Title of Invention

"CORROSION INHIBITING COMPOSITIONS FOR HYDROCHLORIC ACID / SULFURIC ACID PICKLING BATHS"

Abstract

A corrosion inhibiting composition is disclosed. The composition essentially comprises of alkarylated polyalkyl pyridinium salts of the general formula (1) (where R,R'.R" is a linear or branched Cl - C5 alkyl chain, R'" is benzyl group, X is an anion preferably halogen) containing at least one or more than one alkanol, a surfactant, a alkynol, said composition inhibits the overpickling of the ferrous metal and its alloys during the hydrochloric acid / sulfuric acid pickling. The steel pickled using present inhibitor is pickled at faster rate, consumes less raw acid and is of brighter aesthetics. Also, said composition reduces the hydrogen evolution during the process resulting to less pollution and less base metal dissolution.

Full Text

FIELD OF INVENTION This invention relates to a novel corrosion inhibiting compositions for hydrochloric acid / sulfuric acid pickling process for iron, steel and ferrous alloys. BACKGROUND OF THE INVENTION The present invention relates generally to additives for acid pickling baths and more particularly, to an improved additive for hydrochloric acid pickling and sulfuric acid pickling bath, utilized for batch and continues pickling of all types of steels that accelerates the pickling rate, reduces raw acid consumption, and increases the brightness of the pickled steel. Hot mill surface scale on steel generally consists of outer layers of iron oxides having high oxygen contents, such as Fe2O3 and FesO^ an inner layer of oxygen oxides having low oxygen content, such as FeO and possibly intermediate layers of mixed iron oxides. In addition to iron oxide scale, the steel may also have surface dirt. Pickling is generally understood to be the chemical removal of the surface scale and dirt with mineral acids, such as sulfuric, hydrochloric and nitric-hydrofluoric acids. When iron oxide dissolve in mineral acid pickling baths, the ferrous salt and water are formed. Metallic iron reacts with mineral acid, the ferrous salt and hydrogen are formed. In hydrochloric acid pickling baths, the reaction of acid with the metallic iron is 2HC1 + Fe ^ FeCl2 + H2 Inhibitors are the agents that are added to mineral acid pickling baths to protect the exposed surface of the metallic iron. They do so by inhibiting or retarding the reaction of acid without affecting, to an appreciable degree, the pickling action which is removing of the iron oxide scale and dirt from the surface. If pickling acid baths were used for pickling without inhibitors, iron oxide scale would be removed, but the acid attack on metallic iron would be rapid and severe, depending upon the acid concentration and the pickling bath temperature. Pitting of the metal surface would occur, undesirable changes in the physical properties of the metal could take place, and the carbon " smudge " could be deposited on the surface. Undesirably, large quantity of hydrogen gas would also be generated and released into the surrounding atmosphere, resulting to an increased corrosion of all the material in the vicinity of the pickling line. The amount of raw acid consumed would be large, and the volume of waste acid generated would increase. For these reasons, inhibitors are typically added to the mineral acid pickling baths. An effective inhibitor should disperse, throughout the pickling bath in lower concentrations, must suppress the hydrogen evolution, and must not leave a smudge or film on line surface of the metal. Inhibitor must also maintain constant effectiveness over a range of acid and iron concentrations and temperatures. We know from prior art that nitrogen-containing compounds are known to be acting as extremely effective corrosion inhibitors. For example, most of the commercially available hydrochloric acid and sulfuric acid pickling inhibitors essentially have amines in their compositions. A number of patents also disclose corrosion inhibitors based on nitrogen bearing molecules, for example, U.S.Patent 3,445,441& U.S.Patent 3,450,646 & U.S.Patent 3,976,593 & U.S.Patent 4,673,436 etc discloses the use of thio-substituted quaternary ammonium salts as hydrochloric acid and sulfuric acid pickling inhibitors. Other patents which discloses another class of hydrochloric acid and sulfuric acid pickling inhibitors are U.S.Patent 3,634,270 & U.S.Patent 3,969,255 and U.S.Patent 4,536,302 etc indicates the usage of Azoles, FfEDPA, HDAA, Quinolines, Hexahydrotriazines, thiazoles, thiazolines, emaraldine base polyanalines etc. These references, however, do not disclose the inhibiting properties