AN ENGINEERING ANALYSIS ON CONTROL OF BREATHING ATMOSPHERES USING ALKALI METAL SUPEROXIDES PHASE I under Omnibus Contract Number N00612 -79 -D -8004 for Delivery Order Number HR-43 Jeffrey O. Stull & Mark G. White School of Chemical Engineering Georgia Institute of Technology Atlanta GA 30332 January 15, 1982 TABLE OF CONTENTS LIST OF FIGURES iii LIST OF TABLES ABSTRACT vii Section I. INTRODUCTION 1 II. AIR REVITILIZATION COMPOUNDS: A LITERATURE SURVEY 4 Oxygen Producing Compounds 5 Carbon Dioxide Absorbents 6 Air Revitilization Compounds (General) 7 Peroxides 8 Superoxides 13 Ozonides 25 Special Air Revitilization Chemical Mistures 29 Comparison of Air Revitilization Chemicals 32 Improvement of Potassium Superoxide Performance 38 III. POTASSIUM SUPEROXIDE THERMODYNAMICS AND EQUILIBRIA 46 Previous Investigations 47 Gas Phase Ideality 48 Thermodynamic Data 49 Reaction System 51 Equilibrium Calculations 54 IV. THE KINETICS OF THE AIR REVITILIZATION REACTIONS OVER K0 2 . 59 Range of Data Base 60 TABLE OF CONTENTS (Cont.) Section IV. KINETICS (Continued) Regressing the Kinetic Data at 25°C 60 Particle Size Effects 63 Temperature Effects 64 V. THERMAL ANALYSIS OF A CLOSED, AIR REVITILIZATION SYSTEM . 65 Description of System 65 Formulation of Model 66 Parameters used in the Model 69 Results 70 Discussion of Results 72 VI. STOICHIOMETRIC SUPEROXIDE BED LOADINGS 75 VII. POTASSIUM SUPEROXIDE CANNISTER DESIGN STUDY 76 VIII. CANNISTER PRESSURE DROP CALCULATIONS 80 IX. RECOMMENDATIONS FOR FUTURE WORK 82 FIGURES TABLES REFERENCES ii LIST OF FIGURES Figure No. Title 1 COMMERCIAL PRODUCTION OF POTASSIUM SUPEROXIDE 2 COMPARISON OF AIR REVITILIZATION COMPOUND / CARBON DIOXIDE ABSORBENT MISTURES 3 RELATIVE THEORETICAL PERFORMANCE AND PURITY OF AIR REVITI- LIZATION COMPOUNDS 4 DISSOCIATION PRESSURE OF NaHCO AND KHCO 3 3 5 THE EFFECT OF TEMPERATURE ON REACTION EQUILIBRIUM CONSTANTS 6 RATE OF HEAT RELEASE: OVER KO2 AT 25 °C AS A FUNCTION OF WATER AND CARBON DIOXIDE CONCENTRATIONS 7 CORRELATION OF WATER. ABSORPTION FROM KO2 AT 25 °C AS A FUNCTION OF WATER AND CO2 CONCENTRATIONS 8 CORRELATION OF CARBON DIOXIDE ABSORPTION ON KO2 AT 25 °C AS A FUNCTION OF WATER AND CO2 CONCENTRATIONS 9 CORRELTATION OF OXYGEN EVOLUTION FROM KO2 AT 25 °C AS A FUNCTION OF WATER AND CO2 CONCENTRATIONS 1 0 CORRELATION OF TEMPERATURE EFFECTS UPON REACTION RATES 11 HEAT CAPACITY OF BREATHING MIXTURE AT 298 °K AS A FUNCTION OF DEPTH (P 3 mm Hg; P = 5 mm Hg) CO2 H2O 12 HEAT CAPACITY OF BREATHING MIXTURE AT 298 °K AS A FUNCTION OF DEPTH (P CO2 P= 11.4 mm Hg) nH2O o 13 HEAT CAPACITY OF BREATHING MIXTURE AT 298 K AS A FUNCTION OF DEPTH (P CO2 = 61 Hg) PH20 m 14 SCHEMATIC OF AIR REVITILIZATION BACK-PACK 15 MODEL OF GAS FLOW PATTERN OF BACK-PACK 16 CORRELATION OF REQUIRED HEAT EXCHANGE RATE (UA) WITH RATE OF HEAT RELEASE (DEPTH = 0.0 ft) 17 CORRELATION OF REQUIRED HEAT EXCHANGE RATE (UA) WITH RATE OF HEAT RELEASE (DEPTH = 90.0 ft) iii LIST OF FIGURES (Cont.) Figure No. Title 18 CORRELATION OF REQUIRED HEAT EXCHANGE RATE (UA) WITH RATE OF HEAT RELEASE (DEPTHS 475 or 1000 ft) 19 NOMOGRAPH FOR KO2 CANNISTER DESIGN. LINES OF CONSTANT 0 2 EVOLUTION RATE 20 KO2 CHARGE WEIGHT AS A FUNCTION OF INLET CONDITIONS 21 SUPPLEMENTAL CARBON DIOXIDE SCRUBBING iv LIST OF TABLES