Process for heat stable salts removal from solvents

Abstract

An apparatus and a method for removing salts from a liquid are described. A first liquid containing at least one salt is mixed with magnetic composite particles. A subsequent separation of the particles from the liquid is achieved using an electromagnetic source.

Claims

1. A method for removing heat-stable salts (HSS) from an aqueous solvent, the method comprising: providing an aqueous solvent containing HSS; feeding a plurality of magnetic composite particles coated with an alginate to the aqueous solvent and mixing the plurality of magnetic composite particles with the aqueous solvent; separating the plurality of magnetic composite particles having at least a portion of the HSS adsorbed on the plurality of magnetic composite particles from the aqueous solvent using an electromagnetic source; discharging a mixture of the plurality of magnetic composite particles with the aqueous solvent after mixing the plurality of magnetic composite particles with the aqueous solvent in a mixing tank (4) to an electromagnetic separator (5) where a separation takes place by which the plurality of magnetic composite particles having at least a portion of the HSS adsorbed on the plurality of magnetic composite particles are separated from the aqueous solvent by turning on and using an electromagnetic source (6) attached to the electromagnetic separator (5); collecting the aqueous solvent in a treated liquid tank (7) after the separation; and turning off the electromagnetic source (6) and feeding a mixture of a regeneration liquid and the plurality of magnetic composite particles having at least a portion of the HSS adsorbed on the plurality of magnetic composite particles to a collecting tank (8).

2. The method according to claim 1 wherein the aqueous solvent is an aqueous amine solvent.

3. The method according to claim 2 wherein the aqueous amine solvent comprises at least one of methyldiethanolamine or alkanolamine.

4. The method according to claim 1 wherein the HSS is formed by one or more protonated amine cations and one or more anions selected from SCN″, HCOO″, CH.sub.3COO″, and CH.sub.3CH.sub.2COO.sup.−.

5. The method according to claim 1 wherein the plurality of magnetic composite particles comprise iron oxide magnetic particles.

6. The method according to claim 1 further comprising feeding the mixture in the collecting tank (8) back to the electromagnetic separator (5) and turning on the electromagnetic source (6) such that the plurality of magnetic composite particles are trapped in the electromagnetic separator (5).

7. The method according to claim 6 further comprising feeding the regeneration liquid from the electromagnetic separator (5) to the collecting tank (8), and further feeding the regeneration liquid from the collecting tank (8) to the tank (3).

8. The method according to claim 7 further comprising feeding additional aqueous solvent from a tank (2) via the mixing tank (4) to the electromagnetic separator (5), turning off the electromagnetic source (6) and feeding a mixture of the plurality of magnetic composite particles and the aqueous solvent to the mixing tank (4).

9. A method for removing salts from a liquid, the method comprising: providing a first liquid containing at least one salt; feeding a plurality of magnetic composite particles to the first liquid and mixing the plurality of magnetic composite particles with the first liquid; separating the plurality of magnetic composite particles having at least a portion of the at least one salt adsorbed on the plurality of magnetic composite particles from the first liquid using an electromagnetic source; collecting the first liquid in a treated liquid tank (7) after the separation; feeding a second liquid as a regeneration liquid from a tank (3) to the mixing tank (4) and then to the electromagnetic separator (5); and turning off the electromagnetic source (6) and feeding a mixture of the second liquid and the plurality of magnetic composite particles having at least a portion of the at least one salt adsorbed on the plurality of magnetic composite particles to a collecting tank (8).

10. The method according to claim 9 further comprising feeding the mixture in the collecting tank (8) back to the electromagnetic separator (5) and turning on the electromagnetic source (6) such that the plurality of magnetic composite particles are trapped in the electromagnetic separator (5).

11. The method according to claim 10 further comprising feeding the second liquid from the electromagnetic separator (5) to the collecting tank (8), and further feeding the second liquid from the collecting tank (8) to the tank (3).

12. The method according to claim 11 further comprising feeding additional first liquid from a tank (2) via the mixing tank (4) to the electromagnetic separator (5), turning off the electromagnetic source (6) and feeding a mixture of the plurality of magnetic composite particles and the first liquid to the mixing tank (4).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be described with reference to the accompanying drawings of which:

(2) FIG. 1 is a schematic diagram for the fully automated process according to the invention where MCM are interacted with the treated amine solvent then reactivated and re-injected back for further reuse.

