Regeneration of ion exchangers that are used for salt removal from acid gas capture plants

[0001] The present invention relates to a gas removal method that can be captured from an incoming gas stream by amines using an amine solvent. In a particularly preferred embodiment, the acid gas containing one or more of the following compounds is captured: sulfur dioxide, hydrogen sulfide and carbon dioxide.

BACKGROUND OF THE INVENTION [0002] Separation of acid gases such as sulfur dioxide, hydrogen sulfide or carbon dioxide from gas streams, such as off-gas or hydrocarbon containing streams, by absorption in aqueous amine solvents is well known. Many of these processes, which are called amine scrubber processes, are described in "Gas Purification", ed. s ", ed. Arthur L. Kohl and Richard B. Nielsen, Gulf Publishing Company, Houston, TX.

[0003] Amine scrubber processes use a regenerative amine solvent, whereby the acid gas is captured in solution at one temperature, and then the acid gas is desorbed or stripped from the solution, usually at a higher temperature.

[0004] The amine solvent for removing a specific component of the acid gas from the incoming stream can be selected in such a way that the gas can be removed from the solution by steam stripping. If steam stripping is used to separate the acid gas from the solution, this acid gas in the solution must be volatile. Preferably, the acid ionization constant for the conjugated amine acid (pKa) has a value not exceeding about 3 or 4 units higher than the pKa of the acid gas. If this pKa difference is greater than about 3 or 4 units, then the salt formed between the amine and the acid will be too stable to practically dissociate by steam stripping.

[0005] In industrial applications, acid gas capture processes are accompanied by the introduction or formation of acids in the process that are stronger than the acids for which the removal process is envisaged. These stronger acids form salts with an amine solvent that cannot be removed by steam, and are therefore called thermally stable amine salts or simply thermally stable salts.

[0006] If thermally stable salts are allowed to accumulate, they will eventually neutralize the entire amine content in the solvent, making it unable to react and remove the acid gas components as intended. Accordingly, in systems where strong acids accumulate in the amine solution, it becomes necessary to ensure the removal of thermally stable salts.

[0007] Various methods are known for removing thermally stable salts from amine gas purification solutions. These include the distillation of the free amine from the salt at or below atmospheric pressure (see, for example, "Gas Purification," p. 255 et seq.), Electrodialysis (see, e.g. US 5,292,407) and ion exchange (see

VP / 2423 / RW

EP 2 004 308 B1 e.g. US 4,122,149; US 4,113,849; US 4,970,344; US 5,045,291; US 5,292,407; US 5,368,818; 5,788,864 and 6,245,128) [0008] One of the problems associated with ion exchange processes is that the ion exchange carrier or resin must be regenerated from time to time. At the loading stage in the ion exchange process, the anion removal capacity decreases with the amount of thermally stable salts removed from the amine solvent. After exhausting or limiting the ability to remove anion exchange resin anions by a certain amount, the administration of an amine solvent rich in thermally stable salts to the ion exchange resin ends so that the ion exchange resin can be regenerated. Since the regenerative agent for ion exchange resin is most often released into the wastewater treatment plant or otherwise removed, the amine solvent in the amine resin layer can be transferred and rinsed with large amounts of water before the resin regenerating agent begins to flow through the column to recover the dilute amine solvent solution before regenerating the resin ion exchange. If the diluted amine solvent solution is recycled to the acid gas capture process, which avoids the loss of the amine solvent, this results in the introduction of water into the amine solution in the acid gas capture process, which leads to a reduction in the amine solvent concentration in the solvent solution during the amine purification process.

[0009] Amine scrubber processes are designed to operate at a fixed, optimal concentration of the amine solvent. Therefore, dilution of the amine solvent is undesirable. Accordingly, if the diluted amine solvent solution is recycled to the acid gas purification process, water should be removed from the amine solvent or the dilute amine solvent stream will be removed to the wastewater, which will result in loss of the amine solvent.

[0010] US Patent 4,170,628 discloses a process for removing sulfur dioxide from inlet gases and for removing thermally stable salts from the absorbent. Thermally stable salts are removed by means of an ion exchange bed. Periodically, the ion exchange bed is regenerated by a three-stage process involving (1) rinsing the ion exchange bed with water using a condensate stream to remove absorbent from the ion exchange bed; (2) regeneration of the ion exchange bed; and (3) rinsing the ion exchange bed with process water to remove excess sodium hydroxide.

SUMMARY OF THE INVENTION [0011] According to the present invention, an improved method is provided for removing the gas captured by an amine from an incoming gas stream, using the amine solvent according to claim No. 1. In particular, it has been found that the disadvantages of diluting the amine and rinsing with large amounts of water for efficient amine recovery after the loading step can be minimized by combining the action of an amine scrubber with an ion exchange process.

