Biodiesel and Biolubricant Production from Waste Cooking Oil: Transesterification Reactor Modeling

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This research work provides information about the conceptual design of a batch reactor to produce biodiesel and biolubricants from waste cooking oil at a commercial scale using a two-step transesterification process catalyzed by sodium methoxide.

Abstract

Biodiesel and biolubricants play strategic roles in green technologies, as they can be produced in biorefineries. The design of industrial facilities is essential to assess the industrial implementation of these processes, with few studies about this subject in the literature. The aim of this work was to produce biodiesel and a biolubricant from waste cooking oil through double transesterification with methanol and trimethylolpropane, obtaining high conversion values (>97 and 98%, respectively). The biolubricant (characterized according to the UNE-14214 standard) had a density of 951 kg·m⁻³, a viscosity of 127 cSt (at 40 °C), an acidity value of 0.43 mgKOH·g⁻¹, flash and combustion points of 225 and 232 °C, and an oxidation stability of 6 h through the Rancimat method. Also, a kinetic study was carried out (at temperatures ranging from 80 to 140 °C and with catalyst concentrations from 0.3 to 0.9% w/w and working pressures from 210 to 760 mmHg) to establish the main kinetic parameters, obtaining a second-order reaction and an activation energy of 17.8 kJ·mol⁻¹. Finally, a conceptual design was included, considering the main components of the facility. Thus, the projected plant worked in a discontinuous regime (producing 2 cubic meters per day), pointing out the feasibility of this plant at an industrial scale.

1. Introduction

Because of the pollution derived from traditional industrial practices, along with the depletion of energy sources, such as oil, there is an increasing environmental concern, which is pointed out in different policies, like Sustainable Development Goals [1]. The environmental impact of fossil fuels has provoked the reactions of international agencies with different agendas, such as the transition toward renewable energies (so-called climate technologies, such as wind energy, solar power, or hydropower) through decarbonization, as promoted by the United Nations’ Framework Convention on Climate Change, which claims that there is a lot of work to do to complete this energy transition, according to the UN Climate Change Conference in Baku [2]. There is still a global dependence on petrol-based industries, requiring further efforts for the implementation of green technologies. Global renewable sources represent 30% of the energy consumption in the electricity sector, with room for improvement in the heating and transportation sectors [1]. Spain is, equally, in an initial transition stage, increasing the production and consumption of renewable energies (at around 20%). However, as observed in Figure 1, oil is still the most consumed primary energy source in this country (Figure 1a). Thus, increased efforts should be made to reduce oil dependence. According to Figure 1b, different renewable energy sources seem to play important roles in Spain, such as wind energy, photovoltaic and thermal solar energy, or biomass, whereas other sources, like seawater, geothermal energy, biogas, or biofuels, could considerably contribute to a greener transition, as there is room for improvement in these sectors.

Regarding biofuels and other bioproducts, they can constitute a sound alternative for those derived from petrol, with biodiesel and biolubricants playing important roles. Specifically, a wide range of vegetable oils (such as soybean [4,5], rapeseed [6,7], corn [8,9], or palm oils [10,11]) or animal fats [12,13,14] have been used for the synthesis of these products through different methods, such as transesterification or epoxidation among others [15,16]. The role of waste cooking oil in Spain could be promising, as its reuse is considerable in the service sector (above 70%), whereas it is reduced in households (5%). In total, around 350 million liters of WCO are generated yearly [17].

Concerning transesterification, it is an interesting process for biodiesel and biolubricant production, as double transesterification with methanol (or ethanol) and a superior alcohol (such as trimethylolpropane, TMP, or pentaerythritol, PE) could be the starting point for the implementation of a biorefinery. Thus, different valuable products (such as biodiesel, glycerol, or biolubricants) could be produced from natural sources, like vegetable oils, animal fats, or even microalgae, with intermediate products that can be reused. That is the case for methanol, which is generated in transesterification to produce biolubricants and can be reused in the first transesterification of fatty acids to obtain fatty acid methyl esters [18,19]. Even though the products obtained in this biorefinery context have very interesting and sustainable properties, such as high biodegradability or low environmental impact during their production, some challenges should be overcome, like low oxidation stability because of the presence of double bonds in their final molecular structures. Different measures can be taken to avoid this problem, like the selection of vegetable oils with high oleic and palmitic acid contents or the addition of antioxidants, like propyl gallate (PG) [20], tert-butylhydroquinone (TBHQ) [21,22], or natural antioxidants/green additives [23,24].

Different kinds of waste can be used for biolubricant production, as in the case of waste cooking oil (WCO), which is a waste with difficult environmental management. Accordingly, great interest has arisen on this subject, with multiple studies devoted to the valorization of WCO for biodiesel and biolubricant production. Specifically, transesterification of WCO methyl esters with several alcohols to produce biodiesel [25] or biolubricants has been studied, offering a similar performance compared to those of standard products found on the market [26]. Another study focused on transesterification of WCO fatty acid methyl esters with trimethylolpropane (TMP), observing high yields (above 85%) and requiring the addition of antioxidants to improve the oxidation stability [27]. Furthermore, heterogeneous catalysts, like hydrotalcite loaded with potassium carbonate, were applied to the transesterification of WCO FAMEs with TMP, showing high FAME conversion rates (above 95%) and requiring the reactivation of the catalyst through calcination [28]. In this sense, the use of lipase in esterification processes was also effective, with yields and selectivity values above 80% [29]. Similarly, a magnetic cross-linked enzyme aggregate of Eversa was used in the enzymatic synthesis of biolubricants by transesterification of WCO with several alcohols, such as isoamyl alcohol. As a result, maximum yields of around 90% were achieved [30]. Other chemical routes (hydrolysis, dehydration/ketonization, Friedel–Crafts acylation/alkylation, and mild hydrotreatment) are possible for biolubricant production from WCO, as pointed out by some authors [31].

Other works are devoted to the optimization of biolubricants based on WCO, which is an important step for the possible implementation of this technology at an industrial scale. Some studies focused on the optimization of the esterification of free fatty acids from WCO with octanol, using Novozyme 435 as a catalyst. Thus, Taguchi’s design method was selected, offering high conversion (95%) under the optimized reaction conditions [32]. In a similar way, the effect of water on hydrolysis, as well as those of other parameters, such as the octanol molar ratio, temperature, stirring rate, or catalyst amount, were determined in WCO hydrolysis and esterification with octanol to produce biolubricants, with a total conversion for this purpose [33].

