MXPA01003346A - Composition and process for removal of acid gases - Google Patents

Abstract

Aqueous compositions comprising a mixture of a tertiary alkanolamine and a primary alkanolamine of the formula (I):R-CH(NH2)-CH2-OH, or mixtures thereof wherein R is H, or an alkyl group having from 1 to 8 carbon atoms are effective in the removal of acidic gases from a fluid stream containing same and show superior degradation properties as well as unexpectedly low degradation, corrosivity and metals solubility properties.

Description

COMPOSITION AND PROCESS TO REMOVE ACID GAS This invention relates to a composition and method for removing acid gases such as, for example, H2S, CO2 and COS from a fluid stream containing them. The purification of fluids involves the removal of impurities from fluid streams. Various methods for fluid purification are known and practiced. These methods for fluid purification generally fall into one of the following categories: absorption in a liquid, adsorption in a solid, penetration through a membrane, chemical conversion to another compound, and condensation. The absorption purification method involves the transfer of a Component from a fluid to an absorbent liquid in which said component is soluble. If desired, the liquid containing the transferred component is subsequently stripped to regenerate the liquid. See, for example, "Gas Purification" by A. Kohl and R. Nielsen, 5th edition, Gulf Publishing, 1997; "Gas Purification" by A. Kohl and F. C. Riesenfeld, 4th edition, Gulf Publishing, 1 985; "Gas Purification" by A. Kohl and F. C. Riesenfeld, 3rd edition, Gulf Publishing, 1979; and "The Gas Conditioning Fact Book" published by The Dow Chemical of Canada, Limited, 1 962; all incorporated by reference to this. Aqueous solutions of various primary, secondary and tertiary alkanoamines have been used, such as, for example, monoethanolamine (MEA), diethanolamine (DEA), diglycolamine (DGA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), and triethanolamine (TEA) , as absorbent liquids to remove acid gases from liquid and gaseous streams. In a regeneration method, the aqueous alkanolamine solution containing acid gas is then subjected to heating to regenerate the aqueous alkanolamine solution. Primary alkanolamines such as M EA and DGA, or secondary alkanolamines such as DEA or DIPA are generally suitable for highly exhaustive removal of CO2, however, they have the disadvantage of requiring high energy expenditure for regeneration. Corrosion is also a major concern when these alkanolamines (especially primary alkanolamines, ie, M EA and DGA) are used for gas treatment applications. DuPart et al., Hydrocarbon Processing, Parts 1 and 2 March / April 1 993, examines the corrosivity of several alkanolamines. It shows that the corrosivity order for carbon steel is M EA > DEA > MDEA. Tomoe et al., Proceedings of the First Mexican Symposium on Metallic Corrosion, 1 994, March 7-1 1, Mérida, Yucatán México, reports that after one year of operation with 65 percent by weight of DGA, the carbon steel and even the stainless steel of the plant was found to is attacked vigorously. Harruff, L. G., Proceedings of The 1 998 Gas Conditioning Conference, Norman, OK, March 1 -4, p. 76-98, also reports violent foam formation for a plant that uses DGA. In this particular case, the addition of large carbon filter beds in combination with a thermal reclaimer was required to improve operations. It is also known that aqueous solutions containing about 20 weight percent or more of M EA, due to corrosivity for carbon steel, often require the addition of toxic heavy metals (ie, for example, arsenic, antimony or vanadium) to control plant corrosion at acceptable levels. Another disadvantage of using primary and secondary alkanolamines such as MEA, DEA and D IPA is that the CO2 reacts with these alkanolamines to form degradation compounds such as ureas, oxazolidinones and ethylenediamines. CJ Kim, Ind. Eng. Chem. Res. 1988, 27, and references cited therein show how DEA reacts with CO2 to form 3- (2-hydroxyethyl) -2-oxazolidinone (HEO) and N, N, N '-tris (2-hydroxyethyl) ethylene diamine (THEED). This reference also shows how DI PA reacts to form 3- (2-hydroxypropyl) -5-methyl-2-oxazolidinone (HPMO).

These degradation compounds reduce the amount of alkanolamine available to collect acid gases, increase the viscosity of the solution, and potentially increase the corrosion power of the solvent.

