Catalyst Selection in Biodiesel Processes · choice for the production of FAME type biodiesel, - especially in large scale production facilities; • 1.5 and 2nd generation type biodiesel

Catalyst Selection in Biodiesel Processes

Johannes RuwweBioFuelsMarkets Asia, June 10,2008 Delhi, India

24.07.2012 | www.evonik.com/biodiesel Seite 2

Contents:

• Catalysts used in biodiesel processes

• Market share of various processes

• Comparison of alkali type catalysts

• Success factors of most popular catalyst

• Perspective


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


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)


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)


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%.


Most important: Hydroxides and alkoxides. How does it work?

Reaction mechanism alkaline catalyzed trans-esterification:Alkoxide (OMe*) is catalytically active species not hydroxide


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


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


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


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:


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.


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


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.


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.


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.


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.


Biodiesel in motorsports

No matter how you do it– quality biodiesel is a performance product

Documents

Catalyst Selection in Biodiesel Processes · choice for the production of FAME type biodiesel, - especially in large scale production facilities; • 1.5 and 2nd generation type biodiesel