[0012] During operation, the anionite resin may be contained in the packing, which is supplied e.g. in a column. The amine solvent rich in thermally stable salts flows through this column. Thermally stable salts are captured by the ion exchange resin while the amine solvent is flowing through the column. When it is determined that the ion exchange resin should be regenerated,

VP / 2423 / RW

The flow of the amine absorbent through the column is terminated and a regenerating agent is fed to the column. Preferably, all or substantially all of the amine solvent is removed from the column prior to regeneration of the ion exchange carrier.

[0013] The degree of dilution of the amine occurring during the recycling of the diluted amine solution resulting from the leaching of the amine from the column before the regeneration process of the ion exchange resin is limited by means of the stream of acidic condensate from the regeneration column of the amine scrubber used to remove and wash the amine from the ion exchange column at the end of the stage depletion. The used peak acid condensate stream containing the amine solvent is then recycled to the amine scrubber process. To ensure a high rate of recovery of the amine from the column and return it to the amine scrubber process, large volumes of the peak acid condensate stream can be used because this peak acid stream is derived from the purification solvent itself and therefore does not result in dilution of the amine during the process. Preferably, the anionite resin flushing bed of the peak acid condensate stream, which is obtained from the top acid condensate stream of the steam stripper and is used to leach the amine absorbent from the anionite resin bed, is recycled to the acid gas capture process without adding any water.

[0014] According to the present invention, the peak acid condensate stream is used to remove the acid gas absorbent from the ion exchanger prior to regeneration of the ion exchange resin. The peak acid condensate stream used may contain all or only part of the peak acid condensate stream that is obtained from the steam stripper used in the amine scrubbing process. For example, if an amine scrubber process is used to purify an inlet gas stream containing sulfur dioxide, then the condensate (return) will contain sulfuric acid, or sulfur dioxide hydrate, in solution. On the other hand, if the amine scrubber process is used to purify the inlet gas stream containing hydrogen sulfide and / or carbon dioxide, then the condensate stream will contain carbonic acid and / or hydrogen sulfide. According to the present invention, such condensate streams are acidic but do not affect the regeneration process, provided that the concentration of acid gases dissolved in the condensate stream is less than 5 wt.%, More preferably less than 3 wt.%, And most preferably less than 2 wt.% .

[0015] In an amine scrubber process, the hot inlet gas is typically cooled before the inlet gas contacts the aqueous amine solvent solution to prevent degradation and dehydration of the amine solvent. The cooling process uses water evaporation to cool the gas and saturate it with water. Cooling is often carried out, for example, in a spray pre-scrubber. The water in the pre-scrubber is recycled through the spray nozzle pump, with some water being blown out to control the pH, concentration of dissolved solids and level of suspended solids. The added water, usually deionized water or steam condensate, is added to the pre-scrubber to maintain a constant water supply. According to another aspect of the present invention, the streams flowing from the ion exchange process are used as make-up water in the pre-scrubber, which eliminates or significantly reduces the volume of wastewater resulting from the regeneration of the ion exchange resin, which otherwise must be treated for disposal.

VP / 2423 / RW

[0016] In one embodiment, the method of the present invention also includes selecting an amine capture gas as one or more of the group consisting of SO2, H2S and CO2.

[0017] In a further embodiment, the method also comprises selecting a lean amine solvent in step c) according to claim 1 as an amine solvent which comes into contact with the anionite resin.

[0018] In a further embodiment, the method further comprises rinsing the regenerated anionite resin with water to remove regenerating agent therefrom before using the regenerated anionite resin in step (c).

[0019] In another embodiment, the method further includes:

(a) subjecting the intake gas stream to a pre-wash operation;

(b) using all or part of the regenerating agent solution used or the effluent after rinsing the regenerating agent, or both, in the pre-wash operation.

[0020] In another embodiment, the method further comprises providing an amine solvent containing an amine having a pK_and in the range of 2.5 - 6. Preferably, the method further comprises selecting SO2 as the amine capture gas.

[0021] In a further embodiment, the method further comprises providing an amine solvent containing an amine having a pKa in the range of 7.5-10. Preferably, the method of the present invention also includes selecting an amine capture gas as one or more of H2S and

CO2.

[0022] In another embodiment, the thermally stable salt low in amine is recycled to Step (a).

[0023] In another embodiment, the thermally stable salt low in amine is recycled to Step (b).

[0024] In another embodiment, the method further includes selecting SO2 as the amine capture gas.

[0025] In another embodiment, the overhead acid condensate stream is used undiluted to leach out the amine solvent from the anionite resin.

BRIEF DESCRIPTION OF THE DRAWINGS [0026] These and other advantages of the present invention will become fully understood from the following description of preferred embodiments of the invention, in which:

Figure 1 is a block diagram of an exemplary amine scrubber process illustrating the streams connecting it to the ion exchange process of the present invention;

Figure 2 is an illustration of an exemplary implementation of a block diagram of an ion exchange process that can be used in the amine scrubber process of Figure 1, which illustrates the streams connecting it to the amine scrubber process of the present invention; while

VP / 2423 / RW

EP 2 004 308 B1

Figure 3 is an illustration of the preferred order of operations in one cycle of operation of the ion exchange column, ranging from resin depletion to final rinsing with water after regeneration.