Finally, the possible implementation of this technology in industrial plants has been accomplished in some works. For instance, biolubricant production from WCO through transesterification with ethylene glycol was studied, simulating the process at an industrial scale, with encouraging results that prove the possible applicability of this process [34]. Equally, the optimization and simulation of biolubricant production through transesterification of a mixture of FAMEs (from animal fats and waste cooking oil) with ethylene glycol were carried out, obtaining high yields (above 90%) and indicating that this process could be applied at an industrial scale. For this purpose, a Box–Behnken design was carried out [35]. It should be noted that WCO, in general, presents a variable composition depending on culinary habits. For instance, WCO in Europe might vary compared to WCO in Asia (where other vegetable oils, such as palm oil, can be the majority). Consequently, the fatty acid content of WCO might vary. For instance, oleic acid (from 0.8 to 18%), palmitic acid (from 0.4 to 43%), or linoleic acid (from 0.1 to around 34%) compositions present a wide range depending on the kind of sample [36]. This fact points out the requirement of a thorough characterization of WCO, especially the fatty acid composition, to understand the properties of the raw material used in this process and, subsequently, the design of plants based on these sources.

Even though some studies have attempted the total or partial design of this kind of plant (especially concerning the reactor design for biolubricant production [37]), works devoted to the design of chemical plants for the implementation of this technology at an industrial scale are not commonly found in the literature, presenting a great opportunity to spread knowledge about this field, where multiple disciplines (such as chemical engineering or chemistry) play important roles. It is especially interesting because of the multiple variables affecting biolubricant production, where the nature of the raw material and, especially, the selected alcohol play important roles in kinetics and conversion. Therefore, each case presents particularities that require a thorough study of each process, with the subsequent relevance of studies that can complete and extend the knowledge about the design of plants based on such heterogeneous raw materials.

Considering the above, the aim of this work was to produce biodiesel and a biolubricant from waste cooking oil. Thus, the main operating conditions at a laboratory scale were covered, with the subsequent design of a plant devoted to biolubricant production. Specifically, the objectives were the following:

• Fatty acid methyl ester (biodiesel) production using a first transesterification with methanol and waste cooking oil, including its characterization according to the UNE-EN 14214 standard;
• Biolubricant production through double transesterification of fatty acid methyl esters with 2-ethyl-2-hydroxymethyl-1,3-propanediol, with a study about the effects of the temperature, pressure, and catalyst concentration on the conversion. The viscosity and oxidation stability, among others, were determined;
• Improvement of the oxidation stability of the biolubricant by antioxidant addition;
• Kinetic study of the second transesterification of FAMEs;
• Preliminary design and economic feasibility study of an industrial plant for biodiesel and biolubricant production, with a special focus on the reactor design.

2. Materials and Methods

The procedures followed in this work were similar to those included in previous research [38], with slight modifications, which will be specified in the following subsections:

2.1. Waste Cooking Oil

Waste cooking oil (WCO) was collected from hotels, restaurants, bars, and private households in Badajoz (Spain). All the samples were blended together to obtain a composite sample, which was filtered with filter paper to remove possible food waste and dried to avoid moisture. The acidity of the WCO composite sample was as low as 1.2%; therefore, the WCO composite sample was suitable for further processing into biodiesel and the biolubricant. The samples were stored in 25 L opaque tanks at room temperature until their further use.

2.2. Biodiesel and Biolubricant Production

Biodiesel was obtained from WCO at a lab scale, following a transesterification process described elsewhere [39]. Thus, about 450 g of WCO was allowed to react with methanol (pure, pharma grade, Panreac Applichem, Barcelona, Spain) in the presence of sodium methoxide (30% in methanol, Merck, Darmstadt, Germany) as a catalyst. The process conditions were as follows: methanol/WCO mass ratio = 6; catalyst concentration = 1% w/w; reaction time = 90 min; reaction temperature = 60 °C; stirring rate = 350 rpm. After the programmed reaction time, several washing steps were carried out with distilled water until a neutral pH was obtained for the spent distilled water. Thus, a biodiesel sample was obtained as a mixture of fatty acid methyl esters (FAMEs). Finally, biodiesel samples were dried at 110 °C and stored in opaque containers for further characterization or processing. These samples were labeled as WCO-FAMEs. For biolubricant production, around 250 g of the WCO-FAME samples were added to a thermoregulated batch reactor coupled to a vacuum pump and a methanol collector. Trimethylolpropane (TMP, pure, analytical grade, Merck, Darmstadt, Germany) and sodium methoxide (i.e., the catalyst) were added to the reactor to start the transesterification of the WCO-FAMEs to the biolubricant.

Table 1. Operating conditions for biolubricant production from WCO.

Parameter	Value
WCO FAME/TMP ratio	3
Catalyst concentration, %	0.3–1.0
Reaction time, min	120
Reaction temperature, °C	80–140
Stirring rate, rpm	350
Working pressure, mmHg	210–760

summarizes the process conditions used for biolubricant production.

Once the reaction time had elapsed, the resulting biolubricant was filtered through filter paper to remove unreacted TMP. The final biolubricant (labeled as WCO-TMP) was stored in opaque containers for further characterization.

Different experiments were carried out to assess the effects of the pressure (210, 360, 510, and 760 mmHg), temperature (80, 100, 120, and 140 °C), and catalyst concentration (0.3, 0.5, 0.7, and 0.9% w/w) on the conversion of the FAMEs.

2.3. Biodiesel and Biolubricant Characterization

Regarding WCO-FAME and WCO-TMP characterizations,

Table 2. WCO-FAME and WCO-TMP characterizations, including references to the corresponding standards.

Parameter	WCO-FAME	WCO-TMP	Details
FAME content	Yes	No	[40]
Viscosity	Yes	Yes	[41]
Density	Yes	Yes	[42]
Oxidation stability	Yes	Yes	[43]
Acidity value	Yes	Yes	[44]
Flash and combustion points	Yes	Yes	[45]
Cold filter plugging point	Yes	No	[46]

shows the main analyses carried out for each sample. The characterization methods were detailed in previous research, including the most representative characteristics of biodiesel and biolubricants [37]. It should be noted that most of the analyses were performed on both samples, with some exceptions, such as the FAME content and cold filter plugging points, typical tests applied to biodiesel. In any case, previous work and standards, such as those included in the table, have proven the suitability of these tests on both kinds of samples.

