EP0760402A1 - Carbon dioxide steel corrosion inhibition with synergetic, environmental friendly composition of N-acyl sarcosines and N-alkyl-amidopropylbetaines - Google Patents

Abstract

The compsn. of aqueous soln. consisting of a hydrosoluble salt of N-alcoyl-sarcosine and N-alkyl-amido-propylbetaine with formula (I) or (II) (where R and R' = 9 - 19 C (un)saturated hydrocarbon; and Z<+> = inorganic cation or organic monovalent) for inhibiting carbonic acid corrosion to steel is claimed. The ratio of N-alcoyl-sarcosine to N-alkyl-amido-propylbetaine is 1:3-3:1. The compsn. content in active component, soluble salt of N-alcoyl-sarcosine and of N-alkyl-amido-propylbetaine is 20-30 wt.%.

Description

The present invention relates to the field of protecting steel against corrosion in aqueous media loaded with carbon dioxide.

Corrosion of carbon steel by carbonic acid (for short, carbonic corrosion) is a type of corrosion that occurs very frequently in industry, especially in crude oil production wells and in pipelines ( pipelines) which are used for their transport. The remedy usually provided is the use of corrosion inhibitors, in particular amine-based inhibitors, quaternary ammonium salts, imidazolines or phosphoric esters. These compounds are not entirely satisfactory because they are ecotoxic and not biodegradable.

dans laquelle R est une chaîne hydrocarbonée saturée ou insaturée et Z⁺ est un cation minéral ou organique monovalent, comme inhibiteurs de la corrosion carbonique de l'acier, et certaines de leurs associations avec d'autres inhibiteurs non biocompatibles.The use of N-alkyl sarcosines (sarcosides) and their salts, slightly toxic and biodegradable compounds corresponding to the general formula, was known from British patent GB 2028810.

wherein R is a saturated or unsaturated hydrocarbon chain and Z ⁺ is a monovalent inorganic or organic cation, as inhibitors of carbon dioxide corrosion of steel, and some of their associations with other non-biocompatible inhibitors.

dans laquelle R' est une chaîne hydrocarbonée saturée ou insaturée, ainsi que celle de certaines de leurs accosiation avec des inhibiteurs non biocompatibles.An activity of the same type was also known from EP 446.616 in N-alkyl-amidopropylbetaines, compounds which are also not very toxic and biodegradable, of general structure

in which R 'is a saturated or unsaturated hydrocarbon chain, as well as that of some of their accosiation with non-biocompatible inhibitors.

We have now found a surprising synergy in inhibiting carbonic corrosion of iron in the association of N-alkyl-sarcosines and N-alkylamidopropylbetaines. This synergy can be exploited advantageously with compositions whose weight ratios between these two types of components are between 25:75 and 75:25, the maximum efficiency being obtained in an approximately equal weight ratio.

et d'un sel soluble monovalent de N-alcoyl-sarcosine de formule générale

formules dans lesquelles R ou R' sont indépendamment l'un de l'autre des chaînes hydrocarbonées comportant de 9 à 19 atomes de carbone, et où Z est un cation minéral ou organique monovalent.The subject of the invention is therefore a process for the inhibition of carbonic corrosion of steel in aqueous media, which consists in the use, as corrosion inhibitor, of an aqueous composition comprising as active material the mixture of N-alkyl-amidopropyl betaine of general formula

and a monovalent soluble salt of N-alkyl-sarcosine of general formula

formulas in which R or R 'are independently of each other hydrocarbon chains containing from 9 to 19 carbon atoms, and where Z is a monovalent inorganic or organic cation.

Preferred here is N-lauryl-amidopropylbetaine or the corresponding industrial derivative N-coco-amidopropylbetaine [RN 61789-39-7], or N-lauroyl-sarcosine or N-cocoyl-sarcosine, in the form of their sodium salt whose RN are respectively [137-16-6] and [61791-59-1]. (In the present text, coco- and cocoyl- respectively have the meaning remain R- or remain R-CO- of coconut fatty acid.)

The invention is preferably implemented by continuous injection into the corrosive fluid, at doses of between 2 and 10 ppm of active material relative to the corrosive fluid. It is also possible to film the metal (batch processing).

The inhibitory compositions consisting of aqueous solutions containing approximately 30% by weight of a mixture of a monovalent soluble salt of N-alkyl-sarcosine and of N-alkyl-amidopropyl betaine in a weight ratio of 1: 3 to 3: 1 are also objects. of the invention.

The following examples will better understand the invention.

Example 1

The inhibitory power of the control compositions and of the compositions according to the invention is evaluated by measuring the polarization resistance of a test piece of steel immersed in a corrosive medium of NACE type consisting of an aqueous solution of 50 g / l of sodium chloride and 0.25 g / l of acetic acid, saturated at room temperature with carbon dioxide.

