# Transesterification Studies on Avocado Seed Oil Using Carbon Supported CuO Nano Catalyst: Rate Kinetics and Thermodynamic Aspects

Authors: Bashyam Sasikumar; Prabahar Jeevanandam; Venkatesh Babu Samikkannu; J. B. Veeramalini
Journal: Journal of Nanomaterials
 (2022)

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## Abstract

This study focused on the production of biodiesel using avocado seed oil (ASO) through esterification of free fatty acids (FFA) in the presence of carbon supported CuO nanoparticles (CuO/C). ASO was obtained using hexane as a solvent by Soxhlet extraction. Further characterization of ASO revealed that the oil had 8.2-10.2% (±0.2%) of FFA content. Using a two-step technique, the FFA content was decreased below 1% through esterification using a catalyst prepared from carbon supported nanoparticles of CuO. Additionally, CuO/C catalyst was characterized by different techniques, such as XRD and BET. From the investigations, the optimal time for the esterification process was found to be 6 h at 673 K. The use of carbon supported CuO nanoparticle for the transesterification process of ASO has not been attempted in earlier. Also, the studies on FFA present in the avocado seed oil had a significant outcome in this investigation. Further, the data observed from the reactions conducted at different temperatures were subjected for kinetic analysis to determine the reaction rate and thermodynamic study for activation energy.


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## Body

## 1. Introduction

At present, global energy requirement is accelerating daily. Undeniably, fossil fuels are depleting, which result in a serious look for alternative renewable fuels [1]. Alternative renewable fuels can be obtained from biogenic wastes and residues through chemical, biochemical, and thermochemical processing. In this view, a numerous researches are showing interest towards the synthesis biodiesel which refers to any diesel fuel substitute. Biodiesel is classified as a combustion fuel which derived from renewable resources that can be used in diesel engines. It is an environmentally friendly fuel equivalent to petroleum diesel [2–7]. As an alternative to fuel, biodiesel has many benefits over petroleum diesel. It is derived from a sustainable, domestic resource that relieves the dependence on imports of petroleum fuel. Biodiesel exhibits a more comfortable emission profile relative to petroleum fuel, such as low carbon monoxide emissions and particulate matter. Yet, another salient advantage of biodiesel are biodegradable, nontoxic, and unburned hydrocarbons. Furthermore, the CO2 expelled by the combustion process can be reused using photosynthesis technique. Hence, the greenhouse effect is reduced considerably [8]. However, the feedstock required for the production of biodiesel needs approximately 75% of the overall cost. The biodiesel feedstocks are selected based on some notable properties of the oil such as low price, good free fatty acid content and high content of oil, low cost for cultivation, controllable growth and effective harvesting, rate of maturity of the seeds, and comparable better market for byproducts [9, 10].Biodiesel holds many advantages because of its significant molecular similarities between biodiesel and paraffinic diesel fuel compounds, which makes a suitable alternative fuel that likely to meet the diesel engine’s fuel requirements. Basically, there is no need for engine modifications to replace biodiesel with diesel fuel that can improve the performance of the IC engine. Further, the biodiesel has superior lubricating property, but no nonparticulate matter pollutants, aromatic content, and sulfur content which produce lesser toxic emissions.Still now, biodiesel produced from different edible oils was not yet attained successfully worldwide since the cost of production is very high due to the elevated budget of raw materials and food security; consequently, a look for cutting-edge low price nonedible feedstock goods for biodiesel production still continues. In this regard, avocado seed oil (ASO) can be a promising feedstock for biodiesel production due to its low price. It comprises with 80% of unsaturated fatty acids. Hence, a significant content of the fatty acid can aid to increase the value of cloud point and cetane number for the biodiesel [11].Generally, an ASO extracted by cold press method contains a significant content of free fatty acids that provides better appropriateness for esterification. However, with the excess of poly unsaturation, cloud point, cetane number, and stability of the biodiesel may be decreased. Hence, a suitable alkali or acid is used as a catalyst during the transesterification process to yield biodiesel. Due to their lower catalyst cost and shorter reaction time, alkali route is more preferable than the acid route. Commonly, palm oil, soybean oil, and rapeseed oil are the widely used as biodiesel feedstock. The alkali route shows high sensitivity to both water and FFA [12–14]. The performance of catalytic activity for the nanoparticles has been observed better than the solid catalysts due to its special characteristic of high surface to volume ration. Also, the nanoparticles have shown relatively high rate of the reaction. However, the immobilization of the nanoparticles in the reaction mixture is found to be difficult task. Hence, several researches have been undertaken to immobilization of nanoparticles to carry out the reaction. In such a way, this study focused to immobilize the CuO nanoparticles using carbon support.So far, no detailed studies using avocado seed oil have not been conducted towards the biodiesel production. Moreover, the investigations on the CuO/C catalyst have not been studied on the ASO. In addition, the attempt on the kinetics of the reactions also needs further scale-up process. Keeping this novel view, the present study aimed to use the carbon supported CuO nanoparticles (CuO/C) as a catalyst for esterification of the FFA present in the ASO. Additionally, the rate kinetic studies and thermodynamic studies were performed for the esterification reaction.


