BR112020015239B1 - METHOD FOR TRANSESTERIFICATION OF CARBOXYLIC ACID ESTERS, USE OF THE METHOD, TRANSESTERIFICATION CATALYST, AND, USE OF CATALYST - Google Patents

Abstract

METHOD FOR TRANSESTERIFICATION OF CARBOXYLIC ACID ESTERS, USE OF THE METHOD, CARBOXYLIC ACID ESTER, USE OF CARBOXYLIC ACID ESTER, TRANSESTERIFICATION CATALYST, AND, USE OF CATALYST. The present invention relates to a method for transesterification of carboxylic acid esters by heterogeneous catalysis, using a catalyst that can be obtained by calcination of surface-treated calcium carbonate. The invention further relates to the use of said method in the production of fuel or fuel components, such as biodiesel. Additional aspects of the present invention relate to the transesterified ester that can be obtained by the method of the invention and its use as a fuel or fuel component. Still another aspect of the present invention relates to a corresponding transesterification catalyst and its use in transesterification reactions.

Description

[001] The present invention relates to a method for transesterification of carboxylic acid esters by heterogeneous catalysis, using a catalyst that can be obtained by calcination of surface-treated calcium carbonate. The invention further relates to the use of said method in the production of fuel or fuel components, such as biodiesel. Additional aspects of the present invention relate to the transesterified ester that can be obtained by the method of the invention and its use as a fuel or as a fuel component. Yet another aspect of the present invention relates to a corresponding transesterification catalyst and its use in transesterification reactions.

[002] Transesterification is the process of exchanging the organic group R” of an ester with the organic group R' of an alcohol according to the following reaction scheme:

[003] This type of reaction is applied in several large-scale industrial processes. For example, the synthesis of polyesters can be achieved by transesterification of diesters with diols. During the last decades, the transesterification of fats (consisting of triglycerides) has gained importance in the production of non-fossil fuels, especially biodiesel.

[004] The term biodiesel refers to a fuel based on vegetable or animal fat that can be obtained by chemically reacting these fats with an alcohol to produce fatty acid esters. Methanol is the most frequently used alcohol that produces fatty acid methyl esters (so-called FAMEs). In the case of transesterification of fats, glycerin is obtained as a marketable by-product.

[005] Typically, transesterifications are carried out in the presence of a suitable catalyst, which can be either a basic catalyst or an acid catalyst. Commonly used basic catalysts include sodium hydroxide (NaOH), potassium hydroxide (KOH) or sodium methoxide (H3CONa). On the other hand, commonly used acid catalysts include sulfuric acid (H2SO4) and phosphoric acid (H3PO4).

[006] Specific requirements with regard to transesterification methods are total conversion, high reaction rates and the avoidance of unwanted impurities. Unwanted impurities from transesterification processes include, for example, carboxylic acid salts.

[007] In general, acid catalysts are known to act less efficiently when compared to basic catalysts and the transesterification process requires large amounts of excess alcohol. The formation of water during transesterification can further reduce the reaction rate or even stop the reaction. Typically, to achieve full conversion at high reaction rates, strong acids (e.g., sulfuric acid) are required, which in turn requires the use of acid-resistant equipment.

[008] On the other hand, the use of known basic catalysts, such as sodium hydroxide or potassium hydroxide, also presents disadvantages. In this regard, the formation of carboxylic acid salts is an important issue. In the case of transesterification of fats, these carboxylic acid salts are salts of fatty acids that act like soaps and can cause problems at different stages of the process. A subsequent washing step may therefore be necessary.

[009] Sodium hydroxide (NaOH) is a cheap and readily available catalyst, but handling and dissolving sodium hydroxide is difficult and dangerous. Potassium hydroxide (KOH) dissolves more easily, but is more expensive and more sensitive to humidity during storage.

[0010] Finally, removal of the catalyst itself is also a problem, especially in the case of soluble catalysts such as NaOH or KOH. As mentioned above, the catalyst may be present as or lead to the formation of impurities in the ester obtained as a product. Depending on the substrate, i.e. the starting material, impurities in marketable by-products (e.g. in glycerin in the case of fat transesterification) are also problematic.

[0011] There is a general need to overcome one or more of the above disadvantages or to improve the methods described above.

[0012] Thus, an object of the present invention can be seen in the provision of a transesterification method, in which the catalyst can be easily separated from the reaction mixture.

[0013] Another object can be seen in the provision of a more efficient transesterification method or in the provision of a corresponding catalyst.

[0014] Yet another object of the present invention can be seen in the reduction of process impurities and the provision of a corresponding catalyst.

[0015] Yet another object can be seen in the provision of a transesterification method that can be handled easily and in the provision of a corresponding catalyst that can be stored or used easily and safely. The environmental compatibility of the method or catalyst can be seen as another object of the present invention.

[0016] Finally, yet another object of the present invention can be seen in the provision of a more economical catalyst system for use in transesterification reactions.

[0017] The above and other problems can be solved by the subject matter as defined herein in the independent claims.

[0018] In this regard, a first aspect of the present invention relates to a method for transesterification of carboxylic acid esters by heterogeneous catalysis, wherein the method comprises the following steps: (a) providing a substrate comprising a first carboxylic acid ester carboxylic acid; (b) provide a first alcohol; (c) providing a catalyst; 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 ; distinguished by the fact that the catalyst comprises surface-treated calcined calcium carbonate, wherein the surface-treated calcium carbonate is a reaction product of a mineral containing ground natural calcium carbonate (GNCC) or precipitated calcium carbonate (PCC). with carbon dioxide and one or more H3O+ ion donors and wherein the carbon dioxide is formed in situ by treatment with H3O+ ion donors and/or is supplied by an external source.

[0019] The inventors surprisingly found that the use of a catalyst comprising surface-treated calcined calcium carbonate leads to efficient transesterification. As will be explained in more detail below, surface treated calcium carbonate is a specific type of calcium carbonate obtained by reacting a material containing calcium carbonate, carbon dioxide and one or more H3O+ ion donors. Before use, the catalyst is activated by subsequent calcination at elevated temperatures. Furthermore, the inventors have surprisingly found that the use of a catalyst comprising surface-treated calcined calcium carbonate leads to a reduction in impurities.

[0020] Another aspect of the present invention relates to the use of the method of the invention in the production of fuel or fuel components.

[0021] Yet another aspect of the present invention relates to the fact that a carboxylic acid ester can be obtained by the method of the invention.

[0022] Yet another aspect relates to the use of a carboxylic acid ester that can be obtained by the method of the invention as a fuel or as a fuel component.

[0023] Yet another aspect relates to a transesterification catalyst comprising surface-treated calcined calcium carbonate, wherein the surface-treated calcium carbonate is a reaction product of a material containing ground natural calcium carbonate (GNCC) or precipitated calcium carbonate (PCC) with carbon dioxide and one or more H3O+ ion donors and wherein the carbon dioxide is formed in situ by treatment with H3O+ ion donors and/or is supplied by an external source.

[0024] Finally, yet another aspect of the present invention relates to the use of a catalyst comprising surface-treated calcined calcium carbonate as a catalyst in a transesterification reaction, wherein the surface-treated calcium carbonate is a product of the reaction of a material containing ground natural calcium carbonate (GNCC) or precipitated calcium carbonate (PCC) treated with carbon dioxide and one or more H3O+ ion donors and in which carbon dioxide is formed in situ by treatment with H3O+ ion donors and/or is provided by an external source.

