Cataldo De Blasio, Dr. Sc. (Tech.)

Transcription

1 Biodiesel Cataldo De Blasio, Dr. Sc. (Tech.) Aalto University, School of Engineering. Department of Mechanical Engineering. Laboratory of Energy Engineering and Environmental Protection. Sähkömiehentie 4, Otaniemi, Espoo. Finland. P.O. Box

2 Source To produce biodiesel we need vegetable oil They are rich in neutral triacylglycerols (TAG) Vegetable oil can be rich in free fatty acids, FFA

3 Non conventional sources non-edible vegetable oils (e.g., Jatropha oil and Polanga oil) or Animal fat wastes (AFWs) [e.g., chicken fat and choice white grease (CWG)], are characterized with high free fatty acids (FFAs) and water.

4 Transesterification and esterification If hey are rich in neutral triacylglycerols (TAG) If vegetable are rich in free fatty acids, FFA The catalyst is commonly HCl or H2SO4

5 Triacylglycerol, TAG, or triglyceride Transesterification The biodiesel is obtained by the reaction of a vegetable oil with an alcohol, in presence of a catalyst, to give mono-alkyl esters. Fatty acid R COOR is the ester group Reference: Lotero, synthesis of biodiesel via acid catalysis Reference: Morrison, Organic Chemistry; Caye, Biofuels Eng. Process. Tech.

6 Side reactions: saponification and hydrolysis Free fatty acids are formed when oils are treated at high temperatures where they undergo an oxidation process.

7 Formation of Soap When a FFA, Free Fatty acid (ROOH is the acidic group) is present in the feedstock, then There could be the formation of soaps, if the same catalysts are used. This is very negative For separation processes, viscosity increase etc. In waste oil the amount of FFA can be up to 15% (wt) and this reduces the quality. Water is eliminated by centrifugation to acceptable level of 0.5% (wt). Fatty acids directly affect the main parameters of the biodiesel: Cloud point (the minimum temperature at which small solid cristals can be observed. The cold filter plugging point, (the temperature at which the fuel filter pluggs due to cristals and solid components) The pour pont (the minimum temperature at which the fuel is actually moving sufficiently, it becomes a gel)

8 Nomenclature of groups of interest: carboxylic acids and Esters carboxylic acid Source: Maitland Jones, Organic Chemistry, Chapter 17.

9 Formation of the tedrahedral intermediate in the esterification of hydroxyl acids Remember the periodic table at slide 5 with the Electron affinities, note that oxygen has an electron affinity higher than carbon, for this reason the alcohol will bound on the carbon and not on the oxygen. Source: Maitland Jones, Organic Chemistry, Chapter 17.

10 All steps in Fischer Esterification Source: Maitland Jones, Organic Chemistry, Chapter 17.

11 Transesterification mechanisms The reaction with the alkoxide group ( - OR) is reversible and catalytic, while the reaction of the hydroxide froup ( - OH) is not reversible and not catalytic. The hydrogen from the hydroxyl acid can t just be replaced by the R of the alkohyde, Because an acid when loses the hydrogen is actually stabilized by resonance.

12 Catalysts used The catalysts used in the process of biodiesel production are mainly alkaline: NaOH KOH Formation of the methoxide ions, they are strong nucleophyles and attach the glyceride molecules.

13 Base catalyzed production of biodiesel This can be methoxide ion CH 3 O - The base catalysts create a alkoxide ion, This ion is more nucleofile, the alkyl ion OR- Attack directly the doubble bond. This is the nucleophyle Typical base catalysts are: NaOH, KOH. Source: Lotero, Synthesis of biodiesel via acid catalysis

14 Formation of the methoxide ion from a base catalyst and an alcohol Methoxide ion is a strong nucleophile, which means it is able to link at lower electrophile carbon. Reference: Lotero, synthesis of biodiesel via acid catalysis

15 Acid catalyzed production of biodiesel Acid catalysts do not show measurable susceptibility to FFA, Free Fatty Acids This is a nucleophyle because can give some electrons to the cation. Nucleophyles are also called Lewis bases. The carbonil oxygen becomes more electrophilic, because obtains a + charge, this makes more easy to host the OH group of the alcohol Source: Lotero, Synthesis of biodiesel via acid catalysis

16 Biodiesel production from waste cooking oils Alkali-catalyzed transesterification of waste cooking oils Composition of Waste Cooking Oils, WCO Temperature of the experiments: 30 C, 50 C or 70 C. Residence time: 20 min,40 min, 60 min, 90 min or 120 min The molar ratio of methanol and WCO: 5:1 to 12:1 Amount of KOH catalyst: 0.5 wt% to 1.5 wt% of the WCO the transesterification is commonly carried out with an extra amount of alcohol in order to shift the equilibrium to the proposed product, methyl ester. Reference: Fuel 87 (2008)

17 Methanol / catalyst effect on the biodiesel yield

18 Effect of temperature Effect of temperature on the conversion of biodiesel at 0.75 wt% KOH and the methanol/wco ratio of 8:1. Cloud Point is the temperature at which the crystals of solid biodiesel first become visible, in case we decrease the temperature. Pour Point also called Gel Point, is the temperature where biodiesel becomes solid and can no longer be pumped. The Flash point is the minimum temperature at which the vapours of the fuel ignite using a ignition source. The auto-ignition temperature is instead the temperature at which the vapours ignite with no source. While the Fire-point is the minimum temperature at which the flame is still burning with no source of ignition.

