REMOVAL OF TRACE AMOUNTS OF METAL CONTAMINANTS FROM ORGANIC SOLVENT PROCESS STREAMS

FIELD OF THE INVENTION

This invention relates to organic solvent process streams. In one aspect, the invention relates to the removal of trace amounts of metal contaminants from organic solvent process streams while in another aspect, the invention relates to the removal of metal contaminants from the internal surfaces of process equipment with which the organic solvent process stream is in contact. In still another aspect, the invention relates to the removal of trace amounts of copper from a glycol ether process stream with the simultaneous removal of deposited copper from the internal surfaces of the process equipment with which the process stream comes in contact. In yet another aspect, the invention relates to glycol ether comprising low levels of carbonyl compounds.

BACKGROUND OF THE INVENTION

While the scope of this invention extends to the sequestering and/or removal of trace amounts of metal contaminants, particularly copper, from organic solvent process streams and the removal of deposited metal contaminants from the internal surfaces of process equipment with which the process stream comes in contact, it will be described, in both background and enablement, in the context of the manufacture of glycol ethers because the manufacture of glycol ethers is a representative embodiment of the invention.

Small amounts of copper, usually in the form of copper oxides, adversely impact the quality of glycol ethers when present in the glycot ether reactors and/or distillation columns. The copper enters the glycol ethers production facility as a trace contaminant (typically at parts per billion (ppb) levels) in the alcohol feed to the process. This trace amount of copper accumulates

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on the surface of the carbon-steel equipment through an electrochemical displacement reaction. Copper and its oxides can act as alcohol dehydrogenation catalysts and in the heated regions of the reactors, distillation columns and associated process equipment, the copper/copper oxide can catalyze the dehydrogenation of the alcohol to aldehydes. These aldehydes further react via aldol condensation chemistry associated with the carbonyl group to form unstable, colored and odiferous compounds. This, in turn, results in a glycol ether product that can be off-specification in color, amount of peroxides and/or carbonyls, shelf-life stability and/or odor.

The use of ion-exchange resins and/or chelating agents to reduce the levels of metal contaminants in chemicals used in the electronics industry has been known and practiced for many years. These resins and agents are also used in the treatment of waste water for the removal of transition and heavy metals before the waste water is discharged to the environment. However, these resins are used on finished products or exit streams, not organic solvent process streams.

Metal contaminant removal from the surfaces of process equipment is typically accomplished through a chemical cleaning process that utilizes acid washing and/or amine stripping agents. This process, however, is both labor and cost intensive, can result in damage to the process equipment, and requires process downtime that results in lost production.

Consequently, a strong interest exists in identifying and developing sequestering processes for removing metal contaminants from organic solvent process streams without the need of stopping or otherwise suspending the process for the manufacture of these solvents. If the sequestering process also removes existing metal contaminants from the internal surfaces of the process equipment while the organic solvent process streams course through the process equipment under process conditions, e.g., heat, pressure and in the presence of other process

reagents, then the sequestering process will have an added interest to the manufacturers of organic solvents, particularly to the manufacturers of glycol ethers, alcohols, glycols and polyglycols.

SUMMARY OF THE INVENTION

In a first embodiment of the invention, trace amounts of metal contaminants are sequestered within an organic solvent process stream by a process comprising the steps of (i) adding to the organic solvent process stream a chelating amount of a chelating agent, and (ii) contacting the metal contaminant with the chelating agent to form a chelated metal contaminant. The ability of this sequestered metal contaminant to catalyze unwanted reactions within the organic solvent process steam, or combine with the one or more of the other components of the stream to form unwanted compounds within the stream, or otherwise significantly degrade the final organic solvent product, is significantly reduced, if not eliminated, relative to the unsequestered metal contaminant. In a variation on this embodiment, the chelated metal contaminant is removed from the organic solvent process stream, e.g., by distillation.

In a second embodiment of the invention, metal contaminants are removed from the internal surfaces of the process equipment with which an organic solvent process stream is in contact as it passes through the equipment during the manufacture of an organic solvent by a process comprising the steps of (i) adding to the organic solvent process stream a chelating amount of a chelating agent, and (ii) contacting the chelant with the metal contaminant on the internal surface of the process equipment to form a chelated metal contaminant. Like the sequestered metal contaminant of the first embodiment, the sequestered or chelated metal contaminant of this embodiment can remain within the final organic solvent product or it can be removed from the final organic solvent product by any suitable means, e.g., distillation.

