Name: Determination of Carbonyl Functional Groups in Bio-oils by Potentiometric Titration: The Faix Method (Video) | JoVE Journal
Uploaded: 2017-02-07T14:00:00.000+00:00
Duration: 7 min 56 s
Description: Learn potentiometric titration for quantifying carbonyl compounds in pyrolysis bio-oils using the Faix method. This technique offers higher precision with smaller samples and less toxic materials.

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This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08GO28308 with the National Renewable Energy Laboratory. Funding provided by U.S. DOE Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

Caution: Please review all relevant material safety data sheets (MSDS) before beginning. Ethanol is flammable. All applicable chemical handling procedures should be followed, as well as all applicable waste disposable and handling procedures.
1. Reagent Solutions
<ol>
	<li>Prepare the hydroxylamine hydrochloride solution (Solution A): Add 7.7 g of hydroxylamine hydrochloride and 50 mL of deionized water to a 250 mL volumetric flask. When all solids have dissolved, dilute to mark with ethanol. This results in a 0.55 M hydroxylamine hydrochloride solution in 80% (v/v) ethanol.</li>
	<li>Prepare the triethanolamine solution (Solution B): Add 17.4 mL of triethanolamine to a 250 mL volumetric flask. Add 10 mL of water, and then dilute up to the mark with ethanol. 95% ethanol can also be used if the addition of water is skipped. This results in a 0.48 M triethanolamine solution in 96 % (v/v) ethanol</li>
	<li>Prepare the hydrochloric acid solution. Either purchase 0.1 N solution or prepare using 10 mL concentrated HCl and 1 L water.</li>
</ol>
2. Bio-oil Sampling and Handling
<ol>
	<li>Make sure the oil sample is at room temperature prior to withdrawing a sample. Thoroughly homogenize (mix by shaking vigorously for at least 1 minute, and visually inspect the sample to ensure it is homogenous. Some bio-oils may require longer shaking times) bio-oil to obtain a representative sample.</li>
	<li>For the bio-oil sample, use 100 to 150 mg of bio-oil.</li>
	<li>Minimize exposure to oxygen and heat to prevent sample degradation prior to analysis.</li>
</ol>
3. Analytical Procedure
<ol>
	<li>Standardization of the Base Solution
	<ol>
		<li>Dry Na2CO3 primary standard in an oven at 105 °C overnight to ensure a dry sample. Allow the Na2CO3 to cool to room temperature before weighing.</li>
		<li>Weigh 100 to 150 mg of sodium carbonate to a titration vessel, record the actual weight, add a stir bar and add enough water to cover the pH electrode bulb and junction.</li>
		<li>Transfer the sample to a titration vessel, washing the reaction vial several times separately with ethanol and water in proportions to make a final 80% solution of ethanol/water. Titrate with the acid solution using an automatic titrator to the endpoint. Record the endpoint. The endpoint is defined as the inflection point on the titration curve.</li>
		<li>Repeat the process twice to obtain three points.</li>
		<li>Use the average value as the normality of the acid solution.</li>
	</ol>
	</li>
	<li>Preparation of Titration Blanks
	<ol>
		<li>For Blank A: add 0.5 mL dimethyl sulfoxide (DMSO) to a 5 mL vial with a spin vane.</li>
		<li>Add 2 mL hydroxylamine hydrochloride solution (solution A).</li>
		<li>Add 2 mL triethanolamine solution (solution B).</li>
		<li>Cap tightly, place in preheated (80 °C) heater block or water bath and stir for 2 hours.</li>
		<li>Titrate with acid solution using an automatic titrator to the endpoint, and record endpoint.</li>
		<li>For Blank B: If mineral acid is suspected to be present in sample, add 0.5 mL DMSO to 5 mL vial with a spin vane.</li>
		<li>Add 2 mL triethanolamine solution (solution B).</li>
		<li>Cap tightly and stir at 80 °C for 2 hours.</li>
		<li>Transfer the sample to a titration vessel, washing the reaction vial several times separately with ethanol and water in proportions to make a final 80% solution of ethanol/water. Titrate with the acid solution using an automatic titrator to the endpoint. Record the endpoint.</li>
		<li>Repeat process three times to obtain three points.</li>
	</ol>
	</li>
	<li>Validation of the Method Using a Known Carbonyl
	<ol>
		<li>Weigh ~ 100 mg of 4-(benzyloxy)benzaldehyde (4-BBA) to a 5 mL vial, record the actual weight, add a spin vane.</li>
		<li>Add 0.5 mL DMSO.</li>
		<li>Dissolve the sample in 2 mL hydroxylamine hydrochloride solution (solution A).</li>
		<li>Add 2 mL triethanolamine solution (solution B).</li>
