FR2738018A1 - INHIBITION OF CARBON CORROSION OF STEEL BY N-ALCOYL-SARCOSINES - Google Patents

Abstract

Aqueous compositions containing a water-soluble salt of N-alkyl-sarcosine, or both a water-soluble salt of N-alkyl-sarcosine and an N-alkyl-amidopropylbetaine constitute remarkable inhibitors of carbonic corrosion of steel. These are very non-toxic and easily biodegradable products. Their use is advantageous at doses of 2 to 10 ppm relative to the corrosive fluid, in particular in the oil production industry.

Description

The present invention relates to the field of the protection of steel.

against the

  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) that are used for their transportation. The remedy usually provided is the use of corrosion inhibitors, in particular based inhibitors.

  amine, quaternary ammonium salts, imidazolines or phosphoric esters.

  These compounds are not entirely satisfactory because ecotoxic and not

1 biodegradable.

  We have now found that N-alkyl-sarcosines (sarcosides), and more precisely their salts corresponding to the general formula CH3 RC-NCH2-COO t Il o in which R is a saturated or unsaturated hydrocarbon chain comprising from 9 to 19 carbon atoms and Z + is a monovalent organic or mineral cation, can be used as inhibitors of carbonic corrosion of steel. In addition, these molecules are slightly toxic and biodegradable. In the vast field of corrosion of iron and steel, they have been known until now only by their oil-soluble combinations as agents for protection against rust, or as water-soluble compositions to limit the corrosiveness of aqueous fluids present

  oxygen from the air (see for example, JP 60013084).

  But above all, we have just found a surprising synergy of inhibition against

  carbon corrosion in the association of an N-alkyl-sarcosine and an N-alkyl-

  amidopropylbetaine (according to ACS, 1-propanamium, 3-amino-N- (carboxymethyl) -

  N, N-dimethyl-, N-acylderivs.) Of structure CH3 +1

R'-C-NH-CH2 - CH2-CH2-N-CH2 - COO

O CH3

  N-alkyl-amidopropyl betaines had already been mentioned as carbonic corrosion inhibitors in a biphasic medium (see EP 446,616), but the sarcosine / betaine synergy is unexpected. It can be used advantageously for weight ratios between 25:75 and 75:25, the maximum efficiency being

  obtained in an approximately equal weight relationship.

  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 a monovalent soluble salt of Nalcoyl-sarcosine, or better still of an aqueous composition of a mixture of Nalkyl-amidopropylbetaine and of a monovalent soluble salt of N-alkylsarcosine. Preferred here is N-lauryl-amidopropyl betaine or the corresponding industrial derivative N-coco-amidopropyl betaine [RN 61789-39-7], or N-lauroyl-sarcosine or N-cocoyl-sarcosine, in the form of their salt sodium of which

  the RN are respectively [137-16-6] and [61791-59-1]. (In this text, coco-

  and cocoyl- have respectively the meaning remains R- or remains 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 in matter active with respect to corrosive fluid. It is also possible to film the metal

(batch processing).

  The inhibitory compositions consisting of aqueous solutions at approximately% by weight of mixture of a monovalent soluble salt of N-alkylsarcosine and of 15 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

  Inhibiting carbon dioxide efficiency of N-lauroyl-sarcosinate.

  The inhibitory power of N-lauroyl-sarcosinate is evaluated by measuring the polarization resistance of a steel test tube immersed in a corrosive medium of NACE type consisting of an aqueous solution of 50 g / A 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 cm2, 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 CO2 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

  French standard NF 15-602-9 protocol.

  The inhibitory power of each formula tested is estimated by a percentage of protection calculated in a known manner according to P% = 100 x (Rp Rpo) / Rp o Rp is the polarization resistance measured with inhibitor, and Rp0 the polarization resistance in the medium corrosive witness, to which corresponds a speed of

corrosion of 1.3 mm / year.

  The N-lauroyl-sarcosinate used is the ORAMIX L30 from SEPPIC with approximately 30% of active ingredient in water. Table I gives the protection percentages according to the

  concentration of sarcosinate, expressed in ppm of active ingredient.

  Table 1: Corrosion-inhibiting efficacy of sodium N-lauroyl-sarcosinate (active ingredient) Sarcosinate (ppm) 0 I1 2 5 10 20 50 Corrosion rate (mm / year) 1.3 1.17 0.750.280.17 0, 08 0.05 Percentage of protection 0 10 42 78 88 94 96 We see that from 5 ppm N-lauroyl-sarcosinate protects

  steel effectively against carbonic corrosion.

Example-2

  Marine toxicity and biodegradability of N-lauroyl-sarcosinate The toxicity towards marine organisms is determined according to methods ISO / DIS 10253 for Skeletonema costatum (algae) and ISO / TC / 147 / SC5NVG2 for Acartia tonsa (crustaceans ). These methods are

  recommended by the Paris Convention for the Prevention of Marine Pollution.

  The toxicity is expressed in EC50 (effective concentration in mg / l, to inhibit the growth of 50% of the population for 72 hours) for Skeletonema costatum and in LC50 (lethal concentration in mg / l, to destroy 50% of the population in 48 hours) for Acartia tonsa. Plus the CE50, or the LC50, is

  the larger, 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 toxicity and biodegradability of N-lauroyl-sarcosinate are given

table 2.

