Method for monitoring the effectiveness of atmospheric carbon dioxide removal by seawater alkalization

Abstract

The application discloses a method for monitoring the removal efficiency of atmospheric carbon dioxide in seawater alkalization, and belongs to the technical field of marine negative emission and geochemical monitoring. The method comprises the following steps: step 1) collecting a seawater sample; step 2) determining carbonate alkalinity; and step 3) calculating the CO2 removal efficiency; based on the difference between the carbonate alkalinity before and after alkalization, the removal efficiency CDR of atmospheric carbon dioxide is calculated, and the calculation formula is as follows: CDR=CA t -CA0; wherein CDR is the removal efficiency of atmospheric CO2 after the implementation of seawater alkalization, the unit is mol CO2kg ‑1 ; CA0 and CA t are the carbonate alkalinity before and after seawater alkalization respectively, the unit is mol kg ‑1 .

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of marine geochemistry monitoring, and in particular provides a method for evaluating and quantifying the effectiveness of seawater alkalization engineering in enhancing the absorption of atmospheric carbon dioxide. The method is particularly suitable for monitoring changes in the carbonate system of seawater caused by artificial intervention (such as the addition of alkaline substances) and calculating the corresponding carbon dioxide removal amount. BACKGROUND

[0002] With the rapid development of global industrialization, a large amount of greenhouse gases, especially carbon dioxide (CO2), is emitted into the atmosphere, leading to a series of serious environmental problems such as global warming, sea level rise, and frequent extreme weather events. The ocean is the largest carbon sink on Earth, absorbing about one-fourth of the total amount of anthropogenic CO2 emissions. However, the continuous absorption of CO2 by the ocean also leads to a decrease in seawater pH and carbonate saturation, i.e., ocean acidification, which poses a serious threat to the marine ecosystem, especially calcifying organisms such as corals and shellfish.

[0003] Under this background, ocean alkalinity enhancement (OAE) as a potential ocean negative emission technology has received widespread attention. The core principle is to artificially increase the total alkalinity (TA) of seawater by adding alkaline substances (such as olivine, calcium hydroxide, sodium carbonate, etc.) to seawater, thereby enhancing the ability of seawater to absorb atmospheric CO2 and sequestering the absorbed CO2 in the form of bicarbonate (HCO3 - ) and carbonate (CO3 2- ) ions. In theory, increasing the alkalinity of seawater can effectively reduce the CO2 partial pressure (pCO2) of surface seawater, promote the net flux of CO2 at the sea-air interface from the atmosphere to the ocean, and thus achieve carbon dioxide removal (CDR).

[0004] However, accurately evaluating the actual CO2 removal effectiveness of seawater alkalization engineering is a key scientific issue for the large-scale application of this technology. The existing monitoring and CDR effectiveness evaluation methods for seawater alkalization negative emission technology are based on total alkalinity determination, which assumes that the increase in alkalinity can achieve equivalent alkalinity. However, traditional total alkalinity measurement methods, such as the Grant titration method, although mature, will introduce non-negligible non-carbonate alkalinity into the alkalized seawater under the implementation conditions of seawater alkalization engineering, such as metal ions (aluminum, nickel, chromium, etc.) released by mineral dissolution or organic alkalinity (generated during sewage biological treatment) introduced during the alkalization process of sewage, which will introduce a large error when equating the change in total alkalinity to the CO2 removal amount.

[0005] Therefore, developing a method capable of accurately monitoring the change of carbonate alkalinity (CA) in seawater alkalization process and reliably calculating the atmospheric CO2 removal efficiency based thereon is of great significance for promoting the scientific research and practical application of seawater alkalization technology. The present application aims to provide a seawater alkalization atmospheric CO2 removal efficiency monitoring and calculation method which is relatively simple to operate and reliable in results, so as to provide technical support for related research and engineering practice. SUMMARY

[0006] The present application provides a seawater alkalization atmospheric carbon dioxide removal efficiency monitoring method, which overcomes the interference of non-carbonate alkalinity signals such as aluminate, borate, oligomeric silicate and organic alkalinity in the existing technology based on total alkalinity monitoring seawater alkalization carbon sink accounting technology, so as to effectively avoid the distortion problem of alkalinity increase sink benefit.

[0007] To achieve the above design purpose, the innovation core of the present application is to accurately determine the change of carbonate alkalinity CA before and after seawater alkalization, and to quantify the removal efficiency CDR of atmospheric CO2 based on the difference.

[0008] Specifically, the method comprises the following steps:

[0009] Step 1) seawater sample collection;

[0010] Seawater samples are collected before and after seawater alkalization, and the collected seawater samples are filtered and stored using a filter membrane with a pore size of less than 1.0 μm; the seawater after alkalization is recorded as sample t, and the seawater before alkalization is recorded as sample 0;

[0011] Step 2) determination of carbonate alkalinity;

[0012] Under the condition of ensuring that the carbon dioxide partial pressure between seawater and atmosphere reaches equilibrium, the carbonate alkalinity of seawater sample before alkalization treatment CA0 and after alkalization treatment CA t is determined respectively;

[0013] Step 3) calculation of CO2 removal efficiency;

[0014] Based on the difference of carbonate alkalinity before and after alkalization, the removal efficiency CDR of atmospheric carbon dioxide is calculated, and the calculation formula is as follows: CDR = CA t - CA0;

[0015] Wherein, CDR is the atmospheric CO2 removal efficiency after seawater alkalization engineering implementation, unit is mol CO2 kg -1 ; CA0 and CA t are the carbonate alkalinity before and after seawater alkalization respectively, unit is mol kg -1 .