Regarding the FAME content, the gas chromatography method was applied to measure the fatty acid methyl esters included in the WCO-FAMEs [40]. For this purpose, a VARIAN 3900 gas chromatograph coupled to a flame ionization detector was used. A polyethylene glycol column (Zebron ZB-WAX PLUS, Phenomenex, Torrance, CA, USA, length: 30 m, film thickness: 0.5 µm, and i.d.: 0.32 mm) was selected, using different standards (methyl oleate, palmitate, linoleate, and linolenate) and methyl heptadecanoate as the internal standard, with heptane as a solvent.

Viscosity was determined using an Ostwald viscometer at 40 °C [40], whereas density was measured using a pycnometer (Pobel, Madrid, Spain). Concerning the cold filter plugging point (CFPP), specific equipment included in the standard was used [46], whereas flash and combustion point measurements were carried out according to the Cleveland open-cup method [45].

Finally, the oxidation stability was calculated through the Rancimat method [43,47]. Three grams of the sample was placed in a test tube, heating it at 110 °C and bubbling synthetic air (at 10 L·h⁻¹). The resulting stream bubbled 50 mL of distilled water, increasing the sample’s conductivity because of the dilution of the byproducts generated during oxidation. This value was measured using a conductivity meter. The induction point (or oxidation stability) was the time when the conductivity abruptly increased, which is normally expressed in minutes.

FT-IR analysis of the final biolubricant was carried out using specific equipment (Perkin-Elmer Spectrum 3F-IR, Waltham, MA, USA) and measuring between 4000 and 650 cm⁻¹. Also, TG and DTG analyses were carried out using a thermobalance (STA449F3, QMS403D, VERTEX70, Netzsch–Bruker, Billerica, MA, USA). A certain mass of the biolubricant was heated at a constant heating rate (10 °C·min⁻¹). The carrier gas was nitrogen (100 mL·min⁻¹). TGA and DTG curves were obtained by monitoring the weight loss at various temperatures.

The conversion of FAMEs during the second transesterification with TMP was calculated through the FAME content decrease (using gas chromatography, as previously explained) according to Equation (1). Also, for kinetic studies, the decrease in the FAME content was used for the corresponding calculations, as explained in further subsections.

$$Conversion={\displaystyle \frac{{FAME}_i-{FAME}_t}{{FAME}_i}}\times 100$$

(1)

where FAME_i is the concentration of FAMEs in the WCO-FAME sample, whereas FAME_t is the concentration of FAMEs at a certain reaction time, “t”, during the second transesterification step.

2.4. Antioxidant Addition

To improve oxidation stabilities of the WCO-FAME and WCO-TMP samples, tert-butylhydroquinone (TBHQ) was added to these samples (10 g) at different concentrations (0, 100, 200, 500, 750, and 1000 ppm). After the TBHQ addition, the mixture was homogenized in an ultrasonic bath for 5 min before assessing its oxidation stability through the Rancimat method [43]. Also, WCO-TMP was subjected to extreme oxidation conditions to analyze the increases in the viscosity and acidity value over time (according to the corresponding standard [41,44]) for the control and doped samples (that is, those with a TBHQ addition of 1000 ppm).

2.5. Kinetic Study: Foundations

A kinetic study for the second transesterification reaction was carried out in duplicate. Equation (2) shows the overall reaction considered, where A = FAMEs, B = TMP, C = biolubricant, and D = methanol that was recovered.

$$A+{\displaystyle \frac{1}{3}}B\leftrightarrow {\displaystyle \frac{1}{3}}C+D$$

(2)

The tests were carried out in an isothermal batch reactor. Samples were withdrawn at intervals for the analysis of the concentration of FAMEs over the reaction time. As methanol (D) was continuously removed, the kinetic law of an irreversible reaction can be considered, as shown by Equation (3) as follows:

$${-r}_A={\displaystyle \frac{{-dC}_A}{dt}}=k\times C_A^{\alpha }\times C_B^{\beta }$$

(3)

where k is an apparent rate constant that takes into account the effects of the catalyst concentration, temperature, and pressure; C_A is the concentration of FAMEs; C_B is the concentration of TMP; and α and β are the reaction orders with respect to A and B, respectively. If C_A and C_B are related through stoichiometry, and considering the concept of conversion (X_A), Equations (4)–(6) are obtained as follows:

$$C_A=C_{A_0}\times \left(1-X_A\right)$$

(4)

$$C_B=C_{B_0}\times \left({\theta }_B-{{\displaystyle \frac{1}{3}}X}_A\right)$$

(5)

$${\theta }_B={\displaystyle \frac{C_{B_0}}{C_{A_0}}}$$

(6)

Thus, by replacing the conversion in Equation (3), Equation (7) is obtained as follows:

$${\displaystyle \frac{{dX}_A}{dt}}=k\times C_{A_0}^{\alpha +\beta -1}\times {(1-X_A)}^{\alpha }\times {\left({\theta }_B-{\displaystyle \frac{1}{3}}\times X_A\right)}^{\beta }$$

(7)

By separating the variables and integrating this equation between the limits (t = 0, X_A = 0) and (t = t, X_A = X_A), Equation (8) is obtained as follows:

$${\int }_0^{X_A}{\displaystyle \frac{{dX}_A}{{\left(1-X_A\right)}^{\alpha }\times {\left({\theta }_{\beta }-\frac{1}{3}{X}_A\right)}^{\beta }}}={\int }_0^{t}k\times C_{A_0}^{\alpha +\beta -1}\times dt$$

(8)

This equation depends on α and β, but the transesterification reaction is usually described as a first-order reaction with regard to each reagent, which implies that α = β = 1 and, therefore, a second-order reaction [48]. Furthermore, if the ratio of the initial concentrations of A and B fulfils the stoichiometric relationship shown in Equation (2), the following conditions can be applied (Equations (9) and (10)):

$$C_{B_0}=C_{A_0}/3$$

(9)

$${\theta }_B=1/3$$

(10)

Thus, Equation (11) is obtained after substituting Equation (10) into Equation (8) as follows:

$${\int }_0^{X_A}{\displaystyle \frac{3\times {dX}_A}{{\left(1-X_A\right)}^2}}={\int }_0^{t}k\times C_{A_0}\times dt$$

(11)

Equation (11) can be further simplified to Equation (13) by considering Equation (12) as follows:

$$k^{\prime }=k/3$$

(12)

$${\int }_0^{X_A}{\displaystyle \frac{{dX}_A}{{\left(1-X_A\right)}^2}}={\int }_0^t{k}^{\prime }\times C_{A_0}\times dt$$

(13)

After integrating Equation (13), the linearized equation (Equation (14)) is obtained as follows:

$${\displaystyle \frac{1}{C_{A_0}}}\times {\displaystyle \frac{x_A}{1-x_A}}=k^{\prime }\times t$$

(14)

To sum up, the main steps carried out in this work are included in Figure 2, including both experimental and theoretical studies, with a reactor design and an initial economic feasibility study for WCO-TMP production.

