SECONDARY AND TERTIARY AMINO ALCOHOLS

Abstract: A novel class of secondary and tertiary amino alcohols are prepared which are severely sterically hindered amino alco­ hols, e.g. secondary amino compounds like: or tertiary amino compounds like; These compounds are useful, for example, in absorbent solutions for removing hydrogen sulfide from gaseous streams and are particularly useful for selective removal of hydrogen sulfide from mixtures which also contain carbon dioxide.

Description: SECONDARY AND TERTIARY AMINO ALCOHOLS The present invention relates to a class of secondary and tertiary amino alcohols and the processes for their preparation. These compounds are useful, for example, in the removal of hydrogen sulfide from normally gaseous streams, including selective removal from such streams which also contain carbon dioxide. The specific class of severely sterically hindered secondary and tertiary amino alcohols of the present invention are defined by the general formula: EMI1.1 wherein R3, R4 and R5 are each independently hydrogen or alkyl or hydroxyalkyl radicals having 1 to 4 carbon atoms, x and y are each 2, 3 or 4, and wherein if the alcohol is a secondary aminoether alcohol, R1 has the formula EMI1.2 where R and R' are each independently alkyl or hydroxyalkyl radicals having 1-4 carbon atoms and R" is hydrogen or an alkyl or hydroxyalkyl radical having 1 to 4 carbon atoms, R2 and R6 are hydrogen, and z is 1, 2, 3 or 4, with the proviso that when R" is hydrogen at least one of R3 and R4 bonded to the carbon atom which is directly bonded to the nitrogen atom is an alkyl or hydroxyalkyl radical having 1 to 4 carbon atoms, and wherein if the alcohol is a tertiary amino alcohol, R1 and R2 are each independently alkyl radicals having 1 to 8 carbon atoms or hydroxyalkyl radicals having 2 to 8 carbon atoms or cycloalkyl or hydroxycycloalkyl radicals having 3 to 8 carbon atoms, R6 is hydrogen or an alkyl or hydroxyalkyl radical having 1 to 4 carbon atoms and z is zero, 1, 2, 3 or 4, with the proviso that if the carbon atom of R1 which is directly bonded to the nitrogen atom is secondary and the carbon atom of R2 which is directly bonded to the nitrogen atom is primary, at least one of R3 and R4 is an alkyl or hydroxyalkyl radical. The severely sterically hindered secondary aminoether alcohols can thus generally be defined by the formula: EMI2.1 wherein R, R', R", R3, Rq; x, y and z are defined above for the secondary aminoether alcohols, and the severely sterically hindered tertiary amino alcohols can be defined generally by the formula: EMI2.2 wherein R1,- R2, R3, R4, R5, Rg, x, y and z are defined above for the tertiary aminoether alcohols. It is noted that the tertiary amino alcohols may be aminoether alcohols but need not be (when z=O). These severely sterically hindered secondary and tertiary amino alcohols are found to be particularly useful in the selective'absorption of H2S from normally gaseous mixtures containing H2S and CO2. (The term "normally" refers to ambient conditions of temperature and pressure.) These amino compounds surprisingly maintain their high selectivity for H2S over CO2 at high H2S and C02 loading levels. In the drawings : Fig. 1 is a diagrammatic flow sheet illustrating an experimental sparged absorber unit for use in rapid determination of the selectivity of the amino compound for selective removal of H2S from gaseous streams containing H2S and C02. Fig. 2 graphically illustrates the selectivity for H2S plotted against the H2S and CO2 loading for 3 M solutions of tertiarybutylaminoethoxyethanol (TBEE) as compared to tertiarybutylaminoethanol (TBE) and methyldiethanolamine (MDEA). Fig. 3 graphically illustrates the selectivity for H2S plotted against the H2S and CO2 loading for 3 M solutions of tertiarybutylaminoethoxyethanol (TBEE) as compared to methyldiethanolamine (MDEA), secondarybutylaminoethoxyethanol (SBEE) and isopropylaminoethoxyethanol (IPEE). Fig. 4 graphically illustrates the selectivity for H2S plotted against the H2S and CO2 loading for 3 M solutions of N-methyl-N-tertiarybutylaminoethoxyethanol (MTBEE) and 2-(N-isopropyl-N-methylamino) propoxyethanol (2-IMPE) as compared to methyldiethanolamine (MDEA) Fig. 5 graphically