Accepted Manuscript Title: High performance biodiesel catalyst preparation by direct fluidized bed calcination of shrimp shell: process optimization and intensification Authors: Yong Sun, Valerie Sage, Zhi Sun PII: DOI: Reference:
S0263-8762(17)30422-7 http://dx.doi.org/10.1016/j.cherd.2017.08.010 CHERD 2785
To appear in: Received date: Revised date: Accepted date:
9-3-2017 3-7-2017 14-8-2017
Please cite this article as: Sun, Yong, Sage, Valerie, Sun, Zhi, High performance biodiesel catalyst preparation by direct fluidized bed calcination of shrimp shell: process optimization and intensification.Chemical Engineering Research and Design http://dx.doi.org/10.1016/j.cherd.2017.08.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
High performance biodiesel catalyst preparation by direct fluidized bed calcination of shrimp shell: process optimization and intensification Yong Sun1 *, Valerie Sage2, Zhi Sun3* 1 Edith Cowan University, School of Engineering, 270 Joondalup Drive Joondalup WA 6027 Australia; 2 Commonwealth Science and Industrial Research Organization (CSIRO), Energy Division, 26 Dick Perry Avenue, Kensington, WA 6151, Australia; 3 National Engineering Laboratory of Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China;
*
Corresponding author: Dr Yong Sun, School of Engineering, Edith Cowan University, 270 Joondalup
Drive Joondalup WA 6027 Australia; Email:
[email protected];
[email protected]. Professor Zhi Sun, National Engineering Laboratory of Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China; Email:
[email protected]
Highlights
CaO based catalyst was prepared from fast calcination of shrimp shell in fluidized bed at 800 oC Shrinking core model best describes calcination process The optimal preparation conditions with the largest biodiesel conversion were achieved by RSM Fluidized bed significantly intensify the calcination process and reduce thermal treatment duration from 4 hrs to 0.16 hrs
Abstract Fluidized bed reactor significantly intensified the shrimp shell (SS) calcination process for the preparation of high performance CaO based catalyst. A modified Shrinking-Core Model (SCM) was employed to describe the calcination process at high temperature. The activation energy of the initial stage of the decomposition was 64 kJ/mol, which was controlled by the chemical reaction. The activation energy of the subsequent stage of the decomposition was 22 kJ/mol, which was controlled by the diffusion. The response surface methodology (RSM) and the central composite design (CCD) were used to optimize
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biodiesel preparation conditions. Three critical operational parameters, calcination temperature (oC), catalyst loading (%) and methanol to oil ratio (-) were chosen as independent variables in CCD. The individual effect of the calcination temperature and the combined effect of the calcination temperature with the catalyst loading were significant to biodiesel conversion. The optimal condition for achieving the maximum biodiesel conversion was obtained with: calcination temperature (800 oC), catalyst loading (3%), and the ratio of methanol to oil (10), with conversion reaching 86%. The 0.16 h of calcination duration was achieved using fluidized bed reactor. Keywords: shrimp shell; calcination; fluidize bed; biodiesel; CCD;
Nomenclature b0 intercept coefficient; bi linear coefficient;
bii quadrartic coefficient;
C biodiesel conversion (%); C S 0 initial solid concentration (mol.L-1); C A0 initial gas concentration t (mol.L-1); De effective diffusivity (ms-1);
k g gaseous diffusion rate (-) k s surface reaction rate (-); ms mass of adsorbent (kg)
P pressure (kPa); r radius
of adsorbent (m);
R standard square root (-);
ideal gas constant (8.31 J.mol-1.K-1); t time (min); T temperature (K);
2
x
calcination conversion (%)
X i independent variables (-)
Y predicted response (%)
ANOVA Analysis of Variance CCD Central composite design
RSM Response surface methodology
1. Introduction The energy supply of the world has relied heavily on nonrenewable crude oil for more than two centuries [1, 2]. Explorations for renewable and sustainable energy has become one of the major topics for energy research because of the growing concerns of global warming, geopolitical uncertainties and volatility of crude oil prices. Preparation of biodiesel from renewable feedstock using catalysts generated from the food processing industry is one of the practical technical routes to provide renewable energy, with the apparent advantages of high energy return, replacement of petroleum fuel, and reduction of greenhouse gas emission [3-5]. The catalyst used in the synthesis process is either homogeneous or heterogeneous [6-8]. Alkali based heterogeneous catalysts are commonly used because of their advantages of easiness of