3. Results and Discussion

3.1. WCO-FAME Characteristics

Once the WCO-FAME production was carried out, a product with a FAME content of above 97% was obtained, which indicates the high conversion rate of this process. This value is higher than those in other studies based on rapeseed- or sunflower-derived biodiesel, where FAME contents of 90.9 and 95.5% were obtained, respectively [49]. In our case, this value is above the lower limit established by the UNE-EN 14214 standard [40]. Other works, where WCO biodiesel was produced, obtained FAME contents of nearly 100% [50]. Also, a recent review has pointed out high biodiesel yields in different processes (with different reactors) where WCO was the starting material, with 90–99.9% yields in general [51]. This is a desirable scenario, as high-purity products normally can provide reliable physicochemical parameters.

Indeed, most parameters studied were within the limits established by the standard [40], with the compliance of the density (880 kg·m³), viscosity (4.7 cSt), acidity value (0.37 mg_KOH·g⁻¹), cold filter plugging point (−1 °C), and flash and combustion points (185 and 196 °C, respectively). Regarding the FAME profile, the majority of the compounds found in this study were methyl linoleate (52%), followed by methyl oleate (33%), methyl palmitate (7%), and methyl linolenate (<3%).

Thus, compared to previous studies [52], it should be noted that the fatty acid composition of WCO can be variable, depending on culinary habits and sampling, always requiring the perfect characterization of the raw material used. The presence of monounsaturated or saturated esters is essential to obtain products with high oxidation stabilities, which play important roles in retaining parameters, like viscosity and acidity, during storage or under oxidation conditions [53]. In this case, a high methyl linoleate percentage was found, which possibly contributed to the low oxidation stability of the sample (3.2 h), requiring the use of antioxidants to improve this parameter, increasing it above the upper limit of 8 h [54].

3.2. Effects of Pressure, Temperature, and Catalyst Concentration on WCO-TMP Production

Figure 3 shows the evolution of the conversion of FAMEs during different runs of the experiment. Once WCO-FAMEs were produced and characterized, different experiments about the effects of the pressure, temperature, and catalyst concentration on the FAME conversion were carried out during WCO-TMP production at different pressures (a), temperatures (b), and concentrations of sodium methoxide (i.e., the catalyst) (c).

Regarding the effect of the pressure on the FAME conversion (Figure 3a, where the rest of the variables were kept constant; that is, the temperature was 80 °C, the FAME/TMP ratio was 3, the catalyst concentration was 0.3% w/w, and the stirring rate was 350 rpm), the lower the pressure, the higher the conversion of FAMEs at a given time. This could be due to the fact that methanol, a product of the transesterification reaction, which is generated in this step, is removed from the reaction medium under vacuum, thus increasing the overall conversion rate of FAMEs and facilitating the reaction of the reagents to produce WCO-FAMEs. The same trend was observed in previous works, where different alcohols, such as pentaerythritol [49] or TMP [33], were used. Nevertheless, in this case, it should be noted that a working pressure of 510 mmHg offered similar conversion values close to those observed at lower pressure values (360 and 210 mmHg), so one can assume that a vacuum of 250 mmHg was enough to remove almost all the methanol that was generated. And the FAME conversion rates were comparable to those obtained at lower working pressures used in this experiment, suggesting the selection of 250 mmHg for further analysis.

As expected, higher temperatures increased the conversion rate of the FAMEs (see Figure 3b). In the case of the temperature (Figure 3b, where the rest of the variables were kept constant; that is, the pressure was 510 mmHg, the FAME/TMP ratio was 3, the catalyst concentration was 0.3% w/w, and the stirring rate was 350 rpm), there was a growth in the WCO-TMP yield as the temperature increased, with gradual increases in conversion rates at the beginning of the reaction, especially for the first 30 min. Thus, high temperatures would be advisable from the kinetic point of view. However, a negative effect on the oxidation stability could take place, as was observed in previous work [55]. Therefore, an intermediate temperature should be recommended to balance these opposite effects.

Finally, the catalyst concentration (Figure 3c, where the rest of the variables were kept constant; that is, the temperature was 80 °C, the pressure was 510 mmHg, the FAME/TMP ratio was 3, and the stirring rate was 350 rpm) also accelerated the rate of the transesterification reaction. In this case, the catalyst addition contributed to an increase in the reaction rate, reaching similar conversions at the end of the reaction. The presence of catalyst traces in the final product could catalyze oxidation processes, which are not desirable [55].

Taking into consideration all the discussion above, the following reaction conditions were considered as suitable for the production of WCO-TMP: FAME/TMP molar ratio = 3; working pressure = 510 mmHg; T = 120 °C; stirring rate = 350 rpm; catalyst concentration = 1%; reaction time = 2 h. Under these conditions, a high conversion rate of WCO-FAMEs was obtained (exceeding 98%), with WCO-FAMEs possessing the following properties: a density of 951 kg·m⁻³; viscosities at 40 and 100 °C of 127 and 14 cSt, respectively; an acidity value of 0.43 mg_KOH·g⁻¹; flash and combustion points of 225 and 232 °C, respectively; and an oxidation stability of 6 h. As the oxidation stability is not quite long lasting, the use of an antioxidant additive is advisable. TBHQ was chosen for this purpose, as it is one of the most effective and efficient antioxidants used to stabilize similar products, like biodiesel [56].

In order to determine the presence of some functional groups, the IR profile is shown in Figure 4. As a result, a spectrum corresponding to esters was obtained, with the typical C=O band at 1741 cm⁻¹ and the absence of the prominent peak corresponding to OH groups (at around 3500 cm⁻¹). These spectral features point out the fact that fatty acid esters corresponding to biolubricants were generated, with the high conversion rate of the TMP and purification of the unreacted alcohol.

