Progress in Oxygen Trace Analyses in Biomass Organic Liquids Using

Article pubs.acs.org/EF

Progress in Oxygen Trace Analyses in Biomass Organic Liquids Using a High-Temperature Pyrolysis Reactor and Non-dispersive Infrared Detector Patrick Jame,*,† Erik Bonjour,† Magali Batteau,† Catherine Jose,† Pierre Paul,‡ Jérémie Ponthus,‡ Alain Quignard,‡ and Nadège Charon‡ †

Institut des Sciences Analytiques, UMR 5280 CNRS, Université Lyon 1, ENS-Lyon, 5 Rue de la Doua, 69100 Villeurbanne, France IFP Energies nouvelles, Rond-point de l’échangeur de Solaize, BP 3, 69360 Solaize, France

‡

ABSTRACT: The development of a method for the determination of the oxygen amount in organic liquids is described using a new device made by a vertical pyrolysis unit linked to a non-dispersive CO infrared detector. The outcome signal is amplified using an additional electronic conversion card monitored by homemade software. This system allows for the quantification of oxygen in a range from 0.5 wt % oxygen to a limit of 0.01 wt % oxygen when applied to standard solutions (model oxygenate containing compounds in toluene). Linearity tests were carried out on different oxygen model solutions containing molecules representative of biomass-derived matrices. The method provides relative good results when applied to a biomass product, such as a partially dehydroxygenated biomass fast pyrolysis oil. The most relevant aspects of the study are reported.

1. INTRODUCTION Considering the global energetic context, diversifying the liquid fuel supplies for the transportation field is of the upmost importance and many alternatives are promising, such as products that are obtained from coal or lignocellulosic biomass resources. Processing of non-conventional resources can provide liquids that need further upgrading before integrating classical fuel pools, especially because they contain a high level of oxygenated compounds when compared to petroleum fuels. Working with coal or biomass-derived liquids implies coping with oxygenated compounds and their analytical characterization. Measuring oxygen contents in non-conventional hydrocarbon matrices is a first issue to deal with to be able to evaluate hydrodeoxygenation yield and/or competition with the hydrogenation of sulfur- or nitrogen-containing species during upgrading processes (hydrotreatment, hydroconversion, or hydrocraking). Usually oxygen contents are calculated by difference from the other elements (i.e., carbon, hydrogen, nitrogen, sulfur, ash, etc.); however, this approach does not provide satisfactory in terms of precision and accuracy when small amounts of oxygen compounds need to be measured. Therfore, direct determination of oxygen at low levels in liquids is still an analytical challenge today, despite several techniques having been already described in the literature until now. Since 1940, many methods based on pyrolysis of oxygenated compounds to carbon oxides have been developed using different detection modes (i.e., thermal conductivity, coulometry, infrared spectrometry, etc.).1−5 Neutron activation analysis is another technique that enables oxygen content determination based on the irradiation of a sample with neutrons having sufficient energy to initiate the 13O (n,p) 16N reaction and measurement of 7.4 s 16N activity. This technique has been largely applied in the literature for coal analysis but rarely for liquid matrices, even if it is possible.6,7 However, this approach suffers from several drawbacks (i.e., possible interferences, poor © 2015 American Chemical Society

measurement reproducibility, and complex apparatus) that limit its attractiveness for a routine analysis method. Other techniques, such as measuring dissolved molecular oxygen by electrochemical detection, have also been used in the literature to quantify oxygen contents in hydrocarbon matrices.

Figure 1. Schematic representation of the pyrolysis instrument developed in this work: (1) pressure and flow regulation, (2) copper tube, (3) ascarite−magnesium hydroxide trap, (4) septum for liquid injection, (5) insulating system, (6) pyrolysis unit, (7) non-dispersive infrared CO detector, and (8) amplified detector and electronic data cards. Received: January 28, 2015 Revised: March 26, 2015 Published: March 26, 2015 3176

DOI: 10.1021/acs.energyfuels.5b00211 Energy Fuels 2015, 29, 3176−3180

Article

Energy & Fuels

Figure 2. CO infrared spectrum from the analysis of a benzoic acid solution.

