CN109425686B - Method for detecting cationic degree of synthetic polymer for drilling fluid - Google Patents
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Abstract
The application provides a method for detecting the cationic degree of a synthetic polymer for drilling fluid, which comprises the following steps: purifying a cationic polymer sample by using an ethanol solution, and then dissolving the purified sample by using a sodium chloride aqueous solution to obtain a sample aqueous solution; controlling the apparent viscosity of 1wt% of the sample aqueous solution to be less than or equal to 10mPa & s; detecting the total content of quaternary ammonium salt cations and potassium ions by adopting a sodium tetraphenylborate back titration method; and detecting the content of the potassium ions by adopting an ashing method, and calculating the difference value between the total content of the quaternary ammonium salt cations and the potassium ions and the content of the potassium ions to obtain the actually measured cation degree. Aiming at the defects of low cationic degree determination accuracy or difficult determination caused by external interference and polymer molecular structure influence in the tetraphenylboron sodium method in the prior art, the method for determining the cationic degree of the synthetic polymer is improved, and the improved method has higher accuracy and applicability.
Description
Technical Field
The invention relates to the technical field of analytical chemistry, in particular to a method for detecting the cationic degree of a synthetic polymer for drilling fluid.
Background
Compared with an anionic drilling fluid treating agent, the drilling fluid treating agent containing a cationic group (such as quaternary ammonium salt) has remarkable advantages in the aspects of inhibiting shale hydration, stabilizing a well wall, protecting an oil-gas layer, improving the drilling speed, reducing the energy consumption and the comprehensive drilling cost and the like, and becomes one of the research focuses of oilfield chemists. In order to synthesize the cationic polymer treating agent, some cationic monomers which are easily copolymerized with acrylic acid and acrylamide, such as 3-acrylamido n-propyl dimethyl ammonium chloride, 2-acrylamido ethyl dimethyl ammonium chloride, trimethyl allyl ammonium chloride, etc., have been developed.
The cationic degree generally refers to the mass fraction of cationic groups in the total substances, and is a characteristic index and a key index for directly characterizing the cationic treating agent, and the high cationic degree is also the root cause of strong inhibition and collapse prevention. The cationic polymer has different molecular structures due to different molecular weights, cationic group types and anionic-cationic group ratios, so that the cationic degree of the polymer is higher in difference. At present, the domestic detection method for the cation content or the cation degree of organic chemical products is mainly developed around a chemical analysis method.
Manufacturers of cationic chemical products often incorporate corresponding external impurities, mainly inorganic potassium ions (K in KCl), according to different methods for detecting cationic degree+) Ammonium ion (NH)4NH in Cl4 +) Or water-soluble chloride ions, and small cationic monomers remaining in the synthesis process. Therefore, although chemical analysis methods have the characteristics of strong operability and low requirements on laboratory equipment, the current situation causes the limitations of each chemical analysis method, such as more interference factors or difficult elimination of interferents.
In the literature, "study of quaternary ammonium salt determination by sodium tetraphenylboron back titration" (journal of the university of western's safety petroleum (natural science), 2009, 7.24, vol.4: 62-64, plum-shaped tablets, etc.), it is introduced that the sodium tetraphenylboron method is one of the most effective and extensive methods for detecting the cationic degree of quaternary ammonium salt, and the determination principle is as follows: reacting sodium tetraphenylborate with quaternary ammonium salt to be detected in an alkaline medium to form white precipitate, titrating excessive sodium tetraphenylborate with hexadecyl trimethyl ammonium bromide, forming pink substance by the hexadecyl trimethyl ammonium bromide and the dadanhuang at the end point, and calculating the mass fraction of the quaternary ammonium salt according to the titration result.
FIG. 1 is a schematic flow chart of a conventional cationicity measuring method, in which a polymer is dissolved by pure water, the contents of cations and potassium ions in a quaternary ammonium salt are measured, the content of potassium ions is measured, and the difference is calculated to obtain the cationicity. However, this method is susceptible to external interference such as inorganic potassium ions and ammonium ions and the molecular structure itself (mainly comprising anionic sulfonic acid groups and carboxylic acid groups), resulting in low accuracy of the cationicity measurement result.
Disclosure of Invention
In view of this, the present application provides a method for detecting cationicity of a synthetic polymer for a drilling fluid, and the detection method provided by the present invention has higher accuracy.
