废均相催化剂氧化-络合浸出铑工艺及其动力学

Oxidation–complexation leaching and kinetic study of rhodium from spent homogeneous catalysts

基于Rh在废均相催化剂中的赋存状态,研发出绿色解离Rh-P化学键及Rh的络合浸出新技术,实现了Rh的绿色高效浸出,杜绝了传统废均相催化剂焚烧-碎化-酸浸工艺流程长、污染严重、回收率低等问题.首先通过蒸馏将低熔点有机物去除,然后采用H_(2)O_(2)将均相铑膦络合物中的Rh^(+)氧化成Rh^(3+),减少有机配体对Rh的束缚;同时Rh^(3+)与Cl^(-)络合形成水溶性的RhCl_(6)^(3-)进入溶液中.研究了蒸馏温度、Cl^(-)浓度、H_(2)O_(2)用量、H^(+)浓度、反应时间等对Rh的回收率影响,并采用响应曲面法优化了Cl^(-)浓度、H_(2)O_(2)用量和反应时间等工艺参数.结果表明:各参数对Rh回收率的影响大小为:H_(2)O_(2)用量>Cl^(-)浓度>反应时间,优化的工艺参数为:蒸馏温度260℃、Cl^(-)浓度3.0 mol·L^(-1)、H_(2)O_(2)用量为废均相催化剂的37%(体积分数)、H^(+)浓度1.0 mol·L^(-1)、反应时间4.5 h,Rh的回收率达到98.22%.最后,采用分光光度法研究了Rh的氧化-络合动力学行为,表明该反应的活化能为39.24 kJ·mol^(-1),属于化学反应控速.

Rhodium-containing homogeneous catalysts are the most active catalysts for homogeneous hydrogenation.Spent homogeneous catalysts contain 100-2000 g·t^(-1) of rhodium(Rh)and plenty of hazardous organic components,making them an essential resource of Rh.The recovery of Rh from homogeneous catalysts has excellent economic and environmental benefits.Based on Rh in the spent homogeneous catalysts,a new technology for green dissociation of the Rh-P chemical bond and complexation leaching of Rh was developed,allowing the green and efficient recovery of Rh.Compared with traditional incineration-fragmentation and acid leaching methods,the proposed technology eliminated issues such as long process times,severe environmental pollution,and a low recovery rate of Rh.In this study,first,the low-melting-point organics were removed using distillation.Then,the Rh^(+)in the homogeneous rhodium-phosphine complex was oxidized as Rh^(3+)through H_(2)O_(2),which reduced the binding of organic ligands to Rh.Meanwhile,the RhCl_(6)^(3-)formed by Rh^(3+)and Cl^(-)dissolved into the aqueous solution.The effects of distillation temperature,the concentration of Cl^(-),the dosage of H_(2)O_(2),the concentration of H^(+),and reaction time on the recovery efficiency of Rh were studied.The parameters listed above were optimized using response surface methodology.The results showed that the influence of each parameter on the recovery efficiency of Rh was as follows:H_(2)O_(2) dosage>Cl^(-)concentration>reaction time.The recovery efficiency of Rh reached 98.22%after 4 h of distillation at 260℃,leaching Rh in the mixture solution of 3.0 mol·L^(-1) Cl^(-),37%(volume fraction)of the spent homogeneous catalyst dosage of H_(2)O_(2),1.0 mol·L^(-1) H^(+),and at 90℃for 4.5 h.Finally,the oxidation-complexation kinetic behavior of Rh was studied using spectrophotometry.The activation energy of the leaching reaction was 39.24 kJ·mol^(-1),indicating that the rate-controlling step of this process was a surface chemical reaction.