illustrates the selectivity for H2S plotted against the H2S and CO2 loading for a 1 M solution of N-methyl-N-tertiarybutylaminoethoxyethanol (MTBEE) as compared against a 1.6 M solution of methyldiethanolamine (MDEA). Fig. 6 graphically illustrates the selectivity for H2S plotted against the H2S and CO2 loading for a 3 M solution of N-methyl-N-tertiarybutylaminoethoxyethanol (MTBEE) as compared to N-tertiarybutyldiethanolamine (TBDEA). Fig. 7 is a diagrammatic flow sheet illustrating an absorption-regeneration unit for selective removal of H2S from gaseous streams containing H2S and C02. Fig. 8 graphically illustrates the H2S leak rate plotted against H2S loading in moles/mole amine for a 1.5 M solution of tertiarybutylaminoethoxyethanol (TBEE) compared against a 3 M solution of methyldiethanolamine (MDEA) using the unit of Fig. 7. The secondary aminoether alcohols of the invention are preferably characterized by the following general formula: EMI4.1 where: R = R' = R" = CH3; R3 = R4 = R5 = H; R = R' = RR = CH3; R3 = H or CH3; R4 = R5 = H; R = R' = R" = R5 = CH3; R3 = R4 = H; R = R' = Rt = CH3CH2; R3 = R4 = R5 = H; or R 6 R' 6 R" = H, CH3, CH39H2,¯R3 6 R4 6 R5 = H, CR3, cH3CR2; R = R#R''=H,CH3; R3 = CH3; R4 - R5 H and R = R'#R"=CR3, CH3CH2; R3 = R4 = R5 = H and where x = 2-3. Representative secondary amino compounds defined by the general formulae above include: EMI4.2 Tertiarybutylaminoethoxyethanol EMI4.3 2¯(2¯tertiarybutylamino) propoxyethanol EMI4.4 Tertiaryamylaminoethoxyethanol EMI5.1 (l-methyl-l-ethylpropylamino)ethoxyethanol Among these, the preferred secondary aminoether alcohols herein are tertiarybutylaminoethoxyethanol, 2-(2-tertiarybutylamino)propoxyethanol and 2-(2-isopropylamino)propoxyethanol. Most preferred is tertiarybutylaminoethoxyethanol (TBEE). These novel secondary aminoether alcohols may be prepared by a process comprising reacting, at an elevated temperature, and preferably in the presence of a solvent, a secondary or tertiary alkyl primary amine with an ether alcohol containing a carbonyl functionality in the presence of a source of hydrogen, or with a haloalkoxyalkanol. Typical secondary or tertiary alkyl primary amines useful in the process for preparing secondary aminoether alcohols include isopropylamine, tertiarybutylamine, l-methyl-l-ethylpropylamine, and tertiaryamylamine. Typical haloalkoxyalkanols include 2-chloroethoxyethanol and the like. Typical ether alcohols containing a carbonyl functionality (such as a ketone or aldehyde group) include 6-hydroxy-3-oxa-2-hexanone. Typical solvents include lower alkanols, ether alkanols and acyclic and cyclic ethers and the secondary alkyl primary amine reagent. Examples of typical solvents include hydroxycontaining compounds, such as water, methanol, ethanol, propanol, ethylene glycol monomethylether, tetrahydrofuran, isopropylamine, tertiarybutylamine, tertiaryamylamine and the like. Preferably, the solvent is a polar compound. The preferred solvent are ethanol and ethylene glycol monomethlether. The elevated temperatures which may be employed for the above reaction will depend on the particular type of reaction being carried out and on the particular amine employed and the pressures utilized. For the non-catalytic process wherein the amine is reacted with a haloalkoxyalkanol, the reaction temperatures employed are preferably at least 800C and more preferably at least 1000C at atmospheric pressure. When elevated pressures are employed, e.g., autogenous pressure in an autoclave, this reaction is preferably carried out at temperatures of at least about 1l00C and preferably less than about 2500C, and more preferably from 1250C to about 2000C. Suitable autogenous pressures range from 3.5 kg/cm2 to about 70.3 kg/cm2, more preferably 10.5 to about 28.1 kg/cm2. Such autogenous pressure conditions are particularly preferred in the synthesis of tertiarybutylaminoethoxyethanol. For the process wherein the amine is reacted with an ether alcohol containing a carbonyl functionality in the presence of a source of hydrogen, the temperatures employed are preferably at least 800C, more preferably 90 to l200C. The latter reaction process may be carried out by a catalytic reductive amination in the presence of