[0016] Further, the step 2) can adopt the following two-phase acid-base titration mode, that is, in the two-phase acid-base titration process, first, the pretreated seawater sample is titrated with acid to pH 3.0 or less, the acid consumption (V HCl ) in this process is recorded; then, the dissolved carbon dioxide converted from the carbonate system in the sample is completely removed by nitrogen blowing; finally, the pH of the sample is restored to the initial value by back titration with alkali, and the alkali consumption (V NaOH ) in this process is recorded. The carbonate alkalinity of the sample is finally calculated by the difference between the acid and alkali consumptions: CA=(C HCl ·V HCl -C NaOH ·V NaOH ) / M. The execution process of the two-phase acid-base titration mode is simple and clear, easy to operate and calculate.

[0017] comprising the following steps:

[0018] Step 2.1) weighing the sample;

[0019] Weigh 10-20 g of filtered seawater sample and record the mass M of the seawater filtrate sample;

[0020] Step 2.2) acid titration;

[0021] Detect and record the initial pH value pH0 of the seawater, and then titrate the seawater sample with acid;

[0022] Use a pH meter to monitor and record the change of the pH value of the seawater in real time, stop titration when the pH value drops to 3.0 or less, and record the volume V HCl of dilute hydrochloric acid consumed in the titration process;

[0023] Step 2.3) removal of dissolved CO2;

[0024] After acid titration, use high-purity nitrogen to blow the acidified seawater sample to remove the dissolved carbon dioxide in the sample;

[0025] Step 2.4) base titration;

[0026] After nitrogen blowing is completed, under the protection of nitrogen, use sodium hydroxide solution to titrate the sample solution back to its initial pH value pH0, and record the volume V NaOH of sodium hydroxide solution consumed in this alkali titration process;

[0027] Step 2.5) carbonate alkalinity calculation;

[0028] The carbonate alkalinity CA is calculated by the following formula: CA=(C HCl ·V HCl -C NaOH ·V NaOH ) / M;

[0029] wherein CA is the carbonate alkalinity, in mol / kg; C HCl and C NaOH are the concentrations of hydrochloric acid and sodium hydroxide used for titration, in mol / L; V HCl and V NaOH are the volumes of hydrochloric acid and sodium hydroxide consumed in the acid-base titration, in L; M is the mass of the sample, in kg.

[0030] To meet the demand for higher precision measurement, the method for monitoring the removal efficiency of atmospheric carbon dioxide by seawater alkalization described in the present application can adopt the following double Gran acid titration method in step 2). This method adopts two independent Gran acid titration processes, i.e., the first time before nitrogen blowing, the end point volume (Ve1) corresponding to the total titratable alkalinity is determined by the Gran function method; the second time after nitrogen blowing and base titration, the end point volume (Ve2) corresponding to the non-carbonate alkalinity is also determined by the Gran function method; the difference between the hydrogen ion consumption represented by the two end point volumes (Ve1-Ve2) x C HCl / M is used to more accurately calculate the carbonate alkalinity, thereby eliminating the background interference of various non-carbonate alkalinity in principle. Specifically,

[0031] Step 2.1) weighing the sample;

[0032] Weigh 10-20 g of filtered seawater sample and record the mass M of the seawater filtrate sample;

[0033] Step 2.2) first acid titration;

[0034] The first titration end point volume Ve1 is calculated by the Gran method;

[0035] Step 2.3) removal of dissolved CO2;

[0036] After the acid titration is completed, high-purity nitrogen is used to blow the acidified seawater sample to remove the dissolved carbon dioxide in the sample;

[0037] Step 2.4) second acid titration;

[0038] The second titration end point volume Ve2 is calculated by the Gran method;

[0039] Step 2.5) base titration;

[0040] After the nitrogen blowing is completed, the sample solution is titrated back to its initial pH value pH0 using sodium hydroxide solution under nitrogen protection;

[0041] Step 2.6) carbonate alkalinity calculation;

[0042] The calculation is performed according to the difference between the two titration end point volumes, and the formula is: CA=(Ve1-Ve2)xC HCl / M;

[0043] Wherein, the Gran method refers to constructing a Gran function F=(V0+V acid )×10 -pH and performing linear regression on the data points with pH values in the range of 3.3 to 3.0; in the formula, V0 is the total volume of the sample before this titration; V acid is the volume of the acid added cumulatively; the intersection point of the regression straight line and the x-axis is the titration end point volume.