In specific variations on the first two embodiments of this invention, the organic solvent process stream is a glycol ether process stream and the metal contaminant is copper. The chelant that is added to the glycol ether process stream is triethylenetetraamine (TETA), the chelated or sequestered metal contaminant is removed from the glycol ether process stream by distillation, and the final glycol ether product contains a low level of carbonyl contaminant. Moreover, copper contaminant on the internal surfaces of the process equipment is sufficiently removed from the internal surface and sequestered during the course of the glycol ether manufacturing operation that operational shut-down of the process for removal of the copper contaminants by traditional cleaning methods can be delayed for years, if not indefinitely.

BRIEF DESCRIPTION QF THE DRAWINGS

Figure 1 is a schematic representation of the structural formulas of the four components in a typical TETA mixture.

Figure 2 is a schematic representation of a metal contaminant chelated with the TETA linear component.

Figure 3 is a graph reporting the per pass removal of copper from a bed of iron particles using TETA dissolved in n-butanol.

Figure 4 is a graph reporting the removal of copper from iron particles using TETA and ethoxylated-TETA dissolved in n-butanol over time.

Figure 5 is a graph reporting the effect of TETA on the color of effluents from reactors containing copper oxide.

Figure 6 is a graph reporting the total carbonyl area percent as a function of time.

Figure 7 is a graph reporting the percent of chelation versus the time after which the chelant was added at a 20: 1 chelant: copper ratio.

Figure 8 is a graph reporting the percent of chelation versus the time after which the chelant was added at a 2: 1 chelanfccopper ratio.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As here used, "organic solvent process stream" and like terms mean a process stream used in the production of organic solvents, particularly glycol ethers. This is the stream as it exists under process operating conditions, and it includes a stream within pre-reactor equipment, e.g., storage tanks, mixers, heaters, pipes, etc.; a stream within the reactor; and a stream within post-reactor equipment, e.g., pipes, distillation columns, tankage and the like. The streams are usually in motion of one kind or another but they can be quiescent at certain times, e.g., during a hold period in the reaction process or within certain temporary holding stations of the process. The streams specifically include feed streams to the reactor that do not contain all of the process reagents, e.g., the alcohol feed stream of a glycol ether process. The streams do not include product streams after purification.

"Trace amounts of metal contaminant" and like terms mean, in the context of an organic solvent process stream, the amount of metal contaminant within the stream that originated within the components that are used to make the stream and/or that originated from the erosion of an internal surface of the process equipment with which the process stream was in contact. In a glycol ether process stream, for example, the trace amount of metal contaminants in the stream includes both that amount of metal contaminant, usually copper, that was present in the alcohol used to make the glycol ether process stream and any copper or other metal contaminant removed from an internal surface of the process equipment with which the glycol ether process stream was in contact. Typically, a trace amount of metal contaminant is less than about 10,

more typically less than about 0.5 and even more typically less than about 0, 1, parts per million (ppm).

"Metal contaminant" means (i) an uncombined metal, i.e., a metal not combined with any other element, typically in ionic form, and/or (ii) the metal in combination with one or more other elements, that will have an adverse effect on the organic solvent product. Virtually any metal or metallic compound that can be chelated and that will promote the formation of unwanted by-products can be considered a metal contaminant in the context of this invention. Examples of metal contaminants include most of the transition elements in the lanthanide and HIB to IVA CAS series of elements of the Periodic Table of Elements as published in the CRC Handbook of Chemistry and Physics, 71 ^st Ed., p. 1-10 (1990-1991), and specifically include such metals as copper, chromium, manganese, silver, cobalt, cerium, mercury, nickel, zinc, cadmium, lead and iron. Examples of the metal in combination with one or more other elements include the oxides, sulfides, halides, nitrates and the like of these metals. Typically, the adverse effect of the metal contaminant is the result of the metal contaminant catalyzing an unwanted reaction that produces an unwanted by-product.

