Nano-Magnetic Catalyst CaO-Fe 3 O 4 for Biodiesel Production from Date Palm Seed Oil

A nanocatalyst of CaO supported by Fe3O4 magnetic particles was prepared by a chemical precipitation method. It was characterized by various techniques including X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM); Fourier transforms infrared spectroscopy (FTIR), and Hammett indicator. It has been found that the catalyst consists of CaO and Fe3O4 accompanied by CaFe2O4. This composite catalyst was used for the catalytic transesterification of palm seed oil. The results revealed that the highest biodiesel yields for palm seed oil of 69.7% can be obtained under the conditions of (65 °C reaction temperature, 300 min reaction time, 20 methanol/oil molar ratio, and 10 wt.% of CaO/Fe3O4 catalyst loading). The physicochemical properties of the biodiesel produced from palm seed oil were further studied and compared with the ASTM and the EN biodiesel specifications. The results showed that the properties of the biodiesel produced comply with the international standard specifications. Copyright © 2017 BCREC Group. All rights reserved


Introduction
Since the invention of the diesel engine massive amounts of diesel fuel, derived from fossil oil, had been used.Aside from the environmental issues related to the extraction and refining of the crude oil to get the diesel fuel, the diminishing of the petroleum reserves urges the researchers to find new renewable and sustainable sources for the diesel [1].Over the last years biodiesel has become new energy source that have great importance [2].The name "biodiesels" has been given to transesterifiedvegetable oils to describe their use as diesel fuel [3].In addition to being fully competitive to petroleum diesel in most technical aspects; biodiesel has become more attractive because of several distinctive advantages.It is renewable, nonhazardous, biodegradable, and has low emission profiles, so it is environmentally serviceable [4].
The homogeneous base catalyzed transesterification method is the conventional production method of the biodiesel from vegetable oils.This method utilizes potassium hydroxide or sodium hydroxide as homogenous base catalyst to produce the biodiesel at very high yield under moderate conditions [5].However, the inability to reuse the homogenous catalyst, the use of the chemicals for its neutralization, and the high amount of wastewater produced by its removal processes are the main drawbacks facing the conventional method.Therefore, the use of such production method addresses environmental and cost issues that hinder the commercialization of biodiesel [6,7].
Numerous researches have been conducted to replace the homogenous catalyst by suitable heterogeneous catalyst.The later should have strong basic sites and durable activity.It also must be environmental-friendly and easily to recover and reuse [8][9][10].Many research works showed that CaO has great potential to be used as heterogeneous catalyst in transesterification of vegetable oils [11].However, the separation of CaO from the products of the reaction and its reuse still considerable unsolved issues especially when the CaO nanoparticles are used [12].Despite the higher activity of nanocatalyst, the difficulty of separation is high.
The magnetic catalysts have the advantage over the non-magnetic catalysts in the separation process.As compared with the filtration or centrifugation processes, the use of magnetic separation process can avoid the loss of catalyst and increase its reusability [13,14].Different types of ferrites have been used as magnetic catalyst [10] or catalyst support [12].
In the current work, nano-magnetic heterogeneous base catalyst has been developed.It consists of CaO nanocatalyst supported by Fe3O4 magnetic particles.Palm seeds oil, which is extracted from the seeds of Iraqi date palm (Phoenix Dactylifera), was used to evaluate the catalytic activity of the catalyst in transesterification reaction.The effect of reaction temperature and catalyst content were investigated.

Oil extraction from date palm seeds
The date palm seeds were separated manually from the fruits and washed with distilled water to remove the peels.They were dried under the sun and grinded using a mechanical grinder (RRH-A500).N-hexane, as a solvent, and soxhlet apparatus were used to extract the oil from the grinded seeds.The extracted oil was separated from n-hexane by rotary evaporator (Stuart, England) under vacuum conditions.

