GB2173799A - N-aminoalkyl alkylpiperazine - Google Patents

Abstract

The present invention relates to the novel compound 1-(3-aminopropyl)-2,5-dimethyl-piperazine, and an alkaline salt promoter system which includes 2 to 20% by weight said N-aminoalkyl alkylpiperazine, 10 to 40% by weight an alkali metal salt or hydroxide (e.g. K2 CO3), optionally 2 to 20% by weight amino acid with 4 to 8 carbon atoms per molecule, and water. These scrubbing compositions may be used for removing CO2 from gaseous streams containing CO2.

Description

SPECIFICATION N-aminoalkyl alkylpiperazines Recently, it was shown in U.S. Patent No. 4,112,050 that sterically hindered amines are superior to diethanolamine (DEA) as promoters for alkaline salts in the "hot pot" acid gas scrubbing process. U.S. Patent No. 4,094,957 describes an improvement to this process whereby amino acids, especially sterically hindered amino acids, serve to prevent phase separation of the aqueous solution containing sterically hindered amines at high temperatures and low fractional conversions during the acid gas scrubbing process.

One of the preferred sterically hindered amines described in these patents is N-cyclohexyl-1,3-propanediamine. The bulky cyclohexane ring on this diamino compound provides steric hindrance to the carbamate formed at this site thereby favoring the expulsion of CO, during regeneration, thereby leaving the hindered amine group free to protonate. The primary amino group of this diamino compound assists in maintaining solubility under lean conditions. Under lean conditions when there is insufficient carbonic acid present to protonate the hindered amino group, the molecule would be insoluble were it not for the primary amino group which forms a stable polar carbamate ion. However, even the carbamated primary amino group is insufficient to prevent insolubility of the compound under very lean conditions and an additional additive, as proposed in U.S.Patent No. 4,094,957, an amino acid, is required to maintain solubility of the diamino compound. This amino acid also contributes to additional capacity and faster absorption rates for carbon dioxide, so it therefore acts as a copromoter in addition to solubilizing the sterically hindered diamino compound. Screening studies of available amino acids as possible copromoters for N-cyclohexyl 1,3-propanediamine based on cyclic capacity and rates of absorption ascertained that pipecolinic acid was one of the best amino acid copromoters.

Subsequent studies, however, have demonstrated that the N-cyclohexyl-1,3-propanediamine/pipecolinic acid promoter system has several shortcomings. Firstly, N-cyclohexyl-1,3-prnpanediamine is both chemically unstable and volatile. For example, it degrades into a cyclic urea, especially in the presence of hydrogen sulfide. In fact, the rate of cyclic urea formation has been found to be highly dependent on hydrogen sulfide concentration, a common contaminant of industrial acid gas streams. The cyclic urea formation from this diamine is favored by the stability of the six-membered ring structure of the cyclic urea. In addition to promoter losses due to cyclic urea formation, which may be a serious problem with hydrogen sulfide rich streams, the cyclic urea product has limited solubility, and its separation from solution poses additional problems.Various techniques for coping with this water insoluble cyclic urea have been proposed. See, for example, U.S. Patent Nos. 4,180,548 and 4,183,903. However, these techniques have specific benefits and problems, e.g., specialized equipment is necessary.

Pipecolinic acid also has shortcomings, e.g., it is rather expensive and its picoline precursor is in limited supply.

In view of the commercial potential of using the sterically hindered amino compounds as described and claimed in U.S. Patent Nos. 4,094,957 and 4,112,050, there is a need for finding sterically hindered amino compounds which perform as well as N-cyclohexyl-1,3-propanediamine but do not have the volatility and degradation problems of this compound.

Also, U.S. Patent Nos. 4,094,957 and 4,122,050 disclose various other sterically hindered amines, including specific piperazine compounds. These specifically identified piperazines have been found to be too volatile for economic utilization on large scale acid gas treating facilities. Also, there is a need for finding a less costly replacement for pipecolinic acid which possesses its effectiveness. Preferably, there is a need for finding a single amino compound which performs as well or nearly as well as the N-cyclohexyl-1,3-propane-diamine/ pipecolinic acid mixture, but does not suffer the preparative cost, volatility and degradation problems of this mixture. Such a discovery would be of significant technical and economic merit.

