United States Patent (19) 11) 4,096,085 Holoman Jr
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United States Patent (19) 11) 4,096,085 Holoman Jr. et al. (45) Jun. 20, 1978 (54) GAS SCRUBBING SYSTEM particularly an aqueous N-methyldiethanolamine or 75) Inventors: Smallwood Holoman Jr.; Robert G. diethanolamine acid gas scrubbing system having incor Asperger, both of Midland, Mich.; porated therein (1) a compound or mixture of com Leroy S. Krawczyk, Lake Jackson, pounds having the formula Tex. 73) Assignee: The Dow Chemical Company, f - - - - R Midland, Mich. N--(CH-N-HR, (21) Appl. No.: 736,918 m 22 Filed: Oct. 29, 1976 R --------- 51) Int. Cl.’................................................ C09K3/00 52 U.S. C. ................................ 252/189; 252/389 R; wherein n is an integer from 1 to 3, m is an integer from 252/390; 252/391; 252/392; 203/7; 423/228; 2 to a number sufficient to yield a molecular weight of 423/229; 2 1/2.5 R; 21/2.7 R about 800, R, R2, R and R4 are each independently 58) Field of Search ................... 252/189, 389 R, 390, selected from the group consisting of -H, -CH 252/391,392; 423/228, 229; 203/7; 21/2.5 R, OH, -CH2-1, -CH2NCR)R4 wherein n' is an 2.7 R integer from 1 to 2 and wherein R1-R and R-R may (56) References Cited be joined to form cyclic amines when n is 2; said com pound being present in about 10 to about 2000 parts per U.S. PATENT DOCUMENTS million parts of treating solution; (2) copper or a copper 3,959,170 5/1976 Mago et al. ........................., 252/189 ion yielding compound in from 0 to 1000 ppm; and (3) Primary Examiner-Stephen J. Lechert, Jr. sulfur or a sulfur atom yielding compound in from 0 to Attorney, Agent, or Firm-Glwynn R. Baker 1000 ppm. 57 ABSTRACT An aqueous organic amine acid gas scrubbing system, 15 Claims, No Drawings 4,096,085 1. 2 Is is therefore an object of the present invention to GAS SCRUBBING SYSTEM provide an inhibitor for aqueous amine gas absorbing BACKGROUND OF INVENTION systems which will enable higher concentrations of the Natural and synthetic gases containing acidic compo amine absorbent to be used as well as a higher loading of nents such as CO2, HS, COS, and the like, have been the acid gases in the absorbent with reduced corrosion. treated on a commercial scale with aqueous alkanola These and other advantages of the present invention mine solutions to remove the acidic components. The will be apparent to those skilled in the art from the severe corrosion which results from the presence of following disclosure and claims. these components, particularly in the rich absorbent 10 BRIEF DESCRIPTION OF INVENTION solution regeneration section, has necessitated keeping In accordance with the present invention, a gas the concentration of the amine low, i.e., 10-30 percent scrubbing solution, e.g., an aqueous alkanolamine solu generally and the loading, i.e. the amount of HS/CO, tion, particularly, diethanolamine and N-methyldie in the absorbent solution, low. In light of the recent thanolamine solutions, is rendered less corrosive toward energy shortage and necessity to conserve energy it 15 metals, particularly ferrous metal and their alloys by would be advantageous to more heavily load the gas incorporating into the solution from about 10 to about treating solutions with the acidic components. It would 3000 parts of an inhibitor composition consisting essen be a further advantage to employ more concentrated tially of (1) from 10 to 2000 ppm of a compound having absorbent solutions. However to accomplish these ob the formula jects it is necessary to prevent any increase in corrosion 20 and it would be more advantageous to reduce the corro sion to less than that experienced today at the lower loadings and solution concentrations. A brief review of the prior art discloses that numer ous patents have taught various polyamines as corrosion 25 R sus ava s inhibitors for various fluids: For example, Dickson et al. in U.S. Pat. No. wherein n is an integer from 1 to 3, m is an integer from 3,262,791, which is representative of many patents in 2 to an integer sufficient to yield a molecular weight of the corrosion inhibitor field issued to Petrolite Corpora about 800; each R represents an independently selected tion, describes polyalkylenimines of molecular weight 30 member from the group consisting of -H, -CH above 800 as useful in preventing corrosion of iron, steel OH, -CH21; CH2NCR3)R; wherein n' is an inte and ferrous alloys when using slushing oils. The patent ger from 1 to 2 and wherein R-R3 and R-R may be also suggests these polyalkylenimines as capable of im joined together to form cyclic amines when n' is 2; (2) parting corrosion resistance to brines, weak inorganic copper or a copper ion yielding compound in from 0 to acids, organic acids, CO2, H2S, etc. 