Heterogeneous catalyst synthesis from Ribbon vittata shells and its characterization for biodiesel production from Blighia sapida seed oil

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Introduction
Environmental pollution and global warming are parts of the problems created by petroleum diesel.Therefore, finding a lasting solution to these problems is essential; attention has consequently shifted to biodiesel as an alternative to petroleum diesel.For biodiesel production, non-edible oils are preferred to edible oils and animal fats for biodegradable.Their aromatic content is lower, sulphur content, higher heating value, renewable, and easily transported due to their liquid nature.Second-generation biomass for biodiesel has become attractive and of interest since they do not interfere with the food chain as they are regarded as wastes.Homogeneous and heterogeneous catalysts are used for the laboratory preparation of biodiesel.These catalysts are (1) Homogeneous base catalysts: they are sensitive to FFA, which leads to the formation of soaps, and catalysts cannot be reused.However, operation conditions are severe, there is a high yield, and the reaction rate is fast.(2) Homogeneous acid catalysts: this is suitable for oil with high FFA, but they are corrosive, the rate of reaction is slow, and it is challenging to separate the catalyst from the product.(3) Heterogeneous base catalysts can be easily separated from the product and quickly recovered and reused.(4) Heterogeneous acid catalysts: easy recovery of feedstock water, sensitivity to high FFA is lower, they are easily recovered, washed, and reused [1].Ackee (Blighia sapida) is a tropical fruit of West African origin cultivated in several countries.It was first transported to London by Captain William Bligh and later introduced to Jamaica by Dr. Sir Thomas Clarke in the same century.Blighia sapida was later introduced to several countries (Gordon & Jackson-Malete, 2015).Blighia sapida is an evergreen tree propagated by seed or cutting, which may grow up to a height of 8 -15 m and start bearing fruits within 1 -2 years.The tree bears green pods as fruits which turn red at maturity.The pods split open to reveal seeds-bearing aril with a cream colour when ripe.The seeds in the fruit are usually 2 -4 hard, shiny black [3].There have been occasional reports of Blighia sapida fruit poisoning in Africa, Latin America, and the West Indies.The toxic nature of ackee fruit is due to hypoglycins A and B. These hypoglycins content is lower in ripe fruits while they are 10 to 100 times more in unripe fruits [4].Different researchers have extracted oil from Blighia sapida seed using mechanical and solvent extraction methods.They have also worked on Blighia sapida seed oil for various applications; there is, at present, no record of biodiesel production from Blighia sapida seed oil.

Catalyst preparation and characterization
Waste Ribbon vittata shells were collected from Camps Bay beach in Cape Town, South Africa.Dirt and impurities were removed from the shells by washing them a few times until they were clean.The clean shells were dried overnight in an oven at a temperature of 120 °C.After drying, the particle size reduction of the shells was carried out using an electric blender and then sieved using a 750-micron meter mesh.The crushed shell was placed in a crucible and calcined in a furnace for 4 hr at a temperature of 900 °C.The catalyst was cooled in desiccators and stored in an airtight container to keep it from interacting with the atmosphere.The energy dispersive electroscope (EDS) was used to determine the elemental compositions, while scanning electron microscopy was used to examine the catalyst's microstructure (SEM).

Oil extraction and characterization
Blighia sapida seeds were collected, and a knife was used to remove the seed coat.These seeds were sundried for seven days, after which they were milled with mortar and pestle and sieved using a 2mm Aperture Lab Standard test sieve stainless steel.To get the maximum oil yield from Blighia sapida seed, Orhevba [5] suggested a moisture content of 11.5% for the milled Ackee apple seed.
The solvent extraction technique was used to extract oil from milled Blighia sapida seed utilizing the soxhlet apparatus and n-hexane as the solvent.The extracted oil yield was determined using Equation 1 after the n-hexane evaporated at the operation's end.
(%) = Where: W1 = Weight of filter paper containing ackee apple milled seed before extraction (g) W2 = Weight of the filter paper and the content after drying (g), W = Weight of the milled ackee apple seed (g).