## 2. Materials and Methods

### 2.1. Raw Materials, Apparatus, Chemicals, and Reagents

Avocado seeds were collected at a local plantation and gently washed with pure double distilled water to remove all unwanted impurities and dust. Rota evaporator, grinding mill, heater, water bath, and coffee miller were used wherever it needs. Mass spectroscopy gas chromatography, digital balance, vibro-viscometer, condenser, Soxhlet apparatus, hot air oven, and pH monitors were also used. Methanol,n-hexane, NaOH, copper (II) n nitrate (CN), NaBH4, and CuCl2.2H2O were purchased from Merck (Addis Ababa, Ethiopia) and HiMedia Laboratories Private Ltd. (Addis Ababa, Ethiopia). They were of analytical reagent. Double distilled water was used without further purification.


### 2.2. Preparation of ASO

Avocado seeds were collected and subjected to dry for a day. Then, skins on the seeds were carefully expelled from the kernel. The known weight of seed sample was investigated for the moisture content. The moisture content was ascertained using an oven drying method at 100 °C for 2 h to allow the mass loss by evaporation. Then, the seeds were crushed by using laboratory blender. To increase the volume to surface ratio, crushed seeds subjected to make until the particle size reached to desired point. The obtained powder was sieved using a laboratory sieves (ASTM) for segregate different particle size. Accordingly, the plant materials were ranged from 0.15 to 1. 5 mm. Resulted seed sample powder was kept at 4 °C for the experiments [15, 16]. In this present study, mechanical pressing method was used to extract the ASO. In this method, oil was forced out from the avocado seeds by applying pressure. For this purpose, an oil extracting machine was used (GT-OT-T600, Gorek Tech). The pressure was linearly increased up to 60-70 kgf/m2 within 10-15 min. Using a screw press, it obtained a better yield of ASO. It was found that ASO extraction by this mechanical pressing removed only 45% of the oil. The remaining oil was extracted by Soxhlet method; ASO was extracted from the seeds. About 20 g of crushed seed sample was fed to Soxhlet extractor setup with a 250-ml round bottom flask. Further, 200 ml of n-hexane (food grade solvent) was added into the distillation set-up. Extraction process was carried out at 344.15 K for 360 min. After extracting, the flask allowed to cool to room temperature. In order to evaporate the additional solvent, water bath was used and excess solvent (n-hexane) was removed at 70 °C. Because of the oil has less volatility, they can retain in the experimental flask [17]. The extracted oil was observed to be golden yellowish color. This mixture was kept to settle for 4 h, and the resulted oil as extract was collected. This essential oil was kept in a refrigerator at 4 °C for purification and characterization [18]. Figure 1 depicts the avocado seed and extracted ASO.Figure 1
Image of the avocado seed and the extracted ASO.


