By: Ben King What is Pyrolysis? A technique that is used in the analysis of natural and artificial polymers or macromolecules A sample is heated up (mainly in a inert atmosphere or vacuum) to decomposition to produce smaller units which are carried by a gas such as helium to the next instrument for characterization. Pyrolyzer is usually linked to a GC and a detector such as MS or FTIR. Reference 16, 2 Py-GC/MS Auto sampler Heated transfer line MS GC Pyrolysis controller pyrolyzer http://www.csam.montclair.edu/earth/eesweb/imageU90.JPG How Does it Work? Use either one of three pyrolysis designs: Isothermal furnace, Curie Point filament (inductively heated), and resistively heated filament. Sample heated to a pyrolysis temperature slowly or rapidly and held for a few seconds. Cleavage of chemical bonds within the macromolecular structure producing low molecular weight, more volatile chemical moieties that are specific units of a particular macromolecule. Reference 16,2 Sample Preparation Normally no sample preparation is powdered or particulate materials Some samples require an extraction with an organic solvent to remove any low molecular mass components. Some solid samples need to be dissolved in solvents or ground up. Amount of sample preparation depends on type of polymer and how homogeneous the sample is. Methylating reagents, which increase the volatility of polar fragments, can be added to a sample before pyrolysis. ◦ Tetramethylammonium hydroxide (TMAH) and trimethyl sulfonium hydroxide (TMSH) Reference 16, 2 The Three Pyrolyzers Each type can give reproducible results for small samples Furnace and resistively heated filament pyrolyzers can be used for slow heating or rapid heating. Curie Point is used only in rapid heating mode Selectivity depends on personal preference, experimental requirements, budget, or availability Reference 2 Furnace Pyrolyzer Small mount on the inlet of GC The metal or quartz sample tube is wrapped with heating wire and thermally insulated The furnace pyrolyzer has a much larger sample chamber than the filament pyrolyzers as seen in the figure. Reference 2 Furnace Pyrolyzer Design Carrier gas enters from top or front to sweep past sample inlet (carrying of the pyrolyzate) before moving then directly into injection port of chromatograph Temperature is stabilized to within ±10 °C of the desired temperature setpoint. Thermocouple or resistance thermometer used to indicate wall temperature Reference 2 Furnace Pyrolyzer http://www.sge.com/uploads/lh/_0/lh_0zRR1NSHibbVkFi Po4A/pyrojector.jpg Furnace Pyrolyzer Sample Introduction Can’ t usually admit air during sample introduction due to GC Heat rate dependent on sample material and composition of sample introduction device Liquid samples are injected by a syringe. Solids are dissolved and injected, or injected using a solid injecting syringe A cool chamber is used to load samples into a crucible which is lowered into hot zone. Reference 2 Furnace Pyrolyzer Temperature Control Resistive heating element is around the central tube of furnace Temperature is monitored by sensor with data feedback to the controller for adjustments of thermal energy. Temperature control also depends on size and mass of sample, and residence time inside furnace. Reference 2 Furnace Pyrolyzer Advantages Inexpensive and relatively easy to use Isothermal heating, with no heating ramp rate or pyrolyis time unless that is the intention. Liquid and gas pyrolysis is more easily achieved than with filament type. Reference 2 Furnace Pyrolyzer Disadvantages Since the tube is considerably larger than sample, temperature control is more difficult to achieve Large volume for sample to pass through to get to analytical device Excessively low carrier gas flow may lead to secondary pyrolysis Temperature stability depends on sample size, nature, and geometry Reference 2 Furnace Pyrolyzer Disadvantages Metal systems, initial pyrolysis may produce smaller organic fragments which encounter hot surface of tube and undergo secondary rxns Generally necessitating split capillary analysis Has longer retention times, broad peak shapes, and interference peaks. Reference 2, 13 Heated Filament Pyrolyzer Sample placed directly onto cold heater then rapidly heated to pyrolysis temperature Two Methods: ◦ resistance-controlled current is passed through heating filament ◦ Inductive- current is induced into heating filament which is made of ferromagnetic metal Sample size limited to an amount compatible with mass of filament. (low to high microgram range) A sample must also be compatible for the analytical devices that are linked up to the pyrolyzers. ◦ GC, FTIR, ICP, MS, etc. Reference 2 Filament Pyrolyzer Examples Fischer America Analytix Ltd Curie Point Pyrolyzer Resistively Heated Filament Pyrolyzer Inductively Heated Filament: Curie-pt Pyrolyzer Electrical current induced onto a wire made of ferromagnetic metal by use of magnet or high