Abstract
Spent hydroprocessing catalyst, an environmentally hazardous waste generated in petroleum refining industry, can be used as raw materials for metal recovery in order to meet the circular economic requirements of reducing, reusing and recycling in China. Al in spent hydroprocessing catalyst is usually recovered as low value products because it is cheap. This research investigated the preparation of pseudo-boehmite (AlOOH) from the spent hydroprocessing catalyst to achieve Al recycling with high value-added product.
The purified leaching solution of spent hydroprocessing catalyst was aluminium nitrate solution (Al(NO3)3) with impurity concentration less than 0.1 %. Three different mixing procedures of the reagents were compared, i.e., injection of alkali solution into Al(NO3)3 solution (B→A), injection of Al(NO3)3 solution into alkali solution (A→B) and double jet. The B→A procedure led to amorphous aluminum trihydroxide (Al(OH)3) precipitate, which was not the desired product that should be avoided. AlOOH was produced in the the A→B procedure with both ammonia (NH3·H2O) at 50, 70 and 80 °C and ammonium carbonate ((NH4)2CO3) at 70 °C. In order to explore whether AlOOH was the more likely generated phase at high pH value in the A→B procedure, interactions between NH3·H2O solution and crystal surface with the biggest area of both Al(OH)3 and AlOOH were investigated using molecular simulation. The binding energy of {0 0 1} surface of Al(OH)3 was 892.76 kcal/mol, much smaller than that of AlOOH {0 2 0}'s 1,652.79 kcal/mol, which proved that the surface of AlOOH had stronger interaction with NH3·H2O solution. Then the formation of AlOOH phase was much easier than that of Al(OH)3. The double jet procedure led to AlOOH keeping pH value about 7 at 70 °C. Products synthesized by (NH4)2CO3 had larger pore sizes than the ones by NH3·H2O after calcination, not only in A→B procedure, but also in double jet at 70 °C.