### 2.3. Catalyst Preparation

Initially, the prepared copper nanoparticles were well-dissolved in polyvinyl alcohol (1%), further, deionized water was added to get the appropriate solution. Next, ascorbic acid was added to the PVA solution for maintaining the pH of the solution. After that, copper chloride dihydrate salt and CuCl2 2H2O (0.732 mmol in 2 ml deionized water) were added to the 50 ml PVA solution. It was dissolved into the aqueous solution of PVA by vigorously stirring to maintain 0.0148 M CuCl2·2H2O solution. At this stage, the solution color changed from blue to light yellow. Further, a NaBH4 solution (8.796 mmol) was added drop by drop with the previously prepared precursor solution under gentle stirring. At this stage, color of aqueous phase changed from light yellow to wine red. The occurrence of such a darkness revealed that the reduction reaction had taken place. Further, the mixture was then quickly stirred for about 15-17 min in the ambient atmosphere to complete the reaction and dried in a vacuum oven at 75 °C. The CuO/C catalysts were prepared by carrying out the reaction of activated carbon with CuO NP. CuO/C was prepared by mixing activated carbon with 10% Cu NP solution at 60 °C for 2 h to remove the water. The gel type mixture was placed inside furnace at 400 °C for 6 h. The dry crystalline catalyst was obtained after furnace process.


### 2.4. Characterization of Catalyst

To evaluate the BET surface and pore volume, the nitrogen isotherms of adsorption/striping were obtained using a porometer (US Micrometrics ASAP 2010, American Micrometrics). Prepared catalyst was subjected in to XRD analysis and the observed patterns were recorded. Using a “DiffracPlus” program, the collected data were analyzed. Further, the power diffraction database was examined for the stages.


### 2.5. Esterification of ASO

Esterification was carried out in 500-ml round bottom flasks. The reaction temperature was maintained at 80 °C using a water bath. The mole ratio of RSO to methanol was taken as 1 : 10 with oil to catalyst ratio 1 : 10 (in terms of weight).


## 2.1. Raw Materials, Apparatus, Chemicals, and Reagents

Avocado seeds were collected at a local plantation and gently washed with pure double distilled water to remove all unwanted impurities and dust. Rota evaporator, grinding mill, heater, water bath, and coffee miller were used wherever it needs. Mass spectroscopy gas chromatography, digital balance, vibro-viscometer, condenser, Soxhlet apparatus, hot air oven, and pH monitors were also used. Methanol,n-hexane, NaOH, copper (II) n nitrate (CN), NaBH4, and CuCl2.2H2O were purchased from Merck (Addis Ababa, Ethiopia) and HiMedia Laboratories Private Ltd. (Addis Ababa, Ethiopia). They were of analytical reagent. Double distilled water was used without further purification.


## 2.2. Preparation of ASO

Avocado seeds were collected and subjected to dry for a day. Then, skins on the seeds were carefully expelled from the kernel. The known weight of seed sample was investigated for the moisture content. The moisture content was ascertained using an oven drying method at 100 °C for 2 h to allow the mass loss by evaporation. Then, the seeds were crushed by using laboratory blender. To increase the volume to surface ratio, crushed seeds subjected to make until the particle size reached to desired point. The obtained powder was sieved using a laboratory sieves (ASTM) for segregate different particle size. Accordingly, the plant materials were ranged from 0.15 to 1. 5 mm. Resulted seed sample powder was kept at 4 °C for the experiments [15, 16]. In this present study, mechanical pressing method was used to extract the ASO. In this method, oil was forced out from the avocado seeds by applying pressure. For this purpose, an oil extracting machine was used (GT-OT-T600, Gorek Tech). The pressure was linearly increased up to 60-70 kgf/m2 within 10-15 min. Using a screw press, it obtained a better yield of ASO. It was found that ASO extraction by this mechanical pressing removed only 45% of the oil. The remaining oil was extracted by Soxhlet method; ASO was extracted from the seeds. About 20 g of crushed seed sample was fed to Soxhlet extractor setup with a 250-ml round bottom flask. Further, 200 ml of n-hexane (food grade solvent) was added into the distillation set-up. Extraction process was carried out at 344.15 K for 360 min. After extracting, the flask allowed to cool to room temperature. In order to evaporate the additional solvent, water bath was used and excess solvent (n-hexane) was removed at 70 °C. Because of the oil has less volatility, they can retain in the experimental flask [17]. The extracted oil was observed to be golden yellowish color. This mixture was kept to settle for 4 h, and the resulted oil as extract was collected. This essential oil was kept in a refrigerator at 4 °C for purification and characterization [18]. Figure 1 depicts the avocado seed and extracted ASO.Figure 1
Image of the avocado seed and the extracted ASO.


