Method for transesterification of carboxylic acid esters

Abstract

The present invention relates to a method for transesterification of carboxylic acid esters by heterogeneous catalysis using a catalyst that is obtainable by calcination of surface-reacted calcium carbonate. The invention further relates to the use of said method in the production of fuel or fuel components, such as biodiesel. Further aspects of the present invention relate to the transesterified ester obtainable by the inventive method and to its use as fuel or as fuel component. Still another aspect of the present invention relates to a corresponding transesterification catalyst and to its use in transesterification reactions.

Claims

1. A transesterification catalyst comprising partially or fully calcined surface-reacted calcium carbonate, wherein the calcination is carried out at a calcination temperature of at least 650? C., wherein the transesterification catalyst has a specific surface area of from 15 to 200 m.sup.2/g, measured using nitrogen and the BET method according to ISO 9277:2010, and wherein the surface-reacted calcium carbonate is a reaction product of ground natural calcium carbonate containing mineral (GNCC) or precipitated calcium carbonate (PCC) with carbon dioxide and one or more H.sub.3O.sup.+ ion donors and wherein the carbon dioxide is formed in situ by a reaction with the H.sub.3O.sup.+ ion donors and/or is supplied from an external source, and wherein the surface-reacted calcium carbonate has a specific surface area of from 15 to 200 m.sup.2/g, measured using nitrogen and the BET method according to ISO 9277:2010.

2. The transesterification catalyst according to claim 1, characterized in that the transesterification catalyst has: (i) a d.sub.50(vol) of from 1 to 75 ?m; and/or (ii) a d.sub.98(vol) of from 2 to 150 ?m.

3. The transesterification catalyst according to claim 1, characterized in that the transesterification catalyst has: (i) a d.sub.50(vol) of from 3 to 15 ?m; and/or (ii) a d.sub.98(vol) of 10 to 30 ?m.

4. The transesterification catalyst according to claim 1, characterized in that the transesterification catalyst has a specific surface area of from 25 to 180 m.sup.2/g, measured using nitrogen and the BET method according to ISO 9277:2010.

5. The transesterification catalyst according to claim 1, characterized in that the transesterification catalyst has a specific surface area of from 30 to 150 m.sup.2/g, measured using nitrogen and the BET method according to ISO 9277:2010.

6. A method for transesterification of carboxylic acid esters by heterogeneous catalysis, the method comprising the following steps: (a) providing a substrate comprising a first carboxylic acid ester; (b) providing a first alcohol; (c) providing a catalyst according to claim 1; and (d) reacting the substrate provided in step (a) and the first alcohol provided in step (b) in the presence of the catalyst provided in step (c) to obtain a reaction mixture comprising a second carboxylic acid ester and a second alcohol.

7. The method according to claim 6, characterized in that the substrate is a fat or a fatty oil.

8. The method according to claim 6, characterized in that the first carboxylic acid ester is a triglyceride.

9. The method according to claim 6, characterized in that the first alcohol is a monohydric alcohol.

10. The method according to claim 6, characterized in that the surface-reacted calcium carbonate has: (i) a d.sub.50(vol) of from 0.5 to 50 ?m; and/or (ii) a d.sub.98(vol) of from 1 to 120 ?m.

11. The method according to claim 6, characterized in that the surface-reacted calcium carbonate has a specific surface area of from 25 to 180 m.sup.2/g, measured using nitrogen and the BET method according to ISO 9277:2010.

12. The method according to claim 6, characterized in that: (i) the ground natural calcium carbonate-containing mineral is selected from the group consisting of marble, chalk, dolomite, limestone and mixtures thereof; and/or (ii) the precipitated calcium carbonate comprises aragonitic, vateritic or calcitic mineralogical crystal forms or mixtures thereof.

13. The method according to claim 6, characterized in that the catalyst is obtainable by calcination of surface-reacted calcium carbonate, wherein calcination is carried out: (i) at a calcination temperature of at least 680; ? C., and/or (ii) at a calcination time of at least 5 mins.

14. The method according to claim 6, characterized in that in step (d): the first alcohol is used as reaction medium; and/or the catalyst is used in an amount of from 0.01 to 20 wt. %, based on a total weight of the substrate; and/or the alcohol and the catalyst are contacted in a first step and the substrate is then added in a second step.

15. The method according to claim 6, characterized in that step (d) is carried out at a temperature of at least 20? C.

16. The method according to claim 6, characterized in that the method further comprises step (e) of separating the second carboxylic acid ester from the reaction mixture obtained in step (d).