The invention provides a method for detecting the cationic degree of a synthetic polymer for drilling fluid, which comprises the following steps:
purifying a cationic polymer sample by using an ethanol solution, and then dissolving the purified sample by using a sodium chloride aqueous solution to obtain a sample aqueous solution; controlling the apparent viscosity of 1wt% of the sample aqueous solution to be less than or equal to 10mPa & s at 25 +/-3 ℃;
detecting the sample aqueous solution with the apparent viscosity of less than or equal to 10mPa & s by adopting a sodium tetraphenylborate back titration method to obtain the total content of quaternary ammonium salt cations and potassium ions; and detecting the content of the potassium ions by adopting an ashing method, and calculating the difference value between the total content of the quaternary ammonium salt cations and the potassium ions and the content of the potassium ions to obtain the actually measured cation degree.
The invention provides an improved method for measuring the cationic degree of a synthetic polymer on the basis of the conventional sodium tetraphenylboron method shown in figure 1, aiming at the defects of low cationic degree measurement accuracy or difficult measurement caused by external interference and polymer molecular structure in the sodium tetraphenylboron method in the prior art, and the improved method has higher accuracy and applicability.
Referring to fig. 2, fig. 2 is a schematic flow chart of a cationicity detecting method according to an embodiment of the present invention. The method comprises the operation steps of sample alcohol washing purification, brine dissolution, thermal oxygen degradation, detection of total amount of quaternary ammonium salt cations and potassium ions, determination of potassium ion content, correction factor correction and the like, and mainly comprises the method of eliminating ion interference-correction factor correction, so that the accuracy of cation degree determination is improved.
In the embodiment of the invention, the cationic polymer sample is purified by using ethanol solution to remove small particlesMolecular ammonium ions and other water-soluble impurities to obtain a purified sample. Wherein the cationic polymer is generally used as a drilling fluid treatment agent and has a structure with quaternary ammonium salt cations and different types and contents of anionic groups such as sulfonic acid groups (-SO)3 2-) Carboxyl (-COO)-). The cationic polymer of the present invention includes, but is not limited to, acrylamido propyl trimethyl ammonium chloride-acrylamide (AMPTA-AM) binary cationic polymer, dimethyl diallyl trimethyl ammonium chloride-acrylamide (DMD-AM) binary copolymer, acrylamido propyl trimethyl ammonium chloride-acrylamide-2-methylpropanesulfonic acid (AMPTA-AM-AMPS) terpolymer, acrylamido propyl trimethyl ammonium chloride-acrylamide-2-methylpropanesulfonic acid-acrylic acid (AMPTA-AM-AMPS-AA) tetrapolymer.
Specific improvements of the invention include: according to the molecular weight of the synthetic polymer, a polymer sample to be detected can be generally washed by adopting an ethanol water solution with the concentration of 90-95 percent, and residual cationic monomers, inorganic ammonium salts and other water-soluble impurities contained in the polymer sample are removed, so that the interference of external substances is eliminated. That is, in the present invention, it is preferable that the cationic polymer sample is washed and purified with an ethanol solution having a volume concentration of 90% to 95%. In some embodiments of the invention, if the apparent viscosity of a 1wt% aqueous solution of the polymer at 25 ℃ ± 3 ℃ is greater than 10mPa · s, purification is performed using a 90% ethanol solution; in other embodiments of the invention, a 1wt% aqueous solution of the polymer having an apparent viscosity of 10 mPas or less at 25 ℃. + -. 3 ℃ is purified using a 95% ethanol solution.
After the sample is purified by alcohol elution, the purified sample is fully dissolved by using a sodium chloride aqueous solution in the embodiment of the invention, and a sample aqueous solution is obtained. The existing sodium tetraphenylborate method usually adopts pure water to dissolve a polymer, and the method adopts the steps of adding a proper amount of inorganic salt (sodium chloride NaCl) into water to dissolve the polymer, and utilizing a homoionic effect and the flocculation of the inorganic salt, wherein a certain amount of inorganic salt in a solvent carries out charge shielding on anionic groups on polymer molecular chains, and the repulsion of the anionic groups on tetraphenylborate ions is removed or weakened, so that the sodium tetraphenylborate determination method is corrected.
In the embodiment of the invention, the molar content of sulfonic acid groups in the cationic polymer is 0-25%, the molar content of carboxyl groups in the cationic polymer is 0-70%, and a purified sample is dissolved by using a sodium chloride aqueous solution with the mass fraction of more than 0 and less than 10%. Wherein the mass fraction of the sodium chloride aqueous solution is preferably 5 to 8 percent. In addition, the present invention is not particularly limited to other conditions for the dissolution of brine.
Since the high molecular polymer, when dissolved in water, exhibits a random coil, the coil curls and contains many cationic units within the coil. In the conventional determination method, when the cation synthetic polymer meets a precipitator of sodium tetraphenylborate, a large number of polymer cation units are wrapped and precipitated together with the precipitate, and the wrapped cation units cannot perform sufficient precipitation reaction with the sodium tetraphenylborate, so that the determination result is low. However, the invention adopts chemical means such as thermal oxidative degradation and the like to reduce the molecular weight of the polymer, so that the polymer and sodium tetraphenylborate can generate complete precipitation reaction in a small molecular state, and the cationic degree of the polymer is measured after degradation treatment, thereby improving the accuracy of the result.