Tertiary alkanolamines, especially MDEA and TEA, require less energy consumption for regeneration, but since they do not react directly with CO2, they usually leave as little as a few thousand parts per million (ppm) of CO2 up to as high as a low percent of CO2 in the treated fluid stream. The tertiary alkanolamines are, however, suitable for the selective removal of H2S from a fluid containing both H2S and CO2, since the absorption rate for H2S is approximately the same for all alkanolamines. It is well known that primary or secondary alkanolamin activators can be used in combination with tertiary alkanolamines to remove CO2 from fluid streams as low as 1 00 ppm or less requiring less regeneration energy than is required using primary or secondary alkanolamines alone. . Dawodu and Meisen, Chem. Eng. Comm. , 1 996, 144, p. 1 03, demonstrate, however, that mixtures of MDEA with a primary alkanolamine (MEA) are more difficult to strip than mixtures of MDEA with secondary alkanolamine (DEA or DIPA). Holub et al., Proceedings of The 1998 Gas Conditioning Conference, Norman, OK, March 1-4, p. 146-160, discloses that MEA corrosion in plants coupled with the higher vapor component pressure of MEA reduces the practicality of using MEA as a formulation agent (see, page 147, paragraph 4). For this reason, until now, mixtures of MDEA and secondary alkanolamines are used almost exclusively to increase the capacity and reduce the corrosion concerns instead of aqueous solutions of primary or secondary alkanolamines alone. The Patents of E. U. Nos. 5,209,914 and 5,366,709 show how activators of secondary alkanolamines such as ethylmonoethanolamine (EMEA) or butylmonoethanolamine (BMEA) can be used with MDEA to achieve better CO2 removal than with M DEA alone. However, the aforementioned reference Holub et al. Discloses laboratory and plant information showing that the secondary alkanolamines methylmonoethanolamine (M MEA) and DEA have very high degradation regimes leading to corrosion and loss of capacity (see, page 1 54 , paragraphs 1 and 2). The Holub reference further describes information on mixtures of MDEA formulated with an additive that is not a primary or secondary alkanolamine (see, page 1 51, paragraphs 2 and 3) that reduce the aforementioned disadvantages of formulated mixtures of primary and secondary alkanolamines and MDEA for gas treatment applications. No data on solubility or corrosivity of additives for comparison are given. U.S. Patent No. 4,336,233 discloses that the use of a combination of piperazine (a secondary amine) and MDEA results in an improved acid gas removal. However, a particular disadvantage of piperazine is that the piperazine carbamate formed from the reaction of piperazine and CO2 is not soluble in the aqueous solution of MDEA / piperazine. Thus, the level of additive is limited to approximately only 0.8 mol / liter, which severely limits the capacity of the solvent, or requires higher flow rates to treat the same amount of fluid as those required by other MDEA / alkanolamine activator mixtures. . Canadian Patent No. 1, 091, 429 (G. Sartori et al.) Discloses the use of aqueous solutions containing primary water-soluble monoamines having a secondary carbon atom attached to the amino group in gas purification applications. The primary monoamines having a secondary carbon atom attached to the amino group specifically mentioned in this reference as suitable are 2-amino-1-propanol, 2-amino-1-butanol, 2-amino-3-methyl-1-butanol, 2-amino-1-pentanol, 2-amino-1-hexanol and 2-aminocyclohexanol. However, this reference does not provide information on degradation, metal solubility (ie, Fe, Ni and Cr solubility) or corrosion for MEA compared to the primary monoamines having a secondary carbon atom attached to the amino group that could suggest that these primary monoamines are a commercially viable option as a replacement for MEA. This, combined with the high cost of the primary monoamines having a secondary carbon atom attached to the amino group, are the most likely reasons that there are no known gas treatment plants using these primary amine solutions as alternatives to the MEA. . Furthermore, this reference does not teach or even suggest that aqueous mixtures of the primary monoamines having a secondary carbon atom attached to the amino group such as, for example, 2-amino-1-butanol (2-AB) and MDEA or other Tertiary alkanolamines will unexpectedly have low degradation, corrosivity and metal solubility compared to other MDEA mixtures known in the art. Chem. Eng. Comm. , 1996, Vol. 144, p. 103-1 1 2, "Effects of Composition on the Performance of Alkanolamine Blends for Gas Sweetening", describes the influence of composition and mixing components on some of the parameters that can be used to monitor the performance of amines mixtures for aqueous mixtures of M DEA and M EA, MD EA and DEA, and M DEA and DI PA. The 48th Annual Laurance Reid Gas Conditioning Conference, March 1 -4, 1998, p. 146-160, "Amine Degradation Chemistry in CO2 Service", describes the degradation chemistry of several ethanolamines in CO2 service. The conference promotes gas treatment solvents which are not formulated with primary or secondary ethanolamines as a solution for the loss regimes associated with the use of various ethanolamines such as M DEA, MMEA and DEA. It is evident that there is still a great need and interest in the gas purification industry for alkanolamines compositions which are aqueous mixtures of a primary and tertiary alkanolamine which will be effective in the removal of acid gases from fluid streams and which have properties of low degradation, corrosivity and solubility of metals compared to mixtures of alkanolamines known in the art. It has now been discovered that an aqueous mixture comprising a tertiary alkanolamine and a primary alkanolamine having a secondary carbon atom attached to the amino group is not only effective in removing acid gases from fluid streams but also unexpectedly has low properties. degradation, corrosivity and solubility of metals. In the context of the present invention the term "fluid stream" encompasses both a gaseous stream and a liquid stream.