DETAILED DESCRIPTION OF THE INVENTION [0027] As shown in Figures 1 and 2, the ion exchange system (Figure 2) is integrated with the amine scrubber process (Figure 1) to remove thermally stable salts from the amine solvent. The advantage of this solution is that any solution known in the art can be used in the amine scrubber system and the anionite resin system, and the embodiments shown in Figures 1 and 2 are exemplary. For example, the intake gas may contain only one target gas (e.g. sulfur dioxide) or multiple target gases (e.g. sulfur dioxide and carbon dioxide). If the purpose of removal from the intake gas is several gases, then the amine scrubber system may have a plurality of absorption zones, each using a different solvent stream, thereby forming multiple solvent streams, each of which may be individually regenerated. For example, a first solvent loop may be provided to remove sulfur dioxide from the acid gas and use the first solvent, and regenerate the first solvent. A second solvent loop may be provided to remove carbon dioxide from the acid gas, using the second solvent sequentially after removal of sulfur dioxide and regenerating the second solvent. The first anionite resin system can be used to remove thermally stable salts from the first amine absorbent, and the second anionite resin system can be used to remove thermally stable salts from the second amine absorbent. It is also an advantage that any anionite resin system may contain one or more anionite resin reactors or columns and may use feed tanks and storage tanks, as is known in the art, e.g. to ensure consistent delivery to the anionite resin column and reduce sudden jumps throughout the process.

[0028] The advantage is that the feed gas stream may contain only one or more acidic gases, e.g. SO2 or H2S, or CO2, and the fact that the feed gas stream may be subjected to subsequent purification in various stages to reduce the concentration of each gas acid levels below a predetermined level. Accordingly, the feed gas stream may come in contact with the first amine solvent to reduce the concentration of the first acid gas, e.g. SO2, to below a predetermined level. Then the feed gas stream may come into contact with the second amine solvent so that the second acid gas, e.g. CO2 or H2S, from the feed gas stream is selectively captured. The feed gas stream may then contact the third amine solvent to selectively capture the third acid gas, e.g. NOx, from the feed gas stream. Alternatively, two or more gases may be removed during one purification step. Accordingly, one solvent can be used to capture two or more gases in the feed gas stream. The advantage is that the feed gas stream may also contain NOx, which can be captured by the iron (II) EDTA complex. Since the Fe EDTA (nitrosyl) salt formed in this way resulting from NOx absorption from the feed gas would be removed by the ion exchange resin, it is preferred that the thermally stable salts are removed from the regenerable NOx absorbent by other methods known in the art. According to the present invention

VP / 2423 / RW

The ion exchange process described herein is used in conjunction with regeneration of the absorbent used in the amine capture gas capture process (i.e. one that can be stripped of the feed gas by an amine solvent, e.g.

[0029] SO2, H2S, CO2).

[0030] Thermally stable salts can accumulate in any solvent. Therefore, at least a portion of each amine solvent may be fed separately to the anionic resin system to remove thermally stable salts from the amine solvent. In this way, the first amine solvent can be fed to the first ion exchange column, and the second amine solvent can be fed to the second column of ion exchange resin. In this way, each solvent can circulate in a separate loop to prevent mixing of different amine solvent streams. Alternatively, each amine solvent can be purified separately in a single ion exchange system.

[0031] The feed gas supplied to the amine scrubber process may be any gas stream that contains at least one acid gas. Preferably, the feed gas stream contains at least one gas among SO2, CO2 and H2S, and more preferably contains at least SO2 and CO2. The feed gas can be a process gas stream or a waste gas stream from various sources. For example, the feed gas stream can be:

(a) Acid natural gas containing methane, other hydrocarbons, hydrogen sulfide, carbon dioxide and water, usually at elevated pressure up to a maximum of 100 bar and moderate temperature, close to ambient temperature.

(b) Waste gas from the combustion of sulfur-free solid fuel, containing nitrogen, oxygen, carbon dioxide and water at atmospheric pressure and temperature raised to a maximum of 200 ° C or higher.

(c) Waste gas from the combustion of solid sulfur-containing fuel containing nitrogen, oxygen, carbon dioxide, sulfur dioxide, sulfur trioxide and water at a pressure substantially equal to atmospheric pressure and a temperature raised to a maximum of 200 ° C or even higher.

(d) Residual gas from a sulfuric acid plant containing nitrogen, oxygen, sulfur dioxide and sulfur trioxide at close to atmospheric pressure and a slightly elevated temperature below 200 ° C.

[0032] When sulfur dioxide dissolves in water and reacts with it, it forms sulphurous acid, H2SO3, which is essentially a stronger acid (pKa1 = 1.8) than H2CO3 carbonic acid (pKa1 = 6.4), formed by hydration of carbon dioxide or hydrogen sulfide (pKa1 = 7.0). If it is desired to capture sulfur dioxide from the feed gas by means of a regenerated amine scrubber process, then preferably a suitably weak amine with a pKa preferably less than 6 is used. A weak amine cannot capture any significant amount of CO2 that remains in the gas to be reacted. Accordingly, such a weak amine can be used to selectively capture SO2 from a feed gas containing SO2 and CO2. The sulphurous acid mist (pKa2-3) is so strong that it forms thermally stable salts with regenerated SO2 solvents.