We operate in a Pyrex cell of 600 ml comprising, in addition to an inlet and an outlet of the gases, three electrodes subject to the cell by lapping, namely a working electrode in ordinary carbon steel whose contact surface with the solution corrosive is 1 cm ² , a reference calomel saturated electrode, and a platinum counter electrode with a very large contact surface with the solution. 500 ml of the corrosive solution are placed in the cell; the counter electrode and the reference electrode are then introduced. It is deaerated by bubbling nitrogen for one hour and the solution is saturated by bubbling CO ₂ for an additional hour, the inhibitor is added, and the measuring electrode is introduced, the corrosion potential of which is inspected. When the latter has stabilized, which requires approximately 30 minutes, the polarization resistance Rp is measured according to the protocol of the French standard NF 15-602-9.

où Rp est la résistance de polarisation mesurée avec inhibiteur, et Rp₀ la résistance de polarisation dans le milieu corrosif témoin, à laquelle correspond une vitesse de corrosion de 1,3 mm/an.The inhibitory power of each formula tested is estimated by a percentage of protection calculated in a known manner according to $${\text{P\% = 100 x (Rp - Rp}}_{\text{0}}\text{) / Rp}$$

where Rp is the polarization resistance measured with inhibitor, and Rp ₀ the polarization resistance in the corrosive control medium, to which corresponds a corrosion rate of 1.3 mm / year.

The N-lauroyl-sarcosinate used is the ORAMIX®L30 from SEPPIC with approximately 30% of active ingredient in water. The N-coco-amidopropyl betaine used is obtained according to a known method by condensation of N-coco-amidodimethylpropylamine with chloracetic acid.

Table 1 gives the protection percentages as a function of the concentration of inhibitors, expressed in ppm of active material. Table 1: corrosion inhibition Compositions Betaine 100% 75% 50% 25% 0 Sarcosinate 0 25% 50% 75% 100% Protection% 1 ppm 13 30 58 37 10 2 ppm 44 48 75 62 42 5 ppm 69 77 90 89 78 10 ppm 75 91 94 95 88 20 ppm 88 96 96 96 94 50 ppm 93 96 96 97 96

The synergy between sodium N-lauroyl-sarcosinate and N-coco-amidopropylbétaine develops especially at low dosages, which is very favorable, at a given protection percentage, to the economy of inhibitory substances disseminated in the environment . The optimum corresponds to the 50/50 weight ratio. At 2 ppm, the 50/50 weight proportion mixture effectively protects the steel (75% protection). At the same dosage, N-coco-amidopropylbetaine or N-lauroyl-sarcosinate only gives 44% or 42% protection.

Example 2 : Marine toxicity and biodegradability.

The toxicity towards marine organisms is determined according to methods ISO / DIS 10253 for Skeletonema costatum (algae) and ISO / TC / 147 / SCS / WG2 for Acartia tonsa (crustaceans). These methods are recommended by the Paris Convention for the Prevention of Marine Pollution.

The toxicity is expressed in EC ₅₀ (effective concentration in mg / l, to inhibit the growth of 50% of the population for 72 hours) for Skeletonema costatum and in LC ₅₀ (lethal concentration in mg / l, to destroy 50% of population in 48 hours) for Acartia tonsa. The higher the EC ₅₀ , or the LC ₅₀ , the less toxic the product.

Biodegradability is determined by ISO 1990 standard, BOD -Test for Insoluble Substance-, known as the BODIS method, also recommended by the Paris Convention. It is expressed as a percentage of degradation for 28 days.

The toxicities and biodegradability compared are shown in Table 2 below. Table 2: toxicities and bio-degradability Product Toxicity (mg / l) % Bio-degradability Skel. CE ₅₀ Acart. CL ₅₀ Betaine 0.87 3.3 100 Sarcosinate 6.6 30-53.4 98 Betaine / sarcosine 50/50 2.55 8.01 100

The comparison of Tables 1 and 2 shows that between 2 and 5 ppm of the mixture (50/50) of N-coco-amidopropylbetaine and sodium N-lauroyl-sarcosinate, the steel can be effectively protected against CO ₂ corrosion without causing harm to the environment.

Claims (4)

Composition consisting of an aqueous solution of a water-soluble salt of N-alkyl-sarcosine and of N-alkyl-amidopropylbetaine corresponding respectively to the general formulas

and

in which R and R 'are saturated or unsaturated hydrocarbon chains and containing from 9 to 19 carbon atoms and where Z ⁺ is a monovalent inorganic or organic cation, the weight ratio between N-alkyl-sarcosine and N-alkyl- amidopropyl betaine being between 1: 3 and 3: 1, the content of the active ingredient composition of soluble salt of N-alkyl-sarcosine + N-alkyl-amidopropyl betaine being between 20 and 30 percent by weight. Inhibitory composition according to claim 2 characterized in that the soluble salt of N-alkyl-sarcosine is the sodium salt of N-lauroyl- or of N-cocoyl-sarcosine and in that the N-alkyl-amidopropylbetaine is N -lauryl- or N-coco-amidopropylbetaine. Use of compositions according to claims 1 or 2 for the inhibition of carbonic corrosion of steel in the oil production industry. Use according to Claim 3, characterized in that the inhibiting composition is injected into the corrosive aqueous medium at a rate of 2 to 10 ppm, counted in the active ingredient N-alkyl-sarcosine / N-alkyl-amidopropyl betaine.