HYDROXYSULTAINE- AND SULFOBETAINE-BASED GEMINAL ZWITTERIONIC LIQUIDS, METHOD FOR OBTAINING SAME, AND USE THEREOF AS WETTABILITY MODIFIERS HAVING CORROSION INHIBITING PROPERTIES

Abstract

The present invention is related to obtaining and using sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids as wettability modifiers for rocks such as limestone, dolomite, sandstone, quartz or heterogeneous lithologies, under the presence of brines having high content of divalent ions as calcium, magnesium, barium and strontium, at high temperature and high pressure conditions for enhanced oil recovery processes to increase the oil production.

The geminal zwitterionic liquids of the present invention have also the property of acting as corrosion inhibitors of ferrous metals used in pipelines and equipment for crude oil extraction, production, transport and storage operations. A further advantage shown by zwitterionic liquids derived from their molecular structure is they can be dissolved in distilled water, brine, hydrocarbon solvents, aromatics and alcohols.

Claims

1. Sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, characterized by the following structural formula: ##STR00006## where R.sub.1 is a radical represented by an alkyl or alkenyl, linear or branched chain having preferably from 1 to 30 carbon atoms, or an cycloalkyl or aryl group, preferably having from 5 to 12 carbon atoms; R.sub.2 is a radical represented by —H; or alkyl or alkenyl, linear or branched chain, preferably having from 1 to 30 carbon atoms; or an cycloalkyl or aryl group, preferably having from 5 to 12 carbon atoms; R.sub.3=—CH.sub.2—, —CH.sub.2—CH(OH)—; y can have the values 0 and 1: when is 1, then R.sub.4 is a radical represented by —OH; n can have values from 1 to 500 depending on the molecular weight of the used polyether, which is derived from ethylene oxide whose molecular weight is in the range of 100 to 20,000 g/mol.

2. A process to obtaing hidroxisultaine and sulfobetaine-based geminal zwitterionic liquids, in accordance with the claim 1, characterized by the following synthesis schemes: ##STR00007## ##STR00008## the synthesis of the sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids of the formula VII can be carried out through two synthesis routes comprising the following steps: Route 1: the first step consists in to react polyethylene glycols of the formula I with benzenesulfonyl chloride or tosyl chloride of the formula II; the second step consists in to react the compounds of the formula III through a nucleophilic substitution with primary or secondary amines of the formula IV; so it is obtained the tertiary amines of formula V; the third step consists in to obtain the sulfobetaine and hidroxisultaine -based geminal zwitterionic liquids of the formula VII, which are obtained by reacting the tertiary amines of the formula V with sodium 2-bromoethane sulfonate or sodium 3-chloro-2-hydroxypropane sulfonate of the formula VI. Route 2: the first step consists in to react polyethylene glycol diglycidyl ether of the formula I with primary or secondary amines of the formula IV. the second step consists in to react the aminoalcohols of the formula V with sodium 2-bromoethane sulfonate or sodium 3-chloro-2-hydroxy-propane sulfonate of the formula VI to obtain the sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids of the formula VII.

3. A production process according to claim 2, wherein the molecular weight of the polyethylene glycols of the formula I used in the synthesis Route 1 preferably is at the range from 100 to 20,000 g/mol.

4. A production process according to claim 2, wherein the reaction shown in the Route 1 among polyethylene glycols of the formula I with benzenesulfonyl chloride or tosyl chloride of the formula II is carried out with a molar ratio from 1:1 to 1:4, preferably from 1:1.5 to 1:2.8.

5. A production process according to claim 4, wherein the reaction is carried out in a basic medium composed of sodium, potassium or cesium hydroxide, preferably sodium hydroxide.

6. A production process according to claim 4, where in the reaction is used as the solvent water, tetrahydrofuran, chloroform or acetonitrile or mixtures thereof.

7. A production process according to claim 2, wherein to form the compounds of the formula III of the synthesis Route 1, the reaction is carried out in a reaction time from 1 to 12 hours, preferably from 3 to 8 hours.

8. A process of obtaining according to claim 2, wherein in to form the compounds of the formula III of the synthesis Route 1, the reaction is carried out at a temperature from 0 to 25 ° C., preferably from 5 to 20° C.

9. An obtaining process according to claim 2, wherein the reaction shown in the synthesis Route 1 is carried out with a molar ratio between the compounds of the formula III and the secondary amines of the formula IV from 1:1.5 to 1:4, preferably from 1:1.8 to 1:2.6.

10. A production process according to claim 2, wherein the secondary amines of the formula IV whose R.sub.1 and R.sub.2 can be alkyl or alkenyl, linear or branched chains, preferably having from 1 to 30 carbon atoms; or cycloalkyl or aryl groups, preferably having from 5 to 12 carbon atoms.

11. A production process according to claim 2, wherein the reaction shown in the synthesis Route 1 for the preparation of the tertiary amines of the formula V is carried out in presence of solvents such as acetonitrile, chloroform, dimethylformamide, dimethylsulfoxide, acetone or short chain alcohols, preferably acetonitrile.

12. A production process according to claim 2, wherein the reaction shown in the synthesis Route 1 for preparation of tertiary amines of the formula V is carried out in a reaction time from 5 to 60 hours, preferably from 12 to 36 hours.

13. A production process according to claim 2, wherein the reaction shown in the synthesis Route 1 for preparation of tertiary amines of the formula V is carried out at temperature from 50 to 150° C., preferably from 60 to 90° C.

14. A production process according to claim 2, wherein the reaction shown in the synthesis Route 1 between the compounds of the formula V with sodium 2-bromine-ethane sulfonate or sodium 3-chloro-2-hydroxypropane sulfonate of the formula VI is carried out with a molar ratio from 1:1.5 to 1:4, preferably from 1:1.8 to 1:2.6.

15. A production process according to claim 2, wherein the reaction shown in the synthesis Route 1 for preparation of compounds of the formula VII can be carried out with absence or presence of solvents such as water, alcohols, aromatics or inert hydrocarbon solvents, preferably water.

16. A production process according to claim 2, wherein the reaction time, the temperature and the pressure for the preparation of compounds of formula VII shown in the synthesis Route 1 depend on the compounds structure of the formula V and VI.

17. A production process according to claim 16, wherein the reaction time ranges from 6 to 72 hours, preferably from 6 to 48 hours.

