METHOD AND COMPOSITION FOR REMOVING SULFIDES FROM FLUID STREAMS

Abstract: Scavenger compositions and methods for reducing the level of sulfide impurities present in a fluid stream. The method includes contacting the stream with a composition comprising the reaction product of an aldehyde and a aminoethylpiperazine (AEP) and a second aliphatic amine NHR1R2, wherein R1 or R2 can be hydrogen and wherein R1 and R2 contain a total of from 1 to about 6 crbons. It is possible to obtain a biphasic liquid spent scavenger. One amine-containing phase can be regenerated by addition of aldehyde for reuse as scavenger. Another sulfided product-containing phase can be used as a corrosion inhibitor. A preferred aldehyde is formaldehyde and a preferred second aliphatic amine is n-butyl amine.

Description: METHOD AND COMPOSIΗON FOR REMOVING SULFIDES FROM FLUID STREAMS FIELD OF THE INVENTION This invention features a method and composition for sweetening fluid streams In particular, this invention relates to a method and composition for reducing the amount of hvdrogen sulfide and organic sulfides in such streams, particularly natural gas streams BACKGROUND OF THE INVENTION Natural gas is a mixture of hydrocarbons and non-hydrocarbon gases found in geologic formations beneath the earth's surface, often in association with petroleum As obtained from the ground, raw gas contains a number of impurities which must be removed at some point The pπncφal impurities in natural gas are water, carbon dioxide, hydrogen sulfide, organic sulfides and condensable hydrocarbons, such as propane, butane and pentane Generally speaking, hydrogen sulfide and organic sulfides (collectively here "sulfides"), because of their corrosiveness and toxicitv, are removed in the field prior to introduction to a pipeline for transport to a market or off-site processing plant The maximum level of hydrogen sulfide, "H 2 S", the pnmarv sulfide impurity of natural gas, permitted to be introduced into a pipelme is often limited to 0 25 grains per 100 cubic feet of gas, that is, 4 parts per million (ppm), although in some instances, up to 1 gram per 100 cubic feet (16 ppm) is acceptable H 2 S, like hydrocarbon components of natural gas, exists in the gaseous state at normal temperatures and pressures There is a variety of approaches to removing H 2 S from, or at least substantially reducing the amount of H 2 S in natural gas, l e , "sweetening" natural gas One general approach is to expose the raw natural gas to a treatment liquid containing an agent which chemically reacts with H 2 S, a so-called H 2 S scavenger Usually, the natural gas is bubbled through the liquid and as the bubbles rise through the liquid, H 2 S comes into contact with the agent to react and form a non-gaseous, or relatively non-volatile, product The H 2 S thus becomes trapped m the liquid and is removed from the gas One type of agent often used to react with H 2 S is the reaction product of an organic amme compound having an "active hydrogen" and an aldehyde An active hydrogen herein is a hydrogen directly bonded to a nitrogen atom It is this type of scavenging or trapping agent to which the present invention relates Examples of such agents are descnbed in United States Patent Nos 4,978,512 (issued December 18, 1990 to Dillon) and 5,462,721 (issued October 31 , 1995 to Pounds et al ) The specifications of both of these earlier patents are incorporated herein by reference As descnbed by Pounds et al , there is a number of charactenstics that are considered desirable in treatments containing such active agents Generally speaking, it is desirable that the agent be highly reactive, l e , the H 2 S (or organic sulfides) should react readily with the agent as the H 2 S passes through the treatment liquid At the same time, it is desirable that the agent remain effective even in the presence of a large excess of C0 2 , that is, it should be selective The scavenging agent should be easy to handle, that is, be of appropnate viscosity, have a suitable pour point and low toxicity— it should have no free formaldehyde nor produce a vapor containing formaldehyde In terms of performance, it is also desirable that the agent not foam excessively in use It is also desirable for the reaction product(s) of the H 2 S and the scavenging agent to have certain charactenstics It has generally been the approach to use single phase treatments In particular, liquid treatments in which the products of the H 2 S trapping reaction are soluble m the liquid have thus been considered highly desirable because of the ease of disposal of the spent fluids SUMMARY OF THE E ENTION The present invention, in one broad aspect, is a method for reducing the level of sulfide impurities present in a fluid stream The method includes contacting the stream with a composition compnsing the reaction product of an aldehyde and a aminoethylpiperazine (AEP) and a second aliphatic amine NHR,R 2 , wherein R, or R 2 can be hydrogen and wherein R, and R 2 contain a total of from 1 to about 6 carbons, for a penod of time sufficient to reduce the level of the impunties in the stream According to particular embodiments of the invention, descnbed below, the invention is a scavenger which separates into two liquid phases Such separation may occur as the active agent of the scavenger reacts with sulfides such as H 2 S or organic sulfide(s) of a stream being treated Usually the stream being treated contains hydrocarbon, and is typically an oil or gas stream, usually a natural gas stream It is also possible for a scavenger composition to include two liquid phases prior to reaction with impurities of the stream As the active ingredient of a scavenger composition of the present invention generally mcludes a water soluble phase, the invention includes a method for reducing levels of sulfide(s) in an aqueous system, say, for example, sewage An advantage of the presence of two immiscible liquids, aside from the avoidance of solids formation, which is usually undesirable, is that the two liquids I e , liquid phases can be readilv separated from each other According to a particular embodiment of the invention, descnbed below it is thus possible to isolate one phase, containing amine which is produced during reaction ol the scavenger and react the amine with an aldehvde to produce more scavenger which can then be used to treat the stream The other phase, containing spent scavenger, l e , sulfided components, can be used as an anti-corrosion agent The performance of the embodiments of the invention sub j ected to testing, as descnbed below, was found to be relatively unaffected by the presence of C0 2 , and