Abstract:
A corrosion inhibitor for aqueous solutions of mineral acids consisting essentially of the reaction product obtained by the catalytic ethynylation of a dialkylamine, a substituted benzaldehyde and acetylene, said reaction product being a complex material which contains predominately a 3-dialkylamino-3-(substituted phenyl) prop-l-yne.

Description:
RELATED APPLICATIONS 
     Ser. No. 301,667, filed Sept. 14, 1981, by the same inventors as herein and assigned to the same assignee. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to inhibition of metal corrosion in acidic solutions, and particularly to improved aqueous reaction products for such use. 
     2. Description of the Prior Art 
     In the field of oil-well acidizing, it is necessary to use inhibitors to prevent corrosion of the oil-well equipment by the acid solutions employed. Many different acetylenic amines have been proposed or used as corrosion inhibitors for oil-well acidization; see e.g. U.S. Pat. Nos. 2,997,507; 3,079,345; 3,107,221; 3,231,507; 3,268,524; 3,268,583; 3,382,179; 3,428,566; 3,496,232; 3,705,106; 3,772,208; 3,779,935; 3,802,890; 3,816,322; and 4,002,694; and the articles entitled &#34;Ethynylation&#34; by W. Reppe, et al. Ann. Chem. 59B, 1-224 (1955); and &#34;Acetylenic Corrosion Inhibitors&#34;, by Foster et al., Ind. and Eng. Chem., 51, 825-8 (1959). 
     Nonetheless, there has been a continuing search for new materials which are highly effective in such application. More particularly, it is desired to provide new and improved corrosion inhibitors which are particularly advantageous in commercial use to prevent corrosion of metals in highly acid solutions, even after prolonged periods of use, which have a low vapor pressure and relatively high stability so that they can be employed at the high temperatures which prevail in modern deep drilling operations, which function effectively at low concentrations, and which are relatively inexpensive to make. 
     SUMMARY OF THE INVENTION 
     The corrosion inhibitor composition of the invention is the reaction product of the catalytic ethynylation reaction between a dialkylamine, a substituted benzaldehyde, and acetylene, and is a complex material which contains predominately a 3-dialkylamino-3-(substituted phenyl)prop-1-yne. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The predominate compound in the reaction product is formed by the reaction shown below: ##STR1## where 
     R 1  and R 2  are independently alkyl C 1  -C 8  ; 
     R 3  is independently halo, alkyl C 1  -C 8  or alkoxy C 1  -C 8  ; and 
     n is 1 or 2. 
     The ethynylation reaction product is a complex mixture which probably contains, in addition to the predominate compound, the corresponding bis compound, i.e. an N,N,N&#39;,N&#39;-tetralkylamino-1,4-bis(substituted phenyl)-1,4-(2-butynediyl)diamine, having the formula: ##STR2## In addition, it may contain some 3-dialkylaminobutyne, having the formula: 
     