hydrogen gas, preferably at a pressure of 70.3 to 98.4 kg/cm2. Alternatively, the latter reaction process may be carried out by a non-catalytic reductive amination wherein the hydrogen source is a metal hydride. In all types of reactions for preparing the secondary aminoether alcohols, the reaction mixture preferably contains a molar excess of the amine, preferably at least a 2:1 molar excess. The tertiary aminoether alcohols of this invention are preferably characterized by the following formula: EMI6.1 wherein R1 is a tertiary butyl, tertiary amyl or hydroxy tertiary butyl radical, x and y are each 2-4 and z is 0 or 1. Preferred tertiary amino compounds defined by the general formula above include: EMI7.1 N-methyl-N-tertiarybutylaminoethoxyethanol EMI7.2 2-(N-isopropyl-N-methylamino) propoxyethanol EMI7.3 3-aza-2,2,3-trimethyl-1,6-hexanediol Among these tertiary aminoether alcohols, the most preferred compound is N-me thyl-N-tertiarybutyl amino- ethoxyethanol. These tertiary amino alcohols may be prepared in a catalytic process by reacting the corresponding severely sterically hindered secondary amino alcohol of the formula: EMI7.4 wherein R1, R3, R4, Rs, R6, x, y and z are defined as described above in the general formula for tertiary amino alcohols with an aldehyde of the formula R2CHO wherein R2 is an alkyl radical having 1 to 8 carbon atoms or a hydroxyalkyl radical having 2 to 8 carbon atoms or a cycloalkyl or hydroxycycloalkyl radical having 3 to 8 carbon atoms, with the proviso that if the carbon atom of R1 which is directly bonded to the nitrogen atom is secondary and the carbon atom of R2 which is directly bonded to the carbon atom of CHO is primary, at least one of R3 or R4 is an alkyl or hydroxyalkyl radical. The reaction takes place at elevated temperatures in the presence of hydrogen gas under hydrogenation conditions or in the presence of an organic and inorganic acid such as formic acid and hydrochloric acid. Hydrogenation conditions may involve temperatures of, e.g., about 60-100 C and pressures of up to, e.g., 1000 psi or more and include the presence of a Pd/C catalyst and an appropriate solvent for the reaction such as, e.g., methanol. The product is typically recovered by separation of the reaction mixture and distillation of the separated portion. The amino compounds herein are found to be particularly useful in removal of H2S from normally gaseous mixtures containing the same, and are found to be superior to amino compounds used in the past, particularly methyldiethanolamine (MDEA) and diethylmonoethanolamine (DEAE), in terms of both selectivity and capacity for maintaining selectivity over a broad loading range, when used for selective absorption of H2S from mixtures containing H2S and CO2. Typically, a gaseous stream to be treated having a 1:10 mole ratio of H2S:CO2 from an apparatus for thermal conversion of heavy residual oil, or a Lurgi coal gas having a mole ratio of H2S:CO2 of less than 1:10 will yield an acid gas having a mole ratio of H2S:C02 of about 1:1 after contacting the stream with an absorbent solution of the amino compound herein under conditions whereby H2S is selectively absorbed from the stream. 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. All PKa values were measured at 20 C. Summation -Es is the Taftas steric hindrance constant measuring the degree of steric hindrance of the secondary aminoether alcohols as calculated from the values given for primary amines in Table V from the article by D. F. DeTar, Journal of Organic Chemistry, 45, 5174 (1980). It has been found that for use in selective H2S removal the secondary aminoether alcohols generally have a summation -Es value greater than 1.75. EXAMPLE 1 Preparation of tertiarybutylaminoethoxyethanol (TBEE) A total of 736 g of tertiarybutylamine and 500 g of 2-chloroethoxyethanol was placed in 2 liters of ethanol and heated at 600C overnight. The temperature was then gradually raised to 800C and held for 5 days. The reaction mixture was cooled to 500C and then treated with 247g of KOH. After 1 hour at refluxing the reaction mixture was cooled, filtered, vacuum stripped and distilled. A total of 491 g of the distilled product, which calculates as a 75.6% yield, was