ELECTROCHEMICAL METHOD AND SYSTEM FOR THE INDIRECT MONITORING OF SCALE INHIBITORS IN ONSHORE AND OFFSHORE INSTALLATIONS

Abstract

The present disclosure refers to an electrochemical method for the indirect monitoring of the concentration of the active matter of scale inhibitors, composed of phosphonates, based on principles of advanced oxidative processes, which is viable for quality control of scale inhibitors in onshore and offshore installations. Additionally, the present disclosure refers to an electrochemical system for the indirect monitoring of the concentration of the active matter of scale inhibitors in onshore and offshore installations.

Claims

1. An electrochemical method for the indirect monitoring of the active matter of scale inhibitors in onshore and offshore installations, the method comprising the following steps: (a) sample preparation; and (b) electrochemical reading, and wherein the active matter of the scale inhibitors is composed of phosphonates that are converted into phosphate.

2. The method according to claim 1, wherein the phosphonate solutions, phosphonic acid (H.sub.3PO.sub.3), ATMP (C.sub.3H.sub.12NO.sub.9P.sub.3), and DTPMP (C.sub.9H.sub.28N.sub.3O.sub.15P.sub.5), are converted into phosphate through an ultraviolet (UV) (/persulfate process, and wherein solutions containing a strong oxidant are exposed to UV light 5-13 W, ?=254 nm for 3-15 minutes.

3. The method according to claim 1, wherein after acidifying the solutions exposed to UV light with sulfuric acid, acetone and ammonium molybdate is added to generate the phosphomolybdenum complex, thereby to allow the electrochemical reading to be carried out.

4. The method according to claim 1, wherein for the electrochemical measurements on the working electrodes, the electrically active region is delimited by a layer of epoxy resin via a photolithographic method, whereby voltammetry tests are performed on a portable potentiostat.

5. An electrochemical system for the indirect monitoring of the active matter of scale inhibitors in onshore and offshore installations, the method comprising a sample container, a UV lamp, a working electrode (WE), a counter electrode (CE), a reference electrode (RE), a potentiostat and equipment to control the interface.

6. The electrochemical system according to claim 5, wherein the photolithographic working electrode (WE) comprises one or more of Au, C, Pt or Pd.

7. The electrochemical system according to claim 5, wherein the counter electrode (CE), external electrodes, Pt wire, and Au films are used, and, for the reference electrode (RE), photolithographic with Ag/AgCl ink, and external Ag/AgCl 3M electrodes are used.

8. The electrochemical system according to claim 5, wherein the electrically active region of the working electrode is delimited by photolithography, using a layer of epoxy resin.

Description

BRIEF DESCRIPTION OF FIGURES

[0021] FIG. 1 shows the experimental apparatus used to convert the phosphonate sample into phosphate species by exposing the solution containing the oxidizing agent to the UV light (?=254 nm) in a plastic container (preferably Teflon, but not limited to this material).

[0022] FIG. 2 shows the two types (A and B) of working electrodes (WE) used, with dimensions of 25 mm long by 10 mm wide, highlighting the delimitation of the electrode area with a layer of SU-8 epoxy resin. As for the counter electrodes (CE) and reference electrodes (RE), in the configuration (A), external electrodes, Pt wire (CE) and Ag/AgCl in KCl 3M (RE) were used. In the configuration (B), Au film (CE) and Ag/AgCl paint (RE) in the area delimited by SU-8 were used.

[0023] FIG. 3 shows the electrochemical results for the H.sub.3PO.sub.4 standard used to investigate the performance of the method through an analytical curve. In (A), average SWV (n=3) for the phosphomolybdenum complex at concentrations of 5.0-20.0 mg L.sup.?1 phosphate. In (B), analytical curve obtained from SWV data, collected at a of +0.21 V, from 3 independent Au electrodes (n=3) for each phosphate concentration. CE: Pt wire and RE: Ag/AgCl in KCl 3M. [K.sub.2S.sub.2O.sub.8]=27.0 ?g L.sup.?1.

