ES2376936B1 - TRANSESTERIFICATION PROCESS OF ESTERS WITH ALCOHOLS USING HETEROGENEOUS CATALYSTS. - Google Patents

Abstract

Transesterification process of esters with alcohols using heterogeneous catalysts # The present invention relates to a process of transesterification of esters with alcohols, in which heterogeneous catalysts are used to obtain biodiesel.

Description

TRANSESTERIFICATION PROCESS OF ESTERS WITH ALCOHOLS USING HETEROGENEOUS CATALYSTS

STATE OF THE PREVIOUS TECHNIQUE

The environmental problems together with the decrease in oil reserves and the instability of the prices of fuels derived from it have stimulated the research and development of new fuels from renewable energy sources that, in addition to being environmentally acceptable, allow us to stop depend on the volatile oil market and ensure the availability of energy nationwide. In this sense, the production of biofuels such as biodiesel has become one of the most attractive alternatives, starting from energy sources as abundant as oils derived from vegetable seeds or animal fats.

Biodiesel is a biodegradable, non-toxic fuel, as it contains hardly any sulfur, and has very low emission profiles compared to diesel obtained from petroleum. Thus, the use of biodiesel in conventional diesel engines results in a substantial decrease in the concentration of unburned hydrocarbons, CO and particulate emissions. Although the specific energy of biodiesel is lower than that of diesel, its high lubricity and higher cetane number make the energy performance of biodiesel similar to that of diesel.

Biodiesel is composed of alkyl esters of fatty acids, usually methyl (FAMEs; fatty acid methyl esters) or ethyl (FAEEs; fatty acid ethyl esters), which have properties similar to those of diesel obtained from petroleum. These esters can be prepared from oils or fats of vegetable or animal origin and used in mixtures with diesel obtained from petroleum without the need for modification of the conventional diesel engine.

Biodiesel can be prepared by transesterification (alcoholysis) processes of glycerides, preferably triglycerides, either vegetable oils or animal fats, in the presence of a catalyst. Transesterification is a chemical reaction that takes place, as indicated in scheme (I), between an ester (1) and an alcohol (2) giving rise to a new ester

(3)

and other alcohol (4).

RCOOR1 + R2-CH2OH ----> RCOOCH2R2 + R1-OH 1 2 34

(I)

Since the transesterification reaction is a chemical equilibrium, alcohol

(2)

it is added in excess to favor a high yield in the ester (3).

Triglycerides are made up of a glycerol molecule, which has its three hydroxyl groups esterified by three fatty acids, saturated or unsaturated. The length of the chains of triglycerides of natural origin, whether animal or plant, ranges from 16 to 22 carbon atoms.

Numerous processes for the production of biodiesel using various catalysts have been described. These catalysts can be basic, such as, for example, sodium and potassium hydroxides, or the corresponding alkoxides; or acids, such as sulfuric acid, sulfonic acids, or hydrochloric acid. The catalytic activity of the bases in this type of reaction is greater than that of the acids, and in addition the acids give rise to corrosion problems in the reactors and can catalyze unwanted side reactions such as isomerizations or dehydrations, so the basic route is generally preferred. As basic catalysts, sodium or potassium hydroxides and sodium methoxide can be used. Although sodium methoxide is very active, it requires anhydrous conditions, so hydroxides are preferred at an industrial level.

The transesterification processes of glycerides with monohydric alcohols, such as methanol or ethanol, in the presence of these alkaline bases, are usually carried out discontinuously, generally in stirred tank type reactors, and have a number of drawbacks. As a secondary product, and practically from the beginning of the reaction, glycerol is formed, which gives rise to a new phase. Due to the high solubility of the alkaline bases in it, the amount of catalyst is diminished in the phase of the reaction, which slows down the reaction. In addition, stable emulsions are formed due to the presence of water and free fatty acids that make it difficult to separate the biodiesel and glycerol phases. Even after eliminating excess alcohol and separating the phases, the biodiesel phase comprises glycerol and catalyst (raw biodiesel) that must be removed by washing, with the consequent environmental and economic disadvantages (generation of discharges). The glycerin phase obtained furthermore comprises water and the alkaline catalyst, that is, it is of very low purity. Therefore, glycerin is subjected to an additional neutralization step which results in glycerin in aqueous solution and large amounts of NaCl as a by-product. This glycerin solution is a product with low added value for the industry, so it is generally subjected to a burning process to obtain energy.