hence scavenger compositions of the present invention are generally "selective" Generally speaking, the second amine, as described above, of a scavenger of the present invention is also referred to as an "enhancing amme" The enhancing amine, NHR,R 2 , can be non-cyclic R, can be hydrogen while R 2 is an aliphatic hydrocarbon group having between 1 and about 6 carbons An aldehyde from which a composition of the present invention is denved can be a monoaldehyde, is usually an aliphatic aldehyde, and usually has between 1 and 4 carbon atoms The aldehyde of the preferred embodiment is formaldehyde Generallv speaking, in the oil and gas industry, it is unacceptable to have unreacted formaldehyde present in a scavenger composition to any significant degree For this reason, when formaldehyde is the aldehyde from which a scavenger composition is derived, the total amine content is sufficient to react with all of the formaldehyde On a molar basis, the aldehyde AEP ratio is between about 1 0 1 6 and about 10 1 and is more preferably between 1 1 and 5 1 or 2 1 and 4 1 An even more preferred the ratio is between about 2 5 1 and 4 5 1, and most preferably, it is about 3 1 In terms of the enhancing amine, the amount selected can depend upon the advantages of the invention that are desired That is, it is possible for a person skilled in the art to modify the tested formulations of the invention to obtain scavenger compositions which vary somewhat m their properties and still remain within the scope of the invention It is possible to vary proportions and retam to varying degrees at least one of the advantages of the present invention formation of a biphasic liquid as the scavenger composition reacts, a biphasic composition prior to reaction with a sulfide-contaimng stream, avoidance of sohd(s) formation, reduced foaming dunng the scavenging operation Generally, the ratio of AEP enhancing amine, again on a molar basis is between about 10 1 and 1 5, but more typically between 5 1 and 1 3, or even 4 1 and 1 2 More preferably still, the ratio is between 2 1 and 1 2 or between about 1 1 and 1 1 5 In a particular embodiment, descnbed below, the molar ratio is 1 1 4 and m another, it is 1 1 According to a method of the invention, there is sufficient amme present to provide between about 1 5 and 3 equivalents of an active hydrogen for every equivalent of aldehyde carbonyl group According to particularly preferred embodiments, combined amounts of aminoethylpiperazine and NHR,R 2 provide between about 1 5 and 3 equivalents of an active hydrogen for every equivalent of aldehyde carbonyl group More preferably, the combined amounts of aminoethylpiperazine and NHR,R 2 provide about 2 equivalents of active hydrogen for said equivalent of carbonyl group The enhancing amme of the scavenger can be a primary amine with a straight chain alkyl group and/or it can be present in an amount sufficient to reduce foaming over that which would be observed in its absence, and/or to it can be present in an amount sufficient to substantially preclude solιd(s) formation and/or it can be present in an amount sufficient to ensure the presence of two immiscible liquid phases in spent scavenger solution The invention includes a method for reducing the level of sulfide impunties present in a stream of gas, or liquid, or a mixture thereof, which includes contacting the stream with a composition compnsing a solution having an aqueous first liquid phase containing a water soluble reaction product of an aldehyde and first amine which reacts with the impurities to form one or more hydrophobic reaction products, and a hydrophobic component which forms a second liquid phase so as to solubilize the hydrophobic reaction products to preclude the formation of solids thereby, the composition being contacted with the stream for a penod of time sufficient to reduce the level of the impunties therein According to the present invention, the enhancing amine can, along with the first amme, react with the aldehyde(s) present in formation of the scavenger, l e , the second amine of the composition can also be at least partially reacted with the aldehyde The first amme can be monoethanolamine The first amine can be, as it is with the previously descnbed aspect, aminoethylpiperazine A scavenging method of the present invention can include first and second phases (immiscible liquid phases) pnor to contact with the stream The reaction product of the second amine with the aldehyde(s) can be part of the scavenging composition and the second phase can form dunng the reaction of the impunties with the composition In another aspect, the present invention is a method for reducing the level of sulfide impunties present in a stream of gas, or liquid, or mixture thereof, including steps of (a) contacting the stream with a composition compnsing a solution havmg at least a first liquid phase which is aqueous and contains a water soluble reaction product of an aldehyde and first amme which reacts with the impurities to form one or more sulfur-containing hydrophobic reaction products, and a hydrophobic component which forms a second liquid phase so as to solubi ze the sulfur-contammg hydrophobic reaction products to preclude the formation of solids thereby, the composition being contacted with the stream for a period of time sufficient to reduce the level of the impurities therein, (b) isolating at least a portion of the second liquid phase containing solubihzed sulfur-contammg reaction products, and (c) employing the isolated portion as a corrosion inhibitor In such a method , the hydrophobic component can include an aliphatic second amine NHR,R 2 , wherein one of R, and R 2 can be hydrogen and wherem R, and R 2 contain a total of from 1 to about 6 carbon atoms R, can be hydrogen and R 2 can be an aliphatic hydrocarbon group havmg between 1 and about 6 carbon atoms According to the method, it is possible to select the second amme and choose sufficient hydrocarbon component such that the first and second phases are formed pnor to the contacting step The aldehyde can be a monoaldehyde and it can be formaldehyde The first amme can be aminoethylpiperazine Employing the isolated portion as a corrosion inhibitor can include addmg the portion to the interior of a pipeline exposed to an aqueous liquid Contents of the pipeline might include hydrocarbon and/or C0 2 and/or S0 2 and/or H 2 S Such a method can also include (d) isolating at least a portion of the first liquid phase, and (e) reacting the amine of the isolated phase with an aldehyde so as to form additional water soluble reaction product It can further include (f) contacting the stream with