obtained having a boiling point (b.p.) of 1170C at 10 mm. Analysis calculated for CgHlgNO2: %C 59.63; %H, 11.80, %N, 8.70; found: %C, 58.99, %H, 11.82; %N, 8.38. EXAMPLE 2 Preparation of tertiarybutylaminoethoxyethanol (TBEE) at higher temperatures A solution of 41.76 g of tertiarybutylamine and 28.66 g of 2-chloroethoxyethanol in 115 ml of ethanol was charged to a 300 ml metal autoclave and heated under autogenous pressure at l500C for 3 hrs. The contents of the cooled reactor were treated with KOH and the product was isolated as described in Example 1. The yield of product was 77%, based on 28.65 g of recovered product. Thus, it can be seen that the high temperature has a dramatic effect on the rate of producing the severely sterically hindered secondary aminoether alcohol. EXAMPLE 3 Preparation of tertiarybutylaminoethoxyethanol (TBEE) A solution of 45.63 g (0.625 mole) of tertiarybutylamine and 31 g (0.25 mole) of 2-chloroethoxyethanol in 100 ml of methanol was charged to a 300 ml steel autoclave and heated under autogenous pressure for 1 hour at 1500C. The reactor was cooled and the contents removed. To the homogeneous solution was added 11 g (0.275 mole) of NaOH pellets and the reaction mixture was refluxed for 0.5-1 hour, cooled, filtered, vacuum stripped, and distilled. The yield was 31.4 g (78%). EXAMPLE 4 Preparation of tertiarybutylaminoethoxyethanol (TBEE) The following example demonstrates the use of water as the polar solvent in preparing TBEE. Tertiarybutylamine, 0.625 mole, 0.25 mole of 2-chloroethoxyethanol and 30 ml of water were heated for 1 hr. at l500C in a steel autoclave. The maximum pressure was about 6.0 kg/cm2. The reactor was cooled and the contents removed. To the homogeneous solution was added 11 g of NaOH and the reaction heated for one-half hour. The reaction was cooled, filtered, and distilled. Bp l21-30C (15 mm). Yield 33.19 g (82.5%). EXAMPLE 5 A solution of tertiarybutylamine, 2-chloroethoxyethanol, and solvent in the ratio detailed in the previous example was charged to a pressure reactor and heated at the temperature and times indicated in Table 1. The solvents employed are also shown in Table 1. The extent of TBEE formation was determined by gas chromotographic analysis. Table 1 Solvent Effects on Rate of TBEE Formation Solvent BuOH EtOH MeOH H2O Temperature/Time % TBEE 4.0 6.6 5.3 19.6 1000/15 mins. % TBEE 38.0 41.8 44.7 76.5 1250/30 mins. As shown in Table 1, water, as the polar solvent, provides a rate enhancement in the production of TBEE. Also, the use of water reduces solvent costs to a negligible amount and eliminates the need for solvent recovery and enables one to enjoy low solvent/reactant concentra tions. Thus, water, as the polar solvent, provides significant technical and economic advantages in producing hindered amines such as TBEE. EXAMPLE 6 Preparation of 2-(2-isopropylamino)propoxyethanol A total of 5.8 moles of isopropylamine, 134 g of 6-hydroxy-3-oxa-2-hexanone and 4 g of 10% Pd/C in 150 ml of ethanol was charged to an autoclave, pressured to 78.0 kg/cm2 with hydrogen and heated at 1000C for 6 hours. The contents of the cooled autoclave were filtered and distilled. Yield, 169g, b.p. 1190C at 20 mm. Analysis calc. for C8H19N02: %C, 59.63; ZH, 11.80; ZN, 8.70; found: %C, 59.07, %H, 11.89; %N, 8.11. EXAMPLE 7 Preparation of 2-(2-tertiarybutylamino)propoxyethanol A total of 314 g of tertiarybutylamine, 110 g of 6-hydroxy-4-oxa-2-hexanone and 3 g of 10% Pd/C in 200 ml of methanol was reacted under 90 kg/cm2 of hydrogen at l000C for 7 hrs. Isolation of product as described in Example 3 yielded 20.8 g of the titled amine, which had a b.p. of 1220C at 19 mm. Analysis calcd. for C9H21N02: ZN, 8.00; found: ZN, 7.28. EXAMPLE 8 Preparation of (l-methyl-l-ethylpropylamino) ethoxyethanol A solution of 124.7 g of l-methyl-l-ethylpropylamine and 76.9 g of 2-chloroethoxyethanol in 300 ml of ethylene glycol monomethylether was refluxed overnight. The reaction mixture was treated with a stoichiometric excess of KOH and refluxed for one hour, filtered, and distilled. The product had a b.p. of l530C (2mm). Analysis calculated for C10H23NO2: %N, 7.4; found: %N, 7.15. EXAMPLE 9 Preparation of tertiaryamylaminoethoxyethanol In the manner