17. The method according to claim 6, characterized in that the substrate is a vegetable oil.

18. A method of producing fuel or a fuel component, comprising: (a) providing a substrate comprising a first carboxylic acid ester; (b) providing a first alcohol; (c) providing a catalyst according to claim 1; and (d) reacting the substrate provided in step (a) and the first alcohol provided in step (b) in the presence of the catalyst provided in step (c) to obtain a reaction mixture comprising a second carboxylic acid ester and a second alcohol; wherein the second carboxylic acid ester is the fuel or fuel component.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1: (a) Phase separation after the transesterification process; (b) Crude glycerol obtained using NaOH as a catalyst; (c) Crude glycerol obtained using KOH as a catalyst.

(2) FIG. 2: X-ray diffractograms of ground natural calcium carbonate activated thermally at different temperatures and different times of thermal activation.

(3) FIG. 3: Evolution of the surface area of ground natural calcium carbonate and surface-reacted calcium carbonate as a function of the activation temperature.

(4) FIG. 4: X-ray diffractograms of surface-reacted calcium carbonate activated thermally at different temperatures and different times of thermal activation.

(5) FIG. 5: (a) SEM micrograph of SRCC prior to calcination, (b) SEM micrograph of SRCC calcined at 900? C. for 3 h in a Nabertherm furnace model Le 6/11, Nabertherm GmbH, Lilienthal, Germany.

(6) FIG. 6: (a) SEM micrograph of GNCC prior to calcination, (b) SEM micrograph of GNCC calcined at 900? C. for 3 hrs in a Nabertherm furnace model Le 6/11, Nabertherm GmbH, Lilienthal, Germany.

(7) FIG. 7: (a) NMR spectrum of sun flower oil; b) NMR spectrum of transesterification product obtained with GNCC calcined at 900? C.

(8) FIG. 8: Crude glycerol obtained by using: 1) KOH, 2) NaOH, 3) calcined GNCC and 4) calcined SRCC as catalysts, 5) is pure glycerol.

EXAMPLES

(9) The scope and interest of the invention may be better understood on basis of the following examples which are intended to illustrate embodiments of the present invention.

(A) ANALYTICAL METHODS

(10) All parameters defined throughout the present document and those mentioned in the following examples are based on the following measuring methods:

(11) Particle Size Distribution

(12) For determining the volume-based particle size distribution, a Malvern Mastersizer 2 000 Laser Diffraction System is used. The raw data obtained by the measurement are analysed using the Fraunhofer theory and Malvern Application Software 5.60. In general, the measurement is performed with an aqueous dispersion with the exception of the calcined surface-reacted calcium carbonate which was measured in dry state (<0.5 wt. % total moisture based on the total weight of the sample) and at a pressure of 400 kPa. The weight determined particle size distribution may correspond to the volume determined particle size if the density of all the particles is equal.

(13) Any weight-based particle size distribution is measured by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field. The measurement was made with a Sedigraph? 5120 from Micromeritics Instrument Corporation, USA. The method and the instrument are known to the skilled person and are commonly used to determine particle size distributions of e.g. fillers and pigments. The measurement was carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonicated.

(14) X-Ray Diffraction (XRD)

(15) XRD experiments are performed on the samples using rotatable PMMA holder rings. Samples are analysed with a Bruker D8 Advance powder diffractometer obeying Bragg's law. This diffractometer consists of a 2.2 kW X-ray tube, a sample holder, a ?-? goniometer, and a VANTEC-1 detector. Nickel-filtered Cu K? radiation is employed in all experiments. The profiles are chart recorded automatically using a scan speed of 0.7? per min in 2?. The resulting powder diffraction pattern can easily be classified by mineral content using the DIFFRACsuite software packages EVA and SEARCH, based on reference patterns of the ICDD PDF 2 database.

(16) Quantitative analysis of diffraction data refers to the determination of amounts of different phases in a multi-phase sample and has been performed using the DIFFRACsuite software package TOPAS. In detail, quantitative analysis allows to determine structural characteristics and phase proportions with quantifiable numerical precision from the experimental data itself. This involves modeling the full diffraction pattern using the Rietveld approach such that the calculated pattern(s) duplicates the experimental one.

(17) Unless indicated otherwise, activated solids were stored temporarily in round bottom flask purged with an inert atmosphere (e.g. N.sub.2) until the XRD measurement is performed.

