Júlio Carlos Afonso

Hydrometallurgical route to recover molybdenum, nickel, cobalt and aluminum from spent hydrotreating catalysts in sulphuric acid medium.

This work describes a hydrometallurgical route for processing spent commercial catalysts (CoMo and NiMo/Al2O3), for recovering the active phase and support components. They were initially pre-oxidized (500 degrees C, 5h) in order to eliminate coke and other volatile species present. Pre-oxidized catalysts were dissolved in H2SO4 (9molL-1) at approximately 90 degrees C, and the remaining residues separated from the solution. Molybdenum was recovered by solvent extraction using tertiary amines. Alamine 304 presented the best performance at pH around 1.8. After this step, cobalt (or nickel) was separated by adding aqueous ammonium oxalate in the above pH. Before aluminum recovery, by adding NaOH to the acid solution, phosphorus (H2PO4-) was removed by passing the liquid through a strong anion exchange column. Final wastes occur as neutral and colorless sodium sulphate solutions and the insoluble solid in the acid leachant. The hydrometallurgical route presented in this work generates less final aqueous wastes, as it is not necessary to use alkaline medium during the metal recovery steps. The metals were isolated in very high yields (>98wt.%).

Niobium sulfides as catalysts for hydrotreating reactions

Abstract Hydrotreating properties of unsupported and supported niobium sulfides are compared to those of molybdenum sulfide catalysts. Niobium catalysts demonstrate higher activities than molybdenum sulfide ones and remarkable selectivity in cracking and isomerisation reactions.

Recovery of platinum from spent catalysts by liquid-liquid extraction in chloride medium.

This work examines a hydrometallurgical route for processing spent commercial catalysts (Pt and PtSnIn/A(2)O(3)) used in Brazilian refineries for recovery of the noble metal with less final wastes generation. Samples were initially pre-oxidized (500 degrees C, 5 h) in order to eliminate coke. The basis of the present route is the partial dissolution of the pre-oxidized catalyst in aqua-regia. Temperature and time necessary to dissolve all platinum were optimized in order to reduce the operation severity and aluminum solubilization. All platinum and 16-18 wt.% of aluminum were dissolved at 75 degrees C in 20-25 min. Separation of platinum from the acidic solution was accomplished by solvent extraction. The best extractant (> 99 wt.%) was Aliquat 336 (a quaternary ammonium salt) in one stage (A/O phase ratio = 1, v/v). Platinum was stripped (> 99.9 wt.%) in one stage (A/O phase ratio = 1, v/v) with aqueous sodium thiosulfate (> or = 0.75 mol L(-1)). Black platinum was obtained from this solution via reduction with magnesium or ascorbic acid.

The chemistry of coke deposits formed on a PtSn catalyst during dehydrogenation of n-alkanes to mono-olefins

Abstract This work presents a detailed study of coke deposition on a PtSn catalyst under industrial conditions. The spent catalyst was submitted to Soxhlet extraction and the “soluble coke” was characterized by means of IR, UV and GC-MS. The catalyst before and after coke extraction was characterized by means of IR, carbon content and temperature-programmed oxidation (TPO). Coke formation on the catalyst involves several processes: (i) successive dehydrogenation/cyclization of alkyl chains (polyene route); (ii) n -alkane oligomerization; (iii) Diels-Alder-type reactions. The structure of insoluble coke is quite different from that of soluble coke: the elimination of the latter one causes disappearance of the low-temperature oxidation zone (TPO). Soluble coke contains dominant proportion of aliphatic groups whereas polyaromatic structures predominate in insoluble coke.

Recovery of platinum, tin and indium from spent catalysts in chloride medium using strong basic anion exchange resins

This work describes a route for platinum recovery from spent commercial Pt and PtSnIn/Al(2)O(3) catalysts using strong basic mesoporous and macroporous anion exchange resins (Cl(-) form). The catalysts were leached with aqua regia (75 °C, 20-25 min). Platinum adsorption was influenced by the presence of other metals which form chlorocomplexes (tin, indium) and also base metals (aluminum). However, it was possible to overcome this fact by a sequential desorption procedure. Aluminum was selectively removed from the resins by elution with 3 mol L(-1) HCl. Platinum was desorbed passing 1 mol L(-1) Na(2)S(2)O(3) (pH 9). Tin was removed by elution with 0.1 mol L(-1) ascorbic acid. Indium was removed using 0.1 mol L(-1) EDTA as eluent. Desorption efficiency exceeded 99% for all metals. Metals were recovered in high yields (>98 wt%).