		<li>Close lid tightly and stir at 80 °C for 2 hours.</li>
		<li>Transfer the sample to a titration vessel, washing the reaction vial several times separately with ethanol and water in proportions to make a final 80% solution of ethanol/water. Titrate with the acid solution using an automatic titrator to the endpoint. Record the endpoint.</li>
		<li>Repeat the process three times, to obtain three points.</li>
	</ol>
	</li>
	<li>Analysis of Bio-oil Using the Method
	<ol>
		<li>Weigh close to 100 mg of the bio-oil to 5 mL vial, record the actual weight and add a spin vane.</li>
		<li>Add 0.5 mL DMSO.</li>
		<li>Dissolve the sample in 2 mL hydroxylamine hydrochloride solution (solution A).</li>
		<li>Add 2 mL triethanolamine solution (solution B).</li>
		<li>Close lid tightly and stir at 80 °C for 2 hours.</li>
		<li>Transfer the sample to a titration vessel, washing the reaction vial several times separately with ethanol and water in proportions to make a final 80% solution of ethanol/water. Titrate with the acid solution using an automatic titrator to the endpoint. Record the endpoint.</li>
		<li>Repeat the process three times, to obtain three points.</li>
		<li>Blank C: If mineral acid is suspected to be present in sample, weigh close to 100 mg of the bio-oil into a 5 mL vial, record the weight and add a spin vane.</li>
		<li>Add 0.5 mL DMSO.</li>
		<li>Add 2 mL triethanolamine solution (solution B).</li>
		<li>Cap tightly and stir at 80 °C for 2 hours.</li>
		<li>Transfer the sample to a titration vessel, washing the reaction vial several times separately with ethanol and water in proportions to make a final 80% solution of ethanol/water. Titrate with the acid solution using an automatic titrator to the endpoint. Record the endpoint.</li>
		<li>Repeat process three times to obtain three points.</li>
	</ol>
	</li>
</ol>
4. Calculations
<ol>
	<li>Standardization of the Base Solution
	<ol>
		<li>Calculate the concentration of the acid solution (mol/L) using the following equation. The weight of the dry sodium carbonate in grams is w1, the purity is written as a fraction (i.e., 99% is 0.99), and the endpoint is in mL. 
		<img alt="Chemical concentration formula for acid calculation using Na2CO3; equation in scientific research." src="/files/ftp_upload/55165/55165eq1.jpg" data-altupdatedat="1788235205000" data-alt="Equation 1">   </li>
	</ol>
	</li>
	<li>Validation of the Method Using a Known Carbonyl
	<ol>
		<li>Calculate the concentration of 4BBA (mol/L) in the sample using the following equation. The weight of the 4BBA in grams is w2, the 4BBA purity is written as a fraction (i.e., 99% is 0.99), the concentration of the acid solution (mol/L) is [acid], the triethanolamine/hydroxylamine•HCl blank endpoint is EPBA (the average value of three blanks, in mL), and the endpoint is EP (in mL). 
		<img alt="Equation for calculating 4BBA concentration, featuring EP and purity, in chemical analysis." src="/files/ftp_upload/55165/55165eq2.jpg" data-altupdatedat="1788235205000" data-alt="Equation 2">   </li>
	</ol>
	</li>
	<li>Analysis of Bio-oil
	<ol>
		<li>Calculate the concentration of carbonyls in bio-oils [CO] (mmol/g-bio oil) using the following equation. The weight of the bio-oil in grams is w3, the concentration of the acid solution (mol/L) is [acid], the triethanolamine/hydroxylamine•HCl blank endpoint is EPBA (the average value of three blanks in mL), and the endpoint is EP (in mL). 
		<img alt="Chemical equilibrium formula, concentration calculation, equation image, educational use, CO concentration." src="/files/ftp_upload/55165/55165eq3.jpg" data-altupdatedat="1788235205000" data-alt="Equation 3">   </li>
	</ol>
	</li>
	<li>Acid Correction 
	NOTE: The presence of mineral acids or organic acids with pKa &lt; 2 can cause artificially low carbonyl values due to the reaction of the acid with triethanolamine.
	<ol>
		<li>If this is suspected, perform the blanks detailed in sections 3.2.6 and 3.4.8. The weight of bio-oil in the sample in grams is w3, EP is the endpoint of the sample and EPBA is the triethanolamine/hydroxylamine blank. EPBB is the endpoint of Blank B, EPBC is endpoint of Blank C and the weight (g) of oil used in Blank C is wBC: 
		<img alt="Static equilibrium equation, formula for corrected CO calculation, use in titration experiments." src="/files/ftp_upload/55165/55165eq4.jpg" data-altupdatedat="1788235205000" data-alt="Equation 4">    
		For bio-oil samples that contain mostly acetic acid, this is an unnecessary step.</li>
	</ol>
	</li>
</ol>

