 .Process according to any one of the daims from 1 to 5 wherein the concentration of total nitrogen ranges from 20000 mg/L to 100000 mg/L.
7. 7 .Process according to claim 6 wherein the concentration of total nitrogen ranges from 30000 mg/L to 100000 mg/L.
8. 8 .Process according to any of the daims from 1 to 7 wherein the amine water further comprises sulfur sulfide whose sulfur sulfide concentration ranges from 1000 mg/L to 10000 mg/L.
9. 9 .Process according to claîm 8, wherein the sulfur sulfide concentration ranges from 2000 mg/Lto 10000 mg/L.
10. 10 .Process according to daim 9 wherein the sulfur sulfide concentration ranges from 3000 mg/Lto 10000 mg/L.
11. 11 .Process according to any one of daims 1 to 10 wherein the amine water has a Chemical oxygen demand which ranges from 100000 mg/L to 1000000 mg/L.
12. 12 .Process according to daim 11 wherein the Chemical oxygen demand ranges from 200,000 mg/L to 1000000 mg/L.
13. 13 .Process according to claim 12 wherein the Chemical oxygen demand ranges from 300000 mg/L to 1000000 mg/L.
14. 14 .Process according to any of the claims from 1 to 13 wherein the amine water has an electrical conductivity that ranges from 500 pS/cm to 150000 pS/cm.

    5 15.Process according to claim 14 wherein the electrical conductivity ranges from 5000 pS/cm to 150000 pS/cm.

    16 .Process according to claim 15 wherein the electrical conductivity ranges from 10000 pS/cm to 150000 pS/cm.

    17 .Process according to any of the claims from 1 to 16 wherein the amine water further 10 comprises boron with a concentration which ranges from 10 mg/L to 1000 mg/L.

    18 .Process according to daim 17 wherein the concentration of boron ranges from 50 mg/L and 1000 mg/L.

    19 .Process according to claim 18 wherein the boron concentration ranges from 100 mg/L to 1000 mg/L.
15. 15 20.Process according to any one of claims 1 to 19 wherein the membrane is selected from inorganic or organic polymers and copolymers, or combinations thereof.

    21 .Process according to claim 20 wherein the membrane is selected from organic polymers and copolymers containing halo gens, or combinations thereof; or organic polymers and copolymers not containing halo gens, or combinations thereof.
16. 20 22.Process according to claim 21 wherein the membrane is selected from polymers or organic copolymers containing fluorine, or combinations thereof; or between organic polymers or copolymers not containing fluorine, or combinations thereof.
17. 23 .Process according to claim 22 wherein the membrane is selected from oxides, sulfides, zeolites, métal- organic materials, carbonaceous materials, polysilanes and their copolymers, 25 polysiloxanes and their copolymers, polysulfones and their copolymers, polyacrylates and their copolymers, proteins, polyamides and their copolymers, polyuréthanes and their copolymers, polyketones and their copolymers, polyesters and their copolymers, polysaccharides, polyethers and their copolymers, polyaromatics and their copolymers, polyolefms and their copolymers, or combinations thereof.

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18. 24.Process according to claim 23 wherein the membrane is polypropylene.
19. 25 .Process according to any one of claims 1 to 24 in which the amine water is heated, before being distilled, at a température ranging from 30°C to 95°C.