The Process Study Of The Recovery Of Deteriorated Rhodium Catalyst For Olefin Hydroformylation

Currently the major industrial application of hydroformylation is to produce butyl aldehyde with the reaction of propylene, then by the hydrogenation or condensation hydrogenation to produce butyl alcohol and octanol. Octanol is an important intermediate in chemical industry and an important raw material for the synthesis of products such as plastic, medicine and perfumes as well. The catalyst of propylene hydroformylation is rhodium-phosphine complex catalyst HRh(CO)(PPh₃)₃ with triphenylphosphine (TTP) as ligand. Because rhodium is one kind of rare and precious metal, the problem of recovery and recycle must be solved. In this paper, a process including incineration, dissolution, extraction, electrodeposition and purification had been developed for the recovery of rhodium from the deteriorated rhodium catalyst for olefin hydroformylation. The related processing parameters were also investigated in this work.First, under a particular programmed temperature, the mixture containing the deteriorated rhodium catalyst and additive were combusted and ash-fired in muffle furnace. After cooling, the recovered rhodium ash was dissolved in hydrochloric acid solution. The process conditions including the additive type and amount, ashing temperature, dissolving temperature and time, solvent amount were investigated in detail. The results indicated that ashing temperature and dissolving temperature exhibited great influences on the recovery rate of rhodium. The preferable additive was calcium hydroxide and the optimum mass ratio of rhodium catalyst and calcium hydroxide was determined as 1:1. Other conditions included the ashing temperature of 320℃, the dissolving temperature of 35℃, the dissolving time of 8 h and the amount of hydrochloric acid of 6 mL per gram of rhodium ash, corresponding to the recovery rate of 97.14%. Second, the solution of rhodium ash was purified using oxidizing acid and organic solvent. Using tributyl-phosphate (TBP) as organic solvent which was not miscible with water for removing the organic impurities was studied in detail. The process conditions including the extractant amount, HCl concentration, extracting temperature and anti-extraction times were investigated in detail. The preferable volume ratio of extractant and solution of rhodium ash was determined as 1:1 and the optimum acidity was 4 mol/L HCl. Other conditions included the extracting temperature of 25℃and anti-extracted times of once, corresponding to the recovery rate of 91.53%.Last, rhodium was reduced and obtained using 3-electrodes system which consisted of graphite and stainless steel by controlling the cathode potential. The effects of several parameters including acidity, Fe³⁺ amount and electrowinning time of rhodium electrodeposition were investigated. The optimum conditions were 1.5mol/L of HCl concentration, 1:2～1:1 of mass ratio of Fe³⁺ and rhodium, -0.75v of the lowest rhodium electrodeposition potential, 4h of electrowinning time, corresponding to the recovery rate of 88.89%. Finally, the recovered rhodium was purified and used for synthesizing the RhCl₃·3H₂O.