In summary, the conventional procedures currently implemented in the industry comprise numerous washing and purification stages, mainly the biodiesel phase, and the obtaining of a very low purity glycerin phase, resulting in an environmentally damaging and economically inefficient global process. One of the ways to avoid all this series of drawbacks and to provide high purity phases by means of an environmentally acceptable process is replacing the alkaline aqueous solutions by basic solid catalysts. As is known to those skilled in the art, the advantages of applying heterogeneous catalysts in replacement of conventional homogeneous catalysts are very numerous. In the technical field, eliminating the water from the reaction medium dramatically reduces the formation of emulsions, allowing a simple separation of the biodiesel and glycerin phases. In addition, high purity phases are obtained that do not require subsequent chemical treatments, since the catalyst can be separated and recovered by simple filtration.

Basicity has been directly related to activity in the bibliography (the stronger the active centers, the greater the activity and, in general, the higher the yields in FAMEs). In the article Biodiesel synthesis using calcined layered double hydroxide catalysts (JL Shumaker et al., Applied Catalysis B: Environmental 82 (2008) 120-130), the activity of calcined hydrotalcites Li-Al, Mg-Al and Mg-Fe is compared . In this sense, the Mg-Al and Mg-Fe catalysts of the mentioned article have very similar basicities and give rise to very similar activities, while the Li-Al catalyst is the most active and has stronger basic centers. Also in this article, the Li-Al catalyst is said to be the most active, and although it has a very low loss of lithium in laboratory tests, which are short-time, it is very likely that in industrial conditions if it significantly affects this loss of lithium given the longer operating times of industrial units.

Also in another article entitled Catalytic properties of layered double hydroxides and their calcined derivatives (W. Kagunya et al., Inorganic Chemistry 35 (1996) 5970-5974), which deals with the use of hydrotalcites and their calcined derivatives in the ethanolysis reaction of propylene oxide, concludes that the activity of hydrotalcites would be directly related to the acidity measurements, while the order of activities of the calcined derivatives (with predominantly basic properties) does not follow a trend based on basicity.

However, the difference between this publication and what is described in the present invention resides in that the publication mentions hydrotalcites for the reaction of ethanolisis of propylene oxide, while in the present invention an ethanolisis or methanolisis of a triglyceride is described, by a transesterification reaction. In summary, catalysts with active centers of different chemical nature are synthesized, mainly the basic character, which is responsible for catalyzing reactions such as propylene oxide ethanolysis. In the present invention it is described that since the chemical reaction is different: triglyceride ethanolysis or methanolysis, by transesterification reaction, active centers of different basic character are required, mainly distribution of basic centers and strength of these centers, to those described in this scientific publication.

DESCRIPTION OF THE INVENTION

The present invention relates to a process of transesterification of esters with alcohols by heterogeneous catalysts of mixed metal oxide type.

Heterogeneous catalysts of the mixed metal oxide type can be obtained from any of the following procedures:

-

Co-precipitation involving, on the one hand, an aqueous solution of soluble metal salts (Zn, Fe, etc.) and, on the other hand, an aqueous solution of sodium carbonate, sodium bicarbonate or sodium nitrate, and the Resulting material is subjected to successive washes until elimination of residual sodium ions. Preferably the coprecipitate formed is a double lamellar hydroxide with a structure of the hydrotalcite type. The material thus prepared is subjected to a thermal decomposition treatment at temperatures lower than between 100 and 1200ºC, preferably between 200 and 1000ºC and even more preferably between 350 and 700ºC, and even more preferably between 400 and 600ºC, thus forming the mixed metal oxide. Thermal decomposition can be carried out under reduced pressure (vacuum), and / or in a static or flowing gas atmosphere, preferably in a gaseous air flow. The duration of the heat treatment can be between 1 and 24 hours, preferably between 2 and 12 hours. Finally, the material can be molded into grains or extruded.

-

 Co-precipitation from a solution comprising the metal ions (Zn, Fe, etc.). This co-precipitation can be carried out, for example, in the presence of urea. The thermal decomposition of urea allows the production of the carbonate anion and the rise in pH, which allows the co-precipitation of metals. The resulting material, preferably a double-layered hydroxide with a hydrotalcite-like structure, is subjected to successive washes until ammonia and residual ions are removed. The material thus prepared is subjected to a thermal decomposition treatment at temperatures lower than between 100 and 1200ºC, preferably between 200 and 1000ºC and even more preferably between 350 and 700ºC, and even more preferably between 400 and 600ºC, thus forming the mixed metal oxide. Thermal decomposition can be carried out under reduced pressure (vacuum), and / or in a static or flowing gas atmosphere, preferably in a gaseous air flow. The duration of the heat treatment can be between 1 and 24 hours, preferably between 2 and 10 hours. Finally, the material can be molded into grains or extruded.

Mixed metal oxides have the following characteristics:

-

A specific surface of between 20 and 300 m2 / g, preferably between 50 and 200 m2 / g, determined by adsorption of N2 at 77 K by the BET method.