[0025] The following terms used throughout this document will have the meanings as set forth below.

[0026] As already explained above, “surface-treated calcium carbonate” is a specific type of calcium carbonate. It is obtained by reacting a mineral containing ground natural calcium carbonate (GNCC) or precipitated calcium carbonate (PCC) with carbon dioxide and one or more H3O+ ion donors, where carbon dioxide is formed in situ by treatment with H3O+ ion donors and/or is provided by an external source.

[0027] The term “calcined”, in this specification, refers to the appearance of a solid material that has been subjected to calcination. Calcination indicates heat treatment at elevated temperatures in the presence or absence of oxygen, preferably in the presence of oxygen, for example atmospheric oxygen. The terms "calcined" and "calcination" are well known to those skilled in the art and it is understood that calcination can lead to partial or total thermal conversion of the starting material (partial or total calcination).

[0028] The term “ground natural calcium carbonate” (GNCC), within the meaning of this document, refers to a particulate material obtained from minerals containing natural calcium carbonate (e.g., chalk, limestone, marble or dolomite) that has been processed in a wet and/or dry comminution step such as crushing and/or grinding and, optionally, has been subjected to additional steps such as sieving and/or fractionation, for example by a cyclone or a classifier.

[0029] A “precipitated calcium carbonate” (PCC) is a synthesized material, obtained by precipitation followed by a reaction of carbon dioxide and calcium hydroxide (hydrated lime) in an aqueous environment. Alternatively, precipitated calcium carbonate can also be obtained by reacting calcium carbonate salts, calcium chloride and sodium carbonate, in an aqueous environment. PCC may also have a crystalline form of vaterite, calcite or aragonite. PCCs are described, for example, in EP 2 447 213 A1, EP 2 524 898 A1, EP 2 371 766 A1, EP 2 840 065 A1 or WO 2013/142473 A1.

[0030] When used in this specification, the particle size distribution based on volume dx(vol) represents the diameter in relation to which x% by volume of particles have diameters less than dx(vol). This means that, for example, the value d20(vol) is the particle size at which 20% by volume of all particles are smaller than that particle size. The d50(vol) value is thus the median particle size by volume, i.e. 50% by volume of all particles are smaller than that particle size and the d98(vol) value, referred to as the upper cutoff with On a volume basis, it is the particle size at which 98% by volume of all particles are smaller than that particle size.

[0031] On the other hand, the particle size distribution based on weight dx(p) represents the diameter in relation to which x% by weight of particles have diameters smaller than dx(p). This means that, for example, the d20(p) value is the particle size at which 20% by weight of all particles are smaller than that particle size. The d50(p) value is thus the median particle size by weight, i.e. 50% by weight of all particles are smaller than that particle size and the d98(p) value, referred to as the upper cutoff based by weight, is the particle size at which 98% by weight of all particles are smaller than that particle size.

[0032] Throughout this document, the term “specific surface area” (in m2/g), which is used to define surface-treated calcium carbonate or other materials, refers to the specific surface area as determined using the BET method (using nitrogen as the adsorption gas).

[0033] When an indefinite or definite article is used in reference to a singular noun, e.g. e.g., “a”, “an”, “the” or “a”, this includes the plural of that noun unless something else is specifically stated.

[0034] When used in the present description and in the claims, the term “comprise” does not exclude other elements. For purposes of the present invention, the term “consist of” is considered a preferred embodiment of the term “comprise”. If, in the following, it is defined that a group comprises at least a certain number of modalities, it should also be understood that a described group preferably consists only of these modalities.

[0035] Terms such as “can be obtained” or “can be defined” and “obtained” or “defined” are used interchangeably. This, for example, means that, unless the context clearly indicates otherwise, the term “obtained” is not meant to indicate that, for example, an embodiment is to be obtained, for example, by the sequence of steps that follow the term “obtained ” although such limited understanding is always included by the terms “obtained” or “defined” as a preferred embodiment.

[0036] Whenever the terms “include” or “have” are used, these terms are intended to be equivalent to “comprise” as defined above.

[0037] Advantageous embodiments of the method of the invention and additional aspects are defined in the corresponding secondary claims.

[0038] In one embodiment of the present invention, the substrate is a fat or a fatty oil, preferably a vegetable oil, more preferably, the substrate is selected from the group consisting of canola oil, cottonseed oil, coconut oil, corn oil, hazelnut oil, linseed oil, mustard seed oil, olive oil, palm oil, peanut oil, rapeseed oil, rice bran oil, safflower oil, sesame oil , soybean oil, sunflower oil, tigernut oil, tung oil and mixtures thereof and, most preferably, the substrate is sunflower oil.

[0039] In another embodiment of the method of the invention, the first carboxylic acid ester is a triglyceride.

[0040] In another additional embodiment, the first alcohol is a monohydric alcohol, preferably a C1-C5 monohydric alcohol, more preferably a C1-C3 monohydric alcohol, even more preferably methanol or ethanol and, most preferably, methanol.

[0041] In another embodiment of the present invention, the catalyst has: (i) d5o(vol) between 1 and 75 μm, preferably from 1.5 to 50 μm, more preferably from 2 to 30 μm and, most preferably, from 3 to 15 μm; and/or (ii) d98(vol) between 2 and 150 μm, preferably from 5 to 120 μm, more preferably from 8 to 80 μm and, most preferably, from 10 to 30 μm.

[0042] In another additional embodiment, the catalyst has a specific surface area between 1 and 200 m2/g, preferably from 5 to 120 m2/g and, most preferably, from 10 to 100 m2/g, measured using nitrogen and the BET method according to ISO 9277:2010.

[0043] In another additional embodiment, the surface-treated calcium carbonate has: (i) d50(vol) between 0.5 and 50 μm, preferably from 1 to 30 μm, more preferably from 1.5 to 20 μm and, most preferably, from 2 to 12 μm; and/or (ii) d98(vol) between 1 and 120 μm, preferably from 2 to 100 μm, more preferably from 5 to 50 μm and, most preferably, from 8 to 25 μm.

[0044] In another additional embodiment, the surface-treated calcium carbonate has a specific surface area between 15 and 200 m2/g, preferably from 25 to 180 m2/g and, most preferably, from 30 to 150 m2/g, measured using nitrogen and the BET method according to ISO 9277:2010.

[0045] In another embodiment, the catalyst is distinguished by the fact that: (i) the mineral containing ground natural calcium carbonate is selected from the group consisting of marble, chalk, dolomite, limestone and mixtures thereof; and/or (ii) the precipitated calcium carbonate comprises mineralogical crystalline forms of aragonite, vaterite or calcite or mixtures thereof.

[0046] In another additional embodiment of the present invention, the catalyst can be obtained by partial or total calcination of calcium carbonate with a treated surface.

[0047] In another embodiment, the catalyst can be obtained by calcining surface-treated calcium carbonate, in which calcination is carried out: (i) at a calcination temperature of at least 650°C, preferably at least 680°C and , most preferably, at a temperature between 700 and 950°C; and/or (ii) in a calcination time of at least 5 minutes, preferably at least 0.25 hours, more preferably at least 0.5 hours and, most preferably, in a calcination time between 1 and 3 hours.

[0048] In another embodiment, the method is distinguished by the fact that, in step (d), the first alcohol is used as a reaction medium, preferably said first alcohol is used in molar excess in relation to the first carboxylic acid ester .