In one aspect the present invention is an aqueous composition adapted for use in the removal of acid gases from a fluid stream containing them, said aqueous composition comprising a mixture of a tertiary alkanolamine and a primary alkanolamine of the formula: R-CH (NH2) -CH2-OH (I) or mixtures thereof wherein R is an alkyl group having from 1 to 8, preferably from 1 to 6, more preferably from 2 to 4, carbon atoms. In another aspect the present invention is a process for removing acid gases from a fluid stream containing them, said process comprising contacting said fluid stream containing acid gases with an aqueous composition comprising a mixture of a tertiary alkanolamine and a primary alkanolamine of the formula: R-CH (NH2) -CH2-OH (I) or mixtures thereof wherein R is an alkyl group having from 1 to 8 carbon atoms, preferably from 1 to 6, more preferably from 2 to 4, carbon atoms. The aqueous alkanolamines mixtures of the present invention have surprisingly been found to be effective in removing acid gases, particularly CO2, H2S, COS or mixtures thereof, from a fluid stream containing them and even to exhibit unexpectedly low degradation properties. , corrosivity and solubility of metals. The alkyl group having 1 to 8 carbon atoms contemplated by R in formula I can be a straight or branched chain alkyl group. Non-limiting examples of such alkyl groups are: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, heptyl, and octyl. Non-limiting examples of the primary alkanolamines of the formula I suitable for the practice of the present invention include 2-amino-1-butanol, 2-amino-propanol, 2-amino-3-methyl-1-butanol, 2-amino-2-amino- 1-pentanol, 2-amino-1-hexanol and 2-amino-1-octanol. 2-Amino-1-butanol (2-AB) is the most preferred primary alkanolamine of formula I. Any known tertiary alkanolamine is suitable for use in combination with the primary alkanolamines of the formula I in the practice of the present invention. Non-limiting examples of suitable tertiary alkanolamines include methyldiethanolamine (MDEA), dimethylethanolamine (DMEA) and triethanolamine (TEA). The tertiary alkanolamine and the primary alkanolamine of the formula I are present in the aqueous composition of the present invention in an amount effective to remove acid gases from a fluid stream. The primary alkanolamine of the formula I is typically present in an amount of from 1 to 30, preferably from 5 to 20, more preferably from 7 to 15, percent by weight based on the total weight of the aqueous mixture. The tertiary alkanolamine is generally used in an amount of from 20 to 50, preferably from 25 to 40, more preferably from 30 to 40, weight percent based on the total weight of the aqueous mixture. The optimum amount of the tertiary alkanolamine and the primary alkanolamine of the formula I will depend on the composition of the fluid stream, fluid outlet requirement, flow rate, and available energy to strip the solvent. A person of ordinary skill in the art could quickly determine the optimum amount of each of the tertiary alkanolamine and primary alkanolamine of the formula I. The process of the present invention can be carried out in any conventional equipment for the removal of acid gases from fluids and detailed procedures that are well known to a person of ordinary skill in the art. See, for example, U.S. Patent No. 1, 783,901 (Bottoms) and subsequent improvements which are known in the art. The process according to the present invention can be conveniently carried out in any suitable absorber. The large number of absorbers used for gas purification operations include packed towers, of dishes, or of dew. These absorbers are interchangeable to a considerable extent even though certain specific conditions may favor one over the other. In addition to conventional packed, or spray, towers, specialized absorption towers have been developed to meet specific process requirements. Examples of these specific towers include shock dish scrubbers and turbulent contact scrubbers. The process of the present invention can be carried out on any, packed, dish or spray towers, and may contain other peripheral equipment as necessary for optimal process operation. Such peripheral equipment may include an inlet gas separator, a treated gas fusion promoter, a solvent flashing tank, a particulate filter and a charcoal bed purifier. The rate of inlet gas flow varies depending on the size of the equipment, but is typically between 0.141863 and 2.837726 million standard cubic meters per day (MCSD). The solvent circulation regime will depend on the amine concentration, gas flow rate, gas composition, total pressure and specification of the treated fluid. The solvent circulation regime is typically between 1 9 and 19,000 liters per minute (Ipm). The internal pressure of the absorber can vary between 0 and 84.5 kg / cm2 man. depending on the type of fluid that is processed. The absorbers, strippers and peripheral equipment useful for carrying out the process of the present invention are well known in the art and are described in many publications including the aforementioned references. In the process of the present invention, a fluid containing an acid gas is contacted with an aqueous mixture comprising a tertiary alkanolamine and a primary alkanolamine of the formula I at a temperature from room temperature (about 25 ° C) to 93 ° C. The temperatures inside the stripping tower, if one is used, can vary between 82 ° C and 1 27 ° C. The pressure above the stripping agent is typically between 0 and 20 psig. Optionally, corrosion inhibitors, scale inhibitors and defoamers can be employed. The following examples are offered to illustrate, but not limit the invention. Percentages, proportions and parts are by weight unless otherwise stated.