Various amino acids have been proposed as promoters for alkaline salts in the "hot pot" gas scrubbing process. For example, British Patent No. 1,305,718 describes the use of beta and gamma amino acids as promoters for alkaline salts in the "hot pot" acid gas treating process. These amino acids, however, are not suitable because the beta-amino acids undergo deamination when heated in aqueous potassium carbonate solutions. The gamma amino acids form insoluble lactams under the same conditions. Also, the alpha-amino acid, N-cyclohexyl glycine, as described in Belgian Patent No. 767,105, forms an insoluble diketopiperazine when heated in aqueous solutions containing potassium carbonate.

It has now been discovered that 1-(3-amino-propyl)-2,5-dimethylpiperazine (APDP) is an excellent promoter for alkaline salts in the "hot pot" acid gas scrubbing process. This amino compound, when used as a promoter, not only provides for high carbon dioxide capacity and high rates of carbon dioxide absorption, but does not form undesirable insoluble degradation products as in the case of N-cyclohexyl1,3-propanediamine, the beta and gamma amino acids and the alpha amino acid, N-cyclohexyl glycine.

Also, this amino compound is less volatile than N-cyclohexyl-1, 3-propanediamine and the piperazines disclosed in U.S. Patent Nos. 4,094,957 and 4,112,050, thereby the economy of this promoter is greater than the previously employed promoters.

Accordingly this invention provides the compound 1-(3-aminopropyl)-2,5-dimethylpiperazine (APDP). In one embodiment of the present invention, there is provided a process for the removal of CO, from a gaseous stream containing CO, which comprises contacting said gaseous stream (1) in an absorption step with an aqueous absorbing solution comprising (a) a basic alkali metal salt or hydroxide selected from alkali metal bicarbonates, carbonates, hydroxides, borates, phosphates and their mixtures, and (b) an activator or promoter system for said basic alkali metal salt or hydroxide comprising at least an effective amount of N-aminoalkyl alkylpiperazine; and (2) in a desorption and regeneration step, desorbing at least a portion of the absorbed CO, from said absorbing solution.

As another embodiment of the present invention, there is provided an acid gas scrubbing composition comprising: (a) 10 to about 40% by weight of an alkali metal salt or hydroxide, (b) 2 to about 20% by weight of an N-aminoalkyl alkylpiperazine and (c) the balance, water.

The N-aminoalkyl alkylpiperazine promoter may be admixed with certain amino acids as copromoters, preferably an amino acid containing 4 to 8 carbon atoms. The amino acid will preferably comprise a sterically hindered amino acid. Especially preferred amino acids include N-secondary butylglycine, N-isopropyl glycine, N-isopropyl alanine, N-sec. butyl alamine, N-n-butyl glycine and pipecolinic acid.

The N-aminoalkyl alkylpiperazine useful as a promoter in the practice of the present invention has the formula:

ie 1-(3-aminopropyl)-2,5-dimethylpiperazine (APDP).

Also, disclosed is the method for preparing N-aminoalkyl alkyl piperazines.

The compound of formula I can be prepared by reductive condensation of isopropanolamine to produce 2,5-dimethyl-piperazine followed by cyanoalkylation and reduction.

In general, the aqueous scrubbing solution will comprise an alkaline material comprising a basic alkali metal salt or alkali metal hydroxide selected from Group IA of the Periodic Table of Elements. More preferably, the aqueous scrubbing solution comprises potassium or sodium borate, carbonate, hydroxide, phosphate or bicarbonate. Most preferably, the alkaline material is potassium carbonate.

The alkaline material comprising the basic alkali metal or salt or alkali metal hydroxide may be present in the scrubbing solution in the range from about 10% to about 40% by weight, preferably from 20% to about 35% by weight The actual amount of alkaline material chosen will be such that the alkaline material and the amino acid activator or promoter system remain in solution throughout the entire cycle of absorption of CO, from the gas stream and desorption of CO, from the solution in the regeneration step.

Likewise, the amount and mole ratio of the amino acids is maintained such that they remain in solution as a single phase throughout the absorption and regeneration steps. Typically, these criteria are met by including from about 2 to about 20% by weight, preferably from 5 to 15% by weight, more preferably, 5 to 10% by weight of this sterically hindered N-aminoalkyl alkylpiperazine. Should an amino acid be included, the amino acid can be added in an amount such that the solution contains 2 to about 20% by weight, preferably 5 to about 15% by weight, and more preferably 5 to 10% by weight.