Regarding the thermal stability of the resulting biolubricant (WCO-TMP), TG/DTG tests were carried out, and the main results are included in Figure 5. Clearly, different thermal events can be observed, pointing out the absence of moisture in the sample (according to the negligible weight loss at around 100 °C), including one event between 200 and 300 °C (possibly because of methyl ester degradation on account of the presence of unreacted biodiesel) and another one between 375 and 475 °C (with a DTG peak at 435 °C), which was the main thermal event in this case. This behavior was similar to that in previous studies, where the maximum weight loss took place at slightly lower temperatures [39]. Consequently, a product with high thermal stability was obtained, which is essential to retain the main properties of a biolubricant at high temperatures.

3.3. WCO-TMP and TBHQ Addition

The effect of the TBHQ addition on the oxidation stability of the WCO-TMP is shown in Figure 6. Clearly, an increasing linear trend was observed for the oxidation stability of the WCO-TMP with increasing addition of THBQ. This is the typical behavior observed for a variety of oil-based samples, including biodiesel and biolubricants produced from a wide range of vegetable oils, such as WCO [21,52], a corn and sunflower oil mixture [57], cardoon oil [20], cottonseed oil [58], or safflower oil [59,60] among others.

Consequently, to prove the effectiveness of the antioxidant addition, 1000 ppm of TBHQ was considered as an interesting antioxidant concentration for further studies, where WCO-TMP was subjected to extreme oxidation conditions, as covered in previous experiments.

Figure 7 shows the main effects of the antioxidant addition (TBHQ at 1000 ppm) on the viscosity and acidity, which are essential properties because the former is decisive for the suitable applicability of the resulting biolubricant, whereas the latter is an undesirable effect that should be avoided to prevent corrosion in equipment and facilities.

Considering viscosity (see Figure 7a), the control samples (that is, without the TBHQ addition) had considerable increases in this parameter, especially after 300 min of extreme oxidation. This is normally because of oxidation processes, which can provoke undesirable effects, such as polymerization. As a consequence, an increase in viscosity, on account of the presence of compounds with a complex molecular structure, was found, as intermolecular interactions promote the resistance to the flow in the resulting product [18]. When TBHQ was added, the viscosity remained constant during the whole process, pointing out the effectiveness of this antioxidant for this purpose, as the antioxidant could have prevented the typical oxidation steps in free radical generation, that is, initiation, propagation, and termination [18].

On the other hand, there was growth in the acidity of the control samples, whereas the acidity was constant when TBHQ was added, as shown in Figure 7b. Concerning the control samples, the abovementioned oxidation processes can equally produce free fatty acids [18], which could contribute to an increase in the acidity, which was delayed by adding TBHQ.

As a result, it was demonstrated that the selected quantity of TBHQ, for its addition to WCO-TMP, was enough to preserve the main properties of the WCO-TMP during its oxidation. Also, it should be noted that low amounts of this antioxidant could enhance the quality of the final product obtained in this work. Previous research has pointed to the same trend, with relatively low quantities of TBHQ or PG required to avoid the negative consequences of the oxidation of biodiesel [57,59] and biolubricants [39].

3.4. Kinetic Study

Batch tests were carried out in the laboratory to assess the apparent rate constant of the transesterification reaction leading to the biolubricant product. Also, the effects of the pressure, temperature, and catalyst concentration on this constant were studied. According to Equation (14), a plot of the right-hand-side term against time should yield a straight line, which slope is the apparent rate constant. As an example, Figure 8 shows the plot for the data for one of the runs carried out.

The apparent kinetic constant (k′) is dependent on the pressure, temperature, and catalyst concentration. Regarding the pressure, according to the results included in Figure 3a, a working pressure of 510 mmHg has the same effect on the reaction rate of the process like those obtained at lower working pressures (which would imply higher energy costs). The effects of the temperature (T) and catalyst concentration (C_cat) on the kinetic constant are represented by Equation (15) as follows:

$$k^{\prime }=k_0\times C_{cat}^n\times e^{\left({\displaystyle \frac{-E_a}{R·T}}\right)}$$

(15)

In this case, the pre-exponential factor (k₀), n, and the activation energy (E_a) are unknown. To study the effect of the temperature on the kinetic constant, runs were performed in the 80–140 °C range, with the catalyst concentration fixed at 0.3% w/w.

Table 3. Apparent kinetic constants (k′) for biolubricant production at different temperatures.

T, °C	T, K	k’
80	353	0.0141
100	373	0.0176
120	393	0.0245
140	413	0.0339

shows the apparent rate constants (k′) obtained from these runs.

To obtain the activation energy, Equation (16) was applied as follows:

$$\ln \hspace{0.17em}{k}^{\prime }=\ln \left(k_0\times {0.3}^n\right)-E_a\times {\displaystyle \frac{1}{R\times T}}$$

(16)

Figure 9 shows the linear regression of the experimental data according to Equation (16), resulting in an activation energy value of 17,858 J·mol⁻¹.

To calculate k₀ and n, a series of runs at a constant temperature (80 °C) was carried out. Thus, the apparent rate constant can be expressed by Equation (17) as follows:

$$k^{\prime }=k_0\times C_{cat}^n\times e^{\left({\displaystyle \frac{-E_a}{R·\left(80+273\right)}}\right)}$$

(17)

Table 4. Apparent kinetic constants (k′₂) for biolubricant production at different temperatures.

Catalyst Concentration, % w/w	k’2
0.3	0.0141
0.5	0.0237
0.7	0.0468
0.9	0.1096

shows the apparent rate constant values (k′) at 80 °C and for different catalyst concentrations in the 0.3–0.9% w/w range.

If a logarithmic approach is applied to Equation (17), Equation (18) is obtained as follows:

$$\ln \hspace{0.17em}{k}_2^{\prime }=n\times \ln \hspace{0.17em}{C}_{cat}+\ln \hspace{0.17em}\left(k_0\times e^{\left({\displaystyle \frac{{-E}_a}{R\times \left(80+273\right)}}\right)}\right)$$

(18)

Thus, Figure 10 shows a linear regression according to Equation (18), yielding k₀ = 51.8 M⁻¹·min⁻¹ and n = 1.8.

The parameters required in Equation (16) were obtained, thus allowing for the estimation of the rate constant at different temperatures and for catalyst concentrations. Although this constant has been calculated for a pressure of 510 mmHg, the effect of the pressure on the reaction rate was negligible in the range 210–510 mmHg. It should be noted that even though few experiments were conducted for this estimation (because of the narrow range of catalyst concentrations), the experimental data fit this reaction model relatively well, justifying the value obtained for the coefficient of determination.

