Patent Grant
6986839
Not applicable.
Not applicable.
The present invention relates to a method for inhibiting and dissolving polymeric deposits that tend to form in caustic or alkaline scrubbers. More particularly, the present invention relates to the use of certain aliphatic amino acids, sultam acid, or lactams to inhibit deposition and dissolve deposits. Still more particularly this invention relates to method for prevention of fouling in a basic solution that is in contact with a gaseous or liquid hydrocarbon stream that is effluent from a hydrocarbon cracking operation.
In pyrolytic cracking operations, feedstocks such as ethane, propane, naphtha, kerosene, gas oil, fuel oil and the like undergo “cracking,” i.e. the removal of hydrogen, to form unsaturated hydrocarbons. Pyrolytic cracking also tends to produce oxygenated hydrocarbons, including carbonyl compounds such as acetaldehyde. In a typical operation, the cracked effluent stream is quenched and fractionated and compressed. Acidic contaminants such as hydrogen sulfide, carbon dioxide and mercaptans are typically then removed from the effluent hydrocarbon stream by washing in a caustic scrubber.
The caustic scrubber partially removes the oxygenated hydrocarbons. At the same time, however, the basic conditions in the scrubber tend to cause base-induced condensation reactions of the carbonyl compounds, including in particular aldehydes (e.g., acetaldehyde) and/or ketones, which in turn result in the formation of polymers. The polymers deposit and form on the internal surfaces of the scrubber. As the mass of polymer grows, it leads to fouling and can eventually obstruct the flow of liquids through the system. This is undesirable, as the down-time required to remove the deposited polymer and clean the equipment can be significant.
In the past, polymerization of oxygenated compounds, such as carbonyl-containing organics in basic solutions, has been stopped by adding amine compounds such as hydroxylamine hydrochloride, hydroxylamine sulfate, hydrazine, carbohydrazides and the like. Several patents relate to methods of inhibiting carbonyl fouling. But no patent has been reported regarding the dissolution of the polymers once formed.
U.S. Pat. No. 4,673,489 discloses using hydroxylamine and its salts of hydrochloric acid and sulfuric acid to inhibit polymer formation caused by condensation reactions of aldehydes contained in caustic scrubber units. One disadvantage of the method is that the additive has to be used in almost molar proportion.
U.S. Pat. No. 4,952,301 discloses using ethylenediamines with the molecular formula N2(CH2CH2NH)xH where x is an integer ranging from 1 to about 10 to inhibit carbonyl based fouling, particularly aldehyde fouling, that often occurs during caustic scrubbing of liquid or gas phase hydrocarbon streams in the base wash unit.
U.S. Pat. No. 5,264,114 also discloses the use of amine compounds to inhibit the deposition of foulants during caustic washing of the hydrocarbon gases contaminated with the carbonyl compounds which comprises of treating the hydrocarbon gases with an aqueous amine solution wherein the aqueous amine solution comprises water and an amine compound having a concentration range of 2 ppm to about 5000 ppm and wherein the amine compound is selected from group of organic compound of the formula RNH2 and R2NH, wherein R is selected from the group of alkyl or aryl groups.
Carbohydrazide has been disclosed in U.S. Pat. No. 5,160,425 as useful for inhibiting polymeric fouling deposits during the caustic scrubbing of pyrolytically-produced hydrocarbons contaminated with oxygen-containing compounds.
U.S. Pat. No. 5,288,394 describes a method of inhibiting formation of polymeric fouling deposits after caustic scrubbing of a hydrocarbon stream contaminated with oxygenated compounds with a basic washing solution having pH more than 7, comprising adding to the hydrocarbon stream a sufficient amount of a compound that inhibits formation and deposition of fouling materials comprising at least one hydrazide compound.
U.S. Pat. No. 5,194,143, granted to Roling describes and claims a method for inhibiting the formation of polymeric based fouling deposits during the basic washings of olefins containing hydrocarbon contaminated with oxygenated compounds comprising adding to the wash about 1 to 10000 parts pre million acetoacetate ester compound having the formula CH3COCH2CxHy where x is an integer from about 1 to about 8 and y is an integer from about 3 to about 17. U.S. Pat. No. 5,220,104 discloses the use of percarbonate salts for the same purpose.
In U.S. Pat. No. 5,770,041 Lewis et al. describe the use of certain aldehydic compounds without alpha hydrogen atom or non-enolizable aldehydes such as formaldehyde or glyoxal as aldol inhibitors. Relatively large amounts of the inhibitors disclosed in the '041 patent must be used per mole of carbonyl species.
U.S. Pat. No. 5,710,455 discloses the use of certain organic amine inhibitor like sulfanilic acid for inhibiting the aldol condensation but this patent does not disclose the use of said inhibitor for dissolving the polymer once made which is extremely severe fouling conditions.