separation, relative fast conversion and large availability of the raw materials [9, 10]. A wide range of alkali oxide, i.e. CaO, MgO, or TiO2, grafted on hydrotalcite support, have been widely explored [11-14]. Among them, CaO is the most widely used alkali based catalyst because of its long catalyst life, high activity, moderate reaction conditions, and large availability [15, 16]. The interests of using renewable biomass resources such as shrimp shells, animal bones etc., as a source of CaO have attracted much attention due to increased public awareness and emphasis on sustainable and eco-friendly developments for local community [1, 17]. In countries like Australia, there are over 30,000 tonnes of shrimp being consumed annually, which is equivalent to approximately 1,000 tonnes high quality CaO rich product on the dry basis each year [18]. This represents a big potential for utilization and high value
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conversion of shrimp shell (SS) based waste. In addition, in order to make the biodiesel generation process more sustainable, instead of using edible oil as feedstock, which creates direct competition with the food processing industry, the utilization of nonedible waste oil such as the waste frying oil (WFO), and poultry fats, will further cut the costs of biodiesel generation down to 50-70% comparing that with the process using editable oil as feedstock [19, 20]. Therefore, in current work, the biodiesel transesterification process using WFO as the feedstock and the calcined SS as the solid catalyst was extensively investigated. One of the most critical steps in preparing active bio-derived CaO catalyst from biomass resources (calcium carbonate) is the calcination step [21]. The current widely adopted operation unit for calcium carbonate calcination are the vertical kiln, and the rotary kiln [22-24]. Other than those conventional processing units, the fluidized bed reactor is another candidate because of its excellent mass and heat transfer [25]. For the sake of process intensification and significant reduction of the CO2 footprint during production, the fluidized bed reactor can be very effective in fast calcination [26, 27]. Up to date, the reports on using the fluidized bed reactor for the fast calcination of SS to produce biodiesel catalysts, to the best of our knowledge, have not yet been reported. Therefore, in this work, the fluidized bed reactor was employed to intensify the SS calcination process. The statistical analysis using response surface methodology (RSM) for process parameters i.e. calcination temperature, catalyst loading and methanol to oil molar ratio, were investigated. The kinetic of calcination process at high temperature was modelled by Shrinking-Core Model (SCM).
2. Experimental 2.1 Preparation of SS catalyst The SS based catalyst was calcined in a fluidized bed reactor at different temperatures. Before calcination, the SS were dried in an air oven at 200 °C for 2 hours. Then the dried SS were crushed and sieved within a range of 0.05-0.45 mm. For better fluidization, the reactor was preloaded with 10 grams of sand with a particle range of 0.15-0.45 mm at the optimal fluidization flow rate (0.1 Nm3.h-1). The detailed configuration and schematic preparation process are depicted in Figure 1. The fluidized bed reactor was preheated to the specific temperature (500-900 °C) with a ramping rate of 10 °C/min. Once the fluidized bed reactor reached the setting temperature and stabilized, 20 grams of SS with a particle
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range of 0.05-0.45 mm were loaded in the fluidized bed reactor. The sample SS calcined at a different temperature is set as SS-p1, where p1 represents a parameter of calcination temperature. For example, SS850, SS-800, SS-750 and SS-700 represent that the samples being calcined at 850 °C, 800 °C, 750 °C, and 700 °C, respectively. In order to determine the calcination temperature and duration in the fluidized bed reactor, the thermo gravimetric analysis in presence of air was performed and results are shown in Figure 2. Three obvious weight lost were observed during the calcination. The peak at around 60 °C indicates the removal of the moisture. The peak at around 350 °C indicates the decomposition of organic compounds e.g. chitin, protein etc. The peak in the temperature range of 700-850 °C corresponds to the reaction: (1)
CaCO3 CaO CO2