Figure 3. Impact of the oxygen chemical function on the pyrolysis response for oxygen contents ranging from 0.05 to 0.6 wt % oxygen.

2. EXPERIMENTAL SECTION

In the present work, we investigate instrumental key parameters to further understand and optimize total oxygen measurement in hydrocarbon matrices derived from lignocellulosic biomass using a pyrolysis-based apparatus. Targeted oxygen contents range from 0.5 to 0.01 wt % oxygen. Molecular analysis of coal or biomass-derived liquids has revealed that such products contain a large diversity of oxygenated compounds: carboxylic acids, ketones, furans, phenols, etc.8−11 Model compounds investigated in this study have been chosen to mimic the major chemical families described from such non-conventional products. The aim of such a work was to evaluate how much an oxygen chemical function can impact the pyrolysis behavior of a compound in standard solutions and to illustrate the interest of the technique when applied to a biomass-derived product.

2.1. Samples. All model compounds used in this study were of analytical grade: benzoic acid (99%, Alfa Aesar), levulinic acid (≈98%, Acros Organics), 2,6-dimethoxyphenol (99%, Sigma-Aldrich), pyrocatechol (99%, Sigma-Aldrich), 4-heptanone (98%, Sigma-Aldrich), ethylstearate (97%, Safc), 2-furaldehyde (99%, Acros Organic), 2-methoxyphenol (≈98%, Alfa Aesar), m-cresol (99%, Sigma-Aldrich), 2-naphtol (98%, Sigma-Aldrich), o-tolualdehyde (97%, Sigma-Aldrich), 3-methyl-2-cyclohexenone (98%, Sigma-Aldrich), dibenzofuran (98%, Alfa Aesar), 9-fluorenol (≈98%, Alfa Aesar), β-butyrolactone (98%, Sigma-Aldrich), and toluene (99.9%, Sigma-Aldrich). Model solutions were prepared by dissolving or diluting a known amount of model compounds in toluene. Fresh model solutions were regularly prepared to avoid any deterioration (by oxidation or absorption of water for example). 3177

DOI: 10.1021/acs.energyfuels.5b00211 Energy Fuels 2015, 29, 3176−3180

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Energy & Fuels A partially dehydroxygenated fast pyrolysis oil from wood supplied by IFP Energies nouvelles was investigated in this study to evaluate the interest of the pyrolysis method on a complex “real” sample. The carbon and hydrogen contents of the sample were equal to 77.8 wt % C and 9.66 wt % H, respectively (results expressed on a wet basis). The density (measured at 15 °C) of the upgraded bio-oil was 0.8996 g mL−1, and the water content was 1.48 wt %. This biomass-derived liquid contained 11.78 wt % oxygen (on a wet basis) and was diluted by toluene to prepare solutions whose oxygen contents varied from 0.02 to 0.12 wt % oxygen. 2.2. Pyrolysis Instrument for Oxygen Content Measurement. The apparatus used in this study was a homemade microanalyzer composed of a vertical heating unit equipped with two furnaces held at 1050 and 1120 °C (see Figure 1). The reactor used consisted of an external silica tube filled to half with black carbon (Microanalysis, U.K.), followed by a layer of 2 cm quartz wool and an internal silica tube. The injection part of the apparatus was insulated by a ceramic material to avoid any discrimination phenomenon during sample injection. Samples were injected into the reaction tube through a heated septum using a microliter syringe. Nitrogen was used as a carrier gas after cleaning through a copper tube held at 450 °C for trapping oxygen traces. Carbon dioxide and residual water were removed by a trap containing ascarite (sodium hydroxide on support) and anhydrous magnesium perchlorate. Pyrolysis on black carbon allowed for the transformation of organic compounds to carbon monoxide according the following reaction: CxHyOz + zC → zCO + CxHy. To avoid the reaction of CO in CO2, temperature on the black carbon furnace was maintained at 1120 °C according the Boudouard reaction: CO2 + C → 2CO. Measurement of the resulted carbon monoxide amount was performed using a nondispersive infrared CO detector (Rosemount NGA 2000). Figure 2 illustrates the CO non-dispersive infrared (NDIR) spectrum resulting from the analysis of a 0.012 wt % oxygen benzoic acid solution analyzed by the pyrolysis method. The analytical signal is proportional to the quantity of oxygen injected. It was an important challenge to measure with accuracy the low signal coming from the samples pyrolyzed. For this purpose, the signal coming from the detector was amplified using a data translation card.

