Juming Tang

A review of catalytic hydrodeoxygenation of lignin-derived phenols from biomass pyrolysis

Catalytic hydrodeoxygenation (HDO) of lignin-derived phenols which are the lowest reactive chemical compounds in biomass pyrolysis oils has been reviewed. The hydrodeoxygenation (HDO) catalysts have been discussed including traditional HDO catalysts such as CoMo/Al(2)O(3) and NiMo/Al(2)O(3) catalysts and transition metal catalysts (noble metals). The mechanism of HDO of lignin-derived phenols was analyzed on the basis of different model compounds. The kinetics of HDO of different lignin-derived model compounds has been investigated. The diversity of bio-oils leads to the complexities of HDO kinetics. The techno-economic analysis indicates that a series of major technical and economical efforts still have to be investigated in details before scaling up the HDO of lignin-derived phenols in existed refinery infrastructure. Examples of future investigation of HDO include significant challenges of improving catalysts and optimum operation conditions, further understanding of kinetics of complex bio-oils, and the availability of sustainable and cost-effective hydrogen source.

Dielectric properties of foods relevant to RF and microwave pasteurization and sterilization

A custom-built temperature-controlled test cell and an Agilent 4291B impedance analyzer were used to determine the dielectric properties of a whey protein gel, a liquid whey protein mixture, and a macaroni and cheese product and their constituents. Dielectric constants, loss factors, and penetration depths for each sample over a temperature range from 20 to 121.1 °C, at frequencies of 27, 40, 915, and 1800 MHz are reported. As temperature increased, dielectric constants of whey protein products increased at 27 and 40 MHz, but decreased at 915 and 1800 MHz. Dielectric loss factors of whey protein products increased sharply with increasing temperatures at 27 and 40 MHz, but increased mildly at 915 and 1800 MHz. Similar results were observed with macaroni and cheese. The penetration depths of electromagnetic energy at 27 and 40 MHz were about four times as great as those at the microwave frequencies 915 and 1800 MHz in all tested samples.

Dielectric properties of fruits and insect pests as related to radio frequency and microwave treatments.

Information on dielectric properties of commodities and insect pests is needed in developing thermal treatments for postharvest insect control based on radio frequency (RF) and microwave energy. Dielectric properties of six commodities along with four associated insect pests were measured between 1 and 1800 MHz using an open-ended coaxial-line probe technique and at temperatures between 20 and 608C. The dielectric loss factor of fresh fruits and insects decreased with increasing frequency at constant temperatures. The loss factor of fresh fruits and insects increased almost linearly with increasing temperature at 27 MHz radio frequency, but remained nearly constant at 915 MHz microwave frequency. Both dielectric constant and loss factor of nuts were very low compared to those of fresh fruits and insects. The temperature effect on dielectric properties of nuts was not significant at 27 MHz. The large difference in the loss factor between insects and nuts at 27 MHz suggests possible differential heating of insects in nuts when treated at the same time in a RF system.

High-temperature-short-time thermal quarantine methods

Abstract In this paper, kinetic models are discussed with respect to their uses in describing the intrinsic thermal mortality of insect pests. A unique heating block system was used to obtain kinetic information for the thermal mortality of codling moth larvae. The kinetic data demonstrated the possibility to develop high-temperature-short-time thermal treatments to control codling moth and reduce thermal impact on product quality. Equations are presented to evaluate cumulative effects of any time–temperature history on the thermal mortality of target insect pests and on the quality of host materials. Computer simulation results demonstrated that the cumulative thermal effects on product quality during the heating period in conventional hot air or hot water treatments are much more important than the cooling period. Radio frequency (RF) heating or microwave heating is suggested as an alternative to reduce adverse thermal impact to treated commodities during the heating period. A case study is presented to demonstrate the effect of RF heating in a high-temperature-short-time thermal treatment to control codling moth larvae in in-shell walnuts.

Radio frequency treatments to control codling moth in in-shell walnuts

‘Diamond’ Walnuts (Juglans regia L.) in the shell were treated with radio frequency (RF) energy in a 27 MHz pilot-scale system to determine the treatment effect on third- and fourth-instar codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), mortality and walnut quality. After 2 and 3 min of RF treatments, infested in-shell walnuts were heated to 43 and 53°C. The corresponding insect mortality reached 78.6 and 100%. The fatty acid (FA) concentration of treated walnuts was not affected by RF treatments. The FA values were B 0.1% after accelerated storage times up to 30 days at 35°C, simulating storage at 4°C for up to 3 years. The effect of RF treatments on walnut oil peroxide values (PV) was not significant. The PV value of walnuts was less than 1.0 meq:kg (the upper limit for good quality walnuts), after 20 days storage at 35°C that simulated 2 year storage at 4°C. The PV was about 1.2 meg:kg after 30 days storage at 35°C. RF treatments can, therefore, potentially provide an effective and rapid quarantine security protocol against codling moth larvae in walnuts as an alternative to methyl bromide fumigation.