         R.sub.1 R.sub.2 NCH(CH.sub.3)C.tbd.CH, 
    
     and, depending upon reaction conditions, unreacted starting materials, and lesser amounts of other materials. 
     The reaction product is particularly attractive from a commercial standpoint since purification of the product of the ethynylation reaction is not required. Furthermore, the reaction product itself usually performs as well as or better under most conditions than the predominate compound in pure form. This effect may be due to the presence of by-products in the reaction product which may act as a synergist with the predominate compound. 
     The reaction is carried out in the presence of an ethynylation catalyst, such as is used for commercial preparation of butynediol; see, e.g. U.S. Pat. Nos. 3,920,759; 4,117,248; and 4,119,790. The preferred catalyst is a complex cuprous acetylide prepared from a precursor containing about 5 to 35% by weight of copper, and 2-3% by weight of bismuth, as the oxides, on a magnesium silicate carrier. However, many other ethynylation catalysts and carriers known in the art may be used as well. 
     The ethynylation reaction can be run under low or high pressure conditions, i.e. a partial pressure of acetylene, as is used for butynediol, generally from about 0.1 atmosphere to 20 or more atmospheres, either in a stirred reactor with a slurried catalyst, or in a fixed bed, through which the acetylene and the solution are passed. 
     The ethynylation process preferably is run in a solvent in which the reactants are at least partially soluble. An organic solvent which is inert to the reaction may be used advantageously; preferably it is also volatile so that it can be easily separated from the reaction product by distillation. Alcohols, hydrocarbons and other organic solvents may be used for this purpose. Preferred organic solvents are either dry or aqueous isopropanol or methanol. 
     Water also is a suitable solvent; however, water does not completely dissolve the reactants, and it wets the catalyst, which interferes with wetting by the organic reactants. The ethynylation reaction rate thus is slower in water than in an organic solvent which forms a single liquid phase. Mixtures of an organic solvent and water may be used, most suitably those which give a single reacting liquid phase. 
     In a typical run, a charge is made of the reactants in a molar ratio of about 1:1 of the dialkylamine and substituted benzaldehyde. The charge then is heated to a temperature of about 70° to 115° C., preferably 85° to 105° C., and acetylene is introduced and maintained at the desired pressure. The reaction then is carried out for from less than 1 to 36 hours, generally for about 0.2 to 8 hours. 
     The crude reaction product then is separated from the catalyst, where necessary, and, preferably, stripped of solvent, usually under reduced pressure. 
     The predominate compound in the reaction product may be characterized by its IR and NMR spectra. The IR spectrum shows the presence of a strong sharp C-H stretching absorption band at about 3320 cm -1 , attributable to the ethynyl group, and an absence of carbonyl absorption in the region of 1600-1700 cm -1 . The NMR spectrum shows distinctive absorptions related to the ##STR3## portion of the molecule. The C-1 proton is evident by a doublet at 3.1-5.2δ due to coupling of the C-3 proton with the C-1 proton. The C-3 proton also shows up as a doublet for the same reason; however, at 2.0-3.0δ. In addition, the NMR spectrum of the compound reveals the absence of both an aldehyde proton absorption, which is present in the starting material at 9-10δ, and an N-H absorption. 
     The corrosion-inhibiting product of the invention may be used at varying concentrations. What is an effective amount in a particular application will depend upon local operating conditions. For example, the temperature and other characteristics of the acid corrosion system will have a bearing upon the amount of inhibitor to be used. The higher the temperature and/or the higher the acid concentration, the greater is the amount of corrosion inhibitor required to give optimum results. In general, however, it has been found that the corrosion inhibitor of the invention should be employed at a concentration of between 0.01 and 2%, preferably between 0.01% and 1.2%, by weight of an aqueous acidic solution, although higher concentrations can be used when conditions make them desirable. An inhibitor concentration between 0.05% and 0.75% by weight is of the most general use, particularly at elevated temperatures, e.g. in the neighborhood of 200° F. 
     The acidic solution itself can be dilute or concentrated as desired, and can be of any of the specific concentrations customarily used in treating metals, e.g. ferrous metals, or for operations involving contact of acidic solutions with such metals in oil-well acidizing. Generally the acid content is about 5 to 80%, and, in most operations of the character indicated, acid concentrations of 10-15% by weight are employed. Non-oxidizing inorganic acids are the most common acids used. 
    
    
     The invention will now be described in more detail by the following examples which are for illustration only, and not by way of limitation. 
     EXAMPLE 1 
     A charge is made to a 1-l. stirred autoclave consisting of 1 mole (129 g) of dibutylamine, 1 mole of 2-chlorobenzaldehyde (140 g), 25 g of a 35 wt. % Cu-containing catalyst, prepared as described in U.S. Pat. No. 4,119,790, as a powder, and 350 ml of isopropanol. 
     The reactor is purged well with nitrogen, released to atmospheric pressure, and the reactants are heated to 95° C. The vapor pressure at this point is recorded. Acetylene then is admitted at a pressure of 100 psig above the recorded pressure. The amount of acetylene furnished to the reaction is measured by the loss in weight of the supply cylinder. 
     After about 12 hrs., corresponding to the absorption of 1 mole of acetylene (26 g), the reactor is cooled and the product is discharged. The reaction mixture is filtered to remove catalyst and stripped of solvent by rotary evaporation. 
     Gas chromatographic analysis of the resulting crude reaction product mixture indicates it contains about 65% by weight of 3-dibutylamino-3-(2-chlorophenyl)prop-1-yne. 
     The IR spectra of this compound shows a sharp band at 3340 cm -1  ; the NMR spectrum contains distinctive doublets at 5.1 and 2.9δ in addition to absorptions associated with the butyl and 2-chlorophenyl groupings. 
     EXAMPLES 2-6 
     Using the same procedure as described in Example 1 except that an equal molar charge of the following dialkylamines and substituted benzaldehydes are used in place of dibutylamine and 2-chlorobenzaldehyde. The predominate reaction product compound also is indicated, and it is present in comparable amounts in the reaction product as in Example 1. 
     (2) Dimethylamine and 4-chlorobenzaldehyde; dimethylamino-3-(4-chlorophenyl)prop-1-yne. 
     (3) Dibutylamine and 4-methoxybenzaldehyde; dibutylamino-3-(4-methoxyphenyl)prop-1-yne. 
     (4) Dibutylamine and 2,4-dichlorobenzaldehyde; dibutylamino-3-(2,4-dichlorophenyl)prop-1-yne. 
     (5) Dibutylamine and 4-chlorobenzaldehyde; dibutylamino-3-(4-chlorophenyl)prop-1-yne. 
     (6) Dihexylamine and 2-chlorobenzaldehyde; dihexylamino-3-(2-chlorophenyl)prop-1-yne. 
     The reaction products of the present invention were tested in the usual way to determine their effectiveness as corrosion inhibitors. In such tests, strips of 1020 carbon steel of the dimensions 2.5&#34;×1.0&#34;×0.20&#34; were first degreased with methylethyl ketone and then descaled by soaking in 10% hydrochloric acid solution containing approximately 0.1% propargyl alcohol. The coupons then were cleaned with a brush and thoroughly rinsed with water. After rinsing, the coupons were soaked in 2% sodium carbonate solution, rinsed successively with water and acetone and air dried. The surface dimensions of the cleaned coupons were determined and the coupons were allowed to dry in a desiccator. Before use the coupons were weighed on an analytical balance. 
     The tests were carried out in a 4 oz. jar containing a weighed amount of the inhibitor. The total solution weight was taken to 100.0 g with the addition of 15% hydrochloric acid. The coupon then was placed in the mixture and the jar loosely capped and placed in a 80° C. oil bath. After 16 hours the jar was removed from the oil bath and the contents were allowed to attain ambient conditions. The coupon was removed from the acid solution, thoroughly washed with water, 2% sodium carbonate solution, again with water, and finally rinsed with acetone. After air drying the coupon was kept in a desiccator before weighing and the net weight loss was calculated by the established procedure. 
     A control also was run using no inhibitor whatsoever, and for comparative purposes, with a reaction product containing dimethylamino-3-phenyl-prop-1-yne, an unsubstituted phenyl compound, prepared by ethynylation of dimethylamine and benzaldehyde. 
     The test results are presented in the Table below, where a lower value of weight loss represent good corrosion inhibition. 
     