the additional water soluble reaction product to react with the impurities as part of step (a), thereby recycling the amme component of the composition Further, steps (b), through (f) can be repeated Accordmg to another aspect, the invention is a method for reducing the level of sulfide impunties present in a stream of gas, or liquid, or mixture thereof, comprising the steps of (A) contactmg the stream with a composition compnsing a solution having at least a first liquid phase which is aqueous and contains a water soluble reaction product of an aldehyde and first amme which reacts with the impunties to form one or more hydrophobic reaction products, and a hydrophobic component which forms a second liquid phase so as to solubi ze sulfur-aldehyde- containing hydrophobic reaction products formed dunng the contacting step to preclude the formation of solids, the composition being contacted with the stream for a period of time sufficient to reduce the level of the impurities therein, wherein the amme is water soluble and at least a portion of the amme is regenerated upon reaction of the reaction product with the impurities and retained in the first liquid phase, (B) isolating at least a portion of the first liquid phase, and (C) reacting the amine of the isolated phase with an aldehvde so as to form additional water soluble reaction product In such a method, the hydrophobic component can include an aliphatic second amme, NHR,R 2 , wherem one of R, and R 2 can be hydrogen and wherein R, and R 2 contain a total of from 1 to about 6 carbon atoms R, can be hydrogen and R 2 can be an aliphatic hydrocarbon group having between 1 and about 6 carbon atoms As with other embodiments, it is also possible for the second amme to be selected and sufficient hydrocarbon component chosen to be present pnor to the contacting step such that the first and second phases are formed pnor to the contacting step The aldehyde can be a monoaldehyde and it can be formaldehyde The first amme can be aminoethylpiperazine The method can further mclude (D) contactmg the stream with the additional water soluble reaction product to react with the impurities as part of step (A), thereby recycling the amine component of the composition The method can included repetition of steps (B), through (D) The method can be such that step (C) includes isolating at least a portion of the second liquid phase contaimng the sulfur-containing reaction products, and employing the isolated portion as a corrosion inhibitor In another aspect, the invention is a scavenger composition for H 2 S and/or organic sulfides compnsing the reaction product of an aldehyde and aminoethylpiperazine and a second aliphatic amme NHR,R 2 , wherem R, or R 2 can be hydrogen and wherein R, and R 2 contain a total of from 1 to about 6 carbons, for a penod of time sufficient to reduce the level of the impunties in the stream The second amme of the composition can be non-cyclic R, can be hydrogen and R 2 can be an aliphatic hydrocarbon group having between 1 and about 6 carbons The aldehyde can be a monoaldehyde, the aldehyde can be aliphatic, the aldehyde can have between 1 and 4 carbon atoms The preferred aldehyde is formaldehyde The amounts of aldehyde and NHR,R 2 can be present in relative amounts sufficient provide between about 1 5 and 3 equivalents of H bonded directly to the N of NHR,R 2 for every equivalent of carbonyl groups in the aldehyde Alternatively, the amounts of aldehyde and NHR,R 2 provide about 2 equivalents of H bonded directly to the N of NHR,R 2 for every equivalent of carbonyl groups in the aldehyde Another aspect of the present invention involves the observation that activity of aldehyde- amine sulfide trapping agents is increased m the presence of water A preferred method for reducing the levels of sulfide impunties thus mcludes adding water to the composition, l e , the amme-aldehyde reaction product The amount of water added to the composition can yield a ratio of water/reaction product of between about 1 10 and about 10 1 by weight, or between about 2 9 to about 9 2 by weight, or between about 3 8 to about 8 3 by weight, or between about 4 7 and about 7 4 by weight, or between about 5 6 and about 6 5 by weight or about 1 1 by weight In another aspect, a scavenger of the present invention is a composition comprising a solution havmg an aqueous first liquid phase containing a water soluble reaction product of an aldehyde and first amine for reaction with sulfide impurities to form one or more hydrophobic reaction products, and a second amine which forms a second liquid phase so as to solubihze at least a portion of the hydrophobic reaction products formed upon reaction of the sulfide impurities and the water soluble reaction product of an aldeh\ de and first amme so as to preclude the formation of solids thereby The aldehyde can be a monoaldehyde and it can be an aliphatic aldehyde having between 1 and about 4 carbon atoms The second amine can have the formula NH 2 R, wherein R is an aliphatic hydrocarbon group having between 1 and about 6 carbons The second amine of the composition can also be at least partially reacted with the aldehyde The first amme can be monoethanolamine The first amme can be aminoethylpiperazine BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in greater detail below, with reference to the attached drawings in which Figure 1 is a schematic diagram of an apparatus used in laboratory scale expenments to test effectiveness of H 2 S scavengers Figure 2 shows the concentration of H 2 S slipping through a test treatment solution as a function of tune for different enhancing amines The residence time for the gas was 2 2 seconds With the exception of Composition "D", the scavenging agent was the reaction product of aminoethylpiperazine and formaldehyde and for each of these the enhancing amme was an equrmolar amount of the amine indicated Composition "C" (n-butylamme (BA) (▼)), monoethanolamine (MEA) (D), aminoethylethanolamine ( AEEA) (X), and methoxypropylamme (•), and Composition "D" (■) (first listed composition in Table 3) Figure 3 shows the concentration of H 2 S (ppm) slipping through a test treatment solution as a function of time (minutes) for different enhancing amines in the presence of the reaction product of formaldehyde and monoethanolamine hexylamine (V), pentylamine (X), w-butylamine (BA) (•), propylarrune (■), ethylamme (T), no enhancing amine (D) Detailed compositions of the scavenging solutions are given in Table 3 Figure 4 shows the concentration of H 2 S slippage as a function of time (days) in field tnals of Composition "A" and Composition "B" In the case of