Finally, amide condensation products of alkylene polyamines with high molecular weight monocarboxylic acids for reducing or preventing the fouling of processing equipment in petroleum or chemical industries are disclosed in U.S. Pat. No. 3,364,130. In the '130 patent, the fouling occurs during heat transfer and is taking place when the system is heated from 200 to 1300° F. The '130 patent does not address fouling that occurs as a result of alkaline conditions. In addition, while the species that cause fouling in '130 is believed to be olefins and dienes; the '130 patent does not address fouling that is derived from carbonyl compounds.
One disadvantage of the prior art systems is that once the acetaldehydes undergo addition reaction to form high molecular weight polymers, the prior art additives are ineffective for removing them. In addition, the prior art additives typically require additive to reactant molar ratios of at least 1:1 for effective performance. The adducts of the high molecular weight polymers with these compounds tend to be insoluble in the basic system. Thus, the prior art additives are ineffective for the purpose of maintaining unobstructed flow through the system.
Another current practice in the industry is to treat the weak caustic with gasoline or another aromatic fraction in order to remove the polymers before sending it to the spent caustic oxidation unit, in order to prevent fouling there. The resulting gasoline-containing streams cause disposal and operational problem, however. Likewise, routing the gasoline-containing stream to other operating units can cause problems due to the presence of the caustic, as it may effect pH, catalyst and the like.
Hence, despite the various advances in the art, it remains desirable to provide an additive that will inhibit polymerization and also dissolve polymers that are already deposited. In addition, the polymeric deposits also cause fouling of downstream units and can pose environment problems of disposal if aromatics are used to remove deposits from the basic wash system. Hence, it is desired to provide a method for preventing fouling that does not create problems in equipment downstream of the scrubber and that does not pose significant environmental problems.
The present invention overcomes the disadvantages of the prior art and provides a method and composition for both preventing fouling and removing polymeric deposits. In a preferred embodiment, the present invention includes a method for inhibiting oxygenated hydrocarbon fouling that does not interfere with overall plant operations or the operation of individual process units. The present method provides the additional advantage of reducing the concentration of oxygenated hydrocarbons and particularly carbonyl compounds in equipment and in product streams. An alternative embodiment of the present invention includes certain aliphatic amino acids, such as 6 amino caproic acid, sultam acid, and/or lactams such as epsilon caprolactam, which not only prevent but also dissolve the polymer formed by aldol condensation. The preferred compounds can be used alone, or in combination with each other and/or in combination with hydroxyl amine sulfate or sulfanilic acid.
The present invention includes a method of inhibiting and dissolving the polymeric deposits formed in caustic or alkaline scrubbers that are used for scrubbing acidic gases such as carbon dioxide and hydrogen sulfide from the effluent streams formed during the pyrolytic cracking of naphtha, ethane, and propane. The cracking operations also produce oxygenated compounds such as vinyl acetate or acetaldehyde, which undergo polymerization under the alkaline conditions in the scrubber. Upon hydrolysis under alkaline conditions vinyl acetate releases acetaldehyde., hence contributes further to the buildup of polymeric deposits
In a preferred embodiment of the present method, certain aliphatic amino acids, including but not limited to 6 amino caproic acid are used to mitigate the effects of polymerization in the system. It has been discovered that aliphatic amino acids, and particularly 6 amino caproic acid, not only prevent but also dissolve the polymers formed by the aldol condensation described above.
In another preferred embodiment of the present method, sultam acid and certain lactams, including but not limited to epsilon caprolactam (molecular weight 113), are used to mitigate the effects of polymerization in the system. It has been discovered that caprolactam not only prevents but also dissolves the polymers formed by the aldol condensation described above.
When amino acids or lactams are used, they react with the low and high molecular weight molecular weight polymer and the reacted adduct is soluble in the caustic solution. Thus, the amino acids both solubilize the polymers formed and prevent precipitation and fouling of the equipment. The present additives have the dual advantage of working as polymerization inhibitor by reacting with acetaldehydes as well as solublizing any existing polymers by reacting with them.
According to a preferred embodiment, 6 amino hexanoic acid or any suitable aliphatic acid or its isomers or any such derivatives having an amino and/or carboxyl and sulfonic acid as described in the structures, when used in accordance with the present invention, will resolve fouling problem associated with acetaldehyde/ketones in alkaline wash towers in petrochemical plants.
Amino acids that are particularly suited for use in the accordance with the present invention include but are not limited to: 6 amino acid such as the amino hexanoic acid made from epsilon caprolactum, glycine, or taurine, or any compound having one of the structures shown below. Also suitable are the derivatives, isomers, and inorganic or organic salts of these compounds. Also suitable are amino acid derived from (HOOZ)w-PH—(CH2)xNH2, where x is an integer from 1 to 6, Z is C or S , w is an integer from 1 to 4, and PH is a phenyl ring, and amino acids derived from ((HOOZ)-(CH2)x)wPH—(CH2)yNH2, where x and y are any integer, Z is C or S, w is an integer from 1 to 4, and PH is phenyl ring.