(18) Specific Surface Area

(19) The specific surface area (in m.sup.2/g) of surface-reacted calcium carbonate or other materials is determined using the BET method (using nitrogen as adsorbing gas), which is well known to the skilled man (ISO 9277:2010). The total surface area (in m.sup.2) can be obtained by multiplication of the specific surface area and the mass (in g) of the corresponding sample. For performing the measurement on thermally activated solids, similar precautions were taken as described above for X-ray diffraction.

(20) Scanning Electron Microscope (SEM)

(21) The SEM images were produced by using the field emission scanning electron microscope (FESEM) Zeiss Sigma VP from Carl Zeiss Microscopy GmbH, Jena, Germany.

(22) Nuclear Magnetic Resonance Spectroscopy (NMR Spectroscopy)

(23) Samples were characterized using a Bruker 300 MHz Spectrometer Avance 300. Specific weights of samples were solubilized in dichloromethane-d.sub.2, prior to the analyses.

(B) EXAMPLES

(24) The following examples are not to be construed to limit the scope of the claims in any manner whatsoever.

Comparative Example 1CE1

(25) A first comparative trial was carried out in a 250 mL round bottom flask using a commercial sunflower oil (M Classic sun flower oil from Migros) using anhydrous methanol (for HPLC, >99.9% from Sigma Aldrich) and NaOH pellets (ACS reagent>97% from Sigma Aldrich) as a homogeneous base catalyst. In this process, an oil/methanol weight ratio of 2:1 was used and an oil/NaOH weight ratio of 170:1, was employed. First, anhydrous methanol was mixed with NaOH pellets at 30? C. for 30 minutes. At the same time, in another round bottom flask, the vegetable oil was also heated at 30? C., after 30 minutes the vegetable oil was added to the methanol/NaOH mixture, dropwise. Further, the temperature was increased gradually to 50? C. In the end of the addition, the temperature of the whole mixture was increased to 60? C. and kept for a duration of 2 to 3 hours.

(26) In the end of the process, the reaction was stopped, methanol was evaporated under vacuum at 50? C./25 mbar for a ca. time of 15 to 20 min. Finally, the mixture was transferred into a separatory funnel, in order to separate the obtained phases (see FIG. 1a). The upper lighter phase corresponds to the transesterification product, the heavy lower phase contains the crude glycerol.

Comparative Example 2CE2

(27) An analogous catalytic evaluation as for CE1 was performed by using KOH as a base source, wherein the oil/KOH weight ratio was 119:1.

Comparative Example 3CE3

(28) Preparation and Activation of the Catalyst

(29) A conventional ground natural calcium carbonate (GNCC) was obtained via wet grinding and spray drying of Carrara marble. The ground calcium carbonate had a specific surface area of 4 m.sup.2/g and a d.sub.50(wt) of 1.6 ?m.

(30) The ground calcium carbonate was calcined for the purpose of catalyst activation. Different thermal activation conditions (i.e. temperatures and time of activation) were employed. After activation, the solids were next characterised using X-ray diffraction (XRD) as well as using BET techniques and SEM imaging (see FIG. 2, FIG. 3 and FIG. 6). Using the latter two techniques, an idea about the chemical composition and surface of the solids is provided.

(31) The thermal activation of GNCC at different temperatures showed that a thermal treatment of at least 700? C. is preferred to achieve full calcination. Further, the results show e.g. a clear increase of the surface area from 4 m.sup.2/g to 14 m.sup.2/g and the formation of micropores for the mineral activated at 900? C. for 2 hours.

(32) Heterogeneous Catalysis Trials

(33) The transesterification carried out with this the heterogeneous catalyst is analogous to the protocol presented in CE1.

(34) 0.75 g of the activated catalyst prepared above were placed in a three-neck bottom flask, then purged with N.sub.2 for about 10 min. 25 g of anhydrous methanol were added to the catalyst, stirred, then again the system was purged with N.sub.2 to eliminate any air traces. The mixture was heated up to 30? C. and stirred for 30 min. 50 g of sun flower oil (M Classic sun flower oil from Migros) were heated in another round-bottom flask at 30? C. for 30 min. After 30 min, the heated oil was added to the catalyst/methanol mixture and then the mixture was progressively heated to 50? C. In the end of the addition, the whole mixture catalyst/methanol/vegetable oil was heated to 60? C. and kept at that temperature 2 to 3 hours. In the end of the process, methanol was evaporated under vacuum at a temperature of 50? C./25 mbar for about 15 to 20 min. Then the solid was separated by a filtration using a Whatman filter paper of a 589/1 grade.