-

They comprise at least one Zinc oxide and at least one second oxide of a second element B, where B is selected from trivalent cations selected from the group consisting of Vanadium, Chromium, Manganese, Iron, Cobalt or any of their combinations, preferably selected from Iron and Chrome or any of their combinations.

-

Mixed metal oxides are selected from the following general formulas:

or (ZnO) a (B2O3) 1-a, where a has a value between 0.05 and 0.95, and where preferably the molar ratio B / (B + Zn) has a value between 0.15 and 0.70.

or (Zn1-αMαO) a (B2O3) 1-a, where M is a metallic element selected from the group consisting of the elements of groups IIA, IIIA, IIIB and IVB with oxidation status +2, +3, +4 or a mixture thereof, preferably with oxidation state +2, where a has a value between 0.05 and 0.95, where α has a value between 0.05 and 0.95, and where preferably the molar ratio N / (B + Zn + M) has a value between 0.15 and 0.70.

or (ZnO) a (B2-βMβOγ) 1-a, where M has an oxidation state of +3, +4 or a mixture thereof, where a has a value between 0.05 and 0.95, where β has a value between 0.05 and 0.95, and where γ is the number of oxygen atoms that satisfies the valence of element B in combination with element M and where preferably the molar ratio (B + M) / (B + M + Zn) has a value between 0.15 and 0.70.

or (Zn1-αM1 αO) a (B2-βM2 βOγ) 1-a, where M1 is a metallic element with oxidation state +2, where M2 is a metallic element with oxidation state +3 or +4, where a has a value between 0.05 and 0.95, where β has a value between 0.05 and 0.95, and where γ is the number of oxygen atoms that satisfies the valence of element B in combination with element M2 and where preferably the molar ratio (B + M2) / (B + M2 + Zn + M1) has a value between 0.15 and 0.70

Catalysts, mixed metal oxides, direct the transesterification reaction between esters and monoalcohols. Preferably the esters are glycerides selected from the group consisting of triglycerides, diglycerides, monoglycerides or any combination thereof, preferably triglycerides.

Alcohols are monohydroxyls selected from the group consisting of monohydric alcohols of 1 to 4 carbon atoms, preferably 1 or 2 carbon atoms, or a mixture thereof.

The transesterification process according to all the aforementioned comprises the following stages:

to.

 Transesterification.

b.

Evaporation and recovery of excess monoalcohol.

c.

Separation by decantation of glycerin and the ester mixture comprising unconverted molecules of glycerides and alcohols.

d.

Transesterification of the ester mixture obtained in step c), with a proportion of the monoalcohol recovered in step b).

and.

Evaporation of excess monoalcohol after step d) and separation by decantation of glycerin and ester mixture.

In this way, yields of at least 85% in alkyl esters of fatty acids are achieved with a glyceride conversion of close to 100% in a continuous process in a fixed-bed reactor, with a VVH value between 0.1 and 3 Obtaining between 80 and 85% in alkyl esters in the biodiesel phase is suitable for a first transesterification stage, after which, the yields are increased by carrying out the second transesterification of the biodiesel phase, after the elimination of the alcohol in excess and separation of glycerin by decantation. The biodiesel fraction obtained has application as a biofuel, for mixtures with other (bio) fuels and as an additive for (bio) fuels.

The transesterification reactions between glycerides and monoalcohol take place according to conventional procedures in fixed-bed reactors with continuous feed of the reagents.

The reaction between glycerides and monoalcohol is carried out in a temperature range of between 50 and 300ºC, preferably between 150 and 250ºC, at a pressure of less than 100 Bar, preferably between 15 and 60 Bar with an alcohol / triglyceride molar ratio , between 5 and 15, preferably between 6 and 9.

Definitions:

•

VVH: Space Speed: Flow rate of liquid fed to the reactor (oil + alcohol) divided by the volume of catalyst. Additionally, the units have not been placed in memory, and it is usually (1 / h), since it is (m3 / h oil + alcohol) / (m3 catalyst).

•

BET method, is a mathematical procedure to calculate the specific surface area of the catalyst from the adsorption isotherm of N2 to 77

k. I add a more detailed definition:

The BET method is based on determining the amount of adsorbate needed to complete an adsorbed monolayer (Vm). For this, values of adsorbed volume (V) must be obtained at different pressures (P), in the interval between 0.05 P0 and 0.33 P0, where P0 is the saturation pressure at the operating temperature. The linear fit of the experimental data to the linear form of the BET equation:

P / V (P0-P) = 1 / (Vm. C) + (c-1) / (Vm. C) (P / P0)

c: constant It allows to calculate Vm, and from this value, that of the specific surface.