Transesterification of Blighia sapida oil
According to stoichiometry, one mole of triglyceride requires three moles of alcohol to produce methyl esters.However, the molar ratio for non-edible oil is usually higher (Thangarasu & Anand, 2019).Under controlled temperature and atmospheric pressure, Blighia sapida seed oil and methanol were transesterified in an autoclave reactor.The transesterification of Blighia sapida seed oil was investigated using the following parameters: reaction temperature of 60 to 70 °C, a reaction time of 60 to 120 minutes, catalyst concentration of 1 to 3 wt.%,and alcohol to oil molar ratio of 6:1 to 12:1.The experiment was designed using Design-Expert version 11.Box-Behnken design on a two-level-fourfactor was employed for the design, as shown in Table 1.The numeric factors were temperature, time, and catalyst amount coded as A, B, C, and D. The response factor was the biodiesel yield.Where: B.Y. = biodiesel yield (%) Mx = recovered biodiesel mass (g) My = mass of Blighia sapida seed oil (g) American Society for Testing and Materials (ASTM) standard test methods were used to determine the fuel properties of the biodiesel produced.

Characterized Ribbon vittata snail shell
The scanning electron microscopy (SEM) reveals the shell microstructure.The energydispersive electroscope (EDS) shows the shell elemental composition.Before calcination, the Ribbon vittata shell structure was irregular with no visible pores, as seen in Figure (1a).After calcination at 900 °C, the Ribbon vittata shell had regular rod-like particle shapes and became porous, as shown in Figure (1b).These pores created after calcination could be due to the release of CO2 present before calcination.Ca, O, and C are the significant elements from the EDS analysis.Other elements found in small quantities include Si, Fe, Na, Cl, and Al.EDS spectra of calcined Ribbon vittata shell at 900 °C from Figure 2 show Ca, O, and C as the only constituent elements.There was an increase in the percentage weight of Ca while O and C decreased in percentage weight.

Fuel properties of Blighia sapida oil
The percentage yield from the extracted Blighia sapida seed oil was 21.75%.This value is within the range of 12.5% -23.41% as recorded by [6]- [12].Fuel properties of Blighia sapida seed oil are presented in Table 2.

Biodiesel yield from Blighia sapida oil using Ribbon vittata calcined shell
The results of biodiesel yield from the transesterification of Blighia sapida seed oil using Ribbon vittata shell as the catalyst, as shown in Table (2).The highest yield of biodiesel, 93.54%, was recorded at temperature 65 °C, 120 min, a catalyst of 2 wt.%, and a 9:1 methanol to oil ratio.The lowest biodiesel yield, of 72.80%, was obtained at 75 °C, 75 min, 3 wt%, and 7.5:1 alcohol to oil ratio.The difference in biodiesel yields is due to the difference in reaction variables.The highest yield of 93.54% is within the range of 92.16%, 93.60%, and 92.7% by [13]- [15], respectively, using RSM for different feedstock.

Statistical analysis of the biodiesel yield
The Analysis of Variance (ANOVA) for the biodiesel production from ackee apple seed oil biodiesel is presented in Table 3.The coefficient of the quadratic polynomial equation for the biodiesel was determined from Table 3.The correlation between biodiesel yield, temperature, time, catalyst, and alcohol-to-oil ratio can be seen in Equation 3. Table 3 was generated with design expert software, and it indicates that the model is highly significant, with an F-value of 141.37 and a Prob>F value of less than 0.0001.The model is statistically significant as Prob>F is less than 0.05.Only AB and AD are negligible components in the model, as seen in Equation 4, and were deleted to simplify the model.

Reaction temperature
Viscosity was higher at a lower temperature of 60 °C; hence the low biodiesel yields.The higher viscosity could be due to low mass transfer between the reactant and the catalyst.When the temperature increased, there was an increase in biodiesel yield.The increase was attributable to a decrease in the mixture's viscosity.Figure 3 shows that the highest biodiesel output was obtained at 65 °C.At temperatures above 65 °C, the biodiesel yield declined and continued to 67.5 °C.There was a drastic decline in biodiesel yield between 67.5 °C and 70 °C.The decrease in biodiesel yield is due to the evaporation of methanol [16].Biodiesel yield of >95% was reported by [17] at a similar temperature of 65 °C.