frequency coil Continual induction of current wire will begin to heat until it reaches a temperature at which it is no longer ferromagnetic Becomes paramagnetic, no further current may be induced in it. Heated to pyrolysis temperature in milliseconds Reference 2 Inductive Heating Characteristics of Alloys Reference 13 Curie-pt Design Insertion: Pyrolysis chamber which is surrounded by coil, is opened and sample wire is dropped or place inside Sample wire is attached to a probe which is inserted through a septum into the chamber which is surrounded by the coil Reference 2, 13 Curie-pt Pyrolyzer Design Chamber can be attached directly to part of GC or isolated from GC by valve Allows for autosampling and for loading wires into glass tubes for sampling and inserting into coil zone. Controls for parameters of pyrolysis wire and also temp selection for interface chamber housing the wire. Reference 2, 13 Curie-pt Pyrolyzer Sample Introduction Sample and wire kept to low mass Samples either coated onto filament as very thin layer Soluble materials dissolved in appropriate solvent and wire dipped into. ◦ Solvent dries and leaves thin deposit Non-soluble: ◦ finely ground samples maybe deposited onto wire from a suspension which is dried to leave coating of particles ◦ Applied as melt ◦ Create a trough with wire ◦ Bend or crimp wire around material ◦ Encapsulate sample with foil of ferromagnetic material and dropped into high frequency cell chamber. Reference 2 Curie-pt Pyrolzer: Temperature Control Pyrolysis temperature is determined by the composition of the ferromagnetic material Reproducible and accurate temp control depends on accuracy of wire alloy, power of coil, and placement of wire into system Use the same manufacturer, same sample loading, and placement to minimize variation of sample results Reference 2, 13 Curie-pt Advantages Self-limiting temperature Rapid heating No temperature calibration to perform Can prepare several samples and store Can be automated b/c no connections to wiresimple insertion Can either clean and reuse wire or discard Gives sharper characteristic peaks than furnace type Demonstrates constant pyrolysis product composition yield even with sample weight increases Good heat transfer Reference 2, 13 Curie-pt Disadvantages Limited temperatures to choose Harder to optimize pyrolysis temperature Concerns of catalytic effect of metals on very small samples. Range of temps 350 - 1000°C (10 - 20 specific alloys ) Can’t have linear heating Reference 2 Resistively Heated Filament Pyrolysis Heat from ambient to pyrolysis temperature quickly also with small samples Current supplied is connected directly to filament A filament made of material with high electrical resistance and wide operating range. (Ex: Fe, platinum, and nichrome Reference 2 Resistively Heated Filament: Design Sample placed onto pyrolysis filament which is then inserted into the interface housing and sealed to insure flow to column. Flat strip, foil, wire, grooved strip, or coil. Coil- tube or boat inserted into filament, like very small rapidly heating furnace Must be connected to controller capable of supplying enough current to heat filament rapidly with some control or limit Temperature measured by resistance of material or by external measure such as optical pyrometry or thermocouple. Reference 2 Resistively Heated Filament Diagram Resistively Heated Filament: Sample Preparation Solution applied to filament by syringe Powder solids use small quartz tubes which is inserted into coiled filament Place in tube, held in position using plugs of quartz wool, weighed, and inserted into coiled element. Rise and final temp different then directly on filament Not used for soils, ground rock, textiles, and small fragments of paint Viscous liquid applied on surface of filament or suspended on surface of filler material. Reference 2 Resistively Heated Filament: Interfacing Can be easily interfaced with other analytical devices as long the filament is positioned right and the probe is sealed off from air. Need a heated interface between pyrolyzer and column Interface has its own heater to prevent condensation of pyrolyzate compounds and should have minimal volume Valve needed between pyrolyzer and column so insertion or removal of filament can be done. Reference 2 Resistively Heated Filament: Temperature Control Temperature is related to current passing through it Conditions have to be very similar for good reproducibility Computers control and monitor filament temp, control voltage used and adjusted for changes in resistance Use photodiode to read actual temp of filament Can select any final pyrolysis temp and any desired rate Can heat as slow as .01 °C/min and as rapidly as 30000 °C/sec Reference 2 Resistively Heated Filament: Advantages Can measure how materials are affected by slow heating (TGA) Permits interface of spectroscopic techniques with constant scanning for 3d, time-resolved