Patent Publication Number: US-4259483-A

Title: Quaternary ammonium salts of α-1,4-thiazine alkanephosphonic acids

Description:
This invention relates to novel quaternary ammonium salts of α-1,4-thiazine alkanephosphonic acids of the formula: ##STR1## where R is a substituted group for example a hydrocarbon group or a substituted hydrocarbon group such as alkyl, cycloalkyl, alkenyl, aryl, aralkyl, substituted aryl, etc.; R&#39; is hydrogen or a substituted group such as a hydrocarbon group, i.e., alkyl, etc. R&#34; is a hydrocarbon group such as alkyl, aralkyl, cycloalkyl, alkenyl, alkynl; Z is S, ##STR2## M is hydrogen or a salt moiety, alkali metal, alkaline earth metal, alkyl ammonium, or ammonium, and X is an anion such as halide, acetate, sulfonate, arylsulfonate, etc.; and to the preparation and uses thereof. 
     These compounds are prepared by reacting an α-1,4-thiazine alkanephosphonic acid compound with an alkylating agent in a suitable polar solvent or a mixture of polar solvents. The reaction may be illustrated by the following equation. ##STR3## 
     Examples of the divinyl sulfur compounds include 
     
         CH.sub.2 ═CH--S--CH═CH.sub.2 ##STR4## 
    
     Solvents useful in the methods of this invention are water, mixtures of water and lower alcohols, lower alcohols, dimethyl formamide, dimethyl sulfoxide, and hexamethylphosphorotriamide. 
     The ratio of alkylating agent to α-1,4-thiazine alkanephosphonic acid is preferably at least 1/1 on a molar equivalent basis. However molar equivalents of 3/1 of alkylating agent to the phosphonic acid may be used. 
     After combining the reactants in a suitable reactive medium, the reaction mixture is heated to from 50° C. to 150° C. with stirring to promote alkylation of the α-1,4-thiazine alkanephosphonic acid. In an atmospheric system, the reaction mass is preferably heated to and held at reflux temperature for a time sufficient to bring the reaction to completion. Where higher temperatures and shorter reaction times are desired, superatmospheric pressure systems may be employed to obtain reaction temperature up to about 150° C. 
     After the reaction is complete, the quaternary ammonium product is recovered by cooling the reaction mass to room temperature or lower. 
     The reaction product may be used as such or it may be further purified. Purification is accomplished by washing with organic solvents, formation and separation of salts, ion exchange, and other conventional methods. 
    
    
     The invention may be illustrated by the following examples: 
     EXAMPLE 1 
     Into a flask equipped with a mechanical stirrer, heating jacket, and reflux condenser are charged 24.3 g. (0.1 mol) of ##STR5## 14.2 g. (0.1 mol) of methyl iodide, and 50 ml. of ethanol. The mixture was heated with stirring to reflux and held there for 8 hours. After the reflux period, the reaction mixture was cooled to room temperature and volatiles were stripped off on a rotary evaporator. The resulting crystalline product was washed several times with acetone, filtered, and again washed several times with acetone. The product was recrystallized twice from aqueous ethanol. 
     The resulting product was identified by H&#39; and P 31  spectrum as ##STR6## 
     Anal. Calc. for C 7  H 17  O 5  INPS, N, 3.64; P, 8.05; I, 33.0; S, 8.05. Found: N, 3.55; P, 7.89; I, 32.7; S, 7.98. 
     EXAMPLE 2 
     In a similar manner 24.3 g. (0.1 mol) of ##STR7## was reacted with 12.7 g. (0.1 mol) of benzyl chloride in 50 ml. of ethanol for 12 hours. The product was identified as ##STR8## 
     Anal. calcd. for C 13  H 21  O 5  Cl NPS: N, 3.78; P, 8.38; S, 8.42; Cl, 9.59. Found: N, 3.68; P, 8.45; S, 8.50; Cl, 10.0. 
     EXAMPLE 3 
     In a similar manner 24.3 g (0.1 mol) of ##STR9## was reacted with 12.3 g (0.1 mol) of propyl bromide in 50 ml. of ethanol for 8 hrs. The product was identified as ##STR10## 
     Anal. calcd. for C 9  H 21  O 5  Br NPS: N, 3.82; P, 8.47; S, 8.74; Br, 21.86. Found: N, 3.78; P, 8.60; S, 8.58; Br, 21.55. 
     EXAMPLE 4 
     In a similar manner 25.7 g. (0.1 mol) of ##STR11## and 11.9 g. (0.1 mol) of propargyl bromide were reacted in 50 ml. of refluxing ethanol for 8 hrs. The product was isolated and purified in the usual manner. The structure of the product was ##STR12## 
     Anal. Calcd. for C 10  H 19  O 5  Br NPS: N, 3.72; Br, 21.27. Found: N, 3.66; Br, 20.98. 
     EXAMPLE 5 
     In a similar manner 25.7 g. (0.1 mol) of ##STR13## was reacted with 25.0 g. (0.1 mol) of dodecyl bromide in diamethylformamide for 8 hrs. The product was ##STR14## 
     To avoid repetitive detail, the following table was constructed to further illustrate examples of this invention. 
     
