Process Analytical Technology. How much oxygen is inside?

Size: px

Start display at page:

Download "Process Analytical Technology. How much oxygen is inside?"

Peregrine Moore
5 years ago
Views:

1 Process Analytical Technology How much oxygen is inside? Jacqueline Waldvogel, Yves Wittwer

2 Process Analytics monitoring of process parameters to ensure: cost-effective production product quality efficient planning of maintenances safe plant operation two important concepts related to Process Analytics: feed-forward: proactive, avoid errors before they occur feed-back: reactive, correct errors after they already occurred W. Kessler. Prozessanalytik: Strategien und Fallbeispiele aus der industriellen Praxis Jacqueline Waldvogel, Yves Wittwer

3 Process Analytics for both correction mechanism, online monitoring of certain process parameters is necessary Jacqueline Waldvogel, Yves Wittwer

Offline Analysis Pro: analysis is performed by experts flexible cheap appropriate surrounding sample is transported to a laboratory with highly-skilled staff W. Kessler.

4 Offline Analysis Pro: analysis is performed by experts flexible cheap appropriate surrounding sample is transported to a laboratory with highly-skilled staff W. Kessler. Prozessanalytik: Strategien und Fallbeispiele aus der industriellen Praxis Contra: slow «ownership of data» not guaranteed direct process control is not possible Jacqueline Waldvogel, Yves Wittwer

Atline Analysis (exline) Pro: relatively fast Contra: usually without qualified personal instruments have to be more solid manually or (half-) automatized sampling and

5 Atline Analysis (exline) Pro: relatively fast Contra: usually without qualified personal instruments have to be more solid manually or (half-) automatized sampling and analysis near by the process W. Kessler. Prozessanalytik: Strategien und Fallbeispiele aus der industriellen Praxis Jacqueline Waldvogel, Yves Wittwer

Online Analysis Pro: fast highly specific analyser feedforward and feedback control possible usually analysis in a bypass Contra: expensive calibration more difficult sampling is accident-sensitive

6 Online Analysis Pro: fast highly specific analyser feedforward and feedback control possible usually analysis in a bypass Contra: expensive calibration more difficult sampling is accident-sensitive condition: t R (investigated property) > t R (sensor) The time needed for a investigated property to change must be smaller than the time required for a complete measurement (including data evaluation). W. Kessler. Prozessanalytik: Strategien und Fallbeispiele aus der industriellen Praxis Jacqueline Waldvogel, Yves Wittwer

Inline Analysis Pro: direct information obtained no sampling needed (therefore less accident-sensitive) similarities to online analysis, but without sample-taking.

7 Inline Analysis Pro: direct information obtained no sampling needed (therefore less accident-sensitive) similarities to online analysis, but without sample-taking. Pro expense calibration no sample-pre-treatement possible high requirements for instruments W. Kessler. Prozessanalytik: Strategien und Fallbeispiele aus der industriellen Praxis Jacqueline Waldvogel, Yves Wittwer

8 Why monitoring oxygen? large interest in measuring oxygen quantitatively variety of different methods available oxygen is important in many fields, e.g: medicine biology industry Jacqueline Waldvogel, Yves Wittwer

9 Industrial usage of O 2 : A few examples production of: sulfuric acid from sulfur S + O 2 SO 2 2SO 2 + O 2 SO 3 H 2 SO 4 nitric acid (Ostwald process) ethylene oxide hydrogen peroxide (Anthraquinone process) Goor, G.; Glenneberg, J.; Jacobi, S. Ullmann s Encyclopedia of Industrial Chemistry, 18, Jacqueline Waldvogel, Yves Wittwer

10 Considered reaction continuous process direct oxidation silver-based catalyst prevent further oxidation to CO 2 and H 2 O oxygen concentration as crucial parameter -> monitoring of oxygen Jacqueline Waldvogel, Yves Wittwer

