Reaction of Hydrogen Chloride Gas with Sodium Carbonate and Its Deep Removal in a Fixed-Bed Reactor

Abstract

The chloridization rates of sodium hydrogen carbonate calcines were determined using both a differential fixed-bed reactor and an integral fixed-bed, flow-through reactor at ambient pressure and a temperature of 500 °C. In the course of the reaction with hydrogen chloride gas, monoclinic or hexagonal Na2CO3 was transformed into cubic NaCl. The expansion of the volume of the solid phase, because of the reaction, was described by means of a simple structural model. The reacted solids remained quite porous (∼29%), having decreased from an initial porosity of 45%. Up to advanced stages of the reaction, the rate-decaying behavior of the chloridization reaction can be approximated by first-order kinetics as a function of either the solids conversion or the elapsed time of reaction. The reaction between hydrogen chloride gas and the Na2CO3-based sorbents is rapid, and a high degree of sorbent utilization can be attained. The unsteady-state sorption of hydrogen chloride gas in a column packed with reactant solids can be described by a pair of partial differential equations, and their analytical, closed-form solution is presented in terms of three dimensionless variables. Unsteady-state experimental runs were carried out in a small integral fixed-bed reactor (14-mm i.d.) with spherical alumina particles having an average diameter of 1.5 mm, impregnated with NaHCO3 and packed to a depth of 6.5 cm. The effective reaction rate constants inferred from the experimental breakthrough curves in accordance with the model were found to be in reasonable agreement with those determined from the experiments executed in the differential mode of reaction. The presented, tractable expressions can readily serve as a rational basis for the conceptual design and effective operation of packed-bed reactors for the deep removal of hydrogen chloride gas from hot producer gas.

Hydrogen chloride removal from hydrogen gas by adsorption on hydrated ion-exchanged zeolites

“…Among the different techniques used to purify hydrogen gas, such as partial condensation [15], chemical reactions [16], membrane and molecular sieve separations [15,16], the preferred approach used in the chemical industry is absorption at high temperatures on mineral based absorbents [17][18][19][20][21][22][23][24][25][26][27][28][29]. Adsorption at low temperatures, offers a very selective and energy-efficient alternative [30,31], however, it is particularly challenging to achieve an efficient HCl removal at high gas velocities and low concentrations.…”

Experimental Investigation of the Reactivity of Sodium Bicarbonate toward Hydrogen Chloride and Sulfur Dioxide at Low Temperatures

“…Verdone and De Filippis extended the study of HCl sorption at higher HCl inlet concentrations (3000–6000 ppm), identifying 400 °C as the optimal reaction temperature for achieving maximum sorbent conversion. Duo et al and, more recently, Hartman et al explored the kinetics of the reaction between thermally decomposed Na 2 CO 3 and HCl at even higher temperatures (respectively, 300–600 °C with 900 ppm of HCl and 500 °C with 100–700 ppm of HCl), demonstrating the possibility to achieve deep removal of HCl with Na-based sorbents even at elevated temperature. Lastly, Ren and co-workers examined the performance of Na 2 CO 3 in the abatement of HCl emissions generated from biomass combustion or torrefaction, both in entrained flow and fixed bed configurations, showing HCl removal efficiencies higher than 50% in the range 300–1100 °C for a molar ratio of Na to Cl in the biomass around 5.…”

Decomposition of Potassium Hydrogen Carbonate: Thermochemistry, Kinetics, and Textural Changes in Solids

“…It can fix and release reversibly CO 2 from flue gas at acceptable cost. It is believed that a more reactive potassium analog of active soda − can be prepared from KHCO 3 under specific operating conditions.…”