Journal of the American Oil Chemists' Society

, Volume 94, Issue 2, pp 285–299

Bias and Imprecision in the Determination of Free Glycerin in Biodiesel: The Unexpected Role of Limitations in Solubility

  • Richard W. Heiden
  • Sigurd Schober
  • Martin Mittelbach
Original Paper
  • 88 Downloads

Abstract

Residual free glycerin (FG) is a critical marker of fatty acid methyl ester (biodiesel) fuel quality. Yet, routine determinations by standard methods display excessive imprecision, and the uncertainties undermine confidence in the data. Various degrees of agitation are used here to evaluate the possibility of heterophase formation as a contributor to imprecision and potential bias. Statistical markers from the analysis of 13 biodiesel samples reveal that seven contain unexpected heterophases, which, due to settling, cause underestimates of 15–68%. Agitation alone re-suspends heterophases for brief periods, easing potential biases, but also increases imprecision. A promising new sample pretreatment is presented, which reduces the deleterious effects of heterophases. Solubility limitations are explored as possible contributing factors, and measurements made at 23 °C in purified soy FAME reveal an equilibrium solubility which is more than 80% below previously published estimates. Strong interactions of liquid FG with small amounts of moisture reduce solubility to below international quality limits, while interactions of initially dissolved forms of moisture and FG produce bias-inducing heterophases at 0.02% FG. The unexpected low solubility of FG, exacerbated by interactions with impurities, is seen as an important contributor to underestimates and imprecision, and a strong influencing factor on the fate of residual FG in commercial biodiesel fuels.

Keywords

Biodiesel Glycerin Bias Solubility 

Abbreviations

0%D

FAME saturated with moisture at 40 °C

20% D

0%D FAME diluted to 20% v/v DDMF (100%D)

40%D

0%D FAME diluted to 40% v/v DDMF (100%D)

60%D

0%D FAME diluted to 60% v/v to DDMF (100%D)

80%D

0%D FAME diluted with 80% v/v to DDMF (100%D)

100%D

100% DDMF, moisture <50 ppm

95CI

95% Confidence interval

95CI1

95% Confidence interval, n = 1

95CI3

95% Confidence interval, n = 3

AG

Concentration of FG after agitation

AGQM

Arbeitsgemeinschaft Qualitätsmanagement Biodiesel, e.V.

ASTM

American Society for Testing and Materials

ASUB

An approximately 100.0 mg subsample of B100

ASUBINT

Time interval in seconds between ~100.0 mg subsamples

B100

Commercial Grade of FAME biodiesel

BSTFA

Bis-(trimethylsilyl)trifluoroacetamide

CDC

US Center for Disease Control

CEN

Comité Européen de Normalisation-European Committee for Standardization

CV

Coefficient of variation

DDMF

Distilled, dry, methanol free

EI

Electron ionization

EN

European normalization

EU

European Union

FAME

Fatty acid methyl esters: here refers to a research grade of biodiesel

FG

Free glycerin

GC

Gas chromatography

GC/MS

Gas chromatography/mass spectrometry

GC-FID

Gas chromatography-flame ionization detection

ILS

Interlaboratory study

IRMM

Institute for Reference Materials and Measurements

ISUB

An approximately 6.0000 g subsample for pretreatment by pyridine augmentation (PA)

ISUBINT

Time interval between 6 g intermediate subsamples

MG

Monoglyceride

MS1

Magnetic stirring with 2.5 cm stir bar, surface turbulence, no vortex

MS2

Magnetic stirring with 3.7 cm stir bar and 2 cm vortex

MSTFA

N-Methyl-N-trimethylsilyltrifluoroacetamide

NIST

National Institute of Science and Technology

P

Treatment procedure

PA

Pyridine augmentation at a level of 30.0000% of B100 ISUB weight

R

Reproducibility-between lab variations

r

Repeatability-within lab variations

REF

Results of six consecutive injections of a single derivatized subsample

SMP

Portion of a B100 process stream or fuel lot submitted to a lab in a container for analysis