Composition "A", 110 liters of scavenger solution were used, for Composition "B", 150 liters were used Figure 5 shows the concentration of H 2 S (ppm) slipping through test treatment solutions as a function of time (mm), the solutions containing solvents of various polarities H 2 0 (■), methanol (X), propanol (•), ethyl acetate (D), butanol (T), pentanol (O), and tπethylamme (*) The residence time for the gas was about 2 2 seconds Figure 6 is a plot of % protection against concentration of spent scavenger (ppm) Composition "C" (D, spent in lab tnal), Composition "B" (■$•, spent in field tnal), and composition described in last line of Table 1 (Θ, spent m lab trial) DESCRIPTION OF PREFERRED EMBODIMENTS In one particular aspect, the present invention involves contacting a stream of raw gas with a composition that mcludes the reaction product of an aldehvde and aminoethylpiperazine and an enhancing amine belonging to the family NH 2 R, wherein R is an aliphatic hydrocarbon group having between 1 and about 6 carbons, for a penod of time sufficient to reduce the level of the impunties in the stream Scavenger compositions containing reaction products of aminoethylpiperazine and particular members of the family of enhancing ammes have the advantage of not forming solids or precipitating out of solution, even when the scavenger solution is spent Enhancing amines in which R is methyl, ethyl, propyl, butyl, pentvl or hexvl have been observed in the lab. see below, to confer this property on scavenger compositions Any one of these amines could be used to obtain the advantage, or a mixture of two or more of the amines might be used It must be borne in mind, that it is necessary to use an appropriate amount of enhancing amιne(s) m combination with other components of a scavenger composition to obtain the desired result Examples of suitable amounts are given below, but a person skilled in the art is capable of using other amounts while obtaining the desired result Scavenger compositions obtained using one of a subgroup of the preceding enhancing amines, I e , butyl, pentyl and hexyl, have been found to have the property that a second liquid phase develops as the scavenger reaction proceeds Actual compositions having this advantage are described below Such a property would be considered an advantage under particular circumstances, which are described more fully below Scavenger compositions containing reaction products involving aminoethylpiperazine and particular members of the family of enhancing amines have the advantage of reduced foammg charactenstics Enhancing amines in which R is propyl, butyl, pentyl and hexyl have been observed m the lab to confer this property on scavenger compositions Before proceeding further with a description of the present invention, it must be said that "enhancing" ammes have been suggested by others for use as a component of H 2 S scavenging compositions Pounds et al found certain enhancing ammes to be useful in inhibiting gel formation which can occur when an aldehyde and polyamme are mixed together Pounds et al descnbe families of etherammes and alkanolamines that may be used with polyamines to inhibit such gel formation, polyamines including organic amines having a plurality of amme groups with two or more of the following a pnmarv amine group, a secondary amine group, or a tertiary amine group The enhancing amines were described by Pounds et al as being effective in reducing gelling problems with polyamines including aminoethylpiperazine, polyoxyalkyleneamines and alkylenepolyamines As a general rule, when using a polyamme as a reactant to form a sulfide scavenger, l e , trapping agent, the polyamme should not be combined with the aldehyde pnor to the enhancing amine, as is described more thoroughly by Pounds et al In expenments descnbed herein, where a composition contains more than one amine, a mixture of the ammes was added to a stirred mixture of formaldehyde and any solvents indicated In any case, there is no suggestion by Pounds et al of using the enhancing ammes of the invention described herein for any purpose In another aspect, the present invention involves contactmg a hydrocarbon stream with a composition that includes a solution having an aqueous liquid phase containing a water soluble reaction product of an aldehyde and first amme which reacts with sulfide impunties in the stream to form one or more hydrophobic reaction products One such product, for example, would be tnthiane formed from a monoaldehyde such as formaldehyde and H 2 S The makeup of the scavenger composition is such that hydrophobic sulfur-containing reaction products, for example, tnthiane, are solubihzed and do not precipitate as solids from the scavenger solution A particular example of such a composition is one in which AEP is the first amine and n-butyl amine is used in sufficient concentration as an enhancing amme Another aspect of the present invention involves the observation that activity of aldehyde- amme sulfide trapping agents is increased in the presence of increasingly polar liquids Of the liquids tested, the highest activity is obtained in the presence of water It was generally found that the performance of the scavengers of the present invention was unaffected by the concentration of C0 2 in the gas stream Laboratory scale results descnbed herein were obtained using the apparatus shown schematically in Figure 1 Mass flow controllers 10, 12, 14 were used to control the inflow of N 2 , C0 2 , H 2 S, respectively Gas flow is through the controllers through glass frit 16 located at the bottom of test column 18 The test column was about 60 cm in height with an inner diameter of about 0 9 cm Helium, admitted through controller 20, was the carrier gas for samples admitted for analysis to gas chromatograph 22 The gas chromatograph permits measurements of levels of H 2 S and C0 2 to be monitored (thermal conductivity detector) in ppm from samples collected at selected intervals m laboratory expenments, the gas fed into the apparatus was typically 5% C0 2 , 0 5 to 1% H 2 S, with the balance being nitrogen, and the flow rate set to obtain a gas residence time in the solution of about 5 4 seconds, unless otherwise stated The H 2 S levels used were higher than those expected to be found m field use, in order to shorten the length of the expenments In expenments where the degree of foaming was evaluated, an unsatisfactory degree of foammg was deemed to occur if the height of the foam became equal to or greater than the height of the liquid column for more than half of the time of the expenment In some expenments, foam spilled out of the top of the