of the composition of the present invention. It is also known from the prior art, that heterocyclic nitrogen compounds such as quaternary derivatives of polyalkyl pyridines are important compounds when quaternized to corrosion inhibiting compositions for pickling of ferrous metal applications. See for instance, U.S.Patent No's 3,06,097 & 3,033,784 and 4,071,746, R.O. 86,593. Quaternary compounds can be prepared by reacting the mixture of polyalkyl pyridines under quaternary forming conditions with mineral acids such as hydrochloric acid, phosphoric acid and glacial acetic acid etc. and alkyl halide, preferably alkyl chloride or the like .The resulting quaternary has high tendency to form protective films on the metal surface, which further provides extremely good corrosion inhibiting results. However, the combination becomes very viscous or sometimes semi-solid mass, not easy to use in the fields. This composition is made less viscous by addition of some solvents like water, alcohol, preferably alcohol, optimum methanol. It is also known in the prior art and is disclosed in the above U.S.Patent 3,033,784 and U.S.Patent 4,071.746 that the quaternized polyalkyl pyridine should be used in combination with ethoxylated alcohol derivative of fatty acids. OBJECT OF PRESENT INVENTION It is an object of the present invention to provide a novel hydrochloric acid pickling inhibitor based upon alkarylated polyalkyl pyridinium compounds, which increases the rate of descaling of metal by hydrochloric acid pickling bath to greater degree than did prior art hydrochloric acid pickling inhibitors. It is another object of the present invention to provide a novel hydrochloric acid pickling inhibitor reduces the net consumption of raw hydrochloric acid to a greater degree than prior art hydrochloric acid pickling inhibitors, and increases the brightness of descaled steel surface to greater degree than did prior art hydrochloric acid pickling inhibitors. It is yet another object of the present invention to provide a novel sulfuric acid pickling inhibitor based upon alkarylated polyalkyl pyridinium compounds, with increased the rate of descaling in sulfuric acid pickling bath to greater degree than did prior art sulfuric acid pickling inhibitors, reduces the consumption of raw hydrochloric acid to a greater degree than prior art sulfuric acid pickling inhibitors, and increases the .brightness of descaled steel surface to greater degree than did prior art sulfuric acid pickling inhibitors. It is another object of the present invention to provide a novel hydrochloric acid pickling inhibitor of the present invention, which is absolutely non-interfering with hydrochloric acid regeneration process and non-detrimental to Titanium components of Acid Regeneration Plant (ARP). It is another object of the present invention to provide a novel acid pickling inhibitor based upon alkarylated polyalkyl pyridinium compounds. Another object of the present invention is to provide a novel acid pickling inhibitor, which is extremely effective, cost effective, non-hazardous and easy to handle corrosion inhibitor composition. SUMMARY OF THE PRESENT INVENTION The above and other objects of the present invention are achieved by corrosion inhibiting composition comprising of alkaryl halide derivatives of polyalkyl pyridinium compounds, alcohol, alkynol, and surfactants. The invention provides methods, which are economical and effective in pickling operations. These composition increase the rate of descaling of metal, decrease the consumption of raw acid and increase the brightness of the metal pickled in hydrochloric acid and sulfuric acid pickling baths to a greater degree than did prior art hydrochloric acid and sulfuric acid pickling inhibitors utilized as inhibitors for pickling baths. Also the present invention provides a corrosion inhibiting composition free of any fluoride impurity and non-volatiles (totally organic) thereby being non-interfering in the acid regeneration process. DETAILED DESCRIPTION Accordingly, the present invention provides a novel hydrochloric acid and sulfuric acid inhibiting composition comprising of 5% - 97% by weight of alkarylated polyalkyl pyridinium salt, 30% - 70% by weight of one or more than one alcohol, 10% - 30% by weight of a surfactant, and 0.1% - 2% by weight of alkynol. In a preferred embodiment, alkarylated polyalkyl pyridinium salts are of the general formula (1) (where R,R'.R" is a linear or branched Cl - C5 alkyl chain, R'" is benzyl group, X is an anion preferably halogen) In an embodiment of the present invention, wherein alkarylated polyalkyl pyridinium salt is the