STD

Standard deviation

STD2

Variance

SUB

A portion of an SMP for analysis by a test method

TMS

Trimethylsilyl

U

Unagitated-concentration of FG before agitation

US DOE

US Department of Energy

VA

Vigorous wrist agitation for 10 s

VA INT

10 s interval between agitation and 100 mg subsample

X

EU rejection limit

References

  1. 1.
    Mittelbach M, Remschmidt C (2004) Biodiesel—the comprehensive handbook. Martin Mittelbach, Graz, pp 119–120Google Scholar
  2. 2.
    Banavali R, Schultz AK, Topp K, Vandersall MT (2013) Ion exchange resins in biodiesel processing. In: Knothe G, Krahl J, Van Gerpen J (eds) The biodiesel handbook, Chapter 4.4. AOCS Press, Champaign, pp 85–96Google Scholar
  3. 3.
    Wall J, Van Gerpen J, Thomson J (2012) Soap and glycerin removal from biodiesel using waterless processes. Trans ASABE 54:5350–5541Google Scholar
  4. 4.
    Atadashi IM, Aroua MK, Aziz AA (2011) Biodiesel separation and purification: a review. Renew Energy 36:437–443CrossRefGoogle Scholar
  5. 5.
    ASTM (2015) Standard specification for biodiesel fuel blend stock (B100) for middle distillate fuels D 6751-15a. American Society for Testing and Materials, West ConshohockenGoogle Scholar
  6. 6.
    CEN (2012) Automotive fuels—diesel-fatty acid methyl esters (FAME)-requirements and test methods. EN 14214, European Committee for Standardization, BrusselsGoogle Scholar
  7. 7.
    ASTM (2013) Research report method D6584, RR:D02-1756. American Society for Testing and Materials, West Conshohocken, pp 2–4Google Scholar
  8. 8.
    ASTM (2013) Standard test method for determination of total monoglycerides, total diglycerides, total triglycerides, and free and total glycerin in B 100 biodiesel methyl esters by gas chromatography D6584-13e1. American Society for Testing and Materials, West Conshohocken, p 4Google Scholar
  9. 9.
    Prinz N, Wilharm T (2013) Biodiesel quality in Germany, Report 2013-3b. Arbeitsgemeinschaft Qualitaetsmanagement Biodiesel, e.V., Berlin, p 22Google Scholar
  10. 10.
    CEN (2011) Fat and oil derivatives—fatty acid methyl esters (FAME)—determination of free and total glycerol and mono-, di-, triglyceride contents, EN 14105-11. CEN, European Committee for Standardization, BrusselsGoogle Scholar
  11. 11.
    Knothe G (2005) Analytical methods for biodiesel. In: Knothe G, Krahl J, Van Gerpen JH (eds) The biodiesel handbook, 2nd edn. AOCS Press, UrbanaCrossRefGoogle Scholar
  12. 12.
    Knothe G (2006) Analyzing biodiesel: standards and other methods. J Am Oil Chem Soc 83:823–833CrossRefGoogle Scholar
  13. 13.
    Pauls RE (2011) A review of chromatographic characterization techniques for biodiesel and biodiesel blends. J Chromatogr Sci 49:384–396CrossRefGoogle Scholar
  14. 14.
    Knothe G (2001) Analytical methods used in the production and fuel quality assessment of biodiesel. Trans ASAE 44:193–200CrossRefGoogle Scholar
  15. 15.
    Monteiro RM, Ambrozin ARP, Ferreira Liao LM (2008) Critical review on analytical methods for biodiesel characterization. Talanta 77:593–605CrossRefGoogle Scholar
  16. 16.
    Freedman B, Kwolek WF, Pryde EH (1986) Quantitation in the analysis of transesterified soybean oil by capillary gas chromatography. J Am Oil Chem Soc 63:1370–1375CrossRefGoogle Scholar
  17. 17.
    Plank C, Lorbeer E (1995) Simultaneous determination of glycerol and mono, di and triglycerides in vegetable oil methyl esters by capillary gas chromatography. J Chromatogr A 697:461–468CrossRefGoogle Scholar
  18. 18.
    CEN (2003) Automotive fuels-diesel—fatty acid methyl esters (FAME) and test methods. EN 14106-2003, European Committee for Standardization, BrusselsGoogle Scholar
  19. 19.
    Lozano P, Chirat N, Graille J, Pioch D (1996) Measurement of free glycerol in biofuels. Fresenius J Anal Chem 354:319–322Google Scholar