Production of phenols and biofuels by catalytic microwave pyrolysis of lignocellulosic biomass

Catalytic microwave pyrolysis of biomass using activated carbon (AC) was investigated to determine the effects of pyrolytic conditions on the yields of phenol and phenolics. Bio-oils with high concentrations of phenol (38.9%) and phenolics (66.9%) were obtained. These levels were higher than those obtained by pyrolysis without AC addition and were closely related to the decomposition of lignin. A high concentration of esters (42.2% in the upgraded bio-oil) was obtained in the presence of Zn powder as catalyst and formic acid/ethanol as reaction medium. Most of the esters identified by GC-MS were long chain fatty acid esters. The high content of phenols and esters obtained in this study can be used as partial replacement of petroleum fuels after separation of oxygenates or as feedstock for organic syntheses in the chemical industry after purification.

Process protocols based on radio frequency energy to control field and storage pests in in-shell walnuts

A practical process protocol was developed to control insect pests in in-shell walnuts using a 27 MHz pilot scale radio frequency (RF) system. Fifth-instars, that had been determined to be the most heat resistant life stage for navel orangeworm (Amyelois transitella [Walker]) using a heating block system, were selected as the targeted insect in the protocol development. RF heating to 55 °C and holding in hot air for at least 5 min resulted in 100% mortality of the fifth-instar navel orangeworm. Rancidity, sensory qualities and shell characteristics were not affected by the treatments. The process slightly reduced the moisture content of the walnut kernels, which could prove an additional benefit by providing even nut moisture content and reducing the growth of microorganisms. If this method can be economically integrated into the handling process, it should have excellent potential as a disinfestation method for in-shell walnuts.

Kinetics of textural and color changes in green asparagus during thermal treatments

The textural and green color degradation of asparagus were determined after heat treatments at temperatures between 70∞C and 98∞C for selected time intervals. Maximum shear stress required to cut through green asparagus and the hue angle of the spear surface color were selected to represent the textural and color changes in thermally treated asparagus. Thermal softening of asparagus followed a first order kinetic reaction. The activation energies for softening of asparagus were 24:0 0:5 kcal/mol and kinetic reaction rates (k84∞C) ranged from 0.016 min ˇ1 at the butt segment to 0.027 min ˇ1 at the bud segment of the spears. Green color changes of asparagus spear surface followed a first order reaction. The activation energies for green color degradation of asparagus were 13:1 0:2 kcal/mol and kinetic reaction rates at 84∞C were 0:0066 0:0002 min ˇ1 . ” 2000 Elsevier Science Ltd. All rights reserved.

Compression strength and deformation of gellan gels formed with mono- and divalent cations

Abstract The influence of divalent (Ca 2+ and Mg 2+ ) and monovalent (Na + and K + ) cations on the failure stresses and strains in gels formed with gellan polymer were investigated. Gellan gels containing 0.6-2.2% polymer and varying cation concentrations were tested using large compressive deformation until failure. Maximal true shear stresses and corresponding shear strains represented gel strength and extensibility. At small cation concentrations, the strength of gellan gels increased while the extensibility decreased with cation concentrations. The strongest gels were obtained at cation levels corresponding to 0.5 cations per carboxylate group in the repeat gellan unit for gels crosslinked with divalent cations and 10 to 30 cations per repeat gellan unit for gels with monovalent cations. At optimum cation levels, gellan gels with Ca 2+ were stronger than with Mg 2+ , and gellan gels with K + were stronger than with Na + . Above the optimum cation levels, gellan gels became brittle, and the strength of the gels decreased with increasing cation concentrations.

Texture profile and turbidity of gellan/gelatin mixed gels

Abstract The effect of gellan (1.6–0.2%) to gelatin (0–1.4%) ratio and calcium ion concentration (0–30 mM) on the textural properties and turbidity of gellan/gelatin mixed gels was examined using instrumental Texture Profile Analysis (TPA) and spectrophotometry. Hardness of the mixed gels decreased as the proportion of gellan decreased. Hardness increased with increasing calcium ions until calcium concentration reached a critical level, after which further increases in calcium resulted in a reduction of hardness. Brittleness, springiness and cohesiveness were very sensitive to low levels of added calcium (0–10 mM), but less sensitive to higher calcium concentrations and gellan/gelatin ratio. In general, the addition of calcium ions caused gels to be more brittle and less cohesive and springy. Decreasing gellan to gelatin ratio caused an increase in gel turbidity at lower calcium ion levels (2–4 mM) and a decrease in turbidity at high calcium levels (20–30 mM). Maximum turbidity was observed in 0.6% gellan–1.0% gelatin gels without added calcium. The results of this study suggested a weak positive interaction between gellan and gelatin when no calcium was added, whereas at higher calcium levels gellan formed a continuous network and gelatin a discontinuous phase.