The Chemistry of Biodiesel xidation
Presentation verview Chemical Properties and Environmental Factors affecting Biodiesel Stability Mechanistic Pathways of Biodiesel Degradation Focus on xidation FAME conversion to volatile compounds Diversity of Chemicals Produced Summary
Instability Concerns Food - Cooking ils - Whole oils / Triglycerides Going Rancid - Production of undesirable odors or flavors Fuel - Biodiesel - FAME Increase in Acidity Corrosion Increase in Viscosity Deposit formation Fuel filter plugging Injector Deposits Fuel economy Excessive smoke emission
Factors Affecting Biodiesel Stability Manufacturing peration conditions and processes used Antioxidants natural or added Potential Impurities Acids, glycerin/glycerides, metals Storage Conditions exposure to water, light or air Composition
Whole il to Biodiesel WHLE IL / TRI GLYCERIDES MeH Catalyst 12 4 H Steryl H 3 C 10 PALM / TALLW H Linoleyl H 3 C 4 SY H leyl H 3 C RAPE SEED
FAME Composition % 80 0 40 20 0 % Poly Unsaturated Fatty Acids Tallow Coconut Yellow Palm Rape Canola Peanut Cotton Soy Sun Linseed
Pathways to Biodiesel Instability Thermal Instability Associated with Polymer forming reactions Hydrolytic Instability Formation of acids via ester cleavage xidative Instability Mixture of degradation products
Mechanisms of Biodiesel Degradation Thermal Degradation Bio Diesel relatively thermally stable in absence of oxygen and water Increasing Temperature increases the rate of other Degradation Pathways
Mechanisms of Biodiesel Degradation Hydrolytic Degradation Breakdown of the Biodiesel by the reaction with water Catalyzed by acids, bases and enzymes Ester Hydrolysis FAME CH 3 Water + CH 3 H Methanol H
Mechanisms of Biodiesel Degradation xidative Degradation Main mode of Biodiesel Instability Two Step Process Peroxide Formation Peroxide Decomposition Peroxide Formation Air CH 3 Complex Mixture Peroxide Decomposition H CH 3
Two Stage xidation Peroxide Content vs Temperature Stage I Stage II Peroxides - distinct step in the oxidation Rancimat measure decomposition products Increased peroxide content directly impacts Induction period Peroxide conteng mg/kg Rancimat Hrs 5.5 5 4.5 4 3.5 3 2.5 2 50 40 30 20 10 0 20 30 40 50 0 0 80 Temperature C Rancimat Response to Stressing 20 30 40 50 0 0 80 Temperature C
Mechanisms of Biodiesel Degradation Peroxide Formation Peroxide Formation Peroxide Decomposition R FAME CH 3 Air H CH 3 Complex Mixture Volatile rganics
Stage I - Peroxide Formation Singlet xygen Formed via a photochemical process H 3 C H Ene mechanism H H 3 C
Stage I - Peroxide Formation Singlet xygen xidation Rancimat Hrs 5 4 3 2 1 0 0 1 2 3 Weeks of Storage Dark Sun Light
Stage I - Peroxide Formation Triplet xygen Free radical oxidation Common Initiation Two pathways for propagation INITIATIN I I (Initiator) I + RH PRPAGATIN [A] ( ) R + 2 R + RH R + CH2=CHX PRPAGATIN [B] (H) RH RH + RH RH + CH2=CHX 2 RH TERMINATIN R + R R + R R + R R + R I R R2 RH + R 2 R R + H R + R + H2 R + HCH2C HX R2 + R + H2 RR or lefin RR RH + 2 + R= RR + 2
Initiation Rate Factors Hydrogen abstraction Allylic hydrogen most easily removed leic Linoleic H 3 C H 3 C 4 Main Component xygen Uptake Rates Rape (18:1) 1 Soy (18:2) 41 Linseed (18:3) 98
Propagation - Peroxy Radical Hydrogen Abstraction H 3 C H leic Peroxy Radical Rearangement H 3 C leic H 3 C H 3 C H 3 C H 3 C Addition / Fragmentation
Propagation - Peroxy Radical Hydrogen Abstraction H 3 C H leic Peroxy Radical Rearangement H 3 C leic H 3 C H 3 C H 3 C H 3 C Addition / Fragmentation
Propagation - Peroxy Radical Hydrogen Abstraction H 3 C H leic Peroxy Radical Rearangement H 3 C leic H 3 C H 3 C H 3 C H 3 C Addition / Fragmentation
Peroxide Decomposition Peroxide Formation Peroxide Decomposition R FAME CH 3 Air H CH 3 H Peroxide Formation Two alternative routes Reasonable well defined Peroxide Decomposition Many reacting species involved Alternative pathways Less well defined
Hydroperoxide Rearrangement + H 2 H CH 3 H + R' H H R' Air H Ketone or Aldehyde H + - H R' H H + H H + - H + R' + H 2 R' H H Hemiacetal / Hemiketal
Peroxide Decomposition Peroxide Formation Peroxide Decomposition Volatile Acids CH 3 R FAME CH 3 Polymers Air H Complex rganics Many different decomposition pathways Free radical Metal mediated Acid induced degradation Many different decomposition products Volatile polar compounds Monomeric compounds Dimers trimers - polymers
Summary xidation main mechanism of Biodiesel degradation xidation occurs at or near sites of un-saturation xidation two distinctive stages Stage I Peroxide formation Stage II Peroxide decomposition Peroxide formation singlet or triplet oxygen Peroxide decomposition follows multiple reaction pathways to yield a diversity products The rate, amount and types of peroxides formed and the subsequent degradation products formed are dependant on a number of different factors All chemical pathways must be considered when stabilizing Biodiesel