WO2010112641A1

WO2010112641A1 - Method for the production of biofuels by heterogeneous catalysis employing a metal zincate as precursor of solid catalysts

Info

Publication number: WO2010112641A1
Application number: PCT/ES2010/000141
Authority: WO
Inventors: Pedro Jésus MAIRELES TORRES; Jose Santamaría González; Ramon Moreno Tost; Juan Miguel Rubio Cabellero; Josefa María MERIDA ROBLES; Enriique Rodriguez Castellon; Antonio Jimenez Lopez
Original assignee: Universidad De Malaga
Priority date: 2009-04-01
Filing date: 2010-03-27
Publication date: 2010-10-07
Also published as: ES2345866B2; ES2345866A1

Abstract

The present invention relates to the use of solid catalysts, obtained by calcination of a zincate of an alkaline earth metal or of a divalent transition metal, for the production of biofuels (biodiesel) through transesterification of vegetable or animal oils or fats with low-molecular-weight alcohols under mild temperature and atmospheric pressure conditions. In addition to the advantages of the heterogeneous catalysis itself, the invention also offers the following advantages: simplicity, reproducibility and easy scaling of synthesis; the precursor of the active catalyst is stable in air; the temperature of decomposition or activation of the catalyst is lower than that of other basic solid catalysts; the kinetics of the reaction are similar to those described in homogenous catalytic reactions and significantly faster than in the case of other solid catalysts.

Description

Title

Production method of biofuels by heterogeneous catalysis using a metallic cincato as a precursor of solid catalysts

Technical sector

The present invention describes the use of solid catalysts, obtained by calcining a cincato of an alkaline earth metal or a divalent transition metal, for the production of biofuels, and in particular biodiesel, by transesterification under mild conditions of temperature and atmospheric pressure , of vegetable or animal oils or fats, with low molecular weight alcohols.

Prior art

The biodiesel is formed by a mixture of fatty acid esters obtained by transesterification of triglycerides present in vegetable oils and animal fats with low molecular weight alcohols (mainly methanol or ethanol).

The use of this biofuel has numerous advantages over other fossil fuels [Biores. Technol 70 (1999) 1-15], highlighting its renewable origin since the sources of triglycerides are fats of vegetable or animal origin, its high lubricating power that protects the engine by reducing its wear, and its biodegradable character. In addition, when used in diesel engines, either pure or mixed with petroleum-derived diesel, it significantly reduces harmful emissions such as CO, aromatic and unburned hydrocarbons, particulate matter and sulfur oxides. However, the use of biodiesel slightly increases the emissions of nitrogen oxides, although this inconvenience can be mitigated with a specific adjustment of the injection or by the use of specific catalysts for selective removal of NOx after post-combustion, and raises viscosity problems at low temperatures, which can be solved by the use of additives.

The transesterification process involves reacting triglycerides, major components of vegetable fats (vegetable oils) and animals (tallow), with methanol or ethanol. Triglycerides are lipids formed by esterification of the three hydroxyl groups of a glycerin molecule with three fatty acid molecules saturated or unsaturated. Depending on whether the alcohol is ethanol or methanol, the transesterification process results in the generation of fatty acid ethyl esters (FAEE, Fatty Acid Ethyl Ester in English) or fatty acid methyl esters (FAME, Fatty Acid Methyl Ester in English), respectively. In the event that the alcohol used is methanol, the transesterification reaction proceeds according to the following three reversible stages:

R ₁ COOCH ₂ HOCH ₂

| Catalyst _| *

R ₂ COOCH + CH ₃ OH <^> R ₂ COOCH + R ₁ COOCH ₃

R ₃ COOCH ₂ R ₃ COOCH ₂

Diglyceride Triglyceride

HOCH, _. „. HOCH ₂

I ² Catalyst _| ^z

R ₂ COOCH + CH ₃ OH _< > ^* HOCH + R ₂ COOCH ₃

R ₃ COOCH ₂ R ₃ COOCH ₂

Digicέrido Monoglicέrido

^HOC I ^H ₂ * _* C-a_twali-zad ^ or HOC ¡H ₂ '

HOCH + CH ₃ OH ^ V> HOCH + R ₃ COOCH ₃

R ₃ COOCH ₂ HOCH ₂

Monoglyceride Glycerin Alkyl ester

The overall reaction between one mole of triglyceride and three of methanol leads to one mole of glycerin and three moles of FAME. Said reaction can be carried out both in the absence and in the presence of catalyst. In any case, the formation of DMARD is normally favored by using an excess amount of alcohol with respect to the stoichiometric ratio. The reaction between triglycerides and methanol, which are immiscible, is accelerated by strong agitation, as it facilitates contact between these two phases.

However, the transesterification reaction can be carried out in the absence of catalyst and stirring, using methanol under supercritical conditions (temperatures above 239.5 ° C and pressures above 81 bar; US6187939, US6288251). However, these drastic reaction conditions involve the use of specific, high-cost equipment, which greatly limits their use for the treatment of low-quality cheap fats (high acidity and high water content). Consequently, the use of catalysts is a widespread practice, so that the speed of reaction is sufficiently high and high yields in biodiesel are obtained quickly, distinguishing homogeneous and heterogeneous catalytic processes, as well as solid and liquid catalysts.

On an industrial scale, the most widespread process employs basic catalysts such as KOH, NaOH or their corresponding methoxides, dissolved in methanol [Biores. Technol., 92 (2004) 297, US4303590], which by homogenous catalysis favor the transesterification of triglycerides with methanol. The use of acid catalysts has also been proposed to directly carry out the transesterification, but the reaction rates are slower than the basic catalytic process. All homogeneous processes require stages of neutralization, as well as intensive washing, both of the biodiesel and the alcoholic phase, which generates a significant volume of aqueous effluents that must be treated before discharge [Bioresource Technology 70 (1999) 1- fifteen]. In addition, the catalyst used in this homogeneous process cannot be reused, since it is lost in the neutralization and washing stages. The use of a solid catalyst, in a heterogeneous catalytic process, reduces the problems associated with homogeneous catalysis, since the solid catalyst can be separated from the reaction medium by simple physical procedures (filtration and / or centrifugation). There are numerous solid catalysts that have been proposed for triglyceride transesterification reactions, which can be classified as acidic, basic and enzymatic.

Among the active acid catalysts are mesoporous silicas functionalized with sulfonic groups (US7122688), carbons derived from polysaccharides functionalized with sulphonic groups [Green Chem. 9 (2007) 434] and vanadium pentoxide (EP2000522), although the latter catalyst is active at 225 ⁰ C and pressures between 35 and 60 Kg / cm ² .

Among the most commonly used basic catalysts is CaO [Bioresource Technology 70 (1999) 249-253; Energy & Fuels 20 (2006) 1310-1314; Appl. Catal. B 73 (2007) 317-326; Appl. Catal. A 334 (2008) 357-365], although MgO and Mg-Al mixed oxides derived from Mg-Al hydrotalcites (WO2006002087, WO2006050925) have also been used. Other solid catalysts used have basic Lewis-type sites, such as those based on guanidines anchored in inorganic or polymeric supports [J. Mol. Catal. A: Chem. 109 (1996) 37-44]. In most of these examples has been worked under mild conditions of temperature (from room temperature to 80 ⁰ C) and atmospheric pressure, although other metal oxides have proved to be active in more drastic conditions of pressure and temperature. Thus, the French Institute of

Oil (IFP) it has patented catalysts based on zinc oxide, aluminum oxide and zinc aluminate spinel type structure, which catalyze the transesterification reaction of triglycerides at temperatures between 170 and 250 ⁰ C, and pressures of 10-60 atm ( US5908946). IFP has also demonstrated the potential of mixed oxides of Ti and Al and mixed oxides of Sb and Al, under similar experimental conditions (US2005266139). A TiO2-based catalyst supported on silica has also been patented to obtain biodiesel (WO2006094986) at temperatures between (100-250 ° C) and the autogenous pressure generated by methanol. At high temperatures (150-350 ⁰ C) and pressures between 0.5-2 atm, a sulfated tin oxide has also proven active in transesterification reactions (US 7442668).