[0024] FIG. 4 shows the electrochemical results for phosphonate standards (A) ATMP and (B) DTPMP in s/UV and c/UV conditions after 15 minutes of exposure to the UV light (5 W, ?=254 nm) in the presence of K.sub.2S.sub.2O.sub.8. [K.sub.2S.sub.2O.sub.8]=27.0 g L.sup.?1. WE of Au (n=3 for each concentration), CE: Pt wire and RE: Ag/AgCl in KCl 3M.

[0025] FIG. 5 shows the average SWV sequence (n=3) of the phosphomolybdenum complex obtained for nine concentrations of the real sample s/UV and c/UV after 15 minutes of exposure to the UV light (5 W, ?=254 nm) in the presence of K.sub.2S.sub.2O.sub.8. [K.sub.2S.sub.2O.sub.8]=27.0 g L.sup.?1. WE of Au (n=3 for each concentration), CE: Pt wire and RE: Ag/AgCl in KCl 3M.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0026] The present disclosure primarily refers to an electrochemical method for the indirect monitoring of the active matter of scale inhibitors, composed of phosphonates, based on principles of advanced oxidative processes, which is viable for the quality control of scale inhibitor products in onshore and offshore installations. The monitoring of wastewater samples containing phosphonate, as well as samples of phosphonate standards, such as, for example, H.sub.3PO.sub.3, ATMP (C.sub.3H.sub.12NO.sub.9P.sub.3) and DTPMP (C.sub.9H.sub.28N.sub.3O.sub.15P.sub.5) also fit into this proposal. Said method comprises the following steps, described in detail below: [0027] (a) Sample preparation; [0028] (b) Electrochemical reading.

[0029] Additionally, the present disclosure refers to a system comprising a sample container, a UV lamp, a photolithographic working electrode (WE) made, preferably, in Au, but not limited to this metal, and may also be in C, Pt and Pd, for example. The electrically active region of the electrode is delimited by a layer of epoxy resin (preferably SU-8, but not limited to the same). The working electrode is not limited to photolithography and can be a disk and printed electrode, for example. The system further consists of a counter electrode (CE) and a reference electrode (RE), external or photolithographic, made of Pt or Au, and Ag/AgCl, respectively, but not limited to these, in addition to a potentiostat and equipment to control the same (cell phone, computer).

[0030] The proposed method and system are easy to use and offer simple sample preparation and portable configuration, providing an attractive strategy for an immediate solution to non-conformities in offshore installations.

a) Sample Preparation

[0031] In the proposed electrochemical method, the active matter of the scale inhibitors must be exclusively phosphonate. However, phosphonate is not electroactive and, therefore, it is necessary to add a step to convert phosphonate to phosphate, based on advanced oxidative processes (LEE et al., 2020). The phosphonate-phosphate conversion, schematically represented in FIG. 1, was carried out by exposing the scale inhibitor sample (preferably diluted 1600 times, but not limited to this dilution factor) to the UV light (preferably ?=254 nm; power range: 5-13 W; time range: 3-15 min) in the presence of a strong oxidant (preferably potassium persulfate (K.sub.2S.sub.2O.sub.8) with a concentration between 270.3 mg L.sup.?1 and 27.0 g L.sup.?1, (M A et al., 2017) but not limited to this, with sodium persulfate (Na.sub.2S.sub.2O.sub.8) and hydrogen peroxide (H.sub.2O.sub.2) as options) (ZHANG et al., 2016). When the phosphonate concentration is previously known, as in the case of the samples of the standards mentioned above (H.sub.3PO.sub.3, C.sub.3H.sub.12NO.sub.9P.sub.3 and C.sub.9H.sub.28N.sub.3O.sub.15P.sub.5), the solution preferably containing between 20 and 120 mg L.sup.?1 of phosphonate, but not limited to this range of concentration, must be exposed to the UV light.

