Study On Extraction Of Oligomeric Sunflower Heads Pectin And Its Corrosion Inhibition To Carbon Steel

Carbon steel corrosion is a common phenomenon in production and in life.Adding corrosion inhibitors is one of the most effective corrosion methods.With the development of industry,people's awareness of environmental protection has increased,and research on green corrosion inhibitors that are environmentally friendly,degradable,and follow sustainable development has gradually increased.Sunflower is one of the main oil crops in China.Every year,a large number of sunflower heads are discarded or burned in the country,causing environmental pollution and waste of resources.As a natural polymer,sunflower head pectin contains a large number of polar oxygen-containing functional groups such as ester groups and hydroxyl groups.They can easily form a protective film with carbon steel in an acidic medium and has a good corrosion inhibition effect on carbon steel.In this paper,two methods are used to extract oligomeric pectin from sunflower head,and the response surface is used to optimize the extraction process.Through static weightlessness,electrochemical workstation and other methods,the corrosion inhibition performance of oligomeric sunflower head pectin on carbon steel in hydrochloric acid was studied.Subsequently,it was combined with halogen ions to inhibit corrosion,and the corrosion inhibition performance and mechanism of halogen ions and pectin on carbon steel under acidic medium were studied.The results show that:(1)Wet sunflower head is used as raw material to extract oligomeric sunflower pectin(FP)by ammonium oxalate method;dry sunflower head is used as raw material to extract oligomeric sunflower pectin(DP)by subcritical water method;response surface optimization design and physical and chemical tests were carried out on the extraction processes of the two pectins,respectively,to obtain the optimal extraction conditions.The results show that the optimal extraction process conditions for FP are extraction time 1.64 h,extraction material-liquid ratio is 1:13.6,ammonium oxalate concentration is 0.69%,pectin yield can reach 9.26%,through verification,the actual pectin yield 9.2±0.13%.The optimal extraction process conditions of DP pectin are:extraction time 19.1 min,extraction material-liquid ratio1:43.3,extraction temperature 121.5?,pectin yield can reach 15.96%,and through experiment,pectin yield reaches 15.82±0.24%.The molecular weight of pectin is measured by gel permeation chromatography.The results show that the weight average molecular weight of the two pectins is between 4 and 10 kDa,and both are oligomeric pectins.(2)Using static weightlessness,combined electrochemical and SEM-EDX methods,at different temperatures(15?~30?),the corrosion inhibition performance of pectin in 1mol/L HCl solution was studied.And study the corrosion inhibition performance of different concentrations(0~2.0 g/L)of pectin in 1 mol/L HCl solution to steel.The results show that under certain conditions,with the increase of temperature,the corrosion inhibition efficiency of pectin decreases.When the addition amount of FP and DP was 2.0 g/L,the temperature increased from 15°C to 40°C,and the weight loss corrosion inhibition efficiency decreased from 93.4%and 94.7%to 52.1%and 55.8%respectively.The corrosion inhibition effect was the best at 15°C.Through the adsorption model fitting and adsorption kinetics and adsorption thermodynamics research,the adsorption of the two pectins on the surface of carbon steel conforms to the Langmuir adsorption model,which is a mixed adsorption mainly based on physical adsorption,and both are spontaneous adsorption;The molecular weights of the two pectins are similar,the difference in corrosion inhibition efficiency is small,and the corrosion inhibition mechanism is the same.The polarization curve results show that the two pectin corrosion inhibitors do not change the corrosion mechanism of carbon steel in the corrosion medium,and they are both mixed anode and anode corrosion inhibitors..(3)At 30°C,0.1 g/L DP pectin was compounded with different concentrations(5-100mmol/L)of KCl,KBr,and KI.The results showed that:under the amount of 5-100 mmol/L,halogen ions have synergistic corrosion inhibition effect on pectin.Under the same halogen ion concentration,the corrosion inhibition effect of compounding with pectin:I~->Br~->Cl~-.The optimal concentration of halide ion combined with 0.1 g/L DP pectin is 10 mmol/L,at this time,the weight loss inhibition efficiency increases from 26.7%to 88.9%,78.5%,and 62.5%.Halogen ions are preferentially adsorbed on the surface of carbon steel,and the charging status of the surface of the carbon steel changes,which in turn facilitates the adsorption of protonated pectin on the surface of the carbon steel,increases the thickness and density of the adsorption layer,and shows a synergistic effect.