VP / 2423 / RW

[0033] The alkanolamine solvent used for selective SO2 capture may be any of those disclosed in US Patent No. 5,019,361. In particular, this solvent can be represented by a structural formula:

R² R³

II

N-R¹ -N

II

R⁵ R⁴ where R¹ is an alkylene with two or three carbon atoms, R², R³, R⁴, and R⁵ they may be the same or different and may be hydrogen, alkyl (e.g. lower order alkyl with 1 to about 8 carbon atoms, including cyclic alkyl), hydroxyalkyl (e.g. lower order hydroxyalkyl with 2 to about 8 carbon atoms), arylalkyl (eg.

up to about 20 carbon atoms), aryl (preferably monocyclic or bicyclic), alkylaryl (e.g., 7 to about 20 carbon atoms) and any of R², R³, R⁴ and R⁵ can form ring structures. Diamines are organic compounds containing two nitrogen atoms and are often favored due to their availability on the market and generally lower viscosity. Amines, e.g. diamines, are preferably tertiary diamines because of their stability. However, others can be used, provided that mild oxidation and thermal conditions exist to minimize the chemical reactivity of the solvent. Frequently preferred amine salt absorbents contain a hydroxyalkyl group and a substituent on the amino group. In some cases, the hydroxy substituent is considered to slow down the oxidation of sulfite or bisulfite to sulfate.

[0034] To allow the large amounts of sulfur dioxide recovered to be absorbed by the absorption medium under atmospheric pressure, it is preferred that the free form of the amine solvent of the amine solvent has a molecular weight of less than about 300, preferably less than about 250. Tertiary diamines often have the formula:

R² R²

II

N-R¹ -N

II

R² R²₁ where R is an alkylene group, preferably containing from 2 to 3 carbon atoms as a straight chain or ₂ branched chain and all R are the same or different and are alkyl groups, preferably methyl or ethyl, or hydroxyalkyl groups, preferably 2-hydroxyethyl. Particularly preferred compounds are N, N'N '- (trimethyl) -N- (2-hydroxyethyl) ethylenediamine (pKa = 5.7); N, N, N ', N'-tetramethylethylenediamine (pKa = 6.1); N, N, N ', N'-tetrakis (2-hydroxyethyl) ethylenediamine (pKa = 4.9); N- (2-hydroxyethyl)

VP / 2423 / RW

Ethylenediamine (pKa = 6.8); N, N'dimethylpiperazine (pKa = 4.8); N, N, N ', N'-tetrakis (2-hydroxyethyl) -1,3 diaminopropane; and N ', N'-dimethyl-N, N-bis (2-hydroxyethyl) ethylenediamine. Useful diamines also include heterocyclic compounds such as piperazine (pKa = 5.8). PKa values ​​are given for nitrogen sorption. [0035] If it is desired to capture weak acid gases such as H2S or CO2, then stronger amines with pKa> 7.5, for example monoethanolamine, diethanolamine or methyldiethanolamine are preferably used. Acids substantially stronger than H2S or carbonic acid will form thermally stable salts. Examples are SO2, formic acid, acetic acid, hydrochloric acid, sulfuric acid and thiocyanic acid.

[0036] The carbon dioxide dissolving amines may be primary, secondary or tertiary with a pKa in the range of 6.0-10, preferably 6.5-10, and more preferably 6.5-9.5. To prevent loss of amine with the gas to be purified, the preferred amines preferably have a saturated vapor pressure of less than 1 mm Hg at 50 ° C above the solvent. Preferred amines include 4- (2-hydroxyethyl) -1-piperazineethane sulfonic acid (pKa = 7.5), morpholinoethanesulfonic acid (pKa = 6.1), N- (2-hydroxyethyl) ethylenediamine (pKa1 = 9.5, pKa2 = 6.5), piperazine (pKa1 = 9.8, pKa2 = 5.6), N- (2-hydroxyethyl) piperazine (pKa1 = 9.0, pKa2 = 4.5), benzimidazole (pk, 5.5), and N, N'-bis (2-hydroxyethyl) piperazine (pKa1 = 7.8, pKa2 = 3.9) and mixtures thereof.

[0037] If it is desired to capture both SO2 and CO2, and in order to avoid the formation of a thermally stable salt through all SO2 during CO2 capture, preferably the first is SO2 capture with a suitable solvent. In the second stage, CO2 is then removed. Since hydrogen sulfide is not thermodynamically stable in the presence of SO2 or oxygen, only small concentrations are found in streams containing SO2 or O2.