[0032] According to the degradation mechanism (WANG et al., 2019), when S.sub.2O.sub.8.sup.2? species are exposed to the UV light, sulfate (SO.sub.4.sup.?) and hydroxyl (OH.sup.) radicals are formed, cleaving the bonds of the phosphonate molecules, leading to the formation of phosphate in the form of phosphoric acid (H.sub.3PO.sub.4), which justifies the choice of this acid (H.sub.3PO.sub.4) to obtain the analytical curve. In this case, although the phosphoric acid used to construct the analytical curve (preferably in the concentration range of 0.0-20.0 ppm phosphate) does not have phosphonate groups, the same procedure for adding potassium persulfate (270.3 mg L.sup.?1-27.0 g L.sup.?1) and exposure to the UV light (preferably ?=254 nm; power range: 5-13 W; time range: 3-15 min) was carried out to maintain the experimental conditions of the samples. The description for constructing the analytical curve will be detailed in the step of electrochemical reading.

[0033] Like phosphonate, phosphate is also not electroactive and, therefore, for its electrochemical detection, it was necessary to complex the same with molybdate (preferably ammonium molybdate, but there are other options such as, for example, lithium molybdate (Li.sub.2MoO.sub.4) (ARVAS et al., 2018) and in situ oxidation of metallic molybdenum (BARUS et al., 2016)), forming the phosphomolybdenum complex (Keggin anion). To do this, an aliquot (preferably 100 ?L, but not limited to this volume) of the sample exposed to the UV light (hereinafter referred to as c/UV) and an aliquot (preferably 100 ?L, but not limited to this) of the sample not exposed to the UV light (named here as s/UV) were added to solutions (900 ?L), previously prepared, containing, preferably, 49.0 g L.sup.?1 of sulfuric acid (H.sub.2SO.sub.4), 16.0% v/v of acetone (C.sub.3H.sub.6O), and 3.7 g L.sup.?1 of ammonium molybdate ((NH.sub.4).sub.6Mo.sub.7O.sub.24.Math.4H.sub.2O), referred to as blank solution.

[0034] The reaction for the formation of the complex depends on the properties of the solution, as neutral and basic media can compromise the conformation of the complex (BAJUK-BOGDANOVI? et al., 2016). A 10% decrease in the concentration of H.sub.2SO.sub.4, C.sub.3H.sub.6O and (NH.sub.4).sub.6Mo.sub.7O.sub.24.Math.4H.sub.2O in the solution generated results similar to those obtained using the solution with the preferred concentrations. The formation of the phosphomolybdenum complex can be visually observed by a change in color, from transparent to light yellow, depending on the concentration of phosphate present in the medium. Soon after, the sample is ready for electrochemical measurements. It is important to note that, after electrochemical measurement of the sample, if the current value obtained is not within the current values obtained in the analytical curve, greater dilutions of the inhibitor exposed to the UV light with the blank solution will be necessary.

b) Electrochemical Reading

[0035] In the present disclosure, scalable photolithographic working electrodes were used, manufactured via thin film deposition preferably of Au, but not limited to this metal, and C, Pt and Pd may be used for example. The electrode manufacturing method is not limited to photolithography, and can be disk and printed electrodes, for example. In the present disclosure, a geometric area of 2 mm (preferably, but not limited to this area) was defined on the working electrode (WE) by means of the photolithographic pattern transfer using an epoxy resin (preferably SU-8, but not limited to this), ensuring greater reproducibility between electrodes (error less than ?10%) and feasibility of mass production. FIG. 2 shows the two types of electrodes used. For electrochemical measurements, a counter electrode (CE) and reference electrode (RE), external or photolithographic, made of Pt or Au, and Ag/AgCl, respectively, were necessary, but not limited to these. For the photolithographic RE, Ag/AgCl ink was used in the area delimited by SU-8.