A mixture of zinc and calcium oxides prepared by precipitation of the corresponding nitrates and subsequent calcination at 600-900 ⁰ C has also been shown to be active in the transesterification of palm kernel oil with methanol, but to obtain higher FAME contents than 94% after 1 hour of reaction at 60 ⁰ C, require the use of 10% by weight of activated catalyst at 700 ⁰ C and a methanokaceite molar ratio of 30: 1 [Appl. Catal. A: Gen. 341 (2008) 77-85]. Other metal oxides that have also shown their usefulness as solid catalysts are those based on mixed oxides of V and P [Appl. Catal. A: Gen. 320 (2007) 1] and Fe-Zn [Appl. Catal. A: Gen. 314 (2006) 148].

In addition, the use of lipases as biocatalysts (enzymatic catalysts) for the transesterification of triglycerides with alcohols (US7473791) has been proposed.

The addition of compounds such as low molecular weight cyclic esters (tetrahydrofuran, 1,2 dioxane, terebutyl methyl ether, di-isopropyl ether, di-ethyl ether) to the triglyceride-alcohol reaction mixture has also been described and patented [Biomass Bionergy 11 (1996) 43, J. Am. OiI Chem. Soc. 75 (1998) 1167, US2003083514, US6712867].

Notwithstanding the foregoing, although several solid catalysts have been proposed for the production of biodiesel through a heterogeneous catalytic process, there are still important limitations that hinder its implementation at the industrial level, and are not yet a viable alternative to the homogeneous process. Among these drawbacks, it is worth mentioning the lower reaction speed of the heterogeneous process and the need for high temperatures (in some cases up to 800 ⁰ C) of activation of the solid catalyst, since it is necessary to remove water and carbonate from the surface of the catalyst, to generate strong basic sites. In addition, the solid catalyst must be able to be reused and eliminate the homogeneous contribution to the catalytic process of transesterification of triglycerides with low molecular weight alcohols, associated with the existence of solubilized basic species in the reaction medium. The invention object of the present patent application implies, in addition to the advantages already mentioned in relation to heterogeneous catalysis compared to homogeneous processes, a series of technical advantages that provide a solution to technical problems not solved by the alternatives that constitute the state of the technique: 1 - Simplicity, reproducibility and easy escalation of the synthesis. '- The precursor of the active catalyst is stable in air.

¹ - The decomposition or activation temperature of the catalyst is lower than that of other basic solid catalysts.

¹ - The kinetics of the reaction is similar to that described in homogeneous catalysis reactions, and significantly faster than in the case of other solid catalysts.

Disclosure of the invention

The present invention proposes a heterogeneous method of obtaining biofuels, particularly biodiesel, by catalytic transesterification using a metallic cincate, particularly an alkaline earth metal or a divalent transition metal, as a precursor to active solid catalysts.

The thermal activation of the metallic cincato used as a precursor can be carried out in a wide range of temperatures. The amount of precursor that can be used, and consequently of the resulting catalyst, so that the process is efficient, is also variable. The oils or fats that can be used as a substrate are also diverse, as well as their degree of acidity or their water content. Acceptable reaction conditions are also variable without the process being efficient. On the other hand, the nature of the precursor, the resulting catalyst, and the process conditions, allow catalyst recycling and reuse of the precursor.

In summary, the transesterification process using metal cincates as precursors is efficient and effective in a wide range of conditions.

