catalyst selection in biodiesel processes · choice for the production of fame type biodiesel, -...
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Catalyst Selection in Biodiesel Processes
Johannes RuwweBioFuelsMarkets Asia, June 10,2008 Delhi, India
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Contents:
• Catalysts used in biodiesel processes
• Market share of various processes
• Comparison of alkali type catalysts
• Success factors of most popular catalyst
• Perspective
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Biodiesel: Net reaction - FAME
Fatty acid spectrum• Depends on raw material;• Influences oil and biodiesel
chemical and physical properties
Fatty acid triglyceride = Oil
FAME, fatty acid methyl ester(s) = Biodiesel Glycerol
3 MeOH
Catalyst
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Trans-esterification catalysts (1)
• Acid type: Slow conversion, requires high temperatures.
• Heterogeneous catalyst (e.g. metal oxides, nano-particles): Elegant concept, high operation costs (energy, MeOH excess).
• Enzymatic process: Expensive; enzymes may be sensitive to MeOH and glycerol.
• Catalyst free process using supercritical methanol: Very high pressure and temperature, high invest costs.
Share in world wide capacity: <5% (all together)
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Trans-esterification catalysts (2)
Alkaline catalysts:
Proceed with high conversion under mild conditions.
Two choices:
1. Hydroxides (NaOH or KOH), come as solids, have to be dissolved in methanol;
2. Alkoxides (NaOMe or KOMe; “NM30” or “KM32”), come as “ready to-use-solution” in methanol.
Share in world wide capacity: >90% (together)
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1.5 and 2nd generation biodiesel catalysts
1.5 generation: hydrogenation of vegetable oils (HDT):
• Hydrogenation catalysts (supported Ni, Co, Mo, Pd, Pt)
• Stoichiometric quantities (2-3%) of hydrogen required,
• Concept is feasible in refineries only. Product obtained is a hydrocarbon type fuel, no FAME.
• 2nd generation: BtL = gasification + Fischer-Tropsch synthesis:
• Supported group VIII Metals (Co, Fe) for F.-T. process.
Product obtained is also a hydrocarbon type diesel fuel.
Market introduction has just started, current share <5%.
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Most important: Hydroxides and alkoxides. How does it work?
Reaction mechanism alkaline catalyzed trans-esterification:Alkoxide (OMe*) is catalytically active species not hydroxide
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Most important: Hydroxides and alkoxides. What’s the difference?
The active catalyst is the alkoxide (NaOMe/KOMe), not the hydroxide!
Hydroxides:
• Pre-forming necessary,
• Unreacted hydroxide remains,
• Water is liberated.
Alkoxides (solutions are not methanol solutions of NaOH or KOH!):
• Pure catalyst = faster and more complete conversion,
• No hydroxides, no water = improved selectivity, better yield.
Preforming reaction
NaOH + MeOH NaOMe + H2 O
KOH + MeOH KOMe + H2 O
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Pure catalyst: Performance advantage
Concentration of active catalyst higher with alkoxides;
• Conversion faster and more complete
• Improved space-time-yield
Better performance especially at low methanol: oil ratio.
See: J. Am. Oil Cham. Soc. 1984, 61 1638
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Pure catalysts: Selectivity advantage–less soaps
Two different reactions yield the same product: soaps
• Neutralization of FFA’s from the oil, unavoidable;
• Saponification, easily avoidable by use of alkoxides.
Any soap obtained will lower the biodiesel yield!
Neutralization
Free fatty acid (FFA)
Saponification
Biodiesel (FAME)OH OMe
Neutralization
SoapONa
NaOHNAOH
or NaOMe
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Biodiesel– products and side products
Glycerol
Soap
Glycerol
MeOH
ffa
Soap
Soap
Bio- diesel
Oil
Bio- diesel
unavoidable
ffaneutraliza
tionffa neutralization
unavoidable
saponification
avoidable
Yield loss!
Alkoxides Hydroxides
Trans-esterification using:
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When to use K- instead of Na-based alkaline catalysts ?
• Phase separation of glycerol phase has to be carried out quickly;
• Byproducts potassium salts (e.g. K2SO4) are of interest (fertilizer);
• Feedstock with relatively high free fatty acid (ffa) content
• Is processed (e.g. crude oils, used cooking oil)
• the resulting (unavoidable) soaps have different properties, depending on whether Na- or K-type:
• solubility in glycerol phase
• solidification point/viscosity.
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Properties of K/Na-soaps
K - soaps are removed much easier than Na – soaps together with glycerol phase
Sodium soaps
usually solids
Potassium soaps
often liquids
R ONa
ONa
R OK
O
partitions in biodiesel and glycerol phase
major fraction dissolves in
glycerol phase
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Handling and safety
Alkoxide catalysts come as ready-to-use solutions:
• no equipment and personnel for catalyst pre-forming reaction,
• no dangerous, exothermic dissolving process,
• no solids handling, no dust from NaOH or KOH flakes,
• no insoluble impurities will plug the lines or disturb flow meters;
Direct metering of the catalyst to the trans-esterification
Requirements:
• Storage tank instead of mixing vessel; nitrogen blanketing,
• Consider tank insulation/heat tracing in cold climate.
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Operational expenses
Small methanol excess required to obtain full conversion:
• Less recycle methanol,
• Recycle methanol is water-free and ready to use;
Less side products:
• Less equipment, less chemicals for work-up,
• Glycerol processing simplified;
Process safety:
• Less off-time, less maintenance efforts.
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Conclusion: Success factors of alkoxides
• Higher biodiesel yield (2-5%) increases sales,
• Good glycerol quality (80-88%) is easily obtained,
• Alkoxide catalysts are apparently more expensive than hydroxide catalysts, but:
• The profits from the higher biodiesel yield compensate for this by far,
• Additional profits due to a better glycerol quality,
• Less side products make the process easier and more stable;
The catalyst handling becomes safe, easy and fast.
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Conclusion and perspective
• Quality biodiesel can be produced by various processes using different types of catalyst;
• Alkoxide catalysts have become the most popular choice for the production of FAME type biodiesel, - especially in large scale production facilities;
• 1.5 and 2nd generation type biodiesel processes (once established) will require heterogeneous transition metal catalysts;
• Co-existence of 1st, 1.5, and 2nd generation biodiesel types–each type will have a share in the future fuel mix.
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Biodiesel in motorsports
No matter how you do it– quality biodiesel is a performance product