[0036] For electrochemical measurements, a sample volume (phosphomolybdenum complex) of 100 ?L was sufficient to carry out, preferably, square wave voltammetry (SWV) tests on the working electrodes (WE). A portable potentiostat conducted the SWV analyses from +0.5 V to +0.1 V using external Ag/AgCl RE and SWV from +0.35 V to ?0.3 V using Ag/AgCl paint RE. These potential ranges may vary depending on the type of RE used. The experimental parameters used were: step of ?0.001 mV, amplitude of 25 mV and frequency of 10 Hz, but not limited to these parameters. Three independent measurements (n=3) were made for each sample on a new electrode, which was discarded after each measurement, since the phosphomolybdenum complex adsorbs on the WE surface (electrochemically irreversible).

[0037] The samples were analyzed electrochemically with (c/UV) and without (s/UV) UV conversion, always in the presence of a strong oxidant, because some samples may contain phosphate residues, making it necessary to correct the phosphate concentration obtained from the phosphonate-phosphate conversion, for the indirect determination of the concentration of phosphonate present in the sample.

[0038] To construct the analytical curve (current vs. concentration), the current value referring to the reduction peak of Mo(IV) to Mo(II) was used. A straight line equation was obtained and applied to determine the concentration of all samples c/UV and s/UV.

Example of Embodiment

[0039] As mentioned, in the phosphonate-phosphate conversion mechanism, there is the formation of H.sub.3PO.sub.4, which was chosen as a standard to investigate the performance of the method by using an analytical curve. To maintain the experimental condition of the phosphonate-containing samples, K.sub.2S.sub.2O.sub.8 at a concentration of 27.0 g L.sup.?1 was added to the H.sub.3PO.sub.4 solution (120.0 mg L.sup.?1) before its exposure to the UV light (5 W, ?=254 nm) for 15 minutes.

[0040] After obtaining the phosphomolybdenum complex from the exposed solution, dilutions were made to 5.0-20.0 mg L.sup.?1 of phosphate using the blank solution, which was also used to obtain curve 0.0 mg L.sup.?1 phosphate. Measurements of SWVs were performed on three (n=3) new WEs for each concentration. FIG. 3A shows the average of these SWVs and is an example of the expected curve profile. The two reduction peaks at +0.38 and +0.21 V vs. Ag/AgCl correspond to reductions of Mo(VI)-Mo(IV) and Mo(IV)-Mo(II), respectively, the latter being chosen for the response of the method for indirect phosphonate quantification. It is important to mention that the position of the Mo reduction peaks may vary, depending on the used reference electrode.

[0041] From the resulting analytical curve, FIG. 3B, a linear trend was observed with a limit of detection (LOD) of 0.1 mg L.sup.?1 of phosphate and analytical sensitivity (?) of ?0.3 ?A mg.sup.?1 L. The LOD was calculated as 3?/?, with ? being the standard deviation of the blank solution. All results are presented as a function of the phosphate concentration.

[0042] As a proof of concept, the phosphonate, ATMP and DTPMP standards were studied. Solutions of 120.0 mg L.sup.?1 of ATMP (?115.6 mg L.sup.?1 of phosphonate) and DTPMP (100.5 mg L.sup.?1 of phosphonate) containing 27.0 g L.sup.?1 of K.sub.2S.sub.2O.sub.8 were exposed to a UV light (5 W, ?=254 nm) for 15 min. Experiments using a higher power lamp (13 W, ?=254 nm) guaranteed a reduction in the sample exposure time to 3 min. As standards were used, the phosphonate concentration in each solution was known in advance. Then, considering that a phosphonate molecule is converted to a phosphate molecule (in a 1:1 ratio), after the phosphonate-phosphate conversion, samples were obtained with the phosphomolybdenum complex at a concentration of 10.0 mg L.sup.?1 (concentration which is within the linear range of the analytical curve) of phosphate, which were monitored electrochemically. Mo reduction peaks (+0.21 V) were observed, FIG. 4, with smaller currents for the s/UV condition. In the c/UV condition, there was a significant increase in current for both standards, reaching values close to ?2.50 ?A. By subtracting the phosphate concentrations obtained under c/UV conditions from the s/UV conditions, the phosphonate concentration was indirectly obtained. Thus, when the recovery percentages were calculated, values of 83.0?2.7% were obtained for ATMP and 85.4?3.8% for DTPMP. These results were obtained using Au photolithographic electrode as WE, Pt wire as CE and Ag/AgCl as reference electrode.