11 Needs in this case: typical concentration of oxygen: 6 8 % temperature range: C pressure range: bar high reliability of the analytical method/ instrument gas is consisting different components (organic compounds) fluctuations of gas pressure might be possible installation of the instrument in explosive protected area (ATEX zone 2) Jacqueline Waldvogel, Yves Wittwer

ATEX Atmosphères Explosibles ATEX 95 2014/34/EU: equipment directive ATEX 137 1999/92/EG: workplace directive explosion protection high-risk areas are divided in zones by ATEX frequency duration of

12 ATEX Atmosphères Explosibles ATEX /34/EU: equipment directive ATEX /92/EG: workplace directive explosion protection high-risk areas are divided in zones by ATEX frequency duration of dangerous explosive atmosphere Jacqueline Waldvogel, Yves Wittwer

13 ATEX Jacqueline Waldvogel, Yves Wittwer

ATEX avoid ignition sources self ignition, static electricity, ultrasonic, hot surfaces, sparks, -> electrical parts are especially critical ignition protection flush critical components with inert

14 ATEX avoid ignition sources self ignition, static electricity, ultrasonic, hot surfaces, sparks, -> electrical parts are especially critical ignition protection flush critical components with inert gas (electrical) separate electrical parts in case of emergency protect electrical components from explosion by stable covers W. Kessler. Prozessanalytik: Strategien und Fallbeispiele aus der industriellen Praxis Jacqueline Waldvogel, Yves Wittwer

15 Major methods for oxygen determination Chemical Reactions Winkler method Chromogenic reactions Electrochemical Lambda electrode Clark electrode Gas chromatography Optical Absorption spectroscopy Quenching based Paramagnetic sensors Jacqueline Waldvogel, Yves Wittwer

Chemical methods: Winkler method developed 1888 by Ludwig W. Winkler only for dissolved oxygen easy to use due to commercially available kits http://www.coleparmer.

16 Chemical methods: Winkler method developed 1888 by Ludwig W. Winkler only for dissolved oxygen easy to use due to commercially available kits hod_50_tests_kit/ew , Jacqueline Waldvogel, Yves Wittwer

17 Chemical methods: Winkler Method Step 1: fixation of dissolved oxygen 2 Mn 2+ + O OH - 2 MnO(OH) 2 Step 2: Use Mn(IV) to generate I 2 in an amount, which is proportional to the original concentration of O 2 MnO(OH) 2 + 2I - + 4H + Mn 2+ + I 2 + 3H 2 O Step 3: determine amount of I 2 by titration (eventually with the help of an indicator) 2S 2 O I 2 2S 4 O I - respectively with I 3 - Winkler, L.W. Die Bestimmung des im Wasser gelösten Sauerstoffes. (1888). Jacqueline Waldvogel, Yves Wittwer

18 Chemical methods: Chromogenic Method colour change of dye due to reaction with oxygen example: Ageless Eye reduction usually done chemically (e.g. by ascorbic acid) Jacqueline Waldvogel, Yves Wittwer

19 Chemical methods: Ageless Eye application in food packaging other examples for chromogenic reactions: haemoglobin based based on oxide formation of nickel Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff. Jacqueline Waldvogel, Yves Wittwer

20 Chemical methods: Pros and Cons Pros Cons - easy to use - no continuous online measurements - often cheap (Winkler Kit: 41.50$ for 50 tests) - time intensive methods - readout often directly by eye, but - subjective readout - very low lifetimes conclusions concerning our case: no online measurements possible no real-time correction of process parameters possible difficult implementation into the plant not suitable for our case Jacqueline Waldvogel, Yves Wittwer

Electrochemical methods example: Lambda-type electrode ZrO 2 behaves like a solid

p1 p2 generation of different oxygen concentrations in p2 and p1 according to the

first-sensor.com/cms/upload/appnotes/an_xya-o2_e_11154.pdf, 23.10.

21 Electrochemical methods example: Lambda-type electrode ZrO 2 behaves like a solid electrolyte for oxygen (needs high T >650 C) ZrO 2 pumping disc pumps oxygen from p1 p2 generation of different oxygen concentrations in p2 and p1 according to the Nernst equation a voltage is generated at the ZrO 2 sensing disc Jacqueline Waldvogel, Yves Wittwer

22 Electrochemical methods Nernst equation measured voltage is compared to reference voltages V 1 and V 5 as V 1 is reached, chamber (p2) is evacuated, as V 5 is reached it is pressurized time needed for one cycle is proportional to sample oxygen concentration Jacqueline Waldvogel, Yves Wittwer

23 Electrochemical methods example: Clark electrode O 2 enters the cell through a barrier (e.g. a membrane) cathode: O 2 + 2e - + 2H 2 O H 2 O 2 + 2OH - H 2 O 2 + 2e - 2 OH - anode: 4Ag 4Ag + + 4e - measure current, which is proportional to the amount of O 2 entering the cell many other cell types available as well picture: Jacqueline Waldvogel, Yves Wittwer

24 Electrochemical methods: Pros and Cons Pros Cons - fast - lifetime: 1-2 years - easy to use - aging requires regular calibration - inline analysis possible - temperature dependence - pressure dependence - interferences possible conclusions concerning our case: inline/ online measurements possible real-time measurements possible possible problems because of process conditions and ATEX guidelines in principle suitable for our case Jacqueline Waldvogel, Yves Wittwer

25 Paramagnetic sensors based on paramagnetic properties of triplet oxygen. working principle: sample gas and auxiliary gas (N 2 ) are injected and divided into two streams sample gas and auxiliary meet in ring-shape path at B side, a magnetic field is created, which draws the oxygen of the sample gas into. the flow rate at B decreases in comparison with the one at A. thermistors at point A and B determine the flowrate, which is converted into an electrical signal. its difference is proportional to the amount of oxygen in the sample gas Jacqueline Waldvogel, Yves Wittwer

26 Paramagnetic sensors: Pros and Cons Pros Cons - long-term stable measurements - interferences with other paramagnetic compounds - high resistance to vibrations - only works at low temperatures - high sensitivity (0-1 vol-%) - no moisture allowed - fast response ( 3s) - only works at low pressure - easy calibration conclusions concerning our case: Suitable for online analysis Process temperature too high Process pressure too high not suitable for our case Jacqueline Waldvogel, Yves Wittwer

27 Gas Chromatography An example separation of gases with GC possible example: Analysis of power plant flue gases carrier Gas: H2 pressure: 2.2 bar two columns Porapak Q (apolar polymer) molecular sieve 5A detector: TCD %20Technical%20Notes/Chromatography/Gas%20Chromatography/AN GC-Flue%20Gases- TRACE% AN10351-EN.pdf, Jacqueline Waldvogel, Yves Wittwer

28 Gas Chromatography Detection? GC-MS: may have some problems with low mass of oxygen GC-IR: does not work since O 2 is IR-inactive TCD (thermal conductivity detector) Jacqueline Waldvogel, Yves Wittwer

(composition) reference and gas cell form a wheatstone bridge record a voltage difference https://de.wikipedia.

29 Thermal Conductivity Detector, TCD measuring thermal conductivity of the sample and a reference electrically heated filament surrounded by gas (sample or reference) heat is conducted by gas to detector block conductivity is dependant of the gas (composition) reference and gas cell form a wheatstone bridge record a voltage difference svg, Jacqueline Waldvogel, Yves Wittwer

30 Gas Chromatography: Pros and Cons Pros Cons - high precision - slow - case specific - potential use of explosive gases conclusions concerning our case: no online measurements possible no real-time correction of process parameters possible process pressure is too high problems with ATEX guidelines? Not suitable for our case Jacqueline Waldvogel, Yves Wittwer

measurement Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff. https://www.piketech.

