Martin C. Hawley

Dehydration of d-fructose to levulinic acid over LZY zeolite catalyst

Abstract Molten d -fructose was catalytically dehydrated to HMF and levulinic acid over solid-acid LZY zeolite powder within a sealed batch reactor at 140°C. Analysis of the product distribution via HPLC after various reaction times (0 to 15 h) revealed that the model for the heterogeneous dehydration of d -fructose over LZY zeolite catalyst was consistent with the model for the homogeneous hydronium ion-catalyzed d -fructose dehydration. After 15 h, the maximum yield of levulinic acid was 0·432 g levulinic acid per 1·00 g of the original d -fructose, but the net yield of HMF was only 0·044 g HMF per 1·00 g of the original d -fructose. The high yield of levulinic acid was due to the strong dehydration ability of the Lewis acid sites on the alumina/silica support of the LZY zeolite. The high selectivity was due to the molecular-sieving capability of the LZY zeolite matrix, which trapped the 0·82 nm diameter HMF molecule within a ‘cage’ adjoining the 0·75 nm LZY zeolite pores.

A study of microwave reaction rate enhancement effect in adhesive bonding of polymers and composites

Microwaves have been investigated as an efficient alternative energy source for polymers and composites processing. In this paper, microwaves are applied in bonding two polymer composites with an epoxy-based adhesive. Results were compared with thermal process. Microwaves reduced the bonding time dramatically, which resulted from faster curing of the adhesives. The literature disagreed on whether localized superheating of functional groups or specific non-thermal effects are the main reason of microwave enhancement of reaction rate. In this study, the mechanism of microwave fast curing was investigated and the experimental results supported localized superheating of the functional groups as the main mechanism of reaction rate enhancement of microwave energy.

A REVIEW OF MICROWAVE-ASSISTED POLYMER CHEMISTRY (MAPC)

As a relatively new source ofprocessing energy, microwave energy offers many compelling advantages in materials processing over conventional heat sources. These advantages include greater flexibility greater speed and energy savings, improved product quality and properties, and synthesis of new materials that cannot be produced by other heating methods. Studies of microwave processing of polymeric materials in the early 1960s led to a successful industrial application in the rubber industry Since the mid-1980’s, there has been a great deal of interest in microwave processing of polymeric materials worldwide. The discipline can be categorized in two major fields: microwave-assisted polymer physics (MAPP) and microwave assisted polymer chemistry (MARC). This paper offers an overview of lie fate-of-the-art research on the field of 1, 1:1PC, including polymer processing (curing ot thermosets, processing of thermoplastics, and joining), polymer synthesis, plasma modification of polymer surfaces, plasma polymerization, polymer degradation, and production of nanomaterials. Most of these studies have focused on laboratory-scale, exploratory efforts. Challenges and possible future directions for the commercialization ofmicrowave processing technologies are discussed.

Behavior of a Microwave Cavity Discharge over a Wide Range of Pressures and Flow Rates

Experiments are conducted over a wide range of pressures, flow rates, and power levels to demonstrate the versatility of a microwave cavity discharge. The experimental results are justified using a linear, cold plasma theory that accounts for the electron-neutral particle collisional losses in the plasma. The resonant coupling of E. M. energy to a surface wave and the resulting formation of a long, large volume plasma column is demonstrated. The absorbed power characteristics of the microwave cavity discharge are examined for gas pressures up to 500 torr and flow rates up to 2500 cm3/min in the TE011 and TE*111 mode operation of the plasma cavity system. The experimental results show that the absorbed power variation as a function of pressure of this discharge is uniform. The power absorbed by the flowing plasma is shown to increase directly as a function of the flow rate initially and reach a saturation at high flow rates. By simultaneously optimizing the cavity length, discharge pressure, and the gas flow, it is possible to couple as much as 90% of the incident power to the plasma.

Dissociation and recombination of oxygen atoms produced in a microwave discharge. Part I. experiment

A microwave-initiated plasma (2.44 GHz) flow system has been developed to generate and detect atomic oxygen as a function of distance from the discharge exit. It was found that an increase in power or a decrease in pressure resulted in larger amounts of atomic oxygen at specific points downstream from the discharge. Flow rate had little effect on the production of atoms, but increasing the flow rate did result in increasing the yield of oxygen atoms. The largest dissociation measured was 70% at a pressure of 12 Torr, a flow rate of 0.4 cm3/sec, and 500 W of absorbed power.