## 2.3. Catalyst Preparation

Initially, the prepared copper nanoparticles were well-dissolved in polyvinyl alcohol (1%), further, deionized water was added to get the appropriate solution. Next, ascorbic acid was added to the PVA solution for maintaining the pH of the solution. After that, copper chloride dihydrate salt and CuCl2 2H2O (0.732 mmol in 2 ml deionized water) were added to the 50 ml PVA solution. It was dissolved into the aqueous solution of PVA by vigorously stirring to maintain 0.0148 M CuCl2·2H2O solution. At this stage, the solution color changed from blue to light yellow. Further, a NaBH4 solution (8.796 mmol) was added drop by drop with the previously prepared precursor solution under gentle stirring. At this stage, color of aqueous phase changed from light yellow to wine red. The occurrence of such a darkness revealed that the reduction reaction had taken place. Further, the mixture was then quickly stirred for about 15-17 min in the ambient atmosphere to complete the reaction and dried in a vacuum oven at 75 °C. The CuO/C catalysts were prepared by carrying out the reaction of activated carbon with CuO NP. CuO/C was prepared by mixing activated carbon with 10% Cu NP solution at 60 °C for 2 h to remove the water. The gel type mixture was placed inside furnace at 400 °C for 6 h. The dry crystalline catalyst was obtained after furnace process.


## 2.4. Characterization of Catalyst

To evaluate the BET surface and pore volume, the nitrogen isotherms of adsorption/striping were obtained using a porometer (US Micrometrics ASAP 2010, American Micrometrics). Prepared catalyst was subjected in to XRD analysis and the observed patterns were recorded. Using a “DiffracPlus” program, the collected data were analyzed. Further, the power diffraction database was examined for the stages.


## 2.5. Esterification of ASO

Esterification was carried out in 500-ml round bottom flasks. The reaction temperature was maintained at 80 °C using a water bath. The mole ratio of RSO to methanol was taken as 1 : 10 with oil to catalyst ratio 1 : 10 (in terms of weight).


## 3. Results and Discussion

Table1 displays the physicochemical properties of the ASO used in the present study, and the properties of ASO reported elsewhere in the literature [16]. Many reports were documented on the appropriateness and suitability of ASO to prepare biodiesel using different catalysts. However, the physicochemical properties of ASO observed from this study have well supported with the results reported by Kaur et al. [17]. Thus, the reliability and viability of obtained ASO were ensured for the further esterification process.Table 1
Physicochemical properties of ASO.
PropertiesExperimental value for ASOAV (mg KOH/g)82.654PV (mg/g)3.5625FFA (wt. %)40.9284IV (mg/I₂/g oil)119.685v (mm2/s)42.147SG0.910HHV (MJ/kg)38.98AV: acid value; PV: peroxide value; FFA: free fatty acids; IV: iodine value;v: viscosity; SG: specific gravity; and HHV: high heating value.The esterification reaction using free fatty acids (FFA) and methanol is represented in Eq. (1)[18].


## 4. Characterization of Prepared Catalyst

### 4.1. BET Analysis

Brunauer-Emmett-Teller method was employed to determine the porosity and precise surface area of the prepared catalysts. In order to conduct textural analysis, a surface area and porosity analyzer were used (BELSORP, MAX G Model). The BET surface area graph is shown in Figure2. The physicochemical assessments of the catalyst are presented in Table 2.Figure 2
BET graph for carbon-supported copper oxide catalyst (CuO/C).Table 2
Typical physicochemical characteristics of the prepared samples.
SampleExternal area(m2g-1)Extreme opening diameter (m)Volume of pore (cm3g-1)CuO/C985.741121.33090.5257


### 4.2. XRD Analysis

Figure3 illustrates the X-ray diffraction pattern of the CuO/C nanoparticles. Copper oxide and the sharp peaks of XRD were compatible with the XRD peak positions indicating the crystalline character. The peaks observed in 2θ=35.043°, 38.521°, 48.467°, 53.81°, 57.97°, and 61.14° correspond to (002,111), (111,200), (202), (020), (202), and (113) Bragg’s representations of CuO’s monoclinic structure, respectively.Figure 3
XRD pattern of CuO/C catalyst.


