OUTLINE

1. CONTROL OF GAS-PHASE CHLOROBENZENE USING TIO2-MEDIATED PHOTOCATALYSIS AND PACKED-BED ABSORPTIONC.RICHARDSONR. MARTINT. FANC. HALBERT VI

2. OUTLINE • INTRODUCTION • EXPERIMENTAL METHOD • RESULTS and DISCUSSION • CONCLUSIONS • FUTURE WORK • ACKNOWLEDGEMENTS

3. INTRODUCTION • WHAT IS PHOTOCATALYSIS? • A HETEROGENEOUS, ADVANCED OXIDATION PROCESS (AOP) INVOLVING THE GENERATION OF HIGHLY REACTIVE HYDROXL RADICALS • WHAT ARE THE PROCESS REQUIREMENTS? • A SEMICONDUCTOR AS A PHOTOCATALYST • UV LIGHT AS AN ENERGY SOURCE • WATER AS THE REACTION MEDIA

4. INTRODUCTION • WHY PHOTOCATALYSIS? • VOCs COMPRISE THE LARGEST CATEGORY OF TOXIC AIR POLLUTANTS • CONVENTIONAL TECHNOLOGIES ARE INEFFECTUAL AND UNECONOMICAL FOR CHLORINATED VOCs • PHOTOCATALYSIS CAN DEGRADE AND MINERALIZE MOST ORGANIC CONTAMINANTS IN WATER AND AIR • HIGH DESTRUCTION RATES ARE POSSIBLE • PROCESS OPERATES AT AMBIENT TEMPERATURE AND PRESSURE • SOLAR INSOLATION MAY BE A POTENTIAL ENERGY SOURCE

5. INTRODUCTION • REQUIREMENTS FOR A SEMICONDUCTOR • BAND GAP ENERGY HIGHER THAN 3.2 eV • STABLE, INEXPENSIVE, AND NON-TOXIC • ANATASE TITANIA (TiO2) @ A BAND GAP ENERGY OF 3.2 eV IS THE MOST COMMONLY USED SEMICONDUCTOR FORM VS RUTILE TITANIA (TiO2) @ 3.O eV • PLATINIZED TiO2 • BAND GAP ENERGY INCREASED FROM 3.2 eV TO 3.5 eV • PLATINUM ACTS AS AN ELECTRON TRAP DECREASING THE RECOMBINATION OF ELECTRONS AND POSITIVE HOLES WITH APPARENT HIGHER QUANTUM YIELD

6. MECHANISM OF PHOTOCATALYSIS

7. INTRODUCTION • ADVANTAGES OF SILICA-SUPPORTED TiO2 OVER SLURRY TiO2 PHOTOCATALYST • EASY SEPARATION FROM AQUEOUS PHASE • EXCELLENT FLUIDITY OF SILICA-GEL IN WATER • LARGER SPECIFIC SURFACE AREA OF SILICA-GEL • SILICA-GEL IS TRANSPARENT TO UV LIGHT • HIGHER QUANTUM YIELD POSSIBLE • ADVANTAGES OF ADDING AN INTERGAL COUNTERCURRENT PACKED-BED ABSORPTION UNIT WITH THE AOP • INCREASED VOC ABSORPTION DRIVING FORCE • INCREASED VOC DEGRADATION POTENTIAL

8. EXPERIMENTAL • CATALYST SYNTHESIS • PLATINIZATION OF TiO2 SLURRY • PLATINIZED, SILICA-SUPPORTED CATALYST • CHEMICAL METHOD (SOL-GEL) • PHYSICAL METHOD • BENCH-SCALE SET-UP, QUANTIFICATION AND OPTIMIMIZATION OF ABSORPTION/PHOTOCATALYTIC UNIT • SAMPLE COLLECTION AND ANALYSIS

9. EXPERIMENTAL • PHOTOCATALYTIC/ABSORPTION • EPA METHOD ZERO AIR DEVICE • SAMPLE FEED AND STABLE CONCENTRATION DEVICE • PHOTOREACTOR • VOC SPARGER • UV LAMP AND FILTER • CATALYST FILTERING DEVICE • MAGNETIC STIRRER • RECIRCULATION PUMP • ABSORPTION COLUMN • RANDOM PACKING WITH DISTRIBUTORS • SAMPLING PORTS