[0049] In another embodiment, the method is distinguished by the fact that, in step (d), the catalyst is used in an amount between 0.01 and 20% by weight, preferably 0.1 to 10% by weight and , most preferably, 0.5 to 5% by weight, based on the total weight of the substrate.

[0050] In another additional embodiment, the method is distinguished by the fact that, in step (d), the alcohol and the catalyst are brought into contact in a first step and the substrate is then added in a second step.

[0051] In another additional embodiment, the method is distinguished by the fact that step (d) is carried out at a temperature of at least 20°C, preferably at least 25°C and, most preferably, in a range between 30 and 80°C.

[0052] In another additional embodiment, the method further comprises step (e) of separating the second carboxylic acid ester from the reaction mixture, obtained in step (d).

[0053] Next, details and preferred embodiments of the transesterification method according to the present invention will be described. It should be understood that these details and embodiments, where applicable, also refer to the use of the method of the invention in the production of fuel or fuel components, to the carboxylic acid ester that can be obtained by said method of the invention and to the use of said ester as fuel or as a fuel component. When applicable, the following details and embodiments further relate to the transesterification catalyst of the invention and the use of said catalyst as a catalyst in transesterification reaction.

(A) Substrate

[0054] According to step (a) of the transesterification method of the invention, a substrate is provided comprising a first carboxylic acid ester that is reacted with the first alcohol provided in step (b). The term “first carboxylic acid ester” indicates that the substrate ester and the product ester, i.e. the “second carboxylic acid ester”, have a different chemical structure.

[0055] In principle, the first carboxylic acid ester used in the present invention can be any organic molecule as long as it has one or more ester moieties that can, in general, be described as R”O(O=)CR, where R” and R may be the same or different and may be any conceivable organic radical.

[0056] In this regard, the first carboxylic acid ester may be a monoester, i.e., an organic molecule having an ester moiety, or it may be a diester, a triester, etc., i.e., an organic molecule having two or more ester portions. If it comprises two or more ester moieties, the first carboxylic acid ester refers especially to polyesterified polyhydric alcohols (e.g., a diglyceride or a triglyceride).

[0057] Especially suitable esters are glycerides, preferably triglycerides, which are the constituents of fats (solid form) or fatty oils (liquid form), collectively referred to as natural “fats”, whereby a further distinction can be made between fats saturated and unsaturated. Therefore, in one embodiment, the substrate is a fat or a fatty oil, preferably a fatty oil. In a more preferred embodiment, the substrate is a vegetable oil, even more preferably selected from the group consisting of canola oil, cottonseed oil, coconut oil, corn oil, hazelnut oil, linseed oil, mustard seed oil, olive oil, palm oil, peanut oil, rapeseed oil, rice bran oil, safflower oil, sesame oil, soybean oil, sunflower oil, tigernut oil, tung and mixtures thereof, more preferably, the substrate is sunflower oil.

[0058] Especially in the case of fats, e.g. e.g., fatty oils, the substrate can be a fresh substrate or a used substrate, i.e. a used fatty oil. In this regard, the method of the invention can further be used for the treatment or conversion of used fats.

[0059] As noted above, the substrate comprises a first carboxylic acid ester that may have the general formula R”O(O=)CR. In one embodiment of the present invention, the first carboxylic acid ester is a glyceride, preferably a triglyceride. The person skilled in the art will recognize that the substrate may comprise a mixture of two or more structurally different carboxylic acid esters, e.g. e.g., different triglycerides as in the case of natural fats.

[0060] The simplest triglycerides are those in which the three fatty acids are identical. In turn, a polyesterified polyhydric alcohol, such as a triglyceride, can be substituted with different acyl radicals.

(B) Alcohol

[0061] In step (b) of the method according to the present invention, a first alcohol is provided. The term “first alcohol” indicates that the alcohol supplied as a reactant in step (b) and the product alcohol, i.e. the “second alcohol”, have a different chemical structure.

[0062] In principle, the first alcohol used in the present invention can be any organic alcohol as long as it has at least one hydroxy group. Alcohol can thus generally be described as R'OH, where R' can be any conceivable organic radical. Specifically, the first alcohol provided in step (b) may be a monohydric alcohol, meaning that it contains only one hydroxy group.

[0063] Therefore, in one embodiment of the present invention, the first alcohol is a monohydric alcohol, preferably a C1-C5 monohydric alcohol and, more preferably, a C1-C3 monohydric alcohol. For example, C1-C5 indicates a substituted or unsubstituted linear or branched alkyl chain having 1 to 5 carbon atoms. Non-limiting examples of suitable monohydric alcohols thus include the structural isomers of pentanol, the structural isomers of butanol, n-propyl alcohol, isopropyl alcohol, ethanol and methanol. In another preferred embodiment, the first alcohol provided in step (b) is selected from n-propyl alcohol, isopropyl alcohol, ethanol and methanol, even more preferably methanol or ethanol and, most preferably, the first alcohol is methanol.

(C) Catalyst

[0064] The catalyst of the method of the invention provided in step (c) comprises surface-treated calcium carbonate activated by calcination, wherein the surface-treated calcium carbonate is a reaction product of a mineral containing ground natural calcium carbonate ( GNCC) or precipitated calcium carbonate (PCC) with carbon dioxide and one or more H3O+ ion donors and wherein the carbon dioxide is formed in situ by treatment with H3O+ ion donors and/or is supplied by an external source.

[0065] The base material of the activated catalyst is surface treated calcium carbonate (SRCC) which is also referred to as modified calcium carbonate (MCC).

[0066] It is recognized that the surface-treated calcium carbonate may be one or a mixture of different types of surface-treated calcium carbonate(s). In one embodiment of the present invention, the surface-treated calcium carbonate comprises, preferably consists of, a type of surface-treated calcium carbonate. Alternatively, the surface-treated calcium carbonate comprises, preferably consists of, two or more types of surface-treated calcium carbonates. For example, surface-treated calcium carbonate comprises, preferably consists of, two or three types of surface-treated calcium carbonates. Preferably, the surface-treated calcium carbonate comprises, more preferably consists of, a type of surface-treated calcium carbonate.

[0067] Surface treated calcium carbonate is a product of the reaction of ground natural calcium carbonate (GNCC) or precipitated calcium carbonate (PCC) treated with carbon dioxide and one or more H3O+ ion donors, in which the dioxide carbon is formed in situ by treatment with H3O+ ion donors and/or is supplied by an external source. Because of the ration of ground natural calcium carbonate or calcium carbonate precipitated with carbon dioxide and one or more H3O+ ion donors, the surface-treated calcium carbonate may comprise GNCC or PCC and at least one water-insoluble calcium salt in addition to calcium carbonate.

[0068] In a preferred embodiment, said surface-treated calcium carbonate comprises GNCC or PCC and at least one water-insoluble calcium salt in addition to the calcium carbonate that is present on at least part of the surface of said GNCC or PCC.

[0069] An H3O+ ion donor, in the context of the present invention, is a Bronsted acid and/or an acid salt.

[0070] In a preferred embodiment of the invention, surface-treated calcium carbonate is obtained by a process comprising the steps of: (a) providing a suspension of ground natural calcium carbonate (GNCC) or precipitated calcium carbonate (PCC ); (b) add at least one acid with a pKa value equal to or less than 0 at 20°C, or with a pKa value of 0 to 2.5 at 20°C to the suspension provided in step (a); and (c) treating the suspension provided in step (a) with carbon dioxide before, during or after step (b).