In this sense, further studies covering the effects of several factors (FAME profiles or different catalysts) on the global conversion, and, therefore, a kinetic study, could be an interesting research line, which could be equally important in the design and economic feasibility study of industrial plants.

3.5. Industrial Equipment, Reactor Design, and Economic Feasibility Study

Once the kinetic study was carried out, a preliminary design for a small plant to produce biodiesel or biolubricants from WCO was also developed, including an economic feasibility assessment. The main steps are included in Figure 11 as follows:

One key step is the previous kinetic study, which will determine different factors, like the WCO supply, the selection of the working regime, or the quantities of the reagents. Equally, the working regime will determine the selection and design of different components, especially in the case of the reactor and, equally, the different processes that take place (including heating, reaction, or separation processes). At the same time, the selection and determination of the different processes have an influence on the equipment selected. Finally, the reagent and energy consumption are dependent on the designed facility and the abovementioned steps. These choices were analyzed from an economic perspective, to assess the feasibility of the designed plant.

3.5.1. Preliminary Considerations: Site Location, Production Regime, and WCO Processing Capacity of the Plant

For the location of the plant, a site located in Badajoz (38°53′45.0″ N, 6°59′36.3″ W) has been selected because of its expansive construction area and advantageous location. It is relevant to mention that although most of the industries in Badajoz are situated in this area, there is currently no industrial plant dedicated to the production of biodiesel or biolubricants in Badajoz, indicating a lack of competition in this sector within this region.

Another important factor in this choice was the excellent road and rail transportation facilities of the site, which favor the commercialization of the manufactured product.

To carry out the preliminary design of the industrial plant for this project, it is essential to estimate the availability of the raw material (that is, WCO) in this area. According to a previous study, an average amount of about 4 L of WCO is generated per person each year [61]. With a population of about 150,000 inhabitants, the total amount of WCO generated in this area is estimated to be approximately 600 cubic meters per year. Considering the typical efficiency of the collection system, this amount is reduced to about 460 m³/year. Considering the density of the WCO, the design capacity of the plant was set at 48.4 kg WCO·h⁻¹. As this is not a high capacity, a batch-mode process was selected.

Thus, a discontinuous regime allows for a work shift regime (8 hours per shift, 5 days per week) with total working hours of 2112 h/year. In detail,

Table 5. Characteristics of the designed plant.

Parameter	Value
Working hours, h·y−1	2112
Collected WCO, kg·y−1	423,823
Processing capacity, kg·h−1	206.03
Processing capacity, kg·d−1	1648
Methanol required *, kg·d−1	357.44

* According to stoichiometric requirements.

shows the information related to a working year at the designed plant [37]. Considering the time required for both transesterification reactions, along with the heating of reagents and separation of products observed in further subsections, 8 hours per shift were enough to carry out the whole process.

3.5.2. Main Equipment

Also, further equipment is required for biolubricant synthesis, according to the following sequence of operations: the storage of reagents and products, a pumping system, electrical steam generation, a jacketed batch reactor, a vacuum system, a vacuum pump, and a vegetable oil purification system (see Figure 12).

It should be noted that the equipment and budget suggested in this work is based on average real prices provided by national companies, which will not be specified because of confidentiality reasons. Thus,

Table 6. Processing steps of the designed plant.

Step	Process/Equipment	Details
WCO supply and preconditioning	Shipment (tank trucks), filtering and storage in tanks	Steel tank for WCO and TMP storage. Bulk containers (HDPEs) were used for methanol and sodium methoxide.
Pumping	Pump system	Pumps materials through the plant.
Steam generation	Electric steam generator	Provides steam to the jacketed batch reactor to control the temperature at desired values.
First transesterification	Jacketed batch reactor	WCO and methanol are mixed in the reactor. Once the catalyst is added, the reaction progresses.
First separation (decantation)	Jacketed batch reactor	Once the previous step is finished, the agitation system is stopped to let the glycerol phase settle and be removed from the bottom of the reactor.
Second transesterification	Jacketed batch reactor	TMP and catalyst are added to FAMEs generated in the previous transesterification, providing steam to retain the isothermal regime of the reaction. Methanol and the biolubricant are obtained as products.
Vacuum	Vacuum system	Vacuum is used to recover methanol, thus accelerating the second transesterification.
Purification	Pumping system and purifier	Once the reaction finishes, the resulting biolubricant is cooled down and purified (removing moisture, particles, and gas), and the resulting biolubricant is placed in a storage tank.
Antioxidant addition	TBHQ supply	A suitable amount of TBHQ was added to obtain the final product.

provides the details of the main equipment for each step of the abovementioned sequence of operations.

The main containers used for this purpose are included in

Table 7. Details about the main containers included in this study.

Equipment	Size	Details
WCO container	Volume = 2 m3; heigh = 2.8 m; diameter = 1.15 m; wall thickness = 1.2 mm	The container (stainless steel) is oversized to ensure WCO collection.
Methanol container	Volume = 0.6 m3; size = 1.2 × 0.8 × 1 m	HDPE containers, a smaller container (V = 0.3 m3), is used for the collection of methanol after vacuum filtration.
Sodium methoxide container	Volume = 0.3 m3; size = 1.2 × 0.8 × 1 m	HDPE container to supply 100 L of catalyst on a daily basis.
Glycerol container	Volume = 0.6 m3; size = 1.2 × 0.8 × 1 m	HDPE container to store 495 kg of glycerol obtained as a byproduct.
TMP container	Volume = 0.3 m3; height = 1.7 m; diameter = 0.74 m; wall thickness = 1 mm	Stainless-steel container to provide TMP.
Biolubricant container	Volume = 2 m3; height = 2.9 m; diameter = 1.15 m; wall thickness = 1.2 mm	Stainless-steel container to store WCO-TMP and to include TBHQ. A cooling and temperature control system is included.
TBHQ container	Volume = 150 L; height = 0.975 m; diameter = 0.48 m	HDPE container to store and supply TBHQ when necessary.

as follows:

Concerning steam generation, specific equipment was selected for this purpose, with a working pressure range from 0.5 to 5 bar and an efficiency of 99% without carbon dioxide emissions. The boiler (840 × 430 × 380 mm) provides a power of 4.5 kW.

Table 8. Steam requirements for the first and second transesterification reactions.