"Copper contaminant" means copper metal and/or copper in combination with one or more other elements, e.g., copper oxides, sulfides, halides, nitrates, etc.

''Organic solvent product" and like terms mean the organic solvent, e.g., glycol ether, alcohol, polyglycol, etc., ready for packaging, shipping and/or use. Examples of organic solvent products include propylene glycol methyl ether and the di- and tri- homologues along with the mono- and di- homologues in the acetate form; propylene glycol n-propy! ether and the di- and tri- homologues; propylene glycol n-butyl ether and the di- and tri- homologues; propylene glycol phenyl ether; ethylene glycol ethyl ether and the di-, tri- and tetra- homologues; ethylene

glycol hexyl ether and the di- and tri- homologues; glycol ethers made with iso-alcohols, and propylene glycol ethyl ether,

"Chelating agent", "chelant" and like terms mean an organic compound that forms coordination bonds with a metal contaminant, typically a metal ion. In the context of this invention, the chelating agent is preferably at least partially soluble and stable in the organic solvent process stream under process conditions. Examples of chelating agents include those based on nitrogen, phosphorus and sulfur, e.g., amines, phosphines and mercaptans. Amine- based chelating agents are preferred for sequestering the copper contaminants in glycol ether process streams,

"Chelating amount" and like terms mean an amount of chelating agent sufficient to combine with and reduce the amount of metal contaminant in an organic solvent process stream to a level at which the remaining, i.e., non-chelated, metal contaminant will not have a significant adverse impact on the quality of the organic solvent product. Typically, a chelating amount of an amine chelating agent on a mole basis is at least about 10.000, more typically about 100 and even more typically about 10, times more than the measured or calculated amount of metal contaminant in the organic solvent process stream.

Organic process streams and systems can be stabilized with respect to undesired side chemistry with the controlled addition of a chelating agent during operation. The chelating agent sequesters and/or removes the trace metal contaminants that are responsible for some, if not most, of the undesired chemistry that occurs in the organic process stream and process equipment during the operation of the process. Preferably, the chelating agent is soluble and active in the organic process stream without the presence of water in contrast to many common chelating agents, e.g., the amino carboxylic acids such as ethylenediamine tetraacetic acid,

diethylene triamine pentraacetic acid, triethylenetetraamine hexaacetic acid, and the polyphosphates such as sodium tripolyphosphate, hexametaphosphoric acid and its salts.

At the broadest level, the production of glycol ethers involves two basic operations, i.e., formation of the glycol ether and purification of the glycol ether product. Formation of the glycol ether can occur in one or more reactors, and the glycol product can be purified in one or more steps, usually over two or more distillation steps. The primary reaction is that of an alkylene oxide with an alcohol, typically using an alkaline catalyst. One example is the reaction of ethanol with ethylene oxide to generate mono ethylene glycol ethyl ether. This is a series- parallel reaction forming a mixture of the mono-, di-, tri-, tetra-, penta- etc., homologues, e.g., a molecule of mono ethylene glycol ethyl ether can react with another molecule of ethylene oxide to produce diethylene glycol ethyl ether. In one embodiment of the invention, mono-, di-, tri-, etc. homologues are recovered or purified as individual components via distillation. This example can be repeated for other alcohols and oxides, e.g., propanol, butanol, etc., and propylene oxide, etc.

The alkylene oxide is typically the limiting reactant in the reaction, and it is essentially completely consumed during the reaction. Although the alkoxylation of the alcohol and glycol ethers are the primary reactions taking place, some side chemistry does take place to form byproducts. The by-product formation includes glycol formation, degradation processes, the alkoxylation of impurities and degradation products.

One of the side chemistries is the formation of carbonyl compounds. Carbonyls, specifically aldehydes, are formed by dehydrogenation of the alcohol, glycols and glycol ethers. This dehydrogenation reaction can be catalyzed by metals, in particular the metal oxides, of various transition metal elements including cerium, copper, iron, manganese, silver and

chromium. For example and as noted earlier, copper oxides are known alcohol dehydrogenation catalysts. The presence of copper oxides in the reactor, distillation columns and heated process equipment adversely impact the quality of glycol ethers due to the formation of aldehydes and other carbonyl compounds. The presence of the copper contaminant in any of the process equipment can result in the formation of the unwanted aldehydes and other carbonyl compounds. These compounds will further react via aldol condensation chemistry associated with the carbonyl group to form unstable, colored, and odiferous compounds.