Inventive ExampleEX1

(35) Preparation and Activation of the Catalyst

(36) In an exemplary trial, a surface-reacted calcium carbonate (SRCC) was obtained as follows: 10 litres of an aqueous suspension of ground marble were prepared in a mixing vessel by adjusting the solids content to 10 wt. %, based on the total weight of the aqueous suspension. The ground marble was obtained from Hustadmarmor, Norway and had d.sub.90(wt) of less than 2 ?m. An aqueous solution was prepared which contained 30 wt. % of phosphoric acid while another solution was prepared which contained 5 wt. % of citric acid. Whilst mixing the suspension, 1.60 kg of the phosphoric acid solution were added to said suspension over a period of 10 min and at a temperature of 70? C. Additionally, starting 2 min after the start of phosphoric acid addition, 0.05 kg of the citric acid solution were added to the slurry. Finally, after the addition of the phosphoric acid, the slurry was stirred for another 5 min before removing it from the vessel. The obtained solid was then filtered and dried.

(37) An analogously prepared surface-reacted calcium carbonate having a specific surface area of 135 m.sup.2/g, a d.sub.50(vol) of 6.2 ?m and a d.sub.98(vol) of 12.8 ?m was used in the following trials.

(38) The surface-reacted calcium carbonate (SRCC) was calcined for the purpose of catalyst activation. Different thermal activation conditions (i.e. temperatures and time of activation) were employed. After activation, the solids were next characterised using X-ray diffraction (XRD) as well as using BET techniques and SEM imaging (see FIG. 3, FIG. 4 and FIG. 5).

(39) The thermal activation of GNCC at different temperatures showed that a thermal treatment of at least 700? C. is preferred to achieve the desired activity. As becomes apparent from FIG. 3, the surface area of the surface-reacted calcium carbonate as a function of temperature is in stark contrast to that of ground natural calcium carbonate, as its surface area decreased in function of the thermal activation conditions. Indeed, the surface area decreased from 135 m.sup.2/g in the fresh sample to 15 m.sup.2/g after activation for 2 hours at 900? C. However, as can be gathered from FIG. 5, the surface structure of the calcined surface-reacted calcium carbonate (SRCC) is comparable to that of the surface-reacted calcium carbonate prior to calcination.

(40) Heterogeneous Catalysis Trials

(41) An identical procedure as described in CE3 was used in the trials with the catalyst prepared from surface-reacted calcium carbonate.

(C) EVALUATION OF CATALYST PERFORMANCE

(42) Where indicated in the following, all yields of transesterification products were calculated based on .sup.1H-NMR spectra and normalised.

(43) Homogeneous Catalysts

(44) Using either NaOH or KOH, the presence of transesterification product was confirmed using proton nuclear magnetic resonance (.sup.1H-NMR), since no vegetable oil signals were observed which confirms its full conversion. The high yields of transesterification products were also confirmed by certified analyses according to EN 14103. A difference could be observed in the physical appearance of the crude glycerol. In case of NaOH, the crude glycerol is less viscous compared to a more viscous crude glycerol obtained in case of KOH (see FIG. 1b and FIG. 1c).

(45) Heterogeneous Catalysts

(46) The evaluation of calcined GNCC as transesterification catalyst showed that the catalysts activated at temperatures above 700? C. were more efficient as full conversion could be observed in this case.

(47) The performance of calcined SRCC as transesterification catalyst was investigated in an analogous manner. The analysis revealed that full conversion was possible with SRCC activated at 900? C. and 700? C., respectively.

(48) The comparison in catalytic performance of calcined GNCC and calcined SRCC can be summarized as follows:

(49) TABLE-US-00001 Type of catalyst Activation conditions Transesterification rate (%) GNCC 900? C./1 h ~98 GNCC 700? C./1 h ~98 GNCC 600? C./1 h traces GNCC 500? C./1 h none SRCC 900? C./1 h ~98 SRCC 700? C./1 h ~98 SRCC 600? C./1 h traces SRCC 500? C./1 h none

(50) The comparison of calcined GNCC and calcined SRCC shows that SRCC, surprisingly, performs equally well although the specific surface area is decreased during activation and the lime (CaO) content is comparably low.

(51) Furthermore, a comparison of the crude glycerol phases shows that the glycerol obtained by using calcined SRCC is clearer than the one obtained using calcined GNCC or conventional catalysts (see FIG. 8). This fact suggests that the crude glycerol obtained by using calcined SRCC has a higher purity grade than the one obtained by using the calcined GNCC or NaOH/KOH.