Preparation of nano-magnetic catalyst
In the current work, it was desired to prepare CaO nanocatalyst supported by Fe3O4 magnetic particles.For this purpose, 0.003 M calcium nitrate solution was prepared by dissolving an appropriate amount of calcium nitrate in deionized water.The 3.5 g of Fe3O4 were added to 5 L of the solution.The mixture was firstly mixed by mechanical stirrer for five minutes at 1500 rpm and then put in an ultrasonic bath (SB 5200 DTD) for 15 minute to get a well dispersed suspension.Sodium hydroxide solution (2 M) was added drop by drop to the suspension, which was under stirring at 1500 rpm, until the pH of 12 was obtained.The suspension was aged overnight under stirring at the same speed.The precipitate was washed by deionized water and centrifugation until the pH around seven was obtained.It was dried overnight in oven at 80 °C.
The product was grinded by mortar and pistil and calcined at 550 °C for one hour in an electric box furnace.The catalyst was kept in a bowl containing silica gel to reduce the risk of contamination by atmospheric CO2 and moisture.

Characterization of nanomagnetic catalyst
The powder X-ray diffraction analysis (XRD) was employed to identify the crystalline structure of nanomagnetic catalyst CaO-Fe3O4.The analysis was performed on a Shimadzu model XRD 6000 Power X-ray diffractometer using Cu-Kα radiation (40 kV and 30 mA) with wavelength (λ) of 1.5406 Å.Data were collected over a 2θ range from 20° to 70° with a step of 0.02° at speed 6 degree/minute.Diffraction peaks of the crystalline phases were matched with those of standard compounds described in the JCPDS (Joint Committee on the Powder Diffraction Standards) databank.The transmission electron microscope (Zeiss-EM10C-80 Kv) and scanning electron microscope (TESCAN, Chic Slovakia) were used to investigate the morphology, the size, and the aggregation of the catalyst particles.FTIR technique was used to inspect the chemical transformation of catalysts using FTIR-8300 spectrometer (Bruker, Germany).
Hammett indicator procedure was followed to determine the basic strength (H─) and basicity of the synthesized catalyst.The basicity is the number of basic sites found on the catalyst surface.Basic strength of a solid base is the ability of the surface to accept a proton or donates an electron pair.It determines the activity of the catalyst.The Hammett indicators used in this work are given in Table 1.
The procedure involved the dilution of 1 mL of Hammett indicator with 10 mL of methanol.300 mg of catalyst was added to the solution and was left for two hours to reach an equilibrium state where no additional change of color took place.The change in the color of the solution was used to indicate the strength of the catalyst.The base strength is quoted as being stronger than the weakest indicator which exhibits a colour change, but weaker than the strongest indicator that produces no change.The basicity value (mmol/g) of the catalyst was determined using Hammett indicator-benzene carboxylic acid (0.02 mol/L anhydrous ethanol solution) titration method.After two hours of the addition of the catalyst to the indicator solution, the benzene carboxylic acid was added until the colour of solution changes back to the original colour before adding the catalyst.

Transesterification reaction
Batch reactor was used for transesterification of palm seeds oil to produce biodiesel.The reactor was 100 mL glass round bottom flask with three necks equipped with a reflux condenser and thermocouple.Ten grams of palm seed oil were preheated to desired temperature by hot plate magnetic stirrer then the desired amount of catalyst was added.After adding the catalyst, 8.34 g of anhydrous methanol was added to the base of the reactor to prevent the evaporation of methanol (methanol/oil molar ratio ≈ 20:1).It has been assumed that the point of adding the methanol represent the starting point of reaction.The agitation speed was kept constant at 400 rpm; also the reaction time was fixed at five hours for all experiments.After reaction, the products were separated by centrifuge (Ultra-8V, Chain) at speed of 3000 rpm for 15 min.They were separated into three layers.The top layer consist of biodiesel and methanol.The middle layer is glycerol and unreacted oil.The bottom layer is catalyst.The biodiesel yield was calculated using Equation ( 1) [6,[15][16][17][18].
The effect of the following parameters on the transesterification reaction were investigated: (1) the amount of the catalyst loading in reactor (1%, 5%, and 10% based on oil weight); (2) the reaction temperature (45 °C, 55 °C, 65 °C).

