Oxidation–complexation leaching and kinetic study of rhodium from spent homogeneous catalysts
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摘要: 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H2O2将均相铑膦络合物中的Rh+氧化成Rh3+，减少有机配体对Rh的束缚；同时Rh3+与Cl–络合形成水溶性的RhCl63–进入溶液中。研究了蒸馏温度、Cl–浓度、H2O2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、H2O2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：H2O2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、H2O2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。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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Key words:
- rhodium /
- spent homogeneous catalysts /
- distillation /
- response surface method /
- kinetics
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图 1 废铑均相催化剂的回收工艺流程图
Figure 1. Schematic of the recovery process of spent Rh homogeneous catalysts
图 3 红外分析光谱.（a）废均相催化剂；（b）蒸馏产物
Figure 3. Infrared absorption spectrum recorded: (a) spent RCHC; (b) distillate
图 4 240~320 ℃下蒸馏产物的体积及Rh浓度
Figure 4. Volume of distillate and concentration of Rh at temperatures ranging from 240–320 ℃
图 5 氯离子浓度(a)、双氧水用量(b)、反应时间(c)、H+浓度(d)对Rh浸出率的影响
Figure 5. Effects of Cl– concentration (a), H2O2 dosage (b), leaching time (c), and H+ concentration (d) on Rh leaching efficiency
图 6 不同因素相互作用对Rh浸出率影响的三维响应图. (a) C, time=4 h; (b) B, c(Cl–) = 5 mol∙L–1; (c) A, H2O2用量为30%
Figure 6. Response surface plots for the interaction effects on the Rh leaching rate: (a) C, time = 4 h; (b) (b) B, c(Cl–) = 5 mol∙L–1; (c) A, H2O2 dosage of 30%
图 7 废均相催化剂氧化浸出Rh的反应示意图
Figure 7. Diagram of oxidation leaching of Rh using spent homogeneous catalysts
图 8 不同浓度的RhCl63–溶液的紫外吸收光谱
Figure 8. Ultraviolet absorption spectra of RhCl63− solution at different concentrations
图 10 40~90 ℃反应条件下Rh氧化浸出的Arrhenius图
Figure 10. Arrhenius plot for oxidation leaching of Rh at temperatures of 40–90 ℃
表 1 Rh氧化浸出回归方程的方差分析
Table 1. ANOVA results of the reduced quadratic model for the Rh leaching efficiency
Source Sum of squares Mean square F value p-value Prob>F Model 10550.87 1172.32 12.38 0.0003 A 3690.05 3690.05 38.97 < 0.0001 B 2460.03 2460.03 25.98 0.0005 C 341.94 341.94 3.61 0.0866 AB 5.41 5.41 0.057 0.8159 AC 484.85 484.85 5.12 0.0471 BC 307.27 307.27 3.25 0.1018 A2 2254.83 2254.83 23.82 0.0006 B2 410.16 410.16 4.33 0.0641 C2 1121.33 1121.33 11.84 0.0063 Residual 946.80 94.68 — — Lack of fit 941.00 188.20 162.32 < 0.0001 Pure error 5.80 1.16 — — Cor total 11497.66 — — — 
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表 2 响应曲面模型的相关性分析
Table 2. Correlation analysis of response surface method
Category Value Category Value Standard deviation 9.73 R2 0.9177 Mean 63.47 Radj2 0.8435 Coefficient of fariance 15.33 Pred R2 0.3791 PRESS 7139.13 Adeq precision 10.702
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表 3 不同温度下Rh氧化络合浸出动力学参数
Table 3. Kinetic parameters of the chemical reaction control model for Rh leaching at different temperatures
T/℃ k R2 45 0.00146 0.9818 60 0.0014 0.9864 75 0.00467 0.9821 90 0.00762 0.9663
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