Therefore, in some embodiments of the present invention, the purified aqueous sample solution has an apparent viscosity of > 10mPa · s at 25 ± 3 ℃, and the sample can be subjected to thermo-oxidative degradation with an oxidizing agent while stirring, and after sufficient degradation, the sample solution is cooled to room temperature to obtain an aqueous sample solution with an apparent viscosity of < 10mPa · s. The oxidant used for the sample thermal oxidative degradation can be hydrogen peroxide, ozone, peracetic acid or sodium hypochlorite, and preferably hydrogen peroxide (hydrogen peroxide, H)2O2). In a preferred embodiment of the invention, the oxidant is hydrogen peroxide with a mass concentration of 30-40%, and the addition amount is 0.25-2 mL. Preferably, the sample thermal oxygen degradation process specifically comprises: and adding hydrochloric acid and hydrogen peroxide into the purified sample aqueous solution, heating to 85-90 ℃, and keeping the temperature for 10-15 min to obtain the sample aqueous solution with the apparent viscosity of less than or equal to 10mPa & s. In other embodiments of the invention, the sample has an apparent viscosity of 10 mPas or less in a 1wt% aqueous solution without degradation treatment.
After controlling the apparent viscosity of 1wt% of the sample aqueous solution to be less than or equal to 10 mPa.s at 25 +/-3 ℃, the invention is implementedFor example, the total content of quaternary ammonium salt cations and potassium ions is determined by sodium tetraphenylborate back titration; the potassium ion content was measured by ashing, and from this, the measured cationic degree A of the synthesized cationic polymer was calculatedFruit of Chinese wolfberry. The specific calculation formula is shown in the following formula (1):
in formula (1):
Afruit of Chinese wolfberry-the measured cationicity of the synthetic polymer is in millimoles per gram (mmol/g);
c1the molar concentration of the sodium tetraphenylborate standard solution is expressed in mol per liter (mol/L);
c2-cetyl trimethylammonium bromide standard solution molar concentration in moles per liter (mol/L);
V1-measuring the volume of the standard solution of sodium tetraphenylborate in milliliters (mL) removed when the total amount is measured;
V2-the volume of the sodium tetraphenylboron filtrate removed after the precipitation is filtered in milliliters (mL) when the total amount is determined;
V3-the volume of the standard solution of cetyltrimethylammonium bromide in milliliters (mL) used in determining the total amount;
V4the volume of the standard solution of sodium tetraphenylborate transferred when the content of potassium ions is measured is milliliter (mL);
V5-the volume of the sodium tetraphenylborate filtrate removed after filtration precipitation in milliliters (mL) when determining the potassium ion content;
V6-the volume of the standard solution of cetyltrimethylammonium bromide in milliliters (mL) used in the determination of the potassium ion content;
m1-the mass of the purified sample, in grams (g), is weighed when determining the total amount;
m2-the mass of the purified sample, in grams (g), is weighed when determining the potassium ion content.
The present invention is not particularly limited to the specific operations of the sodium tetraphenylborate back titration method and the ashing method, and may be carried out according to the technical contents known to those skilled in the art. And (3) respectively obtaining the total content of the quaternary ammonium salt cations and the potassium ions and the content of the potassium ions according to the formula (1), and calculating the difference value of the total content of the quaternary ammonium salt cations and the potassium ions to obtain the actually measured cationic degree.
Compared with the prior art, the invention has the following advantages: (1) by means of a purification mode, interference of inorganic potassium ions, ammonium ions and residual small cationic monomers on the determination of the sodium tetraphenylborate method is removed, and accuracy of determination results is improved. (2) The method is characterized in that a certain amount of chemical treatment agent (salt) is adopted to carry out charge shielding on anionic groups in a polymer molecular structure, and the rejection of the anionic groups to tetraphenylborate ions is removed or weakened to generate larger measurement deviation, namely, a proper amount of inorganic salt (NaCl) is added into water to dissolve a polymer, and the measurement method of sodium tetraphenylborate is corrected by utilizing the homoionic effect and the flocculation of the inorganic salt. (3) The long molecular chain of the synthetic polymer is broken into small molecular units by chemical means such as thermal-oxidative degradation and the like, the molecular weight is reduced, not only is the cationic unit (quaternary ammonium salt group) in the molecular structure and the precipitator sodium tetraphenylborate fully subjected to precipitation reaction, but also the low determination result is avoided; and the ion pair repulsion action of the anion groups on each structural unit on the tetraphenyl borate after degradation can be greatly weakened, so that the determination deviation of the cationic degree is reduced, and the accuracy of the determination result is improved.