[0044] Compared with the prior art, the present application has the following beneficial effects and advantages:

[0045] 1. Flexible method system: taking the convenient "dual-phase acid-base titration method" as the core, it is suitable for rapid evaluation and on-site detection; at the same time, the high-precision "double Gran acid titration method" is provided, which is suitable for precise scientific research, forming a method system that takes into account convenience and precision.

[0046] 2. Strong anti-interference ability: both methods remove CO2 through nitrogen blowing, effectively eliminating the contribution of non-carbonate alkalinity, and are particularly suitable for complex alkalinized seawater systems.

[0047] 3. High measurement precision: the "dual-phase acid-base titration method" and the "double Gran acid titration method" can greatly eliminate the interference of stable non-carbonate alkalinity (such as organic alkalinity, silicate, metal ion complex, etc.) in the background through differential measurement technology, and the measurement precision is significantly better than that of traditional methods.

[0048] 4. High standardization: the method proposed in the present application has standardized operation steps and clear parameters, providing a highly standardized analysis method for the evaluation of seawater alkalinization CO2 removal efficiency.

[0049] 5. Wide application range: the method is not only suitable for laboratory precise analysis, but also can be used for on-site rapid detection, providing technical support for the whole process from research and development to application of seawater alkalinization engineering. BRIEF DESCRIPTION OF DRAWINGS

[0050] The present application will be further described in conjunction with the following drawings;

[0051] Figure 1 The present application is a seawater alkalinization atmospheric carbon dioxide removal efficiency monitoring method flowchart;

[0052] Figure 2 The present application is a seawater alkalinization atmospheric carbon dioxide removal efficiency monitoring method flowchart; Figure 2 (a) is a data schematic diagram of the first Gran titration,Figure 2 (b) is the second Gran titration data after carbon removal by nitrogen blowing;

[0053] Figure 3 Comparison chart of titration data of sample 0 before seawater alkalization and carbonate alkalinity; Figure 3 (a) is the first Gran titration data, Figure 3 (b) is the second Gran titration data after carbon removal by nitrogen blowing; DETAILED DESCRIPTION

[0054] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with specific cases in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0055] Basic experimental conditions and data:

[0056] In order to better compare the differences of different calculation methods, all the embodiments are based on the following unified experimental conditions, standard procedures and measured data.

[0057] 1.1 Reagents and equipment

[0058] (a) Reagents:

[0059] - Artificially alkaline substance: palygorskite (average particle size 28 μm).

[0060] - Titrant: calibrated dilute hydrochloric acid solution (C HCl = 0.0926306 mol / L) and dilute sodium hydroxide solution (C NaOH = 0.0983256 mol / L).

[0061] - Purge gas: high-purity nitrogen (99.999%).

[0062] (b) Main equipment:

[0063] - Filtration device: 20 μm filter silk screen, 0.45 μm pore size acetic acid fiber filter membrane.

[0064] - Constant temperature and stirring: 25°C constant temperature water bath, magnetic stirrer.

[0065] - pH measurement: high-precision pH meter (Thermo Scientific TM Orion Star TMA211, equipped with Orion 8157B N UMD probe, system analysis accuracy ±0.002).

[0066] 1.2 Sample preparation

[0067] (a) Seawater collection: Surface seawater was collected from the coastal area, and pre-filtered through a 20 μm silk screen to remove large particulate matter. The initial salinity of the seawater was 31.310‰.

[0068] (b) Sample grouping:

[0069] - Sample 0 (before alkalization): The pre-filtered seawater was directly taken as the control sample.

[0070] - Sample t (after alkalization): 10 wt% of palygorskite was added to the pre-filtered seawater to perform artificial alkalization treatment, and after 120 hours of standing and open placement at a constant temperature of 25°C, the experimental sample was obtained.

[0071] 1.3 Standard titration procedure

[0072] (a) Filtration and precise weighing: About 50 mL of sample (Sample 0 or Sample t) was taken and filtered through an acetic acid fiber filter membrane with a pore size of 0.45 μm to remove particulate matter that interferes with alkalinity determination while ensuring that the measured seawater sample and the test environment atmosphere are in CO2 partial pressure sea-air equilibrium. Then 10-20 g of filtrate was accurately weighed and the mass (M) was recorded.

[0073] (b) First acid titration: The sample was placed in a 25°C constant temperature water bath and continuously stirred (~100 rpm). After recording the initial pH value, dilute hydrochloric acid was slowly titrated until the seawater pH value dropped below 3.0, and the volume of hydrochloric acid consumed (V HCl,1 ) and pH change data were recorded.

[0074] (c) Nitrogen blowing to remove carbon: After acid titration, high-purity nitrogen was inserted into the sample liquid surface below through a thin tube at a flow rate of about 100 mL / min for 20 minutes to ensure that the dissolved CO2 in the sample was completely removed.

[0075] (d) Base back titration: After nitrogen blowing, nitrogen was maintained above the liquid surface to form a protective atmosphere, and dilute sodium hydroxide solution was used to titrate the sample back to the initial pH value, and the volume of base solution consumed (V NaOH ) was recorded.