Detailed description of the invention

Examples:

Example 1: Synthesis of Catalysts

Solid materials containing Zn-Fe were synthesized by co-precipitation from a homogeneous solution in the presence of urea. Typically, the salts of the divalent metals (total 0.06 mol of metals) are dissolved in 100 ml of a urea solution (resulting solution of 1M concentration), and the aqueous solution comprising dissolved the salts of the trivalent metals (and , where appropriate, tetravalents; in total 0.01 mol of metals) are added dropwise over the first solution with vigorous stirring. Table 1 includes the reagents (mineral and organic sources) used for the synthesis of the materials, and Table 2 shows the molar compositions of the different solutions used for the synthesis of the materials. The mixture is homogenized with stirring for 30 minutes before refluxing (100 ° C) for two days. The thermal decomposition of urea allows the production of carbonate anion and the increase in pH allows the co-precipitation of metals. After synthesis was complete, the material was recovered by filtration, washed with distilled water, dried at 60 ° C for 12 hours, calcined at 450 ° C under air flow, and grain-molded.

Table 1

Reactive Source

Anion Carbonate Urea Zinc ZnCl2 Magnesium MgCl2 · 6H2O Iron FeCl3 · 6H2O Aluminum Al (NO3) 3 · 9H2O Lanthanum La (NO3) 3 Titanium Ti (OCH2CH3) 4

Table 2

Material Molar compositions

ZnO MgO Fe2O3 TiO2 Al2O3 La2O3 H2O Urea ZnFe 6 0.5 --- 555 10.8 ZnFeTi 6 -0.05 0.9 --555 10.8 ZnFeAl 6 -0.05 -0.45 -555 10.8 ZnMgFe 4 2 0.5 --- 555 10.8 ZnMgAlFe 4.8 1.2 0.05 -050 555 10.8 ZnMgFeLa 4.8 1.2 0.45 --0.05 555 10.8 ZnTiFeAl 6 -0.4 0.1 0.05 -555 10.8

Example 2: Reactivity of Catalysts

The transesterification reaction is carried out in a tubular reactor of

10 6.35 cm diameter stainless steel about 20 cm long wrapped in a thermocouple heating blanket. The reactor is charged with silicon carbide in grains of size> 0.6 µm, solid catalyst prepared according to Example 1 in grains of size in the range 0.25-0.50 µm, and silicon carbide in grains of size> 0.6 µm. At the top of the reactor, carbide

15 of silicon acts as a mixer and preheater of the oil / alcohol mixture, before coming into contact with the catalytic bed, and, at the bottom, eliminates the existence of dead volumes before the cooling zone. The reaction is carried out with anhydrous methanol and a refined sunflower oil (content less than 2% in free fatty acids) on a volume of between 1.0 and 2.0 cm3 of catalyst. At the outlet of the reactor a cooling zone and a valve that allows the regulation of pressure and the collection of crude oil. At the desired reagent flows, and at constant pressure, two independent pumps continuously inject the alcohol and oil into the reactor, through its upper part, directly to the silicon carbide that acts as a preheater.

The crude from the reaction is collected in 15 minute differential intervals, so that the results shown below for a given reaction time t (for example 2 hours) correspond to the products collected during said 15 minute interval ( for the example of 2 hours, in the reaction interval 1 hour and 45 minutes - 2 hours). The analysis of the reaction crude is carried out by gas chromatography without prior purification of the sample.

Temperatures are accurate with an error of ± 2%. The VVH parameter is the volume of oil injected per volume of catalyst and per hour. The R ratio is the alcohol / oil molar ratio. The pressure corresponds to the top pressure of the reactor. The contact time (tcont), expressed in minutes, considers the volume of alcohol injected and corresponds to the equation:

V t

=

tcont

V + V

OilAlcohol

The composition of the product mixture is expressed in mol% considering that in a triglyceride (TG) there are 3 ester type groups, in a diglyceride (DG) there are 2 ester type groups, and in a monoglyceride (MG), in an acid free fatty (AGL) and in an alkyl ester (E) there is an ester type group.

Table 3

Catalyst T P t R VVH TG DG MG AGL E tcont (ºC) (Bar) (h) (h-1) (min)

ZnFe 240 56 2 7.2 0.91 0.0 0.0 3.9 0.1 96.0 51

ZnFeTi 240 56 2 7.2 0.86 0.0 0.0 2.3 0.6 97.1 54

ZnFeAl 240 56 2 7.2 0.89 0.0 0.0 3.5 0.3 96.2 52

ZnMgFe 230 52 2.5 7.2 0.85 0.3 0.3 4.4 1.6 93.4 57

ZnMgFeAl 230 52 3 7.2 0.90 1.0 1.6 5.6 1.9 89.9 51

ZnMgFeLa 230 52 3 7.2 0.88 0.8 1.0 6.0 0.9 91.3 52

ZnTiFeAl 240 56 3 7.2 0.77 0.0 0.5 5.1 0.5 93.9 60

The content of fatty acid alkyl esters in the biodiesel phase can be increased after a step of evaporation and recovery of excess alcohol, a step of separating the phases of biodiesel and glycerin by decantation, and a step of feedback of the biodiesel phase on the catalytic bed with part of the recovered methanol or with new methanol.