[0038] In the preferred embodiment of Figure 1, the feed gas stream 12 which is purified in the amine scrubber system 10 contains a single gas being captured by an amine, e.g. SO2. As shown in Figure 1, preferably, the feed gas stream 12 is first pre-flushed to remove solid particles from the feed gas stream 12 and to cool it, preferably at least to a temperature close to its adiabatic saturation temperature. In some cases, the feed gas temperature can be lowered to an even lower level by using a heat exchanger to cool the circulating water. By means of this pre-treatment with water it is also possible to remove other impurities from the feed gas, e.g. hydrochloric acid and sulfuric acid. Any pre-scrubber system known in the art can be used. As shown in Figure 1, the feed gas stream 12 can be introduced into the pre-scrubber 14, in which it comes in contact with the counter-current pre-scrubbing liquid stream 16, preferably water, which can be sprayed into the pre-scrubber 14 through respective nozzles 18. The pre-rinse liquid stream 16 is preferably recycled. Accordingly, the stream 20 to be reused can be fed to the pump 22, from which the condensate stream 24 is recycled to the primary scrubber 14. The exhaust stream 26, intended for wastewater, can be used to control the level of dissolved and suspended solids in the circulating water, and the supplementary stream 28 can be used to replenish the water lost through evaporation to the supply gas and through the exhaust.

VP / 2423 / RW

[0039] After passing through the optional pre-scrubber 14, the pre-purified feed gas stream then flows through the absorption zone 30 in column 32, which may be the sulfur dioxide absorption zone. The pre-cleaned gas 34 can flow from the pre-scrubber 14 to the absorption column 32 through e.g. a chimney shelf 36 which allows gas to flow upwards but prevents the flow of liquid downwards to the pre-scrubber 14.

[0040] The lean amine solvent (i.e., poorly contaminated with acid gas) is preferably a regenerated solvent and can be fed through stream 38 to absorption column 32, where it preferably flows in a counter-current fashion to the pre-purified feed gas stream 34, resulting in a rich amine solvent stream 40 and a purified feed gas stream 42. Preferably, the lean amine solvent stream 38 flows down through e.g. filling in the absorption zone 30, which promotes good gas-liquid contact with the gas flowing upwards. The lean solvent selectively catches the polluting acid gas, leaving the absorption column as a rich solvent stream 40.

[0041] The purified feed gas stream 42 can then be introduced into one or more additional absorption zones (not illustrated), released into the atmosphere, transferred to additional devices for further purification, or reused in the process. For example, a second absorption zone can be designed to remove carbon dioxide from the feed gas stream. A third absorption zone can be designed to remove NOx and optionally some amounts of mercury from the feed gas stream. The advantage here is that acid gases can be removed from the feed gas selectively, in any desired order. For example, the carbon dioxide absorption zone may be before or after the sulfur dioxide and NOx absorption zones. However, since SO2 tends to form thermally stable salts in solvents for weaker gases, it is preferable to capture SO2 from any other pollutant gas.

[0042] The captured pollutant is removed from the rich amine solvent by heating the stream to release the captured pollutant. Preferably, a steam stripping column is used, where the steam provides at least a portion of the heat required to release the captured contaminant from the solvent. As shown in Figure 1, the rich amine solvent stream 40 and the hot poor amine solvent stream 46 can be passed through the intermediate heat exchanger 44 to obtain a hot rich amine solvent stream 48 that is fed to the steam stripping column 50.

[0043] Like the absorption column 32, the steam stripping column 50 can be of any type known in the art and can be made with packing or with shelves. The hot rich amine solvent stream 48 preferably flows down through, e.g., filling 52 in a regeneration or steam stripping column 50. A hot rich amine solvent stream 48 is introduced in the top of column 50 so that it flows down through column 50. If necessary, a pump 64 is used to force circulation 66 from the bottom of the regeneration column 50 to the reboiler (condensate reboiler) 54. The advantage is that the reboiler 54 can be a forced circulation reboiler, boiler reboiler, or thermosiphon reboiler. The hot lean amine solvent pump is preferably used for transport

VP / 2423 / RW

The solvent is poor through the expansion tank rich in the expansion tank (not illustrated). The steam generated by boiling the amine solvent in reboiler 54 enters column 50 as stream 60 to provide energy and assist mass transfer for stripping the acid gas from the amine solvent.

[0044] The reboiler is heated in any manner known in the art. Preferably, the reboiler 54 is indirectly heated by stream 56 (which may be steam and which can be extracted from any source) through e.g. a tubular heat exchanger, forming a steam condensate stream 58 that can be reused to produce additional steam or in any other installation site. Boiling the solvent in reboiler 54 causes steam and desorbed acid gas 60 to flow to column 50. Steam and desorbed acid gas move up through the desorption zone (fill 52) of column 50, heating the downstream hot stream of rich amine solvent 48 and lifting upward gaseous contaminants that have separated from the solvent. Steam and pollutant (in this case sulfur dioxide) leave column 52 as stream 62. Preferably, the steam and desorbed acid gas move up through the rectification column section with recycle 68 of regeneration tower 50 before leaving tower 50 as stream 62.