Table No. Title 1 COMPARISON OF LIFE SUPPORT SYSTEMS FOR SPACE CRAFT 2 THEORETICAL PROPERTIES OF AIR REVITILIZATION COMPOUNDS 3 LITHIUM SUPEROXIDE SYSTEM REACTIONS 4 CALCIUM SUPEROXIDE SYSTEM REACTIONS 5 SODIUM SUPEROXIDE SYSTEM REACTIONS 6 POTASSIUM SUPEROXIDE SYSTEM REACTIONS 7 POTASSIUM OZONIDE SYSTEM REACTIONS 8 ALKALI SUPEROXIDE TEST PROGRAMS 9 FUGACITY COEFFICIENT CALCULATIONS 10 POTASSIUM COMPOUND DATA 11 POTASSIUM SUPEROXIDE INDEPENDENT REACTIONS 12 SUMMARY OF MODEL PREDICTIONS FOR TEMPERATURE-TIME EXCURSIONS OF A BREATHING AIR MIXTURE IN CONTACT WITH K0 2 (UA = 0.0 CAL/ SEC °C). STEADY STATE TEMPERATURE AND EQUATION PARAMETERS 13 SUMMARY OF MODEL PREDICTIONS FOR TEMPERATURE-TIME EXCURSIONS OF A BREATHING AIR MIXTURE IN CONTACT WITH KO (UA = 0.1 CAL/ 2 SEC-°C). STEADY STATE TEMPERATURE AND EQUATION PARAMETERS 14 SUMMARY OF MODEL PREDICTIONS FOR TEMPERATURE-TIME EXCURSIONS OF A BREATHING AIR MIXTURE IN CONTACT WITH K0 (UA = 0.5 CAL/ 2 SEC-0C). STEADY STATE TEMPERATURE AND EQUATION PARAMETERS 15 SUMMARY OF MODEL PREDICTIONS FOR TEMPERATURE-TIME EXCURSIONS OF A BREATHING AIR MIXTURE IN CONTACT WITH KO, (UA = 1.0 CAL/ SEC-°C). STEADY STATE TEMPERATURE AND EQUATION PARAMETERS 16 SUMMARY OF MODEL PREDICTIONS FOR TEMPERATURE-TIME EXCURSIONS OF A BREATHING AIR MIXTURE IN CONTACT WITH KO, (UA = 0.0 CAL/ SEC-°C). TIME TO REACH STEADY STATE TEMPERATURE 17 SUMMARY OF MODEL PREDICTIONS FOR TEMPERATURE-TIME EXCURSIONS (UA = 0.1 CAL/ OF A BREATHING AIR MIXTURE IN CONTACT WITH KO 2 SEC-°C). TIME TO REACH STEADY STATE TEMPERATURE LIST OF TABLES (Cont.) Table No. Title 18 SUMMARY OF MODEL PREDICTIONS FOR TEMPERATURE-TIME EXCURSIONS OF A BREATHING AIR MIXTURE IN CONTACT WITH KO,, (UA = 0.5 CAL/ SEC-°C). TIME TO REACH STEADY STATE TEMPERATURE 19 SUMMARY OF MODEL PREDICTIONS FOR TEMPERATURE-TIME EXCURSIONS OF A BREATHING AIR MIXTURE IN CONTACT WITH KO 2 (UA = 1.0 CAL/ SEC-°C). TIME TO REACH STEADY STATE TEMPERATURE 20 THEORETICAL OXYGEN EVOLUTION EFFICIENCIES FOR SUPEROXIDES 21 THEORETICAL CO2 SCRUBBING EFFICIENCIES FOR SUPEROXIDES VERSUS ALKALI HYDROXIDES 22 DESIGN SPECIFICATIONS FOR KO CANNISTER 2 23 KO CANNISTER DESIGN CASE STUDY 2 24 COMPARISON OF CANNISTER PREDICTIONS WITH LARGE CHAMBER DATA OF KUNARD AND RODGERS 25 PREDICTED CANNISTER PRESSURE DROP 26 RANGE OF EXPERIMENTAL VARIABLES vi ABSTRACT A search of the literature indicates potassium superoxide is a proven choice as a reliable air revitilization chemical. Sodium superoxide must be cooled to prevent the unexpected release of carbon dioxide by the thermal decomposition of sodium bicarbonate. Calcium superoxide and the alkali metal ozonides are not available as pure commercial products and the kinetics for oxygen production are unkown. The effect of pressure on the chemical equilibria is very small; at 25°C the bicarbonate phase is heavily favored by the equilibria at depths to 1000 feet. Most of the reliable kinetic data are available for potassium superoxide tablets and spheres. Particles of small diameter R10 mesh or 2 mm diameter) give high rates of oxygen evolution but suffer from excessive pressure drop and "dusting". With suitable control of humidity, K02 particles of 2 - 4 mesh (5 to 8 mm diameter) will give acceptable, but low, rates of oxygen evolution (r%i 