column, causing problems which were resolved by adding an antifoaming agent such as a long chain alcohol or sihcone polymer In this way, the test could be completed and the efficacy of the test solution in capturing H 2 S could be measured In one early set of expenments, solutions containing reaction products of different AEP formaldehyde ratios were tested The results are given in Table 1 The breakthrough times obtained (greater than 250 ppm H 2 S slippage in exit gas) indicate that the performance of the active ingredient of these compositions compares favorably with the reaction product of MEA and formaldehyde (Dillon et al ) However, the reaction product of AEP and formaldehyde had an unsatisfactory level of foaming when in use, and there was appreciable solids formation in the spent material An otherwise comparable solution having a formaldehyde AEP ratio of 1 67 1 was found to form a gel, and was not tested for scavenging effect AEP and formaldehyde were reacted in several experiments using vanous enhancing amines In this case the testing apparatus was loaded with 5 0 g of test matenal and with 6 0 g of water In some cases the two liquids were partially immiscible, that is, two phases formed pnor to the test The height of the liquid column was 15 to 16 cm, about one quarter the column height of 60 cm The test gas (94% N 2 , 5% C0 2 , 1%) H 2 S) was fed through the scavenger at a rate of 200 ml/mm Samples of the eluted (sweetened) gas were taken every 8 minutes and the H 2 S concentration determined by a gas chromatograph, with the H 2 S concentration in the challenge gas (10,000 ppm) being used as the standard The gas residence time was about 3 3 seconds In all cases, the molar ratio of formaldehyde AEP enhancing amine was 3 1 1 The formaldehyde concentration was kept constant at 30% (of 37% aqueous formaldehyde) See Table 2 (*) " Y" (y es ) descnbes an expenment where the height of the foam was equal to or greater than the height of the liquid column (without gas) for more than half of the time of the expenment " Y+" described an expenment where an antifoam agent was needed to keep the liquid from spilling out of the top of the tower "Y-H-" indicates that an expenment was aborted early due to foammg problems As can be seen, there was no solids formation pnor to H 2 S breakthrough for any of the scavengers produced using enhancing amines that are part of the present invention This is in contrast to the result obtained under similar conditions in which aminoethoxvethanol is the enhancing amine In the case of each of propyl-, butyl, pentyl- and hexylamme, foaming problems were not observed In the case of each of butyl-, pentyl- and hexylamme, two liquid phases were observed to form as the scavenger reaction proceeded It can thus be seen that it is possible to obtain three advantages of the present invention in a single scavenger composition using as an enhancing amine butyl, pentyl- or hexylamme Of course, mixtures of these amines can also be used as an enhancing amme In other words, using one or more of these amines, it is possible to obtain a scavenger composition with (l) reduced foaming charactenstics, in which (n) solids formation does not occur pnor to the scavenger being spent, and in which (in) two liquid phases form as the H 2 S trapping reaction proceeds A complete analysis of the separate liquid phases which formed has not been performed, but it is known that two phases are formed when the aliphatic R chain of the enhancing amme is relatively long It is thus believed that a first phase of the biphasic system is a relatively hydrophi c phase and contams water and mostly other relatively polar solution constituents This would be termed the "aqueous" phase The other second phase contains mostly relatively hydrophobic or non-polar constituents, l e , a portion of the enhancing amme (although this will vary depending upon the hydrophobicity of the particular enhancing amιne(s) present) and tnthiane reaction product The formation of two phases would generally be considered advantageous because this would make it possible, at least under some circumstances, to remove the phase containing the sulfided reaction product (for example, tnthiane) For example, once the scavenger has been "spent", the charge could be pumped from the contactor or bubble tower, to a holding tank In the absence of agitation caused by the gas flow, the scavenger will settle into two immiscible liquid phases The sulfur-nch organic (relatively hydrophobic) phase can then be separated from the aqueous layer, which would generally have a greater volume Feasibility studies, to determine if sufficient partitioning of sulfided products into the hydrophobic phase were earned out and are described below Experiments were performed to compare different enhancing amines butylamme, monoeihanolamme, aminoethanolamme, and methoxypropylamme Scavenger solutions were thus prepared from formaldehyde, aminoethylpiperazine and each of the different enhancing amines In one expenment, the scavenging agent was the reaction product of monoethanolamine and formaldehyde with no second amme present The residence time of the gas being passed through the treatment solution was about 2 2 seconds The results of these expenments are shown in Figure 2 As can be seen, the time taken for a given amount of H 2 S to break through the treatment fluid was greater where n-butylamme is the enhancing amme than in all other cases In another series of tests, various enhancing amines were tested with the reaction product of formaldehyde and MEA as scavenger The test column of the apparatus was charged with 5 gm of each composition and 6 ml of water In this case, the inner diameter of the column was about 1 5 cm The gas flow rate was 300 ml/min to give a residence time of about 2 2 seconds The initial H 2 S concentration in the gas was 6700 ppm, being monitored by gas chromatography, as previously descnbed Results are given m Table 3 and Figure 3 As can be seen from Table 3, solids formation was avoided for all enhancing amines used Two liquid phases were present in the spent matenal in all cases Two liquid phases were also present initially m the case of butyl-, pentyl- and hexylamines, those with the largest R-groups Butylamme was tested further with the reaction product of formaldehyde and AEP as scavenger Expenments were thus earned out to determine the effect of butylamme concentration on foammg behavior, the molar ratio of formaldehyde AEP butylamme being varied from the preferred ratios of 3 1 1 The column was charged with a mixture of 5 grams of the scavenger blend and 6 ml of water Two phases were present at the