Description of the figures Figure 1. X-ray diffractograms obtained after treating calcium cincate dihydrate at different temperatures. From top to bottom: room temperature, from 100 to 800 ⁰ C at intervals of 100 ⁰ C, and after cooling to room temperature. Figure 2. Yield in DMARD (%) as a function of the reaction time, when the percentage of calcium cincate dihydrate used is varied. The reaction conditions have been: activation temperature = 800 ⁰ C, molar ratio methanol: oil = 12: 1, stirring speed = 1000 rpm, reaction temperature = 60 ⁰ C.

Figure 3. Yield in DMARD (%) as a function of reaction time, when the activation temperature of calcium cincate dihydrate is varied. The reaction conditions have been: 1% by weight of precursor with respect to sunflower oil, molar ratio methanol: oil = 12: 1, reaction temperature = 60 ⁰ C, stirring speed = 1000 rpm.

Figure 4. Performance in FAME as a function of reaction time. Reaction conditions: 4% by weight of precursor with respect to sunflower oil, activation temperature = 400 ⁰ C, molar ratio methanol: oil = 12: 1, reaction temperature = 60 ⁰ C, stirring speed = 1000 rpm.

Figure 5. Performance in FAME in three cycles of reuse, and after remaining the calcium cincate dihydrate 14 days in contact with the air. Reaction conditions: 4% by weight of precursor with respect to sunflower oil, activation temperature ^ 400 ⁰ C, molar ratio methanol: oil = 12: 1, reaction temperature = 6O ⁰ C, reaction time = 1 hour, speed stirring = 1000 rpm.

Ways of carrying out the invention

In this invention, biodiesel is defined as a mixture of esters of low molecular weight alcohols, preferably methanol or ethanol, with fatty acids.

The preferred embodiment of the present invention involves the use of calcium cincate dihydrate as a precursor of the active solid catalyst.

The synthesis of calcium cincate dihydrate is carried out following the method proposed by Sharma [J Electrochem. Soc. 133 (1986) 2215-2219]. Said method, in a simplified manner, consists in suspending 5 g of zinc oxide (ZnO, <1 mm, 99.9%, Aldrich) in 500 ml of a 20% by weight solution of potassium hydroxide (KOH, Rectapur Prolabo), in a 1000 ml container, keeping with strong agitation for one hour. Then, without suspending the magnetic stirring, they are added slowly, and in this order 50 g of Ca (OH) ₂ (95%, ACS Reagent Sigma Aldrich), 73 my deionized water and 109.9 g of zinc oxide (ZnO, <1 mm, 99.9%, Aldrich). The reagent mixture is kept under stirring at 200 rpm for 72 hours. After this time the solid obtained is filtered under vacuum and is washed with deionized water thereof, until the pH of the washing waters is close to 11. After the washing process, the solid dried at 60 ⁰ C in the oven, finally obtaining the calcium cincate dihydrate (CaZn ₂ (OH) ₆ .2H ₂ O), and whose usefulness is shown in the embodiments described in the present patent application.

Particularly, the kinetics of the transesterification process is enhanced by the use of a 4% precursor weight, 12: 1 methanol radical oil ratios and 1000 rpm stirring speed, reaching 95% FAME yields after 45 minutes of reaction.

The catalysts obtained by thermal activation of calcium cincate dihydrate are particularly active in the transesterification of sunflower and soybean oil with methanol, causing the formation of methyl esters of fatty acids present in these oils (FAME). In the process of transesterification with sunflower oil, a conversion close to 100% was obtained in a reaction time of 1 hour when the precursor weight percentage was 4%. The only difference observed between the chromatograms of soybean oil and sunflower oil is the presence of a new peak of FAME in the chromatogram of soybean oil, due to the formation of methyl linolenate from the transesterification of triglyceride derived from linolenic acid and methanol In addition, oils with acidity index of 1.1 ° and water percentages of 0.2% can be treated without a drastic decrease in FAME performance.

