Microwave-Assisted Hydrodistillation of Hop (Humulus lupulus L.) Terpenes: A Pilot-Scale Study

Interest in essential oils has consistently increased in recent years. Essential oils have a large variety of applications in multiple fields, including in the food, cosmetics and pharmaceutical industries. The volatile fraction (VF) in hops (Humulus lupulus L.) fits within this domain as it is primarily used in the brewery industry for the aromatization of beer, and is responsible for the floral and fruity tones. This work aims to design an optimized extraction protocol of the VF from hops, using microwaves. Microwave-assisted hydrodistillation (MAHD) has been developed to reduce energy and time consumption in lab-scale reactors up to industrial-scale systems. Hops are principally available in three forms, according to a brewery’s applications: (i) fresh (FH); (ii) dried (DH) and (iii) pelletized (PH). In this work, all three forms have therefore been studied and the recovered volatiles characterized by means of GC-MS. The optimized lab-scale MAHD protocol gave the best extraction yield of 20.5 mL_VF/kg_{dry matrix} for FH. This value underwent a slight contraction when working at the highest matrix amount (3 kg), with 17.3 mL_VF/kg_{dry matrix} being achieved. Further tests were then performed in a pilot reactor that is able to process 30 kg of material. In this case, high yield increases were observed for PH and DH; quadruple and double the lab-scale yields, respectively. In addition, this industrial-scale system also provided marked energy savings, practically halving the absorbed kJ/mL_VF.

Determination of microplastic content in seafood: An integrated approach combined with the determination of elemental contaminants

A method for the determination of microplastic (MP) content in seafood is proposed based on the selective digestion of seafood without the degradation of MP. A simple approach was developed using diluted acid with microwave-assisted wet digestion. The following parameters were evaluated: nitric acid concentration (0.5 to 14.4 mol L^-1), digestion temperature (180 to 220 °C), irradiation program holding time (10 to 30 min), MP particle size (0.3 to 5 mm), and the seafood mass (0.5 to 2 g). To develop a reliable method for the determination of MP amount, up to 2 g of an in natura seafood sample were spiked with a known amount of MP (100 mg of mixed MP). Suitable conditions were obtained using 1 mol L^-1 HNO₃ at 200 °C (10 min holding time). Digests were filtered and the plastic content was gravimetrically determined. The heating program was 20 min, which represents a significant reduction in the time normally reported in the literature for MP analysis (from few hours up to 3 days). The proposed method allowed gravimetric determination of eight plastic types (polyethylene terephthalate, polystyrene, expanded polystyrene, polypropylene, high and low density polyethylene, polycarbonate and polyvinyl chloride) with particle size ≥0.3 mm. Up to 2 g of an in natura seafood sample (shark species, acoupa weakfish, tuna fish, trahira, and pink shrimp) were efficiently digested, which opened the possibility of using the proposed digestion method for determining elemental contaminants (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, La, Mg, Mn, Mo, Ni, Pb, and Zn). Thus, as the main feature of the proposed digestion method is the possibility of determining MP and elemental contaminants using the same digestion protocol, saves time and reagents and provides accurate and precise information about different classes of marine pollutants (MP and elemental contaminants).

Economic and Technical Feasibility of Betanin and Pectin Extraction from Opuntia ficus-indica Peel via Microwave-Assisted Hydrodiffusion

Investigating the feasibility of betanin and pectin extraction from Opuntia ficus-indica peel via microwave-assisted hydrodiffusion and gravity, this study identifies selected important economic and technical aspects associated with this innovative production route starting from prickly pear fruit discards. Which benefits would be derived from this process? Would production be limited to Opuntia-growing countries or, likewise to what happens with dried lemon peel chiefly imported from Argentina, would production take place abroad also? Can distributed manufacturing based on clean extraction technology compete with centralized production using conventional chemical processes?

Sonochemical preparation of alumina-spheres loaded with Pd nanoparticles for 2-butyne-1,4-diol semi-hydrogenation in a continuous flow microwave reactor

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 H₂ (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.

A novel protocol for microwave-assisted alkyne semi-hydrogenation under heterogeneous catalysis in a continuous flow reactor is reported herein.

Controlling the Degree of Esterification of Citrus Pectin for Demanding Applications by Selection of the Source

Analyzed by a quantitative method based on diffuse reflectance infrared Fourier transform spectroscopy, pectins extracted from different regions (outer skin, peel, and waste) of citrus fruits (red orange, lemon, and grapefruit) via microwave-assisted hydrodiffusion show significant variations. All polymers obtained are low-methoxyl pectins, with high contents in galacturonic acid regions. The degree of esterification (DE) of pectin extracted from different regions increases in the order waste < peel < outer skin for red orange, inverting for lemon. Thus, the pectins with the lowest DE are those extracted from red orange waste and lemon outer skin (∼25%). These findings open the route to nutraceutical- and pharmaceutical-grade pectins from citrus, in which the source fruit and its regions may be chosen, according to the desired DE.

Heterogeneous Phase Microwave-Assisted Reactions under CO₂ or CO Pressure

The present review deals with the recent achievements and impressive potential applications of microwave (MW) heating to promote heterogeneous reactions under gas pressure. The high versatility of the latest generation of professional reactors combines extreme reaction conditions with safer and more efficient protocols. The double aims of this survey are to provide a panoramic snapshot of MW-assisted organic reactions with gaseous reagents, in particular CO and CO₂, and outline future applications. Stubborn and time-consuming carbonylation-like heterogeneous reactions, which have not yet been studied under dielectric heating, may well find an outstanding ally in the present protocol.

Fast multigram scale microwave-assisted synthesis of vitamin E and C10-, C15-analogues under vacuum

A novel protocol for the microwave-assisted synthesis of (all-rac)-α-tocopherol, including its C₁₀- and C₁₅-analogues, is reported.

From lignocellulosic biomass to lactic- and glycolic-acid oligomers: a gram-scale microwave-assisted protocol

The conversion of lignocellulosic biomass into platform chemicals is the key step in the valorization of agricultural waste. Of the biomass-derived platform chemicals currently produced, lactic acid plays a particularly pivotal role in modern biorefineries as it is a versatile commodity chemical and building block for the synthesis of biodegradable polymers. Microwave-assisted processes that furnish lactic acid avoid harsh depolymerization conditions while cutting down reaction time and energy consumption. We herein report a flash catalytic conversion (2 min) of lignocellulosic biomass into lactic and glycolic acids under microwave irradiation. The batch procedure was successfully adapted to a microwave-assisted flow process (35 mL min(-1) ), with the aim of designing a scalable process with higher productivity. The C2 and C4 units recovered from the depolymerization were directly used as the starting material for a solvent and catalyst-free microwave-assisted polycondensation that afforded oligomers in good yields.

Efficient H2O2/CH3COOH oxidative desulfurization/denitrification of liquid fuels in sonochemical flow-reactors

The oxidative desulfurization/denitrification of liquid fuels has been widely investigated as an alternative or complement to common catalytic hydrorefining. In this process, all oxidation reactions occur in the heterogeneous phase (the oil and the polar phase containing the oxidant) and therefore the optimization of mass and heat transfer is of crucial importance to enhancing the oxidation rate. This goal can be achieved by performing the reaction in suitable ultrasound (US) reactors. In fact, flow and loop US reactors stand out above classic batch US reactors thanks to their greater efficiency and flexibility as well as lower energy consumption. This paper describes an efficient sonochemical oxidation with H2O2/CH3COOH at flow rates ranging from 60 to 800 ml/min of both a model compound, dibenzotiophene (DBT), and of a mild hydro-treated diesel feedstock. Four different commercially available US loop reactors (single and multi-probe) were tested, two of which were developed in the authors' laboratory. Full DBT oxidation and efficient diesel feedstock desulfurization/denitrification were observed after the separation of the polar oxidized S/N-containing compounds (S≤5 ppmw, N≤1 ppmw). Our studies confirm that high-throughput US applications benefit greatly from flow-reactors.

Fast TiO2-catalyzed direct amidation of neat carboxylic acids under mild dielectric heating

The development of green protocols for amide bond formation is a major socioeconomic goal for chemical and pharmaceutical industries and an important challenge for academic research.

One-pot sequential synthesis of isocyanates and urea derivatives via a microwave-assisted Staudinger-aza-Wittig reaction

A fast and efficient protocol for the synthesis of N,N'-disubstituted urea derivatives from alkyl halides and primary or secondary amines has been developed. The synthetic pathway combines nucleophilic substitutions and a Staudinger–aza-Wittig reaction in the presence of polymer-bound diphenylphosphine under 14 bar of CO₂ pressure and has been performed in a one-pot two-step process. The protocol has been optimized under microwave irradiation and the scale-up experiment has been conducted under conventional conditions in a Parr reactor. The final compounds were isolated after simple filtration in almost quantitative overall yields which makes this procedure facile and rapid to execute.

Enabling technologies for the rapid dechlorination of polychloroarenes and PCBs

Dielectric heating and acoustic cavitation (ultrasound or high-performance disperser) may all dramatically enhance conversion rates and yields in heterogeneous metal-assisted organic reactions even when low reagent excesses are used. These so called "enabling technologies" bring with them process intensification, safer protocols, cost reduction and energy savings. We herein describe a series of rapid polychlorinated aromatic and PCBs dechlorinations (15min) carried out in a moderate excess of metallic sodium and using non-conventional techniques. We compared the results with those obtained for reactions carried out under conventional heating and with those performed with less reactive metals such as magnesium and zinc. In this comparison, high-intensity ultrasound stands out as the technique of choice.

Solvent-free chemoselective oxidation of thioethers and thiophenes by mechanical milling

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)).