### 4.3. Influence of Time on FF Conversion with and without Catalyst

The FFA conversion based on the presence of catalyst was examined. As revealed in Figure4, the esterification reaction did not occur in absence of a catalyst which was consistent with the results recorded. On other hand, a significant conversion of FFA by esterification was observed when the reaction was conducted with catalyst CuO/C. During the reaction, it was found that the maximum FFA of 91.446% was converted at 210 min. Hence, the optimal time needed for the ASO esterification reaction was observed to be 210 min. Beyond this, reaction time there was no significant conversion was not found.Figure 4
Conversion of FFA with catalyst and without catalyst (catalyst: CuO/C; reaction temperature: −75 °C; mass quantity: 10% catalyst; and methanol to FFA ratio: −10 : 1). Black diamond indicates with catalyst, and black box indicates without catalyst.


### 4.4. Influence of Temperature on FFA Conversion

The reaction temperature is one of the important factors which can influence the rate of esterification. In order to examine the influence of temperature on the esterification, reactions at different temperatures (30 to 75 °C) were carried out. Catalyst concentration also plays an important role on conversion of FFA to methyl ester. Hence, the catalyst to oil weight ratio (1 : 10) was kept constant. Figure5 shows the results of FFA conversion on different temperatures which were carried out among the temperature range 30-75 °C. In this esterification, reaction time has significant effect on conversion. Figure 5 demonstrated that certain time interval increases the reaction conversion, but the catalyst activity was observed to be higher at 75 °C compared to other reactions. The response degree (conversion) can remain increased rapidly by increasing the temperature. It clearly showed that the catalyst activity was found to be increased while increasing the reaction temperature. From the results, the maximum conversion was improved significantly from 58.56% to 91.446%, while the reaction temperature increases from 35 °C to 75 °C at 210 min. Further increase in time, the conversion was found to be constant and did not get any change. It is clear that the optimum reaction time for the esterification reaction was 210 min to complete the esterification reaction which results a maximized yield.Figure 5
Impact of temperature on FFA conversion (reaction time, 420 to 720 min; mass catalyst concentration, 10%; methanol/FFA, 10 : 1). Black diamond: 30 °C; black box, 50 °C; black circle 75 °C.


### 4.5. Kinetic Studies

The standard esterification reaction (Eq. (1)) based on the Langmuir-Hinshelwood (LH) mechanism is well known:
(1)FFA+Me−OH+CuO/C⟶R1−COOH+CH3OHR1−COOCH3+H2OFrom Arrhenius equation, we get Equation (2):
(2)k1t=1aα−βlnX−αX−β⋯⋯.By using Eq. (2) ,we get the value of the equilibrium constant K. At the start of reaction, t=t0, CFFAt=CFFA0=0.2636mol/dm3, CFAMEt=CFAME0=0,CWt=CW0=0, and CMeOH0=7.554mol/dm3; and at t=t∞, CFFAt=CFFAe=0.0180mol/dm3, CFAMEt=CFAMEe=CFFA0–CFFAt=0.2456mol/dm3,CWt=CWe=0.2456mol/dm3, and CMeOHe=CMeOH0–CFAMEe=7.3084mol/dm3.From the above equilibrium data substitution in Eq. (2), the obtained Kvalue is 0.4585. A scheme of tversus 1/aα−βlnX−α/X−β remains a straight forward route, and slope of curve gives a rate of the straight reaction constant k1 (Figure 6). The rate of constant for the particular temperature and catalyst concentration is given in Table 3. The reaction was carried out at methanol to FFA molar proportion of 10 : 1.Figure 6
A graph oft versus 1/aα−βlnX−α/X−β (75 °C, CuO/C).Table 3
Reaction rate constant for the particular temperature and catalyst.
Reaction conditionk1 (min-1)75 °C (Cu NP as catalyst)0.9369Graphical representation of Eq. (1) gives a curve which represents conversion with respect to time (the dense line represents theoretical conversion, and the points represent experimental conversion). The curves for different reaction conditions are given in Figure 7 for different temperatures and different catalyst types, respectively. Thermodynamics explains the relationship work, heat, and energy. In the present study, temperature and heat play a key role for the esterification reaction. Hence, thermodynamic study is a must to deal for the determination of energy requirement and to define the amount of mechanical work. The influence of temperature can be assessed by evaluating the activation energy required for the reaction. In order to calculate the activation energy, Arrhenius equation was used which is given in Eq. (2).
(3)K=Ae−Eact/RT⋯⋯⋯⋯⋯⋯⋯⋯⋯Figure 7
The Arrhenius plot for activation energy determination.By solving this equation, we get(4)lnK=−EactR1T+lnA⋯⋯⋯⋯,where Kis reaction rate constant, A is constant, Eact is activation energy, T is the temperature, and R is the gas constant. The plot of ln K vs T-1 (Figure 6) was generated, and the values for A and Eact were determined from intercept and slope, respectively. From the results, slope was found to be 0.2622 and the activation energy is calculated to be −2.180 J/mol K.