19 Tf and Tb, are the flash and the normal boiling point in Kelvin. Source: Lotero et al. Ind. Eng. Chem. Res. 2005, 44, Source: Rao 1992, J. of Hazardous Material 32, 81-85

20 Cetane Number 2,2,4,4,6,8,8-heptamethylnonane (HMN) The cetane number indicates the lowest compression ratio that would produce autoignition.

21 J.A. Dean, Lange s Handbook of Chemistry, 13th edn., McGraw-Hill, New York, NY, Aldrich Catalogue Handbook of Fine Chemicals, Aldrich Chemical Company, Inc., G. Weiss, Hazardous Chemicals Data Book, Noyes Data Corporation, Park Ridge, NJ, 1980.

22 Positive aspects in Biodiesel Production Higher biodegradability Pollutant reduction are highly reduced Higher flash-point biodiesel increases lubricity bio-diesel does not contribute to global warming. (is CO2 free) B20 means fuel blend, in this case 20% of biodiesel is mixed with 80% of normal diesel Source: Caye Biofuels engineering process technology.

23 Negative aspects with biodiesel Higher Nox production higher viscosity, lower volatility, presence of unreacted glycerols

24 Properties of Diesel and Biodiesel Emissions (in %) Compared to normal Diesel

25 Additives Ethanol Ethanol has 60% of the energy of diesel but the octane number is higher therefore the energy amount can be 80 % of the diesel. An engine which has the same self ignition properties of a mixture of 2.2,4- trimethylpentane, so called iso-octane, has the Octane number equal to the percentage of iso-octane in a iso-octane, heptane mixture Heptane, C 7 H 16 Iso-Octane Reference: morrison Boyd, Organic chemistry, pp. 200

26 Sources of Biodiesel 16:01, 16 carbons and one doubble bond Source: Caye, Biofuels engineering process technology Iodine number represents the degree of unsaturation, C = O, The cetane number is a measure of the facility of ignition of the diesel, the more the cetane number the less time takes for the fuel to ignite

27 Sources of Biodiesel

28 Microbial based source of Biodiesel

29 Properties of Diesel, Biodiesel and different kind of fuels

30 Typical Oil Content and Fatty Acid Content in Oils from Microbial Sources

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32 Enzyme Catalyzed enzimatic transesterification for biodiesel production One example: fatty acid methyl ester (FAME) production from waste choice white grease (CWG) biocatalyzed by immobilized lipase [Candida antarctica lipase B (CALB)] TG, DG, MG, and FFA are triacylglycerides, diacylglycerides, monoacylglycerides, and free fatty acids, respectively.

33 Enzyme Catalyzed enzimatic trans-esterification for biodiesel production. Main Parameters Biocatalysts Various Solvents Effect of Speed of Agitation Biocatalyst Amount Effects of Different Alcohols Temperature

34 Ping Pong Bi Bi, mechanism triacylglycerides (TG) and methanol (M) are the substrates, while FAME (F) and glycerol (G) are the products. In this mechanism, the enzyme (E) must bind the first substrate (TG) to form an enzyme substrate complex [ETG], then release the first product (F), and transform intermediate enzyme (E ). This is followed by binding of a second substrate (M) to E and the breakdown of the transitory complex [E M] to free enzyme (E) and the second product (G).

35 Production/consumption rates for the main compounds in enzime transesterification. triacylglycerides (TG) methanol (M) FAME (F) glycerol (G) enzyme (E) the first substrate (TG) enzyme substrate complex [ETG], first product (F), intermediate enzyme (E ). second substrate (M) transitory complex [E M]

36 Titration procedure The titration determines the amount of excess catalyst needed in the chosen reaction mechanism. For alkali-catalyst procedure an excess amount of catalyst may be required to first neutralize the free fatty acids before transesterification of oil triglycerides to ethyl esters can occur. Typical concentrations of catalyst to achieve efficient transesterification range around 1 percent by weight and any excess catalyst is added beyond 1 percent based on the titration values. 1. Measure 10 ml of ethanol in a test tube. 2. Measure 1 ml of oil and mix with ethanol. 3. Add about 0.5 ml of phenolphthalein solution (10 to 20 drops). 4. Titrate the oil/ethanol solution with 1 g/l KOH or NaOH solution in distilled or deionized water using a burette until the color begins to turn pink after adequate mixing (near ph 8.0). 5. Estimate amount of KOH or NaOH needed for trans-esterification from the following formula:y = 9 + x where y is grams of KOH or NaOH catalyst (usually 9 to 15 g) to use in 1 L of oil (about 900 g) and x is the number of milliliters of KOH or NaOH solution used in titration. The 9 g of catalyst gives you a starting value of about 1 wt % in 1 L of oil and the additional catalyst designated by x is required to first neutralize any free fatty acids before rapid transesterification may take place.

37 Results of the titration From page 241 of Caye, Biofuels Engineering process technology

38 Homogeneous Acid- Catalyzed process for biodiesel production. Catalyst preparation feedstock pretreatment acid catalyst removal transesterification and esterification alcohol recycle