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The unique characteristics of supercritical water (SCW) offer potentially attractive processing options that can be explored for reaction and separation purposes. While supercritical water oxidation (SCWO) can achieve high organic conversion efficiencies, low and relative solubilities of inorganic species in SCW may be further utilized for in situ separation of potential by-products from the SCWO process effluent. This paper describes a novel method for separating ionic species under SCW conditions. The concept is based on relative solubilities of different ionic species in SCW. Laboratory-scale demonstration tests were conducted with a Nylon monomer manufacturing process wastewater containing sodium hydroxide, sodium borate, carboxylic acids, and water. The process achieved () effective destruction (>99%) of organic components in the wastewater; () selective precipitation of sodium (>99.5%) as carbonates produced from oxidation of the organic components; and () efficient recovery of boron (>90%) as boric acid in the reactor effluent. The sodium removal efficiency is governed by the solubilities of sodium carbonates in SCW and, therefore, can be directly improved by increasing process temperature. As a result of the temperature increase, both organic destruction and boron recovery efficiencies may be enhanced. This method of selective separation of ionic species in SCW has potential for a wide range of processing applications. [ABSTRACT FROM AUTHOR]

A 25.4-mm diameter hydrocyclone with an underflow receiver was evaluated for its ability to achieve separation of fine particles from water at elevated temperatures and pressures relevant to supercritical oxidation. Temperature was varied from 25°C to 340°C, while pressure was maintained at 27.6 MPa. The particles studied were α-alumina. Particle-removal efficiency was affected by the separation capabilities of the hydrocyclone, deposition on the heater surface, and flocculation of the particles. Particle-size distributions and suspended solids analyses confirmed that cyclone, separation efficiency was controlled by the (densityparticle - densitywater)/viscositywater ratio. Because this ratio is sensitive to temperature, especially in the neighborhood of the supercritical point, separation efficiencies sharply increased with temperature. Contrary to traditional air cyclone theory, removal efficiency was inversely correlated to flow rate. This result was caused by particle deposition and particle flocculation in the heater. Low flow rates increased heater detention times and, thus, opportunities for flocculation and particle deposition. Therefore, the performance of a hydrocyclone used in conjunction with supercritical oxidation depends on phenomena occurring in the heater and the hydrocyclone. [ABSTRACT FROM AUTHOR]