CN105543864B - The method for preparing carbon steel pickling solution as corrosion inhibiter using low molecular weight sunflower disk pectin - Google Patents

Abstract

The invention relates to a method for preparing a carbon steel pickling solution by using low-molecular-weight sunflower pectin as a corrosion inhibitor, and belongs to the technical field of metal material corrosion and protection. The method uses low-molecular-weight sunflower pectin as a corrosion inhibitor for carbon steel pickling, uses hydrochloric acid solution as a carbon steel pickling solution, and uses water as a solvent to prepare carbon steel acid using low-molecular-weight sunflower pectin as a corrosion inhibitor wash solution. The mass concentration of the sunflower pectin is 0.1-2 g/L, and the molar concentration of the hydrochloric acid is 0.5-2 mol/L. The present invention uses low molecular weight sunflower disc pectin as carbon steel pickling corrosion inhibitor, which has the characteristics of low cost, wide source, easy biodegradation, non-toxicity and high efficiency, etc. It is applied in the field of metal corrosion protection and has a broad market Prospect and application value.

Description

Method for preparing carbon steel pickling solution with low molecular weight sunflower pectin as corrosion inhibitor

technical field

The invention relates to a method for preparing a carbon steel pickling solution by using low-molecular-weight sunflower pectin as a corrosion inhibitor, and belongs to the technical field of metal material corrosion and protection.

Background technique

Due to its low cost and excellent mechanical properties, carbon steel is widely used in various machinery manufacturing industries such as buildings, bridges, railways, vehicles and ships. However, during the use of carbon steel products, due to their active chemical properties and the complexity of the use environment, carbon steel often suffers from different degrees of corrosion. In order to restore its function, strong acid cleaning is often used to remove corrosion products and dirt. However, in the process of using strong acid to clean the corrosion products and dirt on the surface of carbon steel and other metals, the phenomenon of "over-corrosion" easily occurs, that is, while removing the corrosion products, it also corrodes part of the metal substrate, resulting in serious waste of resources and environmental pollution. . Therefore, the addition of corrosion inhibitors is often used as an anti-corrosion measure when pickling carbon steel. Most of the commonly used pickling corrosion inhibitors are organic substances containing phosphorus, sulfur, nitrogen and oxygen. However, these corrosion inhibitors have many disadvantages such as toxicity, large dosage and environmental hazards during use. With the continuous improvement of people's awareness of environmental protection, looking for new high-efficiency, low-toxic or non-toxic environment-friendly corrosion inhibitors has become a research hotspot for future corrosion inhibitors.

In my country, a large amount of sunflower waste residues are discharged every year, and these waste residues are often only used in the production of biogas in rural areas, feed or returned to the field as waste. In the north, it is basically burned as fuel or discarded in the field and left to rot, resulting in waste of materials and environmental pollution.

With the deepening of research work in recent years, the use of pectin has been continuously developed, its development potential is huge, and it has broad market prospects. The development of sunflower discs as new raw materials for extracting pectin corrosion inhibitors, and the development and utilization of low-molecular-weight pectin will not only increase the added value of sunflowers, enrich the source of raw materials for pectin production, but also contribute to the protection of the natural ecological environment and social improvement. Benefits also have important practical and social significance.

It has not been reported that low molecular weight sunflower pectin is used as a carbon steel corrosion inhibitor to inhibit steel corrosion under acidic conditions.

Contents of the invention

Aiming at the disadvantages of traditional corrosion inhibitors being toxic and harmful to the environment, the invention provides an application of low-molecular-weight sunflower pectin, which is used as a corrosion inhibitor for carbon steel pickling. The present invention extracts, develops and utilizes the pectin resource in the sunflower dish waste residue, and applies it to the corrosion protection of carbon steel corrosion, which can not only generate certain economic benefits, but also solve the problem of waste pollution and protect the ecological environment. It has significant social and environmental benefits.

The present invention is achieved through the following technical solutions:

A method for preparing a carbon steel pickling solution using low molecular weight sunflower pectin as a corrosion inhibitor, the method uses low molecular weight sunflower pectin as a carbon steel pickling corrosion inhibitor, and uses hydrochloric acid solution as a carbon steel pickling solution The solution is prepared by using water as a solvent to obtain a carbon steel pickling solution using low molecular weight sunflower disc pectin as a corrosion inhibitor.