[0045] Stream 62 is cooled in the overhead condenser 70, which condenses most of the steam, forming a two-phase stream 72, which can be separated in the receiver 74 into a liquid stream of overhead acid condensate 76 and an acid gas stream 78. The acid gas can flow to the removal site or to further processing. The peak acid condensate stream 76 is split into the peak acid condensate stream 80 which is used in the ion exchange process and the stream 82 which is recycled to the regeneration tower 50 to return to the amine solvent.

[0046] Regenerated solvent collects at the bottom of column 50 and is removed from column 50 as stream 66, part of which is reused as hot stream of lean amine solvent 46. The lean amine from the bottom of regeneration tower 50 flows as stream 46 through heat exchanger 44, to create a cold stream of lean amine 84.

[0047] Thermally stable salts typically accumulate in an amine solvent. Accordingly, the amine solvent undergoes an ion exchange process to remove thermally stable salts. According to the present invention, at least a portion of the amine solvent undergoes ion exchange to remove thermally stable salts and preferably only a portion thereof (e.g. bleed). Preferably, the bleed stream is taken from the cold lean amine stream 84. According to such an embodiment, as shown in Figures 1 and 2, stream 86 transfers an amine solvent rich in thermally stable salts to a system 90 to remove thermally stable salts by ion exchange. The ion exchange system 90 returns the first stream of lean amine solvent containing thermally stable salts 88 with a lower content of thermally stable salts. Stream 38 completes the circuit by transferring a lean amine solvent to the scrubbing and gas absorption tower 32.

[0048] As known to those skilled in the art, the details of the amine scrubber process can be changed or enriched without changing the general principles or their relationship with the present invention. For example, use gas to liquid in the absorber and regenerator

VP / 2423 / RW

Various types of devices can be used to achieve the same absorption and stripping effect. Using the present invention, other block diagrams may also be employed, e.g., including lean and half lean amine streams.

[0049] Figure 2 shows one embodiment of an anionite resin system 90 that can be used in accordance with the present invention. As shown in the illustration, the anionite resin system 90 includes an additional expansion tank 92 and a single column with anionite resin 94. Because the anion exchange resin in the ion exchange column 94 must be regenerated from time to time, according to the present invention periodically (i.e. from time to time as required), the flow of a poorly stable amine solvent rich in thermally 96 salt through the ion exchange column 94 will end, allowing regeneration of anionite resin. In another embodiment, the advantage is that multiple columns with anionite resin 94 can be used. Accordingly, a stream of lean amine solvent rich in thermally stable salts 96 may be continuously directed at at least one column with anionite resin 94 to remove thermally stable salts therefrom, while the anionite resin in one or more additional columns 94 is regenerated.

[0050] Any ion exchange reactor design known in the art can be used. According to the present invention, the anion exchange carrier is a ball formed resin. Accordingly, the anion exchange column usually has a base on which to place the resin exchange beads. The anion exchange support (bed) may therefore consist of polymer spheres that have functional groups on the polymer. The anion exchange resin has essentially basic functional groups as the exchange site. A variety of anion exchange resins can be used in the process of the present invention. Strong base anion exchange resins are most often characterized by having solid quaternary amine exchange sites that are positively charged at any pH. Anion exchange resins with weakly basic groups have primary or secondary amine exchange sites. These sites are positively charged depending on the pH of the solution. At higher pH these places have a neutral charge. [0051] Strongly basic resins are those that contain tetramethylammonium functional groups. Strongly basic type II feeds usually contain hydroxyethyltrimethylammonium functional groups. Examples of anionic resins with strongly basic type I groups are styrene-divinylbenzene resins, with quaternary ammonium groups placed on a polymer backbone, such as, for example, Resintech "SBG-1 and Sybron" ASB-1, sold by Resintech Company. Examples of anion exchange resins with strongly basic type II groups are styrene divinyl benzene resins, with quaternary alkanolammonium groups placed on a polymer backbone, e.g. Resintech ™ SBG-II and Sybron ™ ASB-II, also available from the Resintech Company. Other resins that can be used include materials such as MobayTM M500 from Bayer AG, anionic resin with strongly basic type I groups, which is a polystyrene resin with quaternary ammonium groups placed on the polymer backbone, Arnbenysf '' A-26 from Rohm and Haas, resin anionite with strongly basic type I groups, which is a styrene-divinylbenzene copolymer with quaternary ammonium groups located on the polymer backbone; and Arnberlite "IRA-410 from Rohm and Haas, anionic resin with strongly basic type II groups. Also included are styrene-divinylbenzene anionite resins with strongly groups

VP / 2423 / RW

Bases of Dow production having quaternary amines as their functional groups. These materials are available under the DOWEX trade name. Gel acrylic resins with weakly basic groups, e.g. supplied by Purolite ™, can also be used. Either gel or macroporous resins can be used.

[0052] The resins listed above are only examples of useful anionite resins, not a limitation of the list of resins that can be used in carrying out the process of the present invention. For the purposes of the present invention, it is envisioned that any ion exchange resin used to recover spent amine solvents may be regenerated using the process disclosed herein. Those skilled in the art can easily recognize these resins.