[0071] According to another embodiment, surface-treated calcium carbonate is obtained by a process comprising the steps of: (a) providing ground natural calcium carbonate (GNCC) or precipitated calcium carbonate (PCC); (b) provide at least one water-soluble acid; (c) provide gaseous carbon dioxide; and (d) bringing into contact said GNCC or PCC provided in step (a), at least one acid provided in step (b) and the gaseous carbon dioxide provided in step (c); distinguished by the fact that: (i) at least one acid provided in step (b) has a pKa greater than 2.5 and equal to or less than 7 at 20°C, associated with the ionization of its first available hydrogen, and a corresponding anion is formed on the loss of this first available hydrogen capable of forming a water-soluble calcium salt; and (ii) after contacting the at least one water-soluble acid provided in step (b) and the GNCC or PCC provided in step (a), at least one water-soluble salt, which, in the case of a salt containing hydrogen, has a pKa greater than 7 at 20°C, associated with the ionization of its first available hydrogen, and the anion of this salt is capable of forming water-insoluble calcium salts, is also provided.

[0072] The source of calcium carbonate, e.g. e.g., ground natural calcium carbonate (GNCC), is preferably selected from minerals containing calcium carbonate, selected from the group comprising marble, chalk, limestone and mixtures thereof. Natural calcium carbonate may further comprise natural components such as magnesium carbonate, aluminum silicate, etc. According to one embodiment, natural calcium carbonate, such as GNCC, comprises mineralogical crystalline forms of aragonite, vaterite or calcite of calcium carbonate or mixtures thereof.

[0073] In general, grinding of ground natural calcium carbonate can be carried out in a wet or dry grinding process, and can be carried out with any device for conventional grinding, for example, under conditions such that comminution results predominantly of impacts with a secondary body, i.e. in one or more of: a ball mill, a bar mill, a vibrating mill, a roller crusher, a centrifugal impact mill, a vertical ball mill, a friction, a pin mill, a hammer mill, a pulverizer, a crusher, a disintegrator, a knife cutter or other such equipment known to the person skilled in the art. If the ground natural calcium carbonate comprises wet-ground calcium carbonate, the grinding step may be carried out under conditions such that autogenous grinding and/or horizontal roller grinding and/or other such processes known to the person skilled in the art occur. The wet-processed ground natural calcium carbonate thus obtained can be washed and dewatered by well-known processes, e.g. e.g., by flocculation, filtration or forced evaporation before drying. The subsequent drying step (if necessary) may be carried out in a single step, such as spray drying, or in at least two steps. It is also common for such mineral material to go through a processing step (such as a flotation, bleaching or magnetic separation step) to remove impurities.

[0074] As already indicated above, a precipitated calcium carbonate (PCC) within the meaning of the present invention is a synthesized material, generally obtained by precipitation, followed by a reaction of carbon dioxide and calcium hydroxide in an aqueous environment or by precipitation of calcium and carbonate ions, for example, CaCl2 and Na2CO3, from the solution. Other possible ways to produce PCC are the caustic soda process or the Solvay process in which PCC is a byproduct of ammonia production. Precipitated calcium carbonate exists in three primary crystal forms: calcite, aragonite, and vaterite, and there are many different polymorphs (crystal habits) for each of these crystal forms. Calcite has a triangular structure with typical crystalline habits such as scalenohedral (S-PCC), rhombohedral (R-PCC), hexagonal prismatic, pinacoidal, colloidal (C-PCC), cubic and prismatic (P-PCC). Aragonite is an orthorhombic structure with crystal habits typical of twinned hexagonal prismatic crystals, as well as a diverse assortment of thin, elongated, curved laminar, acicular pyramidal, chisel-shaped, tree-branched, coral- or worm-like prismatic crystals. Vaterite belongs to the hexagonal crystal system. The aqueous slurry obtained from PCC can be dewatered and dried mechanically.

[0075] According to an embodiment of the present invention, the precipitated calcium carbonate comprises mineralogical crystalline forms of aragonite, vaterite or calcite of calcium carbonate or mixtures thereof.

[0076] Precipitated calcium carbonate can be milled before treatment with carbon dioxide and at least one H3O+ ion donor by the same means used for milling natural calcium carbonate and described above.

[0077] According to an embodiment of the present invention, the natural or precipitated calcium carbonate is in the form of particles with a median particle size by weight d50(w) between 0.05 and 10.0 μm, preferably 0.2 to 5.0 μm, more preferably from 0.4 to 3.0 μm, more preferably from 0.6 to 1.2 μm and especially 0.7 μm. According to a further embodiment of the present invention, the natural or precipitated calcium carbonate is in particle form with an upper cut-off particle size d98(p) between 0.15 and 55 μm, preferably 1 to 40 μm, more preferably from 2 to 25 μm, more preferably from 3 to 15 μm and especially 4 μm.

[0078] Natural or precipitated calcium carbonate can be used dry or suspended in water. Preferably, a corresponding aqueous slurry has a natural or precipitated calcium carbonate content within the range of 1 to 90% by weight, more preferably 3 to 60% by weight, even more preferably 5 to 40% by weight, and the more preferably, from 10 to 25% by weight, based on the total weight of said pulp.

[0079] One or more H3O+ ion donors used for the preparation of surface-treated calcium carbonate can be any strong acid, medium-strong acid or weak acid, or mixtures thereof, generating H3O+ ions under the preparation conditions. According to the present invention, at least one H3O+ ion donor may also be an acid salt, generating H3O+ ions under the conditions of the preparation.

[0080] According to one embodiment, at least one H3O+ ion donor is a strong acid with pKa equal to or less than 0 at 20°C.

[0081] According to another embodiment, at least one H3O+ ion donor is a medium-strong acid with a pKa value of 0 to 2.5 at 20°C. If the pKa at 20°C is equal to or less than 0, the acid is preferably selected from sulfuric acid, hydrochloric acid or mixtures thereof. If the pKa at 20°C is 0 to 2.5, the H3O+ ion donor is preferably selected from H2SO3, H3PO4, oxalic acid or mixtures thereof. At least one H3O+ ion donor may also be an acid salt, for example, HSO4- or H2PO4-, being at least partially neutralized by a corresponding cation such as Li+, Na+ or K+, or HPO42-, being at least partially neutralized by a corresponding cation such as Li+, Na+, K+, Mg2+ or Ca2+. At least one H3O+ ion donor may also be a mixture of one or more acids and one or more acid salts.

[0082] According to yet another embodiment, at least one H3O+ ion donor is a weak acid with a pKa value greater than 2.5 and less than or equal to 7, when measured at 20°C, associated with the ionization of its first available hydrogen, and having a corresponding anion, which is capable of forming water-soluble calcium salts. Subsequently, at least one water-soluble salt, which, in the case of a hydrogen-containing salt, has a pKa greater than 7 when measured at 20°C, associated with the ionization of its first available hydrogen, and the anion of that salt is capable of forming water-insoluble calcium salts, is also provided. According to a more preferred embodiment, the weak acid has a pKa value of greater than 2.5 to 5 at 20°C and, more preferably, the weak acid is selected from the group consisting of acetic acid, formic acid , propanoic acid and mixtures thereof. Exemplary cations of said water-soluble salt are selected from the group consisting of potassium, sodium, lithium and mixtures thereof. In a more preferred embodiment, said cation is sodium or potassium. Exemplary anions of said water-soluble salt are selected from the group consisting of phosphate, dihydrogen phosphate, monohydrogen phosphate, oxalate, silicate, mixtures and hydrates thereof. In a more preferred embodiment, said anion is selected from the group consisting of phosphate, dihydrogen phosphate, monohydrogen phosphate, mixtures and hydrates thereof. In a more preferred embodiment, said anion is selected from the group consisting of dihydrogen phosphate, monohydrogen phosphate, mixtures and hydrates thereof. The addition of the water-soluble salt can be carried out drop by drop or in one step. In the case of dropwise addition, this addition preferably takes place within a time period of 10 minutes. It is preferable to add said salt in one step.

