Efficient Transformation of Waste Bone Oil into High Quality Biodiesel

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Efficient Transformation of Waste Bone Oil Into High Quality Biodiesel via A Synergistic Catalysis of Porous Organic Polymer Solid Acid and Porous #-Al2O3-K2O Solid Base iman Noshadi, Christopher Carrie, John Borovilas, Baishali Kanjilal, and Fujian Liu Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 11 Aug 2017 Downloaded from http://pubs.acs.org on August 11, 2017

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Industrial & Engineering Chemistry Research

Efficient Transformation of Waste Bone Oil Into High Quality Biodiesel via A Synergistic Catalysis of Porous Organic Polymer Solid Acid and Porous γ-Al2O3-K2O Solid Base

Iman Noshadib*, Christopher Carrieb, John Borovilasb, Baishali Kanjilalc, Fujian Liua*

a

National Engineering Research Center of Chemical Fertilizer Catalyst (NERC-CFC), School of

Chemical Engineering, Fuzhou University, Gongye Road No.523, Fuzhou 350002, Fujian, PR China. E-mail: [email protected] b

Department of Chemical Engineering, Rowan University, Glassboro, 08028. Email:

[email protected] c

Institute of Materials Science, University of Connecticut, Storrs, Connecticut, USA 06269.

ABSTRACT

We report here a novel synergistic catalysis system combined with porous organic polymeric solid acid (H-PDVB-SO3H) and K2O doped porous γ-Al2O3 solid base (γ-Al2O3-K2O). H-PDVB-SO3H and γ-Al2O3-K2O have abundant nanopores, controllable surface wettability and high concentrations of acidic and basic sites. The synergistic catalysis system exploited by us could efficiently transform acidulated bone oil, plant oil into high quality biodiesel under mild conditions, which achieved ASTM specifications pertaining to acid number, total and free glycerin. Acidulated bone is a bone meal treated with sulfuric acid containing high-value hydrocarbons, which is generated in large amounts by the cattle industry. This work develops an efficient and cost effective approach to transform animal waste into high quality biodiesel.

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Keywords: Acidulated bone oil; Biodiesel; Porous solid base; Porous solid acid; Synergistic catalysis.

1. INTRODUCTION

A promising alternative to petroleum fuels is the hydrocarbon based biofuels derived from renewable resources. A sustainable approach to address the economic challenges of waste management and energy costs should use the easily renewable biomass, especially waste, for the fuel production.1-3. An interesting candidate in this regard is the organic fraction of acidulated bone. Acidulated bone is waste ground bone or bone meal treated with sulfuric acid. After acidulation, the inorganic fraction is normally used to make Gelatin, and the organic fraction is a process waste, which consists of abundant hydrocarbons4. The usage of animal fats as animal feed has been discontinued due to the possibility of disease, and such fats present a more abundant raw material source than frying oils for making biodiesel, in addition to being the recourse for recycling such wastes5. Various types of animal fats, in addition to vegetable based yellow grease, have been used for the production of biodiesel5. Lard has also been used to make biodiesel by base catalysis transesterification6. The high free fatty acid (FFA) more than 1% in most animal fat feedstock showed very negative effect on base-catalyzed transesterification due to the fact that FFA reacts with the basic sites in solid base catalysts, which results in saponification. This reduces catalysts efficiency, reusability and makes the process of biodiesel manufacture more costly7,8. Therefore, the FFA can be firstly converted into biodiesel by an esterification pretreatment step catalyzed by acid catalysts, which is then followed by transesterification of the triglycerides catalyzed by a base catalyst.

