Investigation On Modification Of Kraft Lignin And Its Corrosion Inhibition Performance

At present,the rust removal of iron and steel in industrial production is usually carried out by the way of inorganic acid and acid washing.In this process,the strong reactivity of inorganic acid is easy to cause the reaction between the acid and iron in the steel matrix while derusting on the surface of the steel,resulting in excessive pickling and other problems.Pickling corrosion inhibitor is an effective additive to effectively reduce the occurrence of corrosion phenomena in the steel pickling process.High-performance green bio-based corrosion inhibitors have attracted widespread attention due to their non-toxic and harmless,environmentally friendly and green characteristics.Lignin is the second largest natural polymer substance after cellulose.It is considered as an excellent biomass chemical raw material as a by-product of the papermaking industry because of its renewable,biodegradable and non-toxic properties.At present,the lignin of the paper industry is mainly processed by combustion,and has not been developed and applied with high added valuestudy focuses on the lignin using fields and steel corrosion problems in processing and manufacturing industry in our country,the current situation of exploitation of pulp and paper industrial lignin and lignin features of itself,using chemical method in the pulp and paper industry production dominated by sulfate lignin modification and functionalization,and it is used as metal rust removal in the process of corrosion inhibitor in hydrochloric acid solution,explore the structure-activity relationship between lignin modification and corrosion inhibition performance,and use modern analysis Correlative research on corrosion inhibition efficiency and corrosion inhibition technology is carried out to clarify the corrosion inhibition performance and mechanism of sulfate lignin-based inhibitors,and provide technical guidance for the functional modification of lignin and its application in the field of steel corrosion inhibition And theoretical support.In this study,sulfate lignin was used as a raw material,and methacryloyloxyethyltrimethylammonium chloride(DMC),acrylic acid(AA),and acrylamide(AM)were used as functional monomers,and potassium persulfate was used as an initiator to synthesize lignin high polymer lignin-DMC,lignin-AA and lignin-AM.At the same time,2,3 epoxypropyl trimethylammonium chloride(EPTAC)was grafted to modify sulfate lignin under alkaline conditions.The structure and properties of lignin and lignin derivatives were characterized by charge titration,TGA,FTIR and XPS.The four lignin derivatives prepared were used as hydrochloric acid pickling corrosion inhibitors.Static weight loss method,electrochemical method,environmental scanning electron microscope(SEM),atomic force microscope(AFM)morphology analysis,contact angle,etc.The methods were used to study the corrosion inhibition performance of lignin derivatives on carbon steel in a 1 mol/L hydrochloric acid solution.The effects of the concentration and temperature of four lignin derivatives on the corrosion inhibition effects were discussed in detail.The chemical and molecular dynamics have investigated the corrosion inhibition mechanism of lignin derivatives on carbon steel.The results showed that lignin-DMC,lignin-AA,lignin-AM and lignin-EPTAC were successfully prepared.When four kinds of lignin derivatives were used as hydrochloric acid corrosion inhibitors,the corresponding corrosion inhibition rates under the conditions of their respective optimal concentrations follow:lignin-acrylamide(300 mg/L:IE%=50.43%)<lignin-acrylic acid(150 mg/L:IE%=82.18%)<Lignin-DMC(75 mg/L:IE%=87.65%)<Lignin-EPTAC(100 mg/L:IE%=97.80%).Cationic lignin derivatives have better corrosion inhibition effects.The study of corrosion inhibition mechanism of lignin derivatives shown that four kinds of lignin derivatives could form protective film by physical and chemical adsorption on the surface of carbon steel,which hindered the corrosion reaction on the surface of carbon steel.The adsorption of sulfate lignin-based inhibitor molecules on the surface of carbon steel was consistent with Langmuir adsorption.Among the four types of corrosion inhibitors,lignin-DMC and lignin-EPTAC were mixed corrosion inhibitors mainly used to suppress the cathode,while lignin-AA and lignin-AM were mixed corrosion inhibitors mainly used to suppress the anode.After the lignin corrosion inhibitor was used,the surface roughness of the carbon steel was reduced,the uniformity was improved,and the surface hydrophobicity was increased.Quantum chemistry and molecular dynamics(MD)simulation data shown that the four lignin derivatives all had a certain adsorption on the surface of carbon steel and had high reactivity.The adsorption mechanism of the lignin corrosion inhibitor was a conjugated system mainly composed of benzene rings,which formed a chemical bond on the surface of carbon steel through conjugation to generate chemical adsorption.At the same time,positively charged quaternary ammonium salts or lignin derivatives under acidic conditions,the positively charged onium ions formed with H~+were adsorbed on the surface of carbon steel,and the negative ions on the surface of carbon steel form physical adsorption through electrostatic interaction.The adsorption of corrosion inhibitor molecules on the surface of carbon steel was more inclined to plane adsorption.