It has been discovered that the compounds described in the preceding paragraph are effective polymerization inhibitors for aldol condensation reactions, as well as solubilizing any polymer that may already have been formed by that mechanism. For purposes of this invention, an acetaldehyde polymer may be defined as having 2 or more repeating units of acetaldehyde.
In accordance with the invention, the amino acid may be added to the alkaline scrubber in an amount representing a molar ratio of carbonyl to amine from about 1:0.01 to about 1:25 mole. Preferably the amino acid is added to the alkaline scrubber in amount representing a molar ratio of carbonyl to amine from about 1:0.05 to 1:0.0.5. In an alternative embodiment of the invention, a lactam may be added to the alkaline scrubber in an amount representing a molar ratio of carbonyl to lactam from about 1:0.01 to about 1:25 mole. The lactam is preferably added to the alkaline scrubber in amount representing a molar ratio of carbonyl to lactam from about 1:0.5 to 1:0.25.
Further in accordance with the invention, the amino acid in its salt form or in pure amino acid form can be added either as neat product or as an aqueous solution containing 0.05 to greater than 60 weight percent of the amino acid, with 18 wt. % preferred. Similarly, the lactam can be added either as neat product or as an aqueous solution containing 0.05 to greater than 60 weight percent of the amino acid, with 18–38 wt % being preferred.
The preferred amount of additive ranges from 0.5 to 1,000,000 parts of inhibitor per one million part of the aqueous scrubbing medium used in the caustic wash system. In field conditions, treatments of 25 to 200 ppm have been successfully used.
The following Examples are merely illustrative of some embodiments of the present invention and the manner in which it is can be performed and are not intended to limit the scope of the claimed invention in any way:
20 ml 10–11% strength caustic solution is placed in a 50 ml stoppered conical flask and to it is added 1 ml of vinyl acetate. The mixture is shaken thoroughly. The vinyl acetate hydrolyses to acetaldehyde and undergoes polymerization rapidly to form a deep yellow turbid solution. Polymerization may be enhanced by heating. After 10 minutes of polymerization under basic conditions 1.0 g amino caproic acid is added and the mixture is held at 55° C. for 2 hours. At the end of 2 hours the solution is a clear, transparent wine-red liquid, thus a method is described which can then be used for further prevention of fouling in basic solution.
20 ml. 10–11% strength caustic solution is placed in a stoppered 50 ml conical flask and to it is added 1 ml of vinyl acetate. The mixture is shaken thoroughly. The vinyl acetate hydrolyses to acetaldehyde and undergoes polymerization rapidly to form a deep yellow turbid solution. Polymerization is further carried out at 55° C. for 2 hours. After 2 hours of polymerization under basic conditions, a dark red gummy polymer was found floating on the top and the bottom caustic layer was a hazy yellow solution. To this were added 2.8 g of amino caproic acid and the mixture was kept at 55° C. After 24 hours the solution was a transparent wine red liquid, indicating that the polymer that had been present was dissolved. The resulting clear solution is useful for further prevention of fouling in basic solution.
A clean four-necked round bottom flask equipped with a thermometer, stirrer and condenser is charged with caprolactum (18 g, 0.1593 mole), sodium hydroxide (7 g, 0.175 g) and 75.0 g water. The mixture is well agitated and heated to 105° C. to 120° C. for a period of six hours. Small samples are periodically withdrawn and checked for conversion using HPLC. The conversion of epsilon caprolactum to six amino hexanoic acid is greater than 75%.
A clean four-necked round bottom flask equipped with a thermometer, stirrer and condenser is charged with caprolactum (36 g, 0.3186 mole), 3 g of 36% hydrochloric acid in 61g water. The mixture is agitated well and heated to 105° C. to 110° C. for six hours. A small sample is withdrawn and checked for conversion using HPLC. The conversion of epsilon caprolactum to six amino hexanoic acid is greater than 75%.
20 ml of 10% NaOH solution is added to a 50 ml stoppered conical flask. To this inhibitor solution or in solid form is added followed by addition of 1 ml vinyl acetate. Each mixture is shaken well and kept in an oven at 55° C. for 2 hrs. One control sample is prepared, in which all components except the inhibitor are added. After two hours the contents of the flasks are visually checked for clarity or any deposits. In few cases UV at 800 nm is recorded for comparison.
20 ml of 10% NaOH solution is pipetted into a 50 ml stoppered conical flask. To this is added 1 ml of vinyl acetate solution. The mixture is shaken well and kept in oven for 15 minutes. During this period, the vinyl acetate is hydrolyzed and polymerizes to form insoluble products. After 15 minutes the desired amount of inhibitor is added. One control sample is prepared without inhibitor. The flask is shaken well and kept in an oven for 2 hours. After 2 hours the flask is checked visually for clarity and any deposits. In some cases UV transmittance is measured for comparison. The results are shown in Table 2.