10. EXPERIMENTAL • SAMPLE COLLECTION AND ANALYSIS • 5 ML TREATED AIR SAMPLES TAKEN AT SPECIFIC TIMES AND LOCATIONS USING GAS-TIGHT GLASS SYRINGES WITH TEFLON-TIPPED PLUNGERS • CHLOROBENZENE CONCENTRATIONS ANALYZED WITH A HP 5880a GC WITH A FID DETECTOR • OFF-GAS CARBON DIOXIDE ANALYZED WITH ENVIRONMAXTM CO AND CO2 MONITOR • PHOTOREACTOR OPERATION • 450 W QUARTZ MERCURY-VAPOR LAMP AT 19 mW/cm2 at 2.5 cm WITH 280 to 400 nm WAVELENGTH FILTER • AIRFLOW RATES RANGE FROM 0.76 to 3.8 slpm • H2O RECIRCULATION RATE CONSTANT AT 330 ml/min • Ch-SILICA-GEL CATALYST LOADING FROM 20 to 150 gm

11. BENCH-SCALE SET-UP

12. CLASSICAL DEGRADATION KINETIC MODEL

13. THREE -PHASE SLURRY REACTOR • LIQUID AND CATALYST PARTICLES ARE WELL-MIXED AS IN A CONTINOUSLY STIRRED TANK REACTOR (CSTR) • GAS BUBBLES RISE THROUGH THE LIQUID AS A PLUG WITHOUT COMPLETE MIXING • AS A RESULT, THE GLOBAL RATE CAN CHANGE WITH VERTICAL POSITION IN THE CSTR • FOR A GIVEN VERTICAL POSITION, THE OVERALL REACTION CONSISTS OF SEVERAL PROCESSES IN SERIES

14. OVERALL PROCESS STEPS • MASS TRANSFER FROM THE BULK CONCENTRATION IN THE GAS BUBBLE TO THE BUBBLE-LIQUID INTERFACE • MASS TRANSFER FROM THE BUBBLE INTERFACE TO THE BULK-LIQUID PHASE • MIXING AND DIFFUSION IN THE BULK LIQUID • MASS TRANSFER TO THE EXTERNAL SURFACE OF THE CATALYST PARTICLES • REACTION AT THE CATALYST PARTICLE

15. OVERALL REACTION • RESISTANCE IN STEP THREE IS SMALL • RATES OF REMAINING PROCESS STEPS ARE IDENTICAL AT STEADY-STATE WHICH ALLOWS THE ELIMINATION OF UNKNOWN INTERFACIAL CONCENTRATIONS • GLOBAL RATE EXPRESSED AS A SIMPLE FIRST-ORDER IRREVERSIBLE REACTION AT THE CATALYST SURFACE • EQUILIBRIUM EXISTS AT THE BUBBLE-LIQUID INTERFACE AND IS RELATED BY HENRY’S LAW

16. GLOBAL REACTION RATE

17. GLOBAL REACTION RATE

18. THREE-PHASE KINETIC MODEL

19. RESULTS

20. RESULTS

21. RESULTS

22. RESULTS

23. RESULTS

24. RESULTS

25. RESULTS

26. RESULTS

27. RESULTS

28. RESULTS

29. RESULTS

30. CONCLUSIONS • HIGHLY ACTIVE SUPPORTED PHOTOCATALYSTS WERE DEVELOPED AND VIABLE OPTIONS IDENTIFIED • SILICA-SUPPORTED, PLATINIZED TITANIA PHOTOCATALYST SHOWED A HIGHER DEGRADATION RATE THAN SLURRY TITANIA CATALYST • A SOL-GEL GENERATED SILICA-SUPPORTED CATALYST DEMONSTRATED EXCELLENT ABRASION RESISTANCE TO LOSS OF TITANIA FROM ITS SUPPORT WHILE MAINTAINING NO OBSERVED LOSS OF DEGRADATION POTENTIAL