The chelant additive of this invention does not play a direct role in the production of the organic solvent products. The main role of the chelant is to complex the metal contaminant, e.g., the free copper in the fresh alcohol feed (~60ppb in fresh ethanol typically used in a glycol ether process). The chelation of the metal by the chelant prevents the active sites on the metal from participating in the dehydrogenation reaction, and it prevents the deposition of the metal from the solution onto the internal surfaces of the process equipment,

Using the glycol ether process as a continuing example, the copper ions in solution, however, are only one source of the catalytic dehydrogenation of alcohols. Another significant source of catalytic copper is the copper deposits on the internal surfaces of the process equipment, primarily the reactor and distillation columns, In the heated regions of this equipment, these copper deposits can catalyze the dehydrogenation of the alcohol to aldehydes.

Copper in the alcohol accumulates on the internal surfaces of the process steel equipment through an electrochemical displacement reaction, e.g.,

Cu ²⁺ + 2e ^~ → Cu° (1) Fe ⁰ → Fe ²⁺ + 2e ^~ (2)

Cu ²⁺ + Fe ⁰ → Cu ⁰ + Fe ²⁺ (3)

This displacement reaction is a well known means of accumulating copper and will occur even in solutions with low conductivity since the electron transfer is internal. Because the driving force for the plating reaction is the electrochemical potential differences between the two metals, the displacement reaction will continue until the electrochemical potential of the solution and surface have equilibrated thus allowing the slow accumulation of copper over an extended period of time. At pH levels in the glycol ethers process (pH>7.0), the predominant copper surface species is a mixture of the copper oxides, CuO and Cu ₂ O.

The amine chelants of this invention are corrosive to copper, and they will remove copper deposits from the internal surfaces of the process equipment under process conditions, particularly the reactor and distillation columns, given sufficient time. Laboratory studies have shown that the alkoxylated-TETA compounds can chelate copper and remove copper deposits from carbon steel at room temperature.

Chelation is reversible binding of a ligand, i.e., the chelant or chelating agent, to a metal or metal ion in solution to form a metal complex or chelate. The complex or coordination compound is formed when a Lewis base (the ligand) is attached to the metal Lewis acid (the acceptor) by means of a lone-pair of electrons on the ligand. Ligands are classified according to the number of potential donor atoms that they possess. The potential ligands range from uni-dentate molecules with one donor atom to sexi-dentate molecules with six donor atoms. The soluble metals in the solution exist as positively charged ions. Each of these ions has a fixed number of reactive sites. Most metal ions have either four or six reactive sites. Copper has four reactive sites. The donor atoms of the ligand react with these reactive sites on the metal ion to form a three-dimensional structure that block the normal reactive sites of the metal ion. The coordination of the ligands with the reactive metal sites pacifies the reactive sites of the metal.

Since chelation is an equilibrium process, the measure of the efficiency of the chelating agent or ligand is the conditional stability constant of the complex they form with the metal ion. The higher the stability constant, the stronger the complex formed and the more efficiently the metal ions are pacified. By convention, the stability or formation constants are represented as a succession of steps that correspond to the reaction of a single ligand with the metal. The stepwise stability (or formation) constants K are as shown in Equations 1-3.

in which M represents the metal ion, L represents the ligand, and ML represents the metal-ligand complex. The stepwise constants (Ki ₃ K ₂ ,...) are calculated from the concentration of the product complex ([ML]) divided by the concentration of the metal ion ([M]) and the concentration of the ligand ([L]) reactants. The overall stability or formation constant (k) can then be expressed in terms of the stepwise constants (Eq. 4).

k ^ K _l * K ₂ * K, *.... EqA

These stepwise rate constants are thermodynamic constants which relate to the system when it has reached equilibrium and do not necessarily correlate to the speed with which equilibrium is attained.