<ol><li>Oasmaa, A., Kuoppala, E., Solantausta, Y. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/ef020206g">Fast pyrolysis of forestry residue. 2. physicochemical composition of product liquid.</a> Energy Fuels. 17 (2), 433-443 (2003).</li>
<li>Olarte, M., et al. <a target="_blank" href="http://link.springer.com/article/10.1007/s11244-015-0505-7">Stabilization of Softwood-Derived Pyrolysis Oils for Continuous Bio-oil Hydroprocessing.</a> Top. Catal. 59 (1), 55-64 (2016).</li>
<li>Nicolaides, G. The chemical characterization of pyrolytic oils. , Dept. of Chemical Engineering., University of Waterloo. Waterloo, Ontario, Canada. MASc Thesis (1984).</li>
<li>Oasmaa, A., Korhonen, J., Kuoppala, E. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/ef2006673">An approach for stability measurement of wood-based fast pyrolysis bio-oils.</a> Energy Fuels. 25 (7), 3307-3313 (2011).</li>
<li>Chen, C. L. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aChen%2C+CL+%22Methods+in+Lignin+Chemistry%22">Methods in Lignin Chemistry</a>. Lin, S. Y., Dence, C. W. , Springer-Verlag. Berlin, Heidelberg, New York. 446-457 (1992).</li>
<li>Scholze, B., Hanser, C., Meier, D. <a target="_blank" href="https://www.researchgate.net/publication/256996153_Characterization_of_the_water-insoluble_fraction_from_fast_pyrolysis_liquids_pyrolytic_lignin_Part_II_GPC_carbonyl_goups_and_13C-NMR">Characterization of the water-insoluble fraction from fast pyrolysis liquids (pyrolytic lignin) Part II. GPC, carbonyl groups, and 13C-NMR.</a> J. Anal. Appl. Pyrolysis. 58-59, 387-400 (2001).</li>
<li>Bayerbach, R., Meier, D. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0165237008001514">Characterization of the water-insoluble fraction from fast pyrolysis liquids (pyrolytic lignin). Part IV: Structure elucidation of oligomeric molecules.</a> J. Anal. Appl. Pyrolysis. 85 (1-2), 98-107 (2009).</li>
<li>Faix, O., Andersons, B., Zakis, G. <a target="_blank" href="https://www.degruyter.com/view/j/hfsg.1998.52.issue-3/hfsg.1998.52.3.268/hfsg.1998.52.3.268.xml">Determination of Carbonyl Groups of Six Round Robin Lignins.</a> Holzforschung. 52, 268-272 (1998).</li>
<li>Black, S., Ferrell, J. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.5b02511">Determination of Carbonyl Groups in Pyrolysis Bio-oils Using Potentiometric Titration: Review and Comparison of Methods.</a> Energy Fuels. 30 (2), 1071-1077 (2016).</li>
<li>Ferrell, J., et al. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/bbb.1661/abstract">Standardization of Chemical Analytical Techniques for Pyrolysis Bio-oil: History, Challenges, and Current Status of Methods.</a> Biofuels, Bioprod. Biorefin. 10, 496-507 (2016).</li>
</ol>