The procedure of Example 6 was used, except that the polymerization time was increased to 1 hr.
The present invention can be also be used as a blend with hydroxyl amine sulfate and sulfanilic acid without the loss of activity for both inhibition and dissolution of polymers, as described below in Example 8 and shown below in Table 4.
20 ml of 10% NaOH solution are added to a 50 ml stoppered conical flask. To this is added the desired inhibitor in solution or in solid form, followed by the addition of 1 ml vinyl acetate. The mixture is shaken well and kept in an oven for 2 hrs at 55° C. One blank is prepared wherein all reagents except the inhibitor are added. At the end of two hours, the contents of the flask are visually checked for clarity or any deposits. In few cases UV transmittance at 800 nm is measured for comparison. The results are shown in Table 4 below.
A plant was having severe fouling in the benzene stripper. The unit fouled within 24 hrs after the introduction of live steam in the column. The unit was being treated by conventional red oil inhibiting compound described in the prior art. A compound in accordance with the present invention was injected at low dosage in the benzene stripper and the unit ran for more than 25 days without any signs of fouling even after injection of live steam in the column. This illustrates the effectiveness of the present compounds in running difficult to treat units. Thus a method is described which shows the superiority of solubilizing over prior art inhibition and dispersing techniques.
A clean four necked round bottom flask equipped with a thermometer, stirrer and condenser is charged with caprolactum (36 g, 0.3185 mole), sodium hydroxide (14.4 g, 0.36 g) and 49.60 g water. The mixture is well agitated and heated to 105° C. to 120° C. for a period of six hours. Small samples are periodically withdrawn and checked for conversion using HPLC. The conversion of epsilon caprolactum to six amino hexanoic acid is greater than 75%.
20 ml of 10% NaOH solution is added to a 50 ml stoppered conical flask. To this caprolactum (mw 113, m.p 70–72° C.) is added followed by addition of 1 ml vinyl acetate. Each mixture is shaken well and kept in an oven at 55° C. for 24 hrs. One control sample is prepared, in which all components except the inhibitor are added. After two hours the contents of the flasks are visually checked for clarity or any deposits. In few cases UV at 800 nm is recorded for comparison.
Various results are shown in Tables 1–5.
20 ml of 10% NaOH solution is pipetted into a 50 ml stoppered conical flask. To this is added 1 ml of vinyl acetate solution. The mixture is shaken well and kept in oven for 15 minutes at 50–55° C. During this period, the vinyl acetate is hydrolyzed and polymerizes to form insoluble products. After 15 minutes a desired amount of epsilon caprolactum (mw 113 m.p 70–72° C.) inhibitor is added. One control sample is prepared without inhibitor. The flask is shaken well and kept in an oven for 24 hours. After 24 hours the flask is checked visually for clarity and any deposits. In some cases UV transmittance is measured for comparison. The results are shown in Table 6.
20 ml of 10% NaOH solution is pipetted into a 50 ml stoppered conical flask. To this is added 1 ml of vinyl acetate solution. The mixture is shaken well and kept in oven for 30 minutes at 50–55° C. During this period, the vinyl acetate is hydrolyzed and polymerizes to form insoluble products. After 30 minutes the desired amount of epsilon caprolactum (mw 113 m.p 70–72° C.) inhibitor is added. One control sample is prepared without inhibitor. The flask is shaken well and kept in an oven for 24 hours. After 24 hours the flask is checked visually for clarity and any deposits. In some cases UV transmittance is measured for comparison. The results are shown in Table7.
20 ml of 10% NaOH solution is pipetted into a 50 ml stoppered conical flask. To this is added 1 ml of vinyl acetate solution. The mixture is shaken well and kept in oven for 1 hrs minutes at 50–55° C. During this period, the vinyl acetate is hydrolyzed and polymerizes to form insoluble products. After 1 hrs minutes the desired amount of epsilon caprolactum (mw 113 m.p 70–72° C.) inhibitor is added. One control sample is prepared without inhibitor. The flask is shaken well and kept in an oven for 24 hours. After 24 hours the flask is checked visually for clarity and any deposits. In some cases UV transmittance is measured for comparison. The results are shown in Table 8
The basic wash systems in which the present treatments are useful for inhibiting fouling include amine acid gas scrubber and caustic wash systems. While the present invention has been described herein in terms of preferred embodiments, one of ordinary skill in the art will recognize that modifications to the embodiments can be made without departing from the scope of the claimed invention.
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| Number | Date | Country | |
|---|---|---|---|
| 20030205503 A1 | Nov 2003 | US |
