taminco ssct 2011 presentation: understanding the relative volatility of chemicals: implications...
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2011 SSCT Annual MeetingUnderstanding the Relative Volatility ofChemicals: Implications for MeasuringVOC Content and Defining a VOCTRANSCRIPT
2011 SSCT Annual Meeting
Understanding the Relative Volatility of Chemicals: Implications for Measuring VOC Content and Defining a VOC
Definition of Volatility/VOC
Vapor Pressure Equations
Normal Boiling Points
Effect of T, composition, gas phase
Volatility assessment by TGA
Volatility versus GC Rt
Outline of Presentation
The Definition of Volatility
• Volatility is a generic term referring to some type of tendency for a condensed phase material (usually a liquid) to transfer to the gas phase.
• Volatility can be assessed by odor, flammability, etc.
• For scientific & regulatory purposes, volatility must be quantified in a precise and accurate manor. The only reasonable scientific measurement of volatility is derived by equating it with vapor pressure.
• The vapor pressure of a liquid (material) depends on the composition of the liquid phase, the composition of gas phase and on the temperature.
Vapor Pressure Models
• Clapeyron: Log(P) = A/T + B
• Antoine: Log(P) = A/(T-C) + B
• Riedel: LogP = A/T + B + Clog(T) + DT E
Correlative:
Predictive:• ACD Group Additive Methods
• Riedel: LogP = A/T + B + Clog(T) + DT E
Coefficients defined, Reduced T = T/Tc
• Variations: Frost-Kalkwarf-Thodos, etc.
CH3OH(l) → CH3OH(g)Vaporization as anactivated process
K = [CH3OH(g)]/[CH 3OH(l)]
[CH3OH(g)] = partial P
[CH3OH(l)] = 1 (pure liquid)
K = P
ln(P) = ln(K)
∆G = -RTln(K) = -RTln(P)
∆G = ∆H - T∆Sln(P) = -∆G/RT
ln(P) = -∆H/RT+ ∆S/R
∆S/R = B
∆H/R = -A
Two Parameters: Log(P) = A/T + B
Two Parameters: Log(P) = A/T + BDBAE (GMW = 173.30, CAS RN 102-81-8): Below is a table of the literature data that we could find for the boiling point of DBAE versus pressure. BP (oC) BP (oK) P (torr) P (KPa) Reference
230 503.15 760 101.3232 Bouilloux; Bull.Soc.Chim.Fr.; 1958; 1446. 227 500.15 738 98.3902 Burnett et al.; J.Amer.Chem.Soc.; 59; 1937; 2249. 118 391.15 17 2.2664 Leonard; Simet; J.Amer.Chem.Soc.; 77; 1955; 2855, 2857. 100 373.15 0.8 0.1067 Perrine; J.Org.Chem.; 18; 1953; 1356,1361. 85 358.15 3.5 0.46662 Hannig; Haendler; Arch.Pharm.(Weinheim Ger.); 290; 1957; 131,133.
^^ r2 = 0.999942 Apparent ∆Hvaporization = 55.86 KJ/mole & ∆Svaporization (1 Torr) = 166.39 J/(mole-K)
Atmospheric Pressure BP’s are debatable
Slow Decomposition & Raoult’s Law
BBAAT PxPxP +=
Why not just distill at atmospheric pressure?
Raoult's Law (TEA/MEA)
150
170
190
210
230
250
270
290
310
330
350
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Mole Fraction TEA in Liquid
Boi
ling
Tem
pera
ture
(oC
) of
Liq
uid
Boiling Point of Solution
Mole fraction TEA in Vapor
A temperature gradient sets up inthe neck of the distillation!
Impossible to get an accurateBP for pure TEA in the neck
Relative Volatility Changes with Temperature
Is there a good correlation of volatility with normal boiling point?
Real Relative Volatility
Measure as close to the use temperature as is possible
0
2
4
6
8
10
12
14
40 60 80 100 120 140 160 180 200 220
Temperature (oC)
Der
ivat
ive
Wei
ght
Los
s (%
/min
)
AMP MEA TBA DBAEAEPD TXIB Hexadecane BDEAGlycerol TEA Methyl Palmitate
Derivative Weight Loss as a function of Temperature
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
40 60 80 100 120
Temperature (oC)
Der
ivat
ive
Wei
ght L
oss
(%/m
in)
AMP MEA TBA DBAEAEPD TXIB Hexadecane BDEAGlycerol TEA Methyl Palmitate
Expanded View - Derivative Weight Loss - function of Temperature
Exemplary Derivative Weight Loss Ratios
0.00
0.20
0.40
0.60
0.80
1.00
1.20
50.00 80.00 110.00 140.00 170.00 200.00
Temperature ( oC)
Rat
io D
eriv
ativ
e W
eigh
t Los
s
Glycerol/TXIB TEA/Glycerol
DBAE/TBA AEPD/TXIB
MePalm/Glycerol BDEA/2MHD
Volatility Changes with Composition
AzeotropesSaltsChemical ReactionsIncorporation into Crosslinking
Sequential Additive Additionwith Method 24 based
VOC determination
The measurement of real volatility in the coating, but with a problematic method
VOC Determination of Waterborne Coatings
At the request of Dan Marschall of Marschall Labs, the Thames-Rawlins Research Group evaluated twelve (12) waterborne coatings for their volatile organic content using Method 24. Specifically, the coating solids were determined gravimetrically via ASTM D 2369 by heating at 110°C for 1 hour while the water content was determined via Karl-Fisher titration via ASTM D 4017. The test results are reported in Table 1.
Table 1. VOC Results
Sample Solids % Volatiles % Water % VOC (g/L) T20A 53.27 46.73 44.73 26.28 T20B 52.99 47.01 45.15 24.50 T20C 52.99 47.01 46.61 5.26 T20D 53.32 46.68 46.43 3.28 T20E 53.38 46.62 45.84 10.21 T20F 53.29 46.71 46.51 2.67 T21A 57.34 42.66 41.33 28.15 T21B 57.02 42.98 43.51 -7.43 T21C 57.47 42.53 43.49 -13.28 T21D 57.50 42.50 43.95 -20.13 T21E 57.48 42.52 43.99 -20.00 T21F 57.78 42.22 43.91 -23.27
What about GC Rt as an assessment of volatility?
Correlations of GC Rt with volatility are usually fairly good for homologous series of molecules.
Relationship not good across different types of molecules; possibly because ∆(∆S) of vaporization varies significantly.
The GC Conundrum: 1/Rt does not really match volat ility
The GC Conundrum: 1/Rt does not really match volat ility
Accounting for gas compositionMeasuring Entropy of Vaporization
Assumed ∆Hφ = constant(enthalpy can be directly measured @ T)
Accounting for gas compositionMeasuring Entropy of Vaporization
Affected by gas phaseAffected by liquid phase
What is the best way to measure volatility?
Thermal methods operated under conditions as close as possible to the use conditions work the best
T Ramp TGA of Vantex-T (first derivative)
Thermal Methods can be easily adapted to investigate different conditions, etc.
Thermal Methods run at temperature as close to the use temperature as is possible are best.
Chamber testing is the best option developed so far. The chamber test method measures the actual content of the air above the coated object.
Conclusions
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