described in Example 8, 129.7 g of tertiaryamylamine and 92.2 g of 2-chloroethoxyethanol yielded 86.5 g of tertiaryamylaminoethoxyethanol having a b.p. of l240C (10 mm). Comparison Preparation of secondarybutylaminoethoxyethanol (SBEE) (for comparison tests in H2S removal) In the manner described in Example 7, 131 g of secondarybutylamine and 93 g of 2-chloroethoxyethanol yielded 73 g of secondarybutylaminoethoxyethanol having a b.p. of 1200C (10 mm). Analysis calculated for C8H19NO2: %N, 8.70; found: %N, 8.45. EXAMPLE 10 Preparation of N-methyl-N-tertiarybutylaminoethoxyethanol (MTBEE) A total of 145 g of tertiarybutylaminoethoxyethanol, 108 g of 37% aqueous formaldehyde, 10 g of 10% Pd/C, and 1 liter of methanol wvs charged to an autoclave, pressured up to 70.3 kg/cm2 with H2 and heated at 800C for 8 hours. Filtration and distillation of the reaction mixture yielded 128 g of N-methyl-N-tertiarybutylaminoethoxyethanol with b.p. of 1280C at 23 mm. EXAMPLE 11 Preparation of 2-(N-isopropyl-N-methylamino)propoxyethanol (2-IMPE) A total of 155 g of 2-(isopropylamino)propoxyethanol, 122 g of 37% aqueous formaldehyde, 5 g of 10% Pd/C and 1 liter of methanol was charged to an autoclave, pressured to 70.3 kg/cm2 with H2 and heated at 800C for 3 hours. Filtration and distillation of the reaction mixture yielded 159 g of 2-(N-isopropyl-N-methylamino)propoxyethanol with b.p. of l250C at 20 mm. EXAMPLE 12 Preparation of 3-aza-2,2,3-trimethyl-1,6-hexanediol A solution of 60 g of 3-aza-2,2-dimethyl-l,6- hexanediol, 53.5 g of formic acid and 36.3 g of 37% aqueous formaldehyde was refluxed for 40 hours. A total of 20 ml of concentrated hydrochloric acid was added and the reaction mixture was distilled until the overhead temperature was 1100C. Water, in an amount of 40 ml, was added to the distillation residue and made strongly alkaline with KOH. The organic phase was separated and distilled to yield 39.9 g of 3-aza-2,2,3-trimethyl-1,6hexanediol with a b.p. of 1030C at 0.35 mm, a summation E5 value of 2.20 and a PKa of 9.35. EXAMPLE 13 Selective H2S removal from a mixture containing H2S and CO2 Fig. 1 illustrates the sparged absorber unit, operated on a semi-batch mode, used to evaluate the selectivity for H2S removal of the amino compounds of the invention herein. A gas mixture comprised of 10% CO2, 1% H2S and 89% N2, expressed as volume percent, respectively, was passed from a gas cylinder (not shown) through line 30 to a meter 31 measuring the rate at which the gas is fed to the absorber. For all examples this rate was 3.6 liters per minute. The gas was then passed through line 32 to a gas chromatography column (not shown) continuously monitoring the composition of the inlet gas and through lines 33 and 34 to a sparged absorber unit 35, which is a cylindrical glass tube 45 cm high and 3.1 cm in diameter charged with 100 ml of the absorbent amine solution 36. The gas was passed through the solution at a solution temperature of 400C, and 10-ml samples of the solution were periodically removed from the bottom of the absorber unit through lines 34 and 37 to be analyzed for H2S and CO2 content. The H2S content in the liquid sample was determined by titration with silver nitrate. The C02 content of the liquid sample was then analyzed by acidifying the sample with an aqueous solution of 10% HC1 and measuring the evolved CO2 by weight gain on NaOHcoated asbestos. While the solution was being periodically withdrawn from the bottom of the absorber unit, the gas mixture was removed from the top thereof via line 38 to a trap 39 which served to scrub out any H2S in the outlet gas. The resulting gas could optionally then be passed via lines 40 and 41 for final disposal or via line 42 to a gas chromatography column (not shown) for periodic evalua tion of the composition of the outlet gas to check for system leaks. For purposes of the examples, the H2S and C02 contents of the inlet gas phase were measured and the H2S and CO2 contents of the liquid phase were determined as described above. These data were used to calculate selectivity values of the amine as defined above, which were plotted as a function of the loading of the absorbent solution with H2S and CO2, in units of moles acid gas per mole