reaction product of polyalkyl pyridine with alkaryl halide. In another embodiment of the present invention, wherein polyalkyl pyridine is selected from group consisting of various picolines, lutidines, collidines, methyl ethyl pyridines and propyl pyridines alongwith various other higher alkyl substituted pyridine molecules. In another embodiment of the present invention, wherein the alkaryl halide used is Benzyl chloride. In another embodiment of the present invention, wherein the alcohol used is selected from Ci -C5 alcohol, more preferably Ci-C2 or their mixtures thereof. In another embodiment of the present invention, wherein the surfactant is selected from group consisting of alkoxylated nonyl phenol, castor oil, sulfonates, carboxylates and phosphonates or their mixture thereof. Still another embodiment of the present invention, wherein alkynol used is selected from group comprising of acetylenic alcohol, preferably propargyl alcohol. In yet another embodiment of the present invention, additional use of odor masker selected from group of lemon grass oil, menthol, and other fragrance thereof can reduce the odor of the composition. The composition of the present invention is nether a simple admixture nor a product of a chemical reaction but a synergistic composition having improved and unexpected properties. In the present invention, we have found a low cost quaternizing agent for the quaternization of polyalkyl pyridines (AG-RES & PB-RES). Benzyl halide is reacted with the polyalkyl pyridine under quaternary forming condition according to general chemistry. This type of reaction chemistry is quite conventional. The crude polyalkyl pyridines employed were the following "PB-RES " and " AG-RES " from Jubilant Organosys Limited, INDIA. PB-RES and AG-RES contains medium to high boiling alkyl pyridines with an equivalent weight ranging between 100 to 300. Surfactant employed should be soluble or dispersible in the hydrochloric acid / sulfuric acid pickling bath. In general, it is an ethoxylated material, which is water soluble or dispersible so that it enhances the corrosion inhibition. Any suitable surfactant can be employed. The surfactants that are usually employed in practice are oxyalkylated surfactants or, more specifically, polyalkylene ethers or polyoxyalkylene surfactants. Oxyalkylated surfactants as a class are well known surfactants. The possible sub-classes and specific species are legions. The method employed for the preparation of these oxyalkylated surfactants is also well established, hence does not require much elaboration.. Most of these surfactants contains, in atleast one place in the molecule and often in several places, an alkanol or a polyglycoether chain and these are most commonly derieved by, reacting a starting molecule, possessing one or more oxyalkylable eactive groups, with an alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide etc.. However, they may be obtained by other methods as shown in U.S.Patent 2,588,771 & U.S.Patent 2,596,091 or by esterification / emidification with an oxyalkylated material. Mixtures of oxides may be used as well as successive addition of the same or different oxide may be employed. Any oxyalkylable material may be employed as typical starting material may be mentioned such as phenols, phenolic resins, alcohols, glycol's, amines, organic acids, carbohydrates, mercaptans and partial esters of polybasic acids. There are two methods to obtain the mixture of polyalkyl pyridines of this invention. " PB-RES " is obtained by reacting acetaldehyde, formalin and ammonia in presence of silica -alumina catalyst, at temperatures ranging from 400 °C to 500 °C, extracting the reaction product with solvent followed by fractional distillation of the extract. The residue left after the recovery of low boiling alkyl pyridines is the desired " PB-RES " used in the present invention. " AG-RES " is similarly obtained by reacting ammonia and aldehyde in vapor phase and by similar follow up. The residue left after the recovery of desired alkyl pyridine is the desired " AG-RES " used in the present invention The description of polyalkyl pyridinium compound does not restrict the invention to other polyalkyl pyridinium compounds obtained through vapor phase / liquid phase reaction of different aldehydes and or ketones with ammonia over suitable catalyst over fixed / fluidized / movable bed reactors leading to formation of pyridine and its alkylated derivatives. The invention is further explained with the help of following examples, which should not be constraint to limit the scope of the present invention. Example 1 A mixture of 171 gms of PB-RES, 206 gms of Benzyl chloride and 490 gms of methanol was stirred at reflux temperatures for a period of 10 hours. 