Further, the method specifically uses sunflower disk as a raw material, first prepares low molecular weight sunflower disk pectin powder, dissolves the low molecular weight sunflower disk pectin powder with water as a solvent, and prepares a low molecular weight sunflower disk pectin solution, Then add hydrochloric acid solution and water to the low molecular weight sunflower pectin solution to prepare the carbon steel pickling solution using low molecular weight sunflower pectin as corrosion inhibitor.

Further, the preparation of the low molecular weight sunflower disc pectin powder comprises the following steps:

(1) Wash the sunflower dish with deionized water, dry it in a vacuum drying oven at 100° C., use a pulverizer to grind the dried sunflower dish, pass through a 60-mesh sieve, and obtain sunflower dish powder;

(2) Mix the sunflower disc powder obtained in step (1) with water at a solid-to-liquid ratio of 1:20 to 1:25, add a citric acid buffer solution to the mixed system, and adjust the pH of the system to 5 to 5. 5.5, and add cellulase with a mass fraction of 1.5% to 2% to the system, shake at a constant temperature of 55°C to 60°C for 3.5 to 4h, obtain the extract, and place the extract in hot water at 90°C Incubate for 5 minutes, centrifuge after inactivating the enzyme, and store the supernatant at 4°C for a short time after passing through a funnel with a sand core.

(3) Mix the refrigerated pectin extract in step (2) with the acidified ethanol refrigerated at 4°C in a volume ratio of 1:2.5, stir thoroughly, and let stand at 4°C to allow the pectin to fully separate out. Pectin was obtained by filtering with nylon filter cloth, washed with ethanol for 3 times, dried at 60°C, and ground into powder with a mortar to obtain the low molecular weight sunflower disk pectin powder;

The method for preparing the low-molecular-weight sunflower pectin solution is: add water to the low-molecular-weight sunflower pectin powder, heat and stir at a heating temperature of 40°C and a rotating speed of 500r/min, and stop until the pectin is completely swollen Stir.

Further, in the carbon steel pickling solution using low molecular weight sunflower pectin as a corrosion inhibitor, the mass concentration of low molecular weight sunflower pectin is 0.1-2 g/L, and the molar concentration of hydrochloric acid is 0.5-2 g/L. 2mol/L.

Further, the weight average molecular weight of the low molecular weight sunflower pectin is 5-12KDa, and the number average molecular weight is 650.

Further, the degree of esterification of the low molecular weight sunflower pectin is 20.01%-32.52%, and the content of galacturonic acid is 70-80%.

Further, at 25°C, the pretreated 45 ^# carbon steel test piece was soaked for 48 hours in the carbon steel pickling solution using low molecular weight sunflower disc pectin as corrosion inhibitor, and the low molecular weight sunflower disc The corrosion inhibition efficiency of pectin on 45 ^# carbon steel is 86.92%-95.99%.

A carbon steel pickling corrosion inhibitor, the corrosion inhibitor is low molecular weight sunflower disk pectin.

Further, the weight average molecular weight of the low molecular weight sunflower pectin is 5-12KDa, and the number average molecular weight is 650.

Further, the degree of esterification of the low molecular weight sunflower pectin is 20.01%-32.52%, and the content of galacturonic acid is 70%-80%.

Beneficial technical effect of the present invention:

1. the low molecular weight sunflower dish pectin of the present invention is extracted from the sunflower dish residue, and the pectin resource in the sunflower dish waste residue is extracted and exploited, and it is applied to the corrosion protection of carbon steel corrosion, not only It can generate certain economic benefits, and can also solve the problem of waste pollution, protect the ecological environment, and has significant social and environmental benefits.

2. The low-molecular-weight sunflower disc pectin of the present invention is a high-molecular substance polymerized by D-galacturonic acid. It has properties such as biodegradability and non-toxicity, and is a safe and green corrosion inhibitor.