The aqueous scrubbing solution may include a variety of additives typically used in acid gas scrubbing processes, e.g., antifoaming agents, antioxidants, corrosion inhibitors and the like. The amount of these additives will typically be in the range that they are effective for the intended purpose, i.e., an effective amount.

The term acid gas includes CO, alone or in combination with H25, CS2, HCN, COS and the oxides and sulfur derivatives of C, to C4 hydrocarbons. These acid gases may be present in trace amounts within a gaseous mixture or in major proportions.

The contacting of the absorbent mixture and the acid gas may take place in any suitable contacting tower. In such processes, the gaseous mixture from which the acid gases are to be removed may be brought into intimate contact with the absorbing solution using conventional means, such as a tower packed with, for example, ceramic rings or with bubble cap plates or sieve plates, or a bubble reactor.

In a preferred mode of practising the invention, the absorption step is conducted by feeding the gaseous mixture into the base of the tower while fresh absorbing solution is fed into the top. The gaseous mixture freed largely from acid gases emerges from the top. Preferably, the temperature of the absorbing solution during the absorption step is in the range from 25 to 200 C, and more preferably from 35 to 15000. Pressures may vary widely; acceptable pressures are between 5 and 2000 psi, (34.5 and 13790 kPa) preferably 100 to 1500 psia (690 to 10343 kPa) and most preferably 200 to 1000 psia (1379 to 6895 kPa) in the absorber. In the desorber, the pressures will range from 5 to 100 psig (134 to 789 kPa). The partial pressure of the acid gas, e.g. CO, in the feed mixture will preferably be in the range from 0.1 to 500 psia (0.69 to 3448 kPa) and more preferably in the range from 1 to 400 psia (6.9 to 2758 kPa). The contacting takes place under conditions such that the acid gas, e.g., Cho2, is absorbed by the solution.

Generally, the countercurrent contacting to remove the acid gas will last for a period of from 0.1 to 60 minutes, preferably 1 to 5 minutes. During absorption, the solution is maintained in a single phase. The triamino piperazine gives low foam in the contacting vessels.

The aqueous absorption solution comprising the alkaline material, the activator system comprising the sterically hindered aminoalkyl piperazine, which is saturated or partially saturated with gases, such as CO2 and H2S may be regenerated so that it may be recycled back to the absorber. The regeneration should also take place in a single liquid phase. Therefore, the presence of the highly water soluble amino acid provides an advantage in this part of the overall acid gas scrubbing process. The regeneration or desorption is accomplished by conventional means, such as pressure reduction, which causes the acid gases to flash off or by passing the solution into a tower of similar construction to that used in the absorption step, at or near the top of the tower, and passing an inert gas such as air or nitrogen or preferably steam up the tower.The temperature of the solution during the regeneration step may be the same as used in the absorption step, i.e., 25 to about 200 C, and preferably 35 to about 150 C. The absorbing solution, after being cleansed of at least a portion of the acid bodies, may be recycled back to the absorbing tower. Makeup absorbent may be added as needed. The use of an amino acid cosolvent, e.g., Nsecondary butyl glycine, enables one to maintain a single phase regardless of the CO2 content in the acid gas.

As a typical example, during desorption, the acid gas, e.g., C02-rich solution from the high pressure absorber is sent first to a flash chamber where steam and some CO2 are flashed from solution at low pressure. The amount of CO2 flashed off will, in general, be about 35 to 40% of the net CO2 recovered in the flash and stripper. This is increased somewhat, e.g., to 40 to 50%, with the high desorption rate promoter system owing to a closer approach to equilibrium in the flash. Solution from the flash drum is then stream stripped in the packed or plate tower, stripping steam having been generated in the reboiler in the base of the stripper.Pressure in the flash drum and stripper where regeneration occurs is usually 16 to 100 psia (110 to 690 kPa), preferably 16 to 30 psia (110 to 207 kPa) and the temperature is in the range from 25 to 2000 C, preferably 35 to 150 C, and more preferably 100 to 140 C. Stripper and flash temperatures will, of course, depend on stripper pressure, thus at 16 to 25 psia (110 to 172 kPa) stripper pressures, the temperature will preferably be about 100 to about 1400C during desorption. Single phase may be maintained and facilitated by use of an amino acid, preferably N-secondary butyl glycine as a copromoter.