## 4.1. BET Analysis

Brunauer-Emmett-Teller method was employed to determine the porosity and precise surface area of the prepared catalysts. In order to conduct textural analysis, a surface area and porosity analyzer were used (BELSORP, MAX G Model). The BET surface area graph is shown in Figure2. The physicochemical assessments of the catalyst are presented in Table 2.Figure 2
BET graph for carbon-supported copper oxide catalyst (CuO/C).Table 2
Typical physicochemical characteristics of the prepared samples.
SampleExternal area(m2g-1)Extreme opening diameter (m)Volume of pore (cm3g-1)CuO/C985.741121.33090.5257


## 4.2. XRD Analysis

Figure3 illustrates the X-ray diffraction pattern of the CuO/C nanoparticles. Copper oxide and the sharp peaks of XRD were compatible with the XRD peak positions indicating the crystalline character. The peaks observed in 2θ=35.043°, 38.521°, 48.467°, 53.81°, 57.97°, and 61.14° correspond to (002,111), (111,200), (202), (020), (202), and (113) Bragg’s representations of CuO’s monoclinic structure, respectively.Figure 3
XRD pattern of CuO/C catalyst.


## 4.3. Influence of Time on FF Conversion with and without Catalyst

The FFA conversion based on the presence of catalyst was examined. As revealed in Figure4, the esterification reaction did not occur in absence of a catalyst which was consistent with the results recorded. On other hand, a significant conversion of FFA by esterification was observed when the reaction was conducted with catalyst CuO/C. During the reaction, it was found that the maximum FFA of 91.446% was converted at 210 min. Hence, the optimal time needed for the ASO esterification reaction was observed to be 210 min. Beyond this, reaction time there was no significant conversion was not found.Figure 4
Conversion of FFA with catalyst and without catalyst (catalyst: CuO/C; reaction temperature: −75 °C; mass quantity: 10% catalyst; and methanol to FFA ratio: −10 : 1). Black diamond indicates with catalyst, and black box indicates without catalyst.


## 4.4. Influence of Temperature on FFA Conversion

The reaction temperature is one of the important factors which can influence the rate of esterification. In order to examine the influence of temperature on the esterification, reactions at different temperatures (30 to 75 °C) were carried out. Catalyst concentration also plays an important role on conversion of FFA to methyl ester. Hence, the catalyst to oil weight ratio (1 : 10) was kept constant. Figure5 shows the results of FFA conversion on different temperatures which were carried out among the temperature range 30-75 °C. In this esterification, reaction time has significant effect on conversion. Figure 5 demonstrated that certain time interval increases the reaction conversion, but the catalyst activity was observed to be higher at 75 °C compared to other reactions. The response degree (conversion) can remain increased rapidly by increasing the temperature. It clearly showed that the catalyst activity was found to be increased while increasing the reaction temperature. From the results, the maximum conversion was improved significantly from 58.56% to 91.446%, while the reaction temperature increases from 35 °C to 75 °C at 210 min. Further increase in time, the conversion was found to be constant and did not get any change. It is clear that the optimum reaction time for the esterification reaction was 210 min to complete the esterification reaction which results a maximized yield.Figure 5
Impact of temperature on FFA conversion (reaction time, 420 to 720 min; mass catalyst concentration, 10%; methanol/FFA, 10 : 1). Black diamond: 30 °C; black box, 50 °C; black circle 75 °C.


