Al-alginate as acid catalyst for FAME synthesis using electrolysis process

A novel solid acid catalyst, which was prepared from sodium alginate and aluminum chlorides and characterized by SEM-EDS, XRD and FT-IR spectrometry. The catalyst was used for the synthesis of fatty acid methyl ester (FAME) via (trans)esterification reaction using electrolysis process. Purity and FAME components of biodiesel were measured by GC-MS. The results showed that the aluminum-alginate prepared in a cheap and easy way exhibited high catalytic activity. FAME conversion from used-cooking oil was obtained by 93.82% in the presence of 10 wt.% of catalyst dosage upon refluxing for 4 h of methanol and oil in a molar ratio of 6:1.


Introduction
Fossil fuel is now widely recognized as unsustainable resource.The limitations of fossil fuel had demanded to look for other energy sources that can be renewable.A candidate as renewable energy to substitute petroleum is biodiesel.Biodiesel is a mixture of fatty acid methyl esters (FAME) produced from free fatty acids via esterification and/or (trans)esterification with methanolisis process.Various biodiesel standard namely flash point, cold filter plugging point, sulphur content, and oxygen consumption of biodiesel are improved as compared with that of fossil-based diesel.Moreover, it was found out that biodiesel used as engine fuel can effectively reduce the emission of poisonous gases [1][2].
Typically, conventional biodiesel produces straight forwardly by means of homogeneous alkaline catalyst, such as NaOH and KOH.For high proportion of free fatty acid (FFA) and water containing in a low quality of used-cooking oil, homogeneous alkaline catalyst are markedly sensitive to FFA, leading to catalyst losses, saponification problem, lowering the efficiency and economics of the overall process [3].The synthesis of biodiesel from used-cooking oil (UCO) by using electrolysis process had been reported by Guan and Kusakabe with the yield > 97% [4].These methods have some advantages to produce biodiesel from usedcooking oil.For example, the high water content in the oil can be directly used in electrolysis process (i.e. the electron transfer emerged by the formation of H + and OH - ions) is derived indirectly as a catalyst in esterification and transesterification reaction at room temperature [5].In this study, the enhancement of FAME synthesis from used-cooking oil using electrolysis process by Alalginate as heterogeneous acid catalyst.

Chemical and equipment
Used-cooking oil was provided from home industry activities.High grade of methanol, NaCl, AlCl3.6H2O and co-solvent THF were purchased from Merck, Germany and food grade of sodium alginate was purchased from local food industry in Yogyakarta province of Indonesia.Fig. 1 shows an electro-catalytic cell (250 ml) contains two graphite electrodes (∅ 0.8 mm x 130 mm) that were separated by a distance of 2.5 cm [5].The qualities of used-cooking oil were determined by physicochemical analysis and the results were shown in the Tab. 1

Preparation and characterization of catalyst
A novel solid acid catalyst of Al-alginate, which was prepared from sodium alginate and metal chlorides according to publish paper by Qiuyun et al. [6].Briefly, 2 g of sodium alginate was added to 100 mL of 100 °C distilled water, followed by stirring at 700 rpm until a clear viscous solution was obtained.Then, the viscous solution was added drop wise into 100 mL of 0. AlCl3 solution.The resulting solution system was stirred vigorously for 13 h to form a white of Al-alginate complex.Finally, the Al-alginate granules were washed until a neutral pH and then dried at room temperature for 48 h.The X-ray diffraction (XRD) patterns of the catalyst were measured using a Bruker D2 Phaser diffractometer system (equipped with a monochromatic Ni filter using CuKa radiation).Fourier transform infrared (FTIR) spectra was recorded on a Perkin Elmer Spectrum Two equipped with the universal ATR.FTIR spectrophotometer without using the KBr disc technique (4000-400 cm-1) and Scanning electron microscope (SEM) was obtained from a Phenom ProX desktop equipped with an energy dispersive spectroscope (EDS) detector to characterize the microstructures and chemical properties of as-prepared Al-alginate material.In addition, a PinAAcle 900 Perkin Elmer measured the sodium and aluminum concentration in the prepared alginate.

Catalytic testing
Effect of catalyst amount (5, 10 and 15 wt.%) was evaluated on the conversion of FAME from usedcooking oil.The reaction mixture was agitated using magnetic stirrer.The electrolytic cell was filled by 70 ml of reaction mixture containing used-cooking oil, methanol, THF as a co-solvent [5].The methanol-to-oil molar ratio was 24:1, co-solvent-to-methanol molar ratio was 1:0.25 and NaCl concentration was added on the basis of oil weight (0.56 wt.%) of the entire reaction mixture, respectively.The electro-catalytic was carried out at room temperature using a constant voltage of 18.6 V for 2, 4, 6 h.Fig. 2 shows a step of optimization process for biodiesel production in this study.The FAMEs phase were separated from glycerol and the product was washed with deionized water to remove the residual inorganic components.FAME conversion and unreacted oils remaining in the product was measured by GC-MS.