                       TABLE______________________________________EFFECTIVENESS OF REACTION PRODUCT OFINVENTION AS CORROSION INHIBITORSCompound of Formula R.sub.1 &amp; R.sub.2     ##STR4##      Conditions of Test                                Loss (%)Wt.______________________________________Butyl    2-Chlorophenyl                  0.4% Inhibitor;                               0.06                  37.5% HCl;                  4 hrs; 80° C.Ethyl    2-Chlorophenyl                  0.4% Inhibitor;                               0.17                  37.5% HCl;                  4 hrs; 80° C.Hexyl    2-Chlorophenyl                  0.4% Inhibitor;                               0.33                  37.5% HCl;                  4 hrs; 80° C.Methyl   4-Chlorophenyl                  0.4% Inhibitor;                               0.49                  37.5% HCl;                  4 hrs; 80° C.No Inhibitor           0.4% Inhibitor;                               50.94                  37.5% HCl;                  4 hrs; 80° C.Butyl    2-Chlorophenyl                  0.4% Inhibitor;                               0.19                  37.5% HCl;                  16 hrs; 80° C.Methyl   Phenyl*       0.4% Inhibitor;                               14.25                  37.5% HCl;                  16 hrs; 80° C.No Inhibitor           0.4% Inhibitor;                               54.90                  37.5% HCl;                  16 hrs; 80° C.Butyl    2-Chlorophenyl                  0.4% Inhibitor;                               0.03                  15% HCl;                  16 hrs; 80° C.Butyl    4-Chlorophenyl                  0.4% Inhibitor;                               0.04                  15% HCl;                  16 hrs; 80° C.Methyl   4-Chlorophenyl                  0.4% Inhibitor;                               0.09                  15% HCl;                  16 hrs; 80° C.Butyl    2,4-Dichlorophenyl                  0.4% Inhibitor;                               0.07                  15% HCl;                  16 hrs; 80° C.Butyl    2-Methoxyphenyl                  0.4% Inhibitor;                               0.07                  15% HCl;                  16 hrs; 80° C.Methyl   Phenyl*       0.4% Inhibitor;                               0.12                  15% HCl;                  16 hrs; 80° C.No Inhibitor           0.4% Inhibitor;                               26.50                  15% HCl;                  16 hrs; 80° C.______________________________________ *Comparative tests 
    
     As is seen from the data in the Table, the reaction products of the invention exhibit excellent corrosion inhibition for metal in aqueous acid solution. These products perform substantially better than the corresponding reaction products containing unsubstituted phenyl compounds, particularly under the conditions of high concentrations of acid, and long periods of exposure, which conditions are used in commercial applications. 
     While the invention has been described with reference to certain embodiments thereof, it will be understood that modifications and changes may be made which are within the skill of the art. Accordingly, it is intended to be bound by the following claims in which: