Study of a Novel Method for the Thermolysis of Solutes in Aqueous Solution Using a Low Temperature Bubble Column Evaporator

Abstract

An enhanced thermal decomposition of chemical compounds in aqueous solution has been achieved at reduced solution temperatures. The technique exploits hitherto unrecognized properties of a bubble column evaporator (BCE). It offers better heat transfer efficiency than conventional heat transfer equipment. This is obtained via a continuous flow of hot, dry air bubbles of optimal (1-3 mm) size. Optimal bubble size is maintained by using the bubble coalescence inhibition property of some salts. This novel method is illustrated by a study of thermal decomposition of ammonium bicarbonate (NH4HCO3) and potassium persulfate (K2S2O8) in aqueous solutions. The decomposition occurs at significantly lower temperatures than those needed in bulk solution. The process appears to work via the continuous production of hot (e.g., 150 °C) dry air bubbles, which do not heat the solution significantly but produce a transient hot surface layer around each rising bubble. This causes the thermal decomposition of the solute. The decomposition occurs due to the effective collision of the solute with the surface of the hot bubbles. The new process could, for example, be applied to the regeneration of the ammonium bicarbonate draw solution used in forward osmosis.

A Novel Method for Decomposing and Recycling Ammonium Bicarbonate Solutions

“…The efficiency of the single pass membrane degassing process can be estimated in terms of % recovery rate per min (of residence time) and these values can then be compared with the efficiency of the BCE recovery. Decomposition of 0.03M AB solution using the BCE system [2] with an air inlet temperature of 150 °C was compared with single pass PDMS system with feed of 80 °C pre-heated AB solutions. The results of the BCE experiments are shown in Figure 4 and show that the BCE method required 15mins to produce 57% AB recovery rate; whilst for the PDMS (2.1m 2 ) module, the required time was only 5mins (see Table 1).…”

“…A vertical glass column with a porous glass sinter (size no 2) at the base (see ref [2]) was used to produce a continuous flow of fine, dry, air bubbles at a flow-rate of 22.5L.min 2 ) membrane).…”

“…Gokel [1] investigated the decomposition of AB ranging between 35 and 80 °C. The complete decomposition of AB into its individual constituents was observed above 60 °C, which is described by the reaction: Shahid et al, [2] also proposed that the bubble column evaporator (BCE) process could facilitate the thermal decomposition of AB solutions (both dilute and concentrated) at lower solution temperatures (of around 45 °C) and at a faster rate. AB solutions have a wide variety of industrial applications.…”

A Study of the Bubble Column Evaporator Method for Improved Ammonium Bicarbonate Decomposition in Aqueous Solutions: Desalination and Other Techniques

“…2 For the latter application, the ion-exchange resins comprising carboxylic acid and tertiary amine groups for desalination can be thermally regenerated using the BCE process at a lower energy cost than with conventional methods. More recently, Shahid et al 3 studied that solutes, ammonium bicarbonate (NH 4 HCO 3 ) and potassium persulphate (K 2 S 2 O 8 ) can be thermally decomposed in aqueous solutions using a bubble column evaporator (BCE) process at sub-boiling condition (around 45 °C). Fulks et al 4 and Gokel 5 studied, ammonium bicarbonate decomposition in solution over the temperature range 30−85 °C.…”

“…In combination with the effect are size dependent bubble rise rates and rapid watervapour uptake into the bubbles. 3,[7][8][9] These phenomena together offer a variety of applications. The most striking of these we have developed are in desalination.…”