(71p) Potential of Batch Microreactors for Continuous Processing of Particles, Slurry and Polymer Reactants, and Particle Forming Products at High Temperatures and High Pressures

In this work, we review some of the high temperature (>400 C) and high pressure (20 to 2000 MPa) applications that we have studied with batch type microreactors (ca. 50 nL, 10,000 m2/m3) using water as the reaction solvent. We also discuss methods to process materials on a continuous basis using batch microreactors. The applications include:

(i) Boehmite nano-particle formation through reaction of aluminum nitrate (Wang et al, 2002; Li et al., 2002) (ii) Polymer particle reactions (Fang, et al., 1999; Smith et al., 2000) (iii) Dechlorination and conversion of chlorinated particles (Fang et al., 2004; Fang et al., 2005; Nagai, et al, 2005) (iii) Microcrystalline cellulose mixing and conversion (Ogihara, et al. 2005) (iv) Biomass gel formulation, mixing and reaction (Ogihara, et al., 2005)

In-situ observations, which have been recorded through optical windows made of diamond or moissanite, will be presented that demonstrate: (i) particle formation during rapid heating of microreactor contents (ii) heat transfer characteristics at high temperatures and high pressures in the vicinity of the critical point of water and its mixtures (iii) mass transfer during oxidization of particles (iv) oil, particle and gas formation during reactions (v) mixing characteristics for slurry systems

In particle formation steps, it can be observed that during heating of reacting mixtures that particles tend to form at the gas bubble - liquid interfaces. This is probably due to the concentration gradients that develop and is deemed to be important for handling particle forming systems. In the heat transfer to the mixture at the critical point, it was observed that violent cycling of fluid phases occurred. In the heating of slurries of microcrystalline cellulose, intense convection and mixing of the microreactor contents was observed when gas was added to the system. In the oxidation of particles, for the case of deca-chlorobiphenyl, it was observed that oxidation of the particle surface occurred extremely rapidly in the initial formation process of oxygen obtained from breakdown of H2O2. Superfine myriads of O2 bubbles were observed that diffused through the liquid phase and attacked the particle surface. However, as the reaction proceeded, these O2 bubbles tended to coalesce and thus probably reduced the reaction rate. Oil, particle and gas formation during reactions occur as a result of product liquefaction, hydrolysis or decomposition. Examples include dissolution characteristics of polyethylene in supercritical water, dissolution of nylon in supercritical water, and dehlorination of polyvinylchloride in supercritical water. It is expected that for practical application of batch microreactors on a continuous basis that product feeds will be in the form of gels. Therefore, images of biomass gels undergoing reaction will also be shown. Heating of the microreactors is an important aspect for successful operation on a continuous basis. Previous applications have mainly used electrical or resistive heating. As a point of originality of this work, heating by chemical methods will be considered and some examples will be shown including some thermographic images where possible. A conceptual design for continuous processing with batch microreactors will be presented.

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