Calcium cincate dihydrate is stable in air against water and carbon dioxide; The catalysts obtained can be recycled, since calcium and zinc oxides are the raw materials for the synthesis of calcium cincate dihydrate; the catalyst obtained by activation at 400 ⁰ C can be used for at least three catalytic cycles an hour, with yields FAME over 85% when 4% is used in weight zincate dihydrate calcium molar ratio metanohaceite 12: 1 . A series of non-limiting examples are described below, which show the flexibility and advantages of the present invention, and especially the use of this precursor for obtaining an active catalyst in the transesterification of vegetable oils with methanol, for the production of biodiesel. EXAMPLE Ij Reaction of catalytic transesterification of triglycerides to obtain biodiesel with catalysts obtained by heat treatment of calcium cincate dihydrate, with percentages by weight between 1 and 4% of precursor.

The basic heterogeneous transesterification reaction of triglycerides contained in sunflower oil begins with a catalyst activation stage. The previously weighed catalyst is activated in an inert atmosphere of helium (other gases can be used, although avoiding the use of air, since the carbon dioxide present in it could react with the catalyst at high temperature), in a tubular furnace (they can used alternative devices) at the temperature of 400 ⁰ C, using a heating rate of 20 ° C / min, and remaining one hour (shorter times result in less active catalysts) at the temperature of 400 ⁰ C.

The thermal-differential and thermogravimetric analysis of calcium cincate dihydrate reflects, between room temperature and 1000 ⁰ C, a total weight loss of 26.3%, associated with the elimination of hydroxyl groups (dehydroxylation process) and hydration water (dehydration process ). Thus a load of 4% by weight of precursor corresponds to approximately 3% by weight of catalyst. The calcium precursor and the catalyst obtained after thermal activation at 400 ⁰ C is determined by atomic absorption technique (ICP-AA). The values found were 19.9 and 25.1% CaO for the precursor, before and after activation, which are very close to the respective theoretical values of 18.2 and 25.6%. Chemical analysis indicates that calcium cincate dihydrate has no potassium in its chemical composition.

After activation at 400 ⁰ C for one hour, with a heating rate from room temperature to 400 ⁰ C of 20 ° C / min, the zincate dihydrate calcium is transformed into a mixture of zinc oxide and calcium oxide , as confirmed by the X-ray diffraction data.

One of the most relevant aspects of the catalyst obtained at 400 ⁰ C is its high specific surface area (76.7 m ^ g ^"1 ) and pore volume (0.144 crn ^ g ^{" 1} ). The pore size distribution is relatively narrow, centered around 4.3 nm, which allows triglyceride molecules to access the catalyst's basic sites.

The materials used in the transesterification reaction are basically: sunflower oil, methanol and catalyst. The reaction is carried out in a discontinuous reactor of complete mixing under N ₂ atmosphere, with reflux, magnetic stirring and at the temperature of 60 ⁰ C. This temperature is achieved by a silicone bath heated by a heating plate.

The complete mixing batch reactor has three mouths and a gas inlet. The central mouth is connected to a cooling system, to keep the volume of methanol constant inside the reactor. One of the mouths located at the ends is used in the aliquot extraction process for later analysis, while on the other the reactor temperature is controlled by a thermometer.

The system is in continuous agitation, to obtain optimum contact between phases, by means of a magnetic stirrer whose speed range is from 100 rpm to 1000 rpm. Sunflower oil (25 g) is preheated to 60 ° C in the reactor. The catalyst is introduced into the reactor without cutting off the helium current to prevent the entry of air and therefore of CO ₂ . Subsequently, and with continuous magnetic stirring, the methanol (16.5 ce) is poured and the reactor is sealed. Magnetic stirring allows the contact of the two immiscible phases (methanol and oil). The assembly of the complete mixing batch reactor is confined within a gas extraction hood, to prevent possible problems caused by methanol leaks in the assembly.