thermal processing. Can be inserted directly into ion source of MS or light path of FTIR Products monitored in real time throughout heat process. Reference 2 Resistively Heated Filament: Disadvantages Can’t automate process since multiple samples need same filament and multiple filaments need same instrument Any damage or alteration to the resistance of part of the loop will have an effect on actual temp produced by controller. Introduction of some samples into heated chamber before pyrolysis may produce volatilization or denaturation, altering nature of sample before degradation. Not good heat transfer Yields can decrease as sample weight increases Reference 2 Slow-rate Pyrolysis Related to TGA, multiple step degradation Gives time-resolved picture of production of specific products Programmable furnace and resistively heated filament 50-100 °C/min to extract organics Reference 2 Direct/Indirect Transfer of Pyrolyzate to Detectors Direct ◦ Collection directly onto GC, at ambient or subambient conditions ◦ Direct to MS or FTIR ◦ Pyrolyzer inserted into an expansion chamber, which flushed or leaked into spectrometer, or the pyrolyzer is inserted directly into instrument Indirect ◦ A trap is connected to pyrolyzer and is later connected to analytical device Reference 2 Reproducibility of Pyrolysis Sources of error- size and shape, homogeneity, and contamination of sample For polymers, need to make same size and shape samples Overloading affects rate at which sample heats (thickness of material- thermal gradient) 10-50 microgram samples desirable for direct pyrolysis to GC and twice that for FTIR Reference 2 Increasing Reproducibility by Homogeneity Ground up material under cryogenic conditions Chop sample finely using scalpel and then analyze small fragments together Made into solution Bigger samples of .1mg Use a split mode GC injection with a large split ratio to avoid signal saturations Pass pyrolyzate in carrier gas through small sample loop attached to a valve which is interfaced to analytical unit. (clean run to run) Reference 2 Accuracy of Pyrolysis Study of compositional determination of styrene-methacrylate using Py-GC and H NMR ◦ Standard deviation: 1-2% compared to 1% for NMR Accuracy effected by pyrolysis temp rise time, sample size, sample surface area, and sample thickness Small sample size, little sample prep, rapid turnaround time, relatively inexpensive, easily operable, and can be automated Reference 8 Accuracy of Pyrolysis 550-650 °C yielded reproducible fragmentation Difference between NMR and GC pyrolysis results are in the range of 0-4% and 0-4.8% for styrene/n-butyl methacrylate and styrene/methyl methacrylate Standard deviation for py-GC was from 1.2 to 2.1 % Reference 8 Precision of Pyrolysis Evaluating Emission of various materials for PAH’s released (Py-GC/MS) ◦ Pyrolyzed at 1000 °C for 60 sec (resistively heated) ◦ RSD from 7.5% (1-methyl naphthalene) to 18% (acenaphtene) ◦ Most abundant species RSD less than or equal to 15% , less abundant much higher Increase of precision and repeatability if using offline system Shows good repeatability, limit of quantification, and linearity Reasonably good for properly evaluating the quantity of PAHs emitted from different kinds of materials. Reference 9 Precision of Pyrolysis Investigation of Food Stuffs (Py-Elemental Analysis) ◦ 65 Foods analyzed ◦ RSD from 1 to 13% for Carbohydrates in each one of the samples that also contained protein, fats, and dietary fibers Reference 7 Sample Amount and Selectivity Sample amount ◦ Milligrams or micrograms Selectivity ◦ Cellulose Altering heating conditions improve selectivity ◦ Sample vs Standards of PVC, PS, SB, PMMA, and PC mixture All main marker compounds very similar Naphthalene peak of polymer mixture 96% recovered relative to standards Reference 15 Sensitivity of Pyrolysis Volatile elements ◦ Slurries- high sensitivity for pyrolysis temp < 400 °C, decrease from 400-800 °C ◦ Aqueous and digested standards sensitivity plateaus across temps ◦ Digested better sensitivity than aqueous 15% (As) & 65% (Pb) ◦ High sensitivity obtained for As is obviously related to the presence of carbon in the plasma and increase sensitivity at low pyrolysis temp is in agreement with above-discussed charge-transfer mechanism. ◦ Using modifiers Pd/Mg or raising concentrations of organics raises sensitivity at low temps. ◦ Sensitivity changes due to differences in analyte transport from the ETV to the ICP produced by carrier effects and/or changes in analyte ionization in the plasma. Reference 14 Detection Limit and Quantification Limit of Pyrolysis Detection Limit is dependent on analytical device it is attached to GC’ s detection limit Can be as low as ng or pg Analysis of polymer mixture Py - ETV - ICP - MS Limit of Quantification 500ng, 10 mg / kg dry mass Limit of Detection 150ng, S/N=3 Linearity in a range from .5 to 100 microgram Reference 15 Application of Pyrolysis