[0083] According to an embodiment of the present invention, at least one H3O+ ion donor is selected from the group consisting of hydrochloric acid, sulfuric acid, sulfurous acid, phosphoric acid, citric acid, oxalic acid, acetic acid, formic and mixtures thereof. Preferably, at least one H3O+ ion donor is selected from the group consisting of hydrochloric acid, sulfuric acid, sulfurous acid, phosphoric acid, oxalic acid, H2PO4-, being at least partially neutralized by a corresponding cation such as Li+, Na+ or K+, HPO42-, being at least partially neutralized by a corresponding cation such as Li+, Na+, K+, Mg2+ or Ca2+ and mixtures thereof, more preferably at least one acid is selected from the group consisting of hydrochloric acid, acid sulfuric acid, sulfurous acid, phosphoric acid, oxalic acid or mixtures thereof. An especially preferred H3O+ ion donor is phosphoric acid.

[0084] One or more H3O+ ion donors can be added to the suspension as a concentrated solution or a more dilute solution. Preferably, the molar ratio of the H3O+ ion donor to the natural or precipitated calcium carbonate is 0.01:1 to 4:1, more preferably 0.02:1 to 2:1, even more preferably 0.05 :1 to 1:1 and more preferably from 0.1:1 to 0.58:1.

[0085] In another preferred embodiment, at least one H3O+ ion donor is selected from the group consisting of hydrochloric acid, sulfuric acid, sulfurous acid, phosphoric acid, citric acid, oxalic acid, acetic acid, formic acid and mixtures thereof. same, wherein the molar ratio of the H3O+ ion donor to the natural or precipitated calcium carbonate is from 0.01:1 to 4:1, more preferably from 0.02:1 to 2:1, even more preferably from 0 0.05:1 to 1:1 and more preferably 0.1:1 to 0.58:1.

[0086] In an especially preferred embodiment, at least one H3O+ ion donor is a mixture of phosphoric acid and citric acid, more preferably the molar ratio of the H3O+ ion donor to natural or precipitated calcium carbonate is 0.01: 1 to 4:1, more preferably from 0.02:1 to 2:1, even more preferably from 0.05:1 to 1:1 and most preferably from 0.1:1 to 0.58:1. In this embodiment, phosphoric acid is preferably used in excess in relation to citric acid.

[0087] Alternatively, it is also possible to add the H3O+ ion donor to the water before the natural calcium carbonate or precipitate is suspended.

[0088] In a next step, the natural or precipitated calcium carbonate is treated with carbon dioxide. If a strong acid, such as sulfuric acid or hydrochloric acid, is used to treat the H3O+ ion donor of natural or precipitated calcium carbonate, carbon dioxide is automatically formed. Alternatively or in addition, carbon dioxide may be supplied from an external source.

[0089] H3O+ ion donor treatment and carbon dioxide treatment can be carried out simultaneously, which is the case when a strong or medium-strong acid is used. It is also possible to carry out treatment with the H3O+ ion donor first, e.g. e.g., with a medium-strong acid with pKa in the range of 0 to 2.5 at 20°C, in which carbon dioxide is formed in situ and thus the carbon dioxide treatment will automatically be carried out simultaneously with the with the H3O+ ion donor, followed by additional treatment with carbon dioxide supplied from an external source.

[0090] Preferably, the concentration of gaseous carbon dioxide in the suspension is, in terms of volume, such that the ratio (suspension volume):(gaseous carbon dioxide volume) is 1:0.05 to 1:20 , even more preferably 1:0.05 to 1:5.

[0091] In a preferred embodiment, the H3O+ ion donor treatment step and/or the carbon dioxide treatment step are repeated at least once, more preferably several times. According to one embodiment, at least one H3O+ ion donor is added over a period of time of at least approximately 5 minutes, preferably at least approximately 10 minutes, typically between approximately 10 and 20 minutes, more preferably approximately 30 minutes, even more preferably nearly 45 minutes and sometimes approximately 1 hour or more.

[0092] Subsequent to treatment with H3O+ ion donor and treatment with carbon dioxide, the pH of the aqueous suspension, measured at 20°C, naturally reaches a value greater than 6.0, preferably greater than 6.5, more preferably greater than 7.0, even more preferably greater than 7.5, thereby preparing the surface-treated natural or precipitated calcium carbonate as an aqueous suspension with a pH greater than 6.0, preferably greater than 6.5, more preferably greater than 7.0, even more preferably greater than 7.5.

[0093] Additional details on the preparation of surface-treated natural calcium carbonate are described in WO 00/39222 A1, WO 2004/083316 A1, WO 2005/121257 A2, WO 2009/074492 A1, EP 2 264 108 A1, EP 2 264 109 A1 and US 2004/0020410 A1, where the contents of these references are included herein.

[0094] In the same way, precipitated calcium carbonate with a treated surface can be obtained. As can be taken in detail from WO 2009/074492 A1, surface-treated precipitated calcium carbonate is obtained by placing precipitated calcium carbonate in contact with H3O+ ions and with anions solubilized in an aqueous medium and capable of forming water-soluble calcium salts, in an aqueous medium for forming a paste of surface-treated precipitated calcium carbonate, wherein said surface-treated precipitated calcium carbonate comprises an insoluble, partially crystalline calcium salt of said anion formed on the surface of at least part of the calcium carbonate precipitate.

[0095] Said solubilized calcium ions correspond to an excess of solubilized calcium ions in relation to the solubilized calcium ions generated naturally in the dissolution of calcium carbonate precipitated by H3O+ ions, where said H3O+ ions are supplied exclusively in the form of a counterion to the anion , that is, via the addition of the anion in the form of an acid or a non-calcium acid salt and in the absence of any additional calcium ion or calcium ion-generating source.

[0096] Said excess solubilized calcium ions are preferably provided by the addition of a neutral or acid-soluble salt of calcium, or by the addition of an acid or a non-acidic or neutral salt of calcium that generates a neutral or acid-soluble salt of calcium. in situ.

[0097] Said H3O+ ions can be supplied by the addition of an acid or an acid salt of said anion, or the addition of an acid or acid salt that acts simultaneously to supply all or part of said excess solubilized calcium ions. .

[0098] In a more preferred embodiment of the preparation of surface-treated natural or precipitated calcium carbonate, the natural or precipitated calcium carbonate is reacted with acid and/or carbon dioxide in the presence of at least one compound selected from from the group consisting of silicate, silica, aluminum hydroxide, alkaline earth aluminate such as sodium or potassium aluminate, magnesium oxide, aluminum sulfate or mixtures thereof. Preferably, at least one silicate is selected from aluminum silicate, calcium silicate or alkaline earth metal silicate.

