M. C. Depew

Free radical induced oxidation of alkoxyphenols : some insights into the processes of photoyellowing of papers

The photoyellowing of lignin-rich papers has been demonstrated to depend on the formation of phenoxyl radical intermediates and their ultimate conversion into various products, including quinones. Molecular oxygen has also been observed as a necessary adjunct to this process, although the mechanism is not understood. This work demonstrates the requirement for the reaction of O2 with active radical intermediates (in processes analogous to autoxidation reactions) in order for the photoyellowing of the phenolic moieties to occur. Photo-oxidations of a variety of alkoxyphenols and their reactions with model alkyl, alkoxy and alkylperoxy radicals are studied by CIDEP.

A mechanistic study of the microwave induced catalytic decompositions of organic halides

A series of model organic haliae compounds were decomposed by the technique of microwave catalysis. The reactions were 100% efficient which were followed and characterized by gas chromatography, mass spectrometry, and direct electron spin resonance detection. The results clearly establish the primary free radical mechanisms of the decomposition by breaking selectively the C-X bond, leading to an organic fragment/radical and a stable form of solid metal halides. Many of the non-halogenated organic products are of economic and chemical value and can be recovered in the microwave processing.

Microwave Induced Catalytic Reactions of Carbon Dioxide and Water: Mimicry of Photosynthesis

In an attempt to emulate the highly successful photosynthetic recycling of CO2 to form energetically useful fuels in nature this study investigates the microwave induced reaction of carbon dioxide and water in a continuous flow system using a supported nickel catalyst and 2.45 GHz microwave radiation with an average incident power of 2.2 kW. The major reaction products were methane, ethane, methanol, acetone, C3 and C4 alcohols. The yields of methane, C3 and C4 alcohols reached maximum values after 30 s of irradiation, while the yields of ethane, methanol and acetone were proportional to the irradiation time within the investigated range.

Microwve inducdd catalytic decomposition of some alberta oil sands and bitumens

The processing of oil sands materials and upgrading of bitumens present a variety of problems for conventional technologies. This article describes a preliminary study of the concept of using microwave induced catalytic techniques to decompose the complex and viscous hydrocarbon compounds contained in these materials to allow efficient extraction of volatile and economically useful organic products such as C2 and C3 hydrocarbons. Addition of water to the tar sand material prior to reaction facilitated separation from the sand component as well as promoting the formation of economically very useful, liquid, oxygenated hydrocarbon products.

Pulsed microwave catalytic decomposition of olefins

The application of the recently developed, versatile and economic technique of microwave assisted catalysis to the reactions of olefinic hydrocarbons, principally ethylene, propylene and 1-pentene is discussed. The reactions are believed to involve free radical intermediates and can result in efficient conversions to selected aliphatic and aromatic hydrocarbons.

Some mechanistic insights in the behaviour of thiol containing antioxidant polymers in lignin oxidation processes

Modified polyethylene glycol polymers are described in which thiol containing groups have been added via a simple esterification step. The resultant thiol end-capped polyethers retain the antioxidant behaviours of the monomeric thiols, but mitigate essentially completely the undesirable properties of the monomers, including offensive odour, volatility, and insolubility in aqueous solvents. This concept substantially enhances the number of potential practical applications of the thiol containing polymers as compared to the monomeric substances. A class of polyethylene glycols substituted with thiolactic acid or thioglycolic acid is described with potential in the pulp and paper industry, for the inhibition of radical induced oxidative processes including brightness reversion in lignin containing papers. Several techniques are used to elucidate aspects of the mechanism by which such thiols are effective: a novel photoacoustic technique demonstrates the scavenging effects of the thiol end capped polyethylene glycols towards alkoxy radicals. ESR studies demonstrate the ability of these thiol polymers to quench both the exogenous “phenoxy” radicals present in CTMP and TMP papers as well as the enhanced radical signal resulting from irradiation of these papers. The strong uv absorbance of these relatively persistent phenoxy radicals may decrease the optimal initial brightness of papers made from mechanical pulps.

Some mechanistic aspects of the light-induced yellowing of lignin: A further study of the photochemical reactions of α-guaiacoxy-β-hydroxy-proprio-veratrone, and some substituted methoxybenzenes

The primary photoreduction of a model lignin system α-guaiacoxy-β-hydroxypropioveratrone occurs via a triplet mechanism leading to polarized ketyl radicals which undergo β-ether cleavage similarly to the photochemical reactions of α-guaiacoxyacetoveratrone. Comparison of the photoyellowing rates of solutions of the two lignin models showed a slightly greater rate for the derivative with the βhydroxymethyl function, with some subtle differences in behavior between the two compounds probably due to the intramolecular hydrogen bonding in the former. In addition it was found that photooxidation of several methoxybenzenes was considerably slower than that of corresponding methoxyphenols. This is reassuring that the ubiquitous presence of methoxybenzene groups in lignin matrices is unlikely to contribute significantly on the timescale relevant to the photoyellowing of CTMP pulps.

Acetylene from benzene: A novel and selective microwave assisted cracking synthesis

A novel and efficient process for the cracking of benzene to acetylene with over 90% selectivity is described. The reactions are induced by a pulsed microwave technology over alumina and silica supported Nickel catalysts.

Highly effective methane conversion to aromatic hydrocarbons by means of microwave and rf-induced catalysis

Conversion of methane to higher hydrocarbon products, in particular, aromatic hydrocarbons has been achieved with good methane conversion and selectivity to aromatic products over heterogeneous catalysts using both high power pulsed microwave and rf energy. For example, under microwave irradiation > 85% conversion of methane and 60% selectivity to aromatics could be achieved. Cu, Ni, Fe and Al metallic materials are highly effective catalysts for the aromatization of methane via microwave heating; however, with a variety of supported catalysts the major products were C2 hydrocarbons and the conversion of methane was low. The use of sponge, wire and net forms of these metal catalysts was found advantageous in effective methane conversion. The reactions are considered to be free radical in nature and to proceed through an intermediate stage involving formation of acetylene. The influence of catalyst nature and configuration, as well as the microwave and rf irradiation parameters on the reaction efficiency and product selectivity has been examined in both batch and continuous flow conditions.

Bleaching Mechanical Pulps With H2O2: a Unique Alkali-Free Approach

A unique hydrogen peroxide bleaching process for mechanical pulps is described, in which the bleaching is carried out at near neutral pH and without the use of any soluble alkali or alkali generating reagents for peroxide activation. Neither metal chelating agents nor peroxide stabilizer agents such as silicates, are required. ISO brightness and b* values at least as good as, and in many cases considerably better than, conventional alkali peroxide bleaching can be obtained by this process.