Selective conversion of methanol toward dimethyl ether over zeolite ZSM-5 loaded with copper recovered from printed circuit boards

In recent years, the short lifecycle of electronic devices combined with the unrelenting advancement in modern technology has made the generation of electronic waste (e-waste) a major environmental problem [1]. One of the most di!used components of electronic equipment are printed circuits boards (PCBs) which usually contain precious metals like Cu, Ni, Fe, Au. Copper is widely used in catalysis, for example, as tuner of aluminosilicates catalytic properties. These materials, especially zeolites, are commonly employed as acid catalysts for methanol-to-olefins (MTO) reaction thanks to their strong acid sites, and the reaction course could be also driven to methanol-to-dimethyl ether (MTD) by decreasing the strength of the acid sites. In this work, copper was tested as tuner of the acidic properties of a common commercial zeolite (ZSM-5) employed in MTO/MTD reactions. Especially, MTD reaction is helpful for the ecological transition since from a sustainable feedstock as methanol (obtainable from biomass or municipal waste [2]) is possible to produce dimethyl ether (DME) which is a great alternative to petrol diesel, thanks to its high cetane number and the absence of direct C-C bonds, which allows to obtain almost zero particle matter (PM) emissions when DME is employed as fuel. [3] Therefore, the first step of this work was aimed at exploring the impact of copper on the catalytic performance of zeolite ZSM-5, employing copper acetate as copper source. The second step was focused on the use of PCBs as copper source. Indeed, PCBs from old and disposed computers were collected, cut into small pieces and lixiviated. Copper was selectively extracted form the lixiviate solution using the ligand LIX-84I, and the zeolite ZSM-5 was impregnated with the obtained copper complex. The obtained final material was able to catalyse the selective conversion of methanol to DME, meanwhile by using ZSM-5 alone as the catalyst the MTO route was the preferential pathway observed.