3. When the low-molecular-weight sunflower disc pectin of the present invention is used as a carbon steel pickling corrosion inhibitor, the dosage is small and the corrosion inhibition efficiency is high.

Description of drawings

Fig. 1. The infrared spectrogram of low molecular weight sunflower disc pectin;

Figure 2. Nyquist plots of carbon steel electrodes in pickling solutions without and with different concentrations of corrosion inhibitors;

Figure 3. Potentiodynamic polarization curves of carbon steel electrodes in pickling solutions without and with different concentrations of corrosion inhibitors;

Fig. 4. The high-magnification micrograph of the 45 ^# carbon steel test piece without pickling solution immersion;

Figure 5. At 25°C, the 45 ^# carbon steel specimen was soaked in a pickling solution with a hydrochloric acid concentration of 2mol/L without adding any corrosion inhibitor for 48 hours;

Figure 6. At 25°C, the concentration of hydrochloric acid is 2mol/L, and the concentration of sunflower disc pectin corrosion inhibitor is 2g/L in the pickling solution after soaking for 48 hours. The high-power microscope resolution of 45 ^# carbon steel is 100 times picture.

Figure 7. At 25°C, the concentration of hydrochloric acid is 2mol/L, and the concentration of sunflower disc pectin corrosion inhibitor is 2g/L in the pickling solution after soaking for 48 hours. The high-power microscope resolution of 45 ^# carbon steel is 500 times picture.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

On the contrary, the invention covers any alternatives, modifications, equivalent methods and schemes within the spirit and scope of the invention as defined by the claims. Further, in order to make the public have a better understanding of the present invention, some specific details are described in detail in the detailed description of the present invention below. The present invention can be fully understood by those skilled in the art without the description of these detailed parts.

Example 1

A method for preparing a carbon steel pickling solution using low molecular weight sunflower pectin as a corrosion inhibitor, the method uses low molecular weight sunflower pectin as a carbon steel pickling corrosion inhibitor, and uses hydrochloric acid solution as a carbon steel pickling solution Solution, using water as a solvent to prepare a carbon steel pickling solution using low molecular weight sunflower disc pectin as a corrosion inhibitor. The corrosion inhibition effect of the carbon steel pickling solution using low molecular weight sunflower pectin as corrosion inhibitor was studied.

One, the method for preparing the pickling solution that contains the sunflower disc pectin corrosion inhibitor of different concentrations and different hydrochloric acid concentrations

1. The preparation steps of low molecular weight sunflower pectin:

(1) Wash the sunflower disc with deionized water, dry it in a vacuum drying oven at 100° C., use a pulverizer to grind the dried sunflower disc, and pass it through a 60-mesh sieve to obtain sunflower disc powder.

(2) Mix the sunflower disc powder obtained in step (1) with water at a solid-to-liquid ratio of 1:20 to 1:25, add a citric acid buffer solution to the mixed system, and adjust the pH of the system to 5 to 5. 5.5, and add 1.5% to 2% (mass fraction) of cellulase to the system, shake at a constant temperature of 55°C to 60°C for 3.5 to 4h, obtain the extract, and place the extract in hot water at 90°C Centrifuge after 5 min to inactivate the enzyme, and store the supernatant at 4°C for a short time after passing through a sand core funnel (No. G3).

(3) Mix the refrigerated pectin extract in step (2) with the acidified ethanol refrigerated at 4°C in a volume ratio of 1:2.5, stir thoroughly, and let stand at 4°C to allow the pectin to fully separate out. Nylon filter cloth to filter the pectin. Then wash with ethanol for 3 times, dry at 60°C, and grind into powder with a mortar to obtain low molecular weight sunflower disc pectin powder.