EXAMPLE 1 AND COMPARATIVE EXAMPLES C-1 A C-5 Fe corrosivity and solubility tests were performed in an autoclave at 121 ° C for 6 days by stirring aqueous solutions (1, 000 grams) of each of DGA (5 moles), MEA (5 moles), 2-AB (5 moles), mixture of MDEA (2.5 moles) with DGA (2.5 moles), mixture of MDEA (2.5 moles) with MEA (2.5 moles) and mixture of MDEA (2.5 moles) with 2 -AB (2.5 moles) which were saturated at room temperature with CO2. In each autoclave, a custom basket containing a sample of carbon steel was placed for testing so that it allowed the test steel sample to be completely submerged in the liquid. Each sample of steel was weighed before being placed in the autoclave. After 6 days of immersion in the liquid, each sample of steel was cleaned and weighed again. The weight loss of the steel sample was attributed to the corrosivity of the liquid in which the steel sample was immersed. The results are given in Table 1 below.

Table 1 As expected from the known literature, the data in Table 1 confirm the high corrosivity of primary alkanolamines in carbon steel commonly used to purify fluid streams. It was also noted that severe stings were detected in the carbon steel sample submerged in the DGA. However, 2-AB (a primary alkanolamine not conventionally used for fluid purification applications) has surprisingly low corrosivity on carbon steel which has not been described or even suggested in Canadian Patent No. 1, 091, 429 or expected based on information in the literature showing the corrosivity of primary alkanolamines. The corrosivity in carbon steel of each of the solutions comprising a mixture of MDEA with either DGA, MEA or 2-AB was considerably lower than that of the solution of 2-AB, MEA or DGA. In addition, the solubility of Fe for the solution comprising a mixture of MDEA with 2-AB is surprisingly much lower than any other solution tested.

EXAMPLE 2 AND EXAMPLE COMPARATIVE APPLICATIONS C-6 AND C-7 Autoclave tests were performed to determine the solubility of metals at 1 21 ° C for 6 days by stirring aqueous solutions (1, 000 grams) of each of the MDEA mixture (2.5 moles) with DGA (2.5 moles), mixture of MDEA (2.5 moles) with MEA (2.5 moles), and mixture of MDEA (2.5 moles) with 2-AB (2.5 moles) which were saturated at room temperature with CO2. In each test in each autoclave a custom basket containing a sample of carbon steel, chromium or nickel was placed in a way that allowed the test steel sample to be completely submerged in the liquid. After 6 days, each solution was analyzed by inductively coupled plasma (ICP) for metal solubility. The results are given in Table 2 below.

Table 2 This information clearly shows the unexpected advantage of the aqueous composition of the present invention, ie, the solution comprising a mixture of MDEA with 2-AB, on conventionally used MDEA mixtures and either MEA or DGA.

