Preparation Of Different Molecular Weight Apple Pectin And Study Its Corrosion Inhibition

Anti-corrosion of steel has always been a research hotspot in the chemical industry,and the pickling process is an indispensable part in the industry.When the steel is pickled,it is extremely prone to excessive corrosion.The addition of corrosion inhibitors is a simple and effective method of reducing corrosion.Natural products as corrosion inhibitors and no general synthetic inhibitors of high cost,environmentally unfriendly and other defects,become a research hotspot.The use of pectin as a natural product as a corrosion inhibitor can effectively slow the corrosion of many metals.Because the molecular weight of pectin affects its own performance,it is necessary to find a simple,rapid,environmentally friendly and effective method for the treatment of pectin.And to study the relationship between the molecular weight of pectin and its inhibition performance.Therefore,in this article subcritical water treatment is used of apple pectin to obtain different molecular weight pectin.After that,the inhibition performance of apple pectins with different molecular weights were evaluated by weight loss method and electrochemical method?potential polarization curve method and AC impedance method?as corrosion inhibitors of 45^#carbon steel in 1 mol/L hydrochloric acid.Corrosion Inhibition while low concentrations of pectin and iodide complex was evaluated and studied the mechanism of iodide ion complex.The results show:?1?By controlling the temperature and time of subcritical water treatment of apple pectin,apple pectins with different molecular weights were successfully obtained.The results show that:the molecular weight decreases significantly as the treatment temperature increases and the processing time becomes longer,and a trimodal molecular weight distribution becomes a single-peak distribution,the molecular weight decreased to 8.43 kDa 246.06 kDa;the treated apple pectin,galacturonic acid content increased with increasing treatment temperature and time increased,increased from 79.12%to 89.04%,and while the degree of esterification contrary,with increasing treatment temperature and time is reduced,decreased to 51.93%from the 66.85%;by characterization of the treated pectin and the infrared spectra of the precipitates produced in the process,apple pectin was proved to contain a large number of polar groups,and apple pectin treated group before and after the large change does not occur substantially,and illustrates the link between the precipitation process and the pectin produced.?2?Four molecular weight segments were selected,including crude apple pectin?Y?,apple pectin(T₁₁₅)at 115°C for 1 h,apple pectin(T₁₂₁)at 121°C for 1 h,and apple pectin(T₁₂₇)at 127°C for 1 h was evaluated for its corrosion inhibition performance by weight loss and electrochemical methods,and the results shows that:the inhibition efficiency of four apple pectin corrosion inhibitors increases with increasing concentrations over the temperature range studied;with the decrease of the molecular weight,the corrosion inhibition efficiency showed an upward trend at 25°C,and the order was in accordance with:Y<T₁₁₅<T₁₂₁<T₁₂₇,and at 30 and 40°C,the inhibition efficiency of four apple pectin corrosion inhibitors is approximately equal;at low concentrations,the corrosion inhibition performance of Y increases with increasing temperature,whereas the low molecular weight pectin decreases first and then rises within the temperature range studied;however,in the range of temperature under study,four kinds of pectin inhibitors all reached a corrosion inhibition efficiency of90%or more at the maximum added amount,indicating that all four pectin inhibitors are suitable for the temperature range studied;through the measurement of the polarization curve,four pectin inhibitors belong to the mixed corrosion inhibitors that mainly suppress the cathode;adsorption model fitting,adsorption kinetics and adsorption thermodynamics of the four pectin inhibitors showed that the adsorption processes of the four pectin inhibitors on the surface of carbon steel were all based on physical adsorption,and all belong to spontaneous adsorption.?3?The corrosion inhibition effect of four pairs of molecular weight apple pectin and iodide ion was evaluated.The results showed that:addition of iodide ions enhances the inhibition efficiency of four kinds of pectin inhibitors;when 0.5 g/L I^-was added,the corrosion inhibition efficiency of T₁₁₅15 apple pectin increased from 23.6%to 62.9%when the corrosion temperature was 40°C and the addition amount was 0.1 g/L;through the study of the mechanism of iodide ion recombination,the corrosion mechanism and corrosion inhibition mechanism are described.