In addition, the conventional sodium tetraphenylboron method uses the measured cationic degree as the final result. In fact, the cationic degree cannot be truly reflected by the measurement result because a large number of anionic groups in the polymer can repel the tetraphenylborate. The method further comprises the steps of measuring the content change of the cationic monomer before and after the polymerization reaction to calculate the theoretical value of the cation of the polymer, and verifying the accuracy and reliability of the theoretical value of the cationic degree by an element analysis method. The invention also includes: the measured value of the cationic degree is compared with a theoretical value to calculate the measurement deviation of the cationic degree, the influence of the types and the quantity of different anionic groups in the molecular structure of the polymer on the measurement of the cationic degree is investigated, a correction factor template is creatively proposed and established by utilizing mathematical Datafit software and MATLAB software and using an index coordinate axis, the measured value of the cationic degree is corrected, and the accuracy of the measured result of the cationic degree is greatly improved.
In the examples of the invention, the molar content of anionic groups in the polymer is in different ranges, corresponding to different cationicity correction factors. The embodiment of the invention examines the indoor synthetic cationic polymer-SO3 2-The molar content of the groups is 0-25% (considering the control of product cost), -COO-When the molar content of the groups is 0-70%, 8% of NaCl aqueous solution in percentage by mass is adopted to dissolve the polymers, and the cationic degree of the polymers with different anionic contents is measured, so that the corresponding cationic degree measurement deviation and correction factor are calculated. The results are shown in Table 1:
TABLE 1 relationship between different anion contents and polymer cationicity correction factor
Table 2 reflects the case where the correction factor is zero within a range of partial anion content. In order to simply and visually search the rest of the correction factors which are not zero, the test data in the attached table 1 are processed by utilizing mathematical data software. Using the correction factor as-SO3 2-Molar content of radicals and-COO-And fitting a function of the molar content of the groups to obtain a multivariate nonlinear equation, and preferably selecting an equation with good correlation coefficient and relatively simple expression as a fitting equation from a nearly 300-group equation provided by software.
By using a fitting equation and MATLAB software, correction factor graphs under different conditions are drawn by using an exponential coordinate axis, referring to FIGS. 3 and 4, FIG. 3 is a cationicity correction factor graph with the molar content of polymer sulfonic acid groups of 16% -21% in the embodiment of the present invention, and FIG. 4 is a cationicity correction factor graph with the molar content of polymer sulfonic acid groups of 22% -25% in the embodiment of the present invention. In fig. 3 and 4, the molar sulfonic acid group contents represented by the respective curves are: 1-16%, 2-17%, 3-18%, 4-19%, 5-20%, 6-21%, 7-22%, 8-23%, 9-24%, 10-25%.
TABLE 2 relationship between molar content of different anions in the polymer and cationicity correction factor
| Sulfonic acid group molar content/%) | Molar content of carboxyl groups/%) | Correction factor t |
| <15 | <70 | 0 |
| 16～18 | <30 | 0 |
| 19～21 | <20 | 0 |
| 22～23 | <15 | 0 |
| 24～25 | <7 | 0 |
Wherein, a method for measuring the content of the sulfonic acid group is provided according to SY/T5242-1991: after the purified sample solution passes through a cation exchange resin column, sodium carbonate groups are completely converted into sulfonic acid groups, and then sodium hydroxide standard solution is used for titration. And according to the change of the conductivity, determining the volume of the sodium hydroxide standard solution consumed when the conductivity is the lowest value, and calculating to obtain the content of the sulfonic acid group.
The procedure for determination of the degree of hydrolysis in GB/T13940 provides a method for carboxylic acid group content: adopting hydrochloric acid standard solution for titration, and selecting methyl orange-indigo disulfonic acid sodium as an indicator. And calculating the hydrolysis degree of the sample according to the volume of the consumed hydrochloric acid standard solution, thereby obtaining the carboxyl content in the molecular structure of the sample. Therefore, the embodiment of the invention determines the kind and content of the anionic group in the polymer sample structure, and determines the cationic degree correction factor t according to the cationic degree correction factor chart (see the attached fig. 3 and 4, tables 1 and 2) summarized by the above experiment.
In the examples of the present invention, the true cationicity value A isTrueComprises the following steps: actually measured cationic degree AFruit of Chinese wolfberryX (1+ correction factor t), see formula (2):
Atrue＝AFruit of Chinese wolfberry(1+ t) formula (2);
in formula (2):
Afruit of Chinese wolfberry-the measured cationicity of the synthetic polymer is in millimoles per gram (mmol/g);
t-correction factor for cationicity of the synthetic polymer; t is more than or equal to 0 and less than 1.