EXAMPLE 3 AND COMPARATIVE EXAMPLES C-8 AND C-9 Autoclave degradation and corrosivity tests were performed on equimolar amine solutions using 0.050 moles of CO2 per mole of amine at 126.7 ° C. An aqueous solution (1, 100 ml) was added. ) containing MDEA (35 weight percent), and either 2-AB (15 percent by weight), EMEA (15 percent by weight), or BMEA (1-5 percent by weight) to a Parr autoclave of two liters. Then each solution was charged with CO2 such that the charged CO2 was 0.050 mol of CO2 per mol of total amine. The solution was then heated for 28 days at 126.7 ° C. After 28 days, the solutions were analyzed by gas chromatography (GC) and chromatography / gas mass spectrometry (GC / MS) to determine the amount of the additive amine (primary or secondary) remaining in the solution and for the presence of degradation / conversion products. The amount of 2-AB (two runs), EMEA, and BM EA, in the solution after 28 days was 14.8 (average), 0.6, and 0.4 percent by weight, respectively. This information shows that 30 percent by weight of EMEA and BMEA were lost by degradation in 28 days compared to less than 1.5 percent by weight of 2-AB lost by degradation (0.2 percent by weight of what is possibly a oxazolidinone or substituted ethylenediamine was detected by GC and GC / MS) for 28 days. The EMEA was converted to 3 weight percent of N, N '- (2-hydroxyethyl) ethylene diamine. The BMEA was converted to 3.2 weight percent of N, N'-dibutyl-N- (2-hydroxyethyl) ethylene diamine plus a small amount (less than 0.5 weight percent) of N-butyl-2-oxazolidinone. The weight loss of carbon steel for each sample was less than 0.5 mils per year after 28 days. The results are given in Table 3 below.

Table 3 This information shows the unexpectedly excellent stability of the primary alkanolamine (2-AB) of the present invention compared to the known secondary alkanolamines (EMEA and BMEA) while also having very low corrosivity for the carbon steel. The information demonstrates that substantially all of the 2-AB remains in the solution after 28 days without essentially detecting a degradation product while during the same time substantial amount of EMEA and BMEA has been lost due to its reactivity with CO2 and conversion to undesirable reaction products.

Claims (9)

1 . An aqueous composition adapted for use in the removal of acid gases from a fluid stream containing the same, said aqueous composition comprising a mixture of a tertiary alkanolamine and a primary alkanolamine of the formula:

R-CH (NH2) CH2-OH (I) or mixtures thereof wherein R is an alkyl group having from 1 to 8 carbon atoms. 2. The aqueous composition according to claim 1 wherein the primary alkanolamine of the formula I is selected from the group consisting of 2-amino-1-butanol, 2-amino-propanol, 2-amino-3-methyl-1. -butanol, 2-amino-1-pentanol, 2-amino-1-hexanol and 2-amino-1-octanol.

3. The aqueous composition according to claim 1 or claim 2 wherein the tertiary alkanolamine is selected from the group consisting of methyldiethanolamine, dimethylethanolamine and triethanolamine.

4. The aqueous composition according to any one of claims 1 to 3 wherein the primary alkanolamine of the formula I is present in an amount of 1 to 30 weight percent.

5. The aqueous composition according to any one of claims 1 to 3 wherein the tertiary alkanolamine is present in an amount of from 20 to 60 weight percent.

6. A process for removing acid gases from a fluid stream containing them, said process comprising contacting said fluid stream with an aqueous composition comprising a mixture of a tertiary alkanolamine and a primary alkanolamine of the formula: R-CH (NH2) -CH2-OH (I) or mixtures thereof wherein R is an alkyl group having from 1 to 8 carbon atoms. The process according to claim 6 wherein the primary alkanolamine of the formula I is selected from the group consisting of 2-amino-1-butanol, 2-amino-propanol, 2-amino-3-methyl-1. -butanol, 2-amino-1-pentanol, 2-amino-1-hexanol and 2-amino-1-octanol. 8. The process according to claim 6 wherein the tertiary alkanolamine is selected from the group consisting of methyldiethanolamine, dimethylethanolamine and triethanolamine. 9. The process according to any one of claims 6 to 8 wherein the primary alkanolamine of the formula I is present in an amount of 1 to 30 weight percent. The process according to any one of claims 6 to 8 wherein the tertiary alkanolamine is present in an amount of from 20 to 60 weight percent.