## 4.5. Kinetic Studies

The standard esterification reaction (Eq. (1)) based on the Langmuir-Hinshelwood (LH) mechanism is well known:
(1)FFA+Me−OH+CuO/C⟶R1−COOH+CH3OHR1−COOCH3+H2OFrom Arrhenius equation, we get Equation (2):
(2)k1t=1aα−βlnX−αX−β⋯⋯.By using Eq. (2) ,we get the value of the equilibrium constant K. At the start of reaction, t=t0, CFFAt=CFFA0=0.2636mol/dm3, CFAMEt=CFAME0=0,CWt=CW0=0, and CMeOH0=7.554mol/dm3; and at t=t∞, CFFAt=CFFAe=0.0180mol/dm3, CFAMEt=CFAMEe=CFFA0–CFFAt=0.2456mol/dm3,CWt=CWe=0.2456mol/dm3, and CMeOHe=CMeOH0–CFAMEe=7.3084mol/dm3.From the above equilibrium data substitution in Eq. (2), the obtained Kvalue is 0.4585. A scheme of tversus 1/aα−βlnX−α/X−β remains a straight forward route, and slope of curve gives a rate of the straight reaction constant k1 (Figure 6). The rate of constant for the particular temperature and catalyst concentration is given in Table 3. The reaction was carried out at methanol to FFA molar proportion of 10 : 1.Figure 6
A graph oft versus 1/aα−βlnX−α/X−β (75 °C, CuO/C).Table 3
Reaction rate constant for the particular temperature and catalyst.
Reaction conditionk1 (min-1)75 °C (Cu NP as catalyst)0.9369Graphical representation of Eq. (1) gives a curve which represents conversion with respect to time (the dense line represents theoretical conversion, and the points represent experimental conversion). The curves for different reaction conditions are given in Figure 7 for different temperatures and different catalyst types, respectively. Thermodynamics explains the relationship work, heat, and energy. In the present study, temperature and heat play a key role for the esterification reaction. Hence, thermodynamic study is a must to deal for the determination of energy requirement and to define the amount of mechanical work. The influence of temperature can be assessed by evaluating the activation energy required for the reaction. In order to calculate the activation energy, Arrhenius equation was used which is given in Eq. (2).
(3)K=Ae−Eact/RT⋯⋯⋯⋯⋯⋯⋯⋯⋯Figure 7
The Arrhenius plot for activation energy determination.By solving this equation, we get(4)lnK=−EactR1T+lnA⋯⋯⋯⋯,where Kis reaction rate constant, A is constant, Eact is activation energy, T is the temperature, and R is the gas constant. The plot of ln K vs T-1 (Figure 6) was generated, and the values for A and Eact were determined from intercept and slope, respectively. From the results, slope was found to be 0.2622 and the activation energy is calculated to be −2.180 J/mol K.


## 5. Conclusions

In this study, biodiesel was synthesized using avocado seed oil. The use of carbon supported CuO nanoparticle for the transesterification process of ASO has not been attempted in earlier. Also, the studies on FFA present in the avocado seed oil had a significant outcome in this investigation. In this present study, mechanical pressing method was used to extract the ASO. The oil was extracted using a machine by applying a pressure up to 60-70 kgf/m2. Such a mechanical press method reseulted in 45% of oil yeild. The carbon supported nano CuO (CuO/C) was prepared and used as catalyst. CuO/C catalyst was prepared using activated carbon and with 10% of CuO nanoparticles. Further, the catalyst was characterized using XRD and BET techniques. The esterification was carried out using methanol at 1 : 10 oil to catalyst weight ratio. The investigation on different temperatures explicated that the catalyst activity was observed to be more at 75 °C. From the findings, it was cleared that avocado kernel oil can be used potential feedstock for biodiesel production.



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*Source: 5192239-2022-07-25.xml*