[0043] To evaluate the applicability of the proposed method and system for the quality control of scale inhibitors using phosphonate as the active matter, exclusively, the electrodes were challenged with a real sample. In order to validate the results, the sample was first characterized by the nuclear magnetic resonance (NMR) technique, as seen in Table 1.

TABLE-US-00001 TABLE 1 Phosphonate species found in the real sample through the analyses of the .sup.1H, .sup.13C and .sup.31P NMR spectra. [Phosphonate Phosphonate species].sub.total Sample species Other species (g L.sup.?1) Real DTPMP 15.3 g L.sup.?1 phosphate 74.5 sample 31.1% m/m monoethylene glycol 25.4% m/m ethanol

[0044] The NMR results revealed a mixture of phosphate species, ethanol, monoethylene glycol and DTPMP (target), whose phosphonate concentration was found to be 74.5 g L.sup.?1. Nine solutions were prepared from the real sample (1.2 to 20.5 mg L.sup.?1 phosphate, labeled as samples 1 to 9), using the 27.0 g L.sup.?1 K.sub.2S.sub.2O.sub.8 solution. SWVs were obtained for each solution in the s/UV and c/UV cases, FIG. 5. The determined and expected phosphonate concentrations (NMR) were compared, and an overall accuracy of 86.0?2.6% was obtained. The NMR result validated the data obtained in the present disclosure, which means that the method showed reliable accuracy.

[0045] Notwithstanding, although there is a commercial colorimetric kit dedicated to samples containing phosphonate, these face problems related to variations in refractive index and turbidity effects, unlike the proposed method and system, which still offer the advantages of more accurate and faster analyses, as they can be carried out immediately after exposure to the UV light, taking advantage of the instantaneous formation of the phosphomolybdenum complex, which certainly makes the same an alternative tool for quality control of scale inhibitors in onshore and offshore installations. This analysis will enable rapid decision-making to readjust the dose of inhibitor to be applied or corrected in the production lines. Additionally, the proposed method and system are not limited only to the quality of the scale inhibitors, but can also be applied to the determination of phosphorus residuals in production water.

Application of the Disclosure

[0046] The proposed method and system were developed for in loco quality control of scale inhibitors (which have phosphonate groups as active matter) before they are injected into oil and gas production lines. As it is a portable system, it can be used on offshore and onshore oil platforms to determine the concentration of the active ingredient (phosphonate), thus making it possible to determine the quality of the received scale inhibitor. This analysis will enable rapid decision-making to readjust the dose to be applied or corrected in the production lines. Furthermore, the method is not limited only to the quality of the inputs, but can also be applied to the determination of phosphorus residuals in production waters.

Advantages

Reliability

[0047] From more efficient dosing and monitoring, there is greater reliability of combat systems and minimization of the scale, reducing stoppage and maintenance occurrences.

Health/Safety

[0048] By minimizing the scale formation, equipment cleaning events are also reduced. With this, interventions on equipment are reduced, avoiding exposure and risks inherent to the activity.

Economic/Productivity

[0049] Optimization of the dosage of scale inhibitors. Minimizing occurrences of scale and eventual stoppages of equipment for cleaning. Reduction of losses due to loss of profit due to production reduction or maintenance stoppage.

BIBLIOGRAPHIC REFERENCES

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