Example 3: Catalyst Stability

Under reaction conditions of 240ºC, 56 Bar pressure, R = 7.2, VVH = 0.89 h-1 and a contact of 52 min, the ZnFeAl catalyst is completely stable for at least 24 hours (Figure 1).

Example 4: Regeneration and Reuse

A second transesterification reaction is carried out with the ZnTiFeAl catalyst, after regeneration by calcination at 450ºC in air flow, after 24 hours of a first transesterification reaction according to Example 2. At 240ºC, 56 Bar pressure, R = 7.2, VVH = 0.77 h-1 and contact = 60 min, after 3 hours of reaction the product mixture has a composition of 93.3% in E, 0.5% in AGL, 4.8% in MG, 0.8% in DG and 0.6% in TG.

Example 5: Comparative study of transesterification processes

In the present study, the results obtained in transesterification processes carried out by using the catalysts developed in the present invention and the catalysts developed in the US patent US5908946, hereinafter IFP, are compared.

When IFP carries out the reaction at 240 ° C, 50 Bar pressure, VVH = 0.5, an oil / methanol ratio = 2/1 v / v, and for a contact time of 80 minutes, in the presence of a catalyst containing 12.7 % wt. from ZnAl2O4,

43.92% wt. ZnO and 43.38% wt. of Al2O3 obtained by calcination at 600ºC, they obtain a biodiesel with the following composition: 0.02% TG, 1.3% DG, 4.35% MG and 94.1% FAMEs. If the oil / methanol ratio = 1/1 v / v (contact time 60 minutes) and keeping the other reaction parameters constant in the presence of the same catalyst, then they obtain a composition biodiesel: 0.23% TG, 1.6% DG, 5.3 % MG and 92.6% FAMEs.

When these results are compared with those obtained with the catalysts developed in the present invention, they are obtained by carrying out the reaction at 240ºC, 50 Bar pressure, VVH = 0.9, an oil / methanol ratio = 3.3 / 1 v / v and a contact time of 52 minutes (much less than IFP, therefore much more active catalysts) the following results:

-

 Mass ZnFe catalyst obtained by calcination at 450ºC (Fe3 + / Fe3 ++ Zn2 + = 0.16 molar ratio), a biodiesel composition is obtained: 1.3% TG, 1.2% DG, 7.5% MG and 90.0% FAMEs.

-

 Mass ZnCr catalyst obtained by calcination at 450ºC (molar ratio Cr3 + / Cr3 ++ Zn2 + = 0.33), a biodiesel with a composition of 1.0% TG, 1.2% DG, 8.0% MG and 88.2% FAMEs is obtained.

-

Mass ZnFeAl catalyst obtained by calcination at 450ºC (78.0% wt Zn, 1.4% wt Fe and 5.7% wt Al; molar ratio M3 + / M3 ++ Zn2 + = 0.17 and Al / Fe = 8), a biodiesel of composition 0.01% is obtained TG, 0.14% DG, 6.9% MG and 92.3% FAMEs.

-

Mass ZnTiFe catalyst obtained by calcination at 450ºC (72.8% wt Zn, 1.6% wt Fe and 8.2% wt Ti) a biodiesel is obtained with composition: 0.01% TG, 0.3% DG, 7.0% MG and 92.1% FAMEs.

-

 ZnFeAl / Al2O3 catalyst obtained by calcination at 450ºC (starting from 40% hydrotalcite dispersed in alumina) at the same temperature and pressure, VVH = 0.75, an oil / methanol ratio = 3.3 / 1 v / v and a contact time of 61 minutes, biodiesel is obtained with the following composition: 1.2% TG, 0.6% DG, 5.3% MG and 90.9% FAMEs.

These results, including those shown in IFP, are for a biodiesel sample after 24 hours of reaction, and expressed in% by weight. From the comparison of said results, it is observed that the biodiesel compositions are very similar, but the difference is that the catalysts developed in the present invention produce, for the same reaction time, almost twice as much biodiesel as for the same amount of catalyst ( Higher VVH) and with less amount of methanol (higher oil / methanol volume ratio).

On the other hand, in ethanolysis processes there are differences. The same IFP catalyst, for a reaction temperature of 240ºC, VVH = 0.25, oil / ethanol = 1/1 v / v, and contact time 120 min, gives a biodiesel of composition: 0.01% TG, 0.2% DG, 3.4% MG and 96.3% FAEEs.