  Table 2: Toxicity and biodegradability of sodium N-lauroyl-sarcosinate (as active ingredient)

  Product Toxicity (mg / Il) (%) of bio-

  degradability Skeletonema Acartia Sarcosinate 6.6 30-53.5 98 At 7 ppm, N-lauroyl-sarcosinate offers up to 80% protection of steel against carbonic corrosion without causing environmental damage. In

  the more it is completely biodegradable.

ExampleL3

  Synergy between sodium N-lauroyl-sarcosinate and N-coco-amido-

  propylbéta'ine Table 3 gives the protection percentages obtained for

  compositions with indicated variable proportions of N-coco-

  amidopropylbetaine and N-lauroyl-sarcosinate. The inhibitor doses are

  expressed as active ingredients (sodium N-lauroyl-sarcosinate, N-coco-

  amidopropylbetaine). The N-coco-amidopropyl betaine used is obtained according to a known method by condensation of N-coco-amidodimethylpropylamine with chloracetic acid

  Table 3: Corrosion-inhibiting efficacy of N-coco-

  amidopropyl betaine, sodium N-lauroyl-sarcosinate and their mixture in

various weight proportions.

  Compositions Béta'ne 100% 175% 50% 125% 0 Sarcosinate 0 125% 50% 75% 100% Protection% 1 ppm 13 30 58 37 10 2 ppm 44 48 75 62 42 ppm 69 77 90 89 78 ppm 75 91 94 95 88 ppm 88 96 96 96 94 ppm 93 96 96 97 96 There is a synergy between sodium N-lauroyl-sarcosinate and N-cocoamidopropylbétaine especially at low dosages. The optimum corresponds to the 50/50 weight ratio. At 2 ppm the 50/50 weight proportion mixture protects

  steel effectively (75% protection). At the same dosage, N-coco-

  amidopropylbetaine or N-lauroyl-sarcosinate gives only 44% or 42% protection.

Example-4

  Marine toxicity and biodegradability of the mixture (50/50) of N-coco-

  amidopropylbetaine and N-lauroyl-sarcosinate.

  The toxicity and biodegradability of the 50/50 mixture of N-coco-

  amidopropylbetaine and sodium N-lauroyl-sarcosinate are given in table 4, in comparison with those of N-coco-amidopropylbetaine and

  o0 Sodium N-lauroyl-sarcosinate alone.

  Table 4: Toxicity and biodegradability of N-coco-amidopropylbétaine, of N-lauroyl-sarcosinate and their mixture of weight ratio (50/50)

Product Toxicity (mgAI)% Bio-

  Skel degradability. CE50 Acart. LC50 Betaine 0.87 3.3 100 Sarcosinate 6.6 30-53.4 98 Betaine / 2.55 8.01 100 sarcosine 50/50 Between 2 and 5 ppm of the mixture (50/50) of N-cocoamidopropylbetaine and sodium N-lauroyl-sarcosinate, steel can be effectively protected against

  CO2 corrosion without causing environmental damage.

Claims (8)

  1. Method for limiting the carbonic corrosion of steel in aqueous media, characterized in that an aqueous composition is used, as corrosion inhibitor, comprising as active material a monovalent soluble salt of N-alkyl -sarcosine corresponding to the formula CH3 RCN-CH2-COO to II in which R is a saturated or unsaturated hydrocarbon chain containing from 9 to 19 carbon atoms,   Z + is a monovalent mineral or organic cation.   2. Method according to claim 1, characterized in that the soluble salt of N-alkyl-sarcosine is sodium N-lauroyl-sarcosinate or its equivalent industrial on coconut chain.   3. Method according to claim 1, characterized in that in combination with an N-alkyl-sarcosine, an N-alkyl-amidopropyl betaine is used corresponding to the general formula CH3 + _ R'-C-NH-CH2-CH2-CH2-N-CH2-COO O CH3   in which R 'is a saturated or unsaturated hydrocarbon chain comprising 9 to 19 carbon atoms.   4. Method according to claim 4, characterized in that N-alkyl-   amidopropylbetaine is N-lauryl- or N-coco-amidopropylbetaine.   5. Method according to claims 1 to 4, characterized in that one injects   in the corrosive aqueous medium an N-alkyl-sarcosine or an N-alkylsarcosine and   an N-alkyl-amidopropyl betaine at 2 to 10 ppm.   6. 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 CH3 R-C-N-CH2-COO t o and CH3 R'-C-NH-CH2-CH2-CH2 - N-CH2-COO O CH3   J in which R and R 'are saturated or unsaturated hydrocarbon chains and containing from 9 to 19 carbon atoms and o Z + is an inorganic cation or   monovalent organic, the weight ratio between N-alkyl-sarcosine and N-alkyl-   amidopropylbétaine being between 1: 3 and 3: 1, the content of the composition in active ingredient soluble salt of N-alkyl-sarcosine + Nalkyl-amidopropylbétaine being about 30% by weight.   7. Inhibitory composition according to claim 6 characterized in that the soluble salt of N-alkyl-sarcosine is the sodium salt of N-lauroylou of N-cocoyl-sarcosine and in that the N-alkyl-amidopropylbetaine is N -lauryl- or the i0 N-coco-amidopropyl betaine.   8. Use of compositions according to claims 6 or 7 for   the inhibition of carbonic corrosion of steel in the oil production industry.