Reaction time
Biodiesel yield increased with time from 60 min to 120 min.As seen in Figure 4, the highest biodiesel yield was achieved at 120 minutes, which was the equilibrium point.If the reaction is left to continue for a longer time, there will be a backward reaction resulting from the equilibrium being exceeded.Reduction in biodiesel yield is imminent once the reaction equilibrium is exceeded [18].The 120 min for the highest yield is similar to the time recorded by [19].

Catalyst loading
With catalyst loading between 1% and 1.5%, the mixture of catalyst and oil had a higher viscosity.This high viscosity made mixing difficult hence the reason for low biodiesel yield.The highest biodiesel yield was recorded when the catalyst amount was increased to 2%, as shown in Figure 5.The increase in the catalyst increased the total number of active sites hence the higher biodiesel yield.When the catalyst loading was further increased above 2%, there was a decline in biodiesel yield.The reduction in the yield was due to an increase in the mixture's viscosity [20].A 2% catalyst loading was recorded by [21] for the transesterification castor oil using a mussel shell as the catalyst.

Alcohol to oil molar ratio
There was a significant increase in biodiesel yield when the methanol/oil molar ratio was increased from 6 to 9.This increase was due to the forward shift in the equilibrium reaction.A decline in biodiesel yield was noticed when the methanol/oil molar ratio was further increased.At this point, the reaction is inhibited, possibly due to the glycerol dissolving in excess methanol [22].As shown in Figure 6, the highest biodiesel yield was recorded at a methanol/oil molar ratio of 9:1.[19] also reported alcohol to oil molar ratio of 9:1 for their work.

Physicochemical properties of Blighia sapida biodiesel
When compared to biodiesel, fossil diesel has a lower flash point.This is because of their low molecular weight and complex branching molecules [23].Although the flash point of Blighia sapida seed biodiesel falls short of the ASTM standard, it is greater than that of fossil diesel, making it safer to transport.After transesterification, the flash point of Blighia sapida seed oil was found to be lower.Transesterification also lowered the density of Blighia sapida seed oil.According to [24], biodiesel will allow complete combustion in diesel engines because the value is under the ASTM limit.When utilized in a diesel engine, the kinematic viscosity of Blighia sapida seed biodiesel implies that it will not leak in the fuel system and that the air-fuel mixing will not be delayed.The biodiesel's cetane number suggests that there will be no ignition delay, which is beneficial to fuel economy.It also means that there will be fewer emissions.The cetane number of the biodiesel product is 58.06, indicating that it can be used in colder areas.

Conclusion
Evaluation of the results from this study leads to the following conclusions: • The oil content of Blighia sapida seed oil indicates it is a good substitute for petroleum diesel.• The yield of biodiesel makes it a promising feedstock for biodiesel production.
• Ribbon vittata shell has a high content of calcium oxide, which is an excellent catalytic property in the transesterification of oils to produce biodiesel.• The use of Blighia sapida seed reduced the overall cost of biodiesel production since the seed is regarded as a waste.• The RSM proved effective in predicting optimum biodiesel yield from methanolysis of Blighia sapida seed oil.• The highest biodiesel yield of 93.54% was obtained with a reaction temperature of 65 °C, a reaction time of 120 min, a catalyst amount of 2 wt.%, and methanol to oil ratio of 9:1.• The fuel properties of Blighia sapida seed biodiesel produced were under ASTM standards.

Fig. 6 .
Fig. 6.Plot of biodiesel yield vs methanol to oil molar ratio.

Table 1 .
Box-Behnken design for independent variables and levels.With a controlled temperature, time, and stirring speed of 400 rpm, a mixture of Blighia sapida seed oil, calcined Ribbon vittata shell, and methanol was injected into the reactor.According to the design, the reaction parameters were changed.The product was then transferred to a separatory funnel and left to sit for 24 hours after the experiment.After removing the excess methanol and catalyst from the biodiesel, it was washed with warm distilled water and dried with anhydrous sodium sulphate.Equation 2 was used to calculate biodiesel yield.B. Y. =