Table 1. Recovery of Oxygen in Model Solutions by the Pyrolysis Method reference

3. RESULTS AND DISCUSSION 3.1. Optimization of Key Experimental Parameters. A correct liquid sample injection into the upper furnace is one of the main experimental parameters that needs to be under control because it enables an efficient sample vaporization and avoids any condensation occurring on the glass reactor. In this work, we used a syringe equipped with a long needle (i.e., 7 cm length); the homemade injector as well as the part between the injector and upper furnace were warmed at a temperature over 350 °C to prevent condensation of injected liquid into the glass reactor. Good sensitivity and repeatable measurements were achieved by injecting a sample volume of 10 μL. Increasing the injected volume to reach a lower limit of quantification would imply experimental problems, such as higher pressure and accumulation of pyrolyzed carbon in the inner tube. All experimental data presented here were obtained in the following optimized experimental conditions: nitrogen gas flow of 40 mL min−1, sample volume of 10 μL, and septum SGE (reference autosepta 11 mm P/N 0418712). 3.2. Study of Model Solutions. Several model solutions were prepared in toluene from model oxygenated compounds (see the Experimental Section). The oxygen contents of such solutions were measured experimentally using the apparatus constructed by the Institut des Sciences Analytiques (ISA, Villeurbanne, France) to evaluate the quality of the method (precision, accuracy, and sensitivity). Two oxygen content arrays were investigated: from 0.01 to 0.05 wt % oxygen and from 0.05 to 0.6 wt % oxygen. Analyzing different types of model

expected oxygen content (wt %)

methoxyphenol

0.043

pyrocatechol

0.035

dimethoxyphenol

0.034

benzoic acid

0.032

methoxyphenol

0.022

dibenzofuran

0.019

pyrocatechol

0.018

ethylstearate

0.014

dibenzofuran

0.010

toluene

0.004

measured oxygen content (wt %)

recovery rate (%)

RSD (%)

0.045 0.040 0.041 0.046 0.045 0.030 0.034 0.036 0.032 0.029 0.032 0.030 0.036 0.027 0.035 0.037 0.028 0.035 0.025 0.028 0.024 0.019 0.024 0.027 0.019 0.021 0.021 0.020 0.020 0.021 0.015 0.016 0.013 0.019 0.018 0.015 0.013 0.012 0.012 0.016 0.010 0.009 0.010 0.010 0.009 0.007 0.003 0.004 0.004 0.006

105 94 94 106 105 87 98 103 92 82 95 88 105 79 103 115 89 109 78 88 111 89 112 124 89 109 113 104 107 113 83 89 74 109 102 108 95 88 88 115 102 96 108 110 90 175 75 100 100 150

6.3

9.1

11.5

16.2

14.6

3.6

15.3

12.6

8.3

40

compounds aims also to know whether the oxygen chemical function (alcohols, ketones, esters, etc.) has a significant effect on the pyrolysis response of the molecules. A first set of model compounds (heptanone, methylcyclohexenone, ethyl stearate, furfural, tolualdehyde, and cresol) dissolved in toluene in the range of 0.05−0.6 wt % oxygen was investigated. Figure 3 represents the relation between the signal 3178

DOI: 10.1021/acs.energyfuels.5b00211 Energy Fuels 2015, 29, 3176−3180

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Energy & Fuels

Figure 4. Measurements versus “expected” oxygen contents for solutions prepared from diluted fast pyrolysis bio-oil (dotted lines refer to ±20% relative difference).