However, with the catalysts developed in the present invention, ZnFeAl, for a temperature of 240ºC, VVH = 0.9, oil / ethanol = 2.3 / 1 v / v, and contact time 47 min, a biodiesel of composition is obtained: 0.4% TG, 1.5% DG, 10.6% MG and 87.0% FAEEs. Although the composition of biodiesel is different, it should be noted that the conditions that have been used are much more drastic (the contact time is almost three times less and more than triple the oil is processed, the VVH parameter is 3.6 times greater) .

To check these comparisons, a Zn-Al mass catalyst derived from a hydroxide with a lamellar structure (Al / Al + Zn = 0.53; deduced from chemical analysis) is prepared by calcination at 450 ° C. Although the catalyst contains (according to chemical analysis) an excess of Al (over the range of formation of pure double hydroxides), the characterization by X-ray diffraction shows only the presence of ZnO and spinel ZnAl2O4 phases, being the absence of peaks of diffraction corresponding to an Al2O3 phase (expected from chemical analyzes) interpreted as due to crystal size (<4-5 nm not detectable by the diffraction technique).

Based on these data, it can be considered that the prepared Zn-Al catalyst would be similar to those claimed in the IFP patent (US 5908946). This catalyst based on Zn-Al is tested in the methanolysis of sunflower oil at 240ºC, 50 Bar, VVH = 0.9, oil / methanol ratio = 3.3 by volume and for a contact time of 52 minutes (that is, in the same conditions than with the catalysts used in the present invention). It is observed that the biodiesel composition values obtained with said material based on Zn-Al are: 0.8% TG, 0.7% DG, 10.2% MG and 85.0% FAMEs, after 24 hours of reaction.

According to this comparative test, the catalysts developed in the present invention, under the same reaction conditions, give a biodiesel with a higher content of the methyl esters (the greatest differences are found with the catalysts based on Zn-Fe). And from the above comparisons with the examples in the IFP patent, the catalysts used for the process developed in the present invention convert larger amounts of oil. The advantage, therefore, would lie mainly in the

production capacity.

The differences between the catalysts used in the present invention and Zn-Al lie in the concentration of metals leached to biodiesel. Thus, by carrying out the reaction with the Zn-Al catalyst (prepared by calcination at 450ºC) under the aforementioned conditions, the biodiesel generated for 18 hours continuously (after evaporation of the methanol and decantation of the glycerin) is analyzed by ICP giving as result the presence of 1.60 ppm of Zn (without Al leaching). In the case of the supported catalyst ZnFeAl / Al2O3 (prepared by calcination at 450ºC) the biodiesel generated after 18 hours in continuous (under the same reaction conditions) presents 0.20 ppm of Al, 1.72 ppm of Fe and 1.84 ppm of Zn.

In the case of the mass ZnFeAl catalyst, carrying out the reaction under the same reaction conditions (but with an oil / methanol ratio of 4.8 by volume, that is, higher than that of the two previous examples), the biodiesel generated during 18 hours continuously shows 36 ppm of Fe and 47 ppm of Zn.

Claims (19)