According to the embodiment of the invention, the theoretical value of the cation of the polymer can be calculated by measuring the content change of the cationic monomer before and after the polymerization reaction, the cationic degree measurement deviation is calculated by comparing the cationic degree measurement value obtained by the improved sodium tetraphenylborate method with the theoretical value, the influence of the types and the number of different anionic groups in the molecular structure of the polymer on the cationic degree measurement is investigated, a correction factor template is initially proposed and established by utilizing mathematical Datafit software and MATLAB software and using an index coordinate axis, and the measured value of the cationic degree is corrected, so that the accuracy of the cationic degree measurement result is greatly improved.
Drawings
FIG. 1 is a schematic flow chart of a conventional cationicity measuring method;
FIG. 2 is a schematic flow chart of a cationicity detecting method according to an embodiment of the present invention;
FIG. 3 is a cationicity correction factor graph of 16-21% molar sulfonic acid group content in the polymer of the embodiment of the present invention;
FIG. 4 is a cationicity correction factor graph of a polymer having a sulfonic acid group molar content of 22% to 25% in an example of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
For further understanding of the present application, the following examples are provided to specifically describe the method for detecting the cationicity of the synthetic polymer for drilling fluid.
The test samples in the examples are room synthetic polymers of known theoretical values of cationicity due to the introduction of a correction factor by the method of the invention.
Example 1
(1) Weighing 1.00g of an acrylamido propyl trimethyl ammonium chloride-acrylamide (AMPTA-AM) binary cationic polymer sample, soaking for 2h in 100mL of 90% ethanol solution, washing to remove small molecular ammonium ions and other water-soluble impurities, filtering with a layer of medium-speed qualitative filter paper, washing the sample on the surface of the filter paper for three times by using 30mL of 90% ethanol, removing residual impurities on the surface of the sample, drying for 2h at 105 +/-3 ℃, and cooling to room temperature for later use.
(2) Weighing the purified sample m10.2000g (to the nearest 0.0001g) was added with 8.0g of sodium chloride and distilled water to dissolve sufficiently.
Adding 1mL of hydrogen peroxide and 2-3 drops of diluted hydrochloric acid (volume ratio is 1:1), heating at 80 ℃ for 10min, cooling to room temperature after full degradation, adjusting by using acetic acid-sodium acetate buffer solution with pH value of 3.6, controlling the pH value to 3.0-4.0,then accurately transferring excessive sodium tetraphenylborate standard solution V1The resulting solution was precipitated into 25mL, and the volume was determined in a 100mL volumetric flask. Standing at room temperature for 30min, filtering the precipitate with double-layer quantitative slow-speed filter paper, and accurately transferring filtrate V with a certain volume2Adjusting the pH value to 7.0-8.0 with a sodium hydroxide solution (25 mL), adding a bromophenol blue indicator, titrating with a cetyl trimethyl ammonium bromide standard solution, and obtaining a titration end point when the solution changes from blue purple to light blue. According to the consumption V of a hexadecyl trimethyl ammonium bromide standard solution3And calculating the total content of the quaternary ammonium salt cations and the potassium ions in the sample.
(3) Weighing mass m2After 0.2g (accurate to 0.0001g) of purified acrylamide propyl trimethyl ammonium chloride-acrylamide (AMPTA-AM) binary cationic polymer sample is incinerated at the high temperature of 800 ℃, 2mL of 2mol/L hydrochloric acid solution is used for dissolving ash, and then excessive Sodium Tetraphenylborate (STPB) standard solution V is accurately transferred into the sample4The resulting solution was precipitated into 25mL, and the volume was determined in a 100mL volumetric flask. Standing at room temperature for 30min, filtering the precipitate with double-layer quantitative slow-speed filter paper to obtain clear filtrate containing excessive sodium tetraphenylborate, and accurately transferring filtrate V with a certain volume5Adjusting the pH value to 7.0-8.0 with a sodium hydroxide solution (25 mL), adding a bromophenol blue indicator, titrating with a cetyl trimethyl ammonium bromide standard solution, and obtaining a titration end point when the solution changes from blue purple to light blue. According to the consumption V of a hexadecyl trimethyl ammonium bromide standard solution6And calculating the content of potassium ions in the sample.
(4) The difference between the two is the actually measured cationic degree A of the acrylamide propyl trimethyl ammonium chloride-acrylamide (AMPTA-AM) binary cationic polymerFruit of Chinese wolfberryThe calculation formula is as follows:
wherein, C1＝0.02293mol/L；C2＝0.005994mol/L；V1＝V4＝25mL；V2＝V5＝25mL；V3＝16.1mL；m1＝0.2g，m2＝0.2g。
Since the indoor synthetic polymer has no potassium ion interference and the binary copolymer has no measurement deviation caused by anionic groups, the correction factor t is 0, and the cationic degree A is measuredFruit of Chinese wolfberryThe calculation process of (2) is as follows:
examples 2 to 4
The test sample in example 1 was changed to a copolymer of different cationic monomers and a terpolymer and a tetrapolymer containing anionic groups, and other test conditions were controlled to be unchanged, and the test results are shown in table 3 below.
