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Matt-Wasilowski-Analytical-Problem-Biodesiel From Wastewater Sludges

Waste water sludge has shown to be a valuable lipid feedstock for the synthesis of Biodiesel fuel comprised of monoalkyl esters. This is due to the high cost of vegetable oils and animal fats relative to the cost of standard petroleum sources of diesel fuel. Biodiesel fuels made from waste water sludge are a %100 carbon neutral fuel source and as such represent an enormous step forward in the field of green chemistry.

The problem with the synthesis of this fuel lies in the purity of the lipidic material needed to perform the desired transesterification, and many methods have been proposed. These methods include cosolvents and shear mixing, but none show cost effectiveness. Even if a reasonable method is found to separate these fatty oils, a challenge lies in quickly and effectively characterizing the desired compounds, as the desired reactant that can be transesterified is very similar to the other lipidic material present in the waste water sludge. Certain methods of reaction, such as acid catalyzed transesterification, have been suggested, but these react very selectively with only a certain subset of lipid chains present in the sludge mixture. (1)

The analytes in this process are the lipidic material present and the biodiesel monoalkl ester that is desired. The matrix that these analyltes are found in includes the original filtered waste water feedstock and the final product stream that includes the biodiesel fuel. (1)

UV-Vis Absorption Spectroscopy

Because Diesel fuel is a mixture of saturated hydrocarbons and aromatic hydrocarbons, any analytical technique involving UV/VIS spectroscopy would likely yield spectra with far too many indistinguishable peaks. Like many analytical techniques, cost effective forms of UV/VIS spec requisite reasonably pure samples in order to distinguish individual compounds. Because of this, the raw form of this diesel fuel can not be identified or characterized using solely UV/VIS techniques. (1)

In order to make the mixture of paraffins and aromatics susceptible to UV/VIS, the individual compounds present in even a purified form of the diesel fuel must be isolated. This can be done effectively by separating the compounds by both mass and polarity. Roughly 25% of the diesel mixture classically consists of napthalenes and alkylbenzes and all of these should be separable through techniques such as GC or through column chromatography. (2) After these techniques are employed, it would be possible to characterize each individual portion of the fuel in order to determine both the composition and, to a certain extent, the purity of the compound.

The analytical issue lies determining the optimal purity and composition when balanced with the cost of performing seperative techniques on a large scale. As of now the analytical issue lies in determining how to separate the desired reactants/product from the waste water sludge. (1)

The hypothesis in this problem lies in determining how to best separate the final fuel from the FAME, Methanol, and other organic compounds present in the Matrix. The analyze in this case could be any of the components of diesel fuel, but the trouble lies in separating and then determining when the product is pure enough to be consumed as a transportation fuel.

Analyte Structure and Standard Purchasing Information

View image

Shown here is the structure of FAME (fatty acid methyl esters) which can be seen as the largest component of most biodiesel fuels, as it is synthesized from fatty acid chains present in the wastewater sludge. Both analytes are shown here in the reaction scheme. These analytes being FAME and fatty acids and oils.

Image Citation: (1)

FAMEs can be purchased from http://fullgreenfood.en.alibaba.com/ with several different options for purity. This can be useful for determining how pure the final product analyte must be in order to be both analyzed and used as a fuel. The Oils and fatty acids that must be analyzed in both the product and reactant mixtures can be purchased from any company that sells standard cooking oils (1). Studies pertaining to the formation of FAMEs have explored similar methods. Otherwise, to use the intended wastewater sludge, this can be procured from any wastewater treatment plant.

Atomic and Mass Spectroscopies

Atomic Spectroscopies are unsuitable to accurately detect the analytes for this problem. Both analytes are relatively large molecules (FAMEs are roughly 280-350 Da and oils and fatty acids are roughly 600-1000 Da) with a large range of masses that are present. Its likely that any absorption or emission spectroscopy would likely be too imprecise because of the large number of varying molecular weights present in a realistic matrix. (3) Because of this, Mass Spectroscopy would be a better fit.

The best method of ionization would be ESI. This is due to it being a soft ionization technique, which works well for larger molecules without risking destroying the relatively sensitive structure of large fatty acids. The best type of selection and detection is likely a linear quadrupole ion trap analyzed using FT-ICR. The large molecules that make up the matrix would be easily separated by a linear ion trap. FT-ICR would simply make quick analysis quicker and easier, as many trials of various reaction conditions would be run. (4)

Sample Preparation Procedures

Because the stock samples needed for analysis in this case can be purchased in pure forms, separation for analysis is not necessary when preparing from stock solutions. However, separating analytes both before and after the trans-esterification is important for analysis and fuel purity. The separative technique for mass producing the biofuel suggested in studies has been shear mixing and phase separation in methanol (1). For analysis:

1. Liquid Phase separation in Ethyl Ether or Ethyl Acetate would work well, followed by a brine wash to dry the solution as much as possible would likely be effective (1).

2. Evaporation of the solvent may be necessary depending on the analytical technique being employed. If GC/MS is used this my not be needed. However, for H1NMR analysis or IR analysis is may be necessary to concentrated the analytes.

This technique may be used for analysis both before and after the reaction takes place.