2 lb 02 /man-day). A rippled plate configuration of the superoxide is promising but more kinetic reaction data are needed. The preferred K0 2 cannister inlet conditions established by our studies are: 3 mm Hg < P < 11 mm Hg and 15 mm Hg < P < 20 mm Hg at a tempera- CO2 H 2 ture of 25 °C. These conditions over an adequate potassium superoxide bed will produce initial oxygen evolution rates of 1.75 to 2 pounds 0 2/man-day. It is desirable to control the inlet humidity independent from the inlet partial pressure of carbon dioxide to the superoxide bed. Upstream carbon dioxide scrubbing of the breathing gases is indicated for optimum utilization of the potassium superoxide. vii The theoretical superoxide bed loading for an eight hour mission, assuming 1.87 pounds of oxygen are needed for one man-day, and 60% of the theoretical K0 utilization, is three pounds. The kinetics for revitilizing 2 humid air, PP._H = 15 to 20 mm Hg, demand 3 to 4 pounds superoxide bed if the volumetric gas flowrate is 20 liters per minute. The correlated rate equa- tion used in predicting these bed loadings is based on initial rate data; we expect the "aged" K02 beds will show reaction rates lower, by a factor of 3, than our predictions. The superoxide exit carbon dioxide partial pressure is predicted at less than 0.3 mole percent, surface equivalent. For the preferred potassium superoxide cannister inlet conditions, supplemental carbon dioxide scrubbing in the amount of 0.8 to 1.7 lb. CO 2/ man-day must be provided for the total air revitilization system to cleanse 2.21 lb. CO /man-day. Soda-sorb, lithium hydroxide, etc., are possible 2 scrubbing agents. The steady state gas temperature can be controlled to less than or equal to 35 °C with heat exchange to the environment using less 2 than 8 ft of area assuming the "worst" case for heat transfer. Additional kinetic measurements are necessary to document the effect of pressure to 30 atmospheres and the effect of temperature upon the reaction rate. viii SECTION I INTRODUCTION Any sort of enclosed space for which human activity is to be sustained for some period of time, necessitates a means of life support. Usually this situation results any time man is subjected to a hostile environment, such as beneath the water, in space, or in the presence of a hazardous atmosphere. Pressurized oxygen in cylinders had been the acceptable means of air revitilization for many years in several appli- cations. However, the weight and volume of such systems has precluded its efficient use required by the technology for submarines, aircraft, space vehicles, and even portable breathing apparatus. There have been a variety of different atmosphere regeneration techniques developed in the past several decades. These include using some sort of umbilical method, cryogenic oxygen (both supercritical and subcritical), high pressure oxygen storage, electrochemical methods, and chemical methods. Depending on the type of application, each of the aforementioned systems can perform air revitilization either alone or in concert with another system. Each has its advantages and disadvantages. Three factors of consideration to the design of a life support system are weight, volume (space occupied), and energy requirements.