[0076] (e) Second acid titration: Immediately under nitrogen protection, dilute hydrochloric acid was used again for titration until the pH value dropped below 3.0, and the volume of hydrochloric acid consumed (V HCl,2 ) and pH change data were recorded.

[0077] 1.4 Summary of titration experimental data

[0078] The above standard procedure was applied to sample 0 and sample t, respectively, to obtain the following experimental data:

[0079] (a) Sample t (after alkalization):

[0080] - titrated sample mass (M t ): 0.014976 kg

[0081] - initial pH: 7.542

[0082] - first acid titration consumed HCl volume (V HCl,t,1 ): 0.003063 L, pH values between 3.8 and 3.0 titration data as shown in Figure 2 (a);

[0083] - base back titration consumed NaOH volume (V NaOH,t ): 0.000977 L

[0084] - second acid titration consumed HCl volume (V HCl,t,2 ): 0.000984 L, pH values between 3.8 and 3.0 titration data as shown in Figure 2 (b);

[0085] (b) Sample 0 (before alkalization):

[0086] - titrated sample mass (M0): 0.019828 kg

[0087] - initial pH: 7.953

[0088] - first acid titration consumed HCl volume (V HCl,0,1 ): 0.0008326 L, pH values between 3.8 and 3.0 titration data as shown in Figure 3 (a);

[0089] - base back titration consumed NaOH volume (V NaOH,0 ): 0.0003205 L

[0090] - second acid titration consumed HCl volume (V HCl,0,2 ): 0.0003298 L, pH values between 3.8 and 3.0 titration data as shown in Figure 3 (b);

[0091] Example 1, a method for monitoring the effectiveness of atmospheric carbon dioxide removal by seawater alkalization based on a biphasic acid-base titration process, comprising the following steps:

[0092] Step 1) seawater sample collection;

[0093] The seawater samples were collected before and after the seawater alkalization, and the collected seawater samples were filtered and stored by using a filter membrane with a pore size of less than 1.0 μm; the seawater after alkalization is recorded as sample t, and the seawater before alkalization is recorded as sample 0;

[0094] Step 2) Determining the carbonate alkalinity;

[0095] Under the condition of ensuring that the carbon dioxide partial pressure between the seawater and the atmosphere reaches equilibrium, a two-phase acid-base titration process was adopted to determine the carbonate alkalinity of the seawater samples before CA0 and after CA t alkalization treatment, respectively;

[0096] Step 2.1) Weighing the sample;

[0097] Weighing 10-20 g of the filtered seawater sample, and recording the mass M of the seawater filtrate sample;

[0098] Step 2.2) Acid titration;

[0099] Detecting and recording the initial pH value pH0 of the seawater, and then performing acid titration on the seawater sample;

[0100] Using a pH meter to monitor and record the change of the pH value of the seawater in real time, and stopping the titration when the pH value decreases to below 3.0, and recording the volume V HCl of the dilute hydrochloric acid consumed in the titration process;

[0101] Step 2.3) Removing dissolved CO2;

[0102] After the acid titration is completed, the acidified seawater sample is purged with high-purity nitrogen to remove the dissolved carbon dioxide in the sample;

[0103] Step 2.4) Base titration;

[0104] After the nitrogen purging is completed, under the protection of nitrogen, the sample solution is titrated back to its initial pH value pH0 using sodium hydroxide solution, and the volume V NaOH of the sodium hydroxide solution consumed in the base titration process is recorded;

[0105] Step 2.5) Carbonate alkalinity calculation;

[0106] The carbonate alkalinity CA is calculated by the following formula: CA = (C HCl · V HCl -C NaOH · V NaOH ) / M;

[0107] In the formula, CA is the carbonate alkalinity, with a unit of mol / kg; C HCl and C NaOH are the concentrations of the hydrochloric acid and the sodium hydroxide used in the titration, respectively, with a unit of mol / L; V HCl and VNaOH The consumed volumes of hydrochloric acid and sodium hydroxide in the acid-base titration process, respectively, are L; M is the sample mass, kg.

[0108] The calculation principle of this embodiment is based on the biphasic acid-base titration method, including (a) acid titration to low pH: determining the amount of acid consumed; (b) nitrogen purging: removing CO2; (c) base back titration: determining the amount of base consumed to restore the initial pH; (d) carbonate alkalinity = (consumed acid amount x acid concentration - consumed base amount x base concentration) ÷ sample mass.

[0109] Based on the acid-base titration volume data in the unified titration data, the following calculation of carbonate alkalinity is performed:

[0110] Carbonate alkalinity of seawater after alkalization (CA t ): The titration sample mass M t = 0.014976 kg, the first acid titration consumes HCl volume V HCl,t,1 = 0.003063 (L), after nitrogen purging, the base back titration consumes NaOH volume V NaOH,t = 0.000977 (L). At the same time, the calibration concentration of the hydrochloric acid solution is C HCl = 0.0926306 mol / L, and the calibration concentration of the sodium hydroxide solution is C NaOH = 0.0983256 mol / L.