         ______________________________________                                    
 ##STR15##                                                                
Example    R             R&#34;        X                                      
______________________________________                                    
            ##STR16##    CH.sub.3  I                                      
7          C.sub.2 H.sub.5                                                
                          ##STR17##                                       
                                   Br                                     
8                                                                         
            ##STR18##    C.sub.4 H.sub.9                                  
                                   Br                                     
9          C.sub.11 H.sub.23                                              
                         CH.sub.3  I                                      
10         C.sub.2 H.sub.5                                                
                         C.sub.4 H.sub.9                                  
                                   Br                                     
11         C.sub.3 H.sub.7                                                
                          ##STR19##                                       
                                   Cl                                     
12         C.sub.17 H.sub.33                                              
                         CH.sub.3  I                                      
13         C.sub.17 H.sub.35                                              
                         CH.sub.3  I                                      
14         C.sub.2 H.sub.5                                                
                         CH.sub.3  SO.sub.3                               
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     USE AS A SCALE INHIBITOR 
     Scale formation from aqueous solutions containing an oxide variety of scale forming compounds, such as calcium, barium and magnesium carbonate, sulfate, silicate, oxalates, phosphates, hydroxides, fluorides and the like are inhibited by the use of threshold amounts of the compositions of this invention which are effective in small amounts, such as less than 2.5 p.p.m. 
     The compounds of the present invention (i.e., the acid form of the compounds) may be readily converted into the corresponding alkali metal, ammonium or alkaline earth metal salts by replacing at least half of the hydrogen ions in the phosphonic acid group with the appropriate ions, such as the potassium ion or ammonium or with alkaline earth metal ions which may be converted into the corresponding sodium salt by the addition of sodium hydroxide. If the pH of the amine compound is adjusted to 7.0 by the addition of caustic soda, about one half of the --OH radicals on the phosphorous atoms will be converted into the sodium salt form. 
     The scale inhibitors of the present invention illustrate improved inhibiting effect at high temperatures when compared to prior art compounds. The compounds of the present invention will inhibit the deposition of scale-forming alkaline earth metal compounds on a surface in contact with aqueous solution of the alkaline earth metal compounds over a wide temperature range. Generally, the temperatures of the aqueous solution will be at least 40° F., although significantly lower temperatures will often be encountered. The preferred temperature range for inhibition of scale deposition is from about 130° to about 350° F. The aqueous solutions or brines requiring treatment generally contain about 50 p.p.m. to about 50,000 p.p.m. of scale-forming salts. The compounds of the present invention effectively inhibit scale formation when present in an amount of from 0.1 to about 100 p.p.m., and preferably 0.2 to 50 p.p.m. wherein the amounts of the inhibitor are based upon the total aqueous system. There does not appear to be a concentration below which the compounds of the present invention are totally ineffective. A very small amount of the scale inhibitor is effective to a correspondingly limited degree, and the threshold effect is obtained with less than 0.1 p.p.m. There is no reason to believe that this is the minimum effective concentration. The scale inhibitors of the present invention are effective in both brine, such as sea water, and acid solutions. 
     The following examples are presented to illustrate the use of the phosphonates prescribed herein and are presented for purposes of illustration and not of limitation. 
     The following test was used to evaluate these compositions as scale inhibitors. Procedure: 
     1. Make up stock CaCl 2 .2H 2  O, 2.94 g/L or 56 g/5 gallons (18.9 liters) 
     2. Stock NaHCO 3  should be 3.35 g/L or 64 g/5 gallons. 
     3. Inhibitors--Make 0.1 percent solutions in deionized water. 1 ml in 100 sample=10 p.p.m. (Test at 5, 20, and 50 p.p.m.). 
     Put 50 ml bicarbonate solution into 100 ml milk dilution bottle. Add inhibitor (for 100 ml final volume). Then added 50 ml CaCl 2  solution and set in bath at 180° F. Do not cap. Always prepare a blank. Run a hardness determination on a 50--50 mixture before heating. 
     Heat at 180° F. Take 10 ml samples from bottles after 2 hours and 4 hours. 
     Filter through millipore filter. 
     Run total hardness on filtrate. 
     Calculate as % Ca still in solution, i.e., ##EQU1## 
     The compounds were tested at 180° F. at the concentration indicated. Hardness readings were taken after 2 and 4 hours. 
     