The cheiants used in the practice of this invention are preferably at least partially soluble in both organic and organic/aqueous process streams. The cheiants are from the families of

compounds containing free electrons available for binding with the metal contaminant. These groups include amine, phosphorus and sulfur-based compounds. Regarding amine-based chelants, representative compounds include polyamines such as ethylenediamine and triethylenetetraamine, and amino-alcohols such as triethanolamine and diethanolamine, Preferably these chelants react primarily with the metal contaminant, in soluble and/or deposited form, and they do not react to any significant extent with the process equipment metallurgy. However, the chelant can and does react with aldehydes and other carbonyl compounds that are the precursors of color bodies thus providing an added benefit to the maintenance of clean organic solvent process streams.

These chelants can be added to the process at any point in the process, but preferably are added with the feed material, e.g., a reactant or the catalyst, before or as they enter the production process. The chelant is added in very small amounts, typically in a range (in moles) of about 1 to about 10,000, more typically of about 1 to about 100 and even more typically of about 5 to about 20, times the molar metal contaminant concentration. Because the chelant and metal contaminant are present in the organic solvent process streams at such very low concentrations, chelation may take time. However, in many commercial operations major parts of the organic solvent process streams are subject to constant recycling which affords ample opportunity for chelation to occur.

Triethylenetetraamine (TETA), also known as Trien, is an amine of choice in the practice of this invention with respect to copper contaminants. TETA is commercially available in various grades. The technical grade usually comprises a mixture of four compounds (Figure 1) with the linear component as the primary compound (60-70 weight percent). Purified TETA is available or can be prepared in which the linear component comprises greater than 99 weight

percent of the mixture. The linear TETA molecule reacts with transition metals through the lone electron pairs on the nitrogen atoms. The linear TETA effectively wraps itself around the metal atom forming a three dimensional "cage" as shown in Figure 2.

TETA is very selective towards copper, and it forms very stable chelation complexes. The log Kl formation constant is 20.4 for TETA with Cu(II) (k=10.0 HE20.4). Modeling shows complete chelation of copper (75 ppb weight basis) with 1 ppm (weight basis) TETA in ethanol. The formation constant of TETA with Cu(II) is large enough that 1 :1 TETA: Copper (mol basis) is likely sufficient to completely chelate the copper in an alcohol feed to a typical glycol ether manufacturing process.

In addition to reaction with copper, TETA can react with an alkylene oxide, e.g., ethylene oxide (EO), propylene oxide (PO), butylene oxide (BO), etc. TETA will react fairly rapidly with EO and/or PO. The primary and secondary amine nitrogen atoms in the ethylene amine will react with the alkylene oxide to form an alkoxylated polyamine.

The chelation process between TETA and copper is an equilibrium reaction. At the low levels of copper and TETA in a typical reactor feed, time is required for TETA to find and react with the soluble copper. In one typical embodiment for the production of glycol ether, the chelating agent is added to the reactor feed directly before the entrance to the reactor. At the very low levels of metal contaminant in the organic process stream and limited reaction time, TETA will unlikely completely chelate the copper before TETA enters the reactor and is exposed to alkylene oxide. In the presence of alkylene oxide (which is multiple orders of magnitude higher in concentration than copper or other metal contaminants), TETA will rapidly become alkoxylated. However, alkoxylated-TETA is still active for copper or other metal contaminant chelation and will react with any copper or other metal contaminant in the reactor.

When the addition of the chelating agent is in excess of the amount necessary, the excess chelating agent, e.g., TETA, will be available to remove copper and other metal contaminant deposits from the inside of the reactor and distillation columns. Laboratory studies at room temperature showed that TETA and alkoxylated-TETA can remove copper deposits from iron particles. Any TETA in excess of the amount necessary to chelate the solvated copper or other metal contaminants in the organic solvent process stream will be able to remove copper deposits that exist on the internal surfaces of process equipment and with which the TETA-containing organic solvent process stream is in contact. This removal of copper deposits will take time (the actual time dependent on a number of factors such as the extent of the deposits, their locations, the amount of excess TETA, etc.), but eventually a sufficiently large part of the deposits will be removed to reduce carbonyl formation that resulted from these deposits to a negligible amount.