Chromatographic Techniques

HILIC, Reverse Phase, Normal Phase, Ion-exchange, and Gas Chromatography would all be acceptable for separating and analyzes both sets of analytes for this particular problem. Size-Exclusion, Affinity, and Chiral Chromatography are not applicable here. Size- Exclusion Chromatography would not be useful as it the hydrocarbon analytes are mixtures of many hydrocarbons ranging from C8 to C18 and the FAME products are mixtures of many different types of hydrocarbons, all of which can be seen as a 'FAME' type fuel. The issues with this type of chromatography is that it will not give detailed information on the concentrations of the useful analytes, as it can not tell them apart. (2) Affinity Chromatography simply doe not apply. Chiral Chromatography is also not useful as the analyte chirality is not an issue that affects the formation of FAMEs or the way in which this biofuel combusts (1).

The most useful seperative technique would likely be HILIC, as the hydrophilic and hydrophobic interactions of the individual hydrocarbons would easily separate different weight lipids, including FAMEs from the matrix mixture and give clear data on the different compositions of the product and reactant mixtures. (5)

A useful column for this separation can be purchased from ES Industries. The column is stainless steel, is 5cm in length, and 0.75mm in diameter. The Particles size is 1.8u and the diameter is 120A. The stationary phase of the column is silica gel designed for HILIC separation. The column can be purchased at http://esind.com/pages/products/products_02_2.tpl.

The mobile phase for HILIC would likely be a mixture of acetonitrile or THF and water. For the given analytes, acetonitrile would likely be a better choice as it would separate the composition of the analyze more effectively. (5)

The detector for this type of separation would like be some type of Mass Spectrometer, as mentioned in a previous blog posting. MS would give the clearest data for the separation and be able to analyze each component as it eluted from the column. While the technique may be arduous to analyze, it would be the most effective way to determine the exact composition of the lipidic material reactant and the FAME product.

Preferred Analytical Technique

The preferred technique for the analysis of lipidic material present in waste water treatment plants and FAMEs (the biodiesel fuel that can be synthesized from said lipids) would be HILIC chromatography using Mass Spectroscopy as a detector for. The lipidic material would need to be extracted, via liquid phase extraction, and then concentrated in order to undergo proper analysis using HILIC. The FAME material would best be analyzed after it is filtered and distilled from the reaction media. It is essential that the FAME material be analyzed in its final fuel form, as the composition of this biofuel is the crucial information needed to solve this analytical problem.

The analytical problem which uses the most similar analytical technique as mine would be Andrew Szeliga's problem of Perflourooctonoic acid in human blood. Both techniques involve a chromatographic column followed by mass spectroscopy as the detector. The analyte is also similarly complex and will require similar a similar type of seperatory technique in order to use the specified analytical technique.

Capillary Electrophoresis Techniques

For the FAMEs and lipids present in the reactant and product analytes, standard CE would likely not be effective, as ll of these products are similarly uncharged and present very little charge. For this reason, MEKC would likely work well, as the compounds do show differenced in hydrophobicity. SDS would work well as the surfactant buffer, with water as the mobil phase. For this any MEKC coated capillary would work.

As with other analytical techniques, using MS as a detector would likely work best, considering it would provide the most accurate and distinct information based on the analytes.

Source(s):

(1) Karbo, D. M. Biodiesel Production from Municipal Fuel Sludges. Energy and Fuels. [Online] 2010. http://pubs.acs.org/doi/pdf/10.1021/ef1001106 (accessed September 12th, 2011).

(2) Agency for Toxic Substances and Disease Registry, Center for Disease Control. Toxicology Profiles for Fuel Sources. http://www.atsdr.cdc.gov/toxprofiles/tp75-c3.pdf.

(3) Radziszewski, J.G.; et. al. Infrared Absorbtion Spectroscopy of the Phenyl Biradical. J. Am. Chem. Soc. 1996, 118 (31), pp 7400-7401.

(4) McLafferty, F.W.; et. al. Tandem Fourier Transform Mass Spectroscopy of Large Molecules. Fourier Transform Mass Spectroscopy. [Online] 1987, 7, 116-126 http://pubs.acs.org/doi/abs/10.1021/bk-1987-0359.ch007 (accessed October 25th, 2011).

(5) Alpert, J.A. Hydrophilic-interaction chromatography for the separation of peptides, nucleic acids and other polar compounds. Journal of Chromatography A. 1990, 499, pp 177-196.

Comments

Blog 13? -1 pt

Blogs 9 and 10. Good answers.
Blog 11. SDS cannot be used if the detector will be MS. There are some surfactants that can be hydrolyzed when they reach the electrospray source (acid labile surfactants). These may be useful if you really want to do CE-MS. (-0.1 pt).

blog 8? (-1 pt)

Blog 6. Good answers.
Blog 7. Example of MS? (-0.1 pt)

Blogs 4 and 5? (- 1 pt each)

Matthew,
BLOG 2 -I agree that complex mixtures need to be separated prior to analysis. The question is about the analytes. Do they absorb in the UV? Any other analytical problems that are simialr to yours? (-1pt).

BLOG 3 - ? (-1 pt).

What is the hypothesis that you plan to test? (-0.2 pt)