35 1000 ppm; and (3) sulfur or a sulfur atom yielding com Ting Sin Go in U.S. Pat. No. 3,819,328, also a Petro pound in from 0 to 1000 ppm. lite patent, discloses alkylene polyamines, such as ethyl Amine compounds falling within the scope of the ene diamine, to control acid corrosion in distillation formula set out above are for example, polyethylen columns, such as occurs in petroleum distillation col imine (polyethylene polyamines) having molecular umns. Preferably the alkylene polyamine is used in con weights from about 60 to about 800 which may be mix junction with a corrosion inhibitor, e.g., a film-forming tures of several amines, for example a commercial poly corrosion inhibitor, i.e., morpholine, at regulated pH's alkylene polyamine identified as EA-10 (or E-100) con of about 2. The corrosion of columns which have water taining 8-9 weight percent tetraethylenepentamine, condensers and which water has a high pH due to acidic 30-35 weight percent pentaethylenehexamine, 55 materials such as HS, HCN, CO, HCl, etc. is taught to 45 weight percent hexaethyleneheptamine and the remain be controlled. der branched and cyclic isomers, polyethylenimines, Ulrich et al. in U.S. Pat. No. 2,143,393 discloses ab PEI 3 (molecular weight 300-50), PEI 6 (molecular sorbing acid gases in an aqueous solution of a polymer weight about 600), EA-17 tris(aminoethyl)amine (about ized alkylenimine. 90 percent branched), EA-19 pentaethylenehexamine Johnson et al. in U.S. Pat. No. 3,137,654 teach using 50 (MW about 232), EA-15 (a mixture of 35–45 percent glycines as a corrosion inhibitor in an alkanolamine diethylenetriamine, 10-15 percent triethylenediamine, solution used to absorb CO2 from industrial gases. 5-15 percent piperazine), EA-25 (reaction product of Yeakey et al. in U.S. Pat. No. 3,829,494 teach using a triethylenetetramine divinylbenzene), EA-26 (a divinyl water-soluble trialkanolamine in an aqueous 2-(2-amino benzene-ethylvinylbenzene-diethylenetriamine mix ethoxy)ethanol gas scrubbing medium. 55 ture), EA-11 (aminoethylpiperazine-diethylenetriamine Singh in U.S. Pat. No. 3,535,260 teaches a similar mixture), 1,2-polypropylenimine, tetraethylenepenta result for monoethanolamine gas treating solutions. mine, triethylenetetramine, diethylenetriamine, ethyl The art is rife with disclosures of nitrogen containing enediamine, dihydroxyethyl ethylenediamine, and the compounds useful as corrosion inhibitors, but that only like. a few are commercially acceptable. It is evident to one Copper metal or a copper ion yielding compound skilled in the art operating a commercial installation such as CuCO3, or the like may be employed. (Get that the old limitations on concentration of absorbent, scope from earlier case.) loading of the absorbent solution, etc., while improved Sulfur or a sulfur ion yielding compound may be to some extent with these few commercially accepted present and is present in those compositions containing inhibitors are lacking in ability to carry without exces 65 H2S, COS or other sulfur containing constituents. sive corrosion the demands for more efficient operation, The inhibitors are most effective in diethanolamine higher absorbent concentrations and higher loading, solutions where the HS to CO, ratio is 10/1 to 1/10, brought on by the energy shortage. respectively. The inhibitors reduce corrosion compared 4,096,085 3 4. to present day inhibitors in systems containing up to percent inhibition were calculated using the before and 1/40 HS/CO, respectively. The absorbents DEA and after weighing of the mild steel specimens according to MDEA are effectively provided with less corrosion the following equations: than present day inhibitor systems with HS only but the results are not as dramatic as when CO, is present 5 corrosion rate/yr = (534W/DAT) also. The alkanolamines which have been employed as where W = weight loss in mg; D = density of speci absorbents for the acidic gas are the mono C-3 alkanola men in gm/cc; A = area in square inches; and T = mines, such as monoethanolamine, monisopropanola exposure in hours. mine, the dialkanol C-3 amines, such as diethanolamine 10 and their N-alkyl substituted derivatives, i.e., methyl CR test blank diethanolamine. The dialkanolamines show marked % inhibition = avg. CR blank -- viii. X 100 improvement in corrosion protection when the inhibi tors of the present invention are employed. Each of the following tables tabulate the experiments 15 conducted and the results obtained in a single series of DETAILED DESCRIPTION OF THE tests. The corrosion rate for the uninhibited, blank tests INVENTION was run for each series to enable a direct comparison to PROCEDURE be made with the other tests run in that series. TABLE I 50% DEA HS/CO, 9/I Corrosion Percent COmpound PPM PPM PPM Rate MPY Inhibition 1.