(3) FIG. 2 is an SEM image for the synthesized Iron oxide magnetic particles.

(4) FIG. 3 shows an effect of CaCl.sub.2) concentration on HSS removal.

(5) FIG. 4 shows an effect of magnetic composite microparticles dosage on HSS removal.

(6) FIG. 5 shows an effect of temperature on HSS removal using magnetic composite microparticles.

(7) FIG. 6 shows pseudo-first-order kinetics of a kinetic study of E-1Fe-Magnetic_1.25 M for 4 hours by ln(q.sub.e−q.sub.t) vs. time.

(8) FIG. 7 shows pseudo-first-order kinetics of a kinetic study of E-1Fe-Magnetic_1.25 M for 4 hours by t/qt vs. time.

(9) FIG. 8 shows intra-particle diffusion in a kinetic study of E-1Fe-Magnetic_1.25 M for 4 hours by qt vs. t.sup.1/2.

DETAILED DESCRIPTION OF THE INVENTION

(10) The present invention is generally applicable, and is advantageously especially usable for HSS removal from amine solvents. It is used for the removal of HSS before they accumulate further in the amine solvent unit and deteriorate its quality and performance. The present invention provides a fully automated method to continuously remove HSS from amine solvents. Heat Stable Salts (HSS) in a solvent and more preferably in an amine solvent are adsorbed in MCM and then removed using an electromagnetic separator. The contaminated MCM is then preferably reactivated and reused. Any industry that needs to remove contaminates from a fluid using magnetic particles can benefit from the proposed process. In an especially preferred embodiment, the proposed process can be integrated readily with running natural gas sweetening absorption processes.

(11) Examples of units where amine solvents come in contact with gas stream and are prone to HSS generation and accumulation include dehydration units and gas sweetening units. The present invention can also be used on amine solvents that are used to process hydrocarbon liquids.

(12) Methyldiethanolamine and alkanolamine solutions in general are used in gas sweetening process to strip acid gases, specifically carbon dioxide and hydrogen sulfide. Amine solvents are characterized by their high selectivity to absorb these acid gases. The acid gases are considered as corrosive agents; the existence of acid gases with liquid water in the process vessels and pipes threatens their structures from corrosion. The acid gases should be removed and kept below the preferred design specification of 4-20 ppm H.sub.2S and <3% CO.sub.2.

(13) During the absorption of H.sub.2S and CO.sub.2 by-products such as SON.sup.−, HCOO.sup.−, CH.sub.3COO.sup.−, and CH.sub.3CH.sub.2COO.sup.− are produced by the reaction between oxygen and H.sub.2S and CO.sub.2. These by-products and the protonated amine form a heat stable salt (HSS) system, which could not be removed by system regenerator. The accumulation of these HSS makes the acid gases absorption become less stable. The increase of HSS in solution may lead to the corrosion and fouling of the equipment, and in turn short life of the equipment. Moreover, these HSS contribute to solution foaming which causes the losses of amine and other serious problems. Therefore, the removal of these HSS from the amine solvents is crucial for amine absorption processes.

(14) The present invention can be installed in the lean amine cycle and provide continuous removal of HSS from amine solvents. The present invention introduced the use of magnetic composite microparticles (MCM) to adsorb and remove HSS from amine solvents. HSS can be removed before they accumulate in the amine solvent and deteriorate its quality and performance. The best place to install the presented process 1 in a running amine unit depends in the unit design and configuration, each unit should be dealt with separately; however, the best place for gas sweetening unit can be on the lean amine stream either before the rich-lean heat exchanger to benefit from the high temperature of lean amine around (120° C.) before reducing it down in the heat exchanger or after the rich-lean heat exchanger.

(15) A particularly preferred continuous HSS removal process 1 has a lean amine tank 2, a cleaning solution tank for MCM reactivation 3, a mixing tank 4 to mix the MCM with the untreated amine solvent, an electromagnetic separator 5 equipped with electromagnetic source 6, a treated amine solvent 7, MCM regenerating and collecting tank 8, and centralize control unit 9.