Condition	First Reaction	Second Reaction
Initial temperature, °C	15	60
Final (reaction) temperature, °C	60	120
Heating time, min	35	40
Saturated steam, kg	136.1	112.5
Flow, kg·min−1	3.9	2.82

shows the main heating requirements of this process.

Finally, the biolubricant is purified using a purifier. The quantities of biolubricant and methanol generated in the second transesterification can be calculated according to the data provided in Section 3.5.3, resulting in a volumetric flow of the biolubricant of 42.93 L·min⁻¹ when an equipment power of 44 kW and a high filtration capacity (1 μm) are selected.

3.5.3. Reactor Design

In the case of the reactor, it was designed according to the characteristics included in Table 5. The first and second transesterification reactions were designed to be developed sequentially in the same reactor. Therefore, the effective reactor volume that is required for both reactions was calculated. Because of the available amount of WCO in a medium-sized city, like Badajoz, and considering the expected demand of the biolubricant, these two steps could take place in the same reactor to ensure the desired annual amount of product without requiring two reactors, which would increase the initial costs of the plant. Equation (19) for the first transesterification with excess methanol and Equation (20) for the second transesterification were considered.

$$WCO+6{CH}_{3}OH\leftrightarrow 3FAMEs+Glycerol$$

(19)

$$FAMEs+{\displaystyle \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$3$}\right.}TMP\leftrightarrow {\displaystyle \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$3$}\right.}Biolubricant+{CH}_{3}OH$$

(20)

According to the WCO supply observed in Table 5 (206.03 kg·h⁻¹) and by considering the stoichiometry of the process, the density and molecular weight of each reagent, the daily inlet mass flow, and the reactor size could be obtained for a working day (see

Table 9. Inlet flows for the first transesterification.

Reagent	Molecular Weight, g·mol−1	Density, kg·m−3	Mass Flow, kg·h−1	Inlet Mass, kg	Inlet Volume, m3
WCO	900	920	209.2	1673.80	1.82
Methanol	32.04	792	44.68	357.44	0.45
Sodium methoxide	54.03	970	6.28	50.2	0.05

).

A total inlet volume of 2.32 m³ to the reactor was found if the first transesterification is considered. On the other hand, according to the second transesterification, glycerol is first removed, and the remaining reagent (in this case, TMP) is added along with the catalyst (sodium methoxide). Considering the reaction included in Equation (24), the main inlet flows for the second transesterification are shown in

Table 10. Inlet flows for the second transesterification.

Reagent	Molecular Weight, g·mol−1	Density, kg·m−3	Mass Flow, kg·h−1	Inlet Mass, kg	Inlet Volume, m3
FAMEs	284.52	880	198.37	1586.96	1.8
TMP	134.17	1080	22.33	178.66	0.17
Sodium methoxide	54.03	970	5.95	47.62	0.05

to determine the total volume of the reactor.

Under these circumstances, the total inlet volume was 2.02 m³. Comparing both total volumes, it can be observed that the first transesterification required a higher volume, which will be selected for the reactor design so that both reactions can take place in the same reactor in successive steps. Finally, considering an oversize of 20%, the real volume for the reactor was 3 m³. If a cylindrical reactor is considered, its inner diameter and height can be calculated to minimize the amount of material used for its construction, according to Equations (21) and (22) as follows:

$$S=\left(2\pi \times R\times h\right)+\left(2\pi \times R^2\right)$$

(21)

$$V=\pi \times R^2\times h$$

(22)

If both equations are represented, Equation (23) is obtained, where the surface is a function of R as follows:

$$S(R)={\displaystyle \frac{2\times V}{R}}+\left(2\pi \times R^2\right)$$

(23)

By representing the surface area as a function of the radius, a line is analogous to a parabola. This function, at its lowest point, presents a slope that equals 0; that is, the derivative of the surface, when R is minimized, equals 0, as observed in Equation (24).

$$S^{\prime }\left(R_{min}\right)=0=4\pi \times R-{\displaystyle \frac{2\times V}{R^2}}$$

(24)

Once the radius is obtained, the inner diameter and height can be calculated, as well as the surface area of the reactor, as shown in

Table 11. Reactor size for WCO biodiesel and biolubricant production.

Parameter	Size
Reactor volume, m3	3
Reactor surface area, m2	29.49
Inner diameter, m	1.563
Height, m	1.562
Wall thickness, mm	6
Weight, kg	168.53

. The wall thickness was considered according to previous studies [37].

Concerning the size of the stirring system, a six-blade disk stirrer was selected, following Equations (25) and (26), for the design of the blades as follows:

$${\displaystyle \frac{D_a}{D_t}}={\displaystyle \frac{1}{3}};{\displaystyle \frac{H}{D_t}}=1;{\displaystyle \frac{J}{D_t}}={\displaystyle \frac{1}{12}}$$

(25)

$${\displaystyle \frac{E}{D_t}}={\displaystyle \frac{1}{3}};{\displaystyle \frac{W}{D_a}}={\displaystyle \frac{1}{5}};{\displaystyle \frac{L}{D_a}}={\displaystyle \frac{1}{4}}$$

(26)

where D_a is the diameter of the stirrer, D_t is the inner diameter of the reactor, H is the height of the reaction medium, J is the width of the deflector, E is the distance from the stirrer and the bottom of the reactor, W is the width of the blades, and L is the length of the blades. By applying the previous equations, the results shown in

Table 12. Size of the stirring system (measurements are expressed in m).

Da	H	J	E	W	L
0.521	1.563	0.130	0.521	0.104	0.130

were obtained as follows:

Regarding the vacuum pump, it should be noted that the requirements of this equipment were previously established (510 mmHg and 40 min of working time), resulting in 5.64 L·min⁻¹ of methanol that are removed from the reaction medium in the case of the second transesterification when a pump with a power of 2.2 kW is selected for this purpose.

3.5.4. Economic Feasibility Study

Once the main components of the chemical plant for biolubricant production from WCO were established, a preliminary economic study was conducted to assess the feasibility of the implementation of this kind of facility. The costs of the products were determined according to the location established in this work and described in Section 3.5.1.

Concerning the direct costs and according to the yearly demands of the plant,

Table 13. Direct costs for WCO-based biodiesel and biolubricant production.