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Production of biodiesel from renewable sources is a topic of current interest because of the increasing demand for energy and concerns on the environment9-18. Conventional homogeneous acid and base catalysts such as H2SO4, NaOH, and KOH, while exhibiting excellent catalytic activities also have drawbacks related to the waste, corrosion, and difficult recyclability, which adversely limit their applications. Various solid catalysts such as sulfated zirconia or supported heteropoly acids could be used for catalyzing the production of biodiesel, which has limitations on their catalytic activities for industrial applications arising from low exposure degree of the active site and the leaching. At the same time, they are advantageous concerning catalyst recycling and relatively high stability towards water and CO217-21. Compared with acid catalysts, base catalysts are more active and less expensive. However, solid bases are prone to be poisoned by fatty acids (FFAs) during catalytic reactions, which results in saponification phenomenon19. Recently, we synthesized a family of porous organic polymer solid acids (H-PDVB-x-SO3H) with controllable structural characteristics from solvothermal copolymerization of 4vinylbenzenesulfonate (SVBS) with divinylbenzene (DVB). The synthesized H-PDVB-x-SO3H showed much improved activities in comparison with ZSM-5 zeolite, carbonaceous solid acid and Amberlyst 15 in a variety of acid-catalyzed reactions22. To build a highly efficient approach to catalyzing production of biodiesel, we report here a novel synergistic catalysis process combined with H-PDVB-SO3H and K2O doped porous γ-Al2O3 solid strong base (γ-Al2O3K2O)23-25. γ-Al2O3 support could be easily synthesized from a high temperature induced self assembly system23, and waste acidulated bone oil and plant oil were chosen as the feedstocks. Acidulated bone is bone meal treated with sulfuric acid containing high-value hydrocarbons and free fatty acids (FFAs), which is generated in large amounts by the cattle industry. Notably, nearly all of FFAs in waste acidulated bone oil and plant oil can be quickly transformed into

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biodiesel catalyzed by H-PDVB-x-SO3H, the left triglycerides could be effectively transformed into biodiesel catalyzed by γ-Al2O3-K2O. The activity of γ-Al2O3-K2O was as good as homogeneous KOH26-31. Also, the synergistic catalysis processes could be recycled for 5 times, and obvious decreasing of activities of the catalysts can not be observed. The combination of both H-PDVB-SO3H and γ-Al2O3-K2O catalytic processes, the waste acidulated bone oil was efficiently transformed into high quality biodiesel. More importantly, experimental design and response surface methodology (RSM) was utilized to optimize the variables with the solid base catalyst for transesterification of food grade canola oil. The synergistic catalysis of both solid acids and solid bases catalysts will be an efficient and reusable approach for the transformation of the production of biodiesel from waste animal fats to high-quality biodiesel.

2 METHODS 2.1 Preparation of porous H-PDVB-SO3H DVB was copolymerized with sodium 4-vinylbenzenesulfonate (SVBS) by using 2,2′azobis(2-methylpropionitrile) (AIBN) as the initiator in an autoclave at 100 °C. As a typical experiment, 0.5 g of SVBS and 2.0 g of DVB were mixed into a solution contains 27 mL of THF and 3 mL of distilled water and 0.065 g AIBN. Then the mixture was stirred for 2 h at 27 °C. The sample was transferred into an autoclave and solvothermally treated at 100 °C for 24 h. The solid powder was dried by evaporating the solvents. The sulfuric acid was used to ion exchange the sample as follows: 1.0 g of the solid powder was vigorously stirred into a mixture 5mL of sulfuric acid (96 %), 10 mL of ethanol and 30 mL of distilled water for 24 h. Next, the sample was filtered and neutralized with high amount of water. The resultant material dried at 80 °C for 6 h and used for each run. Carbon solid acid was synthesized based on the previous reports32.

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2.2 Preparation of porous γ-Al2O3 supported K2O 4.0 g of 4-vinylpyridine was polymerized initiated with 0.1 g of AIBN at 80 °C in the presence of 20 mL of ethanol solvent. The mixture was cooled down to room temperature, followed by addition of 1 g of aluminum isopropoxide and stirring for 12 h. All the solvent was evaporated at room temperature for 24 h. The resultant solid was autoclaved at 180 °C for 24 h. The autoclaved solid was calcined at 550 °C for 5 h to obtain the porous aluminum oxide. To 0.5 g of this mesoporous aluminum oxide, 2 mol of KF solution was added dropwise until the solid appeared to absorb no more of the KF solution. Then, The sample was dried at 100 °C, hydrothermally treated at 180 °C for 12 h, and calcinated at 550 °C for 3 h.