beginning of the test for those blends which had a molar ratio of BA AEP of 1 or greater The results are summanzed in Table 4 (*) See Table 2 (**) Phase behavior at the end of the test is indicated "2" indicates two liquid phases As can be seen from the third column of Table 2 and the last two columns of Table 3, foammg problems can be reduced through the use of enhancing ammes of the present invention The results shown m the third column of Table 4 show that foaming is reduced as the concentration of the enhancing amme, n-butylamme increases Solids formation was not observed when a sufficient amount of an enhancing amme of the present invention was used The results shown in the second column of Table 4 indicate that solids formation is elunmated in the presence of sufficient n-butylamme as the enhancing amme This is apparently due to the formation of a second liquid phase which solubi zes the sulfided reaction product that is normally insoluble in the aqueous scavenger solution As biphasic (two liquid phases) behavior can be induced by the addition of water to a stock scavenger solution of the present invention, foammg problems can also be reduced by the addition of water One particular formulation, Composition "A", tested in the lab and in field trials had the following composition Water 12 5% ΓPA 5 5% Butyl Cellosolve™ (2-Butoxyethanol) 20.0% Ethylene glycol 5 6% 2-ethylhexanol 0 3% MTBC (methylisobutyl carbinol) 1 9% Formalin (37% formaldehyde) 30 0% AEP 15.9% Butylamme 8 3% Ethylene glycol, an optional ingredient, is a earner having a high boiling point, which is therefore relatively resistant to evaporation In the field trial, natural gas flow was 0 33MSCFD (million standard cubic feet per day) and it contained 20 ppm of H 2 S Sufficient of the foregoing formulation diluted by half with water was used in the field tnal to obtain a gas residence time of 2 seconds The solution was replemshed to its initial volume of 220 liters at day 14 Results obtained are given in Figure 4 An upset, unrelated to the use of the scavenger, occurred at the plant on day 18 and the trial had to be stopped at that pomt A second formulation, Composition "B", was found in laboratory scale expenments to have a breakthrough time about one third longer than that given above, the second formulation having the follow mg composition Water 15 5% IPA 6 5% Butvl Cellosolve 20 5% 2-ethylhexanol 0 3% Oleyl alcohol 0 05% Foπnalm (37% formaldehyde) 32 9% AEP 16 45% Butvlamine 7 8% (Density @ 20°C = 0 993) Results of a field trial of Composition B, under the same conditions as those for Composition A are also shown in Figure 4 Experiments were performed to determine the effect of polarity of the treatment liquid medium A test column (1 5 cm diameter) was loaded with 5 grams of a scavenger solution (30 0% formaldehyde, 30 0% IPA, 14 5% water. 9 3% butylamme, and 16 2% AEP), 1 ml of water, and 5 ml of the selected solvent The gas flow rate was about 300 ml/mm, with an H 2 S flow rate of 2 ml/mm, the balance being 5% C0 2 and 95% nitrogen The H 2 S concentration was 6700 ppm and residence time of the gas about 2 2 seconds Results are summarized in Figure 5 which shows slippage of H 2 S as a function of time for vanous solvents As can be seen, significantly less slippage occuπed when water was mcluded in the treatment solution than for any other of the solvents As indicated above, a useful treatment formulation can have two liquid phases prior to reaction of the scavenger with sulfide It has also been observed for particular formulations, that formation of the second liquid phase occurs as the trapping reaction proceeds, or it can occur merely upon addition of water In a commercial environment, it is often desirable for a formulation to be supplied to an end user in a convenient form In the case of the present invention, it may be desirable to provide a formulation in a relatively concentrated single phase form to which the user would be instructed to add an appropnate amount of water Another unexpected result has been found m that spent reaction products of scavengers of the present invention are useful as coπosion inhibitors Laboratory tests described below were earned out with a brme having the following composition MgSO,-7H 2 0 1 41 g litre ' MgCl 2 6H 2 0 4 69 g litre ' CaCl 2 2H 2 0 4 70 g litre ' NaHC0 3 6 43 g litre ' NaCl 86 89 g litre ' Corrosion rates can be assessed in the laboratory through the use of mild steel test coupons exposed to the coπosive conditions over a period of time The data which follow were obtained in tests in which coupons had been fashioned from a 6" wide, 0 008" thick roll of shimstock (carbon steel) by cutting it into stnps approximately l A" wide A suitable volume of brine, havmg the composition given above, was purged for four hours with a pre-blended mixture of 10% H 2 S and 90% C0 2 Each spent scavenger solution to be tested was added, at the concentration indicated, to a 350 ml glass bottle, together with 100 ml of bnne and a pre- weighed shimstock test coupon The headspace in each bottle was purged with the H 2 S/C0 2 gas mixture to remove oxygen The bottles were sealed and spun at 16 rpm for 7 davs at 60 ° C , after w hich period the coupons were reclaimed, cleaned by immersion in inhibited hydrochloric acid, xvlene and methanol and then re-weighed "Percent protection", or "%P" value was calculated using weight loss from a blank expenment (l e one in which no chemical inhibitor was added to the brine), according to the following equation Weight loss from "blank" coupon - weight loss from "test" coupon 100 0 / Weight loss from "blank" coupon Spent matenal obtained from three scavenger formulations were tested for coπosion inhibition properties Composition "B" (which was exhausted m a field tnal), Composition "C" and a formaldehyde-efhanolamine blend whose composition is given in the first row of Table 3 The latter two scavengers were saturated with H 2 S in the laboratory Composition "C" Water 14 5% IPA 30 0% Formalin 30 0% AEP 16 2% Butylamme 9 3% The results of the coπosion testing of these three ' spent" scavengers are shown in Figure A further aspect of the present invention is thus the use of a spent scavenger as a coπosion inhibitor In practice there are several ways m which this advantage can be realized For, example once the chemical in the contact tower is spent, it can be simply discharged to the sour water disposal system, where it will inhibit coπosion of the water flow line as it passes to deep well disposal Alternatively, the scavenger charge can be pumped to a holding or settling vessel where the two liquid phases are allowed to separate