The authors have nothing to disclose.

Representative titration curves are shown in Figure 2. A blank titration, as well as a titration for a pyrolysis oil sample, are shown. Furthermore, the first derivative of the titration curve (dpH/dV) is shown, which allows for easy recognition of the titration endpoint. The inset table on Figure 2 shows triplicate data for both pyrolysis oil and blank titrations, with average values and standard deviations. The endpoint values shown (in mL) are used in Section 4 to calculate the total ...

While pyrolysis bio-oils are comprised of a large variety of compounds and chemical functional groups, quantification of carbonyl groups is especially important. Carbonyls are known to be responsible for the instability of bio-oil during both storage1 and processing2. The titration method presented here is a simple technique which can reliably quantify the total carbonyl content of bio-oils. Only aldehyde and ketone functional groups are quantified using this method; carboxylic acid and lactone groups are not quantified.
For analysis of bio-oils, quantification of carbonyl groups by titration has traditionally been accomplished using the method of Nicolaides3. This method has been commonly used in the bio-oil literature4,5,6,7. This is a simple procedure where carbonyls are converted to the corresponding oxime (see Figure 1). The liberated HCl reacts with pyridine to force the equilibrium to completion. The conjugate acid of pyridine is titrated with a known amount of NaOH (base titrant). The number of equivalents of NaOH used is stoichiometrically equivalent to the moles of carbonyl present in the bio-oil.
The Nicolaides method, however, has several limitations. It can require reaction times in excess of 48 hours to reach completion. This severely limits sample throughput. It utilizes pyridine, which is toxic. Sample weights of 1 to 2 g are required. Sample weight used is dependent on the amount of hydroxylamine HCl present and the carbonyl content of the sample. If initial estimates of the sample weight used are incorrect, the titration has to be repeated.
Faix et al.8 developed a method that has been modified here to address the issues of the Nicolaides method. The reaction is carried out at 80 &#176;C for 2 hours, thereby increasing sample throughput. Pyridine has been replaced with triethanolamine, which is a less toxic chemical. The sample size can be reduced to 100 to 150 mg. The triethanolamine consumes the liberated HCl, driving the reaction to completion and the unconsumed triethanolamine is titrated directly. A secondary titration of the hydroxylamine is unnecessary. Comparison of these titration methods has shown that the Nicolaides method significantly underestimates carbonyl content of bio-oils9.
The method described here has been modified from the original method8 to be more applicable to the analysis of pyrolysis bio-oils. This method was developed for the analysis of raw pyrolysis bio-oils, but it has been successfully applied to other types of biomass-derived oils, including hydrotreated bio-oils. Additionally, this method has been used to monitor changes in carbonyl content during both aging and upgrading.

