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Article title: Hydroesterification of bio-oils over HZSM-5, BETA and Y zeolites
Journal name: Clean Technologies and Environmental Policy
Authors: Omid Mowla, Eric Kennedy and Michael Stockenhuber
Priority Research Centre for Energy, Faculty of Engineering and Built Environment, School of Engineering, The University of Newcastle, NSW 2308, Australia
Corresponding Author:
1.Methods of Determining the Conversion Level
Conversion, X, is defined as a ratio of reactant that has reacted divided by the amount of reactant in the feed.
Generally, to calculate conversion in a general chemical reaction, such as that described in eq. 1, one of reactants is chosen as a base of calculations and then be linked to other species in the reaction.
(1)
The conversion of reactant A (XA) is defined as the fraction or percentage of reactant A that is converted (reacted) during the period of reaction. XAcan be described as Eq. 2.
(2)
In present study, we report the conversion level of oil (Xoil) in hydrolysis and FA (XFA) in esterification reaction. The methods for determination of conversion are explained in following sections.
1.1Conversion Level (Degree) of Oil Hydrolysis Reaction
Conversion level of hydrolysis reaction () can be defined as Eq. 3.
= (3)
Using GC data, the fraction of each FA in total amount of produced FAs () can be obtained. Considering the molecular weight of each FA () the number of moles of produced FAs () can be calculated as Eq. 4.
(4)
With respect to oil hydrolysis reaction, the stoichiometric ratio of oil:FA is 1:3, therefore the number of moles of reacted oil () is equal to the number of moles of produced FAs divided by 3 (see Eq. 5).
(5)
As shown in Eq. 6 to find the number of initial moles of oil (), mass of soybean oil () used at the beginning of the reaction is divided by average molecular weight of soybean oil ().
(6)
Therefore, the conversion level of hydrolysis reaction can be defined as Eq.7.
(7)
Average molecular weight of soybean oil is 920 g/mol(Patzek 2009).
1.2Conversion of FA during Esterification
Conversion of FA during the esterification reaction () can be defined as Eq. 8.
= (8)
Based on the fraction of each produced FAME () as obtained from GC results and considering the molecular weight of each FAME (), the number of moles of produced FAMEs () can be calculated as Eq. 9.
(9)
Using stoichiometric ratio of 1:1 (FA:FAME), the number of moles of reacted FA and FAME are equal (see Eq. 10).
(10)
Initial number of moles of FA () is equal to the number of moles of produced FAs in hydrolysis reaction as shown in Eq. 11.
(11)
Therefore, the conversion level of esterification reaction can be calculated as Eq. 12.
(12)
2.Determination of the Specific Reaction Rate (Turnover Frequency)
In heterogeneous catalytic reactions, the rate of reaction is normally reported over the catalyst weight or over the number of active sites on the catalyst. The turnover frequency (TOF) (Boudart 1995) is calculated and used to represent the intrinsic rate of catalytic reactions over a solid catalyst. TOF is expressed as number of molecules reacted per time per number of catalyst active sites (see Eq. 13).
(13)
In this study, zeolite-catalysed hydrolysis/esterification reactions were usedto produce biodiesel from soybean oil.The TOF calculated from initial rates is estimated to compare the intrinsic catalytic activity of zeolites used in each set of the experiments(Atkins 2010).Brønsted acid sites are assumed to be responsible for both catalytic hydrolysis/esterification reactions (Aracil, Martinez et al. 1992, Melero, Iglesias et al. 2009, Zapata, Faria et al. 2012).
To calculate the TOF values, NH3-TPD of the zeolite wasmeasured, and based on this measurement,the number of moles of Brønsted acid sites per mass of zeolite (mol/g) was estimated. The number of acid (catalytic) sites on the zeolite is based on integration and normalisation of the NH3 area (ion current from the m/z= 17 ion) from the mass spectrometer (Xiao, Zhou et al. 2014).The peak areas from NH3-TPD can be employed to indicate the number of moles of acid sitesvia using a calibration zeolite with a known acid site concentration.
The concentration of products, based on GC analysis of samples obtainedafter 15 min on stream (t=15 min) was used to calculate the initial reaction rate. Products concentrationsthen reveal the number of moles reacting per unit time per mass of catalyst. Determining the number of moles reacted per unit of time and divided by number of moles of acid sites, the value of TOF will be estimated.
3.References
Aracil, J., M. Martinez, N. Sa and A. Corma (1992)Formation of a jojoba oil analog by esterification of oleic acid using zeolites as catalyst. Zeolites 12(3): 233-236.
Atkins, P. (2010)Shriver and Atkins' inorganic chemistry, Oxford University Press, USA.
Boudart, M. (1995)Turnover rates in heterogeneous catalysis. Chemical Reviews 95(3): 661-666.
Melero, J. A., J. Iglesias and G. Morales (2009) Heterogeneous acid catalysts for biodiesel production: current status and future challenges. Green Chemistry 11(9): 1285-1308.
Patzek, T. W. (2009) A first law thermodynamic analysis of biodiesel production from soybean. Bulletin of Science, Technology & Society 29(3): 194-204.
Xiao, G., J. Zhou, X. Huang, X. Liao and B. Shi (2014)Facile synthesis of mesoporous sulfated Ce/TiO2 nanofiber solid superacid with nanocrystalline frameworks by using collagen fibers as a biotemplate and its application in esterification. RSC Advances 4(8): 4010-4019.
Zapata, P. A., J. Faria, M. P. Ruiz, R. E. Jentoft and D. E. Resasco (2012) Hydrophobic zeolites for biofuel upgrading reactions at the liquid–liquid interface in water/oil emulsions. Journal of the American Chemical Society 134(20): 8570-8578.
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