18. A production process according to claim 16, wherein the temperature is from 40 to 180° C., preferably from 80 to 130° C.

19. A production process according to claim 16, wherein the pressure generally is atmospheric, so it can range from 585 to 760 mmHg.

20. A production process according to claim 2, wherein the polyethylene glycols of the formula I used in the synthesis Route 2 contain two epoxide groups, one at the end and the other at the beginning of the polymeric chain.

21. A production process according to claim 2, wherein the molecular weight of the polyethylene glycols of the formula I used in the synthesis Route 2 preferably is in the range from 100 to 22,000 g/mol.

22. A production process according to claim 2, wherein the reaction described in the synthesis Route 2 between the compounds of the formula I and the primary or secondary amines of the formula II is at molar ratios from 1:1.5 to 1:4, preferably from 1:1.8 to 1:2.6.

23. A production process according to claim 2, wherein primary and secondary amines used in the synthesis Route 2 of the formula IV, R.sub.1 and R.sub.2 are alkyl or alkenyl, linear or branched chains, preferably from 1 to 30 carbon atoms; or cycloalkyl or aryl groups, preferably 5 to 12 carbon atoms and wherein R.sub.2 are also hydrogen.

24. A production process according to claim 2, wherein the reaction shown in the synthesis Route 2 for the preparation of amino alcohols of the formula V is carried out in absence or presence of solvents such as acetonitrile, dioxane, chloroform, dimethylformamide, dimethylsulfoxide, acetone or short-chain alcohols.

25. A production process according to claim 2, wherein the reaction described in the synthesis Route 2 for the preparation of amino alcohols of the formula V is carried out in a reaction time from 6 to 48 hours, preferably 12 to 20 hours.

26. A production process according to claim 2, wherein the reaction described in the synthesis Route 2 for the preparation of aminoalcohols of the formula V is carried out at temperatures from 50 to 150° C., preferably from 60 to 90° C.

27. A production process according to claim 2, wherein the reaction described in the synthesis Route 2 between compounds of the formula V with sodium 2-bromine ethane sulfonate or with sodium 3-chloro-2-hydroxypropane sulfonate of the formula VI is carried out in a molar ratio from 1:1.5 to 1:4, preferably from 1:1.8 to 1:2.6.

28. A production process according to claim 2, wherein the reaction described in the synthesis Route 2 for preparation of compounds of the formula VII may be carried out in the absence or the presence of solvents such as water, dioxane, alcohols, aromatics or hydrocarbons, preferably water.

29. A production process according to claim 27, wherein the reaction time ranges from 6 to 48 hours, preferably from 12 to 36 hours.

30. A production process according to claim 27, wherein the temperature ranges from 40 to 180° C., preferably from 80 to 130° C.

31. A production process according to claim 27, wherein the pressure is generally atmospheric, so it can vary from 585 to 760 mmHg.

32. Use of sulfobetaine and hydroxysultaine-based geminal zwitterionic liquids, having structural formula described in claim 1, in improved oil recovery processes, wherein it is modified the wettability of rocks such as limestone, dolomite, sandstone, quartz or heterogeneous lithologies.

33. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1 in enhanced oil recovery processes, wherein under presence of brines with high content of salts and divalent ions such as calcium, magnesium, barium and strontium.

34. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1 in enhanced oil recovery processes, wherein the temperature is up to 220° C.

35. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1 in enhanced oil recovery processes, wherein the pressure is up to 8,000 psi.

36. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1 in enhanced oil recovery processes, wherein the concentration of salts is up to 400,000 ppm.

37. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1 in enhanced oil recovery processes, wherein the concentration of divalent ions is up to 180,000 ppm.

38. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1 in enhanced oil recovery processes, wherein the concentration to inject the zwitterionic liquid to modify the rock wettability from oil wet is in values from 25 to 40,000 ppm.

39. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1 in enhanced oil recovery processes, wherein the injection concentration is preferably from 500 to 10,000 ppm.

40. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1 wherein it is inhibited the corrosion of ferrous metals used in ducts and equipment for crude oil extraction and transport operations.

41. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1, wherein the injection concentration of the zwitterionic liquid to inhibit the corrosion is from 25 to 500 ppm.

42. The use of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids, according to claim 1, wherein the concentration to be injected is preferably from 50 to 300 ppm.

Description

BRIEF DESCRIPTION OF THE FIGURES OF THE INVENTION

[0024] The FIG. 1 shows the production of oil in the Amott cell capillary for: a) system that only contains brine, b) a system containing brine and 300 ppm of sulfobetaine-based geminal zwitterionic liquid described in example 2.

[0025] The FIG. 2 shows the drop forms: a) system that only contains brine, b) a system containing brine and 300 ppm of ppm of sulfobetaine-based geminal zwitterionic liquid described in example 2.

DESCRIPTION OF THE INVENTION

[0026] The present invention relates to obtaining and use of geminal zwitterionic liquids, hidroxisultaine- and sulfobetaine-based, as wettability modifiers of rocks such as limestone, dolomite, sandstone, quartz or heterogeneous lithologies in the presence of crude oil and brine water with high content of divalent ions as calcium, magnesium, barium, and strontium, high temperature and high pressure; to increase oil production in enhanced oil recovery processes.

[0027] The geminal zwitterionic liquids based on hydroxysultaine and sulfobetaine of the present invention have also the property of acting as corrosion inhibitors, in extraction, production, transport, and storage operations, properly preventing and controlling the generalized and localized corrosion problems. An additional advantage presented by the zwitterionic liquids of the present invention is that due to its molecular structure, they may be soluble in brine, crude oil or organic solvents such as toluene, xylenes, chloroform and alcohols.

[0028] The geminal liquid zwitterionic of the present invention constitute a family characterized by having hydrocarbon chains, a polyether type bridge and two zwitterionic type polar groups which may be hydroxysultain or sulfobetaine type.