of the amino compound. The above procedure was employed using as the absorbent solution aqueous 3M solutions of tertiarybutylaminoethoxyethanol (TBEE) (PKa = 10.3, summation E5 = 2.10) , tertiarybutylaminoethanol (TBE) (comparison) (PKa = 10.2, b.p. = 900C at 25 mm), and methyldiethanolamine (MDEA) (comparison - a conventionally used amine for selective H2S removal) (summation -Es = 0.79) . The selectivity plot for each amine solution is shown in Fig. 2. As can be seen from Fig. 2, TBEE is superior to both TBE and especially MDEA in terms of H2S selectivity, particularly at high H2S and CO2 loadings. It is noteworthy that TBEE is superior to TBE even though both compounds have a PKa of about 10.3. EXAMPLE 14 The procedure of Example 13 was repeated using as the absorbent solution aqueous 3M solutions of tertiarybutylaminoethoxyethanol (TBEE), secondarybutylaminoethoxyethanol (SBEE) (comparison) (summation -Es = 1.32 as prepared in Comparison Preparation 2) , isopropylaminoethoxyethanol (IPEE) (comparison) (summation -Es = 1.29) and methyldiethanolamine (MDEA) (comparison). The selectivity plot for each amine solution is shown in Fig. 3. The plots clearly show that TBEE is far superior to SBEE, IPEE and MDEA in terms of H2S selectivity. The plots taken together with the summation (Taft) E5 values for the compounds tested also indicate that the severe steric hindrance of TBEE (resulting from the additional carbon atoms attached to the carbon atom directly attached to the nitrogen atom) has a profound effect on the selective H2S absorption properties of the amino compound. EXAMPLE 15 The procedure of Example 13 was repeated using as the absorbent solution aqueous 3M solutions of N-methyl N-tertiarybutylaminoethoxyethanol (MTBEE) (summation -Es = 2.17, PKa = 10.15), 2-(N-isopropyl-N-methylamino)pro- poxyethanol (2-IMPE) (summation -Es = 1.93, PKa = 9.55), and methyldiethanolamine (MDEA) (comparison) using the same gas mixture and conditions. From the plots of selectivity for H2S removal and loading shown in Fig. 4 it can be seen that MTBEE and 2-IMPE have a higher H2S selectivity than MDEA. EXAMPLE 16 The procedure of Example 13 was repeated except that an aqueous 1M solution of N-methyl-N-tertiarybutylaminoethoxyethanol (MTBEE) was used as absorbent solution along with an aqueous 1.6M solution of methyldiethanolamine (MDEA) as comparison using the same gas mixture and conditions. From the plots of selectivity for H2S removal shown in Fig. 5, it can be seen that the capacity for H2S of MTBEE increases with decreasing solution concentration, whereas the capacity for H2S of MDEA decreases with decreasing concentration. EXAMPLE 17 The procedure of Example 13 was repeated except that an aqueous 3M solution of N-methyl-N-tertiarybutylaminoethoxyethanol (MTBEE) was compared with N-tertiarybutyldiethanolamine (TBDEA) (summation E5 = 2.46, PKa = 8.2) as comparison using the same gas mixture and conditions. From the plots of selectivity for H2S removal shown in Fig. 6, it can be seen that MTBEE has a higher H2S selectivity than TBDEA. The data in Figs. 2, 4 and 5 also show that the amino compounds of the present invention have very high capacity for both H2S and CO2 compared to methyldiethanol amine (MDEA) in addition to high H2S selectivities. It will be apparent from an inspection of the data in Fig. 2 that if the absorption process is conducted under conditions such that the amino compound has a long contact time with the gases to be absorbed, the selectivity for H2S decreases, but the overall capacity for both COS and H2S remains rather high. Therefore, one may, in some instances, wish to carry out a "non-selective" acid gas absorption process to take advantage of the large absorption capacity of the amino compounds of the invention. Such °non-selectiveN processes are particularly useful in scrubbing natural gases which contain relatively high levels of H2S and low to nil levels of CO2. As such, the amino compounds of the present invention may replace some or all of monoethanolamine (MEA) or diethanolamine (DEA) commonly used for such scrubbing processes. The amino compounds herein are typically capable of reducing the H2S in gaseous mixtures to a relatively low level, e.g., less