Catalytic characterization
Fig. 3 shows the XRD patterns of Na-alginate and the Al-alginate catalyst.Crystalline of sodium alginate was formed by strong interaction between the alginate chains through intermolecular hydrogen bonding [7].The degree of crystallinity of the alginate was estimated by using the software DIFFRAC.EVA version 4.0.The Naalginate presents a 18.6% crystallinity degree; and the Al-alginate, a 11.0%.Three diffraction peaks at 2θ values 13.5º, 22º and 39º were observed for sodium alginate due to the reflection of their (110) plane from polyguluronate unit, (200) plane from polymannuronate and the other from amorphous halo [8].In case of Alalginate sample, the intensity of diffraction peaks of alginate decreased notably which indicates that the formation of aluminum oxyhydroxide particles on the grid of alginate affected the crystalline nature of sodium alginate.In other words, this procedure is successful in the preparation of the aluminum-alginate catalyst.The broadening of the diffraction peaks in all prepared alginate indicates nature of the sample.Fig. 4 shows the FTIR spectra of Na-Alginate and Al-Alginate.The FTIR spectrum of Na-alginate shows the characteristic peaks at 3242 cm −1 (OH − stretching) [9], peaks at 1591 and 1407 cm −1 (COO − asymmetric and symmetric stretching), 1081-1024 cm −1 (C-O-C antisymmetric stretching), and carboxyl and carboxylate at peaks about 1000 to 1400 cm −1 [10].In FTIR spectra of Al-alginate, the asymmetric band of carboxylate ion has shifted to lower frequencies from 1591 cm −1 to 1593 cm −1 , and the hydroxy band of sodium alginate has shifted from 3242 cm −1 to 3253 cm −1 , because of the interaction between sodium alginate and AlCl3 [9].The band at 1025 cm -1 was given by the guluronic units [11] in all the spectra.The results from SEM revealed that bigger micro architecture of Al-alginate formed than Na-alginate in terms of their pore sizes (Fig. 5).A wide and porous surfaces layer of the Al-alginate give a large catalytic activity so that increased the performance of esterification in electrolysis process.EDS spectra of the composite films clearly show the characteristic peaks of aluminum (AlCl3) used for the synthesis along with notable amounts of carbon and oxygen from alginate backbone.The quantify of ion exchange process between sodium alginate and the contacting AlCl3 solution was measured by an atomic absorption spectrometer.Initial sodium concentration in the Na-alginate was 0.00247 mg/Kg.While, aluminum concentration was 0.0648 mg/Kg in the Al-alginate.Therefore, the ratio of ion exchange between aluminum to sodium was 26.23 Al : Na.

Influence of electrolysis time
Tab. 2 shows the FAME yield increased by the increase of electrolysis time.It can be seen that the FAME yield rapidly reached up to 95.94% within 2 h.After 6 h of reaction, the conversion rate leveled off as the products attained a near-equilibrium composition as high as 96.51%.However, the optimum reaction time for electrolysis was 4 h since total FAME yield was the highest (see Fig. 6) and it was more efficient for electrolysis time.Fig. 6 shows typical of FAME conversion from used-cooking oil in the electrolysis process.When the FFA present in the used-cooking oil, the electrolysis process were successively subjected to esterification reaction with methanol, the high to low FFA conversion (%) from used-cooking oil was as follow oleic acid > palmitic acid > stearic acid > myristic acid, respectively.In this regards, the electrolysis was conducted at room temperature (25 °C) without catalyst.Tab. 3 shows the effects of wt.% catalyst to oil ratio on the FAME yield using electrolysis.The biodiesel yield increased by the increase of catalyst loading.It was discovered that excellent conversion rates (as high as 93.76% were obtained in 10 wt.% of catalyst loading since total FAME yield was the highest (see Fig. 7).This fact shows that aluminum-alginate was an appropriate solid catalyst that has a very high reactivity to catalyze esterification reaction.This study showed that the Alalginate catalyst could be a good candidate to enhance the electrolysis conversion of cheap feed-stocks containing high amount of FFAs (such as inedible oils [12], waste vegetable oils [13], waste cooking oils [14], etc.) into biodiesel.In this regards, the electrolysis was conducted at room temperature (25 °C) in 4 hours process.

Conclusions
The enhancement of FAME yield from the (trans)esterification of used-cooking oil using electrolysis process with Al-Alginate as acid catalyst had already evaluated.High catalyst concentration (10 wt.%) with 4 hours of electrolysis time at room temperature was required in order to get a high FAME yield as much as 93.82%.Future works will need to explore high specific catalytic surface of Al-Alginate aiming to enhance the catalyst in the electrolytic biodiesel production.

Fig. 1 .
Fig. 1.Electrolysis reactor set up (a) and illustrated functional apparatus in the reactor (b).

Fig. 2 .
Fig. 2. Steps on FAME synthesis using electrolysis process and Al-alginate as catalyst

Fig. 5 .
Fig. 5. SEM images showing the topology of Al-alginate (a) and Na-alginate (b) in x10.000 magnificent.The red arrow indicated the porous surface in the material.Al-alginate images and its corresponding EDS analysis (c).

Fig. 6 .
Fig. 6.FAME conversion from used-cooking oil in the electrolysis process without catalyst.

Fig. 7 FAME
Fig. 7 FAME conversion from used-cooking oil in the electrolysis process enhanced by catalyst

Table 1 .
Physicochemical properties of used-cooking oil

Table 2 .
Effect of electrolysis time on the FAME yield without catalyst

Table 3 .
Effect of catalyst loading on the FAME yield in electrolysis process