Transcript Liquid Carbon Dioxide-Based Leather Process

Jeremy Kroon
Department of Chemistry and Biochemisty
South dakota state University
Purpose of Tanning
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To bring about irreversible stabilization of the skin
substance that is to prevent putrefaction.
stabilize it against enzymatic degrading and increase
its resistance to chemicals
raise its shrinking temperature and increase its
resistance to hot water
reduce or eliminate its ability to swell
enhance its strength properties
lower its density by isolating the fibers
reduce its deformability
reduce its shrinkage in volume, area and thickness
enhance the porosity of its fiber texture.
Current Tanning processing
Hide/Skin
Curing &
Storagae
Soaking,
brining
Pre-Tannery
BeamHouse
Operations
Unhairing & Liming
Deliming & Bating
Wet Processes
Tanyard
Operations
PostTanning
Operations
Finishing
Operations
Pickling
Degreasing
Tanning
Retanning
Fat Liquoring
Dying
Mechanical
Surface
Coating
Dry Processes
Beamhouse
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Unhairing & Liming
 pH is raised to 12 to 12.6
 Removes the epidermis
including the hair
 calcium hydroxide,
sodium hydroxide,
sodium sulfide, and
enzymes
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Deliming & Bating
 Ammonium salts added
 Enzymes are added to
remove non-collogen
proteins
Tanyard
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Degreasing (pigs and sheep)
 Organic Solvents
○ Hexane, trichloroethylene
 Aqueous Surfactants
○ nonylphenol ethoxylates
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Pickling
 pH lowered to 3
 Hydrochloric or Sulphuric acid
Tanyard
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Vegetable Tanning
 2 to 4 days
 Tannic acids for tree bark
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Chrome Tanning
 Most common
 8 hours
 Cr+3
Post Tanning Operations
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Neutrilizing
 Brings hides back to
neutral pH
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Retanning
 Vegetable tannins,
syntans
 Used to impart specific
characteristics
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Dyeing
 Anionic dyes
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Fatliquoring
 Oils added back to
leather
Disadvantages
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metric ton of salted
cattle hides
 15-50 m3 of wastewater
○ 5-6 kg of chromium
○ 10 kg of sulfide
 40 kg of volatile
organics (VOC)
 .8 x 106 to 4.0 x 107
BTU of energy
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Capital investment for
pollution control
purposes can be as
high as 50% of the
total value of plant
Leather and CO2
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Replacing Water with liquid CO2
 diffusion advantage
 simple adjustments of temperature and
pressure may result in the precipitation of
residual leather treatment agents
○ allows subsequent recycling or disposal of
these materials
 cheap and readily accepted
Approach
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Dyeing and waterproofing
 greatest probability of success
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Degreasing and Fat liquoring
 Fats and oils are highly soluble
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Tanning and retanning
 Largest challenge since chrome ions are highly
insoluble
 Focus largely on vegetable tannins and syntans
Waterproofing
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fluorocarbons, silicones, waxes,
aqueous-based oils, and fluoropolymers
 Each was loaded onto cotton
 Extracted using supercritical CO2 at 2500psi
and 50°C
 All were found to be soluble
Waterproofing
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Allowed to soak with leather sample
 Mass loading showed equal weight to manufactures'
method
 No caking, or discoloration
Oil Based Agent
CO2 treatment
Manufactures’
Silicone Based Agent
CO2 treatment
Manufactures’
Dyeing
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CO2 dyeing currently
commercialized in textile
industry
○ Introduced in early 1990’s
○ Even color distribution
Degreasing and Fat Liquoring
Been used in oilseed extraction
 Supercritical CO2 limited use in leather
industry
 reported degreasing efficiencies up to
94%
 With sheep reported no damage to the
skin structure
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Tanning and Retanning
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Tanning agents
 Metal tanning
○ Not soluble in CO2
 Vegetable tanning
○ Soluble
○ Make hard leather
 Saddles, belts, etc.
 Syntans
○ Soluble
○ Mainly for retanning
○ Used to impart
specific
characteristics
Conclusion
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Our goal for this project is to develop a
technique that will make leather
production:
 FASTER
 MORE ECONOMICAL
 CLEANER
Acknowledgements
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Dr. Raynie
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Environmental Protection Agency
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BASF