2.3 Characterizations The BET surface area was measured by using a Micromeritics ASAP Tristar system. The samples were degassed for 10 h at 150 °C. The Barrett–Joyner–Halenda (BJH) model was used to measure the pore-size distribution. FT-IR spectra were recorded by using a Bruker FTIR instrument was used the record the FTIR spectra. A Rigaku D/max2550 PC powder diffractometer using nickel-filtered Cu/Kα radiation was used to record the X-ray powder diffraction. A Tecnai T12 transmission electron microscope (TEM) and a JEOL 6335F field emission scanning electron microscope (FESEM) with an EDX detector were used to obtain the electron microscopy images. A TGA7 (Perkin Elmer) with a heating rate of 20 °C/min was used to measure the thermogravimetric analysis (TGA).

2.4 Separation of bio-oil from bio-solid

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The organic fraction of the acidulated bone was obtained from a bone processor. Slow stirring of this material at 35 °C, over a period of 16 h, effected the separation of additional water from the oil and residual solids. After separating the supernatant oil, the water and resultant material were similarly treated with overnight stirring two more times, at 35 °C, to separate additional oil from the mixture.

2.5 Esterification of oleic acid Esterification reaction was performed with the solid acid catalyst at 65 °C temperature in a round bottom ﬂask fitted with a reﬂux condenser. The molar ratio of oleic acid to methanol was kept at 1:9. The mass concentration of 5 (w/v %) of the catalyst was used for all the experiments. The samples were withdrawn periodically and centrifuged at 3500 rpm for 2 min to form two layers, the upper layer being the mixtures of methanol and water, and the lower layer being methyl oleate. The titration method was used to determine the free fatty acid conversion.

2.6 Transesterification of food grade canola oil The solid base catalyst was used for transesterification of food grade canola oil for control experiments according to a statistical design of experiments. A careful experimental protocol was undertaken in this section of the work to explore this new catalyst for transesterification of triglyceride oils. The reactions were carried out in a three-neck round bottom flask, provided with thermometer, mechanical stirring and condenser. The flask with cooking oil was preheated to 65 °C, then the methanol was added. The amount of methanol was calculated to give a molar ratio of methanol:oil at 10:1, assuming a molecular weight of canola oil equal to 880 g/mol7. The reaction was catalyzed by using the solid base catalyst, which was added after the methanol had

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been added. Samples were withdrawn and centrifuged at 3500 rpm for 2 min. The upper phase consisted of methyl esters and the lower phase contained glycerin. The methyl ester layer was washed with water and dried using sodium sulfate and analyzed by GC. A Box-Behnken design with three factors was used to evaluate the effect of variables on the oil conversion to methyl ester. The three factors investigated were the reaction temperature (T), reaction time (t) and catalyst concentration (C). Seventeen experiments, including five replications at the design center, were carried out to measure the errors. Design-Expert 10.1 software was used to plot the response surfaces and analyze the experimental data8.

2.7 Two-step esterification-transesterification of acidulated bone oil Acidulated bone oil was converted into biodiesel via solid catalysts for the first time. 20 mL of acidulated bone oil was separated from remaining water and impurities by heating and centrifugation. The esterification reaction of FFA was carried out with methanol by either H2SO4 or H-PDVB-SO3H solid acid catalyst to eliminate the saponification in the high free fatty acid (FFA) content oil. The esterification reaction was carried out until the FFA content was lower than 0.5 %. Then, the solid acid catalyst was separated from esterified oil and methanol by centrifugation. The treated oil and methanol with either KOH or super base solid catalyst 5.5 (w/v%) were mixed in a round bottom flask equipped with reflux condenser at temperature of 65 °C for 60 min. The samples were centrifuged for 2 min to remove the methyl ester from the glycerol. The samples were washed three times with distilled water to remove the

methanol.

The ester layer was dried by using anhydrous magnesium sulfate and filtered for Gas Chromatography (GC) analysis.

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2.8 Analysis of acidulated bone oil and biodiesel The composition and quality of the biodiesel obtained from acidulated bone oil as the feedstock was analyzed in several ways. The FFA content of the product was calculated, as per ASTM D7651, by titration with 0.07 M potassium hydroxide solution. GC instrument with FID detector was used to measure the free and total glycerin content in the biodiesel based on the ASTM 6584 standard. The solid catalyst could be regenerated from centrifugation, washing with abundant dioxane to remove residual reactants and products. The sample was dried at 80 °C to be used for the next run.