In the most preferred embodiment of the present invention, the acid gas, e.g., CO2 is removed from a gaseous stream by means of a process which comprises, in sequential steps, (1) contacting the gaseous stream with a solution comprising 10 to 40 weight percent, preferably 20 to 30 weight percent of potassium carbonate, an activator or promoter system comprising 2 to 20 weight percent, preferably 5 to 15 weight percent, more preferably 5 to 10 weight percent of the sterically hindered aminoalkyl piperazine, as herein defined, and 2 to 20 weight percent, preferably 5 to 15 weight percent, more preferably 5 to 10 weight percent, of the amino acid as herein defined, the balance of said solution being comprised of water, said contacting being conducted at conditions whereby the acid gas is absorbed in said solution, and preferably at a temperature ranging from 25 to 2000C, more preferably from 35 to 150 C and a pressure ranging from 100 to 1500 psig (789 to 10442 kPa) and (2) regenerating said solution at conditions whereby said acid gas is desorbed from said solution. By practising the present invention, one can operate the process above described at conditions whereby the working capacity, which is the difference in moles of acid gas absorbed in the solution at the termination of steps (1) and (2) based on the moles of potassium carbonate originally present, is greater than obtained under the same operating conditions for removing acid gases from gaseous streams, wherein said same operating conditions do not include an aminoalkyl piperazine as the promoter.In other words, working capacity is defined as follows: CO2 in solution CO2 in solution at completion of less at completion of absorption desorption Which is: Moles of CO2 Absorbed less Moles Residual CO2 Absorbed IQCC! Initial Moles K2CO3 Initial Moles K2CO3 It should be noted that throughout the specification wherein working capacity is referred to, the term is defined as the difference between CO2 loading in solution at absorption conditions (step 1) and the CO2 loading in solution at regeneration conditions (step 2) each divided by the initial moles of potassium carbonate. The working capacity is equivalent to the thermodynamic cyclic capacity, that is the loading is measured at equilibrium conditions.This working capacity may be obtained from the vapor-liquid equilibrium isotherm, that is, from the relation between the CO2 pressure in the gas and the acid gas, e.g,.

CO2 loading in the solution at equilibrium at a given temperature. To calculate thermodynamic cyclic capacity, the following parameters must usually be specified: (1) acid gas, e.g., CO2 absorption pressure, (2) acid gas, e.g., CO2 regeneration pressure, (3) temperature of absorption, (4) temperature of regeneration, (5) solution composition, that is weight percent of triamino piperazine and the weight percent of the alkaline salt or hydroxide, for example potassium carbonate, and (6) gas composition. The skilled artisan may conveniently demonstrate the improved process which results by use of the sterically hindered amine a comparison directly with a process wherein the sterically hindered amino compound is not included in the aqueous scrubbing solutions.For example, it will be found when comparing two similar acid gas scrubbing processes (that is similar gas composition, similar scrubbing solution composition, similar pressure and temperature conditions) that when the sterically hindered amines are utilized the difference between the amount of acid gas, e.g., CO2 absorbed at the end of step 1 (absorption step) defined above and step 2 (desorption step) defined above is significantly greater. This significantly increased working capacity is observed even though the scrubbing solution that is being compared comprises an equimolar amount of a prior art amine promoter, such as diethanolamine, 1,6-hexanediamine, etc.It has been found that the use of the aminoalkyl piperazine of the invention provides a working capacity which is at least 15% greater than the working capacity of a scrubbing solution which does not utilize the sterically hindered amine. Working capacity increases of from 20 to 60% may be obtained by use of the sterically hindered amino compound compared to diethanolamine.

Besides increasing working capacity and rates of absorption and desorption, the use of triamino piperazine leads to lower steam consumption during desorption.

Steam requirements are the major part of the energy cost of operating an acid gas, e.g., CO2 scrubbing unit. Substantial reduction in energy, i.e, operating costs will be obtained by the use of the process utilizing the triamino piperazine. Additional savings from new plant investment reduction and debottlenecking of existing plants may also be obtained by the use of the triamino piperazine. The removal of acid gases such as CO2 from gas mixtures is of major industrial importance, particularly the systems which utilize potassium carbonate activated by the unique activator or promoter system of the present invention.