The separation process consists of a stage of extraction, filtration, neutralization and decantation. The extraction step is to obtain a sample aliquot (1.5 ml) of the reaction medium, by means of a syringe. The filtration step is then carried out by means of a microfilter, in order to remove the catalyst particles present. The neutralization step is based on the addition of 1 ml of the 0.1 M solution of HCl, to neutralize the remaining basic catalyst residues. Subsequently we reach the stage of decantation, adding 1.5 ml of dichloromethane and vigorous stirring to the sample. Two phases are obtained: an organic phase (ester phase) and an aqueous phase (alcoholic phase).

The ester phase also contains dichloromethane and traces of methanol that must be removed before analyzing the biodiesel phase. For this, the solution is maintained for 5 hours in a sand bath at a temperature of 90 ⁰ C. The samples were analyzed by high performance liquid chromatography.

(HPLC) with a JASCO device equipped with a quaternary gradient pump (PU-2089), an ultraviolet detector (MD-2015), an automatic injector (AS-2055) and a column oven (co-2065). The column used was PHENOMENEX LUNA Cl 8 (250 mm x 4.6 mm x 5 μm). The solvents were microfiltered and degassed with helium. A linear gradient from 100% methanol to 50% - 50% methanol-isopropanol: hexane (5: 4 v / v). The injection volumes in the column were 15 μL, with a constant column temperature equal to 40 ⁰ C. The purified samples were previously prepared for analysis in the HPLC, dissolving 80 μl of the sample in 10 ml of the isopropanol / hexane mixture (5: 4 v / v).

For the analysis of methyl esters (biodiesel) an array diode detector has been used, at a wavelength of 205 nm. The double bonds C = C of the alkyl chains of the fatty acids absorb in the UV region of the electromagnetic spectrum.

The triglyceride areas of the unreacted oil have been recorded, as have the areas of methyl esters (biodiesel or FAME) and mono-, diglycerides and free fatty acids.

Samples were taken at certain reaction times and the content of methyl esters, FAME, of the lipid phase was analyzed.

In Figure 1 the X - ray diffractograms of zincate dihydrate calcium occur at room temperature and after activation at different temperatures, which can be seen that at 400 ⁰ C only appear diffraction signals crystal ZnO (*), while that the crystalline CaO is visible from a temperature of 500 ⁰ C. After calcining at 800 ⁰ C and cooling, the solid is formed by a mixture of crystalline CaO and ZnO. The increase in the precursor percentage favors the formation of FAME (Figure 2), and thus after its activation at 800 ⁰ C, with a 4% precursor, FAME yields greater than 93% are obtained with a reaction time of 1 hour , molar ratios methanol: oil of 12: 1 and a reaction temperature of 60 ⁰ C. The influence of the precursor weight used is observed mainly at the shortest reaction time, since, after two hours, the yields to FAME They are similar (> 85%).

EXAMPLE 2: Reaction of catalytic transesterification of triglycerides to obtain biodiesel with catalysts obtained by activating calcium cincate dihydrate at different temperatures.

This example demonstrates the influence of the activation temperature of calcium cincate dihydrate on the catalytic behavior in the transesterification of sunflower oil with methanol. Temperatures of 350, 400, 500 and 800 ⁰ C were used, a weight percentage of calcium cincate dihydrate of 1%, methanol: oil molar ratios of 12: 1 and a reaction temperature of 60 ⁰ C. After thermal activation at 350 ⁰ C, the catalyst obtained needs a reaction time of 3 hours to reach a yield of 89% (Figure 3). However, with temperatures at or above 400 ⁰ C, the values obtained are higher over the entire range of reaction times studied, and two hours yields FAME are over 85%.