According to the test method, a series of theoretical cationic degrees and actual cationic degrees of polymers with different anionic group contents synthesized in a laboratory are compared, and a query chart of correction factors of the cationic degrees is summarized through data analysis.
TABLE 3 cationicity measurement results of different cationic polymers
Note: DMD-AM is a binary copolymer of dimethyl diallyl trimethyl ammonium chloride and acrylamide; AMPTA-AM-AMPS is acrylamide propyl trimethyl ammonium chloride-acrylamide-2-methyl propane sulfonic acid terpolymer; AMPTA-AM-AMPS-AA is acrylamide propyl trimethyl ammonium chloride-acrylamide-2-methyl propane sulfonic acid-acrylic acid quadripolymer.
Comparative example 1
The comparative example is a method for measuring the cationic degree of the terpolymer AMPTA-AM-AS (the sulfonic acid group molar content is 30 percent, and the AS is sodium propylene sulfonate) by a silver method, and the specific operation steps are AS follows:
0.2g of the purified sample (accurate to 0.0001g) is weighed and placed in a dry clean beaker. 50mL of distilled water was added and sufficiently dissolved with stirring. 1mL of 30% hydrogen peroxide and 2-3 drops of dilute nitric acid (1:1) are added, the mixture is heated at 70-80 ℃ for 10min, the mixture is cooled to room temperature after being fully degraded, the pH value is adjusted to be neutral or alkalescent by using a sodium hydroxide solution, the solution is diluted to be 100mL in constant volume, 25mL of the solution is accurately transferred, 8-10 drops of 50g/L potassium chromate solution are added, under full shaking, the silver nitrate standard solution is used for titration, the solution is changed from bright yellow to brick red just appearing, namely the end point, and meanwhile, a blank test is carried out. The cationicity is calculated as follows:
in formula (4):
Afruit of Chinese wolfberry-measured cationicity of the synthetic polymer in millimoles per gram (mmol/g);
M(Cl-)——Cl-in millimoles per gram (mmol/g);
m is the weight of the sample, and the unit is gram (g);
c, concentration of silver nitrate standard solution, wherein the unit is moL per liter (moL/L);
V1-consuming the volume of silver nitrate standard solution in milliliters (mL);
V0blank test consumes the volume of silver nitrate standard solution in milliliters (mL).
Comparative example 2
The comparative example is a method for measuring the cationic degree of the terpolymer AMPTA-AM-AS (30 percent of sulfonic acid group molar content) by a colloid titration method, and the specific operation steps are AS follows:
accurately weighing 0.01g (weighed to 0.0001g) of purified cationic polymer, adding 50mL of distilled water to dissolve for 4h, washing with 50mL of distilled water, transferring to a 250mL conical flask, adjusting the pH value to 3.0 by using 0.5mol/L hydrochloric acid solution, dropwise adding 2-3 drops of TBO indicator, titrating with 0.0025mol/L polyvinyl potassium sulfate (PVSK) solution (the titration speed is 2mL/min), and obtaining the end point when the color of the solution is changed from blue to deep purple and is kept for 10 seconds; the volume of the titration solution consumed was recorded and a blank run was made.
The measured cationic degree is calculated according to the following formula:
in formula (5):
Afruit of Chinese wolfberry-measured cationicity of the synthetic polymer in millimoles per gram (mmol/g);
C-PVSK standard solution concentration, unit is moL per liter (moL/L);
V1-the volume of PVSK standard solution consumed by titration of the sample in milliliters (mL);
V2titration of the volume of PVSK standard solution consumed by the blank in milliliters (mL).
m is the mass of the purified sample in grams (g).
Comparative example 3
The comparative example is a phosphotungstic acid method for determining the cationic degree of the terpolymer AMPTA-AM-AS (sulfonic acid group molar content is 30 percent), and the specific operation steps are AS follows:
0.2g (to the nearest 0.0001g) of the purified sample is weighed and placed in a dry clean beaker. 50mL of distilled water was added and stirred to dissolve completely. 1mL of 30% hydrogen peroxide and 2-3 drops of diluted hydrochloric acid (1:1) are added, heated at 80 ℃ for 10min, cooled to room temperature after sufficient degradation, transferred to a 250mL conical flask, and rinsed with 50mL of distilled water 2-3 times, and the rinse is poured into the conical flask. Regulating the pH value to 3-4 by using a 5mol/L hydrochloric acid solution, dropwise adding 6-8 drops of Congo red indicator, titrating by using a phosphotungstic acid standard solution, and after generating a precipitate (no precipitate is generated, which indicates that a sample has no cation), slowly titrating until the red color completely disappears and the solution is pure blue as an end point. The measured cationic degree is calculated according to the following formula:
in formula (6):
Afruit of Chinese wolfberry-measured cationicity of the synthetic polymer in millimoles per gram (mmol/g);
c-phosphotungstic acid molar concentration, unit is mol per liter (mol/L);
v-volume of phosphotungstic acid consumed in milliliters (mL);
m is the mass of the purified sample in grams (g).