While the sterically hindered amines, as shown in U.S. Patent No. 4,112,050, provide unique benefits in their ability to improve the working capacity in the acid scrubbing process, their efficiency decreases in alkaline "hot pot" (hot potassium carbonate) scrubbing systems at high temperatures and at low concentrations of the acid gas due to phase separation. Therefore, full advantage of these highly effective sterically hindered amines cannot always be utilized at these operating conditions. The addition of an amino acid, as a co-solvent and copromoter as shown in U.S. Patent No. 4,094,957, solves the problem of phase separation and enables a more complete utilization of sterically hindered amino compounds as the alkaline materials activator or promoter.

The absorbing solution of the present invention, as described above, will be comprised of a major proportion of two alkaline materials, e.g., alkali metal salts or hydroxides and a minor proportion of the amino compound activator system. The remainder of the solution will be comprised of water and/or other commonly used additives, such as anti-foaming agents, antioxidants, corrosion inhibitors, etc. Examples of such additives include arsenious anhydride, selenious and tellurous acid, proteins, vanadium oxides, e.g., V203, chromates, e.g., K2Cr2O#, etc.

The N-aminoalkyl alkylpiperazine for use in the present invention include is

Many of the amino acids useful in the practice of the present invention are either available commercially or may be prepared by various known procedures. Preferred amino acids are sterically hindered amino acids having 4 to 8 carbon atoms, e.g., N-isopropyl glycine, N-isopropyl alanine, N-sec. butyl glycine, N-sec. butyl alanine, N-n-butyl glycine, N-(2-pentyl)-glycine, and pipecolinic acid.

The invention is illustrated further by the following examples which, however, are not to be taken as limiting in any respect. All parts and percentages, unless expressly stated to be otherwise, are by weight.

Example 1 Preparation of l-(3-aminopropyV-2,5-dimethylpfperazine (APDP) 3009 of isopropanolamine (4 moles), 600 ml. t-butyl alcohol and 20g wet Raney Ni are charged into a 1 gallon autoclave. Hydrogen was introduced to a pressure of 400 psi, (2857 kPa) then the temperature was increased and maintained between 166-180 for four hours. The catalyst was separated by filtration and the product distilled through a 30 cm column to a pot temperature of 168 C. The condenser was kept at 150 C. The condensate quickly solidified and gave 202.4g of 2,5-dimethylpiperazine. An additional 69 was obtained by boiling out the column with ether. Total yield, 91%.

2289 of 2,5-dimethylpiperazine (2 moles), 1 16.6g of acrylonitrile and 750 ml, of t-butyl alcohol were refluxed for 48 hours (8 hours is sufficient). The cooled product, a slurry, was charged into 90 gallon (340 I) autoclave with 250 ml. of t-butyl alcohol, 75g Raney Ni (washed with ethanol, then with t-butyl alcohol) and 209 of 50% KOH.

Hydrogen was introduced to a pressure of 1100 psi (7684 kPa). The temperature rose spontaneously to 42 C. A pressure drop corresponding to 610 psi (4305 kPa) was observed. The autoclave was opened, catalyst separated by filtration, and the filtrate was neutralized with 50 ml, of 6 N HCI. The product was distilled through a 30 cm column to a pot temperature of 170 C. 195.49 of 1-(3-aminopropyl)-2,5-dimethylpiperazine, boiling at 132-136 C/17 mm Hg, was collected. The yield was 57%.

The above procedure can be combined in a one pot synthesis provided the H20 generated by the formation of the 2,5-dimethylpiperazine is removed. One method to accomplish this is the use of selective drying agents which will not interact strongly with the tertiary alcohol.

Other tertiary alcohols are suitable solvents for this invention as are ethers such as tetrahydrofuran, however, tertiary butyl alcohol is preferred.

Example 2 Use of l-(3-aminopropyl)-2,5-dimethylpiperazine (A POP) as an activator for K2CO3 in CO2 Removal The reaction apparatus consists of an absorber and a desorber as shown in Figure 1 of U.S. Patent No.

4,112,050. The absorber is a vessel having capacity of 2.5 liters and a diameter of 10 cm, equipped with a heating jacket and a stirrer. A pump removes liquid from the bottom of the reactor and feeds it back to above the liquid level through a stainless-steel sparger. Nitrogen and CO2 can be fed to the bottom of the cell through a sparger.

The desorber is a 1-liter reactor, equipped with teflon blade stirrer, gas sparger, reflux condenser and thermometer.

The following reagents were charged into a two-liter flask: 60.3g 1-(3-aminopropyl)-2,5-dimethyl piperazine (APDP) 22.59 Pipecolinic acid (PA) 225g K2CO3 442.59 H20 When all the solid had dissolved, the mixture was placed in the absorber and brought to 800C. The apparatus was closed and evacuated until the liquid began to boil. The CO2 was admitted until the solution was saturated.