Transesterification Process	Reagent	Price, €·T−1	Amount, T·y−1	Annual Cost, €·y−1
First	WCO	82	435.12	35,679.84
	CH3OH	265	92.93	24,626.45
	Sodium methoxide	1800	13.05	23,490
	Total	--	541.1	83,796.29
Second	TMP	150	46.45	6967.5
	Sodium methoxide	1800	12.38	22,284
	Total	--	58.83	29,251.5

shows the estimated costs of the reagents for the first and second transesterifications (the data were obtained from local and national distributors, and average values are presented).

Also, the TBHQ addition should be considered. In this case, the addition of 300 ppm of TBHQ could be suitable to obtain at least 8 h of oxidation stability, according to the results observed in Figure 4, where 262 ppm of TBHQ assured an oxidation stability of 8 h, rounding up to 300 ppm to simplify the calculations in this case (assuming the minimum standard for biodiesel samples [43]). This way, assuming a total biolubricant production of 424,989.8 kilograms per year, 127,497 g of TBHQ would be necessary, with a total cost of 37,739.11 € (at 29.60 €·g⁻¹). As a result, the total cost related to raw materials was 150,808.43 €.

Regarding staff costs, the results observed in

Table 14. Staff costs for WCO-based biodiesel and biolubricant production.

Job Post	Number of Workers	Salary	Total Salary + Social Charges
Plant manager	1	44,658.05	60,288.37
Chemist	1	28,985.65	39,130.63
Qualified worker	2	21,739.23	51,087.19
Total	4	95,382.93	150,506.19

were based on national work agreements [62]. It should be noted that the salary and social charges (around 35% of each salary) are constantly changing, with the subsequent impact of this factor on the implementation of a plant with these characteristics.

When it comes to energy costs, different stages were considered to assess the power required and the annual costs, as observed in

Table 15. Energy costs (related to a working year) of the WCO-based biodiesel and biolubricant production plant.

Step	Power, kW	Daily Working Time	Yearly Energy Consumption, kWh	Annual Cost, €·y−1
Heating	25.54	1.3	8632.52	1553.85
Stirring	22.25	2.51	14,520.35	2613.66
Vacuum	2.2	0.67	383.24	68.98
Purification	44	0.7	8008.00	1441.44
Total	91.87	--	31,544.11	5677.94

. If an average value of 0.180 €·kWh⁻¹ is considered, according to several electric companies, the total annual cost of the plant would be above 5500 €.

Also, machine costs should be considered in this preliminary study, as observed in

Table 16. Machine costs for this study.

Equipment	Cost (VAT Included), €
WCO container	2660
Methanol container	235.95
Recovered-methanol container	179.95
Sodium methoxide container	179.95
Glycerol container	235.95
TMP container	1180
Biolubricant container	4500
TBHQ container	42.35
Steam generator	3194
Vacuum pump	2360.60
Purifier	4100
Reactor	33,741
Stirrer	35,639

. The total cost of the reactor (including the container and stirrer) was 69,380 €, whereas the total cost of the industrial equipment for biodiesel and biolubricant production was 88,248.8 €.

Regarding the water cost, it can be considered as a direct cost, as water is used to wash the reactor and supply the boiler to produce steam (with estimates of 124.8 and 0.36 m³, respectively); for the former, tap water is enough to carry out this task, whereas for the latter, distilled water is required, estimated at different costs per liter (1.97 and 940 €·m⁻³, respectively). As a result, the total annual cost of the water was 588.02 €.

To sum up,

Table 17. Annual costs and income for the designed biodiesel and biolubricant production plant, including the gross profit.

Annual Production Costs		Annual Income
Production	Cost, €	Product	Production, L·y−1	Selling Price, €·L −1	Annual Income, €
Raw materials	150,808.43	Biolubricant	446,424	2.89	1,290,165.36
Energy	5677.94		Production, T·y−1	Selling price, €·T −1	Annual income, €
Water	588.02	Glycerol	128.56	250	32,140
Annual Profit
Total annual costs (production), €			157,074.39
Total annual incomes, €			1,322,305.36
Annual gross profit, €			1,165,230.97

indicates the annual costs for production and annual incomes. As observed, the annual gross profit was obtained as the difference between the income (because of the annual production of the biolubricant and glycerol, which would be used in glycerol steam reforming processes not requiring purification steps that could increase its production costs) and the annual production cost (because of the raw materials, energy, and water used). These costs have been estimated for this production process, without considering the machinery costs, salaries, or depreciation because of the service life of the equipment.

The net profit can be calculated as 75% of the gross profit, resulting in 873,923.23 €. Finally, considering machinery costs and salaries, the final profit of the plant for the first year of operation was 694,856 €.

As in the experimental section, the economic feasibility approach faces different challenges that should be considered, like price fluctuations, which are beset by the current unstable geopolitical scenario. Accordingly, prices related to electricity, water, or reagents could considerably vary, influencing the final income of the designed plant. Also, local or national policies about taxes or labor law could equally affect these results, requiring the adaptation of the working regime of the plant (among other factors, like the supply area of the WCO, required to obtain further benefits).

4. Conclusions

In this work, biodiesel and biolubricant production from waste cooking oil through transesterification was studied, including the characterization of the main products obtained and the design and economic feasibility study of a chemical plant to produce biolubricants. As a result, and according to the properties of the biodiesel and biolubricant obtained from the waste cooking oil, this waste can be considered as a suitable raw material to obtain valuable products for energy purposes and lubrication in various industries. It should be noted that the thorough determination of WCO’s physicochemical properties is important to establish and predict some properties of its derived products (like oxidation stability). Thus, the WCO composition might vary depending on the culinary habits in each sampling area.

However, the oxidation stability was low, requiring the use of antioxidants to improve this property, which is essential to retain the viscosity and acidity of the final product during storage or oxidation processes. In this sense, the use of TBHQ was effective to considerably increase the oxidation stability.

According to the experimental data, the operating conditions to obtain biolubricants were the following: FAME/TMP ratio = 3; working pressure = 210 mmHg; temperature = 120 °C; catalyst concentration = 0.3% w/w. Under these circumstances, the FAME conversion was above 98%. Regarding kinetics, transesterification of FAMEs with TMP followed a pseudo-second order model. According to the kinetic data and the design of the chemical plant (discontinuous regime), a daily production of 2 m³ of biolubricant was obtained in batches. The economic feasibility study indicated that the implementation of this facility at an industrial scale is feasible, as there is a favorable economic potential, with an annual net profit of around 700,000 €. Finally, the influences of different factors could be decisive in the design of the plant or its economic performance, requiring an updated adaptation to these circumstances so that biolubricant production from WCO can be economically feasible.