                       TABLE A                                                     
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Scale Inhibitor Tests                                                     
                  Concen-    % Protec-                                    
Compound          tration    tion                                         
______________________________________                                    
Example 1         5 p.p.m.   28                                           
                  50 p.p.m.  52                                           
Example 1 (sodium salt)                                                   
                  50 p.p.m.  50                                           
Example 3         5 p.p.m.   25                                           
                  50 p.p.m.  40                                           
Example 4         5 p.p.m.   30                                           
Example 5 (sodium salt)                                                   
                  5 p.p.m.   20                                           
                  50 p.p.m.  32                                           
Typical Commercial                                                        
                  5 p.p.m.    24%                                         
Inhibitor         50 p.p.m.   30%                                         
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     USE IN THE CHELATION OR SEQUESTRATION OF METAL IONS 
     The chelating or sequestering agents of the present invention are of wide utility such as when it becomes necessary to sequester or inhibit the precipitation of metal cations from aqueous solutions. Among their many uses are the following applications: 
     Soaps and detergents, textile processing, metal cleaning and scale removal, metal finishing and plating, rubber and plastics industry, pulp and paper industry, oil well treatment, chelation in biological systems. 
     An important function of these compounds is their ability to sequester Fe +2 . In secondary oil recovery by means of water floods, waters are frequently mixed on the surface prior to injection. Frequently these waters contain amounts of Fe +2  and H 2  S. If these incompatible waters are mixed, an FeS precipitate results which can plug the sand face of the injection well. Another of their functions is to prevent formation of gelatinous iron hydroxides in the well and in the effluent production waters. 
     To demonstrate the effectiveness of the quaternary ammonium salts of the present invention in chelating Fe +2 , the following test procedure was utilized. Into a flask that contained a known concentration of the sequestering agent, and enough sodium hydroxide or hydrochloric acid to give the desired pH was placed a 100 ml. aqueous sample of ferrous ammonium sulfate (20 p.p.m. of Fe +2 ); after final pH adjustment the solution was allowed to remain at ambient temperatures for 48 hours. The solution was centrifuged for one hour to remove colloidial iron hydroxide and an aliquot of the supernatant solution was analyzed by atomic absorption to determine the iron concentration. 
     The following table illustrates the ability to the sequestering agents of the present invention to sequester Fe +2 , as compared to the well known sequestering agent tetra-sodium ethylenediamine tetra-acetate (EDTA). 
     
                       TABLE II                                                    
______________________________________                                    
                            Amount                                        
                            of iron                                       
            Sequestering    sequestered                                   
pH          agent (p.p.m.)  (p.p.m.)                                      
______________________________________                                    
5           Ex. 1 (50)      10                                            
            Ex. 3           9                                             
            Ex. 4 (50)      7                                             
             EDTA (50)      7                                             
7           Ex. 1 (50)      10                                            
            Ex. 3 (50)      7                                             
            Ex. 4 (50)      7                                             
             EDTA (50)      7                                             
 10         Ex. 1 (150)     8                                             
            Ex. 3 (150)     7                                             
            Ex. 4 (50)      6                                             
             EDTA (150)     6                                             
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     As one can observe from the preceding table, the sequestering agents of this invention are as effective, and in some cases superior, to EDTA when tested over a wide pH range. 
     The sequestering agents of this invention are also quite effective in sequestering other metal cations in aqueous solutions. For example, a test was conducted in which 60 p.p.m. of the sequesterant were dissolved in 100 ml. of water. The pH was adjusted to 9 and maintained there. Metal cations were added, in the following amounts, before a noticeable precipitate was formed. 
     