3. RESULTS AND DISCUSSION 3.1 Structural characterization Figure 1A, B showed the N2 adsorption-desorption isotherm and pore size distribution of HPDVB-SO3H. H-PDVB-SO3H showed a type-IV curve with a sharp capillary condensation step at P/P0=0.8-0.95 with high volume adsorption, showing the presence of abundant mesopores in the sample

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. A BET surface area of 171 m2/g was achieved in H-PDVB-SO3H, which was

larger than Amberlyst 15, and smaller than H-ZSM-5 (Table 1). The obtained pore volume of HPDVB-SO3H (0.52 cm3/g) was significantly higher than both Amberlyst 15 and H-ZSM-5 (Table 1). H-PDVB-SO3H showed very uniform pore diameter centered at 21.2 nm, which is close to our previously reported catalyst studies

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. The S content and H concentrations of H-PDVB-

SO3H were 1.3 and 1.8 mmol/g respectively, higher than those of H-ZSM-5, and lower than Amberlyst 15. In general, the increasing of concentration of active sites usually results in the decreased BET surface areas in the samples 27-31,33.

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Figure 1C showed the FT-IR data for the H-PDVB-SO3H. The peaks near 620 and 1092 cm-1 are related to S-O and S=O bond

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. Also, the weak peak at 1042 cm-1 assigned to the

formation of the C-S bond. The results confirmed the successful introduction of the sulfonic group into H-PDVB-SO3H. Figure 2A showed the XRD patterns of crystalline nanoporous γ-Al2O3-K2O before and after treatment with KF solution. Notably, the peaks associated with the cubic structure of γAl2O3-K2O could be clearly observed (Figure 2A), in good agreement with the literature results 29,30

. After treatment with KF, and a second calcination, a weak peak at around 2θ=42.7 ° was

observed, which was assigned to the presence of K2O, indicating the transformation of KF into K2O during the calcination process

30,31,33

. The above results demonstrated that the K2O active

site has been successfully loaded into mesoporous γ-Al2O3. On the other hand, Figure 2B&C showed the SEM images of nanoporous γ-Al2O3-K2O, which showed monolithic morphology with rough surface characteristics and abundant nanoporous structure. Figure 2D&E showed TEM images of H-PDVB-SO3H, which exhibited sponge-like structural characteristics with abundant nanoporosity. Abundant nanopores were favorable for the mass transfer of various guest molecules in these samples. Figure 3 showed the N2 adsorption-desorption isotherms and pore size distribution of porous γ-Al2O3 and porous γ-Al2O3-K2O. The γ-Al2O3 sample showed type IV isotherm, exhibiting a sharp capillary condensation step at relative pressure (P/P0) ranging from 0.70 to 0.95, confirming the presence of mesopores in the sample 22,27. Correspondingly, the pore sizes of γ-Al2O3 was centered at around 4.0 nm. After functionalization of γ-Al2O3 with KF to give γAl2O3-K2O, which showed decreased volume adsorption and BET surface area (Table 1). On the other hand, γ-Al2O3-K2O showed increased pore size (8.4 nm) in comparison with that of γ-