Pectin is a natural polymer made of D-galacturonic acid linked by α-1,4 glycosidic bonds. Its structural formula is as follows:

The structure analysis of the low molecular sunflower disc pectin powder sample was carried out by Fourier transform infrared spectrometer, and the results are shown in Figure 1. The broad peak at 3411.49cm ^-1 is the stretching vibration absorption peak of OH, the peak around 2929.92cm ^-1 is caused by the stretching vibration absorption of CH (including: CH, CH ₂ and CH ₃ ), 1733.28cm ^-1 and 1608.26cm ^-1 is the vibration absorption peak of esterified carbonyl and unesterified carbonyl, respectively, and 1249.29cm ^-1 is caused by the asymmetric stretching vibration of COC, indicating the existence of -O-CH ₃ . Fourier transform infrared spectroscopic analysis further verified that sunflower disc pectin contains a large number of functional groups such as carboxyl, hydroxyl and ester groups. These functional groups can coordinate with metal elements and adsorb on the surface of carbon steel to form a protective film to prevent corrosion of the medium. In contact with carbon steel surfaces, slows down corrosion.

2. The method for preparing the pickling solutions containing different concentrations of sunflower pectin corrosion inhibitors and different concentrations of hydrochloric acid

(1) Take 15 beakers, each group of five, respectively add 0g, 0.01g, 0.05g, 0.1g, 0.2g of the low molecular weight sunflower pectin powder in each group of 5 beakers, and then add 50mL Distilled water, heated and stirred at a speed of 500r/min and a temperature of 40°C until the pectin was completely swollen to prepare pectin solutions with different concentrations.

(2) The first group of treatment methods is: transfer the five different concentrations of pectin solutions prepared in step (1) to five 100mL volumetric flasks respectively, and add 4.85mL of 36% concentrated Hydrochloric acid (or adding 4.6mL mass fraction is the concentrated hydrochloric acid of 38%), is settled to 100mL with distilled water, shakes up, obtains the pickling solution that contains the sunflower disc pectin corrosion inhibitor of different concentrations, described application obtained in preparation In the carbon steel pickling solution in which the low molecular weight sunflower pectin is the corrosion inhibitor, the mass concentration of the low molecular weight sunflower pectin is respectively 0g/L, 0.1g/L, 0.5g/L, 1g/L, 2g /L, at this moment, the molar concentration of hydrochloric acid is 0.5mol/L;

The second group of processing methods is the same as the first group of preparation method steps, except that the added mass fraction is 36% concentrated hydrochloric acid volume is 9.7mL (or adding 9.2mL mass fraction is 38% concentrated hydrochloric acid), In the carbon steel pickling solution prepared using low molecular weight sunflower disc pectin as a corrosion inhibitor, the molar concentration of hydrochloric acid is 1mol/L;

The third group of processing methods is identical to the first group of preparation method steps, except that the added mass fraction is 36% concentrated hydrochloric acid volume is 19.4mL (or adding 18.4mL mass fraction is 38% concentrated hydrochloric acid), In the carbon steel pickling solution prepared using low molecular weight sunflower disc pectin as a corrosion inhibitor, the molar concentration of hydrochloric acid is 2mol/L;

2. Using pickling solutions containing different concentrations of sunflower pectin corrosion inhibitors and different concentrations of hydrochloric acid, the corrosion inhibition effect of low molecular weight sunflower pectin as a corrosion inhibitor for pickling carbon steel was studied.

1. The static weight loss experiment was used to study the corrosion inhibition effect of low molecular weight sunflower pectin on carbon steel.

According to GB10124-88 "Metal Material Laboratory Uniform Corrosion Total Immersion Test Method" to carry out the weight loss test. The size of the 45 ^# carbon steel test piece used in this experiment is 20mm × 10mm × 2mm, and its surface is polished with 100 ^# ~ 2000 ^# water-phase sandpaper in sequence, then cleaned with deionized water, acetone and absolute ethanol, and finally blown by cold air. Dry weighing, wherein, 45 ^# carbon steel is a carbon structural steel with a carbon content of 0.45%, also known as 45 carbon structural steel, which belongs to medium carbon steel.

Under the constant temperature condition of 25°C, soak the treated carbon steel test piece in the pickling solution containing different concentrations of sunflower pectin corrosion inhibitor prepared in the above steps for 48 hours, and then take out the test piece. Wash and dry it, weigh it with an electronic balance, and calculate its corrosion inhibition efficiency according to the weight loss of the test piece. The calculation formula of corrosion rate (R) and corrosion inhibition efficiency (EI (%)) is as follows:

In the formula:

W ₀ : mass of unsoaked carbon steel test piece (g);

W ₁ : the mass (g) of carbon steel soaked in corrosive medium for 48 hours;

A: surface area of carbon steel test piece (mm ² );

t: soaking time of carbon steel in corrosive medium (48h);

R _blank : corrosion rate of carbon steel without corrosion inhibitor;

R _{corrosion inhibitor} : corrosion rate of carbon steel with different concentrations of corrosion inhibitor.