The lower volume "sulfiir-nch" organic layer can then be drawn off and injected or batched into sour flow- lines to inhibit coπosion therein In this way it will act as a water dispersible inhibitor of acid gas coπosion As mentioned above, feasibility studies were earned out to determine if sulfided product is sufficiently partitioned into the hydrophobic layer A solution of 5g of Composition "A" and 6g of water was loaded into a bubble tower (1 5 cm diameter) 6000 ppm of H 2 S was bubbled through the solution for a period of time sufficient to ensure that the solution was past the point of H 2 S breakthrough The spent sample was turbid immediately after saturation was complete For the purposes ol analvsis, m order to effect a clean separation, the solution was centnfuged, heated and collected in a separatory funnel Samples of the organic and aqueous phases were analyzed on an Antek Sulpher Analyzer The wt% of sulphur in the organic phase was found to be about 6 4%, while that in the aqueous phase was found to be 0 75% These results indicate that it is feasible to formulate a scavenger composition, which when spent, can form two separable lmmiscble liquid phases, one of which can be used as a coπosion inhibitor and the other of which contains recyclable amine The aqueous layer, which contains amιne(s) released from the scavenger as the scavenger reacts with sulfides, can be retained and reconstituted into an active scavenger through the addition of formaldehyde Additional enhancing amines can be added, as appropriate to reconstitute the composition for use as a scavenger In this way, amme can be recycled

Claims: CLABVIS 1 A method for reducing the level of sulfide impurities present in a fluid stream, compnsing contacting the stream with a composition compnsing the reaction product of an aldehyde and aminoethylpiperazine and a second aliphatic amme NHR,R 2 , wherein R, or R 2 can be hydrogen and wherem R, and R 2 contain a total of from 1 to about 6 carbons, for a penod of time sufficient to reduce the level of the impunties m the stream 2 The method of claim 1 wherein said fluid stream compnses a gas, or liquid, or a mixture thereof 3 The method of claim 1 or 2 wherein the fluid stream contains hydrocarbon 4 The method of any preceding claim wherem the second amme is non-cyclic 5 The method of any preceding claim wherem R, is hydrogen and R 2 is an aliphatic hydrocarbon group having between 1 and about 6 carbons 6 The method of any preceding claim wherem the aldehyde is a monoaldehyde 7 The method of claim 6 wherein the aldehyde is an aliphatic aldehyde 8 The method of any preceding claim wherein the aldehvde has between 1 and 4 carbons 9 The method of claim 8 wherein the aldehyde is formaldehyde 10 The method of any preceding claim wherem sufficient amme compounds are present to provide between about 1 5 and 3 equivalents of an active hydrogen for every equivalent of aldehyde carbonyl group 1 1 The method of any preceding claim wherem combined amounts of aminoethylpiperazine and NHR,R 2 provide between about 1 5 and 3 equivalents of an active hydrogen for every equivalent of aldehyde carbonyl group 12 The method of any preceding claim wherem the combined amounts of aminoethylpiperazine and NHR,R 2 provide about 2 equivalents of active hydrogen for said equivalent of carbonyl group 13 The method of any preceding claim wherein the second amme has the formula NH 2 R and R is a straight chain alkyl group and NH 2 R is present in an amount sufficient to reduce foammg 14 A method for reducing the level of sulfide impunties present m a stream of gas, or liquid, or a mixture thereof, compnsmg contacting the stream with a composition compnsing a solution havmg an aqueous first liquid phase containing a water soluble reaction product of an aldehyde and first amine which reacts with the impunties to form one or more hydrophobic reaction products, and a hydrophobic component which forms a second liquid phase so as to solubi ze the hydrophobic reaction products to preclude the formation of solids thereby, the composition being contacted with the stream for a period of time sufficient to reduce the level of the impurities therein 15 The method claim 14 wherein the aldehyde is a monoaldehyde 16 The method of claim 14 or 15 wherein the monoaldehyde is an aliphatic aldehyde having between 1 and about 4 carbon atoms 17 The method of claim 14, 15 or 16 wherem the second liquid phase includes a second amme 18 The method of claim 17 wherem the second amme has the forumla NH 2 R, wherein R is an aliphatic hydrocarbon group having between 1 and about 6 carbons 19 The method of claim 17 wherein the second amme of the composition is also at least partially reacted with the aldehyde 20 The method of claim 15, 16, 17, 18 or 19 wherein the first amine monoethanolamine 21 The method of claim 15, 16, 17, 18 or 19 wherein the first amme is aminoethylpiperazine 22 The method of claim 15, 16, 17, 18 or 19 wherem the composition includes said first and second phases pnor to contact with the stream 23 The method of claim 17, 18 or 19 wherein the composition mcludes the reaction product of the second amme with the aldehyde and the second phase forms dunng the reaction of the impunties with the composition 24 A method for reducing the level of sulfide impunties present in a stream of gas, or liquid, or mixture thereof, comprising the steps of (a) contacting the stream with a composition compnsing a solution having at least a first liquid phase which is aqueous and contains a water soluble reaction product of an aldehyde and first amine which reacts with the impunties to form one or more sulfur-contammg hydrophobic reaction products, and a hydrophobic component which forms a second liquid phase so as to solubi ze the sulfur-contammg hydrophobic reaction products step to preclude the formation of solids, the composition being contacted with the stream for a period of time sufficient to reduce the level of the impurities therein, (b) isolating at least a portion of the second liquid phase containing the sulfur-contammg reaction products, and (c) employing the isolated portion as a coπosion inhibitor 25 The method of claim 24 wherein the hydrophobic component includes an aliphatic second amme NHR,R 2 , wherem one of R, and R 2 can be hydrogen and wherem R, and R 2 contain a total of from 1 to about 6 carbon atoms 26 The method of claim 25 wherein R, is hydrogen and R 2 is an aliphatic hydrocarbon group having between 1 and about 6 carbon atoms 27 The method of claim 25 or 26 wherein the second amine is selected and sufficient hydrocarbon component is present prior to the contactmg step