  20. 20.
    Bondioli P, Marianni C, Lanzani A, Fedeli E, Veronese S (1992) Vegetable oil derivatives as diesel fuel, analytical aspects, note 2: determination of free glycerol. Riv Ital Sostanze Gr 69:7–9Google Scholar
  21. 21.
    Household Products Database (2015) National Institutes of Health, National Library of Medicine, Specialized Information Services. http://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=chem&id=6. Accessed 1 Sept 2015
  22. 22.
    Pierce Biotech (2003) MSTFA product instructions 0371. Pierce Biotechnology, Rockford, p 2Google Scholar
  23. 23.
    Buchanan MD, Stenerson KK, Yearik V (2011) Determination of free and total glycerin in B100 biodiesel. Sigma Aldrich Reporter US 27.1Google Scholar
  24. 24.
    Evershed RP (1993) Advances in silylation. In: Blau K, Halket JM (eds) Handbook of derivatives for chromatography, 2nd edn. John Wiley, Chichester, pp 51–100Google Scholar
  25. 25.
    Zaikin V, Halket J (2009) Silylation. Handbook of derivatives for mass spectrometry. IM Publications, Chichester, pp 1–24Google Scholar
  26. 26.
    CDC (2013) Method 6703.04. Center for Disease Control, Organic Analytical Toxicology Branch, Division of Laboratory Sciences, National Center for Environmental Health, p 7Google Scholar
  27. 27.
    Knothe G, Cermak SC, Evangelista RL (2009) Cuphea oil as source of biodiesel with improved fuel properties caused by high content of methyl decanoate. Energy Fuel 23:1743–1747CrossRefGoogle Scholar
  28. 28.
    Haas MJ, Nadawi N, Berry WW, Feldman E, Kasprzyk S, Ratigan B, Scott K, Landsburg EB (2010) Food butter as a feedstock for biodiesel production. J Agric Food Chem 58:7680–7684CrossRefGoogle Scholar
  29. 29.
    Ulberth-Buchgraber M, Morales V, Miguel LR, Charoud-Got J, Held A (2015) New certified rapeseed-based biodiesel reference material for effective biodiesel testing. Energy Fuel 29:3732–3738CrossRefGoogle Scholar
  30. 30.
    Speight JG (2015) Handbook of petroleum product analysis, 2nd edn. Wiley, New York, pp 50–51Google Scholar
  31. 31.
    Rostami M, Raeissi S, Mahmoodi M, Nowroozi (2013) Liquid liquid equilibrium in biodiesel production. J Am Oil Chem Soc 90:147–152CrossRefGoogle Scholar
  32. 32.
    Van Gerpen JH, Hammond EG, Johnson LA, Marley SJ, Yu L, Lee I, Monyem A (1996) Determining the influence of contaminants on biodiesel properties. Iowa State University, Ames, pp 11–12Google Scholar
  33. 33.
    ASTM (2012) Standard test method for acid and base number by color-indicator titration D974-12. American Society for Testing and Materials, West ConshohockenGoogle Scholar
  34. 34.
    CEN (2010) Automotive fuels-diesel-fatty acid methyl esters (FAME)-requirements and test methods (determination of methanol). EN 14110:2003-10, European Committee for Standardization, BrusselsGoogle Scholar
  35. 35.
    ASTM (2011) Standard test method for water and sediment in middle distillate fuels by centrifuge-D2709-96 2011e1. American Society for Testing and Materials, West ConshohockenGoogle Scholar
  36. 36.
    CEN (2012) Automotive fuels-diesel-fatty acid methyl esters (FAME)-requirements and test methods (determination of moisture). EN ISO 12937:2000, European Committee for Standardization, BrusselsGoogle Scholar
  37. 37.
    CEN (2012) Fat and oil derivatives–fatty acid methyl esters (FAME)-determination of oxidative stability (accelerated oxidation test). EN 14112, European Committee for Standardization, BrusselsGoogle Scholar
  38. 38.
    ASTM (2012) Determination of fuel filter blocking potential of biodiesel (B100) by cold soak filtration test (CSFT) D 7501-12a. American Society for Testing and Materials, West ConshohockenGoogle Scholar
  39. 39.
