WP1 and WP2 highlights

Stefan Persijn

KEY-VOCs Webinar 5 September 2017

www.key-vocs.eu

WP1 Adsorption and reaction effects on surface materials and zero gas standards

WP2 Reference standards to underpin atmospheric monitoring of VOCs

Challenges in measuring VOCs

2

optimum

bad

typical

Why study the surface interaction?

Make sure that your

measurements are correct

Reduce the use of your

valuable reference gas

mixtures

Speed up the

measurements

3

Obtain accurate gas

standards for calibration of

your analyser

Approaches followed to investigate VOC adsorption

Adsorption in tubings Experimental and modeling studies of adsorption-desorption kinetics of

OVOCs in sampling lines

Surface analysis Characterize chemical speciation on surfaces via x-rays

Adsorption in cylinders Decanting studies of OVOC gas mixtures and comparison with

dynamically prepared gas mixtures

4

Set-up for quantifying the adsorption in tubings

Step 1

Methanol mixture via bypass to CRDS

Test tube flushed with N2

Step 2

Methanol mixture via test tube to CRDS

Methanol : 182 nmol/mol

Flow : 0.55 L/min

Temperature : 20 °C

Test tube

5

Set-up for quantifying the adsorption in tubings

Step 1

Methanol mixture via bypass to CRDS

Test tube flushed with N2

Step 2

Methanol mixture via test tube to CRDS

Methanol : 182 nmol/mol

Flow : 0.55 L/min

Temperature : 20 °C

Test tube

6

Adsorption in SS304 with(out) coating

LID = 15.25 m5.3 mm

Inner volume = 0.34 L

Transit time ~ 37 seconds

7

Polymers: lowest

Coated metals: intermediate

Uncoated metals: highest

Results adsorption measurements in tubings

Aluminum Copper

PTFE PVDF

SS304

Sulfinert

Silconert

2000

Methanol

amount

fraction:

182 nmol/mol

Material

Molecules

adsorbed

(x1011 cm-2)

Corrected for

gas exchange

PTFE 1.44±0.09

PVDF 1.8±0.1

Silconert 2000

coated SS304 3.2±0.1

Sulfinert

coated SS 50 ±2

SS304 (2.6±1.6)·102

Aluminium (3.8±1.8)·102

Copper (6.4±2.8)·103

8

Methanol adsorption (3 ppm) in tubings at elevated temperatures using FID

Material Type Treatment 50 °C 100 °C

Stainless

steel

321 none =

strong adsorption

=

no methanol detectable

316 Electro-

polished =

strong adsorption

=

moderate/strong adsorption

316 Sulfinert®

coating

< <

304 < <

Polymer

PFA

none

< =

high outgassing

PEEK some adsorption some outgassing/adsorption

<

<

Test tubing inside GC oven

9

4,7

4,8

4,9

5,0

5,1

5,2

5,3

5,4

5,5

5,6

5,7

Cy

lin

der

1

Cy

lin

der

2

Cy

lin

der

3

Mea

n v

alu

e

Cylinders

Acetone 1.0 %

Homogeneity of OVOC mixtures at 100 ppb

2,9

3,0

3,1

3,2

3,3

3,4

3,5

3,6

3,7

3,8

3,9

Cy

lin

der

1

Cy

lin

der

2

Cy

lin

der

3

Mea

n v

alu

eCylinders

Ethanol

3.5 %

0,9

1,0

1,1

1,2

1,3

1,4

1,5

1,6

1,7

1,8

1,9

Cy

lin

der

1

Cy

lin

der

2

Cy

lin

der

3

Mea

n v

alu

e

Cylinders

Methanol

4.7 %

Formaldehyde: decanting and pressure effect

\

11

Decanting losses cylinders

Cylinder type

A B C D * Other (SW)

Formaldehyde (○) + ○ +

Methanol ▬ ○ ▬ ▬ ○

Ethanol ○ + ▬ ▬ (+)

Acetone + + (○) (+) +

Methacrolein + + + + +

MVK + + + + +

MEK + + ○ ○ +

* Formaldehyde cylinders differ from OVOC cylinders

+ (D < 5 %) ○ (D 5…10 %) ▬ (D >10 %)

12

Formaldehyde: Long term stability

13

1 year stability performance of short-lived species (100 nmol/mol) in different cylinders types with sampled enriched-GC-FID

14

+5%

- 5%

Analytical uncertainty 2 % Analytical uncertainty 5 %

+5%

- 5%

Towards analysis of surface adsorption: ethanol on SS

▬ EtOH in gas phase measured in

transmission mode (for comparison)

▬ surface signal with EtOH in gas cell

▬ surface signal without EtOH in gas cell

15

ReGaS2 : Mobile Gas Generator

Uncertainty budget

MVK 23 ppb ± 3.1%

MVK generation & measurement with ATD-GC-FID Dynamic generation with permeation

VOCs at ppb level

1-5 compounds simultaneously

Stability of RGM ≤ 0.4 %

Reproducibility of RGM ≤ 0.7 %

SilcoNert2000® coating

VOC-free zero gas: removal dependent on type of purifiers

17

VOC-free zero gas important for dilution and zero point calibration. Types: inorganic media and metal catalysts VOCs: NMHCs, monoterpenes, OVOCs

More info in the 5 min presentation of Jennifer Englert (DWD)

Conclusions

Gas standards for atmospheric monitoring

Cylinder treatment plays a crucial role in the accuracy and stability

ldentified cylinder types with best performance (in general coated SS)

Methanol, acethaldehyde and formaldehyde do not meet the DQOs for

uncertainty and stability

Zero gases Removal of impurities is purifier dependent

Extending the certification protocol zero gas to VOCs

18

Adsorption in tubings Polymer tubings best (when not heated) but subject to permeation.

Coated tubings good alternative & preferred for applications where

heating is required.

Portable generators Portable generators produce reference gas mixtures of reactive

compounds at atmospheric level to calibrate instruments in the field