<table><tbody><tr><td>Analytical balance</td><td></td><td></td><td>accurate to 0.1 mg</td></tr><tr><td>dry block heater with magnetic stirrer, or hot water bath with magnetic stirrer</td><td></td><td></td><td></td></tr><tr><td>Automatic titrator</td><td></td><td></td><td>We used a Metrohm Titrando 809 automatic titrator, though other equivalent systems are acceptable</td></tr><tr><td>Deionized water</td><td></td><td></td><td></td></tr><tr><td>Ethanol (reagent grade)</td><td></td><td></td><td>CAS # 64-17-5</td></tr><tr><td>Hydroxylamine hydrochloride&amp;nbsp;</td><td></td><td></td><td>CAS # 5470-11-1</td></tr><tr><td>Triethanolamine&amp;nbsp;</td><td></td><td></td><td>CAS #102-71-6</td></tr><tr><td>Hydrochloric acid (37%)&amp;nbsp;</td><td></td><td></td><td>CAS # 7647-01-0</td></tr><tr><td>Sodium Carbonate (primary standard)&amp;nbsp;</td><td>SigmaAldrich</td><td>223484</td><td></td></tr><tr><td>4-(benzyloxy)benzaldehyde&amp;nbsp;</td><td></td><td></td><td>CAS # 4397-53-9</td></tr><tr><td>Dimethyl sulfoxide</td><td></td><td></td><td>CAS # 67-68-5</td></tr><tr><td>5 mL glass Reacti-vials with solid lid and teflon spinvane</td><td>Thermoscientific</td><td>TS-13223</td><td></td></tr><tr><td>200 mL volumetric flask</td><td></td><td></td><td></td></tr><tr><td>Volumetric or mechanical pipettes</td><td></td><td></td><td></td></tr></tbody></table>

determination of carbonyl functional groups in bio-oils by potentiometric titration: the faix method

Determination of Carbonyl Functional Groups in Bio-oils by Potentiometric Titration: The Faix Method

Carbonyl compounds present in bio-oils are known to be responsible for bio-oil property changes upon storage and during upgrading. Specifically, carbonyls cause an increase in viscosity (often referred to as &#39;aging&#39;) during storage of bio-oils. As such, carbonyl content has previously been used as a method of tracking bio-oil aging and condensation reactions with less variability than viscosity measurements. Additionally, carbonyls are also responsible for coke formation in bio-oil upgrading processes. Given the importance of carbonyls in bio-oils, accurate analytical methods for their quantification are very important for the bio-oil community. Potentiometric titration methods based on carbonyl oximation have long been used for the determination of carbonyl content in pyrolysis bio-oils. Here, we present a modification of the traditional carbonyl oximation procedures that results in less reaction time, smaller sample size, higher precision, and more accurate carbonyl determinations. While traditional carbonyl oximation methods occur at room temperature, the Faix method presented here occurs at an elevated temperature of 80 &#176;C.

A typical titration curve consists of a single endpoint, as shown in Figure 2. Typical titrations for both a raw bio-oil sample, and a blank titration, are shown. As the endpoint lies at the inflection point in the titration curve; the endpoint can be easily identified by plotting the first derivative of the titration curve (shown on the right axis, dpH/dV, in Figure 2). Many automatic titration systems have software that calculates the derivative of the ...

Here we present a potentiometric titration technique for accurately quantifying carbonyl compounds in pyrolysis bio-oils.

Carbonyl compounds present in bio-oils are known to be responsible for bio-oil property changes upon storage and during upgrading. Specifically, carbonyls ...