The chelant and any related chelant compounds, e.g., chelated metal, can be either left in or removed from the organic solvent product stream. The chelant and its related compounds can be left in the organic solvent product if their presence does not render the product off- specification. If their presence does render the product off-specification, then these materials can be removed from the product by any convenient method. One such method is to select a chelant with a boiling point significantly higher than that of the boiling point of the other components of the organic solvent process stream, and then subject this stream to distillation. The chelant and its related compounds will remain in the bottoms of the distillation column while the other components can be removed as overheads. For example, the boiling point of TETA (274C) is significantly higher than that of ethanol (78.5C) and the other components of a glycol ether product stream. Thus, TETA and any TETA-compounds (TETA-Cu complexes and

alkoxylated -TETA) will remain at the bottom of the distillation columns and leave through the bottoms stream.

The invention is further described and illustrated by the following examples. Unless indicated to the contrary, all parts and percentages are by weight.

SPECIFIC EMBODIMENTS Exchange Column Experiments:

In the initial part of a study, experiments were conducted using n-butanol (and TETA) over a bed of iron particles (40 mesh). In the first experiment, butanol with 100 ppm copper (from copper nitrate salt) was passed through a 75g bed of iron particles (1.5 cm internal diameter by 13 cm height) at a flow rate of 3 ml/min and room temperature (20-24C). The copper concentration in the effluent was measured by ultra violet-visible (UV-VIS) spectroscopy with an identified peak at 260-270 nm for copper. The copper concentration of the column effluent rapidly fell from 100 ppm to less than 3 ppm after three passes through the iron particle bed (Figure 3).

Next, a solution with 1100 ppm TETA, 100 ppm copper in n-butanol was passed over the same bed of iron particles. Figure 3 shows that the copper concentration of the effluent increased rapidly to 115 ppm (15% higher than that of the feed solution). This shows that TETA is able at room temperature to remove electrochemically deposited copper from the iron particles. Subsequent passes of the TETA/Cu/Butanol solution through the bed resulted in only slight increases in the copper concentration.

In the next part of the study, iron particles were pre-treated with a copper nitrate solution. These copper containing iron particles were then loaded onto the exchange column and washed with fresh butanol until the copper concentration of the effluent was lower than lppm. The feed

was then switched to a butanol solution with lOOppm TETA. The resulting copper concentration in the effluent with time is shown in Figure 4. The copper concentration of the column effluent rapidly increases to 11 ppm after 30 minutes. The copper concentration then steadily decreases with time.

The final part of the study examined the performance of ethoxylated-TETA for copper removal from iron particles. The ethoxylated-TETA was obtained by reacting TETA with ethylene oxide (EO) in a Parr reactor with a feed ratio of three moles of EO for every mole of TETA. The study again used iron particles that had been pre-treated with exposure to a copper nitrate in butanol solution. The copper containing iron particles were loaded onto the exchange column and washed with fresh butanol until the copper concentration in the column effluent was less than 1 ppm. The feed was then switched to 100 ppm ethoxylated-TETA in n-butanol. The copper concentration in the column effluent as a function of time is also shown in Figure 4. Like the TETA/butanol study, the copper concentration of the effluent reaches a maximum after approximately 30 minutes of exposure and then decreases with time, The copper concentration with ethoxylated-TETA was slightly less than that observed with TETA. After 210 minutes, the feed was switched to 100 ppm TETA in butanol. The initial TETA/butanol solution was slightly higher than that seen with ethoxylated-TETA, but rapidly approached the values observed with ethoxylated-TETA.

These experiments showed that TETA and ethoxylated-TETA are capable of removing copper that has been elcctrochemically deposited on iron. Parr Reactor Studies:

Parr Reactor studies were conducted with TETA and copper oxide (CuO) powder (which was used to simulate the presence of copper deposits on the internal surfaces of organic solvent process stream equipment). Several different product systems were looked at during these