[0099] In another preferred embodiment, said at least one compound is aluminum sulfate hexadecahydrate. In an especially preferred embodiment, said at least one compound is aluminum sulfate hexadecahydrate, wherein at least one H3O+ ion donor is selected from the group consisting of hydrochloric acid, sulfuric acid, sulfurous acid, phosphoric acid, citric acid , oxalic acid, acetic acid, formic acid and mixtures thereof, more preferably the molar ratio of said H3O+ ion donor to natural or precipitated calcium carbonate is from 0.01:1 to 4:1, more preferably from 0. 02:1 to 2:1, even more preferably from 0.05:1 to 1:1 and most preferably from 0.1:1 to 0.58:1.

[00100] The above components can be added to an aqueous suspension comprising natural or precipitated calcium carbonate before adding the acid and/or carbon dioxide.

[00101] Alternatively, the above components can be added to the aqueous suspension of natural calcium carbonate or precipitate while the reaction of natural calcium carbonate or precipitate with an acid and carbon dioxide has already started. Additional details on the preparation of surface-treated natural or precipitated calcium carbonate in the presence of at least one silicate and/or silica and/or aluminum hydroxide and/or alkaline earth aluminate component(s) are described in WO 2004/ 083316 A1, where the content of that reference is included herein in this document.

[00102] The surface-treated calcium carbonate can be kept in suspension, optionally further stabilized by a dispersant. Conventional dispersants known to those skilled in the art may be used. A preferred dispersant is composed of polyacrylic acids and/or carboxymethylcelluloses.

[00103] Alternatively, the aqueous suspension described above can be dried, thus obtaining natural or precipitated calcium carbonate with a treated surface in a solid state (that is, dry or containing a minimum of water so as not to be in fluid form). in the form of granules or a powder.

[00104] Surface treated calcium carbonate can have different particle shapes, such as, e.g. e.g., in the shapes of roses, golf balls and/or brains.

[00105] In a preferred embodiment, the surface-treated calcium carbonate has a specific surface area between 15 and 200 m2/g, preferably from 25 to 180 m2/g and, most preferably, from 30 to 150 m2/g, measured using nitrogen and the BET method according to ISO 9277:2010. In a further embodiment, the surface-treated calcium carbonate has a specific surface area of 120 m2/g or less, more preferably 60 to 120 m2/g, and most preferably 70 to 105 m2/g, measured using nitrogen and the BET method according to ISO 9277:2010. For example, surface treated calcium carbonate may have a specific surface area between 75 and 100 m2/g, measured using nitrogen and the BET method in accordance with ISO 9277:2010.

[00106] It may further be preferred that the surface-treated calcium carbonate particles have a volume median grain diameter d50(vol) between 0.5 and 50 μm, preferably 1 to 30 μm, more preferably 1. 5 to 20 μm and, most preferably, 2 to 12 μm. According to another preferred embodiment, the surface-treated calcium carbonate particles have a volume median grain diameter d50 (vol) between 1.5 and 12 μm, preferably 2 to 5 μm or 6 to 10 μm.

[00107] It may further be preferred that the surface-treated calcium carbonate particles have a grain diameter d98(vol) between 1 and 120 μm, preferably 2 to 100 μm, more preferably 5 to 50 μm, and the more preferably, from 8 to 25 μm. According to another preferred embodiment, the surface-treated calcium carbonate particles have a volume median grain diameter d98 (vol) between 5 and 20 μm, preferably 8 to 12 μm or 13 to 18 μm.

[00108] According to another embodiment, the surface-treated calcium carbonate has a specific pore volume per intraparticle intrusion in the range of 0.1 to 2.3 cm3/g, more preferably 0.2 to 2.0 cm3 /g, especially preferably from 0.4 to 1.8 cm3/g and more preferably from 0.6 to 1.6 cm3/g, calculated by measuring mercury porosimetry.

[00109] The intraparticle pore size of the surface-treated calcium carbonate is preferably in a range between 0.004 and 1.6 μm, more preferably in a range between 0.005 and 1.3 μm, especially preferably 0.006 to 1.15 μm and more preferably from 0.007 to 1.0 μm, p. e.g., 0.004 to 0.50 μm, determined by mercury porosimetry measurement.

[00110] The catalyst provided in step (c) of the method of the invention and used in the subsequent transesterification step (d) is a surface-treated calcined calcium carbonate, meaning that the catalyst is a material that can be obtained by calcination of carbonate calcium with treated surface. As already explained above, calcination indicates a heat treatment at elevated temperatures that leads to a partial to total thermal conversion of the starting material (partial to total calcination).

[00111] Therefore, in one embodiment, the catalyst comprises surface-treated calcined calcium carbonate that can be obtained by partial or total calcination of surface-treated calcium carbonate. In the meaning of the present invention, full calcination indicates that the percentage of calcium carbonate (CaCO3) in the calcined substrate, as determined by XRD, does not decrease (unlike in the case of partial calcination) by more than 1%, based on the total composition , over a period of 15 minutes at a given calcination temperature. For example, if the initial percentage of calcium carbonate in a calcined sample is 5%, determined by XRD, full calcination means that the percentage of calcium carbonate in said sample does not fall below 4%, determined by XRD, over the course of a period of 15 minutes at the relevant calcination temperature.

[00112] The degree of calcination (partial or total calcination) can influence the activity of the transesterification catalyst, which, in turn, can depend on the calcination temperature and calcination time. Thus, in one embodiment, the catalyst is obtained by partial or total calcination of surface-treated calcium carbonate, preferably by total calcination.

[00113] Furthermore, the activation of the catalyst or the degree of calcination can be defined through a specific calcination temperature and/or a specific calcination time. In one embodiment, the catalyst can thus be obtained by calcining surface-treated calcium carbonate, wherein the calcination is carried out at a calcination temperature of at least 650°C, preferably at least 680°C and, most preferably, at a temperature of 700 to 950°C; and/or in a calcination time of at least 5 minutes, preferably at least 0.25 hours, more preferably at least 0.5 hours and, most preferably, in a calcination time of 1 to 3 hours. In an especially preferred embodiment, the catalyst can be obtained by calcining surface-treated calcium carbonate, wherein the calcination is carried out at a temperature of 700 to 950°C and a calcination time of 1 to 3 hours.

[00114] As can be seen from Figure 3, the specific surface area of surface-treated calcium carbonate surprisingly decreases upon thermal activation. This is in contrast to what can be observed in the case of conventional ground natural calcium carbonate and the person skilled in the art would therefore expect little total conversion and reduced reaction rate from the transesterification reaction. However, the opposite is true as comparison of calcined GNCC and calcined SRCC shows that the performance of the catalysts is equally good although the specific surface area decreases during activation and the lime (CaO) content of the catalyst is comparably low.

[00115] As can be seen from Figure 5, the characteristics of the SRCC surface structure are essentially preserved or only slightly changed upon thermal activation. On the contrary, Figure 6 shows the formation of micropores upon thermal activation of GNCC.

[00116] Specifically, in another embodiment of the present invention, the catalyst has a specific surface area between 1 and 200 m2/g, preferably from 5 to 120 m2/g and, most preferably, from 10 to 100 m2/g, measured using nitrogen and the BET method according to ISO 9277:2010. In another further embodiment, the catalyst may have a specific surface area of between 1 and 120 m2/g, preferably 3 to 50 m2/g, and most preferably 5 to 25 m2/g, measured using nitrogen and the BET method. in accordance with ISO 9277:2010.