[0029] The geminal zwitterionic liquids, hidroxisultaine- and sulfobetaine-based of the present invention have the following structural formula:

##STR00003##

Where:

[0030] R.sub.1=is a radical represented by alkyl or alkenyl chain, linear or branched, preferably of 1 to 30 carbon atoms; or an cyclo alkyl or aryl group, preferably of 5 to 12 carbon atoms; [0031] R.sub.2=is a radical represented by —H or a alkyl or alkenyl chain, linear or branched, preferably of 1 to 30 carbon atoms; or an cyclo alkyl or aryl group, preferably of 5 to 12 carbon atoms; [0032] R.sub.3=—CH.sub.2—, —CH.sub.2—CH(OH)—; [0033] y=can have values from 0 to 1; [0034] When y is equal to 1: [0035] R.sub.4=is a radical represented by —OH [0036] n can have values from 1 to 500, depending on the molecular weight of polyether used, where the polyether used is derived from ethylene oxide whose molecular weight is in the range 100 to 20,000 g/mol.

[0037] For the development of the present invention a procedure was followed that consists of the following stages: 1) molecular design through computational chemistry, 2) synthesis of branched geminal zwitterionic liquids, 3) spectroscopic characterization of geminal zwitterionic liquids and (4) experimental evaluation of wettability modifiers and corrosion inhibitory properties.

[0038] An additional advantage presented by the hidroxisultaine-and sulfobetaine-based geminal zwitterionic liquids of the present invention is that due to its molecular structure, they may be soluble in brine, crude oil or water.

[0039] 1) Molecular Design by Means of Computational Chemistry

[0040] Before going into details, and for clarification purposes, it is worth mentioning that the current trend, involving the development of new chemical products with industrial application, is as the first stage the molecular design by means of computational chemistry, of moieties that will have the potential ability to solve the problems of interest. This molecular design is intended to systematically direct the efforts aimed to the synthesis of new molecules with enhanced properties.

[0041] The first thing to determine within molecular design for problems related with wettability modification and corrosion inhibition is:

[0042] i) The interaction forces magnitude between the characteristic rock surface of a given reservoir and the polar molecules of high molecular weight in the crude oil, since these data constitute the reference energy that must be overcome by the appropriate insertion of a wettability modifier agent.

[0043] ii) It also requires a deep understanding of the wettability modification molecular mechanisms with the objective of suggest a surfactant with the most suitable molecular structure.

[0044] iii) In addition, in connection to the viscosity reduction application is required to determine the nature and magnitude of the intermolecular forces that generate oil high viscosity with a high content of polar compounds of large molecular weight such as asphaltenes and resins. These data provide the reference energy that must be overcome by insertion of an appropriate viscosity reducer agent.

[0045] iv) Finally, optimal structural parameters that it should include a wettability modifier and viscosity reducer molecule are selected, this from a technical-economic standpoint in order to propose an initial molecular structure to which it calculates the interaction energy with rock surface to determine whether this interaction will be greater or lesser in energy with respect to the polar organic compounds of high molecular weight, which are required to be removed from the surface in such a way to increase the oil recovery factor in the reservoir. In this point the design process can be iterative up to find a molecular species that effectively has an interaction energy with greater than oil polar compounds adsorbed on the rock.

[0046] In the specialized literature mentions that the effectiveness of wettability change in rock depends on the ionic nature of surfactant involved involucrado (Colloids Surf. A: Physicochem. Eng. Aspects 1998, 137, 117-129. Austad, T.; Matre, B.; Milter, J.; Saevareid, A.; Oyno, L. Chemical flooding of oil reservoirs 8. Spontaneous oil expulsion from oil- and water-wet low permeable chalk material by imbibition of aqueous surfactant solutions; J. Pet. Sci. Eng. 2000, 28, 123-143. Standnes, D. C.; Austad, T. Wettability alteration in chalk: 2. Mechanism for wettability alteration from oil-wet to water-wet using surfactants) and that in oil-wet limestone cores, cationic surfactants have better perform than anionic. It has been proposed that in the case of cationic surfactants, the mechanism through which modify the wettability in an oil wet rock is the formation of ion pairs between the surfactant cationic head of the surfactants and the oil acidic components adsorbed on the carbonate rock surface.

[0047] The formation of this ion pairs could remove the layer of crude oil components adsorbed on the rock surface, thus exposing the calcium carbonate rock surface, which is water-wet in origin. In contrast, anionic surfactants form a monolayer on the rock surface through hydrophobic interaction between tails of the surfactant molecules and crude oil components adsorbed on the rock surface. Thus, the rock would be covered by surfactant molecules layer formed with hydrophilic groups on the surface, which could modify the rock wettability characteristics, oil-wett to water-wet.

[0048] In the case of the present invention, hidroxisultaine-and sulfobetaine-based geminal zwitterionic liquids have the ability to alter the wettability of carbonate rocks from oil-wet to water-wet through the two mechanisms mentioned above in parallel and thus present more efficiently than cationic or anionic surfactants traditionally they have been used.

[0049] In addition, duality charge having in the structure would allow interact effectively with different types of rock and oils, as they may form ionic pairs with species both positive and negative charge.

[0050] Just as it was stated in the Background of the Invention, zwitterionic surfactants present significant advantages compared to cationic or anionic surfactants because as zwitterions have both positive and negative charge in its structure, which increases the possibility to interact with rock surfaces with both positively and negatively, charged in contrast with one type of charge surfactants.

[0051] In many fields internationally, is present the cases of heterogeneous lithologies, that hinder the enhanced oil recovery process by wettability change, in these cases requires the use of effective wettability modifiers that in contact with different types of rock such as limestone, dolomite, sandstone, quartz or heterogeneous lithologies, even in the presence of brine with high content of divalent ions such as calcium, magnesium, barium and strontium, high temperature and pressure in enhanced oil recovery processes to increase oil production.

[0052] From the previous data is seen that the generated branched geminal zwitterionic liquids have advantages over conventional surfactants, used as wettability modifiers in different types of lithologies under high salinity and temperature conditions.

[0053] In order to prove the above declared premises, theoretical calculations were performed simulating the adsorption process of polar molecules of high molecular weight on the rock surface originally water-wet with the purpose of determine the adsorption energy that must overcome the wettability modifier molecule; in the same way it was simulated the branched sulfobetaine type geminal zwitterionic liquid adsorption process, corresponding to the present invention, on the same rock which is originally water-wet; then, the adsorption energies are compared for establishing whether or not, from the theoretical viewpoint, if the asphaltene desorption process would be favorable thermodynamically by introducing a wettability modifier of the present invention. The obtained results are described in the following examples:

EXAMPLE 1

Asphaltene-Calcite Interaction

[0054] By means of computational chemistry, and using Density Functional Theory methods and LDA-WNV functional were optimized in a water-solvated medium (Dielectric constant 78.54) the asphaltenes average molecular structure model that globally represent their characteristics of heavy oil from the Marine Region in Mexico 1, the calcite surface geometry (CaCO.sub.3) 2 and the adsorption geometry of the product generated 3 from the interaction of asphaltene structure molecular model 1 with calcite surface (CaCO.sub.3) 2 (3) and the energy results for the adsorption process of the asphaltenes molecular model structure 1 on the calcite surface (CaCO.sub.3) 2 (4) shown in Table 1.

TABLE-US-00001 TABLE 1 Energy results obtained for the adsorption of asphaltene molecular model structure 1 on calcite surface (CaCO.sub.3) 2 obtained with Density Functional Theory and LDA-VWN functional in a water-solvated medium. Density Functional Theory, LDA- VWN functional Molecule or Total energy Interaction energy Complex (kcal/mol) (kcal/mol) 1 −1,727,746.029 −188.63 2 −70,629,899.29 3 −72,356,833.96

[0055] According to the results of Table 1, is noted the adsorption of asphaltenes on the calcite surface would be a thermodynamically favorable process, given the negative sign, with a magnitude of 188.63 kcal/mol. This example simulates the oil recovery in a carbonate rock oil-wettable process which is experimentally attributed to polar compounds adsorption of the oil on the rock over hundreds and thousands of years; and is the energy that must overcome a wettability modifier injected into the reservoir in enhanced recovery process.

EXAMPLE 2

[0056] By means of computational Chemistry and by using quantum chemical methods which employ Density Functional Theory along with the LDA-VWN functional were optimized in a water-solvated medium (Dielectric constant 78.54); the asphaltenes average molecular structure model that represents their characteristics of heavy oil from the Marine Region in Mexico (Garcia-Martinez; J.; Tesis de Maestria. 2004) 1, dolomite surface geometry (CaMg (CO.sub.3).sub.2) 4 and the adsorption geometry of the product generated 5 from the interaction of asphaltene structure molecular model 1 with dolomite surface (CaMg (CO.sub.3).sub.2) 4 and the energy results for the adsorption process of the asphaltenes molecular model structure 1 on the calcite surface (CaMg (CO.sub.3).sub.2) 4 (6) shown in Table 2.

TABLE-US-00002 TABLE 2 Energy results obtained for the adsorption of asphaltene molecular model structure (1) on dolomite surface (CaMg (CO.sub.3).sub.2) 4 obtained with Density Functional Theory and LDA-VWN functional in a water-solvated medium. Density Functional Theory, LDA- VVWN functional Molecule or Total energy Interaction energy Complex (kcal/mol) (kcal/mol) 1 −1,727,746.029 −178.07 4 −52,685,382.68 5 −54,412,756.79

[0057] According to the Table 2 results, is noted that the asphaltenes adsorption on the dolomite surface would be a thermodynamically favorable process, with a magnitude of -178.07 kcal/mol.

EXAMPLE 3

[0058] By means of computational chemistry, and using Density Functional Theory methods and LDA-VWN functional, the molecular structure geometry were optimized in a water-solvated medium (Dielectric constant 78.54), a geminal zwitterionic liquid, sulfobetaine base of the present invention 6, calcite surface geometry (CaCO3) 2 and adsorption product geometry 7 generated from the interaction of zwitterionic liquid molecular structure 6 with the calcite surface (CaCO.sub.3) 2 (7) and the energy results obtainded of the adsorption process of the zwitterionic liquid molecular structure 6 on the calcite surface (CaCO.sub.3) 2 (8) shown in Table 3.

TABLE-US-00003 TABLE 3 Energy results obtained for the adsorption process of a molecular structure of a geminal zwitterionic liquid, sulfobetaine base 6 on calcite surface (CaCO.sub.3) 4 obtained with Density Functional Theory and LDA-VWN functional in a water-solvated medium. Density Functional Theory, LDA-VWN functional Molecule or Total energy Interaction energy Complex (kcal/mol) (kcal/mol) 6 −2926939.86 −151.0772 2 −70629859.1 7 −73556950

[0059] According to the Table 3 results, is noted that the adsorption of geminal zwitterionic liquid, sulfobetaine base on the calcite surface would be a thermodynamically favorable process, given the negative sign, with a magnitude of 151.08 kcal/mol. Moreover, when comparing this last result with the one presented in the table 1 corresponding to the asphaltene-calcite interaction, must be the zwiterionic liquid-calcite interaction is more favorable or of less energy so it is checked from the theoretical viewpoint that the zwitterionic liquids have the potential to function adequately as wettability modifiers for rocks with high tendency to be oil-wettable such as carbonate rocks.

EXAMPLE 4

[0060] By means of computational chemistry, and using Density Functional Theory methods and LDA-VWN functional the molecular structure geometry were optimized in a water-solvated medium (Dielectric constant 78.54) a geminal zwitterionic liquid, sulfobetaine base of the present invention 6, dolomite surface geometry (CaMg (CO.sub.3).sub.2) 4 and adsorption product geometry 8 generated from the interaction of zwitterionic liquid molecular structure 6 with dolomite surface geometry (CaMg (CO.sub.3).sub.2) 4 (9) and the energy results obtained for the adsorption process of the molecular structure of zwitterionic liquid 6 on dolomite surface geometry (CaMg (CO.sub.3).sub.2) 4 (10) shown in Table 4.

TABLE-US-00004 TABLE 4 Energy results obtained for the adsorption process of a molecular structure of a geminal zwitterionic liquid, sulfobetaine base 6 on dolomite surface (CaMg (CO.sub.3).sub.2) 4 obtained with Density Functional Theory and LDA-WVN functional in a water-solvated medium. Density Functional Theory, LDA- VWN functional Molecule or Total energy Interaction energy Complex (kcal/mol) (kcal/mol) 6 −2926943.99 −176.82325 4 −52685348.2 8 −55612469.1

[0061] According to the results of Table 4, is noted that the adsorption of geminal zwitterionic liquid, sulfobetaine base, of the present invention, on the dolomite surface would be a thermodynamically favorable process, given the negative sign, with a magnitude of 176.82 kcal/mol. Moreover, when comparing this last result with the one presented in the table 2 corresponding to the asphaltene-dolomite interaction, you have that the zwitterionic liquid-dolomite interaction is more favorable or less energy so it is checked, from the theoretical viewpoint, the zwitterionic liquids have the potential to function adequately as wettability modifiers for rocks with high tendency to be oil-wettable such as carbonate rocks.

[0062] 2) Synthesis of Geminal Zwitterionic Liquid, Sulfobetaine- and Hidroxisultaine Base

[0063] Once completed the molecular design stage, the zwitterionic liquids selected are synthesized at laboratory level and subsequently evaluated to ascertain the design details. Thereafter, the performance of the zwitterionic liquids of the present invention was evaluated experimentally as wettability modifiers on carbonate rocks with heavy and light crude oil under conditions of high salinity and high temperature and as corrosion inhibitors under characteristic conditions of crude oil production pipelines.

[0064] The germinal zwitterionic liquid, sulfobetaine- and hidroxisultaine base, object of the present invention, are prepared according to the following synthesis route:

##STR00004## ##STR00005##

[0065] The synthesis scheme comprises the following:

[0066] For route 1:

[0067] The first step is to react Polyethylene Glycols of formula I, derived from ethylene oxide with two hydroxyl groups, one at the end and the other at the beginning of the polymer chain, and whose molecular weight is in the range from 100 to 20,000 g/mol; with benzenesulfonyl chloride or tosyl chloride; where the reaction is carried out with a molar relationship 1:1 to 1:4 between polyethylene glycols of formula I and benzenesulfonyl chloride or tosyl chlorides, preferably 1:1.5 to 1:2.8; with an alkaline base of sodium, potassium or cesium, preferably sodium hydroxide; using water as a solvent, tetrahydrofuran, acetonitrile or clororoform or mixtures thereof; in a reaction time of 1 to 12 hours, preferably of 3 to 8 hours; and at a temperature of 0 to 25° C., preferably of 5 to 20° C.; to form compounds of formula III.

[0068] The second stage consists of reacting the compounds of formula III by a nucleophilic substitution with secondary amines of formula IV which R.sub.1 and R.sub.2 may be alkyl or alkenyl chains; linear or branched, preferably of 1 to 30 carbon atoms; or cycle alkyl or aryl groups, preferably of 5 to 12 carbon atoms and R.sub.2 also can be Hidrogen, wherein the reaction is carried out in a molar ratio between the compounds of formula III and IV of 1:1.5 to 1:4, preferably 1:1.8 to 1:2.6; in the presence of solvents such as acetonitrile, chloroform, dimethylformamide, dimethylsulfoxide, acetone or short chain alcohols; in a reaction time from of 6 to 60 hours, preferably 36 hours; and at a temperature of 50 to 150° C.; for obtaining tertiary amines of formula V.

[0069] The third stage is the reaction between the compounds of formula V and 2-bromoethane sulfonate of formula VI or sodium 3-chloro-2-hydroxy propane sulfonate of formula VII, in a molar ratio of 1:1.5 to 1:4, preferably 1:1.8 to 1:2.6; the reaction is carried out in the presence of solvents such as water or short-chain alcohols, preferably water; the reaction time, the temperature and the pressure depend of the structure of them compounds of formula V; usually the reaction time varies from 6 to 72 hours, preferably of 12 to 48 hours, temperature of 40 to 180° C., preferably 80 to 130° C., and the pressure is generally atmospheric, to obtain compounds of formula VII: base germinal zwitterionic liquid, sulfobetaine- and hidroxisultaine-base

[0070] For route 2:

[0071] The first step is to react polyethylene glycol diglycidyl ether of formula I, derived from ethylene oxide with two epoxide groups, one at the end and the other at the beginning of the polymer chain, and whose molecular weight is in the range from 100 to 20,000 g/mol; with amines of formula IV which R.sub.1 and R.sub.2 may be alkyl or alkenyl chains; linear or branched, preferably of 1 to 30 carbon atoms; or cycle alkyl or aryl groups, preferably of 5 to 12 carbon atoms and R.sub.2 may be also hydrogen and wherein the reaction is carried out in a molar ratio between the compounds of formula III and IV of 1:1.5 to 1:4, preferably 1:1.8 to 1:2.6; in the presence of solvents such as water or short chain alcohols; in a reaction time from of 4 to 15 hours, preferably 8 hours; and at a temperature of 50 to 150° C.; for obtaining amino alcohols of formula V.

[0072] The second stage is the reaction between the compounds of formula V and 2-bromoethane sulfonate of formula VI or sodium 3-chloro-2-hydroxy propane sulfonate of formula VII, in a molar ratio of 1:1.5 to 1:4, preferably 1:1.8 to 1:2.6; the reaction is carried out in the presence of solvents such as water or short-chain alcohols, preferably water; the reaction time, the temperature and the pressure depend of the structure of them compounds of formula V; usually the reaction time varies from of 6 to 72 hours, preferably of 12 to 48 hours, temperature of 40 to 180° C., preferably 80 to 130° C., and the pressure is generally atmospheric, to obtain compounds of formula VII: hidroxisultaine-and sulfobetaine-based geminal zwitterionic liquids.

[0073] Below are described some practical examples of branched geminal zwitterionic liquids obtaining, through the above-mentioned reaction schemes to have a better understanding of the present invention, without this limiting its scope.

EXAMPLE 5

[0074] Preparation of germinal zwitterionic liquid, sulfobetaine base (Product 1).

[0075] First stage, In a 50 ml round bottom balloon flask containing 5.0 g of an aqueous solution to 17 w % of sodium hydroxide (0.85 g) were added 4.24 g of polyethylene glycol whose number average molecular weight is 600 g/mol, the mixture stirred for 20 minutes. Then, at room temperature (20° C.) and atmospheric pressure very slowly 7.37 g of a solution of tosyl chloride at 40 w % (2.95 g) in tetrahydrofuran were added, keeping the temperature below 25° C. throughout the addition. After completion of addition, the reaction mixture was stirred for about an hour at room temperature and atmospheric pressure, then the reaction mixture was made and extraction of organic phase and evaporated the solvent at reduced pressure, to obtain 6.27 g of product PE-TS (polyether ditosylate) as a viscous clear yellow liquid.

[0076] As a second stage, in a 500 ml balloon flask, equipped with a magnetic stirrer, condenser and thermometer were added 1.97 g of dioctylamine, 6.27 g of PE-TS, 4.77 g of potassium carbonate and 18 g of acetonitrile. The reaction mixture was stirred vigorously at reflux temperature and atmospheric pressure for eight hours.

[0077] After which time the reaction, the reaction mixture was made and extraction of organic phase and evaporated the solvent at reduced pressure, to obtain 6.18 g of bis-N, N-dioctyl-N-polyether as a viscous amber liquid.

[0078] As a third stage, in a flask of 100 ml equipped with a condenser, magnetic stirrer and thermometer, 6.18 g of bis-N, N-dioctyl-N-polyether and 2.77 g of sodium chloroacetate in solution of 50 g of water was added. The reaction mixture was stirred vigorously at a reflux temperature and atmospheric pressure for 48 hours.

[0079] When the reaction time was completed, the aqueous phase was separated and evaporated under reduced pressure. The dry product was washing with chloroform to remove by filtration salts present. The organic fraction was evaporated under reduced pressure for obtain 6.84 g of zwitterionic liquid as a viscous amber liquid called Bis N, N-dioctyl-N-polyether sulfobetaine.

[0080] The spectroscopic characteristics of Product 1 are the following:

[0081] Representative bands of FTIR (cm.sup.−1): 2,922; 2,853; 1,641; 1,464; 1,221 and 1,098.

[0082] Representative chemical shifts of NMR .sup.1H (CDCl3), 200 MHz, δ (ppm): 0.86, 1.28, 1.75, 3.05, 3.27, 3.61 and 3.94 ppm.

[0083] Representative chemical shifts of NMR 13C (CDCl3), 50 MHz, δ (ppm): 13.9, 22.3, 31.1, 52.1, 53.3, 65.4 and 70.4 ppm

EXAMPLE 6

[0084] Preparation of germinal zwitterionic liquid, hidroxisultaine base (Product 2).

[0085] For this example the product bis-N, N-dioctyl-N-polyether is used and described in second stage of example 7.

[0086] In a 100 ml balloon flask, equipped with a magnetic stirrer, condenser and thermometer were added 2 g of bis-N, N-dioctyl-N-polyether and were added in solution 0.86 g of sodium 3-chloro-2-hydroxy propane sulfonate in 15 g of water. The reaction mixture was stirred vigorously at reflux temperature and atmospheric pressure for 72 hours.

[0087] When the reaction time was completed, the aqueous phase was separated and evaporated under reduced pressure. The dry product was washing with chloroform to remove by filtration salts present. The organic fraction was evaporated under reduced pressure for obtain 1.4 g of zwitterionic liquid as a viscous amber liquid called bis N, N-dioctyl-N-polyether hydroxysultaine.

[0088] The spectroscopic characteristics of Product 2 are:

[0089] Representative bands of FTIR (cm.sup.−1): 3,423; 2,922; 2,853; 1,647; 1,465; 1,222 and 1,098.

[0090] Representative chemical shifts of NMR .sup.1H (CDCl3), 200 MHz, δ (ppm): 0.83, 1.24, 1.26, 1.67, 2.99, 3.03, 3.20, 3.25, 3.58 and 3.85.

[0091] Representative chemical shifts of NMR .sup.13C (CDCl3), 50 MHz, δ (ppm): 13.8, 22.3, 31.0, 52.1, 53.2, 65.5 and 70.3.

EXAMPLE 7

[0092] Preparation of germinal zwitterionic liquid, sulfobetaine base (Product 3).

[0093] First stage. In a 50 ml round bottom balloon flask containing 10 g of polyethylene glycol diglycidyl ether whose molecular weight is in the range of 526 g/mol were added 3.5 g of dioctylamine. The reaction mixture was stirred vigorously to temperature of 95° C. and atmospheric pressure for one hours to obtain 13.5 g of bis N, N-dioctyl-N-hydroxy polyether as a viscous yellow liquid.

[0094] In a 100 ml balloon flask, equipped with a magnetic stirrer, condenser and thermometer were added 2 g of bis-N, N-dioctyl-N-polyether and were added in solution 0.86 g of sodium 2-bromoethane sulfonate in 15 g of water. The reaction mixture was stirred vigorously at reflux temperature and atmospheric pressure for 72 hours.

[0095] When the reaction time was completed, the aqueous phase was separated and evaporated under reduced pressure. The dry product was washing with chloroform to remove by filtration salts present. The organic fraction was evaporated under reduced pressure for obtain 1.4 g of zwitterionic liquid as a viscous amber liquid called bis N, N-dioctyl-N-hydroxy polyether sulfobetaine.

[0096] The spectroscopic characteristics of Product 3 are:

[0097] Representative bands of FTIR (cm.sup.−1): 3,423; 2,922; 2,853; 1,647; 1,465; 1,222 and 1,098.

[0098] Representative chemical shifts of NMR .sup.1H (CDCl3), 200 MHz, δ (ppm): 0.83, 1.24, 1.26, 1.67, 2.99, 3.03, 3.20, 3.25, 3.58 and 3.85.

[0099] Representative chemical shifts of NMR .sup.13C (CDCl3), 50 MHz, δ (ppm): 13.8, 22.3, 31.0, 52.1, 53.2, 65.5 and 70.3.

[0100] 3) Performance Testing of the Branched Geminal Zwitterionic Liquids as Wettability Modifiers

[0101] For the evaluation of the wettability modifying properties of limestone rocks, dolomite, sandstone, quartz or heterogeneous lithologies, in the presence of brine with high salt content and divalent ions such as calcium, magnesium, barium and strontium, the recovery factor is determined by spontaneous imbibition process in Amott cellls using limestone cores, in order to evaluate the wettability modifiers efficiency of the present invention with respect to a reference system without the presence of chemical. For the evaluations are selected Bedford limestone cores composed mainly of calcium carbonate, for being a rock that presents strong adsociones of polar organic compounds of the oil, and therefore, is the most severe case for a wettability modifier, which would be guaranteed that such chemicals would function adequately in other rock with less tendency to be oil-wettable.

[0102] The test method is described below.:

[0103] Recovery Factor Determination by Spontaneous Imbibition Process in Limestone Cores through Amott Cells.

[0104] The testing method consists in measure the amount of crude oil recovered from carbonate cores rock, initially oil-saturated due to spontaneous imbibition processes by water; in Amott cells at constant temperature and atmospheric pressure.

[0105] Elements Required for the Test: [0106] Amott cells. [0107] Controlled temperature recirculation device. [0108] Limestone core of 3.81 cm diameter×7 cm long, permeabilities and porosities known. [0109] Photographic camera. [0110] Crude oil. [0111] Connate water with high salinities. [0112] Glass equipment for SOXHLET extraction. [0113] Glass volumetric materials. [0114] Convection oven.

[0115] Test Procedures:

[0116] 1) Submit rock cores (dolostone, limestone or sandstone) to hydrocarbon extraction processes with different organic solvents in a SOXHLET system. The extraction processes are carried out continuously, sequentially or by reflux, using as solvents: a) Hexane b) Xylene, c) Chloroform, d) Methanol, e) Hexane, f) Xylene and g) Chloroform. The duration of each extraction stage is one day and the time for the entire process is 7 days.

[0117] 2) Determine the absolute permeability to helium in cores and effective porosity.

[0118] 3) Dry the rock cores in a stove at a temperature of 100° C. and record the weight once a constant weight is reached.

[0119] 4) Put the rock cores in contact with dead oil originating from the reservoir of interest for 24 hours at the required temperature and at a pressure of 140±5 psi, in an aging cell.

[0120] 5) Strain the rock cores saturated with dead oil at atmospheric temperature and pressure until no dropping is observed. The straining process lasts about 12 hours and a number 200 wire mesh is used for this purpose.

[0121] 6) Weigh rock cores soaked with dead oil and, by weight difference, obtain the amount of oil adsorbed by the porous medium.

[0122] 7) Prepare 500 mL of the aqueous solution (connate water) to be assessed at the concentration of chemical product required in the test.

[0123] 8) Place a rock core in the Amott cell and add carefully 350 mL of the chemical product to be assessed at the required concentration.

[0124] 9) Increase the temperature of the system to the temperature desired for the assessment of the performance of the chemical product or sample under study and maintain the same for the period of time at which the recovery factor is intended to be determined under the temperature and salinity conditions.

[0125] 9) Quantify the amount of oil produced due to spontaneous water imbibition processes under study conditions and determine the recovery factor according to the following equation:

R.sub.f=O.sub.r/O.sub.a×100

Where:

[0126] Rf=Recovery factor; Or=Recovered oil; Oa=Original oil adsorbed on the porous media.

EXAMPLE 8

[0127] Evaluation Results of Spontaneous Imbibition Process by Wettability Change Using Light Crude Oil.

[0128] According to the methodology described above, was placed in the Amott cells carbonated cores that were impregnated with light oil (see table 5) and in contact with solutions of product 1, 2 and 3 in connate water 1 (see table 6) with duration of 15 days to 90° C.

TABLE-US-00005 TABLE 5 SARA analysis, acid and basic total number data of light crude oil. Total Total acid basic SARA number number Oil Saturated Aromatic Resins Asphaltenes (TAN) (TBN) Light 30.68 28.62 39.35 1.32 0.21 1.7 oil

TABLE-US-00006 TABLE 8 Connate water 1 properties. Physical properties Temperature 20° C. pH 7.65 @ 20° C. Density 1.0043 g/cm.sup.3 @ 20° C. Conductivity μS/cm @ 20° C. Turbidity 4 FTU Chemical properties Cations (mg/L) (meq/L) Anions (mg/L) (meq/L) Sodium (Na.sup.+) 1 703.66 74.116 Chlorides (Cl.sup.−) 3 200.00 90.260 Potassium (K.sup.+) — — Sulphates (SO.sub.4.sup.═)  350.00 7.287 Calcium (Ca.sup.++)  416.00 20.758 Carbonates (CO.sub.3.sup.═)   0.00 0.00 Magnesium (Mg.sup.++)  106.95 8.799 Bicarbonates (HCO.sub.3.sup.−)  405.04 6.638 Iron (Fe.sup.++)   0.06 0.002 Hydroxides (OH.sup.−) — — Manganese (Mn.sup.++) — — Nitrites (NO.sub.2.sup.−) — — Barium (Ba.sup.++)   35.00 0.510 Nitrates (NO.sub.3.sup.−) — — Strontium (Sr.sup.++) — — Phosphates (PO.sub.4.sup.−3) — — Total:  2261.88 104.186 Total: 3 955.04 104.186 Dissolved and suspended solids (mg/L) (mg/L) Total solids — Total hardness as CaCO.sub.3 1 480.00 Total Dissolved Solids (TDS) 6216.92 Calcium hardness as CaCO.sub.3 1 040.00 Total Dissolved Solids (SST) — Magnesium hardness as CaCO.sub.3  440.00 Fats and oils — Alkalinity to the “F” as CaCO.sub.3   0.00 Soluble silica — Alkalinity to the “M” as CaCO.sub.3  332.00 Ferric oxide — Salinity as NaCl 5 275.00 Acidity as — Stability Index   0.288 10 Tendency Encrusting

[0129] Table 7 shows the recovery data obtained in the Amott cells for products 1, 2 and 3 at concentration of 300 mg/L. Brine 1 was used without additives as reference.

TABLE-US-00007 TABLE 7 Light oil recovery results in Amott cells. Concentration Grams of of Product Grams of oil Total Oil Percent (mg/L) impregnated Recovered recovery Reference 12.2874 4.5796 37.27 1 12.1547 6.3253 52.04 2 11.8760 6.0987 51.35 3 11.5244 5.6878 49.35

[0130] From the results of Table 7 it is possible to observe that hidroxisultaine-and sulfobetaine-based geminal zwitterionic liquids (products 1, 2 and 3) recover about 1.5 times more light crude oil than the reference therefore functioning properly as wettability modifiers in spontaneous imbibition processes.

EXAMPLE 9

[0131] Evaluation of a Spontaneous Imbibition Process Due to Wettability Change by Using a Heavy Crude Oil.

[0132] According to the methodology described above, it was placed in the Amott cells heavy oil-impregnated carbonate cores in contact to products 1 and 2 in solution with connate water 2 at a 300 mg/L concentration.

[0133] The properties of both the heavy crude oil and the connate water 2 are shown in Tables 8 and 9, respectively.

TABLE-US-00008 TABLE 8 SARA analysis as well as total acid and base numbers for heavy oil. Total Total SARA acid base Asphal- number number Oil Saturated Aromatic Resins tenes (TAN) (TBN) Heavy oil 13.4 24.76 51.01 10.44 1.83 2.12

TABLE-US-00009 TABLE 9 Physicochemical properties of the brine 2. Physical properties Temperature 20° C. pH 6.68 @ 20° C. Density 1.0216 g/cm.sup.3 @ 20° C. Conductivity 45,600 μS/cm @ 20° C. Turbidity 15 FTU Chemical properties Cations (mg/L) (meq/L) Anions (mg/L) (meq/L) Sodium (Na.sup.+) 11,630.06 505.907 Chlorides (Cl.sup.−) 22,000.00 620.540 Potassium (K.sup.+) — — Sulphates (SO.sub.4.sup.═) 825.00 17.177 Calcium (Ca.sup.++) 1,976.00 98.603 Carbonates (CO.sub.3.sup.═) 0.00 0.00 Magnesium (Mg.sup.++) 427.86 35.197 Bicarbonates (HCO.sub.3.sup.−) 122.00 1.999 Iron (Fe.sup.++) 0.25 0.009 Hydroxides (OH.sup.−) — — Manganese (Mn.sup.++) — — Nitrites (NO.sub.2.sup.−) — — Barium (Ba.sup.++) — — Nitrates (NO.sub.3.sup.−) — — Strontium (Sr.sup.++) — — Phosphates (PO.sub.4.sup.−3) — — Total: 14,034.41 639.716 Total: 22,947.00 639.716 Dissolved and suspended solids (mg/L) (mg/L) Total solids — Total hardness as CaCO.sub.3 6,700.00 Total Dissolved Solids (TDS) 36,981.41 Calcium hardness as CaCO.sub.3 4,940.00 Total Dissolved Solids (TSS) — Magnesium hardness as CaCO.sub.3 1,760.00 Fats and oils — Alkalinity to the “F” as CaCO.sub.3 0.00 Soluble silica — Alkalinity to the “M” as CaCO.sub.3 100.00 Ferric oxide — Salinity as NaCl 36,265.59 Acidity as — Stability Index −0.71714 Tendency Corrosive

[0134] Table 10 shows the results obtained from Amott cells containing carbonate cores in contact with solutions of sulfobetaine and hidroxisultaine-based geminal zwitterionic liquids (Products 1 and 2) at a 300 mg/L concentration in brine 2 and using heavy crude oil.

TABLE-US-00010 TABLE 10 Heavy oil recovery results in Amott cells. Grams of Grams of impregnated Total Recovery Chemical oil Recovered Oil Percentage Reference 6.8124 0.8364 12.2776 1 6.8124 0.8364 12.2776 2 6.8124 0.8364 12.2776

[0135] From results of Table 10 it is possible to observe that the sulfobetaine-based geminal zwitterionic liquid (Product 1) recovers about 3 times more heavy crude oil than the reference, and the hydroxysultaine-based zwitterionic liquid (Product 2) recovers about 1.5 times more oil than the reference. So, the sulfobetaine and hydroxysultaine-based branched geminal zwitterionic liquids function adequately as wettability modifiers in spontaneous imbibition processes.

[0136] Corrosion Inhibition Eficiency Determination through the NACE 1D-182 Method.

[0137] The NACE 1D-182 method is a gravimetric test commonly called dynamic wheel (wheel test) that simulates the corrosive environment characteristic of the oil production; it is a dynamic procedure developed for fluids (oil, water and inhibitor).

[0138] Equipment and Reagents for Tests

[0139] a) Dynamic evaluator for corrosion inhibitors with temperature controller, 30-rpm stirrer speed and capacity for 52 bottles of 180 ml.

[0140] b) 200-ml bottles.

[0141] c) SAE 1010 carbon steel coupons having 1″×0.5″×0.010″ dimensions.

[0142] d) Glassware for the preparation of the corrosive environment. It consists of a 2 L glass reactor equipped with a cooling bath, a mechanical stirrer, a bubbler for gas (nitrogen and hydrogen sulfide), and has an outlet joined to two in series-connected traps (the first one is charged with sodium hydroxide in pellet form and the second one with a 20% sodium hydroxide solution), so hydrogen sulfide does not contaminate the environment.

[0143] e) Potentiometer for pH measuring.

[0144] The test conditions are shown in Table 11.

TABLE-US-00011 TABLE 11 Test conditions. Temperature 60° C. Aqueous medium Synthetic brine with 600 ± 50 ppm of H.sub.2S Test time 46 hours Organic medium Kerosene Brine/organic medium 90/10 volume ratio Test volume 180 mL Medium pH 4 Corrosion witness SAE 1010 steel (metal coupons)

[0145] The composition of brine 3 is shown in Table 12:

TABLE-US-00012 TABLE 12 Composition of the brine 3. Salts Amount (g/L) NaCl 60.0 CaCl.sub.2•H.sub.2O 6.0 MgCl.sub.2•6H.sub.2O 10.48 Na.sub.2SO.sub.4 3.5

[0146] Results.

[0147] The weight difference of the coupons before and after they have been exposed to the corrosive liquid during 46 hours is a direct indication of the metal lost due to the corrosion.

[0148] The efficiency as a corrosion inhibitor is obtained by comparing the corrosion speed of the reference or blank with the speed of the witness having a determined corrosion inhibitor concentration, through the following formula (2):

Efficiency=(V.sub.0−V)/V.sub.0×100

where V.sub.0 is the corrosion velocity of the reference coupon (blank), and V is the corrosion velocity of the coupon having the corrosion inhibitor.

[0149] Table 13 shows the results for the Products 1 and 2 used at different concentrations.

TABLE-US-00013 TABLE 13 Results of the corrosion rate and the efficiency. Corrosion Concentration velocity Efficiency, Chemical (ppm) (mpy)* (%) Reference 0 32.9 0 1 50 2.8 91.4 1 100 2.0 93.8 2 50 2.9 90.9 2 100 2.8 91.4 *mpy: thousandths of an inch per year.