This higher catalytic activity observed after activation zincate dihydrate calcium at or above 400 ⁰ C temperature is attributed to the higher degree of dehydroxylation of calcium oxide present in the catalyst, although zinc oxide should also contribute to Catalytic transesterification process. The use of 4% by weight of precursor and an activation temperature of 400

⁰ C improves the kinetics of the catalytic process of transesterification of sunflower oil with methanol compared to other solid catalysts. Thus, FAME yields of 73% are obtained at 30 minutes of reaction, 94% at 45 minutes, and 100% is reached at 60 minutes (Figure 4).

EXAMPLE 3: Reaction of catalytic transesterification of triglycerides to obtain biodiesel with a catalyst obtained after calcining calcium cincate dihydrate at 400 ⁰ C. in different reuse cycles.

The catalyst obtained after calcining the calcium zincate dihydrate in inert atmosphere at 400 ⁰ C was used in several cycles of reuse. For reuse tests, the solid catalyst is separated from the solution (reagents and reaction products) by centrifugation at 7000 rpm for 7 minutes. Then the catalyst obtained in the centrifugation process is reused, but without performing the previous activation stage. The results obtained are shown in Figure 5, where it is observed that this catalyst can be used for at least three 1-hour catalytic cycles, with FAME yields greater than 86%.

In this Figure 5, the catalytic activity is also presented after leaving the calcium cincate dihydrate in contact with the air for 14 days, and activating at 400 ⁰ C. With 4% by weight of precursor yields greater than 91% are observed. . The analysis of gases emitted by mass spectrometry (EGA-MS) as a function of temperature is very similar to that of the fresh precursor, which demonstrates that calcium cincate dihydrate is stable against moisture and carbon dioxide in the atmosphere. EXAMPLE 4j Catalytic transesterification reaction of triglycerides to obtain biodiesel with a catalyst obtained after calcining the calcium cincate dihydrate at 400 ⁰ C using an oil with an acid number of 1.1 ° and water percentages greater than 0.1%.

The catalyst obtained after activating calcium zincate dihydrate 400 ⁰ C has been used to study the influence of the acidity of the oil on the performance of FAME. To this end, different amounts of oleic acid (C ₁₈ H ₃₄ O ₂ ) have been added to sunflower oil, to achieve acid values of 0.55 ° and 1.1 ° (typical acidity of a used vegetable oil).

According to the results obtained from activity for reactions with 4% calcium cincate dihydrate, it is observed that acidity hardly affects the activity of our catalyst (Table 1) While with virgin sunflower oil with an index of 0.2 ° reach conversions close to 100% at the time of reaction, an increase in acidity at 1.1 ° produces a moderate decrease in activity by only 12% lowering the conversion. This decrease in activity can be attributed to the fact that the increase in free fatty acids in the reaction medium favors the solubilization of the active phase (CaO), by formation of the corresponding calcium oleates. In the presence of an acid value of 0.55 ° there is no apparent decrease in catalytic activity.

% by weight of Time H ₂ O Acidity Yield FAME precursor (h) (wt%) O (%)

1 3 <0.1 <0.2 100

1 3 0.2 <0.2 79

1 3 1.0 <0.2 61

4 1 <0.1 <0.2 100

4 1 <0.1 0.55 99.7

4 1 <0.1 1.1 88.3

Table 1. Influence of the presence of water and free fatty acids in sunflower oil on the yield in FAME (activation temperature = 400 ⁰ C, 4% by weight of calcium cincate dihydrate, molar ratio methanol: sunflower oil = 12: 1, reaction temperature = 60 ⁰ C)

In relation to the presence of water in the oil, the results obtained show the negative effect of the concentration of water present in the oil, observing a 20% decrease in the conversion after 3 hours of reaction, in the case of oils with a water content the same as a used oil (Table I)). As expected, the negative effect of water at higher concentrations is much greater, since for 1% H ₂ O there is a 40% decrease in conversion.

Water concentration partially affects the catalyst, lowering the conversion to FAME. An explanation of this decrease in activity would lie in the hydroxylation of CaO, to cause Ca (OH) ₂ of lower activity.