Jg ₀ J-- 23

studies including: ethylene glycol ethyl ether (EE), propylene glycol n-propyl ether (PnP), ethylene glycol butyl ether (EB), and propylene glycol n-butyl ether (PnB). Similar trends in the results were seen with different studies. The presence of copper oxide was found to increase the color of the effluent and increase the concentration of trace compounds. The addition of TETA along with CuO was found to decrease the color and amount of trace compounds relative to the CuO only experiments. Samples with higher concentration of TETA in the feed (relative to CuO) had lower color and trace compounds than lower TETA:CuO ratio samples (Figure 5). In all cases, the gas chromatograph (GC) peaks for the four TETA components "disappeared" within 30-60 minutes after the addition of ethylene oxide (EO) or propylene oxide (PO). Carbonyl formation with Copper Oxide and TETA:

TETA will react readily (and exothermically) with aldehyde and carbonyl compounds. To investigate the impact of addition of TETA on carbonyl formation, a series of experiments were conducted with the addition of various amounts of CuO powder and TETA to n-butanol in the Parr reactors. The mixture was heated to 160C and agitated for 2 hours. The carbonyl concentration in the reactor effluents was determined by summation of the GC peaks associated with known carbonyls from standards (butryaldhyde, 2-ethyl-2-hexanaI, 2-ethyl-2-hexenal, and 2-ethyl-2-hexanol). Figure 6 shows the total carbonyl area percent in the reactor as a function of time. The results show that the addition of CuO increases the concentration of carbonyl compounds. The results also show that the carbonyl concentration decreases when TETA is added to the reactor feed. Removal of Copper from Carbon Steel with TETA During Reaction:

Parr reactor experiments were conducted with TETA and carbon steel pall rings coated with copper deposits. The experimental study consisted of seven reactions. The first reaction

did not use any TETA and served as a baseline for the subsequent experiments. The next 6 reactions contained 5 ppm TETA in the initial reactor charge. The reaction effluents from the study were analyzed by GC, UV-VIS spectroscopy, and total carbonyl testing. With the addition of 5 ppm TETA to the reactor feed material, the carbonyl concentration in the reaction effluent dropped by 65-80% from the baseline value as shown in Table 1 below. In addition to the decrease in carbonyl concentration, the color of the coating or patina on the carbon steel rings changed from a dull black to a medium gray. Analysis of the reaction effluent by UV-VIS spectroscopy showed that the baseline material did not contain any copper in the liquid phase. The concentration of copper in the studies with 5 ppm TETA showed between 1.5-2.7 ppm copper in a TETA-copper complex.

Table 1

Chelation Rate of TETA & Efhoxylated-TETA with Copper:

TETA is known to have a very high equilibrium stability constant (log k = 20.1). The rate of formation of the chelation complex is not known. An experimental program was initiated to investigate the rate of chelation complex formation using UV-VIS spectroscopy. The TETA-Cu complex has a strong signal in the UV region at 260-270nm. The TETA chelating agent also has a relative strong signal at -210 nm. The study consisted of placing a butanol solution with various amounts of copper (0.1-1.0 ppm) in a quartz UV-VIS cell and taking signal readings at 230nm, 260nm, 280nm, 360nm, and 600nm every 30-60 seconds. After 5 minutes, a

small amount of TETA (or ethoxylated-TETA) was added to the UV-VIS cell (with no additional mixing) and the change in signal at the identified wavelength was taken for the next 60-90 minutes.

For both TETA and ethoxylated-TETA, the formation of the chelation complex appears almost immediately after addition of the chelating agent to the Cu/butanol solution. For high ratios of chelating agent relative to copper (>20 mole chelating agent: moleCu) on a mol basis, the chelation complex formation is almost complete after 15 minutes (Figure 7). TETA has a higher relative chelation complex formation rate than ethoxylated-TETA. This is not unexpected since the ethoxylated-TETA is more sterically constrained than TETA due to the additional ethoxylate units on the nitrogen atoms (with the lone-pair of electrons) that are the active sites for reaction with the copper ions,

At lower ratios of chelating agent to copper (2: 1 - chelating agent:Cu), the reactivity differences between TETA and ethoxylated-TETA are more pronounced. With TETA, the chelation complex formation is essentially complete after -15 minutes as shown in Figure 8. With ethoxylated-TETA, the formation of the chelation complex is essentially complete after 80 minutes (or five times longer than TETA).

Although the invention has been described in considerable detail by the preceding examples, this detail is for the purpose of illustration and it is not to be construed as a limitation upon the scope of the invention as it is described in the appended claims.