130 gms of Nonyl phenol EO 9.5 was added with constant agitation. Example 2 A mixture of 162 gms of AG-RES, 167 gms of Benzyl chloride and 464 gms of methanol was stirred at reflux temperatures for a period of 5 hours. 206 gms of AlphoX-200 was added with constant agitation. Example 3 A mixture of 171 gms of PB-RES, 211 gms of Benzyl chloride and 488 gms of methanol was stirred at reflux temperatures for a period of 10 hours. 129 gms of AlphoX-200 was added with constant agitation. It was found that quaternary polyalkyl pyridinium salts thus obtained by reacting polyalkyl pyridines and benzyl chloride had much more of an inhibiting properties for hydrochloric acid / sulfuric acid pickling inhibition than other quaternary compounds of the same polyalkyl pyridines with acetic acid / hydrochloric acid / phosphoric acid / or the like, as can be seen from the following examples. TABLE 1 Compositions derived out of salts obtained in examples 1 - 4. Composition: VAM/STEEL/GEN Constituent percentage by weight 1. Quaternary polyalkyl pyridinium salt 45.0 From Example 1 2. Methanol 18.5 3. Nonyl Phenol EO 9.5 Moles 36.5 Composition: VAM/STEEL/AG-I Constituent percentage by weight 1. Quaternary polyalkyl pyridinium salt 68.0 From Example 2 2. Methanol 30.0 3. Propargyl alcohol 02.0 Composition: VAM/STEEL/HC1 -1 Constituent percentage by weight 1. Quaternary polyalkyl pyridinium salt 68.0 From Example 3 2. Methanol 31.0 3. Propargyl alcohol 01.0 Composition: VAM/STEEL/HCI Constituent percentage by weight 1. Quaternary polyalkyl pyridinium salt 68.0 From Example 3 2. Methanol 30.0 3. Propargyl alcohol 02.0 These compositions were tested towards their corrosion inhibition properties for hydrochloric acid and sulfuric acid pickling baths on different grades of steels, viz., HR steel, CR steel, Silicon steel, and Stainless steels. VAM/STEEL/AG-I and VAM/STEEL/HCI was specifically used to study the corrosion inhibition properties in hydrochloric acid pickling bath whereas VAM/STEEL/GEN was used in general for both hydrochloric acid pickling bath and sulfuric acid pickling bath. Different test specimens of known metallurgy were arranged and cut into specimens of size having 30 mm x 30 mm x 4 mm dimension. Experiments were run at 90 + 5 °C of bath temperature. The acid concentration in the bath was maintained at 15 % (for hydrochloric acid) and 22% (for sulfuric acid). Inhibitor dosage was varied between 0.1 % to 0.5 % with respect to the bath volume. Also, the exposure period was varied between 30 seconds to 30 minutes. DATA TABLES Inhibitor : VAM/STEEL/GEN Metal : CR STEEL PICKLING MEDIUM: 22% SULFURIC ACID Concentration : 0.5 % with respect to total bath volume WEIGHT LOSS IN CMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 5 Minutes 2.0143 0.0378 98.12 10 Minutes 3.8639 0.0457 98.81 15 Minutes 5.8250 0.0884 98.52 30 Minutes 10.5647 0.1541 98.54 Concentration : 0.4 % with respect to total bath volume WEIGHT LOSS IN CMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 5 Minutes 1.3822 0.0783 94.33 10 Minutes 2.6872 0.0576 97.85 15 Minutes 6.8502 0.0955 98.60 30 Minutes 13.290 0.4993 96.24 Concentration : 0.3 % with respect to total bath volume WEIGHT LOSS IN CMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 5 Minutes 1.7794 0.1707 90.40 10 Minutes 3.6769 0.0879 97.60 15 Minutes 7.0261 0.1489 97.88 30 Minutes 13.453 02966 97.79 Concentration : 0.25 % with respect to total bath volume WEIGHT LOSS IN CMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 5 Minutes 2.5676 0.0831 96.76 10 Minutes 5.3134 0.0834 98.43 15 Minutes 8.4652 0.0976 98.84 30 Minutes 13.760 1.0454 93.01 Inhibitor : VAM/STEEL/GEN Metal : CR STEEL PICKLING MEDIUM: 15% HYDROCHLORIC ACID EXPOSURE PERIOD 15 MINUTES 30 MINUTES INHIBITOR CONC.(wt.loss) % efficiency (wt.loss) % efficiency BLANK 7.6240 - 13.9860 1.00 0.3192 95.81 01.0754 92.31 0.50 0.9395 87.67 01.4802 89.41 0.25 1.1606 78.93 01.8572 86.72 0.12 0.8390 88.91 02.3139 83.46 Inhibitor : VAM/STEEL/AG -1 Metal : CR STEEL PICKLING MEDIUM: 15% HYDROCHLORIC ACID EXPOSURE PERIOD 15 MINUTES 30 MINUTES INHIBITOR CONC.