The calcination in the temperature range of 700-850 °C corresponds to the weight loss of 25%, which is slightly larger than the theoretical weight loss of complete decomposition of CaCO3 (23%), this discrepancy comes from the incomplete decomposition of CaCO3 at experimental condition and existence of impurities such as organic materials, magnesium carbonate, and silica in the SS matrix. In this work, in order to produce active CaO based catalyst, 800 oC was set for the study of the flow characteristic of the fluidized bed. And the fluidization flow rate of 0.1 (Nm3.h-1) was kept to maintain the good fluidization. The corresponding pressure drop result is shown Figure 2. The pressure drop changed significantly during the first 10 minutes in all temperatures, indicating the occurrence of the significant calcination. The variation of pressure drop became less once the calcination duration was over 10 minutes. After the first 10 minutes, no significant pressure change was observed. Therefore, the 10 minutes calcination duration was chosen as the optimal calcination duration for catalyst preparation. 2.2 Characterization of catalyst and biodiesel The samples were characterized by X-ray diffraction (XRD) spectra of samples were characterized on a Philips X-Pert (50 kV) diffractometer using Co Kα radiation at a wavelength of λ=0.1789 nm, samples were scanned from 10 to 120 °. X-ray fluorescence spectrometer was used for elemental composition characterization by a Rigaku-2100 XRF spectrometer. Fourier transform infrared spectroscopy (FTIR) using a Perkin Elmer Spectrum 2 with UATR-single
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reflection diamond) was used to study functional groups of samples. Samples were scanned in spectra range of 4000-370 cm-1. Scanning electron microscope (SEM) morphology and Energy-dispersive X-ray spectroscopy (EDX) were examined using a JSM-7001F+INCA X-MAX Field emission electron microscope. Gas chromatograph GC were obtained on a Shimadzu 2014 GC equipped with a flame ionized detector (FID). The separation was carried out on a DB-1HT capillary column (30 m×0.25 mm id, Agilent Tech). The operating conditions were set as following: the temperature of sampling inlet was 370 °C, detector temperature was set at 375 °C, and the column temperature was set at 350 °C. The BET (Brunauer-Emmett-Teller) specific surface area was determined by nitrogen gas adsorption at 77 K at a saturation pressure of 106.65 kPa using a Micromeritics ASAP 2020 automated gas sorption system. The BET specific surface area was assessed within the range of relative pressures from 0.05 to 0.3. Thermogravimetric analysis (TGA): TGA was performed on a Shimadzu TGA-50 under air (Q=20 ml/min) atmosphere at the ramping rate of 10 °C min-1. Elemental analysis was obtained by induced coupled plasma-optical emission spectroscopy (ICP-OES) (OPTIMA 7100DV, Perkin Elmer, USA), the detailed microwave digestion, dilution and the operational procedures can be found from the previous literature reports [28, 29]. 2.3 Experimental design and statistical analysis RSM is a set of mathematical and statistical techniques seeking to optimize an objective function that is affected by multiple factors using the design of experiments (DoE) methods and statistical analysis [30]. Instead of seeking the optimal solution within a large number of randomly generated candidates, RSM utilizes the reduced and simplified experimental designs to gain a thorough understanding of the system as well as to obtain the optimal combination of operating parameters [31]. In this work, a central composite design (CCD) with three independent variables (calcination temperature, catalyst loading and the molar ratio of methanol to oil) was investigated to study the response pattern and to determine the optimal combination of calcination temperature, catalyst loading and the molar ratio of methanol to oil to maximize biodiesel conversion. The design with three independent variables at five different levels (total of 17 runs)
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was adopted to find the offset, and the linear, quadratic and interaction terms, using the following equation [32]: 3
Y b0
i 1
3
bi X i
i 1
3
bii X i 2
(2)
bij X i X j i j, j 2
The range and levels of optimized variables are shown in Table 1. The statistical significance of the regression term was checked by analysis of variance, ANOVA. In this work, the biodiesel conversion was set as the optimization goal. The biodiesel samples were set as the following patterns: SS-p1-p2-p3, where p1 represents calcination temperature, p2 represents catalyst loading (catalyst/oil on weight percentage), and p3 represents molar ratio of methanol to oil. For example, SS-800-3-10 represents biodiesel sample being prepared from the SS being calcined at 800 °C, which was then added into oil at 3% on the weight with a methanol to oil molar ratio of 10. 2.4 Preparation of biodiesel and determination of conversion The biodiesel was prepared by the well-known transesterification process [33]. The waste frying oil (WFO) used in this work is an Australian premium vegetable oil (supplied by Crisco, with 90% fatty acid, 5% protein, 1% carbohydrates, and