The rich solution so obtained was transferred to the desorber and boiled for one hour during which CO2 was desorbed. The regenerated solution was placed back in the absorber and brought to 80 C. The apparatus was evacuated until the liquid began to boil. Then CO2 was admitted and the rate of absorption and the total capacity was measured. The result is presented in the table below.

The experiment was repeated substituting secondary butylglycine (SBG) for PA. The experiment was repeated using equimolar quantities of some methylpiperazines. The results of these tests are shown in Table I.

1 TABLE I 2 C02 SCRUBBING BY TRIAMINO PIPERAZINE PROMOTED K2CO3 SOLUTIONS

3 Capacity Time (Min:Sec) to Absorb: 4 Amine Amino Acid (Liters) 10 Liters 15 Liters 20 Liters Cq3 BY 5 N(CH2)3NH2 PA(1 30.5 0:59 1:35 2:35 CH3 C H, 3 BC#N(CH2)3NH2 6 sBG(23 0:45 1:23 2:16 Cr3 7 HNN(CH2)3NH2 pA(1 27.8 0:59 1:46 2:55 8 (comparative) 9 CH3NN(CH2)3NH2 PA(1 26.0 1:40 2:48 4::23 10 (comparative) 11 1) PA is pipecolinic acid 12 2) SBG is N-sec. butylglycine The results in Table I show that 1-(3-amino-propyl)-2,5-dimethyl piperazine (APDP) in combination with amino acid is more effective than as a promoter for hot carbonate scrubbing related piperazines in terms of capacity and rates of absorption.

Example 3 Stability Scrubbing solutions containing 1-(3-amino-propyl)-2,5-dimethylpiperazine (APDP) were subjected to severe aging experiments at 1200C and 1000 hours under CO2 in sealed steel bombs. The solutions were desorbed and retested in the batch absorber.

A mixture of 80.4g APDP, 31g PA, 24g K2S, 391g KHCO2, 554g H2O was heated at 1200C for 1000 hours.

The solution refluxed and a 765g sample absorbed, desorbed, and reabsorbed CO2.

The experiment was repeated with sulfur being present.

TABLE II 1,000 Hour (1200C) Aging Experiment Capacity Time rMin:Sec) to Reabsorb: Amine Amino Acid Sulfur (Liters) 10 liters 15 liters 20 Liters APDP" PA2 Present 29.7 1:02 1:45 2:45 APDP PA None 27.2 1:10 2:07 3:40 APDP SBG2) Present 28.5 1:02 1:52 3:10 APDP SBG None 28.2 1:04 1:52 3:02 I'APDP is 1-(3-aminopropyl)-2,5-dimethylpiperazine 2'PA is pipecolinic acid 3'SBG is N-sec. butylglycine Table li shows that APDP is stable and sulfur tolerant.

Claims (10)

1. 1-(3-aminopropyl)-2,5-dimethyl-piperazine (APDP).

2. An aqueous acid gas scrubbing composition comprising: (a) 10 to about 40% by weight of an alkali metal salt or hydroxide, (b) 2 to about 20% by weight of the N-aminoalkylpiperazine claimed in claim 1 and (c) the balance, water.

3. A composition according to claim 2 wherein said alkali metal salt is potassium carbonate.

4. A composition according to claim 3 comprising: (a) 20 to 30% by weight of potassium carbonate, (b) 5 to about 15% by weight of 1-(3-aminopropyl)-2,5-dimethyl-piperazine and (c) the balance, water.

5. A composition according to any one of claims 2 to 4 which additionally contains 2 to 20% by weight of an amino acid having 4 to 8 carbon atoms per molecule.

6. A composition according to claim 5 which contains 2 to 20% by weight of N-secondary butyl glycine.

7. A composition according to any one of claims 2 to 6 wherein the composition additionally includes an antifoaming agent, an antioxidant and a corrosion inhibitor.

8. A process for the removal of CO2 from a gaseous stream containing CO2 according to claim 1 substantially as hereinbefore described with reference to Example 2.

9. Carbon dioxide-free gaseous streams obtained by the process according to claim 23.

10. An aqueous acid gas scrubbing composition according to claim 2 substantially as hereinbefore described with reference to Example 2.