[00117] In relation to the lime content, it can be seen from Figure 4 that the chemical composition of the surface-treated calcium carbonate changes upon thermal activation. In an exemplary embodiment, the chemical composition of surface-treated calcined calcium carbonate, as determined by XRD, comprises: 0.5 to 50% calcium oxide (CaO), 0.5 to 50% calcium carbonate (CaCO3 ), 70 to 99% hydroxyapatite (Ca5(PO4)3OH) and 0 to 5% calcium hydroxide (Ca(OH)2), each based on the total composition.

[00118] In addition or alternatively, in an embodiment of the present invention, the catalyst has d50(vol) between 1 and 75 μm, preferably from 1.5 to 50 μm, more preferably from 2 to 30 μm and, most preferably, from 3 to 15 μm and/or d98(vol) between 2 and 150 μm, preferably from 5 to 120 μm, more preferably from 8 to 80 μm and, most preferably, from 10 to 30 μm.

[00119] Surface-treated calcium carbonate and the catalyst that can be obtained by calcining said calcium carbonate can be in the form of a loose powder. However, the catalyst may be in a compacted form, e.g. in the form of a granule, a pellet, a tablet or an extrudate which may be formed either by compaction of the catalyst precursor (i.e. uncalcined surface-treated calcium carbonate) or by compaction of the activated catalyst (i.e. , calcined calcium carbonate with treated surface). Compacted forms can be advantageous for separating the catalyst from the reaction mixture.

[00120] The person skilled in the art will recognize that the particle size distribution and/or specific surface area of the catalyst can be controlled by applying the appropriate calcination temperature and/or calcination time. In an additional embodiment, the catalyst can be obtained by calcining surface-treated calcium carbonate, wherein the calcination temperature and calcination time are such that the catalyst has d50(vol) between 1 and 75 μm, preferably of 1.5 to 50 μm, more preferably from 2 to 30 μm and most preferably from 3 to 15 μm and/or d98(vol) between 2 and 150 μm, preferably from 5 to 120 μm, more preferably from 8 to 80 μm and, most preferably, from 10 to 30 μm and/or a specific surface area between 1 and 200 m2/g, preferably from 5 to 120 m2/g and, most preferably, from 10 to 100 m2/g, measured using nitrogen and the BET method according to ISO 9277:2010. In any of these embodiments, the calcination temperature may be at least 650°C, preferably at least 680°C and, most preferably, 700 to 950°C and/or the calcination time may be at least 5 minutes, preferably at least 0.25 hour, more preferably at least 0.5 hour and most preferably 1 to 3 hours, for example calcination can be carried out between 700 and 950°C for 1 to 3 hours.

[00121] In general, the catalyst of the present invention is defined in such a way that it comprises calcined calcium carbonate with a treated surface. However, as explained above, the term "consist of" is considered as a preferred embodiment of the term "comprise" and therefore any aspect and embodiment described herein equally refers to a catalyst consisting of calcium carbonate calcined with treated surface.

(D) Transesterification step

[00122] In step (d) of the method of the invention, the substrate provided in step (a) and the first alcohol provided in step (b) are reacted 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.

[00123] As explained in the introductory part, the reaction in step (d) is a transesterification which can be illustrated by the following reaction scheme: in view of which, the person skilled in the art will recognize that R' and R” are structurally different radicals. However, R can be the same radical or different from R' or R”.

[00124] Therefore, the method according to the present invention can be described by the following steps: (a) providing a substrate comprising a first carboxylic acid ester R”O(O=)CR; (b) providing a first alcohol R’OH; (c) providing a catalyst; 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 R'O( O=)CR and a second alcohol R”OH; distinguished by the fact that the catalyst comprises surface-treated calcined calcium carbonate, wherein the surface-treated calcium carbonate is a reaction product of a mineral containing ground natural calcium carbonate (GNCC) or precipitated calcium carbonate (PCC). with carbon dioxide and one or more H3O+ ion donors, wherein the carbon dioxide is formed in situ by treatment with H3O+ ion donors and/or is supplied by an external source, and wherein R' and R” are radicals structurally different organics.

[00125] The inventors found that a calcined calcium carbonate with a treated surface is capable of catalyzing the transesterification reaction illustrated above.

[00126] The catalyst can be applied in the method of the invention in various concentrations. In one embodiment, the catalyst is used in step (d) of the method of the invention in an amount between 0.01 to 20% by weight, preferably from 0.1 to 10% by weight and, most preferably, from 0.5% by weight. to 5% by weight, based on the total weight of the substrate.

[00127] In order to improve the total conversion or reaction rate, it may be beneficial if the first alcohol is used in molar excess relative to the first carboxylic acid ester contained in the substrate. Therefore, in one embodiment, the first alcohol provided in step (a) is used as a reaction medium in step (d) of the method of the invention, preferably the first alcohol is used in molar excess with respect to the first carboxylic acid ester. More preferably, alcohol is used as the reaction medium in step (d), wherein the molar ratio of the first carboxylic acid ester to the first alcohol is at least 1:1.5, preferably at least 1:2, more preferably at least 1:3 and, most preferably, at least 1:5.

[00128] The transesterification step can be carried out at room temperature or, more preferably, at elevated temperature, where the reaction mixture must be in a liquid state allowing adequate stirring. In one embodiment, step (d) is carried out at a temperature of at least 20°C, preferably at least 25°C and, most preferably, in a range between 30 and 80°C. In another additional embodiment, step (d) is carried out at a temperature between 40 and 60°C. The reaction temperature can be adjusted in order to control the total conversion and reaction rate.

[00129] In many cases, it may be appropriate to adjust the reaction temperature to a temperature that is slightly below the boiling point of the reaction mixture, or the reaction mixture is heated under reflux. If the first alcohol is used as the reaction medium in step (d), it may be preferred that the reaction temperature in step (d) is slightly below the boiling point of said alcohol. Therefore, in a preferred embodiment, the substrate and the first alcohol are reacted in step (d) at a temperature that is 25 to 5°C below the boiling point of said alcohol under the given conditions. For example, if methanol is used as the reaction medium at ambient pressure, the reaction temperature may be in a range between 40 and 60°C. In an especially preferred embodiment, the first alcohol is a monohydric alcohol as defined above, wherein said first alcohol is used as the reaction medium in step (d), preferably the molar ratio of the first carboxylic acid ester to said first alcohol is at least 1:1.5, more preferably at least 1:2, even more preferably at least 1:3 and most preferably at least 1:5, and wherein the substrate and the first alcohol are reacted in step (d) at a temperature which is 25 to 5°C below the boiling point of said alcohol under the given conditions.

[00130] In another additional embodiment, the transesterification step (d) is carried out at ambient pressure or increased pressure, preferably at ambient pressure. Although it is more convenient to carry out the method of the invention under ambient pressure, increased pressure may allow for higher reaction temperatures and higher reaction rates. In another further embodiment according to the present invention, step (d) is carried out under the atmosphere of an inert gas, wherein the preferred inert gases are nitrogen, argon and mixtures thereof.

[00131] Regardless of whether or not the first alcohol is used in molar excess in relation to the first ester, an inert solvent can be used in step (d) of the method of the invention and act as a cosolvent and be beneficial to control the total conversion or the reaction rate. In the present case, inert means that the solvent is inert under the conditions applied in step (d) of the method of the invention. Preferred examples include aprotic solvents such as acetonitrile, dimethylformamide or dimethylsulfoxide.