1.- A process of transesterification of esters with alcohols, characterized in that the reaction is carried out in the presence of at least one mixed oxide with a specific surface area of between 20 and 300 m2 / g determined by adsorption of N2 at 77 K by the BET method, comprising at least: a Zn oxide; and at least one oxide of a second element B, where B is a trivalent cation. 2. The process according to claim 1 characterized in that element B is selected from V, Cr, Mn, Fe, Co and any of its combinations, preferably it is selected from Fe, Cr and any of its combinations. 3. The process according to any of claims 1 or 2, characterized in that the mixed oxide has a specific surface between 50 and 200 m2 / g determined by adsorption of N2 at 77 K by the BET method. 4. The process according to any of the preceding claims, characterized in that the mixed oxide is obtainable from the thermal decomposition of at least one double hydroxide, preferably from the thermal decomposition of at least one double hydroxide of lamellar structure. The process according to claim 4, characterized in that the thermal decomposition of the double hydroxide is carried out at a temperature of between 100 and 1200ºC, preferably between 200 and 1000ºC, and even more preferably between 350 and 700ºC, and even more preferably between 400 and 600ºC. 6. The process according to claim 4, characterized in that the double hydroxide is obtainable by co-precipitation from a solution comprising metal ions and a solution comprising a precipitating agent, and where preferably the precipitating agent does not contain alkali metals. 7. The process according to claim 4, characterized in that the double hydroxide is obtainable by co-precipitation from a solution comprising metal ions and a solution comprising a precipitating agent, where preferably the precipitating agent contains alkali metals. 8.- The process according to any of the preceding claims, characterized in that the mixed oxide comprises a mixture of oxides corresponding to the general formula (ZnO) to (B2O3) 1-a, where a has a value between 0.05 and 0 , 95, and where preferably the molar ratio B / (B + Zn) has a value comprised between 0.15 and 0.70. 9. The process according to any of the preceding claims 1 to 7, characterized in that the mixed oxide comprises a mixture of oxides that respond with the general formula (Zn1-αMαO) to (B2O3) 1-a, where M is a metallic element with oxidation state + 2, + 3, +4 or a mixture thereof, preferably +2, selected from the elements of groups IIA, IIIA, IIIB and IVB, where a has a value between 0.05 and 0, 95, where α has a value between 0.05 and 0.95, and where preferably the molar ratio N / (B + Zn + M) has a value between 0.15 and 0.70. 10. The process according to any of the preceding claims 1 to 7, characterized in that the mixed oxide comprises a mixture of oxides that respond with the general formula (ZnO) to (B2-βMβOγ) 1-a, where M is a metallic element with oxidation state +3, +4 or a mixture thereof, where a has a value between 0.05 and 0.95, where β has a value between 0.05 and 0.95, and where γ is the number of oxygen atoms that satisfies the valence of element B in combination with element M and where preferably the molar ratio (B + M) / (B + M + Zn) has a value between 0.15 and 0.70. 11. The process according to any of the preceding claims 1 to 7 ,, characterized in that the mixed oxide comprises a mixture of oxides that respond of general formula (Zn1-αM1 αO) to (B2-βM2 βOγ) 1-a, where M1 is an element with oxidation state +2, where M2 is a metallic element with oxidation state + 3, + 4 or a mixture thereof, where a has a value between 0.05 and 0.95, where β has a value between 0.05 and 0.95, and where γ is the number of oxygen atoms that satisfies the valence of element B in combination with element M2 and where preferably the molar ratio (B + M2) / (B + M2 + Zn + M1) has a value between 0.15 and 0.70 12.- The process according to any of the previous claims characterized in that it comprises the following stages: a) an initial transesterification, b) evaporation and recovery of excess monoalcohol, c) separation by decantation of glycerin and mixture of esters that comprises unconverted molecules of reagents, d) a second transesterification of the ester mixture obtained in step c) with a proportion of the monoalcohol recovered in step b), and e) evaporation of the excess monoalcohol after step d) and the decanting of the glycerin and ester mixture. 13.-The process according to the preceding claim, characterized in that glycerides and alcohols are transesterified. 14. The process according to any of the preceding claims 12 or 13, characterized in that it comprises at least one glyceride selected from a triglyceride, a diglyceride, a monoglyceride and any of their combinations, and preferably comprises at least one triglyceride. 15. The process according to any of claims 12 or 13, characterized in that the alcohol is monohydroxylic comprising from 1 to 4 carbon atoms, preferably the alcohol is methanol, ethanol, propanol, butanol, or mixtures between them, more preferably the alcohol is methanol, ethanol, or 5 mixes between them. 16. The process according to any of the preceding claims 12 to 15, characterized in that the starting alcohol / glyceride molar ratio is between 5 and 15, preferably between 6 and 9. The process according to any of the previous claims, characterized in that the reaction is carried out at a temperature comprised between 50ºC and 300ºC, preferably between 150ºC and 250ºC. 18. The process according to any of the preceding claims, characterized in that the reaction is carried out at a pressure of less than 100 Bar, preferably between 15 and 60 Bar. 19. The process according to any of the preceding claims, characterized in that the reaction is carried out continuously. 20.-The process according to the preceding claim, characterized in that the reaction is carried out in a fixed bed reactor, with a VVH value between 0.1 and 3. SPANISH OFFICE OF THE PATENTS AND BRAND Application number: 201030494 SPAIN Application filing date: 03/31/2010 Priority Date: REPORT ON THE STATE OF THE ART 51 Int. Cl.: See Additional Sheet RELEVANT DOCUMENTS

Category

56 Documents cited Claim is affected

X

US 5908946 A (INSTITUT FRANCAIS DU PETROLE) 06.01.1999, column 1, lines 5-17; column 5, lines 38-67; column 6, lines 12-16,53-59; column 11, example 7; column 16, claims 1-11. 1.3-7.12-20

X

MACEDO, C. et al. "New hetereogeneous metal-oxides based catalyst for vegetable oil transesterification". Journal of the Brazilian Chemical Society, 2006, Vol. 17, N. 7. [online], retrieved on 02/13/2012. Recovered from Internet: URL: <http://www.scielo.br/scielo.php?pid=S0103-50532006000700014&script=sci_arttext&tlng=en> See Experimental; Results and Discussion, Table 1, entry 2. 1.3-5.7-8