[0111] Therefore, CA t = (0.003063 x 0.0926306 - 0.000977 x 0.0983256) ÷ 0.014976 = 0.0125309 (mol / kg) = 12350.9 (μmol / kg);

[0112] Carbonate alkalinity of seawater before alkalization (CA0): The titration sample mass M0= 0.019828 kg, the first acid titration consumes HCl volume V HCl,0,1 = 0.0008326 (L), after nitrogen purging, the base back titration consumes NaOH volume V NaOH,0 = 0.0003205 (L). At the same time, the calibration concentration of the hydrochloric acid solution is C HCl = 0.0926306 mol / L, and the calibration concentration of the sodium hydroxide solution is C NaOH = 0.0983256 mol / L.

[0113] Therefore, CA t= (0.0008326 x 0.0926306 - 0.0003205 x 0.0983256) ÷ 0.019828 = 0.0023003 (mol / kg) = 2300.3 (pmol / kg);

[0114] Step 3) Calculate the CO2 removal efficiency;

[0115] Based on the difference between the carbonate alkalinity before and after alkalization, the removal efficiency of atmospheric CO2, CDR, is calculated according to the following formula: CDR = CA t - CA0;

[0116] Wherein, CDR is the removal efficiency of atmospheric CO2 after the implementation of seawater alkalization project, with the unit of mol CO2 kg -1 ; CA0and CA t are the carbonate alkalinity before and after seawater alkalization respectively, with the unit of mol kg -1 .

[0117] Specifically, CDR = CA t - CA0= 12350.9 - 2300.3 = 10050.6 (pmol / kg) in this embodiment.

[0118] Therefore, as in this embodiment, after the implementation of the simulated alkalization project, 10050.6 pmol of atmospheric CO2 can be additionally fixed per kg of seawater.

[0119] Embodiment 2, a method for monitoring the removal efficiency of atmospheric CO2 in seawater alkalization based on a double Gran acid titration process, comprising the following steps:

[0120] Step 1) Collecting seawater samples;

[0121] Collect seawater samples before and after the implementation of seawater alkalization, and store the collected seawater samples by filtering with a filter membrane with a pore size of less than 1.0 pm; the seawater after alkalization is recorded as sample t, and the seawater before alkalization is recorded as sample 0;

[0122] Step 2) Determining the carbonate alkalinity;

[0123] Under the condition of ensuring that the carbon dioxide partial pressure between seawater and atmosphere reaches equilibrium, the carbonate alkalinity of seawater samples before alkalization CA0and after alkalization CA t is determined respectively;

[0124] In order to obtain more accurate measurement results, the following double Gran acid titration process is adopted;

[0125] Step 2.1) Weighing the sample;

[0126] Weigh 10-20 g filtered seawater sample and record the seawater filtrate sample mass M;

[0127] Step 2.2) First acid titration;

[0128] The first titration end point volume Ve1 is calculated using the Gran method;

[0129] Step 2.3) Removal of dissolved CO2;

[0130] After the acid titration is complete, the acidified seawater sample is purged with high purity nitrogen gas to remove dissolved carbon dioxide from the sample;

[0131] Step 2.4) Second acid titration;

[0132] The second titration end point volume Ve2 is calculated using the Gran method;

[0133] Step 2.5) Base titration;

[0134] After the nitrogen purge is complete, the sample solution is titrated back to its initial pH value pH0 using sodium hydroxide solution under nitrogen protection;

[0135] Step 2.6) Carbonate alkalinity calculation;

[0136] The carbonate alkalinity is calculated from the difference between the two titration end point volumes, according to the formula: CA = (Ve1-Ve2) x C HCl / M;

[0137] Wherein, the Gran method refers to the data points with pH value in the range of 3.3 to 3.0, constructing the Gran function F = (V0+V acid ) x 10 -pH And linear regression; In the formula, V0 is the total volume of the sample before this titration; V acid is the cumulative volume of acid added; The intersection of the regression straight line and the x-axis is the titration end point volume.

[0138] The double Gran acid titration method described above can effectively eliminate the interference of non-carbonate alkalinity through the differential measurement technology of two acid titrations. At the same time, the pH calculation interval of the Gran titration is set to 3.3-3.0, which can effectively avoid the buffer pH 3.7 of aluminum hydroxide and the buffer pH value of organic alkalinity (mainly carboxylate) ~ 4.0. The calculation principle includes (a) first acid titration (Ve1): determination of total titratable alkalinity; (b) second acid titration (Ve2): determination of non-carbonate alkalinity after removing CO2; (c) carbonate alkalinity = (Ve1-Ve2) x acid concentration ÷ sample mass.