(wt.loss) % efficiency (wt.loss) % efficiency BLANK 4.4686 - 14.6971 95.99 00.3404 97.68 89.41 00.4349 97.03 85.29 01.5976 89.12 47.04 08.5811 41.61 1.00 0.1790 0.50 0.4732 0.25 0.6570 0.12 2.3663 Inhibitor : VAM/STEEL/GEN Metal : SILICON STEEL - SIL -3 PICKLING MEDIUM: 15% HYDROCHLORIC ACID Concentration : 0.3 % with respect to total bath volume WEIGHT LOSS IN GMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 30 sees 0.3501 0.018894.63 60 sees 0.4643 0.029993.56 120 sees 0.8026 0.061092.39 Concentration : 0.4 % with respect to total bath volume WEIGHT LOSS IN GMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 30 sees 0.3501 0.022393.63 60 sees 0.4643 0.0420 90.35 120 sees 0.8026 0.071991.04 Inhibitor : VAM/STEEL/GEN Metal : CR STEEL GRADE: CRMA-6 PICKLING MEDIUM: 15% HYDROCHLORIC ACID Concentration : 0.4 % with respect to total bath volume WEIGHT LOSS IN CMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 30 sees 0.1712 0.030282.35 60 sees 0.1969 0.034282.63 120 sees 0.2051 0.035582.69 Concentration : 0.3 % with respect to total bath volume WEIGHT LOSS IN CMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 30 sees 0.1712 0.068460.04 60 sees 0.1969 0.070364.29 120 sees 0.2051 0.070165.82 Inhibitor : VAM/STEEL/GEN Metal : HR STEEL GRADE: D24A1 PICKLING MEDIUM: 15% HYDROCHLORIC ACID Concentration : 0.4 % with respect to total bath volume WEIGHT LOSS IN CMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 30 sees 0.1422 0.00979317 60 sees 0.1879 0.012893.18 120 sees 0.2613 0.048581.43 Concentration : 0.3 % with respect to total bath volume WEIGHT LOSS IN CMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 30 sees 0.1422 0.011292.12 60 sees 0.1879 0.063566.20 120 sees 0.2613 0.0497 80.97 Inhibitor : VAM/STEEL/HCI Metal : HR STEEL PICKLING MEDIUM: 15% HYDROCHLORIC ACID Concentration : 0.5 % with respect to total bath volume WEIGHT LOSS IN CMS Exposure period BLANK (no inhibitor) INHIBITED Inhibition % efficiency 30 sees 0.0198 0.0014 92.92 60 sees 0.0603 0.0013 96.93 120 sees 0.1153 0.0030 97.39 15 Minutes 1.2221 0.0150 98.77 30 Minutes 2.3278 0.0298 98.72 These examples clearly exhibit high performances in metal protection properties of the corrosion inhibitor composition derived out of polyalkyl pyridiniun compounds. It should be noted that these quaternaries can perform with surfactants and / or without surfactants and / or alcohol and / or alkynols, but their presence in the composition, enhances the corrosion inhibition properties of the composition. While the specific examples have been set forth herein above, it is not intended to limit the invention solely thereto, but to include all variations and modifications with in the spirit of this invention. For example, surfactants other than oxyalkylateed can be employed, eg. Sulfonates, carboxylates etc., Alcohol other than methyl alcohol can be employed such as Iso propyl alcohol, butanol etc. ADVANTAGES OF THE INVENTION The above invention provides a corrosion inhibitor for hydrochloric acid and sulfuric acid pickling composition, which minimizes corrosion, overpickling and hydrogen embrittlement. Thus, the pickling inhibitor described herein not only prevents excessive dissolution of base metal, but effectively limit the amount of hydrogen absorption thereby during pickling. The pickled steel is far greater brighter and the pickling process consumes less amount of raw acid followed with accelerated rate of pickling. We claim: 1. A novel corrosion inhibiting composition for hydrochloric acid/sulfuric acid pickling baths, comprising of from 5% - 97% by weight of an alkarylated polyalkyl pyridinium salt, from 30% - 70% by weight of one or more alcohol such as herein described, from 10% - 30% by weight of a surfactant such as herein described and 0.% - 0.2% by weight of an alkynol such as herein described. 2. A composition as claimed in claim 1 wherein said alkarylated polyalkyl pyridinium salt is of the general formula (Formula Removed) 3. where R,R'.R" is a linear or branched Cl - C5 alkyl chain, R'" is benzyl group, X is an anion preferably halogen 3. The composition as claimed in any preceding claim, wherein the alcohol comprises an alkanol. 4. The composition as claimed in claim 3, wherein the alkanol is selected from Cl - C5 alcohol, more preferably Cl - C3, with an optimum of Cl - C2 and / or mixture thereof. 5. The composition as claimed in any preceding claim wherein the surfactant is selected from group consisting of alkoxylated nonyl phenol ethylene oxide 9.5 moles, castor oil ethylene oxide, sulfonates, carboxylates and phosphonates 6. The composition as claimed in any preceding claim, wherein the alkynol is propargyl alcohol. 7. The composition as claimed in any preceding claim wherein the said composition is used as pickling inhibitor for a continuous/ batch hydrochloric acid or a continuous / batch sulfuric acid pickling process. 8. A novel corrosion inhibiting composition substantially as herein described with reference to the foregoing examples. Dated this the

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