[0053] The lean amine solvent stream rich in thermally stable salts 96 (which can be taken from the expansion tank 92) or can only be an extension of the bleed stream 86, if no expansion tank 92 is foreseen can flow through the ion exchange column 94 to form the first lean stream amine solvent with thermally stable salts 88. This is the resin loading or resin depleting step. During this step, the resin in column 94 reacts with the amine solvent to remove thermally stable salts from the amine solvent. When the ability of the anionite resin to remove thermally stable salts from the amine solvent reaches the desired level or after a predetermined time, the flow of the amine solvent through the column 94 is terminated.

[0054] It is more preferable to remove thermally stable anions from an amine solvent that is poor in gas absorbed by the amine than from an amine solvent which is rich in gas absorbed by the amine because the anionite resin will also tend to react with anions gases absorbed by amine, which are present in an amine solvent. Accordingly, if a lean amine solvent is supplied to column 94, most of the anionite resin will react with the thermally stable salts present in the lean amine solvent, and not with anions from gases absorbed by the amine, such as sulfite ion. Therefore, based on the volume unit of amine solvent flowing through the anion exchanger, most of the thermally stable salts will be removed from the amine solution.

[0055] The interaction of the amine solvent with the anionite resin results in the amine solvent being returned to its free base form. The amine solvent with reduced concentration of thermally stable salts (i.e., the first stream of thermally stable amine solvent 88) is then recycled to the amine scrubber system 10 (see Figure 1). The first stream of thermally stable salt-poor amine solvent 88 can be recycled to any desired location in the amine scrubber process and preferably is fed downstream of the heat exchanger 44 and before column 32 as illustrated in Figure 1.

[0056] Some amine scrubber processes may operate at a high concentration of thermally stable salts (see, e.g., US Patent Application No. 10 / 639.678). In this case, it is only desirable to partially lower the concentration of the thermally stable salts, but also the flow of the amine solvent containing the thermally stable salts through the column 94 in the amount necessary for full saturation of the anionite resin with thermally stable anions before regeneration of this anionite resin. It increases

VP / 2423 / RW

EP 2 004 308 B1 to the maximum efficiency of the ion exchange process with respect to amine losses and the demand for regenerative agent and scrubbing liquid based on the amount of anions removed.

[0057] After the depletion step, the anionite resin is, according to the present invention, subjected to an amine solvent removal process that precedes the regeneration step. Therefore, according to the present invention, the ion exchange resin is combined with a stream of top acid condensate to remove the amine solvent from column 94.

[0058] The peak acid condensate stream, after passing through column 94, forms a second lean amine solvent stream with thermally stable salts 98 due to the addition of water in a portion of the peak acid condensate stream 80 supplied to column 94. The amine concentration in stream 98 is lower in compared to the amine circulating in the amine scrubber system 10. However, by recycling stream 98 to the amine scrubber system 10, substantially all of the water and amine diverted to the ion exchange system 90 is recycled to the amine scrubber system 10, maintaining essentially the mass balance of the amine scrubber system 10 and, accordingly, preventing dilution of the amine in the amine scrubber system 10, which would occur if fresh water was used instead of the peak acid condensate stream 80 in the rinsing step.

[0059] An advantage of an alternative embodiment is that part of the make-up water can be added to the overhead acid condensate stream 80, if required. The need for additional rinsing water may arise in cases where the generated peak acid condensate stream is too low, due to the low demand for regeneration steam, but where the concentration of thermally stable compounds is high, which requires high speeds of the IX system. A maximum of 3 parts of water can be added to one part of the overhead acid condensate stream, but it is preferable to add as little as possible.

[0060] Stream 98 can be recycled to the continuous amine loop in the amine scrubber system 10 downstream of the heat exchanger 44 and upstream of column 32 (similar to stream 88). Alternatively, stream 98 may be recycled to the steam stripping portion of the amine scrubber process (it may be added to one or both of stream 82 and stream 48). This alternative flow can be used if the gas absorbed by the amine is SO2.

[0061] An additional advantage of using the overhead acid condensate stream to leach the amine from column 94 is that metal cations that are precipitated from the amine (e.g. Fe3 +) or settle in the ion exchange resin column from amine suspended particles (e.g. carbonate calcium), they tend to dissolve again. If these metal cations are not dissolved again, they will slow down the flow of liquid through the anion exchange resin column or possibly interfere with the transport of anions into or outside the resin.

[0062] According to the present invention, at the end of the rinsing step and before the regeneration step, the ion exchange resin is rinsed with deionized water, which can be supplied with stream 100. Rinsing water is provided to remove the peak acid condensate stream from column 94. Rinsing water flow 100 through column 94 creates a stream of wastewater for rinsing water 102 that can be directed to storage tank 104 for reuse.