The results of the weight loss test are shown in Table 1: It can be seen that at 25°C, when the concentration of hydrochloric acid in the pickling solution is 0.5mol/L, 1mol/L, and 2mol/L, the corresponding optimal corrosion inhibition efficiencies are: 86.92% and 92.23% respectively , 95.99%, and the corrosion inhibition efficiency was higher than 85%, indicating that low molecular weight sunflower pectin is an efficient corrosion inhibitor. Among the three different concentrations of hydrochloric acid, the maximum corrosion inhibition efficiency in 2mol/L hydrochloric acid solution is 95.99%. This is because the molecular chain of pectin is degraded in high-concentration hydrochloric acid solution and can be oriented to form an adsorption film on the surface of carbon steel. And the mutual entanglement is small, the molecular weight of pectin degraded by low hydrochloric acid concentration is weak, and a large number of molecular chains are entangled together, which will hinder the adsorption of pectin molecules to the surface of carbon steel. The efficiency is higher than that of sunflower pectin corrosion inhibitor in low concentration hydrochloric acid solution.

Table 1 Weight loss results of carbon steel pickling in pickling solutions containing different concentrations of sunflower pectin corrosion inhibitors and different concentrations of hydrochloric acid

2. Using electrochemical impedance method to study the corrosion inhibition effect of low molecular weight sunflower pectin on carbon steel

Use epoxy resin to seal the non-working area of the 45 ^# carbon steel electrode, and its working area is 1cm ² . Before the test, the surface of the electrode was polished step by step with 100 ^# ~ 2000 ^# sandpaper, then polished with 1 ^# ~ 3 ^# metallographic sandpaper, degreased with acetone and ethanol, rinsed with deionized water, and then put into the electrolytic cell for experiment.

Electrochemical tests were performed by an electrochemical workstation. The experiment adopts a three-electrode system, the reference electrode is a saturated calomel electrode (SCE), the auxiliary electrode is a platinum electrode, and the working electrode is the above-mentioned 45 ^# carbon steel. Put the above-mentioned 45 ^# carbon steel test piece into the electrolytic cell, and measure the potentiodynamic polarization curve and AC impedance spectrum after the open circuit voltage is stable. The scanning rate of potentiodynamic polarization is 1mV/s, and the scanning range is: -1~0.2V, and the fitting software that comes with the workstation is used for fitting.

The electrochemical impedance scanning frequency was 10mHz-100kHz, the amplitude of the sine wave disturbance signal was 5mV, and the analysis and fitting were carried out using ZsimpWin software, and the test temperature was 25°C.

At 25°C, 45# carbon steel in acid with a hydrochloric acid concentration of 2mol/L and sunflower plate pectin corrosion inhibitor concentrations of 0g/L, 0.1g/L, 0.5g/L, 1g/L, and 2g/L respectively Nyquist diagram of wash solution. As shown in Figure 2, curve 1, curve 2, curve 3, curve 4, and curve 5 respectively represent the concentration of sunflower plate pectin corrosion inhibitor as 0g/L, 0.1g/L, 0.5g/L, 1g/L , 2g/L. It can be seen from Figure 2 that the main part of the Nyquist diagram is an approximately semicircular capacitive reactance arc, which mainly represents the size of the charge transfer resistance, which controls the charge transfer of carbon steel corrosion. The larger the arc length is, the larger the charge transfer resistance is, and the corrosion charge The less likely to transfer, the better the corrosion inhibition effect. It can be seen from the figure that when the concentration of the sunflower pectin corrosion inhibitor is 2g/L, the impedance arc is the largest and the corrosion inhibition efficiency is the largest, which is consistent with the results of the weight loss experiment. It can be seen from the figure that in addition to the capacitive reactance arc, there is a second time constant, especially at high concentrations. This time constant may be caused by the adsorption of Fe dissolved ions on the carbon steel surface.

