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Bio-waste valorisation has been one of the hottest research topics worldwide over the last decade. Following the biorefinery concept, the main goals have been the search for inexpensive renewable resources for the production of chemicals, materials and energy, the transformation of bio-waste into useful by-products and the development of new technologies for process intensification to make all these conversions economically profitable. Bio-waste is generally a negative-cost feedstock for the potential production of high value-added chemicals and bioenergy. The present review has the aim of describing existing studies and applications of non-conventional energy sources such as microwaves, ultrasound and ball milling within this field. We have focused our attention on suitable protocols for the conversion of biomass into fine chemicals. Comparisons with classic procedures are a good means with which to highlight the huge advantages and potential scalability of these so-called “enabling technologies”. [ABSTRACT FROM AUTHOR]

A novel protocol for microwave-assisted alkyne semi-hydrogenation under heterogeneous catalysis in a continuous flow reactor is reported herein. This challenging task has been accomplished using a multifaceted strategy which includes the ultrasound-assisted preparation of Pd nanoparticles (average Ø 3.0 ± 0.5 nm) that were synthesized on the μ-metric pores of sintered alumina spheres ( Ø 0.8 mm) and a continuous flow reaction under H 2 (flow rate 7.5 mL min -1 ) in a microwave reactor (counter-pressure 4.5 bar). The semi-hydrogenation of 2-butyne-1,4-diol in ethanol was chosen as a model reaction for the purposes of optimization. The high catalyst efficiency of the process, in spite of the low Pd loading (Pd content 111.15 mg kg -1 from ICP-MS), is due to the pivotal role of ultrasound in generating a regular distribution of Pd nanoparticles across the entire support surface. Ultrasound promotes the nucleation, rather than the growth, of crystalline Pd nanoparticles and does so within a particularly narrow Gaussian size distribution. High conversion (>90.5%) and selectivity to ( Z )-2-butene-1,4-diol (95.20%) have been achieved at an alkyne solution flow rate of 10 mL min -1 . The lead-free, alumina-stabilized Pd catalyst was fully characterized by TEM, HR-TEM, EDX, IR, XRPD and AAS. Highly dispersed Pd nanoparticles have proven themselves to be stable under the reaction conditions employed. The application of the method is subject to the dielectric properties of substrates and solvents, and is therefore hardly applicable to apolar alkynes. Considering the small volume of the reaction chamber, microwave-assisted flow hydrogenation has proven itself to be a safe procedure and one that is suitable for further scaling up to industrial application., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Organosulphur compounds can be easily and selectively oxidized to sulfones using a small excess of Oxone(®) (1.6 eq.) under solventless mechanical milling conditions. This green procedure has been efficiently applied to a series of model compounds and to the desulphurization of medium/high sulphur content paraffins (up to 3000 mg kg(-1)).