[0139] According to the above double Gran acid titration method, the carbonate alkalinity of the sample is calculated from the difference between the two titration end point volumes:

[0140] Carbonate alkalinity of seawater after alkalization (CA t ): As Figure 2 The first acid titration in the range of pH 3.3-3.0, the slope and intercept of the Grane function fitting are 0.05257 and -1.41823E-4, respectively, and thus Ve1=1.41823E-4 / 0.05257=0.0026978 (L) is calculated; the second acid titration, the slope and intercept of the Grane function fitting are 0.05851 and -3.62105E-5, respectively, and thus Ve2=3.62105E-5 / 0.05851=0.0006189 (L) is calculated. Meanwhile, the mass of the titration sample M t =0.014976 kg; the calibrated concentration of the hydrochloric acid solution is C HCl =0.0926306 mol / L.

[0141] Therefore, CA t =(0.0026978-0.0006189)×0.0926306÷0.014976=0.0128586 (mol / kg)=12858.6 (μmol / kg);

[0142] Carbonate alkalinity of seawater before alkalization (CA0): As Figure 3 The first acid titration in the range of pH 3.3-3.0, the slope and intercept of the Grane function fitting are 0.07492 and -3.93544E-5, respectively, and thus Ve1=3.93544E-5 / 0.07492=0.00052529 (L) is calculated; the second acid titration, the slope and intercept of the Grane function fitting are 0.07465 and -2.07883E-6, respectively, and thus Ve2=2.07883E-6 / 0.07465=0.00002785 (L) is calculated. Meanwhile, the mass of the titration sample M0=0.019828 kg; the calibrated concentration of the hydrochloric acid solution is C HCl =0.0926306 mol / L.

[0143] Therefore, CA t =(0.00052529-0.00002785)×0.0926306÷0.019828=0.0023239 (mol / kg)=2323.9 (μmol / kg);

[0144] Step 3) Calculate the CO2 removal efficiency;

[0145] Based on the difference between the carbonate alkalinity before and after alkalization, the removal efficiency of atmospheric carbon dioxide CDR is calculated, and the calculation formula is as follows: CDR=CA t -CA0;

[0146] where CDR is the CO2 removal efficacy of seawater after alkalization, with unit of mol CO2 kg -1 ; CA0and CA t are the carbonate alkalinity before and after seawater alkalization, with unit of mol kg -1 .

[0147] Specifically, in this embodiment, CDR = CA t - CA0= 12858.6 - 2323.9 = 10534.7 (pmol / kg);

[0148] Therefore, it can be seen that after the simulation of the alkalization project, 10535.4 pmol of atmospheric CO2 can be additionally fixed per kilogram of seawater.

[0149] Example 3, as a comparative case, the following is a calculation example of CO2 removal efficacy based on theory and prior art disclosure, including a theoretical calculation method based on chemical equilibrium and a total alkalinity measurement method used in the prior art.

[0150] I. Theoretical CO2 removal efficacy calculation:

[0151] Carbonate alkalinity (CA) is an important component of total alkalinity (TA), which is defined as:

[0152]

[0153] The coefficient "2" in the formula is because each carbonate ion (CO3 2 -) can accept two protons (H + ) in the process of reacting with acid to CO2. Given four basic parameters of seawater: salinity (S), water temperature (T), total dissolved inorganic carbon (DIC), and pH, the concentrations of various carbonic species can be accurately calculated, and then the carbonate alkalinity is obtained. The core of the calculation is to use the two apparent dissociation constants of carbonic acid, K1 and K2, whose values depend on water temperature, salinity and pressure.

[0154]

[0155] First, calculate the apparent constant of carbonic acid dissociation according to seawater temperature and salinity:

[0156]

[0157] Based on the salinity (31.310) and water temperature (25°C, i.e., 298.15 K) of the seawater used in the experiment, K1 = 1.405 x 10-6 and K2 = 1.126 x 10-9 are calculated.

[0158] The distribution ratio (a) of each component of the carbonate system is calculated:

[0159] Then, the hydrogen ion activity [H + ] is calculated according to the pH value: -pH The ratio (a) of each component of the carbonate system to DIC is calculated:

[0160] The ratio (al) of bicarbonate ion:

[0161]

[0162] The ratio (a2) of carbonate ion:

[0163]

[0164] In this example, the pH values of seawater before and after alkalization are 7.953 and 7.542, respectively. Substituting these data into the calculation formula of the distribution ratio of each component of the carbonate system, the ion ratios before alkalization are a 1,0 = 90.2% and a 2,0 = 9.1%. After alkalization, the ion ratios change to a 1,t = 94.4% and a 2,t = 3.7%.

[0165] The concentrations of each component of the carbonate system are calculated:

[0166] The concentrations of each component of the carbonate system can be obtained by multiplying DIC by the corresponding ratio:

[0167]

[0168] In this example, the total dissolved inorganic carbon (DIC) of seawater before and after alkalization is 2216.5 μmol / kg and 12725.4 μmol / kg, respectively. According to this, the concentrations of bicarbonate and carbonate before alkalization are 1999.3 and 201.7 μmol / kg, respectively, and those after alkalization are 12012.8 and 470.8 μmol / kg, respectively.