than about 200 ppm and typically have a relatively high capacity for H2S, e.g., greater than about 0.5 mole of H2S per mole of amine. The amino compounds are characterized as having a "kinetic selectivity" for H2S, i.e., a faster reaction rate for H2S than for CO2 at absorption conditions. In addition, they have a higher capacity for H2S at equivalent kinetic selectivity for H2S over CO2. This higher capacity results in the economic advantage of lower steam requirements during regeneration. EXAMPLE 18 Continuous Process for Selective H2S Removal This example demonstrates a comparison of the severely sterically hindered secondary aminoether alcohol, tertiarybutylaminoethoxyethanol (TBEE) , with methyldiethanolamine (MDEA) using a unit such as that shown in Fig. 7. An aqueous 1.5M solution of tertiarybutylamino ethoxyethanol (TBEE) was charged via pipe 5 into the upper portion of a gas-liquid countercurrent absorption column 2 having a lower section 3 and an upper section 4 and being segregated by three packed beds. The gas to be purified was a synthetic mixture containing 1% H2S, 11% CO2 and 88% N2, expressed as volume percent, respectively. The gas was introduced through line 1 into the lower portion of column 2 at a gas flow rate of 67 standard cubic feet per minute. The absorber pressure was adjusted to 31 psia. The gas freed from H2S -left through pipe 6 and was analyzed. The aqueous amine solution containing H2S and CO2 was flowed toward the lower portion of the absorber, from which it was discharged through pipe 7. The solution was then passed via pump 8 through a simulated heat exchanger and cooler 9 disposed in pipe 7, which allowed the hot solution from the regenerator 12 to equilibrate in temperature with the cooler solution from the absorber column 2. The hot rich solution was then entered, via pipe 7, to a flash drum 10 equipped with a line (not shown) which vents to line 13 and then introduced by pipe 11 into the upper portion of the regenerator 12, which is equipped with several plates and effects desorption of the H2S gas. The pressure of the regenerator was set at 2.3 kg/cm2. The H2S gas was passed through a pipe 13 into a condenser 14 wherein cooling and condensation of water and amine solution from the gas occurred. The gas was then entered into a separator 15 where further condensation took place. The condensed solution was returned through pipe 16 to the upper portion of the regenerator 12. The gas remaining from the condensation which contains H2S and some CO2 may be removed through pipe 17 for final disposal (e.g., to a vent or incinerator or to an apparatus which converts the H2S to sulfur such as a Claus unit or a Stretford conversion unit (not shown)). The solution liberated from the gas which it contained was flowed downward through the regenerator 12 and left through pipe 18 at the bottom of the regen erator for transfer to a reboiler 19. Reboiler 19, equipped with a steam injection pipe 20 and a condensate exit pipe (not shown), vaporized a portion of this solution to drive additional H2S therefrom. The H2S driven off was returned via pipe 21 to the lower section of the regenerator 12 and left . through pipe 13, for entry into the condensation stages of gas treatment. The solution remaining in the reboiler 19 was drawn through pipe 22, cooled in heat exchanger 9, and introduced via the action of pump 23 through pipe 5 into absorber 2. The flow rate was slowly adjusted downward until the H2S leak rate showed a dramatic increase. The experiment was repeated using in place of tertiarybutylaminoethoxyethanol (TBEE) , an aqueous 3M solution of methyldiethanolamine (MDEA) as comparison. The results of both experiments were plotted wherein the H2S leak rate, in parts per million by volume (Vppm), was plotted against H2S loading in mols/mol amine. The results are shown in Fig. 8. These results show that tertiarybutylaminoethoxyethanol gives far greater cleanup, even at higher H2S loadings, in a continuous selective H2S removal process than methyldiethanolamine (MDEA) In summary, this invention is seen to provide a special class of amino compounds characterized as being severely sterically hindered acyclic secondary and tertiary amino alcohols.