3. Using the potentiodynamic polarization curve method to study the corrosion inhibition effect of low molecular weight sunflower pectin on carbon steel

Figure 3 shows: at 25°C, 45 ^# carbon steel has a hydrochloric acid concentration of 2mol/L, and the concentrations of sunflower pectin corrosion inhibitors are 0g/L, 0.1g/L, 0.5g/L, 1g/L, Polarization curves in 2g/L pickling solution, wherein curve 1, curve 2, curve 3, curve 4, and curve 5 respectively represent the concentration of sunflower pectin corrosion inhibitor as 0g/L, 0.1g/L, 0.5g/L, 1g/L, 2g/L, the corresponding corrosion potential E _corr (mV) and corrosion current density I _corr (μA) are shown in Table 2 below, and the corrosion inhibition efficiency η (%) is calculated according to the following formula:

Among them, I ₀ and I represent the corrosion current density of the pickling solution without corrosion inhibitor and with different concentrations of sunflower pectin corrosion inhibitor at a hydrochloric acid concentration of 2 mol/L, respectively.

It can be seen from Table 2 that with the increase of corrosion inhibitor concentration, the corrosion current density gradually decreases, and the corrosion inhibition efficiency increases with the increase of corrosion inhibitor concentration. Corrosion in solution, the results are consistent with the results of weight loss experiments and polarization curves. It can be seen from Table 2 and Figure 3 that the corrosion potential moves to the positive electrode, and the current density of the polarization curve decreases gradually with the addition of the corrosion inhibitor. Although both the anode and the cathode show a decrease with the increase of the concentration, the The cathodic current density is larger than that of the blank solution, but the anode is smaller than that of the blank solution, and the corrosion potential gradually shifts positively, and the current density decreases, indicating that the low molecular weight sunflower disc pectin is an anodic inhibitor.

Table 2 Corrosion current density and corrosion inhibition efficiency of pickling solutions with different concentrations of sunflower pectin corrosion inhibitor at a hydrochloric acid concentration of 2mol/L

4. Using a high-power microscope to observe and study the corrosion inhibition effect of low molecular weight sunflower pectin on carbon steel

Figure 4 is a 45 ^# carbon steel test piece that has not been soaked in a pickling solution; Figure 5 is a 45 # carbon steel specimen soaked in a pickling solution with a hydrochloric acid concentration of 2 mol/L without any corrosion inhibitor at 25 ° ^C for 48 hours Steel test piece; Figure 6 (resolution 100 times) and Figure 7 (resolution 500 times) are at 25 ° C, the concentration of hydrochloric acid is 2mol/L, and the concentration of sunflower pectin corrosion inhibitor is 2g/L acid 45 ^# carbon steel test piece soaked in washing solution for 48h.

It can be seen from Figure 4 that the surface of the sample just polished is very smooth, and scratches are clearly visible; Figure 5 shows that the surface of the sample was severely corroded after soaking in the pickling solution without adding any corrosion inhibitor, and there were unevenness According to the software data, the height of the corrosion gully is 136.5 μm, and the width is 137.5 μm; Figure 6 and Figure 7 show that the concentration of the sunflower disc pectin corrosion inhibitor soaked in 2mol/L is Compared with the blank etching solution, the sample surface of 2g/L pickling solution has a relatively smooth surface morphology, and there are no corrosion grooves, but corrosion pits one by one, and the corrosion height is 8.44μm; the above data It shows that after adding the corrosion inhibitor, the carbon steel specimen is significantly protected, and the corrosion effect of HCl on the carbon steel structure can be weakened after adding the sunflower disc pectin corrosion inhibitor, and the corrosion inhibition effect is obvious.