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Al2O3 (4.9 nm) because of partially etching of the network of γ-Al2O3 by K2O (Table 1). The abundant nanoporous structure found in γ-Al2O3-K2O was favorable for the enhancement of its catalytic performances. Figure S1 showed TG curves of pristine mesoporous γ-Al2O3, calcinated mesoporous γAl2O3, and γ-Al2O3-K2O. All the samples showed obvious weight loss (~6.5 wt%) ranged from 50-150 °C, which was attributed to desorption of water in these samples. Except for desorption of water, the as synthesized mesoporous γ-Al2O3 had another weight loss (~42 wt%) from 300 to 600 °C, which was due to the decomposition of P4VP template in the sample. On the contrary, calcinated sample with opened mesopores in nanoporous γ-Al2O3 showed very weak weight loss (~5 wt%) ranged from 300 to 1000 °C, and no obvious weight loss platform could be observed, which may be due to partially collapse of the framework in nanoporous γ-Al2O3. After loading KF in nanoporous γ-Al2O3, giving the sample of γ-Al2O3-K2O, which showed very weak weight loss (~2 wt%) ranged from 200 to 1000 °C, indicating its enhanced thermal stability in comparison with that of nanoporous γ-Al2O3. The enhanced thermal stability found in γ-Al2O3K2O was attributed to the loading of KF in the samples, which may result in partial decomposition of unstable units during its synthetic processes. Acidulated bone sample was at a temperature of 35 °C for 12 h to separate the water and residual solids from the oil layer, as shown in Figure 4A&B. Figure 4A showed the acidulated bone before the separation procedure. Figure 4B showed the separated layers of the dewatered acidulated bone oil from the water and solid. The average yield of oil from acidulated bone was 40 %. The oil layer was found to be approximately 20 % FFA and roughly 80 % triglycerides.

3.2 Catalytic production of biodiesel over H-PDVB-SO3H

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The esterification of oleic acid catalyzed by H-PDVB-SO3H was shown in Figure 5 with all catalysts at 5 (wt/v %) with respect to the oleic acid. The conversions increase steadily, reach the maximum values (ca. 97.1 %) after a reaction time of 5 h and plateau afterwards. In the meanwhile, the catalytic activities of HCl, carbon solid acid, and Amberlyst 15 for the esterification of oleic acid with methanol have also been investigated in Figure 5. Notably, HPDVB-SO3H showed much higher activity in comparison with those of carbonaceous solid acid and Amberlyst 15, a little lower than that of homogeneous HCl. After less than 3h the acid number was achived to 0.23 mg of KOH/g oil (Figure 7A).

3.3 Catalytic activity of γ-Al2O3-K2O and effect of different variables on oil conversion The relationship between canola oil conversion and three independent variables (reaction temperature, reaction time and catalyst concentration) were studied by using Design Expert Software 7.1. The experimental design listed in Table 2 represents the conversion of canola oil for each experimental run. The catalyst concentration was identified statistically as the most important for the conversation of the oil to biodiesel. A response surface plot for oil conversion in Figure 6A depicted the change of oil conversion with varying catalyst concentration and reaction time, plotted for the case where the reaction temperature is 60 °C. The maximum oil conversion of 99.07 % was achieved at 5.5 % catalyst concentration. Reaction time has a positive effect on the oil conversion. The maximum oil conversion of 99.07 % was achieved when the reaction time is 50 min. Figure 6B showed the influence of reaction temperature and catalyst concentration on oil conversion for the case where the reaction time is 50 min. The reaction temperature has a

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positive effect on the oil conversion. By increasing reaction temperature, oil conversion increased. The maximum oil conversion of 99.07 % was achieved when the reaction temperature is 70 °C. However; the temperature did not appear alone as a significant variable in the regression model due to the narrow range of temperatures tested.

3.4. Regression model and statistical analysis The responses obtained were presented in Table 3. A polynomial model was used to correlate the three independent variables with the response. Least square regression model was utilized to fit the data to the polynomial and the best fit model obtained was Eq. (1):

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Conversion (%)=+98.15+6.42t+26.63C+8.15Tt-8.44tC-9.25t -21.21C

(1)

where T was temperature, t was time, and C was catalyst concentrations.

Table 4 presented the Analysis of Variance (ANOVA) of this model. The results indicated that this model describes the experiments well 8. The correctness of the fit between the suggested model and experimental data were evaluated regarding the F-value, R2, R2adj, and p-value 8. Table 4 also presented the statistical parameters, and it showed that the F-value was 35.58 and p-value were less than 0.0001, which indicates that the significance of the quadratic model. The corresponding model term is significant with the p-value smaller than 0.05. The significance of the linear terms for reaction time (t) and catalyst concentration (C) on the conversion were apparent as shown in Table 4 in the corresponding high F values. The p-values lower than

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Efficient Transformation of Waste Bone Oil into High Quality Biodiesel

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