[0169] The carbonate alkalinity (CA) is calculated:

[0170] Substituting the above concentrations into the definition formula of carbonate alkalinity:

[0171] CA = DIC · (al + 2 · a2)

[0172] In this example, the carbonate alkalinity of seawater before and after alkalization increases greatly from CA0= 2402.7 μmol / kg to CA t = 12954.4 μmol / kg

[0173] Finally, the theoretical CO2 removal efficacy (CDR theory ) is calculated as follows:

[0174] CDR theory = CA t - CA0= (12954.4-2402.7) pmol / kg = 10551.7 pmol / kg

[0175] Note: In the calculation of the total alkalinity (TA) of seawater, the carbonate ion (CO32-) contributes two chemical equivalents due to its -2 charge. This calculation rule is completely consistent with the stoichiometric relationship of CDR and does not overestimate its potential. The chemical principle is that for every 1 mol of carbonate introduced into seawater, under the effective dispersion in the global ocean system, it will ultimately drive the ocean to additionally absorb 1 mol of CO2 from the atmosphere and stably convert it into 2 mol of bicarbonate ion (HCO3-), thereby achieving efficient carbon sequestration.

[0176] II. Example of total alkalinity method for calculating CO2 removal efficacy in the prior art:

[0177] This method directly uses the change in total alkalinity to calculate the CO2 removal efficacy and is the most commonly used method in the study of seawater alkalization, but has certain limitations. The calculation principle is based on the determination of total alkalinity by the Gran titration method and assumes that the increase in total alkalinity is completely from the carbonate system, and directly equates the change in total alkalinity to the amount of CO2 removed.

[0178] Using the total alkalinity single Gran titration end point volume in the unified titration data:

[0179] The total alkalinity of seawater after alkalization is calculated based on the acid titration Gran function between pH 3.8 and 3.0 Figure 2 a), the fitting slope and intercept of the first acid titration Gran function are 0.03721 and -9.70927E-5, respectively, according to which Ve1 = 9.70927E-5 / 0.03721 = 0.00260932 (L), at the same time, the calibration concentration of hydrochloric acid solution is C HCl = 0.0926306 mol / L, and the mass of the sample titrated M0 = 0.019828 kg. Therefore, TA t = (0.0000970927 / 0.03721) x 0.0926306 ÷ 0.014976 = 0.0161393 (mol / kg) = 16139.3 (pmol / kg).

[0180] The total alkalinity of natural seawater before alkalization is calculated based on the acid titration Gran function between pH 3.8 and 3.0 Figure 3a), the first acid titration of Gran function fitting slope and intercept are 0.07343 and -3.82191E-5, according to which Ve1=3.82191E-5 / 0.07343=0.0005205(L), at the same time, the calibration concentration of hydrochloric acid solution is C HCl =0.0926306 mol / L, the mass of the titration sample M0=0.019828 kg. Therefore, TA0=(0.0000382191 / 0.07343) x 0.0926306 ÷ 0.019828=0.0024315(mol / kg)=2431.5(μmol / kg).

[0181] The traditional method calculates the CO2 removal efficiency:

[0182] CDR 传统 =TA t -TA0=16139.3-2431.5=13707.8(μmol / kg).

[0183] The monitoring method described in the present application is compared with the above-mentioned embodiment 3 (comparative case):

[0184] For the same batch of samples, the actual measured CO2 removal efficiency of 10535.4 μmol CO2·kg -1 using the method of embodiment 2 (double Gran acid titration) is very close to the theoretical calculation value (10551.7 μmol / kg) in comparative embodiment 3. However, the result (13707.8 μmol CO2·kg -1 ) of the traditional total alkalinity method in comparative embodiment 3 is about 30.1% (3172.4 μmol CO2·kg -1 ) higher.

[0185] This significant deviation mainly comes from: first, the introduction of non-carbonate alkalinity (such as aluminate, silicate, etc. released by mineral dissolution) in the alkalization process. It can be found in comparative Figure 2 b and Figure 3 b that the second Gran titration amount after carbon removal after alkalization also increases, indicating the introduction of non-carbonate alkalinity in the alkalization process; second, too much non-carbonate alkalinity may change the linear performance of Gran titration, such as Figure 2 a shows that the Gran function does not show a linear rule in the titration interval of pH 3.8-3.0.

[0186] This comparison clearly shows the serious limitations of the traditional total alkalinity method in the evaluation of CO2 removal efficiency in seawater alkalization engineering, and the necessity and superiority of the method of the present application. The overestimation of the traditional method may lead to the wrong evaluation of the actual carbon sink effect of seawater alkalization engineering.

[0187] Summary:

[0188] The present application provides a systematic method based on the biphasic acid-base titration method to monitor and calculate the atmospheric CO2 removal efficiency of seawater alkalinization projects. This method is easy to operate and can effectively deal with the interference of non-carbonate alkalinity. At the same time, the present application also provides a high-precision double-Gran acid titration method as an alternative.