The sodium tetraphenylborate process modified in this application was compared with comparative examples 1, 2 and 3 for the measured cationicity value and the measurement deviation of the terpolymer. From the results of Table 4, it is shown that, for the terpolymer, the cationicity measurement deviation of the silver amount method used in comparative example 1, the colloid titration method used in comparative example 2, and the phosphotungstic acid method used in comparative example 3 are higher than the measurement deviation of the modified sodium tetraphenylborate method of the present application. Therefore, the improved sodium tetraphenylborate method has higher accuracy than other methods.
TABLE 4 comparison of several cationization methods
Note: in all of the four measurement methods, the polymer was dissolved sufficiently with pure water.
Example 5 Effect of molecular Structure on cationic degree determination
The zwitterionic polymer contains a certain amount of anionic-SO3 2-A radical and-COO-When the radical is used, the sodium tetraphenylborate determination method has larger deviation along with the increase of the molar content of the anionic radical in the polymer, when the polymer is in a state of-SO3 2-The molar content of the groups is 20%, -COO-At a molar group content of 20%, the sodium tetraphenylboron method has a measurement deviation of up to 93%, from which it is clear that the sodium tetraphenylboron method has exhibited a large inadaptability. Is composed ofIn the method, a certain amount of chemical treatment agent (salt) is adopted to carry out charge shielding on anionic groups and remove or weaken the rejection of the anionic groups to tetraphenylborate ions, namely, a proper amount of inorganic salt (NaCl) is added into water to dissolve a polymer, and the sodium tetraphenylborate determination method is corrected by utilizing the homoionic effect and the flocculation of the inorganic salt, so that the determination deviation is greatly reduced. The comparative results are shown in Table 5 below:
TABLE 5 Effect of different NaCl additions on the cationic degree determination of the tetrapolymer
As can be seen from the data in Table 5 above, the cationicity deviation (correction factor) measured with the saline-soluble polymer showed a significantly decreasing trend with increasing inorganic salt addition, even in the case of polymer-SO3 2-The group molar content (5%) is low, when the addition of the inorganic salt NaCl is 10%, the positive deviation of the measurement appears, and the positive deviation is derived from the impurity K contained in the analytical grade NaCl+When the amount of NaCl added as inorganic salt is selected, the polymer-SO3 2-The molar content of radicals is preferably low, SO that no positive deviations of the cationicity measurements occur, when the polymer-SO3 2-At higher molar contents of the groups, the better the measurement deviation of the cationicity is, so that the recommended concentration of the inorganic salt NaCl is 8%.
EXAMPLE 6 Effect of molecular weight on cationicity determination
Aiming at the AMPTA-AM binary cationic polymer, a nonthermal oxidative degradation mode and a hydrogen peroxide thermal oxidative degradation mode with different addition are respectively adopted, the molecular weight of the polymer is continuously reduced, other test conditions are controlled to be the same, and the cationic degree is measured. The results are given in the table below.
TABLE 6 comparison of measured cationic degree values under degradation conditions
As can be seen from the above table, in a certain range, with the increase of the addition of the hydrogen peroxide, the apparent viscosity of the polymer solution tends to be stable after being reduced, and the measured value of the cationic degree of the polymer tends to be stable after being increased. When H is present2O2When the addition amount is 0mL, the molecular chain of the polymer is in a random coil curl, a plurality of cation units are contained in the polymer and wrapped and precipitated along with the precipitation, and the full precipitation reaction is not generated, so that the measurement result is low. When H is present2O2When the adding amount is 1.0mL, the apparent viscosity of the polymer solution is basically reduced to the lowest value, the measured value of the cationicity of the polymer is the largest, the polymer is completely degraded at the moment, the measured result of the cationicity of the polymer basically tends to be stable, and the measured deviation is less than 5 percent compared with the theoretical value of the cationicity. Therefore, the molecular mass of the polymer is reduced by adopting a chemical means of thermal oxygen degradation, and the accuracy of determining the cationic degree of the polymer is effectively improved.