                       TABLE III                                                   
______________________________________                                    
                    Metal (p.p.m.)                                        
                    sequestered                                           
Sequesterant,       per 60 p.p.m.                                         
product of          sequesterant                                          
______________________________________                                    
Example 1           Fe.sup.+3 (50)                                        
                    Al.sup.+3 (100)                                       
                    Cu.sup.+2 (100)                                       
                    Ni.sup.+2 (50)                                        
Example 3           Fe.sup.+3 (50)                                        
                    Al.sup.+3 (60)                                        
                    Cu.sup.+2 (60)                                        
                    Ni.sup.+3 (40)                                        
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     Other heavy metals sequestered by the sequestering agents of this invention such as cobalt, manganese, chromium and the like. 
     The amount employed to chelate is controlled by stoichiometry in contrast to scale inhibition where the amount employed is threshold or less than stoichiometric. 
     USE AS A MICROBIOCIDE 
     (I) In water treatment 
     This phase of the present invention relates to the treatment of water. More particularly, it is directed to providing improved means for controlling microbiological organisms including bacteria, fungi, algae, protoza, and the like, present in water. 
     It is well known that ordinary water contains various bacteria, fungi, algae, protozoa and other microbiological organisms which, if uncontrolled, multiply under certain conditions so as to present many serious problems. For example, in swimming pools the growth of these microbiological organisms is very undesirable from a sanitary standpoint as well as for general appearances and maintenance. In industrial water systems such as cooling towers, condenser boxes, spray condensers, water tanks, basins, gravel water filters, and the like, microbiological organisms may interfere greatly with proper functioning of equipment and result in poor heat transfer, clogging of systems and rotting of wooden equipment, as well as many other costly and deleterious effects. 
     In other industrial applications where water is used in processes, as for example, as a carrying medium, etc., microbiological organisms may also constitute a problem in maintenance and operation. Illustrative of such industrial applications are the pulp and paper manufacturing processes, oil well flooding operations and the like. 
     The products of this invention are suitable as biocides for industrial, agricultural and horticultural, military, hygienic and recreational water supplies. They provide an inexpensive, easily prepared group of products which can be used, in minimal amounts, in water supplies, in cooling towers, air-conditioning systems, on the farm and ranch, in the factory, in civilian and military hospitals and dispensaries, in camps, for swimming pools, baths and aquaria, waterworks, wells, reservoirs, by fire-fighting agencies, on maritime and naval vessels, in boilers, steam-generators and locomotives, in pulp and paper mills, for irrigation and drainage, for sewage and waste disposal, in the textile industry, in the chemical industries, in the tanning industry, et cetera, and which will render said water supplies bactericidal, fungicidal and algicidal. They further provide a simple process whereby water supplies, for whatever purposes intended, are rendered bacteriostatic, fungistatic and algistatic, i.e., said water supplies treated by the process of this invention will resist and inhibit the further growth or proliferation of bacteria, fungi, algae and all forms of microbial life therein. 
     (II) Water flooding in secondary recovery of oil 
     This phase of the present invention relates to secondary recovery of oil by water flooding operations and is more particularly concerned with an improved process for treating flood water and oil recovery therewith. More particularly this invention relates to a process of inhibiting bacterial growth in the recovery of oil from oil-bearing strata by means of water flooding taking place in the presence of sulfate-reducing bacteria. 
