Continuous Production of Polylactic Acid Utilizing Dextrose from Corn

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Continuous Production of Polylactic Acid
Utilizing Dextrose from Corn

• Elizabeth Bol
• Landon Carlberg
• Senja Lopac
• David Roland
• May 7, 2004

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Overview

• Scope
• Market Analysis
• Basic Chemistry
• Key Design Assumptions
• Process Specifications
• Key Design Decisions
• Safety and Environmental Concerns
• Economic Evaluation
• Recommendations

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Breakdown of Waste
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Scope

• Plant built in Midwest
• Two key assumptions
• Built next to corn milling facility
• Dextrose production can be increased with
  increased demand of PLA
• Total capacity of 500 million pounds per year
• Cargill and Dow Chemical co-venture resulted in a
  300 million pound polymer plant, with second
  plant in planning

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Properties of Polylactic Acid

• Insoluble in water, moisture and grease resistant
• Biodegradable and compostable
• Clarity and glossiness similar to its other
  plastic competitors
• Requires 20 to 50 less fossil fuels to produce
  than regular plastics
• Comparable physical properties to polyethylene
  terephthalate (PET)

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Uses

• Single-use items such as plates, utensils, cups,
  and film wrap
• Plastic bottling and fast-food companies
• Paper coatings
• Clothing fibers
• Compost bags
• Biomedical field

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Current Market

• Plastics
• 2000 150 million tons
• 2010 Expected to reach 258 million tons
• Biodegradable Plastics
• 1997 20 million pounds
• 2004 Expected to capture 20 of the market for
  plastics (approximately 50 million tons)
• Current selling price of PLA 1.50/lb
• Current selling price of PET 0.60/lb

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Chemistry of Fermentation Step

• Bacteria breaks down one molecule of dextrose to
  form two molecules of lactic acid

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Chemistry of Lactide Formation Step

• Two molecules of lactic acid combine to form one
  molecule of lactide

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Chemistry of Polymerization Step

• The lactide polymerizes through ring opening
  polymerization to a molecular weight of
  approximately 30,000

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Block Flow Diagram
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Key Design Assumptions

• Industrial scale equipment behaves similarly to
  laboratory testing equipment
• Equipment from differing experiments is compatible

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Fermentation Step
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Polymerization Step
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Key Design Decisions - Fermentation

• Two-stage membrane cell recycle bioreactor with
  ammonia resistant strain of Lactobacillus
  rhamnosus
• High productivity
• More feasible for scale-up
• Electrokinetic bioreactor
• Relieves product inhibition
• Alleviates need for additional pH control chemical

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Key Design Decisions - Neutralization

• Calcium carbonate/Sodium hydroxide
• Ammonia
• Easy to recycle
• No salt formation
• Does not damage cells
• Electrodialysis
• Does not introduce additional chemical for
  separation

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Key Design Decisions Polymerization Catalyst

• Tin Octanoate
• Catalyst used by Cargill Dow
• Less expensive
• Harmful to humans and the environment
• Zinc ß diiminate complex catalyst
• Gives 94 conversion in 30 minutes
• Immobilized in a packed bed

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Safety

• Flammables, corrosives, and explosion hazards
• Careful chemical storage placements
• Strict personal protective equipment policies
• Implementation of process control
• Execution of extensive safety procedures

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Environmental Concerns

• Produces n-butanol waste stream which needs to be
  treated
• Further research is necessary
• All process solvents and catalysts require
  secondary containment and careful monitoring

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Key Economic Assumptions

• Interest Rate, 12
• Working capital is 15 of fixed capital
• Addition to existing corn milling facility
• Project life of 15 years
• 8000 hours of operation per year
• 40 tax rate and MACRS depreciation (5 year
  accelerated)
• Nearly 100 regeneration of catalysts
• PLA demand will meet facility output by start-up

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Equipment Costs(in millions of dollars)
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Manufacturing Costs (in millions of dollars)

• Cost of Manufacturing, without Depreciation
  159 million

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Utility Costs(In millions of dollars)

• Total utility costs 126 million

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Effect of percent change in price of material to
ROI
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Discounted Cash Flow Diagram

• ROI _at_ .60/lb 26.34
• ROI _at_ 1.50/lb 144.42

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Economic Summary

• FCI 265 million
• DCFROR
• At PLA selling price 101.4
• At PET selling price 28.1
• Payback Period
• At PLA selling price 0.8 years
• At PET selling price 3.4 years

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Recommendations

• Further research on alternative catalysts for
  both the lactide formation and the polymerization
  steps
• Sizing and cost estimates of extruders
• Continued research on properties of lactide, and
  polylactic acid
• Research alternative methods for recycle/removal
  of n-butanol from waste stream
• Heat integration study
• Improve water recycle rate

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Acknowledgements

• Dr. Ryan OConnor, Cargill Dow LLC
• Rafael Auras, Michigan State University
• Dr. Christopher Jones, and Kunquan Yu, Georgia
  Institute of Technology

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Question Session