(16) The operation of the process 1 is described with respect to FIG. 1. The lean amine tank 2 has a solvent inlet that is withdrawn as a side stream from the process solvent i.e. the lean amine stream in amine gas sweetening unit. The untreated amine solvent is pumped to the mixing tank 4; a MCM is manually added to the mixing tank 4. After sufficient time in the mixing tank the amine solvent with the MCM are discharged from the mixing tank to the electromagnetic separator 5. The electromagnetic source 6 is turned on by the central control unit 9 so that the contaminated MCM with HSS are trapped in the electromagnetic separator 5. The treated amine solvent then is collected in treated amine solvent tank 7, the treated amine solvent can then be sent back to the main unit. The central control unit 9 then will close the treated tank inlet valve 10, and open the MCM regenerating and collecting tank inlet tank 11.

(17) The regeneration cycle starts by pumping the regeneration liquid from tank 3 to the mixing tank 4 and then to the electromagnetic separator 5. The electromagnetic source 6 is turned off by the central control unit 9 so the contaminated MCM with HSS are washed from the electromagnetic source 6 by the regeneration solution to the MCM regenerating and collecting tank 8. After sufficient time the regenerated MCM with the regeneration solution are pumped back to the inlet of the electromagnetic separator 5, the electromagnetic source 6 is then turned on by the central control unit 9 so that the reactivated MCM are trapped in the electromagnetic separator 5. The regeneration solvent (water) is then collected in collecting tank 8 and pumped back to the cleaning solution tank 3 for further reuse.

(18) Then the central control unit 9 will pump untreated lean amine solvent from tank 2 for washing the reactivated MCM trapped in the electromagnetic source 6, the electromagnetic source will be turned off by the central control unit 9. The amine solvent with the reactivated MCM will be recycled to the mixing tank 4 for another cycle of removing HSS.

(19) Magnetic Composite Microparticles (MCM) Syntheses and Testing for HSS Removal

(20) A homogenized solution of 1.0 wt % alginate is prepared by mixing sodium alginate in distilled water. Concentration of 1.0 wt % magnetic particles is added to homogenized alginate solution. The magnetic particles are uniformly dispersed in alginate solution by vigorous mixing on a vortex, followed by ultrasound. The resulting suspension is then added dropwise into CaCl.sub.2 solution (1M) through a micropipette tip by means of a peristaltic pump. The prepared hydrogels beads are left to cure in the calcium bath overnight in order to ensure complete polymerization. Finally after the curing period, the small magnetic hydrogel beads are recovered using a magnet and washed several times with deionized water to remove the unbound calcium ions. The beads are then dried for two hours at room temperature and stored for further analysis.

(21) Batch Adsorption for Screening:

(22) Adsorption experiments are performed by adding various amounts of magnetic alginate microparticles into a 25 ml conical flask containing 10 ml of Industrial Lean amine solvent. The flask is then allowed to equilibrate on a water bath at 140 rpm for 4 hours. After reaching equilibrium, the magnetic alginate metal oxide composite beads are removed from the Lean amine samples using magnetic force and the Lean amine is filtered. The concentrations of HSS in the Lean amine samples before (C.sub.i) and after (C.sub.e) adsorption are measured using UVI-vis spectrophotometer.

(23) The adsorption percentage of HSS (% removal) is calculated using following equation:

(24) $\%\mathrm{Removal}=\left(\frac{C_i-C_e}{C_i}\right)*100$

(25) TABLE-US-00001 TABLE 1 Removal of HSS using various magnetic alginate composite sorbents Weight, LA Volume, Ci, % Name of adsorbent g ml ppb Ce, ppb Removal Strontium Ferrite 1.003 10 4630 4030 12.96% Strontium Ferrite 2.002 10 4630 3790 18.14% MgFe.sub.2O.sub.4 1.003 10 4630 4375 5.51% ZnFe.sub.2O.sub.4 1.003 10 4630 4235 8.53% ZnFe.sub.2O.sub.4 2.002 10 4630 3900 15.76% Iron oxide particle 2.002 10 4630 3770 18.57%

(26) From the screening, it is identified that Iron oxide magnetic particles are found to have the best removal of total HSS (18.57% for 2.0 g MCM) from industrial lean amine solvent. Hence further optimization, kinetics and thermodynamics are carried out using Alginate/Iron oxide magnetic composite.

