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廢均相催化劑氧化?絡合浸出銠工藝及其動力學

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

  • 摘要: 基于Rh在廢均相催化劑中的賦存狀態,研發出綠色解離Rh–P化學鍵及Rh的絡合浸出新技術,實現了Rh的綠色高效浸出,杜絕了傳統廢均相催化劑焚燒–碎化–酸浸工藝流程長、污染嚴重、回收率低等問題。首先通過蒸餾將低熔點有機物去除,然后采用H2O2將均相銠膦絡合物中的Rh+氧化成Rh3+,減少有機配體對Rh的束縛;同時Rh3+與Cl絡合形成水溶性的RhCl63–進入溶液中。研究了蒸餾溫度、Cl濃度、H2O2用量、H+濃度、反應時間等對Rh的回收率影響,并采用響應曲面法優化了Cl濃度、H2O2用量和反應時間等工藝參數。結果表明:各參數對Rh回收率的影響大小為:H2O2用量>Cl濃度>反應時間,優化的工藝參數為:蒸餾溫度260 ℃、Cl濃度3.0 mol?L–1、H2O2用量為廢均相催化劑的37%(體積分數)、H+濃度1.0 mol?L–1、反應時間4.5 h,Rh的回收率達到98.22%。最后,采用分光光度法研究了Rh的氧化–絡合動力學行為,表明該反應的活化能為39.24 kJ?mol–1,屬于化學反應控速。

     

    Abstract: 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 Rh3+ through H2O2, which reduced the binding of organic ligands to Rh. Meanwhile, the RhCl63? formed by Rh3+ and Cl dissolved into the aqueous solution. The effects of distillation temperature, the concentration of Cl, the dosage of H2O2, 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: H2O2 dosage > Cl concentration > reaction time. The recovery efficiency of Rh reached 98.22% after 4 h of distillation at 260 °C, leaching Rh in the mixture solution of 3.0 mol?L–1 Cl, 37% (volume fraction) of the spent homogeneous catalyst dosage of H2O2, 1.0 mol?L–1 H+, and at 90 °C 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.

     

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