formic acid, (o) lactic acid, (Δ) propylene glycol, ( □ ) ethylene glycol, (+) methanol, and (×) CO 2 . Reprinted with permission from ref 13.

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The demand for hydrogen peroxide is booming since it is considered as one of the most environmentally friendly and versatile chemical oxidants available and has a wide range of applications. The annual market, close to 3000 kt per year being produced via the auto-oxidation process (with 2-ethyl anthraquinone (traditional) or amyl anthraquinone for mega-plants), is mostly supplied by the company Solvay (30%), followed by Evonik (20%) and Arkema (13%). Nevertheless, the dream of a direct synthesis process is close to a century old and it has gained momentum in research efforts during the last decade with more than 15 groups active in the world. In this review, we focus the discussion on the targets, e.g. plant tonnage, the reactors and the most feasible industrial operational conditions, based on our experience and point of view using the chemical engineering tools available. Thus, direct synthesis can be competitive when on-site production is required and capacities less than 10 kt per year are He has led and participated in 3 EU, 6 national/regional projects and 10+ SME contracts and has published 30+ research papers. Teresa MorenoTeresa Moreno obtained her degree in Chemical Engineering from Complutense University (Madrid, Spain) and later completed her PhD in Chemical Engineering at the University of Valladolid (Spain, 2011) studying the catalytic direct synthesis of hydrogen peroxide in supercritical CO 2 and the online determination of the product using Raman spectroscopy. She is currently a Research Scientist in the Industrial Bioactive Technologies Group at Callaghan Innovation (New Zealand) working on the development of processes for adding value to natural materials toward high value products and applications, including the development of sustainable technologies using supercritical fluids. View Article OnlineView Journal | View Issue and semi-continuous modes of operation. However, at the moment, demonstrations of continuous operations as well as carefully determined kinetics are needed in order to scale up the process. Finally, operational conditions, including the catalyst composition (active metal, oxidation state and support), promoters (halides and acids-pH-isoelectric point), solvents, pressure and temperature need to be carefully analysed. In our opinion, as we try to show here, H 2 O 2 direct synthesis is a competitive process and is ready for larger scale demonstration. Also, more than a hundred patents within the area support this claim, although the barriers of technology demonstration and further licensing are still pending.

The antioxidant activity, in terms of radical scavenging capacity, of altogether 15 different lignans was measured by monitoring the scavenging of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). The effect of differences in skeletal arrangement or the degree of oxidation of the lignans was investigated in a structure-activity relationship study. A large variety in the radical scavenging capacities of the different lignans was observed and related to some structural features. Lignans with catechol (3,4-dihydroxyphenyl) moieties exhibited the highest radical scavenging capacity, while the corresponding guaiacyl (3-methoxy-4-hydroxyphenyl) lignans showed a slightly weaker scavenging capacity. In addition, the butanediol structure was found to enhance the activity, whereas a higher degree of oxidation at the benzylic positions decreased the activity. Additionally, the readily available lignans (-)-secoisolariciresinol, a mixture of hydroxymatairesinol epimers and (-)-matairesinol were studied in more detail, including kinetic measurements and identification of oxidation products in the reactions with DPPH and ABAP (2,2-azobis(2-methylpropionamidine) dihydrochloride. The identification of reaction products, by GC-MS, HPLC-MS and NMR spectroscopy, showed that dimerisation of the two aromatic moieties was the major radical termination reaction. Also, the formation of adducts was a predominant reaction in the experiments with ABAP. The kinetic data obtained from the reactions between the lignans and DPPH indicated a complex reaction mechanism.

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