    Hefter GT (2003) Liquid–liquid solubilities. In: Hefter GT, Tomkins RPT (eds) The experimental determination of solubilities, pp 237–256Google Scholar
  40. 40.
    ASTM (2014) Conducting an interlaboratory study to determine the precision of a test method-E691-14. American Society for Testing and Materials, West ConshohockenGoogle Scholar
  41. 41.
    OeNorm (2007) Petroleum products-determination and application of precision data in relation to methods of test. EN ISO 4259 2007-04-01, Austrian Standards Institute, Wien, p 25Google Scholar
  42. 42.
    ASTM (2014) Determination of precision and bias data for use in test methods for petroleum products and lubricants-D 6300-14a. American Society for Testing and Materials, West ConshohockenGoogle Scholar
  43. 43.
    Alleman TL, Fouts L, Chupka G (2013) Biodiesel quality survey-2011. DOE Technical Report, NREL/TP-5400-57662, National Renewable Energy Laboratory, Boulder, CO, USA, pp 13–14, 25–28Google Scholar
  44. 44.
    Soap and Detergent Association (1990) Glycerine: an overview. Soap and Detergent Association, Oleochemicals Division, New YorkGoogle Scholar
  45. 45.
    Shah P, Wee C, White JM, Sanford S, Meier G (2010) Experimental determination and thermodynamic modeling of water content in biodiesel–diesel blends. Renewable Energy Group, Ames, Iowa, USA. http://www.regfuel.com
  46. 46.
    He BB, Thomson JC, Routt DW, Van Gerpen JH (2007) Moisture absorption in biodiesel and its petro-diesel blends. Appl Eng Agric 23:71–76CrossRefGoogle Scholar
  47. 47.
    Lamb H (1992) Hydrodynamics, 6th edn. Cambridge University Press, Cambridge. ISBN 978-0-521-45868-2Google Scholar
  48. 48.
    Viana MB, Freitas AV, Leitao RC, Pinto GAS, Santaella ST (2012) Anaerobic digestion of crude glycerol: a review. Environ Technol Rev 1:81–92CrossRefGoogle Scholar
  49. 49.
    Schmidt C (2010) Microbes quickly degrade a popular biofuel. Chem Eng News 88(22):50CrossRefGoogle Scholar
  50. 50.
    Passman F, Dobranick JK, (2005) Relative biodegradability of B-100 biodiesel and conventional low sulfur diesel fuels. In: Morris RE (ed) Proceedings of the 9th international conference on the stability and handling of liquid fuels, Sitges, Spain, pp 18–22Google Scholar
  51. 51.
    Prince RC, Haitmanek C, Lee CC (2008) The primary aerobic biodegradation of biodiesel B20. Chemosphere 71:1446–1451CrossRefGoogle Scholar
  52. 52.
    Rauch ME, Graef HW, Rozenzhak SM, Jones SE, Bleckmann CA, Kruger RL, Naik R, Stone MO (2006) Characterization of microbial contamination in United States Air Force aviation fuel tanks. J Ind Microbiol Biotechnol 33:29–36CrossRefGoogle Scholar
  53. 53.
    Battelle Memorial Institute (2012) Corrosion in systems storing and dispensing ultra low sulfur diesel (ULSD), hypothesis investigation. Final Report Contract CON00008697, Battelle Memorial Institute, ColumbusGoogle Scholar
  54. 54.
    Mansfield E, Sowards JW, Crookes-Goodson (2015) Findings and recommendations from the NIST Workshop on alternative fuels and materials: biocorrosion. J Res NIST 128:28–36 (NIST Boulder, CO 80305) CrossRefGoogle Scholar
  55. 55.
    Grant DJW, Higuchi T (1990) Solubility behavior of organic compounds. Wiley, New YorkGoogle Scholar
  56. 56.
    Wilhelm E (2007) Thermodynamics of nonelectrolyte solubility. In: Letcher TM (ed) Developments and applications in solubility, Chapter 1. RSC Publishing, Cambridge, pp 3–15CrossRefGoogle Scholar

Copyright information

© AOCS 2016

Authors and Affiliations

  • Richard W. Heiden
    • 1
  • Sigurd Schober
    • 2
  • Martin Mittelbach
    • 2
  1. 1.R. W. Heiden Associates LLC, Laboratory/Burle Business ParkLancasterUSA
  2. 2.Institute of ChemistryUniversity of Graz-NAWI GrazGrazAustria

Personalised recommendations