Claims: CLAIMS: 1. A secondary or tertiary amino alcohol characterized by the general formula: EMI19.1 wherein R3, R4 and R5 are each independently hydrogen or alkyl or hydroxyalkyl radicals having 1 to 4 carbon atoms, x and y are each 2, 3 or 4, and wherein if the amino alcohol is a secondary aminoether alcohol, R1 has the formula EMI19.2 where R and R' are each independently alkyl or hydroxyalkyl radicals having 1-4 carbon atoms and R" is hydrogen or an alkyl or hydroxyalkyl radical having 1 to 4 carbon atoms, R2 and R6 are hydrogen, and z is 1, 2, 3 or 4 with the proviso that when R" is hydrogen at least one of R3 and R4 bonded to the carbon atom which is directly bonded to the nitrogen atom is an alkyl or hydroxyalkyl radical having 1 to 4 carbon atoms; and wherein if the amino alcohol is a tertiary amino alcohol, R1 and R2 are each independently alkyl radicals having 1 to 8 carbon atoms or hydroxyalkyl radicals having 2 to 8 carbon atoms or cycloalkyl or hydroxycycloalkyl radicals having 3 to 8 carbon atoms, R6 is hydrogen or an alkyl or hydroxyalkyl radical having 1 to 4 carbon atoms and z is zero, 1, 2, 3 or 4, with the proviso that if the carbon atom of R1 which is directly bonded to the nitrogen atom is secondary and the carbon atom of R2 which is directly bonded to the nitrogen atom is primary, at least one of R3 and R4 is an alkyl or hydroxyalkyl radical. 2. A secondary aminoether alcohol according to claim 1 having the general formula: EMI20.1 wherein R, R', R", R3, R4, Rs, x, y and z are as defined for secondary aminoether alcohols in claim 1. 3. A secondary aminoether alcohol according to claim 2 which is 2-(2-tertiarybutyl amino) propoxyethanol or 2-(2-isopropylamino) propoxyethanol. 4. A secondary aminoether alcohol according to claim 2 which is tertiarybutylamino ethoxyethanol. 5. A process for preparing a secondary amino ether alcohol according to any one of claims 2-4 .which comprises reacting, at an elevated temperature, a secon dary or tertiary alkyl primary amine with an ether alcohol containing a carbonyl functionality in the presence of a source of hydrogen, or with a haloalkoxyalkanol. 6. A process according to claim 5 which comprises reacting tertiarybutylamine with 2-chloro ethoxyethanol in the presence of a solvent at a tempera ture of at least ll00C at autogenous pressure to produce tertiarybutylaminoethoxyethanol. 7. A tertiary amino alcohol according to claim 1 having the general formula: EMI21.1 wherein R1, R2, R3, R4, Rs, R6, x, y and z are as defined for tertiary amino alcohols in claim 1. 8. A tertiary amino alcohol according to claim 7 which is - 2- (N-isopropyl-N-methyl- amino) propoxyethanol or 3-aza-2,2,3-trimethyl-l,6-hexa- nediol. 9. A tertiary amino alcohol according to claim 7 which is N-methyl-N-tertiarybutylaminoethoxyethanol. 10. A process for preparing a tertiary amino alcohol according to any one of claims 7-9 characterized by reacting a compound of the following formula: EMI21.2 with an aldehyde of the formula R2CHO at elevated temperatures in the presence of hydrogen gas under hydrogenation conditions or in the presence of an organic and inorganic acid, wherein R1 and R2 are each independently alkyl radicals having 1 to 8 carbon atoms or hydroxyalkyl radicals having 2 to 8 carbon atoms or cycloalkyl or hydroxycycloalkyl radicals having 3 to 8 carbon atoms, R3, R4, R5 and R6 are each independently hydrogen or C1-C4 alkyl or hydroxyalkyl radicals, with the proviso that if the carbon atom of R1 which is directly bonded to the nitrogen atom is secondary and the carbon atom of R2 which is directly bonded to the carbon atom of CHO is primary, at least one of R3 or R4 is an alkyl or hydroxy alkyl radical, x and y are each positive integers independently ranging from 2 to 4, and z is either zero or a positive integer ranging from 1 to 4.

Inventors: SARTORI, GUIDO, STOGRYN, EUGENE LEO
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1983
Main classification: C07C93
IPC codes: B01D53