Claims

1. Procedure for the production of biofuels by heterogeneous triglyceride catalysis with alcohols characterized in that it comprises the following stages: a. Thermal activation of the precursor of a basic solid catalyst, b. Transesterification, c. Extraction of the transesterification product, d. Filtration of the transesterification product in order to remove the catalyst particles present, e. Neutralization of persistent catalyst residues in the transesterification product after extraction and filtration, f. Decantation and obtaining of the organic (ester phase) and aqueous (alcohol phase) phases, and g. Elimination of traces of alcohol and its derivatives of the ester phase by heat treatment.

2. Method according to the preceding claim characterized in that the precursor of the basic solid catalyst consists of a metallic cincato.

3. Method according to the preceding claim, characterized in that the precursor consists of a cincato of an alkaline earth metal or a divalent transition metal.

4. Method according to the preceding claim characterized in that the precursor consists of calcium cincate dihydrate.

5. Method according to the preceding claim characterized in that the thermal activation of the precursor of the basic solid catalyst is carried out at a temperature in the range 350-800 ⁰ C.

Method according to the preceding claim characterized in that the activation is carried out in an inert atmosphere of a noble gas.

7. Method according to the preceding claim characterized in that the activation is carried out in an inert atmosphere of helium.

8. Method according to claim 6 or 7 characterized by activation is performed using a heating ramp of 2O ⁰ C / min.

Method according to any one of claims 5 to 8, characterized in that the thermal activation of the precursor of the basic solid catalyst is carried out at 400 ^° C.

Method according to any one of claims 5 to 9, characterized in that the residence time at the activation temperature is 1 hour.

11. Method according to the preceding claim characterized in that the activation is carried out in a tubular oven.

12. Method according to any of the preceding claims characterized in that the transesterification substrates comprise animal or vegetable oils or fats and a low molecular weight alcohol.

13. Method according to the preceding claim characterized in that the vegetable oils or fats come from sunflower or soy.

14. Method according to any of claims 12 to 13 characterized in that the low molecular weight alcohol is methanol.

15. Method according to any of claims 12 to 14, characterized in that the transesterification is carried out in a discontinuous reactor of complete mixing under N ₂ atmosphere, with reflux, magnetic stirring and at a reaction temperature of 60 ⁰ C.

16. Method according to the preceding claim characterized in that the reactor is connected to a refrigerant system to keep the volume of alcohol constant and because it allows the reaction temperature to be monitored.

17. Method according to claim 15 or 16, characterized in that the reaction temperature of the transesterification stage is obtained by a silicone bath heated by a heating plate.

18. Method according to any of claims 12 to 17 characterized in that the reaction conditions are: 1-4% by weight of thermally activated precursor at 400 ⁰ C with respect to the amount of substrate oil, 12: 1 methanol radical ratio, temperature of 6O ⁰ C transesterification reaction, and stirring speed of the reaction mixture 1000 rpm.

19. Method according to the preceding claim characterized in that the reaction conditions are: 4% by weight of thermally activated precursor at 400 ⁰ C with respect to the amount of substrate oil, 12: 1 methaneite molar ratio, 6O ⁰ C transesterification reaction temperature , and stirring speed of the reaction mixture 1000 rpm.

20. Method according to any of the preceding claims characterized in that the filtration of the transesterification product once extracted is carried out by means of a microfilter.

21. Method according to any of the preceding claims characterized in that the neutralization of the extracted and filtered transesterification product is carried out by HCl.

22. Method according to any of the preceding claims characterized in that the decantation is carried out by adding dichloromethane and vigorously stirring the resulting mixture.

23. Method according to any of the preceding claims characterized in that the removal of dichloromethane and alcohol traces from the ester phase after the decantation stage is carried out by heating it for 5 hours in a sand bath at 90 ⁰ C.