Claims (7)

1. a kind of application low molecular weight sunflower disc pectin is the method that corrosion inhibitor prepares carbon steel pickling solution, it is characterized in that, described method is used as carbon steel pickling corrosion inhibitor with low molecular weight sunflower disc pectin, with hydrochloric acid The solution is a carbon steel pickling solution, and water is used as a solvent to prepare a carbon steel pickling solution using low molecular weight sunflower disc pectin as a corrosion inhibitor; The method specifically uses sunflower pectin as a raw material, first prepares low molecular weight sunflower pectin powder, dissolves the low molecular weight sunflower pectin powder with water as a solvent, prepares a low molecular weight sunflower pectin solution, and then pours it into the Adding hydrochloric acid solution and water to the low molecular weight sunflower pectin solution to prepare the carbon steel pickling solution using low molecular weight sunflower pectin as a corrosion inhibitor; The preparation of described low molecular weight sunflower disc pectin powder comprises the following steps: (1) Wash the sunflower dish with deionized water, dry it in a vacuum drying oven at 100° C., use a pulverizer to grind the dried sunflower dish, pass through a 60-mesh sieve, and obtain sunflower dish powder; (2) Mix the sunflower disc powder obtained in step (1) with water at a solid-to-liquid ratio of 1:20 to 1:25, add a citric acid buffer solution to the mixed system, and adjust the pH of the system to 5 to 5. 5.5, and add cellulase with a mass fraction of 1.5% to 2% to the system, shake at a constant temperature of 55°C to 60°C for 3.5 to 4h, obtain the extract, and place the extract in hot water at 90°C Incubate for 5 minutes, centrifuge after inactivating the enzyme, and store the supernatant at 4°C for a short time after passing through a funnel with a sand core; (3) Mix the refrigerated pectin extract in step (2) with the acidified ethanol refrigerated at 4°C in a volume ratio of 1:2.5, stir thoroughly, and let stand at 4°C to allow the pectin to fully separate out. Nylon filter cloth is filtered to obtain pectin, and then washed with ethanol for 3 times, dried at 60 ° C, and ground into powder with a mortar to obtain the low molecular weight sunflower disc pectin powder; preparation of the low molecular weight sunflower disc pectin solution The method is as follows: adding water to the low-molecular-weight sunflower disc pectin powder, heating and stirring at a heating temperature of 40° C. and a rotating speed of 500 r/min, and stopping the stirring after the pectin is completely swollen. 2. according to claim 1, a kind of application low-molecular-weight sunflower-disk pectin is the method for corrosion inhibitor to prepare carbon steel pickling solution, it is characterized in that, in the described application low-molecular-weight sunflower-disk pectin is the carbon steel of corrosion inhibitor In the steel pickling solution, the mass concentration of the low-molecular-weight sunflower pectin is 0.1-2 g/L, and the molar concentration of hydrochloric acid is 0.5-2 mol/L. 3. according to claim 1, a kind of application low molecular weight sunflower pectin is the method for corrosion inhibitor to prepare carbon steel pickling solution, it is characterized in that, the weight average molecular weight of described low molecular weight sunflower pectin is 5～12KDa , The number average molecular weight is 650. 4. a kind of application low molecular weight sunflower pectin according to claim 1 is the method for corrosion inhibitor to prepare carbon steel pickling solution, it is characterized in that, the esterification degree of described low molecular weight sunflower pectin is 20.01%～ 32.52%, and its galacturonic acid content is 70-80%. 5. according to claim 1, a kind of application of low molecular weight sunflower disc pectin is the method for corrosion inhibitor to prepare carbon steel pickling solution, it is characterized in that, at 25 ℃, pretreated 45# carbon steel test piece Soak for 48 hours in the carbon steel pickling solution using low molecular weight sunflower pectin as corrosion inhibitor, and the corrosion inhibition efficiency of low molecular weight sunflower pectin on 45# carbon steel is 86.92%-95.99%. 6. A carbon steel pickling corrosion inhibitor, characterized in that, the corrosion inhibitor is low molecular weight sunflower disc pectin; The weight-average molecular weight of the low-molecular-weight sunflower pectin is 5-12KDa, and the number-average molecular weight is 650. 7. A kind of corrosion inhibitor for carbon steel pickling according to claim 6, characterized in that, the degree of esterification of the low molecular weight sunflower pectin is 20.01%～32.52%, and the content of galacturonic acid is 70%～ 80%.