31 Absorption spectroscopy absorption bands of O 2 : 760 nm, one deep in the UV 760 nm: b 1 Σ + g Χ 3 Σ - g (triplet singlet) emission peak: 1270 nm UV/Vis absorption continuous measurement Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff Jacqueline Waldvogel, Yves Wittwer

32 Absorption spectroscopy TDLAS: Tuneable diode laser absorption spectroscopy excitation by tuneable laser measure absorption to determine concentration, temperature or pressure Pro: high sensitivity wide temperature range (up to 1000 C) ser-absorption-photonik pdf, Jacqueline Waldvogel, Yves Wittwer

33 Absorption spectroscopy: Pros and Cons Pros Cons - easy to handle - expensive instrument (TDLAS) - fast (TDLAS) - bulky instrumentation - interferences (H 2 O, CO 2 ) conclusions concerning our case: online measurement possible real-time measurement possible problems with interferences? in principle suitable for our case Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff. ser-absorption-photonik pdf, Jacqueline Waldvogel, Yves Wittwer

34 Quenching based methods Jablonski diagram dynamic quenching: collision induced energy transfer Jacqueline Waldvogel, Yves Wittwer

with oxygen, K SV : Stern-Volmer constant (function of probe lifetime and polymeric solvent)

35 Quenching based methods Stern-Volmer equation describes the relation between the luminescence intensity and the oxygen concentration Stern-Volmer equation: F 0 / F: fluorescence without/ with oxygen, K SV : Stern-Volmer constant (function of probe lifetime and polymeric solvent) Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff. Jacqueline Waldvogel, Yves Wittwer

36 Quenching based methods in reality luminescence intensity is often not linearly dependent on oxygen concentration this is caused by different surroundings of the fluorophore by the polymer (see next slide) this can be corrected by using e.g. multiple Stern-Volmer constants representing the different environments f: fraction of total emission corresponding to each component Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff. Jacqueline Waldvogel, Yves Wittwer

Quenching based methods optical isolation non-transparent layer avoid interferences e.g. by ambient light oxygen sensing layer luminophore solid support polymer matrix/ layer Wang X.

37 Quenching based methods optical isolation non-transparent layer avoid interferences e.g. by ambient light oxygen sensing layer luminophore solid support polymer matrix/ layer Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff. Jacqueline Waldvogel, Yves Wittwer

38 Oxygen sensing layer in principle, every luminophore interacting with oxygen can be used properties of the luminophore (e.g. stability, lifetime of excited states, ) mainly (but not only) determine properties of sensor suitable luminophores are for example: fullerenes diverse metal-ligand complexes porphyrins Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff. Jacqueline Waldvogel, Yves Wittwer

39 Solid support either protection layer or host matrix for luminophore requirements optically transparent oxygen permeability long-term stability if used as host matrix, solid support and luminophore must be compatible diverse functions protection of luminophore modify luminophore properties, e.g. lifetime of excited state selective diffusion of oxygen for example: silicones Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff. Jacqueline Waldvogel, Yves Wittwer

40 Quenching based methods: Pros and Cons Pros Cons - highly adjustable - possible interferences with other quenchers, e.g. SO 2, NO x, many olefins, halogenated organic species, humidity,... - high sensitivity possible - not many sensors working at high temperatures - fast - extremely case specific conclusions concerning our case: online/ inline measurements possible real-time measurements possible difficult to find proper sensor, e.g. Mo 6 Cl 12 sensor can be used at high temperature (> 600 C) In principle suitable for our case Wang X., Wolfbeis O.S., Chem. Soc. Rev., 2014, 43, 3666ff. Jacqueline Waldvogel, Yves Wittwer

41 Conclusion suitable electrochemical methods absorption spectroscopy quenching based methods not suitable chemical methods paramagnetic sensors gas chromatography Jacqueline Waldvogel, Yves Wittwer

42 Abbreviations LMB: leucomethylene blue MB: methylene blue Jacqueline Waldvogel, Yves Wittwer

Thermo Scientific Electrochemistry Products

Comparing Performance of DO Methods The world leader in serving science in Water and Seawaters Thermo Scientific Electrochemistry Products Dissolved Oxygen Measurement Oxygen is essential for most of the