[0063] Next, the anionite resin is regenerated using a regenerative agent. The regenerating agent may be, for example, a sodium hydroxide solution (e.g., a 4% sodium hydroxide solution), which is supplied by stream 106. The regenerating agent restores the resin

VP / 2423 / RW

Anionite to its initial state. Accordingly, if the ion exchange resin is an anionic resin and if the regenerating agent is hydroxide, then this hydroxide returns the anionic resin to its basic form (e.g. free amine in the case of a resin with weakly basic groups and the hydroxide form in the case of a resin with strongly basic groups). The result of the regeneration step is the used regenerating agent solution 108. Stream 108 can be fed to the primary scrubber 14 (it may be part or all of stream 28). Accordingly, the water in stream 108 may be used to cool the feed gas. In addition, any amount of unreacted hydroxide will serve to neutralize strong acids, such as sulphurous acid, which is present in the water stream of the scrubber.

[0064] After the regeneration step, the anionite resin is rinsed again to remove hydroxide from it. Accordingly, fresh water and / or water from reservoir 104 can be fed to the anionite column 94 via stream 110. Removal of the corrosive regenerative agent from the anionite bed prevents contamination of the amine solvent with hydroxide or sodium salts during the next loading step. The used rinse water, which will contain a certain amount of hydroxide, can also be directed to the pre-scrubber through stream 28.

[0065] Preferably, the final rinse of the anionite resin is done with deionized water or steam condensate which is supplied through stream 100 to remove additional amounts of hydroxide and salts from the anionite resin. The rinse water can be directed to the tank 104 through the stream 102 for reuse, because the used rinse water contains a relatively small amount of dissolved hydroxide. After the last rinsing step, the resin loading step can be started.

[0066] It has been found that the removal of thermally stable salts from both strong and weak amine solvents can be accomplished by essentially the same process with only the optional adjustment taking into account the type of resin and type and amount of regenerating agent and the volume of rinse water necessary for optimization for each single amine solvent and type of thermally stable salts.

[0067] For example, any SO2, CO2 and H2S solvent known in the art can be used. Solvents can be regenerated and reused and, if this is the case, they can be regenerated and reused using methods known in the art. The anion exchanger system may include expansion tanks and storage tanks for collecting various streams that are used in the anion exchange resin system or which are formed in the anion exchange resin system. Any ion exchange resin or series of such resins known in the art may be used.

EXAMPLES [0068] The operation of the invention is illustrated by the following representative examples. As will be appreciated by those skilled in the art of ion exchange, many of the details in these examples can be changed by continuing to practice the invention described herein.

Example

VP / 2423 / RW

[0069] The operation of the invention was tested in a pilot plant. The experiments were carried out to remove thermally stable salts from the SO2 diamine absorbent (Cansolv 'Absorbent DM) with a concentration of 26.9% amine, 12.5% ​​sulfate and 1.85% sulfite. The thermally stable salt (sulfate) concentration in this amine solvent was 1.36 moles / mole amine. A 6-inch diameter ion exchange column was filled to a height of 21.3 inches with weakly basic functional resin, Purolite ™ A830, which corresponded to 10 liters of resin bed volume (BV). Fluid from heated tanks was fed to the ion exchange column by centrifugal pumps. For the safe and convenient operation of the system, appropriate valves, pressure gauges, thermometers and rotameters have been installed. All fluid was heated to 50 ° C. Synthetic condensate was made by blowing SO2 gas into water until the nominal concentration reached 1.5% (pH = 1.5).

[0070] Amine and anion analysis was performed by ion chromatography, and low sodium ion concentrations were quantified by measuring conductivity using a calibration curve. Low amine concentrations in water matrices were quantified by gas chromatography. The process exploitation cycle took place in the following order:

1. Loading the resin with thermally stable anions by passing 4 BV of the amine solvent through the column.

2. Removal of the amine solvent and leaching of the amine from the resin with 2.25 BV condensate.

3. Condensate removal with 0.5 BV of deionized water.

4. Regenerating the resin back to base form by passing 4 BV of 4% sodium hydroxide through the column.

5. Final rinse with 1.5 BV of water retained after the previous final rinse, followed by 4.5 BV of deionized water.

6. The next loading step has been completed.

[0071] This experimental order gave the following results, averaged over a large number of cycles:

1. A 100 gram SO4 = charge per liter of resin was obtained.

2. The loss of amine was 21 grams per kilogram of 80 / removed from the amine solution, primarily due to the incomplete removal of the amine from the column by condensate rinsing.

VP / 2423 / RW

EP 2 004 308 B1

3. During one cycle, the amine that is recycled to the scrubbing process was diluted by approximately 0.4% (e.g., 26.9% to 26.8% of the amine) as a result of mixing water with the amine at the interface between the final rinse and the amine next cycle. If the amine leaching water was from an external source, the dilution was 34% (from 26.9 to 17.8%). The final amine concentration in this case is calculated as the sum of the 4 BV dilution of the amine solvent by mixing at the interface (0.2 BV water) and 2.25 BV rinsing water.

VP / 2423 / RW

EP 2 004 308 B1