TO

ES 2229948 A1 (UNIVERSIDAD POLITECNICA DE VALENCIA) 16.04.2005, claims 1-4. 1-20

TO

WO 2009.066539 A1 (NIPPON SHOKUBAI CO, LTD.) 28.05.2009, page 4, lines 11-31; page 5, lines 25-33; page 8, lines 15-17; page 9, lines 31-35; page 10, lines 1-2. 1-20

TO

EP 1681281 A1 (SUPERIOR COUNCIL OF SCIENTIFIC INVESTIGATIONS) 04.21.2005, claims 1-7. 1-20

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: referring to unwritten disclosure P: published between the priority date and the date of filing of application E: previous document, but published after the filing date of the application

This report has been made • for all claims • for claims no:

Date of completion of the report 24.02.2012

Examiner N. Martín Laso Page 1/4

STATE OF THE ART REPORT Application number: 201030494 CLASSIFICATION SUBJECT OF APPLICATION C07C67 / 03 (2006.01) B01J23 / 06 (2006.01) B01J23 / 76 (2006.01) Minimum documentation sought (classification system followed by classification symbols) C07C, B01J Electronic databases consulted during the search (name of the database and, if possible, terms of search used) INVENES, EPODOC, WPI, TXT, NPL, XPESP, CAS. State of the Art Report Page 2/4  WRITTEN OPINION Application number: 201030494 Date of Realization of the Written Opinion: 24.02.2012  Statement Novelty (Art. 6.1 LP 11/1986) Claims 2, 9-11 YES Claims 1, 3-8, 12-20 NO Inventive step (Art. 8.1 LP11 / 1986) Claims 2, 9-11 YES Claims 1, 3-8, 12-20 NO The application is considered to meet the requirement of industrial application. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986). Basis of Opinion.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/4  WRITTEN OPINION Application number: 201030494 1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

US 5908946 A (INSTITUT FRANCAIS DU PETROLE) 06/01/1999

D02

MACEDO, C. et al. "New hetereogeneous metal-oxides based catalyst for vegetable oil trans-esterification". Journal of the Brazilian Chemical Society, 2006, Vol. 17, N. 7. 2006

2. Reasoned declaration according to articles 29.6 and 29.7 of the Implementing Regulation of Law 11/1986, of March 20, on Patents on novelty and inventive step; quotes and explanations in support of this statement The application relates to a process of transesterification of esters with alcohols carried out in the presence of a mixed oxide comprising at least one Zn oxide and one trivalent cation oxide, said mixed oxide having a specific surface area of 20-300 m2 / g. Document D01 discloses a process for the transesterification of vegetable or animal oils with alcohols in the presence of a catalyst comprising Zn oxide, Al oxide and Zn aluminates. Said catalyst has a specific area of 50-200 m2 / g. The catalyst can be obtained by coprecipitation of a mixture of aqueous solutions of Zn, nitrates or sulfates of Al and sodium carbonate, heating the coprecipitate obtained in the form of hydrotalcite at a temperature of at least 400 ºC, or by heating a compound of Zn with alumina in the presence of acetic or nitric acid, subjecting the obtained mixture to extrusion and calcination. The catalyst responds to the formula (ZnO) x (Al2O3) and (ZnAl2O4) where x and y have a value between 0 and 2. The transesterification process is carried out with the same steps and conditions as in the application (column 1, lines 5 -17; column 5, lines 38-67; column 6, lines 12-16, 53-59; column 11, example 7; column 16, claims 1-11). The invention defined in claims 1, 3-7 and 12-20 of the application is contained in document D01, therefore lacking novelty (Art. 6.1 LP 11/1986). Document D02 discloses a process for the transesterification of vegetable oil with different alcohols in the presence of a mixed zinc oxide catalyst, of formula (Al2O3) 4 (ZnO) and that has a specific surface area of 82 m2 / g determined by the BET method . The catalyst is prepared by the coprecipitation method, starting from a Zn sulfate solution, an Al nitrate solution and an aqueous sodium carbonate solution mixed with stirring, obtaining a precipitate that is activated by heating at 500 ºC. The transesterification reaction is carried out by heating a mixture of the oil, the alcohol and the catalyst to 60 ° C (Experimental; Results and Discussion, Table 1, entry 2). The characteristics of claims 1, 3-5, 7 and 8 are already known from document D02. Therefore these claims are not new in view of the known state of the art (Art. 6.1 LP 11/1986). However, no documents have been found in the state of the art that, alone or in combination, disclose or direct the person skilled in the art towards a process of transesterification of esters with alcohols in which a mixed oxide comprising a Zn oxide together with a V, Cr, Mn, Fe or Co oxide, which leads to an improvement in the transesterification process, since a greater conversion of glycerides in the corresponding esters is obtained. Therefore, the invention defined in claims 2 and 9-11 is new and has inventive step (Art. 6.1 and 8.1 LP 11/1986). State of the Art Report Page 4/4