高含钒粗TiCl_(4)脂肪酸除钒试剂选择及除钒机制探索

Selection of Vanadium Removal Reagents Using Fatty Acid and Their Mechanisms

为了开发高含钒(三氯氧钒含量0.4%~0.8%(质量分数))粗TiCl_(4)精制除钒工艺,研究了不同脂肪酸对高含钒粗TiCl_(4)除钒效率、除钒产生残渣黏壁及沉降等性能的影响。研究结果表明,不饱和脂肪酸除钒速率要大于饱和脂肪酸,且除钒速率随着不饱和度的增加而增大。但是饱和脂肪酸除钒过程产生的除钒残渣黏壁程度较不饱和脂肪酸除钒残渣轻,同时产生除钒残渣的沉降速率也优于不饱和脂肪酸。油酸质量占比为65%~75%的油酸-壬酸混合脂肪酸是较佳的除钒试剂,它可在1 min内将粗TiCl_(4)的三氯氧钒含量由0.63%降至3×10^(-6)以下,且除钒产生的残渣黏壁较轻,残渣沉降速率也满足后续TiCl_(4)蒸发工序的要求。基于以上结果,进一步阐述了有机物除钒机制:有机物裂解产生还原中间相,中间相进一步还原钒形成低价钒化沉淀物,且有机物裂解等本身特性决定了除钒的除钒效率、除钒残渣黏壁以及沉降分离等效果。

In order to develop a process for removing high vanadium(V)-containing impurities from the coarse titanium tetrachloride(TiCl_(4))(containing 0.4%~0.8%vanadium oxytrichloride(VOCl_(3)))with high efficiency and scaling-and blockage-free,systematic studies were conducted.First,the effects of unsaturated fatty acids(e.g.C17 and C18)and saturated fatty acids(e.g.C17 and XX)on V removal rate and their performances of adhesion and sedimentation of residues produced during the removal process were studied.The results showed that the V removal rates by the unsaturated fatty acids were much higher than those by the saturated fatty acids,and the residues produced from the removal process using the saturated fatty acids had a lower degree of adhesion and greater sedimentation rates than those using the unsaturated fatty acids.This might due to the fatty acids cracking reaction happened in TiCl_(4)solution,and the C=C bond was easier to be cracked than the C-C bond at a given temperature so that the carbonaceous intermediates with strong reducibility was produced rapidly.Therefore,unsaturated fatty acids had a higher vanadium removal reaction rate than saturated fatty acids.Secondly,the effects of four kinds of unsaturated fatty acids with different carbon chain lengths(myristoleic acid(C14),palmitoleic acid(C17),oleic acid(C18)and erucic acid(C22))on V removal rates and their performances of adhesion and sedimentation of residues produced during high V removal process were investigated.The results showed that the V removal rates by four unsaturated fatty acids had little effect,and the different performances of the adhesion and sedimentation of residues were also close.Thirdly,the V removal rates by three kinds of unsaturated fatty acids with different degrees of fatty acids unsaturation(oleic acid(one C=C),linoleic acid(two C=C),linolenic acid(three C=C))and the performances of adhesion and sedimentation of residues were also compared,and the results showed that the V removal rate increased with the unsaturation degree of fatty acids,and the residues produced from the V removal process of unsaturated fatty acids had higher degrees of adhesion and slower sedimentation rates with a higher unsaturation degree of fatty acid.The unsaturated fatty acids were in a valence bond unsaturated state,which was very easy to attract Cl^(-)in the solution to have a negative charge.As the same charges repelled each other,residues produced with negative charges were not easy to be settled.With the increases of unsaturation degrees,the repulsions of the fatty acids were greater,and the sedimentation of residues produced were slower with the repulsion of the same charges,so the sedimentation effect was worse.As unsaturated fatty acids were in the unsaturated state of valence bond,the sizes of the molecular and the viscosities were greater after attracting Cl^(-),and the sizes and viscosities increased if the unsaturated fatty acids absorbed more Cl^(-),so the black residue was easier to adhere on the bottom of the bottle.Finally,based on the above studies,the experiments using mixed reagents of unsaturated fatty acid(oleic acid)and saturated fatty acid(nonanoic acid)were also performed to study the effects of different ratios of fatty acids on V removal rates as well as the performances of adhesion and sedimentation of residues.The results showed that the V removal rates increased with the contents of unsaturated fatty acids.When the content of oleic acid in the mixed reagent was greater than 60%,the vanadium removal rate was high,which could reduce the VOCl_(3)content of the coarse TiCl_(4)solution to below 3×10^(-6)within 1 minute.With the increase of unsaturated oleic acid content in the mixture,the performance of adhesion of residues was more severe.If the content of oleic acid in the mixed reagent was less than 70%,the adhesion by the residues was relatively light,while the adhesion of residues deteriorated rapidly when more than 80%mass fraction of oleic acid and pelargonic acid was used.With the increase of unsaturated components,the sedimentation rate of the residue decreased,but the solid-liquid equilibrium could be reached within 5 h in all cases.Therefore,the mixed fatty acid with 65%~75%mass fraction of oleic acid and pelargonic acid was an optimal reagent for V removal,which could reduce the VOCl^(-)content of coarse TiCl_(4)from 0.63%to below 3×10^(-6)in 1 min.For the residue produced from V removal process,the adhesion of materials was acceptable and the sedimentation rate also met the requirement of the following evaporation process.Based on the above results,the mechanism of V removal was further elaborated:the reducing intermediate phases produced by pyrolysis of organics reduced the V compounds in the coarse TiCl_(4)solution to V-containing residues with lower valence states,and the characteristics of organics(such as pyrolysis performance)determined the V removal rate and the performances of adhesion and sedimentation of residues.