Pyrolysis can be applied to the analysis of many natural and artificial macromolecules Natural: lignin, cellulose, chitin, etc Artificial: PVC, acrylics, varnishes, etc Can be used for applications similar to TGA Used in several specific areas as well Presence of 5-hydroxyguaicyl as Unit Native in Lignin Lignin content was estimated by the Klasan method Curie-pt pyrolyzer, pyrolysis temp- 610 °C Fibers were finely ground to sawdust In samples of eucalypt, abaca, and kenaf, compounds 3-methoxycatechol, 5-vinyl-3methoxycatechol, and 5-propenyl-3methoxycatechol were detected. Compounds arise from the pyrolysis of 5hydroxyguaiacyl lignin moieties Only the first one ever really detected, the other two rarely until using pyrolysis-GC/MS technique Reference 6 Determination of Abaca Fiber Composition for Paper Pulping Nonwoody source for paper for developing countries Curie-pt pyrolyzer, pyrolysis temp-610 °C Pyrolysis in presence of tetramethylammonium hydroxide (prevents decarboxylation) Abaca fiber is 13.2% lignin Main compounds of lignin are p-hydroxyphenyl (H), guaiacyl (G),and syringyl (S) Reference 4 Determination of Abaca Fiber Composition for Paper Pulping S/G-4.9 Efficiency of pulping directly proportional to amount of syringyl units in lignin due to easy delignification of S-lignin syringyl ◦ S-lignin is mainly linked by a more labile ether bond ◦ S-lignin is relatively unbranched ◦ S-lignin is lower condensation degree than the G lignin Reference 4 guaiacyl Pyrogram of Abaca Reference 4 Composition of Abaca Fibers Reference 4 Composition of Abaca Fibers Reference 4 Determination of Kenaf Fiber Composition for Paper Pulping Kenaf alternative raw material for pulp b/c renewable, inexpensive, and grown easily Pyrolysis-GC/MS in presence of TMAH Curie-pt pyrolyzer, pyrolyzed at 500 °C for 4 sec Tried offline pyrolysis and low-temp pyrolysis 250 °C for 30 min Chinpi-3: core 1.53 S/G and bast 3.42 S/G Similar results of wet chemical method core 1.87 S/G and bast 4.71 S/G Reference 11 Early Detection of Fungal Attack on Industrial Pine Lignin Double-shot pyrolyzer, pyrolysis at 500 °C Samples treated with laccase and others with laccase-mediator system Py-GC/MS showed a decrease in phenolic and methoxy-bearing pyrolysis products during the onset of incubation. Immediately, a 22% decrease in the total phenolic lignin content, increase in aldehyde (64%), ketone (50%), and acid groups (.21%). After 48 hrs, 10% decrease in lignin, 10% guaiacyl units, 1% syringyl units, 10% decrease in ethyl phenolic derivatives Klason Lignin (KL) recovered from the laccase-mediator system (LMS) after 48hrs of incubation shows high degree of oxidation and depolymerization ◦ Desirable for industrial applications KL recovered from the laccase shows a lower degree of oxidation, accompanied by a substantial polymerization. ◦ Used for commodity and specialty markets Reference 3 Determination of Grass Fiber Composition for Bio-oil Application 15 Lolium and Festuca grasses Speculated by researchers that reduce lignin content will produce a more stable bio-oil by reducing the chances of phase separation by improving solubility, stability, and homogeneity Pyrolysis by inductive heated coil, pyrolysis at 600 °C, .4 °C/ms Wet chemistry- grass leaves contained 2.14 to 3.72% lignin Abundances of key markers of lignin added up by py-GC/MS were correlated to the amount of Klason Lignin in each grass. Reference 10 Determination of Tagasaste Fiber Composition for Paper Pulping Found in Canary islands, Australia, and New Zealand Usefulness for paper pulp production Microfurnace pyrolyzer, pyrolysis temp- 500 °C, 20 °C/min 18.9% lignin S/G 1.6 Reference 12 Determination of Lignin Contribution in soil-HA by Pyrolysis Lignin contribution to the soil Humic Acid (HA) from maize plants Curie-pt pyrolyzer, 600 °C for 5 sec Pyrolysate of maize plant was dominated by ligninderived products Py-GC/MS determined HA derived from plants was composed of aromatic compound derived mainly for lignin had a high S/G ratio. Hemp and flax showed a predominance of guaiacyl Jute, sisal, and abaca showed a predominance of syringyl P-hydroxycinnamic acids, namely p-coumaric and ferulic acids, are also found in isolated lignin Reference 1 Early Detection of Wood Decay by Lignin Composition Furnace pyrolyzer Characterization of internal wood degradation of London-plane tree (early detection of white rot fungal infection by lignin degradation before cavity formation) Use pyrolysis product composition syringyl/guaiacyl ratio Samples from sound wood, extensively degraded wood, and R-zone (phenolenriched barrier between infected and living). Reference 17 S/G Ratio of Three Wood Areas Area of Wood Disk A Disk B Sound (S/G) 1.61 1.51 R-zone (S/G) 1.39 1.28 Rotten (S/G) 1.12 1.1 Reference 17 Pyrolysis is a technique that has endless possibilities for polymer or macromolecule analysis. 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