1. CE 583 – Control of Volatile Organic Compounds
CE Control of VOCs
CE 583 – Control of Volatile Organic Compounds
Jeff Kuo, Ph.D., P.E.
Jeff Kuo, Ph.D., P.E. (CSUF)

2. Content Vapor pressure, Equilibrium Vapor Content, Evaporation VOCs
Control by Prevention
Control by Concentration and Recovery
Condensation
Adsorption
Absorption (scrubbing)
Control by Oxidation
Combustion
Biological Oxidation (Biofiltration)
Choosing a Control Technology

3. Introduction
2nd most widespread and diverse class of emissions after particulates.
Main concern: participation in “smog” and ozone reaction and formation of secondary particles.
Some are toxic, some are IR absorbers.
More than 150 HAPs are VOCs.
Source Type (US, 1997)
Thousands tons/yr
% of total
Wood burning
1294
5.73
Industrial processing
1457
7.58
Waste disposal
449
2.34
VOC storage
1377
7.17
Solvent use
6483
33.74
Motor vehicles
7660
39.86

4. Vapor Pressure, Equilibrium Vapor Content, Evaporation
VP = f(T). VP of 20 oC = atm = 17.5 torr.
Normal Boiling Point: T at which VP = Patm.
VP of Hg ~ oC, still a concern (toxic).
Metals such as Cd, Zn will vaporize in incinerators.
Partial P in a mixture
VP of a pure compound

5. VOCs Boiling points up to 500 oF (260 oC)
Organic compounds up to 12 carbon atoms
EPA Definition (40 CFR51.100(s)): Any compound of carbon, excluding CO, CO2, carbonic acid, metal carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions (some notable exceptions: methane, ethane, 1,1,1-TCA, some CFCs, PCE).
VOC and HC terms are often practically identical.
Polar organics are ~100x more soluble than HC.
For same family, solubility decreases with increasing MW.

6. Control by Prevention Substitution Water-based paint, CNG
Process Modification
Fluidized-bed powder coating, electric-powered vehicles (but more emission during electricity generation), car-pool.

7. Control by Prevention Filling, Breathing and Empting Losses
Filling (displacement): Gas being displaced is typical saturated with VOCs it has been in contact.
Breathing (diurnal): T increase causes increase in VP, expansion of the liquid, vapor and the tank.
Adjust Reid VP (RVP) of gasoline for different seasons.
Leakage control/fugitive emissions.

8. Control by Prevention

9. Stage 2 control:Dual vapor return system
Stage 1: w/o return from pump.
0.45 g/gal
4.54 g/gal
0.32 g/gal

10. Control by Concentration and Recovery - Condensation

11. Control by Concentration and Recovery - Adsorption
Absorption – the dissolution of gas molecules into bulk liquid.
Adsorption – physical, reversible attachment of gas (or vapor) molecules to a solid surface
Chemisorption – the attractive forces between gas molecule and surface are closer to chemical bonding than physical attraction.
The term “Sorption “ is used to avoid having to make the distinction,

12. Control by Concentration and Recovery - Adsorption
Adsorbents used are high surface area ( ca m2/g) micro-porous particles. Alumina (Al2O3), Silica (Si2O3), activated carbon.
Adsorbent capacity, w* : mass of sorbate per mass of sorbent.

13. Control by Concentration & Recovery - Adsorption
Isotherms for HCs on activated carbon and silica gel
Control by Concentration & Recovery - Adsorption
x-axis: (T ’L/18M)log(fs/f); y-axis = 100 w*/ ’L
’L: liquid density at normal boiling point, g/cm3
M: molecular weight
fs/f: essentially the same as p*/pi (vapor pressure/ partial pressure)

16. Control by Concentration & Recovery – Absorption (scrubbing)
VOC selectively absorbed by bringing gas and solvent in contact in a packed column.
Solvent and VOC separated in another column operating at lower temperature or pressure.

17. Control by Oxidation – Combustion (incineration)
Combustion responsible for most of the air pollutants of concern.
Combustion can also be a solution if practiced properly (i.e. sufficient 3T’s)
Incineration is the term used when the purpose of combustion is the destruction of pollutants rather then energy production.

18. Relatively small changes in T result in large differences in t required for a particular . In most incinerators the  are of the order of seconds. If the T drops,  drops significantly.
Benzene

19. Incineration arrangements
A) simple thermal incinerator
B) regenerative heat recovery
C) catalytic incinerator

20. Control by Oxidation – Incineration
The oxygen and combustible come in contact over a surface instead of being homogeneously mixed.
Solid or liquid combustible usually first vaporizes:
Evaporation = simple phase change
Pyrolysis = breakdown of large combustible molecules thus giving off smaller, more volatile molecules in an inert (or reducing atmosphere), i.e. in the absence of oxygen.
Both are endothermic processes. The required heat is supplied by the combustion of the vapor

21. Control by Oxidation – Biofiltration
Biofilters: gas distributor pipes at the bottom, covered with several feet of soil/compost  VOC dissolved in soil moisture.

22. Control by Oxidation – Biofiltration
Typical: soil depth = 3 – 4 ft; void = 50%, upward gas velocity = to 0.5 fps; residence time = s.
Better for polar compounds (soluble)
Need moisture and nutrients.
Protection of M/O (toxins, pH, T)
Large footage.

23. VOC Control Choices
Would type of VOC matter?