Properties of date seed biodiesel
The fatty acid methyl esters of biodiesel were analyzed using Gas Chromatography-Mass spectrometry (GC-MS)Agilent 7890A GC series (Hewlett Packard, USA) with flame ionization detector (FID) and HP column, 30 m long × 0.32 mm ID × 0.25 μm film thickness (SGE, Australia).An amount of 0.2 mL of the prepared biodiesel was added to 1 mL of hexane and 2-propanol with volume ratio of (4/5).After filteration through 0.2 μm polytetrafluoroethylene syringe micro filter, 1-μL of the sample was manually injected into the GC/MS using a 5-μL micro syringe (SGE, Australia).The GC/MS instrument conditions are given in Table 2. Density and kinematic viscosity of biodiesel was predicated by using Cone-Plate test (DV-III ultra) and four digital high precision density tester, respectively.Saponification value (SV) and iodine value (IV) of oil were calculated from fatty acid compositions of oil with the help of Equations ( 2) and (3), respectively [19]: (2) (3) where MWi is the molecular weight of each component, Ai is the percentage of each fatty acid, and D is the number of double bonds .Higher heating value (HHV), Cetane number (CN) and Flash point (FP) of biodiesel were calculated from Equations ( 4), ( 5) [19], and (6) [3], respectively, where V is the viscosity in cSt.

Characterization of nanomagnetic solid catalyst
Figure 1 shows photograph image of the prepared CaO-Fe3O4 catalyst.It shows the response of the catalyst to the magnet confirming that it is ferromagnetic material.It can be seen that the color of CaO/Fe3O4 catalyst changes from black to brown-red after calcination at 550 °C for 1 h.

Results of XRD test
Figure 2 shows the XRD patterns of the nanomagnetic catalyst after calcination at 550 °C for 1 h.The observed positions the diffraction lines (2θ and corresponding d2θ) for the pattern are in full agreement with the corresponding values reported for calcium oxide (JCPDS, Card No. 028-0775), calcium ferrate (JCPDS, Card No. 032-0168), and magnetite (JCPDS, Card No. .This indicates that the change of the color, after calcination, is due to the formation of calcium ferrate.

Results of FTIR test
The FTIR spectra of the nano-magnetic catalyst CaO-Fe3O4 before and after the calcination are shown in Figure 3.The IR absorption peaks observed at 554 cm -1 are corresponding to the Fe-O stretching vibration of the Fe3O4.The band at 2360 cm -1 corresponds to the presence of atmospheric CO2 whereas the band at 678 cm -1 is due to water release.The broad band at 1369 cm -1 and sharp band at 865 cm -1 correspond to CO3 -2 in CaCO3 [20][21][22][23].After calcination, the intensity of these peaks  was decreased.In addition, a new peak appeared at 441 cm -1 .This peak represents Fe-O band for different components of iron which may belongs to the formed calcium ferrate [23].

SEM and EDX analysis
The SEM images of the Fe3O4 particles before the deposition of CaO are shown in Figure 4.The image at low magnification shows that the powder has narrow particle size distribution, while the image at high magnification shows that the powder consists of submicron multifaceted particles.Figure 5 shows the SEM images of the prepared CaO-Fe3O4 catalyst after calcination.Comparing these images reveals that no significant differences can be observed, before and after calcination, except the coarsening of some Fe3O4 particles due to the heat treatment.This suggests a good dispersion of CaO on the surface of Fe3O4.
The EDX spectrum and the weight percent of the prepared catalyst are shown in Figure 6.EDX spectrum demonstrates that the surface of the catalyst had Ca/Fe/O molar ratio of (1.00/2.16/10.36)indicating, with the help of XRD results, that the surface is mainly composed of CaFe2O4 and CaO.The high molar ratio of oxygen might be due to gases adsorbed on the surface of catalyst.

Results of TEM test
Figure 7 shows the transmission electron microscope image for the prepared nanomagnetic catalyst.It confirms the formation of aggregates of nanoparticles, representing the deposited catalyst, that partially cover the magnetite particles.Based on the XRD results, the deposited nanocatalyst is consisting of calcium oxide and calcium ferrate.

Results of basicity measurement
The basic strength of the nanocatalyst supported on magnetite is 9 < H_< 15, however, the basicity of the catalyst, i.e. the number of basic sites of a certain strength, corresponds to 0.133 mmol/g of basic sites having the strength of H=9.

The effect of amount of catalyst
The effect of the weight percent of the catalyst on the yield of biodiesel is shown in Figure 8.As expected, it has been observed that the yield of biodiesel increases when the weight percent of the catalyst increases.This is due to the increase of the available surface area of the catalyst per unit volume of the reaction media, and hence, the increase of the basic sites required for the catalytic reaction [24].