Review of research and development on the microwave electrothermal thruster

The microwave electrothermal thruster shows promise for spacecraft propulsion and maneuvering. It promises advantages over other electrothermal thrusters in the areas of operating life, efficiency, and propellant selection. In the microwave thermal thruster, the electric power is first converted to microwave-fre quency radiation. In a specially designed microwave cavity system, the electromagnetic energy of the radiation is transferred to the electrons in a plasma sustained in the working fluid. The resulting high-energy electrons transfer their energy to the atoms and molecules of the working fluid by collisions. The heated working fluid expands through a nozzle to generate thrust. In the microwave electrothermal thruster, no electrodes are in contact with the working fluid, since nonthermal, radiative mechanisms transfer the energy into the working fluid. The main requirements for the materials of construction are that the walls of the discharge chamber be insulating and, at least in part, transparent to microwave radiation at operating conditions. Several experimental configurations of microwave electrothermal thrusters are described and compared. Diagnostic methods used to study microwave plasmas under conditions used in the thruster are described and selected results presented for titration, spectroscopy, calorimetry, electric field measurements, and gas-dynamic methods. Estimated performance efficiencies are reported and compared with other electrothermal systems. Results of computer modeling of the plasma and of the gas flowing from the plasma are summarized.

Gasification of wood char and effects of intraparticle transport

Abstract Kinetic parameters for gasification of hybrid poplar spp. char have been measured. A differential reactor was used to obtain rate data for catalytic and non-catalytic reactions of small wood char particles (1–2 mm in size) at 100 kPa for temperatures in the range 400–700 °C, steam partial pressures between 45–100 kPa, and space velocities in the range 2.0–7.3 s −1 During pyrolysis of wood without the addition of either K 2 CO 3 or Na 2 CO 3 , the cellular structure of the wood was preserved. Additionally, this cellular structure remained intact during most of the gasification process. Addition of K 2 CO 3 and Na 2 CO 3 before pyrolysis caused a degradation of the regular cellular structure and an increase in the rate of gasification of the resulting char. Effectiveness factor calculations were made for particles of various sizes and results indicate that diffusion control of the gasification reaction becomes important for particles larger than 0.5 CM.

Microwave heating and dielectric diagnosis technique in a single‐mode resonant cavity

A single‐mode microwave heating and dielectric measurement technique has been developed. The single‐ and swept‐frequency methods were used to simultaneously heat the material and measure its complex permittivity in this single‐mode technique. A cylindrical cavity and Nylon 66 rods were used in this study. The cavity was always resonated in the TM012‐mode at 2.45 GHz. The measured changes in the resonant frequency and cavity Q factor of the cavity with and without the sample were related to complex permittivity of the sample using material‐cavity perturbation. Temperature measurement was made using a fluoroptic thermometer. On‐line measurements of complex permittivity and temperature were made during single‐ and swept‐frequency microwave heating of the sample. Complex permittivity of Nylon 66 as a function of temperature using the single‐frequency method was compared to that using the conventional swept‐frequency method during microwave heating. It shows that dielectric measurements using the single‐ and s...

Characterization of Asphalt Binders Based on Chemical and Physical Properties

Abstract The chemical compositions and physical properties of unmodified and polymer-modified asphalts were studied using high-performance gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), thermal mechanical analysis (TMA), and differential scanning calorimetry (DSC). Two viscosity-based asphalt grades (AC-5 and AC-10) and two polymers, namely, styrene-butadiene-styrene (SBS) and styrene-ethylene-butylene-styrene (SEBS) were used to modifiy asphalt in this study. The combination of GPC and FTIR was found to be an excellent approach for fingerprinting and quality control of polymers and asphalt binders. The rheological properties of asphalt binders were determined to be good characteristics for determining the optimum polymer concentrations for effective modification. The DSC results indicated that different asphalt grades have different levels of polar associations as detected from changes in enthalpy. Polymer modification alters these ...

The Effect of Network Formation on the Rheological Properties of SBR Modified Asphalt Binders

Abstract Styrene-butadiene rubber (SBR) was used to modify asphalt binders. The rheological and thermo-mechanical properties of the binders were investigated using rotational viscometry, dynamic shear rheometry, and thermal mechanical analysis. The optimum SBR content and mixing procedure were determined based on the rheological properties of the asphalt/SBR blends. The addition of 3–5% (w/w) SBR resulted in enhanced high temperature performance of the binders. The SBR progresses from a dispersed polymer to local networks to a global network with increasing SBR content. This phenomenon is exhibited in rheological properties such as complex modulus and melt viscosity. It is also verified visually by using a Laser Scanning Confocal Microscope. Because of this network formation, the binders showed a large increase in the complex modulus which indicates resistance to rutting.