31. CONCLUSIONS • THE ADDITION OF AN INTEGRAL ABSORPTION COLUMN ON THE TOP OF THE PHOTOREACTOR DID NOT SHOW ANY ASSISTANCE TO THE STEADY-STATE CHLOROBENZENE DEGRADTION RATES • THE ACTIVE OXIDATION SPECIES HYDROXYL RADICALS COULD ONLY EXIST ON THE CATALYST SURFACE AND DID NOT RESIDE WITHIN THE RECIRCULATED ABSORPTION COLUMN WATER

32. CONCLUSIONS • MODERATE DEGRADATION OF CHLOROBENZENE WAS ACHEIVED WITH THIS PHOTOCATALYTIC APPARATUS • RESIDENCE TIME IN THE PHOTOREACTOR HAD A SIGNIFICANT IMPACT ON DEGRADATION AND MINERALIZATION OF CHLOROBENZENE • DEGRADATION AND MINERALIZATION DECREASED AS INLET MASS LOADING INCREASED • MAXIMUM CHLOROBENZENE REDUCTION ACHIEVED WAS 50 PERCENT WITH 37 PERCENT MINERALIZATION TO CO2 AT A LOADING OF 0.37 mg/min AT 1.3 SECONDS APPARENT RESIDENCE TIME • OVERALL REDUCTION WAS SLIGHLTY LOWER AT A LOWER PLATINIZATION RATIO OF TITANIA

33. CONCLUSIONS • A PREDICTIVE THREE-PHASE REACTOR MODEL USING FIRST-ORDER IRREVERSIBLE DEGRADATION KINETICS PROVIDED A MEANS TO QUANTIFY ABSORPTION AND DEGRADATION MASS-TRANSFER UNDER VARIED CONDITIONS • BOTH MASS-TRANSFER COEFFICIENTS INCREASED AS INLET MASS LOADING INCREASED • A LINEAR CORRELATION EXISTS BETWEEN INLET LOADING AND THE RESPECTIVE COEFFICIENT • A CONSTANT INTERCEPT FOR BOTH ABSORPTION AND DEGRADATION EXPERIMENTS WAS VERIFIED FOR CONSTANT AIR FLOW RATE EXPERIMENTS

34. FUTURE WORK • OPTIMIZE COMPOSITION OF SUPPORTED CATALYST (TiO2/SILICA-GEL WEIGHT RATIO, Pt/TiO2 WEIGHT RATIO, AND OPTIMUM CATALYST DOSAGE) • INVESTIGATE DEGRADATION MECHANISM BY QUALITATIVE AND QUANTITATIVE ANALYSIS OF FORMED INTERMEDIATES • TEST DIFFERNT GAS-PHASE CHLORINATED COMPOUNDS TO COMPARE KINETIC PARAMETERS AND SUBSTANTIATE CONCLUSIONS OF THIS STUDY

35. FUTURE WORK • IMPROVE REACTOR DESIGN TO ACHIEVE LONGER RESIDENCE TIME • TEST VARIOUS COMPOUNDS THAT SHOW AN APPARENT SURFACE ADSORPTION FOR THE SILICA-GEL SUPPORTED CATALYST • ESTIMATE THE QUANTUM YIELD FOR THE THREE-PHASE PHOTOREACTOR AND INVESTIGATE MEANS TO OPTIMIZE QUANTUM EFFICIENCY

36. ACKNOWLEDGEMENTS • WASTE-MANAGEMENT and EDUCATION, RESEARCH CONSORTIUM (WERC) FOR FINANICIAL SUPPORT • DR. MICHAEL PRAIRIE, SANDIA NATIONAL LABORATORIES FOR TECHNICAL ADVICE DURING THE INITIAL PROJECT PHASE • MS. JENNIFER KNOWLTON, NEW MEXICO TECH ENVIRONMENTAL ENGINNERING UNDERGRADUATE FOR LABORATORY ASSISTANCE AND DATA REDUCTION