such that the first and second phases are formed prior to the contacting step 28 The method of claim 24, 25, 26 or 27 wherem the aldehyde is a monoaldehyde 29 The method of claim 24, 25, 26, 27 or 28 wherein the aldehyde is formaldehyde 30 The method of claim 24, 25, 26, 27, 28 or 29 wherem the first amme is aminoethylpiperazine 31 The method of claim 24, 25, 26, 27, 28, 29 or 30 wherein employing the isolated portion as a coπosion inhibitor includes adding the portion to the mtenor of a pipeline exposed to an aqueous liquid 32 The method of claim 24, 25, 26, 27, 28, 29, 30 or 31 wherem fluid within the pipeline includes hydrocarbon and/or C0 2 and/or S0 2 and/or H 2 S 33 The method of claim 24, 25, 26, 27, 28, 29, 30, 31 or 32 further comprising the steps of (d) isolating at least a portion of the first liquid phase, and (e) reacting the amine of the isolated phase with an aldehyde so as to form additional water soluble reaction product 34 The method of claim 33, further compnsing the step of (f) contactmg the stream with the additional water soluble reaction product to react with the impurities as part of step (a), thereby recycling the amme component of the composition 35 The method of claim 34, further comprising repetition of steps (b), through (f) 36 A method for reducing the level of sulfide impurities present in a stream of gas, or liquid, or mixture thereof, comprising the steps of (a) contacting the stream with a composition comprising a solution having at least a first liquid phase which is aqueous and contains a water soluble reaction product of an aldehyde and first amme which reacts with the impunties to form one or more hydrophobic reaction products, and a hydrophobic component which forms a second liquid phase so as to solubihze sulfur-aldehyde - contaming hydrophobic reaction products formed during the contacting step to preclude the formation of solids thereby, the composition being contacted with the stream for a penod of time sufficient to reduce the level of the impurities therein, wherem the amme is water soluble and at least a portion of the amme is regenerated upon reaction of the reaction product with the impurities and retained in the first liquid phase (b) isolating at least a portion of the first liquid phase, and (c) reacting the amme of the isolated phase with an aldehyde so as to form additional water soluble reaction product 37 The method of claim 36 wherem the hydrophobic component includes an aliphatic second amme, NHR,R 2 , wherem one of R, and R 2 can be hydrogen and wherem R, and R 2 contain a total of from 1 to about 6 carbon atoms 38 The method of claim 37 wherem R, is hvdrogen and R 2 is an aliphatic hydrocarbon group having between 1 and about 6 carbon atoms 39 The method of claim 37 or 38 wherem the second amine is selected and sufficient hydrocarbon component is present prior to the contacting step such that the first and second phases are formed pnor to the contacting step 40 The method of claim 36, 37, 38 or 39 wherem the aldehyde is a monoaldehyde 41 The method of claim 36, 37, 38, 39 or 40 wherein the aldehyde is formaldehyde 42 The method of claim 36, 37, 38, 39, 40 or 41 wherein the first amine is aminoethylpiperazine 43 The method of claim 36, 37, 38, 39, 40, 41 or 42 further comprising the step of (d) contacting the stream with the additional water soluble reaction product to react with the impurities as part of step (a), thereby recycling the amine component of the composition 44 The method of claim 43, further comprising repetition of steps (b), through (d) 45 The method of claim 36, wherem step (c) includes isolating at least a portion of the second liquid phase contaimng the sulfur-contammg reaction products, and employing the isolated portion as a coπosion inhibitor 46 A composition for scavenging H 2 S and/or organic sulfides m fluid streams, comprising a solution having an aqueous first liquid phase containing a water soluble reaction product of an aldehyde and first amme for reaction with sulfide impunties to form one or more hydrophobic reaction products, and a second amme which forms a second liquid phase so as to solubihze at least a portion of the hydrophobic reaction products formed upon reaction of the sulfide impurities and the water soluble reaction product of an aldehvde and first amme so as to preclude the formation of solids thereby 47 The composition of claim 46, wherein the aldehyde can be a monoaldehyde 48 The composition of claim 46 or 47 wherein the aldehyde is an aliphatic aldehyde having between 1 and about 4 carbon atoms 49 The composition of claim 46, 47 or 48 wherem the second amme has the formula NH 2 R, wherem R is an aliphatic hydrocarbon group having between 1 and about 6 carbons 50 The composition of claim 46, 47 , 48 or 49 wherem the second amine of the composition is at least partially reacted with the aldehyde 51 The composition of claim 46, 47, 48, 49 or 50 wherein the first amine is monoethanolamine 52 The composition of claim 46, 47, 48, 49 or 50 wherein the first amme is aminoethylpiperazine 53 The method of any of claims 1 to 45 wherem the composition further includes water added to said reaction product 54 The method of claim 53 wherem the ratio of water/reaction product is between about 1 10 and about 10 1 bv weight 55 The method of claim 53 wherein the ratio of water/reaction product is between about 2 9 to about 9 2 by weight 56 The method of claim 53 wherein the ratio of water/reaction product is between about 3 8 to about 8 3 by weight 57 The method of claim 53 wherein the ratio of water/reaction product is between about 4 7 and about 7 4 bv weight 58 The method of claim 53 wherem the ratio of water/reaction product is between about 5 6 and about 6 5 bv weight 59 The method of claim 53 wherein the ratio of water/reaction product is about 1 1 by weight 60 A method for reducing the level of sulfide impunties present in a hydrocarbon-containing stream, compnsing contacting the stream with a composition compnsing the reaction product of a formaldehyde and aminoethylpiperazine and butylamme for a penod of time sufficient to reduce the level of the impunties in the stream, wherem the composition includes sufficient butylamme to substantially preclude solids formation by sulfided products 61 The method of claim 60 wherein the ratio of butylamme to aminoethylpiperazine is at least 1/3

Inventors: COSSAR JOHN, WARRENDER NEIL ANDREW, COSSAR, JOHN, WARRENDER, NEIL, ANDREW
Applicants: COSSAR JOHN, STANCHEM INC, WARRENDER NEIL ANDREW, COSSAR, JOHN, STANCHEM INC., WARRENDER, NEIL, ANDREW
Application year: 1997
Main classification: B01D53
IPC codes: B01D53, C10G29, C10K1