Example 7 elemental analysis method for verifying cationicity theoretical value
Aiming at four cationic polymer samples synthesized in a laboratory, the cationic degree value of the sample is obtained by an element analysis test method, so that the cationic degree value is compared with the cationic degree theoretical value of a feeding calculation method, the measured values of the cationic degree value and the cationic degree theoretical value are basically consistent, and the calculation method of the cationic degree theoretical value of the polymer is accurate and reliable. The alignment results are as follows:
TABLE 7 comparison of experimental results of the feed calculation method and the elemental analysis method
Example 8 accuracy verification test
During chemical analysis, the accuracy of the measurement is measured by the recovery of the added standard of the measurement sample. The formula for the recovery of spiked is as follows: the recovery on the standard is (standard sample measurement value-sample measurement value) ÷ standard amount × 100%, and the test results are shown in the following table.
TABLE 8 recovery of cationic degree of synthetic polymers using normalized
As can be seen from Table 8, when the terpolymers AMPTA-AM-AA (AA molar content 30%) and AMPTA-AM-AS (AS molar content 10%) were used AS the study objects and cetyltrimethylammonium bromide QAS was added, the normalized recovery rates reached 92% and 94.4%, respectively, and reached the normalized recovery rate index range of 90% -110% required by the analytical test.
In summary, the technical scheme of the invention has the following advantages: the method firstly carries out alcohol elution purification on the synthetic cationic polymer for the drilling fluid, eliminates external interference factors, adopts saline solution and hydrogen peroxide thermal oxidation degradation means, creatively proposes and establishes a correction factor template, ensures that the sodium tetraphenylborate back titration method has higher accuracy, wide applicability and stronger operability, and can be popularized and applied in a conventional detection laboratory.
The above description is only a preferred embodiment of the present invention, and it should be noted that various modifications to these embodiments can be implemented by those skilled in the art without departing from the technical principle of the present invention, and these modifications should be construed as the scope of the present invention.
Claims (6)
1. A method for detecting the cationicity of a synthetic polymer for a drilling fluid comprises the following steps:
purifying a cationic polymer sample by using an ethanol solution, wherein the molar content of sulfonic acid groups in the cationic polymer is 0-25%, the molar content of carboxyl groups in the cationic polymer is 0-70%, and the purified sample is dissolved by using a sodium chloride aqueous solution with the mass fraction of more than 0 and less than 10% to obtain a sample aqueous solution; carrying out thermal oxidative degradation on a sample by using an oxidant, and controlling the apparent viscosity of a 1wt% sample water solution to be less than or equal to 10mPa & s at 25 +/-3 ℃;
detecting the sample aqueous solution with the apparent viscosity of less than or equal to 10mPa & s by adopting a sodium tetraphenylborate back titration method to obtain the total content of quaternary ammonium salt cations and potassium ions; detecting the content of the obtained potassium ions by adopting an ashing method, and calculating the difference value between the total content of the quaternary ammonium salt cations and the potassium ions and the content of the potassium ions to obtain the actually measured cationic degree;
comparing the actually measured cationic degree with a theoretical value for calculation to obtain cationic degree measurement deviation; according to the relation between the cationic degree determination deviation and the contents of different anionic groups in the cationic polymer, establishing a correction factor template by utilizing mathematical Datafit software and MATLAB software and using an index coordinate axis through fitting a multivariate nonlinear equation, and correcting the actually measured cationic degree to obtain a cationic degree true value;
true value of the cationicity ATrue= measured cationicity AFruit of Chinese wolfberryX (1+ correction factor t), t is more than or equal to 0 and less than 1.
2. The detection method according to claim 1, wherein the cationic polymer sample is washed and purified by an ethanol solution with a concentration of 90-95%.
3. The detection method according to any one of claims 1 to 2, wherein the apparent viscosity of the purified sample aqueous solution at 25 ± 3 ℃ is greater than 10 mPa-s, and the sample is subjected to thermal oxidative degradation by using an oxidizing agent, and the apparent viscosity of 1wt% of the sample aqueous solution at 25 ± 3 ℃ is less than or equal to 10 mPa-s.
4. The detection method according to claim 3, wherein the oxidizing agent for the thermo-oxidative degradation of the sample is hydrogen peroxide, ozone, peracetic acid, or sodium hypochlorite.
5. The detection method according to claim 4, wherein the oxidant is hydrogen peroxide with a mass concentration of 30-40%, and the addition amount is 0.25-2 mL.
6. The detection method according to claim 5, wherein the sample thermo-oxidative degradation process is specifically as follows: adding hydrochloric acid and hydrogen peroxide into the purified sample aqueous solution, heating to 85-90 ℃, keeping the temperature for 10-15 min, and controlling the apparent viscosity of 1wt% of the sample aqueous solution to be less than or equal to 10mPa & s at 25 +/-3 ℃.
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