Pyrolysis: Instrumentation and Application

1
Pyrolysis Instrumentation and Application

• By Ben King

2
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

3
Py-GC/MS
Auto sampler
Heated transfer line
MS
GC
Pyrolysis controller
pyrolyzer
http//www.csam.montclair.edu/earth/eesweb/imageU9
0.JPG
4
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

5
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

6
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

7
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

8
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

9
Furnace Pyrolyzer
http//www.sge.com/uploads/lh/_0/lh_0zRR1NSHibbVkF
iPo4A/pyrojector.jpg
10
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

11
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

12
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

13
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

14
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

15
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

16
Filament Pyrolyzer Examples
Fischer America Curie Point Pyrolyzer
Analytix Ltd Resistively Heated Filament Pyrolyzer
17
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

18
Inductive Heating Characteristics of Alloys
Reference 13
19
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

20
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

21
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

22
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

23
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 wire-
  simple 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

24
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 - 1000C (10 - 20 specific
  alloys )
• Cant have linear heating
• Reference 2

25
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

26
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

27
Resistively Heated Filament Diagram
28
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

29
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

30
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

31
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

32
Resistively Heated Filament Disadvantages

• Cant 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

33
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

34
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

35
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

36
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

37
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

38
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

39
Precision of Pyrolysis

• Evaluating Emission of various materials for
  PAHs 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

40
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

41
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

42
Sensitivity of Pyrolysis

• Volatile elements
• Slurries- high sensitivity for pyrolysis temp lt
  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

43
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

44
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

45
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-3-methoxycate
  chol, and 5-propenyl-3-methoxycatechol were
  detected.
• Compounds arise from the pyrolysis of
  5-hydroxyguaiacyl lignin moieties
• Only the first one ever really detected, the
  other two rarely until using pyrolysis-GC/MS
  technique
• Reference 6

46
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

47
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
• 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

syringyl
guaiacyl
48
Pyrogram of Abaca
Reference 4
49
Composition of Abaca Fibers
Reference 4
50
Composition of Abaca Fibers
Reference 4
51
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

52
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

53
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

54
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

55
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
  lignin-derived 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

56
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 (phenol-enriched barrier between
  infected and living).
• Reference 17

57
S/G Ratio of Three Wood Areas
Reference 17
58
Conclusion

• Pyrolysis is a technique that has endless
  possibilities for polymer or macromolecule
  analysis.
• It can give reproducible results with good
  precision and with short amount of time
• Py-GC/MS can be used extensively for analysis of
  lignins in the composition of plants and can be a
  great tool for the paper industry and biofuel
  industry.

59
References

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  Klaas G. J. Biochemical Origin and Refractory
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60
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