Current Organic Chemistry - Volume 19, Issue 5, 2015

Recent works on dry anaerobic digestion (AD) show that not only methane but also hydrogen, volatile fatty acids (VFAs), and ethanol can be produced from municipal solid waste (MSW), dewatered sewage sludge, animal manure or crop residue by dry AD processes. Up to now only methane production from household wastes has already been commercialized by using dry AD technology. Single-stage dry AD processes with semicontinuous or continuous operation mode dominates the commercialized dry AD plants. To get enhanced biogasification efficiency, naturally microbial pretreatment methods (like stack-pretreatment and aerobic or facultative composting) and co-digestion are practically useful for dry AD, especially for the treatment of carbon- and nitrogen- rich organic solid wastes, i.e. crop residue and animal manure. Dry AD could achieve comparable production efficiency to wet AD systems, yielding 121 - 340 L of CH4 from per gram volatile solids (VS) of organic fraction of MSW (OFMSW) and 51 - 55 ml H2/g- VSreduced from OFMSW, sewage sludge, and paper and food wastes. Still, future researches are necessary and demanding for dry AD to better challenge with other low-cost treatment and disposal methods, which are also proposed in this review mainly relating with its longer solids retention time, feedstocks collection, inhibitory substances, online process monitoring, and establishment of process assessment index system.

The practice of disposing of waste in conventional dry-tomb landfills is not sustainable. A sustainable alternative is the landfill bioreactor and its variations. Landfill bioreactor approach includes specific design and operation techniques to enhance waste degradation and landfill gas (LFG) production. Although this approach has been known to landfill researchers and practitioners for a few decades, there are only a few successful field-scale landfill bioreactors in operation. This paper provides a comprehensive review of technological challenges with landfill bioreactors and associated design and operational details. A key issue that should be addressed by a landfill bioreactor designer is moisture and gas movement within a waste matrix that changes its properties continuously in time and space. The design components such as the leachate collection and removal system (LCRS), leachate recirculation system, and gas collection system could be severely impacted if the traditional landfill design and operation practice is not modified to take into consideration the behavior of waste matrix in time and space. Considering that a landfill bioreactor can be used as a biomass waste to energy facility, this paper details the LFG generation processes, the factors affecting the LFG generation and theoretical LFG generation estimation techniques as well as the important design, construction and operational issues associated with landfill bioreactors.

The worldwide demand for energy is ever escalating commensurate with increasing populations and development. While fossil fuels as the current major energy resource are shrinking drastically, combustion of fossil fuel releases greenhouse gases, which are the main culprit for global warming and climate changes. Development of renewable energy appears to be a prominent solution to address these energy and environmental issues. Pyrolysis process converting biomass into energy offers a promising alternative for renewable energy supply. This paper reviews recent and state-of-art development of biomass pyrolysis research in producing biochar, bio-oil and biogas. Factors affecting pyrolysis processes and intrinsic properties of the pyrolysis products produced from different operating conditions are discussed. Advancement in pyrolysis technology as well as the challenges and prospects of pyrolysis for energy production are also outlined.

Lignocellulosic biomass is regarded as a promising renewable resource that can be potentially used to provide second-generation biofuels or to produce chemicals. Hydrothermal treatment (HTT) of lignocellulosic biomass has received considerable attention because of its feasibility and efficient generation of valuable products. Recently, much attention has been paid to the studies of using HTT as pretreatment of lignocellulosic biomass for biogas production. These studies show that operational parameters (including temperature, retention time, pressure, solid content, particle size and pH) are crucial for lignocellulose conversion into biogas. Up to now, however, no review could be found on this aspect. In order to optimize the pretreatment process for enhanced biogas production, the above-mentioned operational parameters of HTT are summarized and discussed with respect to the pretreatment of lignocellulosic biomass and their enhancement effects on biogasification. Related studies on hydrothermal treatment of lignin, hemicellulose and cellulose are reviewed. The above parameters adopted in the recent research works for biogas production have been critically addressed. In addition, future research directions are also prospected.

As one of the few long-term sustainable clean energy carriers, hydrogen (H2) has attracted a great deal of attention. It has been projected as the most promising source of energy with less pollution on environment, especially without CO2 emission. Biomass as a neutral carbon source is considered as an ideal primary energy source, which can be expected to gradually replace the depleting fossil fuels due to its worldwide availability. As one of the thermo-chemical method, gasification has its advantage for H2 production, such as fast rate of hydrogen production and low cost. Gasification process often at high temperature is mainly accepted as the promising, attractive and effective technology to produce H2 from biomass. There are some vital process parameters which influence gas characteristic. In order to increase H2 concentration and reduce impurities, a reforming process following gasification is generally required, and effective catalysts can coordinate to achieve this. Thus, combining gasification and reforming processes are the most suitable method for obtaining H2 rich producer gas, and choosing a highly effective and suitable catalyst is the key challenge. Hydrogen can be obtained from two-stage gasification in industry level, which is used as chemical raw material.

Ionic liquids (ILS) are typically referred to as “green” or “designer” solvents. These solvents consist entirely of ionic species exhibiting many fascinating properties, such as non-flammability, low vapour pressure, wide electrochemical window and thermodynamic kinetic stability. Moreover, these remarkable properties can also be adjusted by using various synthesis methods. The application of ILs solves many major problems in green energy production and environment including solar energy, biomass and CO2 adsorption. Although, given our current state of knowledge, the applications of ILs are unpredictable; they have nonetheless rapidly attracted enormous attention in the fields of modern physical chemistry, materials science, applied technologies and engineering. This review focuses on the basic ILs synthesis methods and the latest advancements in the clean energy and environmental application of ILs.

(4-Hydroxy-3,5-diiodophenyl)diphenylphosphine oxide, bis(4-hydroxy-3,5-diiodophenyl)(phenyl) phosphine oxide, and tris(4-hydroxy-3,5-diiodophenyl)phosphine oxide were obtained via iodination reactions of corresponding mono-, bis-, and tris(4-hydroxyphenyl)phosphine oxides. Single-crystal X-ray diffraction studies showed each homologue forms O-H···O=P and π-stacking interactions with neighboring molecules to give inversion related dimeric motifs.

Photooxygenation of titled furans followed by reduction gives unsaturated 4-oxoaldehydes quantitatively. Some derivatives cyclize under slightly acid conditions or by silica gel to unusual 5,6- dioxabicyclo[2.1.1]hexenes and/or 5H-furanones. Under appropriate basic conditions 4-oxocarboxylic acids or their ring-tautomers 5-hydroxyfuranones are chemoselectively obtained in almost quantitative yields. All the procedures are one-pot and occur stereoselectively. Due to the electron-poor substituents alternative non-photochemical oxidative methods fail or give not cleanly reaction mixtures.