Processamento de catalisadores gastos de unidade de hidrodessulfurização profunda (ultra-deep HDS)

PROCESSING OF SPENT ULTRA-DEEP HYDRODESULFURIZATION CATALYSTS. This work discusses the recycling of spent NiMo/Al2O3 catalysts from ultra-deep hydrodesulfurization (HDS) units. They contain a refractory coke and fouling elements from the processed feedstocks. Samples were preoxidized (600 ºC) for 12 h using a very slow heating rate to eliminate coke and volatiles. Experiments were performed in the presence of HF + H2O2 mixtures under stirring at 25-60oC for 1-4 h. The amount of insoluble matter was the lowest (&lt; 1 wt.% of the initial mass) after leaching for 2 h at 60oC using an excess of 50 vol.% HF and 20 vol.% H2O2. Leached molybdenum and vanadium were extracted together with Alamine 304 (tri-dodecylamine) in n-heptane at pH below 2. Aluminum and iron were precipitated from the raffinate as Na3AℓF6 (+ Na3FeF6) by adjusting pH at ~4 using 6 mol L-1 NaOH. Nickel was either recovered by solvent extraction using D2EHPA (bis-(2-ethylhexyl)phosphoric acid) in n-heptane at pH 6 or precipitated at pH 8 using 6 mol L-1 NaOH. The first method proved better as less contaminants were present. After slow evaporation of the final aqueous solution, a mixture of Na2SiF6 and NaF was recovered. Fluoride losses were very low (~0.10 wt.%).废超深度加氢脱硫催化剂的处理 本研究探讨了超深度加氢脱硫（ultra-deep hydrodesulfurization, HDS）装置废弃NiMo/Al₂O₃催化剂的回收利用工艺。此类废弃催化剂含有源自加工原料的顽固性积炭与结垢杂质元素。实验前，以极慢升温速率将样品置于600℃下预氧化12小时，以去除积炭与挥发性组分。随后在25~60℃、搅拌条件下，采用HF与H₂O₂混合体系进行浸出实验，反应时长1~4小时。当采用过量50%体积分数HF与20%体积分数H₂O₂混合液、在60℃下浸出2小时后，体系内不溶物含量降至最低，仅为初始物料质量的1%（质量分数）以下。浸出得到的钼与钒可在pH<2的条件下，以正庚烷为稀释剂、采用Alamine 304（三十二胺）作为萃取剂进行共萃取。通过使用6 mol·L⁻¹ NaOH将萃余液pH调至约4，可使铝与铁以Na₃AlF₆（伴生Na₃FeF₆）的形式沉淀析出。镍的回收可采用两种方案：其一为在pH=6条件下，以正庚烷为稀释剂、采用D2EHPA（二(2-乙基己基)磷酸）作为萃取剂进行溶剂萃取回收；其二为使用6 mol·L⁻¹ NaOH将pH调至8，使镍以沉淀形式回收。实验结果表明，第一种方案更优，所得产物的杂质含量更低。将最终水溶液缓慢蒸发后，可回收得到Na₂SiF₆与NaF的混合产物，氟化物的损耗率极低，仅约0.10%（质量分数）。