     Water flooding is widely used in the petroleum industry to effect secondary recovery of oil. By employing this process the yield of oil from a given field may be increased beyond the 20-30 percent of the oil in a producing formation that is usually recovered in the primary process. In flooding operation, water is forced under pressure through injection wells into or under oil-bearing formations to displace the oil therefrom to adjacent producing wells. The oil-water mixture is usually pumped from the producing wells into a receiving tank where the water, separated from the oil, is siphoned off, and the oil then transferred to storage tanks. It is desirable in carrying out this process to maintain a high rate of water injection with a minimum expenditure of energy. Any impediment to the free entry of water into oil bearing formations seriously reduces the efficiency of the recovery operation. 
     The term &#34;flood water&#34; as herein employed is any water injected into oil bearing formations for the secondary recovery of oil. In conventional operations, the water employed varies from relatively pure spring water to brine and is inclusive of water reclaimed from secondary recovery operations and processed for recycling. The problems arising from the water employed depend in part on the water used. However, particularly troublesome and common to all types of water are problems directly or indirectly concerned with the presence of microorganisms, such as bacteria, fungi and algae. Microorganisms may impede the free entry of water into oil-bearing formations by producing ions susceptible of forming precipitates, forming slime and/or existing in sufficiently high numbers to constitute an appreciable mass, thereby plugging the pores of the oil-bearing formation. Free plugging increases the pressure necessary to drive a given volume of water into an oil-bearing formation and oftentimes causes the flooding water to by-pass the formation to be flooded. In addition, microorganisms may bring about corrosion by acting on the metal structures of the wells involved, producing corrosive substances such as hydrogen sulfide, or producing conditions favorable to destructive corrosion such as decreasing the pH or producing oxygen. The products formed as the result of corrosive action may also be pore-plugging precipitates. Usually, the difficulties encountered are a combination of effects resulting from the activity of different microorganisms. 
     (III) Hydrocarbon treatment 
     This phase of the present invention relates to the use of these compounds as biocides in hydrocarbon systems. 
     In addition to being used as biocides in aqueous systems, the compounds of this invention can also be employed as biocides in hydrocarbon systems, particularly when petroleum products are stored. It is believed that bacteria and other organisms, which are introduced into hydrocarbon systems by water, feed readily on hydrocarbons resulting in a loss in product; that microorganisms cause the formation of gums, H 2  S, peroxides, acids and slimes at the interface between water and oil; that bacterial action is often more pronounced with rolling motion than under static conditions, etc. Loss of product, corrosion of the storage tank, clogging of filters and metering instruments, and fuel deterioration are among the harmful effects of bacteria growth in fuels. The activity of microorganism growth is often increased by the presence of rust. Not only do these microorganisms often encourage rust but rust encourages microorganism growth. Since microorganism growth appears to be considerably higher with kerosene than with gasoline, plugged filters experienced with jet fuels which contain large amounts of kerosene is a serious problem. 
     The compositions of this invention can be employed in hydrocarbon systems. 
     MICROBIOCIDAL TESTING 
     The screening procedure was as follows: a one percent by weight solution of the test compound in water was prepared. The solution was aseptically added to a sterile broth that would support the growth of the test organism, Desulfovibro desulfuricans, to provide the specified concentrations given by weight of test compound per million parts by weight of broth. A general growth medium, such as prescribed by the American Petroleum Institute was used. The broth containing the test compound then was dispersed in 5 cc. amounts into sterile disposable tubes and the tubes were inoculated with the growing test organism and incubated at 35° C. for 24 hours. The absence or presence of growth of the microorganisms was determined by visual inspection by an experienced observer. 
     Following is a summary of the results of the testing of examples of this invention. 
     