Catalytic properties of niobium sulphides in the conversion of nitrogen containing molecules

Abstract The catalytic properties of niobium sulphides, i.e. NbS 3 and Nb 1.12 S 2 have been examined in the conversion of nitrogen-containing molecules (n-pentylamine and pyridine), and in the hydrogenation of biphenyl. Compared to MoS 2 , NbS 3 and Nb 1.12 S 2 show higher activities for all these reactions and a peculiar ability to perform CN and CC bond cleavage. The activities for these last reactions have been related to the acid-base properties of niobium compounds. Moreover, the trisulphide is more active than Nb 1.12 S 2 . These differences in activities are discussed in relation to the structural features of both sulphides and the existence in NbS 3 of S 2 2− groups and metal-metal pairing.

Gerenciamento de resíduos laboratoriais: recuperação de elementos e preparo para descarte final

This work shows some laboratory waste management developed in order to recover some elements or to prepare the waste for a correct final disposal. The 25 elements chosen cover basically all chemical behaviors found for the metals in the Periodic Table. The treatments adopted were based on the classical behavior in aqueous solution (wet chemistry) but an important condition for a full success was the previous knowledge of the qualitative composition of the wastes treated. Some general trends were found: the final liquid waste was always saline and normally presented a higher volume than the original waste; most original wastes were acid in nature; steps such as solid-liquid separation, washing, evaporating and calcining were currently performed. This work was also a very good experience in chemistry in solution for students and showed them the need of treating wastes for a better environment.

O inacreditável emprego de produtos químicos perigosos no passado

A method of adjusting a patients undesired hematocrit and/or hemoglobin concentration to a value within a desired range at a predetermined time with an erythropoiesis stimulating agent (ESA) regimen includes obtaining patient parameters required for input into a model for predicting the patients hematocrit and/or hemoglobin concentration at a predetermined time with a selected ESA administration regimen, and employing the patient parameters and an initially selected EPO administration regimen in the model to predict the patients hematocrit and/or hemoglobin concentration at the predetermined time with the initially selected ESA administration regimen. Optionally, if the patients hematocrit and/or hemoglobin concentration is not predicted by the model to be in the desired range at the predetermined time, the method includes employing the model with one or more different ESA administration regimens until the model predicts that the patients hematocrit and/or hemoglobin concentration will be in the desired range at the predetermined time. The method then includes administering ESA to the patient with an ESA administration regimen predicted to adjust the patients hematocrit and/or hemoglobin concentration to the desired range at the predetermined time. The method can be implemented in a computer system for adjusting a patients undesired hematocrit and/or hemoglobin concentration to a desired range at a predetermined time with an erythropoiesis stimulating agent (ESA) regimen.

Importance of pretreatment on regeneration of a Pt-Sn/Al2O3 catalyst

Abstract The influence of pretreatment (H2, N2, soxhlet extraction or none) on the generation of a Pt-Sn/Al2O3 catalyst was studied by means of evaluation of textural properties (surface area, pore volume and pore radius distribution), amount of carbon and chlorine present and catalytic activity on n-heptane dehydrogenation of the regenerated samples. After pretreatment, the catalysts were also characterized by TPR, amount of soluble coke removed and tested with cyclohexane dehydrogenation. The chemical composition of soluble coke before and after pretreatment was determined by GC-MS. Pretreatment is an important procedure for the regeneration process and with H2, regeneration was enhanced. The results can be interpreted by physical meaning due to the partial recovery of textural properties, and by chemical effects due to the reduction (at least partially) of the metallic phase, incipient coke gasification and desorption-cracking processes of coke fragments.

Recovery of manganese and zinc from spent Zn-C and alkaline batteries in acidic medium

The anode and the internal paste of spent Zn-C and alkaline batteries were leached with 2 mol L-1 H2SO4 at 80 oC for 2 h. Solid/liquid ratio was 1/10 (g mL-1). The leachate was treated with Na2S in order to precipitate Hg, Cd and Pb. Zn was quantitatively isolated at pH 1,5-2 by adding Na2S. Mn can be precipitated at pH close to 7. Na2S may be replaced by oxalic acid. Zn precipitated at pH around 0, whereas Mn was quantitatively recovered at pH > 4. Acidity control is a critical parameter. Na2SO4 and carbon are the end products.