The overall goal of this procedure is to measure the complete carbonyl content of various biomass-derived materials by titrimetric methods. This method gives insight into the reactive carbonyl compounds contained within biomass-derived products such as pyrolysis oils and the effect that those compounds have on the aging of bio-oils. This method uses smaller sample sizes, less toxic materials, is more precise and more accurate than previously established methods.To begin this procedure, prepare the reagent solutions as outlined in the text protocol. Dry a sodium carbonate primary standard in an oven at 105 degrees Celsius overnight. After this, allow the sodium carbonate to cool to room temperature.Weigh 100 to 150 milligrams of the dried sodium carbonate into a metal pan. Transfer it to a titration vessel and record the actual weight. Then add a stir bar and enough water to cover the pH electrode bulb and the junction.Using an automatic titrator, titrate with the hydrochloric acid solution to the endpoint which is the inflection point on the titration curve. Repeat this titration twice using a new sodium carbonate sample each time to obtain a total of three endpoint values. To begin preparing blank A, add 5 millimeters of DMSO to a five milliliter vial with a spin vane.Next, add two milliliters of the prepared hydroxylamine hydrochloride solution and two milliliters of the prepared triethanolamine solution. Cap the vial tightly then place the vial in a block heater preheated to 80 degrees Celsius. Stir for two hours.After stirring is complete, transfer the sample to a titration vessel. Wash the reaction vial several times separately with ethanol and water such that the final solution is 80%ethanol. Then use an automatic titrator to titrate with the acid solution to the endpoint.Weigh out approximately 100 milligrams of 4-BBA to a five milliliter vial. Record the actual weight then add a spin vane. Add 5 milliliters of DMSO.After this, dissolve the sample in two milliliters of the prepared hydroxylamine hydrochloride solution. Add two milliliters of prepared triethanolamine solution. Next, tightly cap the vial and place it in a block heater preheated to 80 degrees Celsius.Stir for two hours. After stirring is complete, remove the sample from the heat block and allow it to cool. Then transfer the sample to a titration vessel.Wash the reaction vials several times separately with ethanol and water such that the final solution is 80%ethanol. Then use an automatic titrator to titrate with the acid solution to the endpoint. Repeat this validation twice to obtain three endpoint values.First, weigh out approximately 100 milligrams of the bio-oil sample to a five milliliter vial. Record the actual sample weight. After this, add a spin vane.Add 5 milliliters of DMSO. Next, dissolve the sample in two milliliters of the prepared hydroxylamine hydrochloride solution. Add two milliliters of prepared triethanolamine solution.Then cap the vial tightly and stir at 80 degrees Celsius for two hours. After stirring is complete, transfer the sample to a titration vessel. Wash the reaction vial several times separately with ethanol and water such that the final solution is 80%ethanol.Using an automatic titrator, titrate with the hydrochloric acid solution to the inflection point on the titration curve. Record this endpoint and repeat the bio-oil analysis two additional times to obtain a total of three endpoint values. After this, analyze the data as outlined in the text protocol.In this study, a potentiometric titration technique is used to accurately quantify carbonyl compounds in pyrolysis bio-oils. Representative titrations for both a raw bio-oil sample and a blank titration are shown here. The first derivative is plotted to easily identify the inflection point in each titration curve.These values are then used to calculate the total carbonyl content in the pyrolysis oil samples. The hydrochloric acid titrant concentration has been determined to be 07032 moles per liter. Average acid consumption of the three blanks has been determined to be 13.0085 milliliters while the corresponding endpoint for the first titration has been determined to be 4.8909 milliliters.Subtracting the two volumes dividing by the weight of the sample and multiplying by the acid concentration gives a carbonyl content of 4.9724 millimoles per gram for the bio-oil sample. The traditional Nicolaides method of bio-oil analysis is performed at room temperature with a typical stirring time of 18 to 24 hours which is insufficient for complete reaction of all carbonyls present in this sample due to steric hindrance of some carbonyls. Heating the mixture drastically increases the reaction rate, but the volume of the reagents for the Nicolaides method required can be difficult to stir in heat reliably.The presented Black/Faix method however provides more accurate results more quickly and utilizes fewer materials. Here, hydroxylamine hydrochloride is present in excess and unconsumed hydroxylamine hydrochloride has no impact on titration. This method also includes multiple independent samples per test to check against titration errors.This is a quick and easy method to perform. Up to 11 unique samples can be analyzed in less than an eight-hour shift. Once the procedure starts, it's important to complete the titration as quickly as possible.Triethanolamine can form if the samples are allowed to stand overnight which leads to inaccuracies. This video should provide you with the tools necessary to perform oxidation reactions on carbonyl constituents and biomass-derived materials. This method is rapid, accurate and uses relatively low-hazard reagents.While performing this procedure, be aware that pyrolysis oils, hydroxylamine hydrochloride, triethanolamine and ethanol all have hazards associated with them. Personal protective equipment such as a lab coat, gloves and safety glasses should be worn while using these chemicals.

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Learn potentiometric titration for quantifying carbonyl compounds in pyrolysis bio-oils using the Faix method. This technique offers higher precision with smaller samples and less toxic materials.

Determination of Carbonyl Functional Groups in Bio-oils by Potentiometric Titration: The Faix Method

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