         ______________________________________                                    
Compound       Concen-                                                    
Example        tration                                                    
Number         in p.p.m.   Results                                        
______________________________________                                    
 2 (Sodium salt)                                                          
               75          Gave control.sup.1                             
 5 (sodium salt)                                                          
               25          &#34;                                              
12 (sodium salt)                                                          
               50          &#34;                                              
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 .sup.1 By control is meant that the test compound was biostatic or       
 biocidal  i.e., no growth of the test organism occurred under the test   
 conditions.                                                              
 
    
     USE IN ACID SYSTEMS 
     The compounds of this invention can also be employed as corrosion inhibitors for acid systems, for example as illustrated by the pickling of ferrous metals, the treatment of calcareous earth formations, etc., as described in the following sections. 
     USES 
     This invention also relates to the inhibition of corrosion, particularly the corrosion of metals in contact with the acid solutions. 
     The present invention is especially useful in the acidizing or treating of earth formations and wells traversed by a bore hole. It may also be used in metal cleaning and pickling baths which generally comprise aqueous solutions of inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid and are useful in the cleaning and treatment of iron, zinc, ferrous alloys, and the like. 
     If no corrosion inhibitor is present when the aqueous acidic solution comes in contact with the metal, excessive metal loss and consumption or loss of acid, and other adverse results will be experienced. There has been a continuing search for corrosion inhibitors which can be used effectively in small concentrations, and which are economical to produce. The need is also for corrosion inhibitors which are effective at high temperatures, e.g., 200° F. and above, such as are found in operations involving acidic solutions, particularly oil-well acidizing where higher and higher temperatures are found as the well extends further into the earth. 
     While the compounds of this invention are of themselves particularly good acid corrosion inhibitors, optionally they may be blended with acetylenic alcohols, dispersing and solubilizing agents such as ethoxylated phenols, alcohols, and fatty acids. They may also be blended with such known acid inhibitors as the quinoline or alkyl pyridine quaternary compounds or synergists such as terpene alcohols, formamide, formic acid, alkyl amine, alkylene polyamines, heterocyclic amines, and the like. 
     Quaternary ammonium compounds may be illustrated by C-alkyl pyridine-N-methyl chloride quaternary, C-alkyl pyridine-N-benzyl chloride quaternary, quinoline-N-benzyl chloride quaternary, isoquinoline-N-benzyl chloride quaternary, thioalkyl pyridine quaternaries, thioquinoline quaternaries, benzoquinoline quaternaries, thiobenzoquinoline quaternaries, imidasole quaternaries, pyrimidine quaternaries, carbazole quaternaries, the corresponding ammonium compounds, pyridines and quinolines may also be used alone or in combination with the quaternary compounds. Thus a pyridine plus quinoline quaternary, a quinoline plus quinoline quaternary, or quinoline or amine alone or in combination may be used. 
     The formic acid compound may be selected from the esters and amides of formic acid. The formic acid compound may be from the group consisting of formate esters of the structure: 
     
         HCOOR 
    
     where R is a monoaryl group, an alkyl group having 1 to 6 carbon atoms, cyclo-alkyl residues having 5 to 6 carbon atoms, alkenyl and alkynl groups having 2 to 6 carbon atoms which may contain functional groupings selected from --C--OH, --OH, ═C═O, --COOH, --SH, and NH 2 . Examples of the formic acid compound are: methyl formate, ethylformate, benzyl formate, other alkyl and aryl formates, and the like. Other examples include formamide, dimethyl formamide, formanilide, and the like. Mixtures of the esters and mixtures of the amides may be used. 
     USE IN ACIDIZING EARTH FORMATIONS 
     The compositions of this invention can also be used as corrosion inhibitors in acidizing media employed in the treatment of deep wells to reverse the production of petroleum or gas therefrom and more particularly to an improved method of acidizing a calcareous or magnesium oil-bearing formation. 
     It is well known that production of petroleum or gas from a limestone, dolomite, or other calcareous-magnesian formation can be stimulated by introducing an acid into the producing well and forcing it into the oil or gas bearing formation. The treating acid, commonly a mineral acid such as HCl, is capable of forming water soluble salts upon contact with the formation and is effective to increase the permeability thereof and augment the flow of petroleum to the producing well. 
     Corrosion Test Procedure 
     In these tests the acid solutions were mixed by diluting concentrated hydrochloric acid with water to the desired concentrations. 
     Corrosion coupons of 1020 steel (AISI) were pickled in an uninhibited 10% HCl solution for 10 minutes, neutralized in a 10% solution of NaHCO 3 , dipped in acetone to remove water and allowed to dry. They were then weighed to the nearest milligram and stored in a desicator. 
     In most of the tests, a 25 cc/in 2  acid volume to coupon surface area ratio was used. After the desired amount of acid was poured into glass bottles, the inhibitor was added. The inhibited acid solution was then placed in a water bath which had been set at a predetermined temperature and allowed to preheat for 20 minutes. After which time, the coupons were placed in the preheated inhibited acid solutions. The coupons were left in the acid solutions for the specified test time, then removed, neutralized, recleaned, rinsed, dipped in acetone, allowed to dry, then reweighed. 
     The loss in weight in grams was multiplied times a calculated factor to convert the loss in weight to lbs./ft 2  /24 hrs. The factor was calculated as follows: 
     
         ______________________________________                                    
 ##STR20##                                                                
CORROSION INHIBITION IN 15% HCl                                           
Inhi-            Test     Test   Corrosion Rate                           
bitor   p.p.m.   Temp.    Time   (lbs/ft.sup.2 /day)                      
______________________________________                                    
Ex. 2   2000     150° F.                                           
                          4 hrs. 0.054                                    
Ex. 4   2000     150° F.                                           
                          4 hrs. 0.040                                    
Ex. 9   2000     150° F.                                           
                          4 hrs. 0.035                                    
Blank   2000     150° F.                                           
                          4 hrs. 0.240                                    
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