[0189] Multiple embodiments demonstrate the flexibility and superiority of the method system of the present application:

[0190] - Example 1 (biphasic acid-base titration method): easy to operate, rapid evaluation, CDR = 10050.6 μmol CO2·kg -1 (difference from theoretical value ~ 4.6%);

[0191] - Example 2 (double-Gran acid titration method): highest precision, suitable for scientific research and standard setting, CDR = 10534.7 μmol CO2·kg -1 (difference from theoretical value < 0.2%);

[0192] - Example 3 (comparative case):

[0193] - Theoretical calculation value: CDR theory = 10551.7 μmol CO2·kg -1 ;

[0194] - Traditional total alkalinity method: CDR 传统 = 13707.8 μmol CO2·kg -1 (overestimation of 30.1%)

[0195] Through the comparison of Example 3 and Example 2, it is clear that the traditional total alkalinity method will seriously overestimate the CO2 removal efficiency (about 30.1%), proving the necessity of the method of the present application. This multi-level method system not only guarantees the scientificity and accuracy of measurement, but also takes into account the convenience and economy of practical application, providing reliable technical support for the whole process from laboratory research to engineering application of seawater alkalinization technology.

[0196] The above only describes the preferred embodiments of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for monitoring the effectiveness of atmospheric carbon dioxide removal by seawater alkalinization, characterized by, Comprising the following steps, Step 1) seawater sample collection; Seawater samples are collected before and after seawater alkalization, and the collected seawater samples are filtered and preserved using a filter membrane with a pore size of less than 1.0 μm; the seawater after alkalization is recorded as sample t, and the seawater before alkalization is recorded as sample 0; Step 2) determination of carbonate alkalinity; Under the condition of ensuring the carbon dioxide partial pressure between seawater and atmosphere to reach equilibrium, the two-phase acid-base titration method or double Gran acid titration method is adopted, and nitrogen is used to blow the acidified seawater sample to remove the dissolved carbon dioxide in the sample during the titration process, so as to respectively measure the carbonate alkalinity CA0 of the seawater sample before alkalization treatment and CA t after alkalization treatment. Step 3) calculation of CO2 removal efficiency; Based on the difference between the carbonate alkalinity before and after alkalization, the removal efficiency of atmospheric carbon dioxide CDR is calculated, and the calculation formula is as follows: ; Wherein, CDR is the atmospheric CO2 removal efficiency after the implementation of seawater alkalization project, unit is ; CA0 and CA t are the carbonate alkalinity before and after seawater alkalization, unit is .

2. The method of monitoring the effectiveness of atmospheric carbon dioxide removal by seawater alkalinization according to claim 1, characterized in that: The step 2) adopts a two-phase acid-base titration process, Step 2.1) weighing the sample; Weigh 10-20 g of filtered seawater sample and record the seawater filtrate sample mass M; Step 2.2) acid titration; Detect and record the initial pH value pH0 of the seawater, and then perform acid titration on the seawater sample; The change of seawater pH value was monitored and recorded in real time using a pH meter. When the pH value decreased to below 3.0, the titration was stopped, and the volume V of dilute hydrochloric acid consumed in the titration process was recorded HCl ; Step 2.3) removal of dissolved CO2; After the acid titration is completed, high-purity nitrogen gas is used to purge the acidified seawater sample to remove dissolved carbon dioxide in the sample; Step 2.4) base titration; After the end of the nitrogen purge, under nitrogen protection, the sample solution is titrated back to its initial pH value pH0 using a sodium hydroxide solution, and the volume V of sodium hydroxide solution consumed during this base titration is recorded NaOH ; Step 2.5) carbonate alkalinity calculation; Carbonate alkalinity CA is calculated by the following equation: ; wherein CA is the carbonate alkalinity in mol / kg; C HCl and C NaOH are the concentrations of the hydrochloric acid and sodium hydroxide used for titration, respectively, in mol / L; V HCl and V NaOH are the volumes of hydrochloric acid and sodium hydroxide consumed during the acid-base titration, respectively, in L; M is the sample mass, and the unit is kg.

3. The method of claim 1, wherein: The step 2) adopts a double-grain acid titration process, Step 2.1) weighing the sample; Weigh 10-20 g of filtered seawater sample and record the seawater filtrate sample mass M; Step 2.2) first acid titration; The first titration end point volume Ve1 is calculated using the grain method; Step 2.3) removal of dissolved CO2; After the acid titration is completed, high-purity nitrogen gas is used to purge the acidified seawater sample to remove dissolved carbon dioxide in the sample; Step 2.4) second acid titration; The second titration end point volume Ve2 is calculated using the grain method; Step 2.5) base titration; After the nitrogen gas purge is completed, under the protection of nitrogen gas, the sample solution is titrated back to its initial pH value pH0 using sodium hydroxide solution; Step 2.6) carbonate alkalinity calculation; The calculation is made according to the difference between the two titration end point volumes, with the formula: ; Wherein, the Gran method refers to constructing the Gran function for the data points with pH value in the range of 3.3 to 3.0 and linear regression; wherein, V0 is the total volume of the sample before this titration; V acid is the volume of the acid added cumulatively; the intersection point of the regression straight line and the x axis is the volume of the end point of titration; C HCl is the concentration of the hydrochloric acid used for titration.

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