measuring low concentrations of oxygen in fuels. The main goal of this study was to design and build a reliable device enabling such measurements. This analyzer is based on high-temperature carbon reduction hyphenated to infrared detection. Several instrumental improvements have been performed to obtain fast and steady injections: insulating of the injector for keeping an elevated temperature at the upper point of the pyrolysis tube and optimization of length and diameter of the inner glass tube. Moreover, an additional amplifier system for the data processing permits a raise of the sensitivity with regard to peak detection. Hence, this new analyzer has turned into an efficient tool to determine oxygen amounts in organic biomass-derived liquids. Satisfactory results were obtained using this dedicated device to measure oxygen contents from 0.01 to 0.04 wt % oxygen in organic model solutions. To illustrate the interest of such a technique, a biomass-derived product (i.e., a partially dehydroxygenated biomass fast pyrolysis oil) was analyzed, showing relative good results for measuring oxygen contents from 0.02 to 0.12 wt % for several dilution rates in toluene.

area and expected oxygen contents (calculated from the weighed amounts of model compound and toluene). These results lead to an interesting conclusion showing that the pyrolysis behavior of the studied model compounds is not strongly dependent upon the oxygen content because the maximal difference is lower than 12% relative (between heptanone and cresol). Other sets of model solutions were analyzed to evaluate the accuracy and precision of the pyrolysis method. Expected and measured oxygen contents of these solutions are reported in Table 1. All standards solutions having different concentrations, ranging from 0.01 to 0.04 wt % in oxygen concentration, showed good recovery rates close to the expected values. This proves that the different oxygen chemical functions that were analyzed have no significant effect on the pyrolysis conversion. However, variability arises probably because of the oxygen blank value contained in the toluene solvent. This amount prevents, at this time, determination with efficiency concentrations lower than 100 mg kg−1 of oxygen. 2.3. Study of a Biomass-Derived Liquid. Solutions of a partially dehydroxygenated fast pyrolysis oil diluted in toluene were investigated in this study to test the pyrolysis method when applied to a complex organic matrix. Results reported in Figure 4 show that the oxygen content of such solutions can be measured from 0.02 to 0.12 wt % oxygen with a relatively satisfactory accuracy; the relative difference between measured and expected values is lower than 20% (as arbitrarily represented in Figure 4 by dotted lines). High polydispersity of oxygenated chemical structures in a hydrocarbon matrix does not seem to have a significant impact on the pyrolysis response for total oxygen measurement.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: +33-0437423609. Fax: +33-0437423535. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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4. CONCLUSION Working with coal or biomass-derived liquids implies coping with oxygenated components and measuring low oxygen contents in hydrocarbon matrices as a first issue. However, there is currently no commercial oxygen analyzer suitable for 3179

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Energy & Fuels Reductive Pyrolysis; ASTM International: West Conshohocken, PA, 2000. (6) ASTM International. ASTM E385 Standard Test Method for Oxygen Content Using a 14-MeV Neutron Activation and Direct-Counting Technique; ASTM International: West Conshohocken, PA, 2007. (7) Hannan, M. A.; Oluwole, A. F.; Kehinde, L.; Borisade, A. B. J. Radioanal. Nucl. Chem. 2003, 256, 61−65. (8) Sumbogo Murti, S. D.; Choi, K. H.; Sakanishi, K.; Okuma, O.; Korai, Y.; Mochida, I. Fuel 2005, 85, 135−142. (9) Omais, O.; Courtiade, M.; Charon, N.; Thiebaut, D.; Quignard, A. Energy Fuels 2010, 24, 5807−5816. (10) Omais, O.; Crepier, J.; Charon, N.; Courtiade, M.; Quignard, A.; Thiebaut, D. Analyst 2013, 138, 2258−2268. (11) Tessarolo, N. S.; dos Santos, L. R. M.; Silva, R. S. F.; Azevedo, D. A. J. Chromatogr. A 2013, 1279, 68−75.

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DOI: 10.1021/acs.energyfuels.5b00211 Energy Fuels 2015, 29, 3176−3180