The effect of reaction temperature
Figure 8 shows the effect of the reaction temperature on the yield of biodiesel.In general, the rate of the reaction is directly proportional to the reaction temperature.The in- creasing of the temperature reduces the mass transfer limitations due to decrease in the viscosity of the reactants.This allows more particles to collide due to the increase in the energy supplied to the system.Moreover, temperature rising may reduce the amount of the absorbed gases on the surface of the catalyst, as noticed by EDX test, and hence, the available sites of reaction will eventually increase.
It has been observed that the weight percent of the catalyst has more influence on the yield of biodiesel than the reaction temperature.The effect of temperature at low weight percents is weaker than that at high weight percent of catalyst.This is possibly because the transesterification is a catalytic reaction and goes faster when the basic sites and the contact surface area for reaction increase [25,26].

Gas chromatography analysis
GC analysis was used to diagnose the numerous composites in the produced biodiesel.Fatty acid compositions of the palm seeds oil (PSO) methyl ester detected through the study are listed in the Table 3 and the GC chromatogram is depicted in Figure 9.The results showed that the oleic acid had the highest amount among unsaturated fatty acid while palmitate acid had the highest amount among saturated fatty acid.

Physicochemical properties of the synthesized biodiesel
Table 4 represents some properties of biodiesel which is produced from transesterifica-    [3].High cetane number, low viscosity and low flash point are the main advantages of date seed biodiesel.Because of these factors, the palm seed biodiesel is preferred than the other biodiesel fuels as it can increase engine's output and decrease pollution.These results are comparable with those obtained by Amani et al. [19].These findings are inconsistent with the typical range of ASTM and EN.

Results of FTIR test
Figure 10 shows the FT-IR spectra of the biodiesel.It is similar to the FT-IR spectra of the palm seeds oil (PSO), given in Figure 11, because of the analogous in the chemical natures of the oil and FAME.Nevertheless, slight dissimilarities were noticed.The peaks emerged at 1743, 1376, 1157, and 852 cm -1 in the PSO were moved to 1741, 1361, 1169, and  ASTM (B100) 1.9 -6 --64.7 --130 [27] 845 cm -1 in the FAME, respectively.So, the demise of the peaks at 1418 and 963 cm -1 from the spectra of the PSO and outcrop of new peaks in the biodiesel at 1435 cm -1 and 1195 cm -1 clearly illustrate the transmutation of PSO into FAME.Furthermore, the disappearance of the peak at 3500 cm -1 region, referred to the O-H bonds of the water molecule, proposes that produced FAME has low water content [6].

Conclusions
Heterogeneous base nanocatalyst of CaO-Fe3O4 based on Fe3O4 magnetic core was prepared by chemical precipitation method.Different techniques were used to characterize the catalyst.The consequences showed that the prepared catalyst consist of agglomerates of CaO nanocatalyst supported by the magnetite particles and their composite have ferromagnetic properties.The formation of this composite magnetic catalyst accompanied by the formation of CaFe2O4.A maximum biodiesel yields of 69.7% was obtained under the conditions of (65 °C reaction temperature, 300min reaction time, 20/1 methanol/oil molar ratio and 10 wt.% of CaO/Fe3O4 catalyst amount).
It was found that the catalyst amount and time had the most significant influence on biodiesel yields, while the impact of reaction temperature was not significant at low amount of catalyst.The nanomagnetic solid base catalyst, CaO/Fe3O4, used in the preparation of biodiesel illustrate a good prospect of development and application.The most important advantages of date seed biodiesel are its high cetane number, low viscosity and flash point.These factors can increase engine's output and decrease pollution in comparison with other biodiesel fuels.The present experimental results support that methyl ester of date seed oil can be successfully used as biodiesel in the internal combustion engine.

Figure 8 .Figure 9 .Figure 10 .Figure 11 .
Figure 8.The effect of reaction temperature and weight percent of catalyst on biodiesel yield at reaction time of 5 h, methanol/oil ratio: 20/1 and agitator speed of 400 rpm

Table 1 .
Hammett indicators used to determine the basic strength

Table 2 .
Operating conditions for the GC/MS

Table 3 .
The fatty acid compositions of the palm seed oil

Table 4 .
Characteristics of date palm seed biodiesel in comparison with the other biodiesel fuel Vs, viscosity; Dn, density; CN, cetane number; HHV, higher heating value; FP, flash point