Taminco SSCT 2011 Presentation: Understanding the Relative Volatility of Chemicals: Implications...

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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