(27) Kinetics and Thermodynamics Study on Alginate/Iron Oxide Magnetic Composite

(28) Preparation of Iron Oxide Magnetic Nanoparticles

(29) The chemical reagents used for the preparation of iron oxide particles is Ferric chloride: FeCl.sub.3.6H.sub.2O, Sodium hydroxide: NaOH, and Ethanol.

(30) A typical approach for the synthesis is given as follows: To a homogenized solution of ferric chloride in water, Sodium hydroxide is added and vortexed vigorously until a brownish precipitate is formed. The mixture is then placed inside an oven at 85° C. for 10 hours to remove the excess water. After drying, the brown precipitate is separated by filtration, followed by washing with distilled water. Finally an ethanol wash is performed and the obtained powder particles are oven dried at 85° C.

(31) Synthesis of Alginate/Iron Oxide Magnetic Composite

(32) Initially 1.0 wt % of magnetic iron oxide particles are added to 1.0 wt % homogenized alginate solution. The mixture is allowed to vortex vigorously followed by sonication using ultrasound. The resulting suspension is then added dropwise through a micro pipette tip into CaCl.sub.2 solution using a peristaltic pump. The prepared hydrogels beads are left to cure in the calcium chloride solution overnight in order to ensure complete polymerization. Finally after the curing period, the small magnetic hydrogel beads are recovered using a magnet and washed several times with deionized water to remove the unbound calcium ions. The beads are then dried for two hours at room temperature and stored for further analysis.

(33) Magnetic Composite Microparticles (MCM) Characterization

(34) SEM analysis was performed to confirm the morphology of the synthesized iron oxide particles. FIG. 2 shows an SEM image of Iron oxide magnetic particles. The obtained image using scanning electron microscopy clearly shows that the iron oxide particles have spherical shape.

(35) Effect of CaCl.sub.2 Concentration

(36) The effect of the cross linker concentration on the amount of HSS removal is studied by varying the concentration of CaCl.sub.2 from 0.5 M to 2.0 M, while preparing the magnetic composite. As shown in FIG. 3, it is observed that maximum removal of 21.36% and 21.63% was obtained for a CaCl.sub.2 concentration of 1.25 and 1.5 M respectively. Also it is seen that further increase in concentration above 1.5 M resulted in a decrease in the removal percentage.

(37) Effect of Adsorbent Dosage

(38) FIG. 4 depicts the % removal of HSS with different dosage of magnetic composite microparticles (MCM). The HSS removal is found to increase with MCM dosage.

(39) Effect of Temperature

(40) The % removal of HSS with different MCM dosage at various temperatures is shown in FIG. 5.—The HSS removal is found to increase with increase in temperature confirming that the adsorption process is endothermic in nature. 3.0 g of alginate/iron oxide magnetic hydrogel composite exhibited a removal of 29.24%, 32.04% and 35.38% at 25° C., 35° C. and 45° C. respectively.

(41) Adsorption Kinetics

(42) For predicting the rate of HSS removal using the prepared MCM and estimating the equilibrium time, adsorption kinetics study is performed. For the kinetic study, 1.0 g of MCM is added to each of the conical flasks containing 10 ml of lean amine at room temperature. At definite time intervals, the beads are recovered using magnetic force and the lean amine samples are filtered and analyzed using UV-vis for HSS content. Different kinetics models such as pseudo-first-order, pseudo-second-order and intra-particle diffusion models are studied to analyze the experimental data. Plots of ln(q.sub.e−q.sub.t) versus time can be seen in FIG. 6, t/q.sub.t versus time can be seen in FIG. 7 and q.sub.t versus square root of time is given in FIG. 8. These Figures are made to predict how experimental data fits with pseudo-first-order kinetics, pseudo-second-order kinetics and intra-particle diffusion respectively. From the correlation coefficient values it can be clearly seen that the adsorption kinetics follows pseudo-second-order kinetics with a rate constant of 0.03696 and this indicates that the removal is chemical in nature which is in agreement with the endothermic nature of the batch process.

(43) By doing these specific measurements the capacity of CMC for the removal of HSS from amine solvent can be determined. CMC can be prepared from different composite with different sizes.

(44) The foregoing disclosure and showings made in the drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense.