Prevention of desulfation during preparation of sulfate and sulfonate surfactant mixtures

Abstract

The present invention relates to a process for preparing a surfactant formulation comprising at least water, a sulfate surfactant, and a sulfonate surfactant. The process comprises the steps of mixing a sulfate and a sulfonic acid, obtaining a mixture of pH lower than 4, mixing them with a first mixing device, then adding a neutralizing agent and mixing with a second mixing device. The residence time of the sulfonic acid / sulfate mixture before neutralization of the sulfonic acid is shorter than 90 seconds. The process is suitable for preparing sulfate and sulfonate surfactant formulations to be used in oil recovery activities, such as enhanced oil recovery, or in gel detergents.

Description

[0001] 240782

[0002] 1

[0003] Prevention of desulfation during preparation of sulfate and sulfonate surfactant mixtures

[0004] This invention relates to an inventive process for preparing a surfactant formulation comprising at least water, a sulfate surfactant and a sulfonate surfactant.

[0005] Background

[0006] Surfactant formulations comprising a sulfonate surfactant and a sulfate surfactant have several applications. For example, these surfactant formulations may be used in gas or oil recovery activities, such as in enhanced oil recovery methods, or in liquid or gel detergent compositions (e.g. gel laundry detergents).

[0007] Some desirable characteristics of a surfactant formulation to be used in gas or oil recovery activities are that the manufactured surfactant formulations have 1) a high surfactant content and low water content, to achieve a better surfactant performance and to reduce energy / fuel consumption needed for its transportation from the manufacturing site (e.g. chemical plant) to the oil or gas field, where the formulation will be used; and 2) low viscosity, which facilitates the handling and pumping of the product.

[0008] Aqueous sulfonate surfactant formulations are prepared by mixing a sulfonic acid with a neutralizing agent in aqueous solution. If a preparation of an aqueous sulfonate surfactant formulation with high surfactant / low water content is attempted, these usually leads to a formulation having an undesirable high viscosity due to a semi-solid gel phase formed between the sulfonate and the water. The gel phase formation between sulfonates and water is due to the strong hydration and solvation of sulfonate ions, among others. The viscosity is usually too high to allow for easy handling and pumping of the formulation. These highly viscous formulations then require dilution of the aqueous sulfonate surfactant with large amounts of water to enable its pumping and industrial handling, i.e. obtaining formulations of low surfactant / high water content, which require higher energy and equipment for transportation of the same active surfactant quantity.

[0009] Ether sulfates can be added to surfactant systems containing sulfonates to avoid the formation of the gel phase due to their ability to disrupt the interactions that lead to gelation, for example by increasing ionic strength, competing for water molecule interactions, and altering solubility and electrostatic conditions.

[0010] However, the preparation of surfactant formulations comprising a sulfonate surfactant and a sulfate surfactant also presents several challenges:

[0011] On the one hand, if the sulfonic acid is in contact with the neutralizing agent before the sulfonic acid is homogeneously mixed with the sulfate surfactant, the gel-phase will not be prevented, and it will form as an intermediate phase during the process. Due to the formation of gel-phase, this process will again require the use of 240782

[0012] 2 larger amounts of water and a high mixing strength, e.g. by using a neutralization loop with a high shear homogenization unit.

[0013] On the other hand, when the sulfonic acid and the sulfate are brought into contact, they may react together leading to desulfation of the sulfate. This side reaction is undesired and leads to the formation of undesired byproducts as well as loss of product performance. In particular, when an ether sulfate reacts with sulfonic acid, desulfation may result in an alcohol alkoxy late, which is less water-soluble than the sulfate.

[0014] The desulfation of a neutralized ether sulfate (RO-SO3-M) with an unneutralized organic sulfonic acid (R’-SOs-H) occurs due to the higher strength of organic sulfonic acids over sulfuric acids semi esters. When the ether sulfate and the sulfonic acid react, the neutralized ether sulfate (RO-SO3-M) will be converted into the un-neutralized RO-SO3-H. This compound is quite sensitive: it may directly release sulfur trioxide (SO3) and form the alcohol RO-H or, alternatively, it may react with water to form the alcohol RO-H and sulfuric acid HO-SO3-H. In general, any reaction involving an alkyl aryl sulfonic acid will always comprise a certain amount of water (e. g. 1 wt.%), because water is an additive in the sulfonation process of alkyl aryl compounds.

[0015] As stated above, when an ether sulfate reacts with sulfonic acid, desulfation may result in an alcohol alkoxy late, which is less water-soluble than the sulfate. Additionally, aqueous solutions comprising alcohol alkoxylates typically have lower salt solubility capacity (also known as salt tolerance) compared to aqueous solutions comprising ether sulfates, among other factors this is due to the charged nature of ether sulfates and their enhanced hydrophilicity, which contribute to stronger interactions with salts, allowing for better solubilization and higher salt tolerance of the solution. As it will be explained in the following paragraphs, certain salt tolerance is an important characteristic for surfactant formulations to be used in oil recovery activities. Thus, if a high desulfation of the sulfate surfactant occurs, this may lead to an aqueous surfactant solution having too low salt tolerance and which cannot be successfully used in oil recovery activities.

[0016] For a successful oil mobilization during an enhanced oil recovery operation in a conventional reservoir two key requirements must be fulfilled: a) the injected aqueous surfactant formulation must be clear and stable under the reservoir conditions (e.g. 65 °C). If the formulation is cloudy (i.e. insoluble particles are suspended), the surfactant might phase separate and might be filtered off in the porous rock before it can interact with the oil-bearing zones. In addition, there is the risk that the filtered-off material might plug the reservoir and cause strong increases of injection pressure or even unwanted cracks in the reservoir creating unpredictable new flow directions, b) once the injected aqueous surfactant solution is in contact with crude oil, ultralow interfacial tension must be achieved under the reservoir condition. Interfacial tension refers to the force at the interface between two immiscible fluids, such as water and oil. A higher interfacial tension makes it more difficult for the water to displace and mobilize the oil trapped in the reservoir rock. This results in lower oil recovery rates. 240782

[0017] 3

[0018] Conversely, a lower interfacial tension enhances the ability of water to penetrate and displace the oil, leading to improved oil recovery. The salinity, or salt concentration, of the injected aqueous surfactant formulation in oil recovery operations can significantly influence the interfacial tension between water and oil. Studies have shown that there is an optimum salinity for achieving the lowest interfacial tension. This optimum salinity varies depending on the specific reservoir conditions, such as the composition of the reservoir rock and the oil-water ratio present in the reservoir. The oil-water volume ratio around the injector is typically around 10 : 90.

[0019] Therefore, for a successful enhanced oil recovery operation, it is very important that the aqueous surfactant formulation, e.g. the aqueous surfactant formulation comprising a sulfate surfactant and a sulfonate surfactant, injected into the wellbore has the optimum salinity conditions and that it is, at the same time, clear and stable.

[0020] Some of the known processes for the preparation of surfactant mixtures comprising sulfate and / or sulfonate compounds have been disclosed in the following patents or patent applications:

[0021] US 6,794,347 B2 discloses surfactant compositions comprising 50-90% of water, a surfactant A, selected from the group consisting of anionic, nonionic, cationic and amphoteric surfactants, and a non-neutralized fatty acid. Wherein if surfactant A is anionic, it may be selected from carboxylates, sulfonates and sulfates surfactants. In examples, a surfactant composition comprising linear alkyl benzene sulfonic acid and NaOH (neutralizing agent). However, US 6,794,347 B2 does not teach about any surfactant formulation comprising both a sulfonate compound and additionally a sulfate compound.

[0022] US 4,261,917 discloses a method to prepare an aqueous solution or slurry containing 60-75 wt.% of sulfate of higher alcohol or alkylene oxide adduct of said alcohol. The Examples show that the surfactant formulations obtained by this method have high viscosities, namely between 130 to 180 Poise at 40 °C. However, it does not teach about any formulation which additionally comprises sulfonate surfactants.

[0023] EP 0507402 A1 discloses a continuous process to produce a surfactant composition comprising an anionic surfactant and a nonionic surfactant, whereby the anionic surfactant is prepared by mixing equimolar amounts of a neutralizing agent and an acid precursor of the anionic surfactant. In examples 1-3, the anionic surfactant is alkylbenzene sulfonate. In examples 4-8, the anionic surfactant was a primary alkyl sulphate. And in example 9, the anionic surfactant was lauryl ether sulphate. However, it does not teach about any formulation comprising both sulfonate and sulfate surfactants.

[0024] EP 2922945 B1 and WO 2014 / 079702A1 disclose a continuous process for producing a liquid detergent or cleaning agent, by mixing continuous separate volume flows of at least an acid precursor of an anionic surfactant and a neutralizing agent via a dynamic loop mixer, i.e. a closed in-line mixer with recirculation. Examples of EP 2922945 B1 illustrate a continuous process where firstly, the acid precursor, the neutralizing agent and water are combined, the 240782

[0025] 4 obtained mixture optionally passes through a static mixer and afterwards, the co-surfactant, e.g. fatty alcohol sulfate, is added in the dynamic loop mixer. In example E2, they disclose a process for preparing a surfactant formulation comprising the steps of mixing NaOH and water in a static mixer, followed by adding LAS acid in a dynamic liquid mixer, followed by adding fatty alcohol ether sulfate (an anionic cosurfactant), NaCI and phosphoric acid in another static mixer. However, they do not teach about a process where the sulfonic acid compound and the sulfate compound are mixed before the neutralization of the sulfonic acid.

[0026] WO 2006 / 069118 A2 discloses a continuous process for the preparation of a surfactant composition, by mixing a surfactant acid precursor with at least a molar equivalent of a neutralizing agent by using one or more static mixers. Additional components may also be present and may be fed into the process at any stage. However, none of the examples in WO 2006 / 069118 A2 show a process comprising additional components. In the examples, the acid precursor is a linear alkyl benzene sulphonic acid, and the neutralizing agent is sodium hydroxide. However, it does not teach about any formulation which additionally comprises a sulfate surfactant.

[0027] WO 2015 / 138275 A1 discloses a surfactant composition for use in enhanced oil recovery, comprising a neutralizing agent, e.g. NaOH solution, acid precursor of an anionic surfactant, i.e. C15 / 17 alkyl benzene sulfonic acid (ABS) and a co-surfactant, i.e. an ammonium salt of tristyrylphenyl(TSP)-PO35-EO25 sulfate. WO 2015 / 138275 A1 discloses, in an example on page 8 (1st and 2nd paragraphs on page 8), a process where NaOH is combined with the alkoxy sulfate surfactant, mixed until a homogeneous solution is obtained, and then the ABS is added into the NaOH-Sulfate mixture while mixing. However, they do not teach about a process where the sulfonic acid compound and the sulfate compound are mixed before the addition of the neutralizing agent.

[0028] WO 01 / 79412 A1 discloses, in an example on page 28, a process for preparing a surfactant formulation comprising the steps of mixing linear alkylbenzene sulfonic (LAS) acid and a blend of nonionic surfactants in a static mixer of the Sulzer type, followed adding 50% NaOH to neutralize 30-50% of LAS and pumping the mixture into a static inline mixer, then adding sufficient NaOH to complete neutralization and pumping the resulting mixture through a dynamic inline mixer. However, it does not teach that the surfactant formulation additionally comprises a sulfate surfactant.

[0029] WO 2013 / 092049 A1 discloses, in comparative example A, a process for preparing a surfactant formulation comprising the steps of mixing (among others) C12-14 linear alkylbenzene sulphonic acid (LAS acid), sodium lauryl ether sulphate with 3 moles EO (SLES 3EO) and neutralizing agent NaOH. However, it does not teach about the order of addition of the compounds, and even if the LAS acid and SLES 3EO were combined before the addition of the NaOH, it does not teach about the pH of the mixture before the addition of the NaOH, nor the residence time of the LAS acid and SLES 3EO mixture before neutralization with NaOH.

[0030] JPS 6447755 A discloses, in example 1, a process for preparing a surfactant formulation comprising the steps of mixing a nonionic surfactant with LAS acid in an iron reactor tank, followed by adding 45 wt.% NaOH for neutralization. However, it does not teach about any formulation which additionally comprises a sulfate surfactant. 240782

[0031] 5

[0032] Summary of the invention

[0033] It is the object of the present invention to provide an improved process for preparing a surfactant formulation which comprises a sulfonate and a sulfate compound, wherein the undesired formation of highly viscous gel-phase is prevented and wherein desulfation of the sulfate-surfactant is also prevented or at least reduced. The desulfation must be sufficiently reduced to a level where the prepared surfactant formulation can be used to subsequently prepare an EOR composition with sufficient salt tolerance to obtain a clear and stable solution at optimum salinity for successful application in enhaced oil recovery (EOR) activities.

[0034] Surprisingly, the Applicant has discovered that these problems can be solved by preparing the surfactant formulation by a process comprising the steps of

[0035] I) mixing a sulfate with a sulfonic acid using mixing means,

[0036] II) mixing the mixture obtained in step I) with a neutralizing agent using mixing means, wherein the neutralizing agent reacts with the sulfonic acid obtaining a sulfonate, and ill) obtaining the surfactant formulation comprising the sulfate and the sulfonate, wherein the pH of the mixture obtained in step I) is lower than 4, and the residence time of the sulfate / sulfonic acid mixture from the start of step I) until the start of step ii) is less than 90 seconds.

[0037] The process is suitable for the manufacture of surfactant formulations used in detergent compositions (e.g. gel laundry detergent) and in oil-recovery applications (e.g. in enhanced oil recovery activities), among other applications.

[0038] This new process avoids or reduces product quality deterioration caused by full or partial desulfation of the sulfate- surfactant, and consequently loss of product performance, e.g. loss of surfactant activity. And it provides a formulation with good handling properties, i.e. viscosity lower than 5000 mPas.

[0039] Description of the Figures

[0040] References in Figures 1 and 2:

[0041] (1) source of a sulfonic acid surfactant,

[0042] (2) source of sulfate surfactant, 240782

[0043] 6

[0044] (3) source of neutralizing agent,

[0045] (4) first mixing means, preferably a static mixer,

[0046] (5) second mixing means, preferably a static mixer,

[0047] (6) outlet for the obtained surfactant formulation,

[0048] (7) T-piece and three-way valve connection, and

[0049] (8) recirculation pipe.

[0050] Detailed description of the invention

[0051] Chemical components

[0052] Abbreviations used:

[0053] PC = propylenoxy unit

[0054] EC = ethylenoxy unit

[0055] TSP = tristyryl phenyl

[0056] ABS = alkylbenzene sulfonic acid

[0057] LABS = linear alkylbenzene sulfonic acid

[0058] 2-EH = 2-ethy lhexy I

[0059] The term "sulfate” across the present invention refers to a surfactant comprising a sulfate anion. The sulfate can be represented by formula (I) R1-SO4'Y+, wherein Y+is a monovalent cation and R1is any substituted or unsubstituted, aromatic, cyclic, linear or branched hydrocarbyl radical, which may optionally comprise heteroatoms selected from N, 0 and P.

[0060] The term "sulfonic acid” across the present invention refers to a chemical compound comprising a sulfonic acid group. The sulfonic acid can be represented by formula (II) R2-SC>3H, wherein R2is any substituted or unsubstituted, aromatic, cyclic, linear or branched hydrocarbyl radical, which may optionally comprise heteroatoms selected from N, 0 and P.

[0061] The term "sulfonate” across the present invention refers to a surfactant comprising a sulfonate anion. The sulfonate can be represented by formula (III) R3-SO3'Y+, wherein Y+is a monovalent cation and R3is any substituted or unsubstituted, aromatic, cyclic, linear or branched hydrocarbyl radical, which may optionally comprise heteroatoms selected from N, 0 and P.

[0062] In one embodiment, the sulfate is a substituted or unsubstituted ether sulfate, preferably an ether sulfate comprising PO and EO repeating units. 240782

[0063] 7

[0064] In another embodiment, the sulfate is selected from a styrynated phenol ether sulfate and an alkyl ether sulfate, the alkyl chain comprising 8 to 18 carbons. Preferably, the sulfate is selected from formula (IV) R4- P05-4o-EOo-35S04'Y+, wherein Y+is a monovalent cation and R4is a styrynated phenol or a C8-18 alkyl radical.

[0065] In a preferred embodiment, the sulfate is selected from

[0066] • TSP-PO5-40-EO0-35SO4-Y+, preferably TSP-PO20-40-EOi5-25SO4'Y+;

[0067] • C16-18 al ky l-PO5-40-EO0-35SO4-Y+, preferably C16-18 alkyl -P05-IO-EOO-2S04'Y+, more preferably C16-18 linear alkyl - P05-IO-EOO-2S04'Y+;

[0068] • 2-EH-PO5-40-EO0-35SO4-Y+, preferably 2-EH-POi5-25-EOo-5S04_Y+; and

[0069] • C14-15 al ky I-PO5-40-EO0-35SO4 Y, preferably C14-15 al ky I-PO5-15- E0o-5S04'Y+, more preferably C14-15 branched alky I- PO5-15-EO0-5SO4-Y+, wherein Y+is a monovalent cation.

[0070] The sulfonic acid may be selected from alkyl aryl sulfonic acid, primary and secondary alkyl sulfonic acids, primary or secondary olefin sulfonic acids, alkyl ether sulfonic acids, alkyl toluene sulfonic acids, alkyl xylene sulfonic acids, dialkyl benzene sulfonic acids and fatty acid ester sulfonic acids.

[0071] In one embodiment of the present invention, the sulfonic acid is an alkyl aryl sulfonic acid, preferably an alkylbenzene sulfonic acid, more preferably an alkylbenzene sulphonic acid with an alkyl chain of C10-32, even more preferably an alkylbenzene sulphonic acid with an alkyl chain of C10-24.

[0072] The sulfonate is the anionic form of the above-mentioned sulfonic acids.

[0073] The countercation of the sulfates and sulfonates may be independently selected from an alkali metal cation and a substituted or unsubstituted ammonium cation.

[0074] The neutralizing agent may be a base selected from an aqueous solution of NaOH, KOH, NH4OH, Na2CO3, NaHCOs, K2CO3, KHCO3, Ca(OH)2, Mg(OH)2, Na acetate, K acetate, NH4 acetate, and an organic amine, such as amino ethanol, diethanol amine, triethanol amine, N, N-dimethyl ethanol amine, iso propylamine, H2NCH2CH(CH3)OH, HN(CH2CH(CH3)OH)2, N(CH2CH(CH3)OH)3, Me2NCH2CH(CH3)OH, and triethyl amine. Preferably an aqueous solution of NaOH or an organic amine.

[0075] In a preferred embodiment, the aqueous solution of the neutralizing agent may have an active base content of 2 to 98 wt.%, preferably 20 to 80 wt.%, more preferably 45 to 60 wt.%.

[0076] Step I)

[0077] In step I), the sulfonic acid and the sulfate are mixed using mixing means. 240782

[0078] 8

[0079] The pH of the sulfonic acid / sulfonate mixture obtained in step i) is lower than 4, preferably lower than 3, more preferably lower than 2.

[0080] For this, the sulfonic acid and the sulfate may be fed from their sources into a common pipe via a pump, wherein the common pipe is connected with a mixing device, or alternatively, the sulfonic acid and the sulfate may be independently added into the mixing device.

[0081] The term "source” for any of the components, as used through this invention, is intended to cover any kind of source. In one embodiment, the source may be a tank or an ISO container. Of course, a plurality of sources may be used, for example a plurality of tanks. Preferably, such tanks are mobile, so that they can be easily relocated, for example between manufacturing sites. In certain embodiments of the present invention, the tanks may be tank containers, tank trailers or tank trucks. Basically, the tanks may have any shape and size. In one embodiment, tanks may be cylindrical. The volume of the tanks is not limited. Mobile tanks as mentioned, may have a volume from 1 m3to 100 m3, for example from 10 m3to 50 m3. The tanks may also serve as buffer tanks to ensure an uninterrupted supply with the components. When the storage tanks need to be heated, for example to maintain the components pumpable, i.e. with a viscosity lower than 2500 mPas, electrically heated, liquid heated or steam heated ISO containers or tanks may be used. The source of the sulfonic acid and the sulfate may be independently selected.

[0082] The term "pipe” as used throughout this invention encompasses rigid pipes, such as pipelines, as well as flexible pipes, such as for example hoses or flexible metal pipes. A pipe may of course comprise both, rigid and flexible sections. The diameter of the pipes may be for example from 50 cm to 80 cm. Flows in the system are typically laminar but may also be turbulent.

[0083] Any type of pumps may be used for the present process. Preferably, positive displacement pumps or centrifugal pumps are used.

[0084] In one embodiment of this invention, recirculation lines may be used to adjust the flows of the sulfonic acid and the sulfate to the required values before feeding these components into the common pipe or the mixing device. For this, a three-way-valve and a T-piece may be used. At the start of the process, the three-way-valve is positioned so that the raw components are fed into the recirculation line, once the required flow values are reached, the position of the three-way-valve is switched, and the raw materials are fed into the mixing system. This embodiment provides the advantage that quality issues during the start-up of the process may be avoided as well as faster start up, shut down and idle procedures can be achieved. This embodiment is illustrated in Fig. 2.

[0085] The mixing means may be selected from stirring means (including magnetic stirrers, propeller mixers, and impeller mixers), ultrasonic mixers, high shear mixers, static mixers, continuous stirred tank reactors (CSTR), mixing pumps and mixing nozzles. In a preferred embodiment, the mixing means is a static mixer. 240782

[0086] 9

[0087] High shear mixers are well-known to the skilled person. A high shear mixer is a type of mixing device used in various industries, including pharmaceutical, food, and chemical. It is designed to produce intense mechanical forces that cause liquids and solids to be mixed, dispersed, or emulsified. The mixer typically consists of a rotor and a stator, which create a high velocity flow and impart shear forces of 1000 s1or higher on the materials being processed. This high shear action helps break down particles and enhance the uniformity and stability of the mixture. High shear mixers are commonly used in applications where thorough mixing, particle size reduction, or creating stable emulsions is required.

[0088] Static mixers are well-known to the skilled person. They must be capable of operating in a continuous process and of mixing fluids. Suitable static mixers include, for example split-and-recombine type mixers, micro channel mixers and T-Pieces in pipes. The static mixers preferably have a length to diameter ratio of at least 8. It is desired that the inner diameter of the static mixers is similar or equal to the inner diameter of the pipes.

[0089] Static mixers are particularly preferred over dynamic mixers for the process of the present invention, as static mixers require lower energy inputs and therefore lead to energy saving and lower operating cost. Static mixers also require lower capital investment, and this is especially true for multi-stage high shear dynamic mixers, which have significantly higher lifetime cost than static mixers used for the process of the present invention.

[0090] In one embodiment of the present invention, the mixture prepared in step I) is substantially homogeneous. The homogeneity of the mixture can be evaluated by the coefficient of variation of the concentration. In one embodiment, the coefficient of variation of the concentration of the mixture prepared in step I) is less than 10%, preferably less than 5%, more preferably less than 1%.

[0091] The coefficient of variation of the concentration (CV) can be calculated as follows: where s is the concentration of a randomized sample of the mixture and x"is the average concentration of the mixture.

[0092] A coefficient of variation of the concentration lower than 10% indicates that the mixture has reached such homogeneity that when taking a randomized sample from the mixture, the concentration of that sample will only deviate from the average concentration of the mixture by 10%. Therefore, the lower the coefficient of variation of concentration, the higher the homogeneity of the mixture.

[0093] Achieving a good homogeneity in step I) has the advantage that the ether sulfate will successfully prevent gel-phase formation between sulfonate and water during step ii), keeping the viscosity of the mixture low and manageable.

[0094] Step ii)

[0095] In the step ii) of the process, the mixture obtained in step I) is mixed with a neutralizing agent using mixing means, wherein the neutralizing agent reacts with the sulfonic acid obtaining a sulfonate. 240782

[0096] 10

[0097] The residence time of the sulfate / sulfonic acid mixture from the start of step i) until the start of step ii) is less than 90 seconds, preferably less than 60 seconds, preferably less than 45 seconds, preferably less than 30 seconds, preferably less than 20 seconds, more preferably less than 15 seconds.

[0098] The "residence time of the sulfate / sulfonic acid mixture” throughout this invention refers to the time span from the moment the sulfate and the sulfonic acid start to be mixed together (i.e. the moment when desulfation risk of the sulfate surfactant starts) until the moment the neutralizing agent is mixed with the other chemical components (i.e. the sulfonic acid is neutralized, thus desulfation risk of the sulfate surfactant ends).

[0099] Reducing the time that the sulfonic acid is in contact with the sulfate is beneficial because these two components can undesirably react, thus, forming undesired byproducts (e.g. alcohol alkoxylate) and reducing the efficiency of the process, reducing yield or deteriorate product quality. Namely, the acidic nature of the free sulfonic acid leads to desulfation of the sulfate, causing a loss in product performance.

[0100] Therefore, by maintaining the residence time of the sulfate / sulfonic acid mixture below 90 seconds, the present process provides all the lower viscosity-advantages of mixing the sulfonic acid with the sulfate, while avoiding or reducing the byproduct-disadvantages of the undesired desulfation.

[0101] In the present process, the neutralization of the precursor may be partial or full neutralization.

[0102] In a preferred embodiment, the degree of neutralization of the precursor during the process may be at least 80% wt., more preferably of at least 90% wt., and more preferably substantially all the sulfonic acid is neutralized in the process.

[0103] In a further preferred embodiment, the molar ratio of the sulfonic acid to neutralizing agent is in the range of 1 :1 to 1 :1.5, preferably 1:1 to 1 :1.2, more preferably 1:1 to 1 :1.1.

[0104] The mixing means may be selected from stirring means (including magnetic stirrers, propeller mixers, and impeller mixers), ultrasonic mixers, high shear mixers, static mixers, continuous stirred tank reactors (CSTR), mixing pumps and mixing nozzles. In a preferred embodiment, the mixing means is a static mixer. And they may be the same or different as the selected mixing means in step I).

[0105] In one embodiment, steps I) and II) of the process are carried out at a temperature lower than 100 °C, preferably lower than 80 °C, and more preferably lower than 70°C.

[0106] In step ill), the surfactant formulation comprising the sulfate and sulfonate surfactants is obtained. 240782

[0107] 11

[0108] Neutralization of the sulfonic acid is an exothermic reaction, for this reason during the neutralization a temperature rise is expected. Thus, after the homogeneous surfactant formulation comprising the sulfonate and sulfate is obtained, it shall be cooled down to a stable temperature. For this, heat exchangers or mixing with a cold liquid may be used.

[0109] In one embodiment, the obtained surfactant formulation might be mixed by suitable mixing means while cooling down to achieve laminar flow.

[0110] In a preferred embodiment, the obtained surfactant formulation may have a pH value of at least 7, preferably between 8 and 12.

[0111] The obtained surfactant formulation may have a high concentration of surfactants, namely, the surfactant formulation may have an active surfactant content of at least 80 wt.%, preferably at least 85 wt.%.

[0112] Examples

[0113] The Applicant has carried out the inventive examples IE-1 and IE-2 and the comparative examples CE-1 and CE-2 to quantitatively demonstrate at least some of the advantages of the inventive process, in particular, that the undesired desulfation of the sulfate surfactant is prevented or at least greatly reduced. And that the reduction of the desulfation allows for the preparation of EOR compositions with sufficient salt tolerance to obtain a clear and stable solution at optimum salinity for successful application in enhaced oil recovery (EOR) activities. This is due to the reduction of byproducts formed during desulfation of ether sulfates (such as alcohol alkoxylates) which lead to aqueous compositions with low salt tolerance.

[0114] The Applicant surprisingly observed that when the pH of the mixture obtained in step I) is lower than 4 and the residence time of the sulfonic acid / sulfate mixture before neutralization is 120 seconds or longer > 50 % of the sulfate surfactant is desulfated, due to reaction with the sulfonic acid. This desulfation leads to the formation of alcohol alkoxylates, which are less water-soluble than the ether sulfates, and which additionally leads to the decrease of salt tolerance of the aqueous surfactant formulation. The salt tolerance of aqueous surfactant formulation comprising high amounts of alcohol alkoxylates drops to levels below the optimum salinity conditions for EOR compositions to be injected into the wellbore during EOR operations.

[0115] Therefore, by reducing the desulfation percentage of the sulfate surfactant, surfactant composition can be prepared that can successfully be used for the preparation of EOR compositions with optimum salinity conditions.

[0116] To evaluate the occurrence and impact of this undesired side reaction, comparative examples CE-1 and CE-2 and inventive examples IE-1 and IE-2 were carried out. For each of the examples, (1) the desulfation percentage in the production of the sulfonate I sulfate surfactant formulation was calculated, (2) the maximum salt tolerance of an EOR composition prepared from the surfactant formulation was calculated, and (3) the appearance of an EOR composition 240782

[0117] 12 prepared from the surfactant formulation at the optimum salinity conditions for oil-recovery activities of a crude oil in Northwest of India was evaluated.

[0118] In the following paragraphs, the production of the sulfonate / sulfate surfactant formulation for each of the examples is described, and the methods for determination of the desulfation percentage, maximum salt tolerance, optimum salinity conditions and appearance evaluation are described as well. A summary of the desulfation percentages, maximum salt tolerance and appearance at optimum salinity conditions for all examples is found in T able 1 .

[0119] Comparative Example CE-1

[0120] A process was carried out in a batch process, wherein 38 g of C10-32 alkyl benzene sulfonic acid and 53 g of TSP- PO35-EO19-SO4NH4 were added to a stirred reactor and mixed so that a pH = 3 was obtained at 60°C. The mixture was left resting overnight (16 hours) at 60°C. The following day, the neutralizing agent NaOH in 50% aq. solution was added to the reaction vessel at 60 °C to reach a pH of 7, and the mixture was stirred.

[0121] Comparative Example CE-2

[0122] A process was carried out in a batch process, wherein 18.2 g of TSP-PO35-EO19-SO4NH4 and 13 g of C10-32 alkyl benzene sulfonic acid were added to a 100 mL round bottom flask stirred with 500 rpm at 60°C (pH was between 1- 2). After 120 seconds of stirring, 3.4 g of NaOH in 50% aq. solution were added at 60°C and pH raised from 1 - 2 to 9.6 (measured as 2 wt.% in deionized water).

[0123] Comparative Example IE-1

[0124] A process was carried out according to a setup as illustrated in Figure 2, wherein (1) is the source of C10-32 alkyl benzene sulfonic acid, (2) is the source of TSP-PO35-EO19-SO4NH4, and (3) is the source of 50% NaOH in deionized water. Same starting materials quantities as in CE-1. The process temperature was 60 °C and a pH of the sulfonic acid / sulfate mixture was between 1-2.

[0125] The residence time of the sulfonic acid / sulfate mixture before neutralization in the set up of Fig. 2 depends on I) the flow speed of the components and II) the dimensions of the connection pipe from the first mixing device to the neutralizing agent addition point. The dimension of the connection pipe can be modified as follows: if a longer pipe is installed, the residence time of the sulfonic acid / sulfate mixture is longer or if a wider pipe is installed, the flow pressure, and consequently flow speed, is reduced, which also leads to a longer residence time of the sulfonic acid / sulfate mixture.

[0126] In IE-1, a connection pipe which lead to a residence time of sulfonic acid / sulfate mixture of about 25.7 seconds was installed. Residence time was calculated as the sum of the sulfonic acid / sulfate mixture in first static mixer + in the connection pipe up to the entrance to the second static mixer. 240782

[0127] 13

[0128] Inventive Example IE-2

[0129] Same set up and starting materials quantities as in IE-1 , but the residence time of the sulfonic acid / sulfate mixture prior to neutralization was about 12.2 seconds due to a much shorter connection pipe from the first mixing static mixer to the second static mixer.

[0130] Determination of desulfation percentage in the obtained surfactant formulation

[0131] The desulfation percentage of the obtained surfactant formulation was measured via ion chromatography. The content of sulfate ion in the sulfate surfactant (starting material) was determined, as well as the content of sulfate ion in the surfactant formulation obtained in step iii). The loss of sulfate ion (i.e. desulfation) was calculated by difference.

[0132] Additional methods that can be used for calculating the desulfation percentage are HPCL and Proton NMR spectroscopy.

[0133] In HPLC, the area percentage of signal from TSP-PO35-EO19-SO4NH4 and area percentage of signal from TSP-PO35- EO19-OH can be compared.

[0134] In proton NMR spectroscopy, the integral of signal from the underlined hydrogens (TSP-PO35-EO18-CH2CH2- OSO3NH4) in the sulfate surfactant (starting material) and the obtained surfactant formulation can be compared.

[0135] Determination of maximum salts tolerance of EOR composition at 65 °C

[0136] EOR compositions are prepared comprising

[0137] • the surfactant formulations prepared in the respective examples (quantity of active surfactant in the EOR composition is 1500 ppm of TPS-(PO)35-(EO)i9-SO4NH4, 1056 ppm sodium salt of C10-32 alkyl benzene sulfonate; wherein 1500 ppm of the sulfate surfactant refers to the theoretical amount present if no desulfation had been occurred - real amount of the sulfate surfactant present depends on desulfation percentage),

[0138] • produced water from an oil reservoir in Northwest of India (water, 0.45 wt.% NaCI, 0.01 wt.% KOI, 0.1 wt.% NaHCOs, 0.05 wt.% Na2SC>4; produced water was softened prior to use: Ca2+and Mg2+ions present is < 10 ppm) and

[0139] • varying amounts of Na2CC>3 ranging from 0.25% to 3.5% in increments of 0.25%.

[0140] Methods to soften hard water are commonly known in the art.

[0141] The EOR compositions were heated to 65 °C and visually evaluated.

[0142] EOR compositions are tested at elevated temperatures, such as 65°C, to simulate the reservoir conditions.

[0143] A clear and stable appearance of the EOR composition indicates that the tested amounts of Na2CO3 could be properly solubilized. A cloudy appearance indicates that the tested amounts of Na2CO3 superseded the maximum 240782

[0144] 14 salts solubility capacity of the EOR composition. The highest tested amount of Na2COa which still led to a clear and stable solution were selected as the maximum salts solubility capacity of that EOR composition.

[0145] Determination of optimum salinity of EOR composition at 65 °C for oil recovery activities

[0146] The optimum salinity is determined by microemulsion phase behaviour salinity scans. This method is described in page 5 of Flaaten, A., Nguyen, Q. P., Pope, G. A, & Zhang, J. (2008, January 1). A Systematic Laboratory Approach to Low-Cost, High-Performance Chemical Flooding. Society of Petroleum Engineers, doi: 10.2118 / 113469-MS o Flaaten, A, Nguyen, Q. P., Zhang, J., Mohammadi, H., & Pope, G. A. (2008, January 1). ASP Chemical Flooding Without the Need for Soft Water. Society of Petroleum Engineers, doi: 10.2118 / 116754-MS and in pages 3-4 of Flaaten, A., Nguyen, C. P., Zhang, J., Mohammadi, H., & Pope, G. A. (2008, January 1). ASP Chemical Flooding Without the Need for Soft Water. Society of Petroleum Engineers, doi: 10.2118 / 116754-MS.

[0147] The results of the phase behaviour tests showed that the optimum salinity for recovering the tested crude oil from Northwest of India (high content of paraffins) is 2.75 wt.% of Na2CO3.

[0148] Evaluation of the appearance of EOR composition at optimum salinity

[0149] EOR compositions are prepared comprising

[0150] • the surfactant formulations prepared in the respective examples (quantity of active surfactant in the EOR composition is 1500 ppm of TPS-(PO)35-(EO)i9-SO4NH4, 1056 ppm sodium salt of C10-32 alkyl benzene sulfonate; wherein 1500 ppm of the sulfate surfactant refers to the theoretical amount present if no desulfation had been occurred - real amount of the sulfate surfactant present depends on desulfation percentage),

[0151] • production water from an oil reservoir in Northwest of India (water, 0.45 wt.% NaCI, 0.01 wt.% KCI, 0.1 wt.% NaHCOs, 0.05 wt.% Na2SO4; production water was softened prior to use: Ca2+and Mg2+ions present is < 10 ppm) and

[0152] • 2.75 wt.% of Na2CO3.

[0153] The EOR compositions were heated to 65 °C to simulate reservoir conditions, and visually evaluated.

[0154] A clear and stable appearance indicates that EOR composition can be injected into the wellbore during oil recovery activities with high expectations of success.

[0155] A cloudy appearance indicates that if the EOR composition is injected into the wellbore, the surfactant solution might phase separate, and the suspended particles might be filtered off in the porous rock before it can interact with the oilbearing zones. This has the risk that the filtered-off material might plug the reservoir and cause strong increases of injection pressure or even unwanted cracks in the reservoir with unpredictable new flow directions. able 1 : Summary of experimental results of comparative and inventive examples. pH of mixture comprising sulfate and sulfonic acid obtained in step i). The residence time of the of sulfate / sulfonic acid mixture is calculated from the moment the sulfate and the sulfonic acid are mixed using mixing means until (but not including) neutralization of the ulfonic acid with the neutralizing agent. EOR composition: 1500 ppm* of TPS-(PO)35-(EO)i9-SC>4NH4, 1056 ppm sodium salt of C10-32 alkyl benzene sulfonate and brine comprising produced water from the oilwell (containing water, 0.45 t.% NaCI, 0.01 wt.% KCI, 0.1 wt.% NaHCOs, 0.05 wt.% IXfeSCU) and 2.00-3.25 wt.% of IXfeCOs as indicated in each experiment, ‘theoretical amount of sulfate surfactant present if no desulfation.The optimal salinity is the concentration of TDS in the injected EOR composition that provides the best oil displacement performance (i.e. highest oil recovery). In the present experiments, the optimal alinity for a crude oil from Northwest of India (rich in paraffin) and oilwell conditions: oil-water vol. ratio of 10:90 at 65°C, was calculated as 2.75 wt.% of TDS.

Claims

24078216Claims1 . A process for the preparation of a surfactant formulation comprising the steps of i) mixing a sulfate with a sulfonic acid using mixing means, ii) mixing the mixture obtained in step i) with a neutralizing agent using mixing means, wherein the neutralizing agent reacts with the sulfonic acid obtaining a sulfonate, and ill) obtaining the surfactant formulation comprising the sulfate and the sulfonate, wherein the pH of the mixture obtained in step I) is lower than 4, and the residence time of the sulfate / sulfonic acid mixture from the start of step I) until the start of step ii) is less than 90 seconds.

2. The process according to the previous claim, wherein the pH of the mixture obtained in step I) is lower than 3, preferably lower than 2.

3. The process according to any one of the previous claims, wherein the residence time of the sulfonic acid / sulfate mixture from the start of step I) until the start of step ii) is less than 60 seconds, preferably less than 45 seconds.

4. The process according to any one of the previous claims, wherein the mixing means are independently selected from stirring means, ultrasonic mixers, high shear mixers, static mixers, continuous stirred tank reactors (CSTR), mixing pumps and mixing nozzles. Preferably, the mixing means are static mixers.

5. The process according to any one of the previous claims, wherein the sulfate is a substituted or unsubstituted ether sulfate surfactant, preferably a styrenated phenol ether sulfate or an alkyl ether sulfate with 8 to 18 carbon atoms in the alkyl chain.

6. The process according to claim 5, wherein the ether sulfate comprises alkoxy groups selected from ethylenoxy, propylenoxy or a mixture thereof.

7. The process according to any one of the previous claims, wherein the sulfate is selected from tristyry Ipheny I-PO5- 4O-EOO-35S04'Y+, C16-18 alkyl-P05-4o-EOo-35S04'Y+, 2-ethy lhexy I-PO5-40- EO0-35S 04' Y+, and C14-15 al ky I-PO5-40- EOo ssSC ’ Y, wherein Y+is a monovalent cation.

8. The process according to any one of the previous claims, wherein the sulfate is selected from tristyry Ipheny I-PO20- 40-EOi5-25SO4'Y+, C16-18 alkyl -P05-IO-EOO-2S04'Y+, 2-ethy I hexy l-P015-25- E0o-5S04'Y+, and C14-15 alkyl-PO5.15-EO0.5SO4' Y+, wherein Y+is a monovalent cation.

9. The process according to any one of the previous claims, wherein the sulfonic acid is selected from alkyl aryl sulfonic acid, primary and secondary alkyl sulfonic acids, primary or secondary olefin sulfonic acids, alkyl ether24078217 sulfonic acids, alkyl toluene sulphonic acids, alkyl xylene sulfonic acids, dialkyl benzene sulfonic acids and fatty acid ester sulfonic acids.

10. The process according to any one of the previous claims, wherein the sulfonic acid is an alkyl aryl sulfonic acid, preferably an alkylbenzene sulfonic acid, more preferably an alkylbenzene sulphonic acid with an alkyl chain of CIO- 32, even more preferably an alkylbenzene sulphonic acid with an alkyl chain of C10-24.11 . The process according to any one of the previous claims, wherein the neutralizing agent is an aqueous solution comprising a base selected from the group consisting of NaOH, KOH, NH4OH, Na2CO3, NaHCOa, K2CO3, KHCO3, Na acetate, K acetate and NH4 acetate and an organic amine e. g. amino ethanol, diethanol amine, triethanol amine, N,N-dimethyl ethanol amine, iso propylamine, H2NCH2CH(CH3)OH, HN(CH2CH(CH3)OH)2, N(CH2CH(CH3)OH)3, Me2NCH2CH(CH3)OH, or triethyl amine.

12. A process for the preparation of an Enhanced Oil Recovery composition comprising the steps ofI) mixing a sulfate with a sulfonic acid using mixing means,II) mixing the mixture obtained in step I) with a neutralizing agent using mixing means, wherein the neutralizing agent reacts with the sulfonic acid obtaining a sulfonate, and ill) obtaining a surfactant formulation comprising the sulfate and the sulfonate, wherein the pH of the mixture obtained in step I) is lower than 4, and the residence time of the sulfate / sulfonic acid mixture from the start of step I) until the start of step II) is less than 90 seconds, and iv) diluting the surfactant formulation with water, wherein the EOR composition comprises 500 to 10 000 ppm of total active surfactant.

13. The process according to claim 12, wherein in step iv) salts are added, preferably Na2CC>3 are added, more preferably 2.75 to 3.00 wt.% of Na2CC>3, based on the total weight of the Enhanced Oil Recovery composition, are added.

14. The process according to any one of claims 12 to 13, wherein the water in step in iv) is produced water from an oil reservoir, preferably produced water from an oil reservoir comprising which < 10 ppm of Ca2+and Mg2+ions.

15. The process according to any one of claims 12 to 14, wherein the Enhanced Oil Recovery composition comprises 500 to 5000 ppm of total active surfactant.

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