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Kinetics and Mechanism of Cyclohexanol Dehydration in High-Temperature Water
EPA Grant Number: U915778Title: Kinetics and Mechanism of Cyclohexanol Dehydration in High-Temperature Water
Investigators: Akiya, Naoko
Institution: University of Michigan - Ann Arbor
EPA Project Officer: Thompson, Delores
Project Period: September 1, 2000 through August 1, 2001
Project Amount: $102,000
RFA: STAR Graduate Fellowships (2000)
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Engineering
Description:
Objective:The objective of this research project is to understand the interactions between the reacting system and the water medium to fully exploit the unique properties of high-temperature water (HTW), and to maximize control over the HTW-mediated processes. HTW, which we define broadly as liquid water above 200°C and supercritical water (Tc = 374°C, Pc = 218 atm), is a sustainable medium for different types of chemical reactions. There has been a great deal of previous research in the application of HTW as a reaction medium for chemical synthesis, material synthesis, waste destruction, plastics recycling, coal liquefaction, and biomass processing. The use of HTW for these reactions has been motivated by the desire to create cleaner, safer, and more environmentally benign chemical processes. A successful application of HTW as a reaction medium requires the right combination of chemistry and reaction environment that HTW provides. At times, however, water is not an inert medium, but is an active participant in the reaction.
Approach:We performed experiments at temperatures of 250, 275, 300, 350, and 380°C, water densities of 0.08-0.81 g/cc, and batch holding times of 15-180 minutes to determine the effects of these variables on the product yields and reaction rates. The cyclohexanol concentration was 0.3 mol/L (at reaction conditions) in all experiments. We used batch reactors fashioned from nominal 1/4 inch stainless steel Swagelok tube fittings (one port connector and two caps). The reactor volume is 0.59 cc. The reactors were loaded with a carefully measured amount of cyclohexanol and placed in a glovebox filled with purified helium. In the same glovebox, we vigorously bubbled helium through distilled and deionized water to eliminate dissolved oxygen and carbon dioxide, gases that might influence the reactions. The reactors were then loaded with a measured amount of deaerated water and sealed under a stream of helium in the glovebox. All chemicals were obtained commercially in high purity and used as received. The loaded and sealed reactors were placed in a preheated, fluidized sandbath set at the desired reaction temperature. The reactor heat-up time has been measured to be 2-3 minutes, which is short compared to the typical batch holding times used in this study. Upon reaching the desired holding time, the reactors were removed from the sandbath, and the reaction was quenched immediately by immersing the reactors in a cold water bath. The reactor dropped to room temperature in less than 1 minute. The reactors were further cooled in a freezer for up to 1 hour to condense any volatile components. The reactors were opened, and the contents were recovered through the addition of acetone. We used two Hewlett-Packard model 5890 gas chromatographs, equipped with either a flame ionization detector or a mass spectrometric detector, to analyze the reaction products. Product identification was accomplished by comparing the retention times with those of authentic standards, and by inspecting mass spectra.
Supplemental Keywords:fellowship, high-temperature water, supercritical water, cyclohexanol, dehydration, kinetics, mechanism, green chemistry, benign chemistry, chemical synthesis.