[00132] In principle, the reaction mixture of step (d) can be prepared by mixing each of the components (first carboxylic acid ester, first alcohol and catalyst) in any conceivable order, and in one or more portions. However, to ensure proper mixing and preconditioning, it may be preferred, in one embodiment of the invention, that the alcohol, catalyst and optional cosolvent are contacted and premixed in a first step and the substrate is then added in a second step.

[00133] Although the present invention will not be understood as limited to specific combinations, some advantageous exemplary embodiments will be described below.

[00134] In an exemplary embodiment, the substrate is a fat or a fatty oil, preferably a fatty oil, wherein the first alcohol is a monohydric alcohol, preferably selected from n-propyl alcohol, isopropyl alcohol, ethanol and methanol, even more preferably methanol or ethanol and, most preferably, said first alcohol is methanol.

[00135] In another exemplary embodiment, the substrate is a fat or a fatty oil, preferably a fatty oil, in which the first alcohol is a monohydric alcohol, preferably selected from n-propyl alcohol, isopropyl alcohol, ethanol and methanol, even more preferably methanol or ethanol and, most preferably, said first alcohol is methanol, wherein the catalyst may be obtained by calcining surface-treated calcium carbonate at a calcination temperature of at least 650°C, preferably at least 680° C and, most preferably, at a temperature of 700 to 950°C and/or at a calcination time of at least 5 minutes, preferably at least 0.25 hour, more preferably at least 0.5 hour, and most preferably preferably, in a calcination time of 1 to 3 hours.

[00136] In another exemplary embodiment, the substrate is a fat or a fatty oil, preferably a fatty oil, in which the first alcohol is a monohydric alcohol, preferably selected from n-propyl alcohol, isopropyl alcohol, ethanol and methanol, even more preferably methanol or ethanol and, most preferably, said first alcohol is methanol, wherein the catalyst can be obtained by calcining surface-treated calcium carbonate, wherein the calcination temperature and the calcination time are such that the catalyst has d50(vol) between 1 and 75 μm, preferably 1.5 to 50 μm, more preferably 2 to 30 μm and, most preferably, 3 to 15 μm and/or d98(vol) between 2 and 150 μm , preferably from 5 to 120 μm, more preferably from 8 to 80 μm and most preferably from 10 to 30 μm and/or a specific surface area between 1 and 200 m2/g, preferably from 5 to 120 m2/g and , most preferably, from 10 to 100 m2/g, measured using nitrogen and the BET method in accordance with ISO 9277:2010.

[00137] In any of the previous exemplary embodiments, the catalyst can be used in the transesterification step (d) of the method of the invention in an amount between 0.01 to 20% by weight, preferably from 0.1 to 10% by weight and, most preferably, 0.5 to 5% by weight, based on the total weight of the substrate.

[00138] Furthermore, in any of the previous exemplary embodiments, said first alcohol may be used as a reaction medium in step (d), wherein preferably the molar ratio of the first carboxylic acid ester to the first alcohol is at least 1:1.5, more preferably at least 1:2, even more preferably at least 1:3 and most preferably at least 1:5 and/or the substrate and the first alcohol are reacted in step (d) to a temperature which is 25 to 5°C below the boiling point of said first alcohol under the given conditions.

(E) Optional steps and additional aspects

[00139] Note that, where appropriate, the details and modalities described in the previous sections apply equally to any additional aspects and modalities described below.

[00140] In step (d) of the process of the invention, a reaction mixture is obtained comprising a second carboxylic acid ester and a second alcohol.

[00141] Furthermore, the reaction mixture obtained normally comprises residual catalyst. In one embodiment, the method of the present invention thus further comprises step (e) of separating residual catalyst contained in the reaction mixture of step (d), preferably by filtration.

[00142] In another embodiment, the process of the present invention further comprises step (f) of separating said second carboxylic acid ester from said second alcohol contained in the reaction mixture of step (d). For this, any method known to the person skilled in the art can be used, for example, liquid phase separation, extraction, evaporation or fractional distillation. As noted above, the substrate may comprise a mixture of two or more structurally different carboxylic acid esters, e.g. e.g., different triglycerides as in the case of natural fats. In turn, a polyesterified polyhydric alcohol, such as a triglyceride, can be substituted with different acyl radicals. In each of these cases, a mixture of two or more structurally different esters can be obtained, all of which represent second carboxylic acid esters within the meaning of the present invention.

[00143] In many cases, liquid phase separation can be the method of choice for separating the main products, that is, esters of carboxylic acids and alcohols. Typically, the heavy or polar phase contains a product alcohol obtained in transesterification step (d) together with the unreacted or excess alcohol provided in step (a). the lighter or nonpolar phase typically contains the product ester. For example, if the substrate provided in step (a) is a fat, such as a fatty oil, the carboxylic acid ester is a triglyceride that leads to the formation of one or more esters of fatty acids and glycerin, which can be separated by said liquid phase separation, for example, in a separating funnel. Water or brine can be used to improve phase separation and to remove water-soluble impurities contained in the ester phase.

[00144] As noted above, an especially preferred embodiment utilizes a triglyceride-containing substrate, such as a vegetable oil, which is provided in step (a) and methanol which is provided as the first alcohol in step (b). In this case, a mixture of structurally different fatty acid esters (FAMEs) is obtained, all of which represent second carboxylic acid esters within the meaning of the present invention.

[00145] Depending on the separation method, it is possible to conduct the method as a batch process (batch) or as a continuous process.

[00146] The carboxylic acid esters that can be obtained by the process of the invention, especially those obtained from fat-based substrates, such as vegetable oil, are valuable fuels and represent an alternative non-fossil energy source that can be used either alone or as a fuel component.

[00147] Therefore, a further aspect of the present invention relates to the use of the method of the invention in the production of fuel or fuel components.

[00148] Especially esters based on vegetable or animal fat, obtained by the method of the invention, can be used as fuel or as a fuel component and can be referred to as biodiesel. Thus, according to further aspects, the present invention relates to a carboxylic acid ester obtainable by the method of the invention described herein and to its use as a fuel or as a fuel component.

[00149] Another product obtained by the process of the invention is the second alcohol which is structurally derived from the substrate ester. As mentioned above, the inventors have found that the use of the catalyst of the invention leads to a reduction of impurities, especially in the product alcohol and, in particular, in cases where the second alcohol is glycerin.

[00150] Yet another aspect of the present invention thus relates to an alcohol that can be obtained by the method of the invention. In this regard, a preferred aspect relates to glycerin that can be obtained by the method of the invention, for example, if the substrate contains glycerides as in the case of fat-based substrates described above.

[00151] Finally, additional aspects of the present invention relate to a transesterification catalyst comprising surface-treated calcined calcium carbonate and its use as a catalyst in transesterification reactions. Reference is made to the details and embodiments relating to the catalyst used in the process of the invention, as described in Section (C).

Description of figures

[00152] Figure 1: (a) Phase separation after the transesterification process; (b) Crude glycerol obtained using NaOH as catalyst; (c) Crude glycerol obtained using KOH as catalyst.

[00153] Figure 2: X-ray diffraction patterns of ground natural calcium carbonate thermally activated at different temperatures and at different times of thermal activation.

[00154] Figure 3: Evolution of the surface area of ground natural calcium carbonate and surface-treated calcium carbonate as a function of activation temperature.

[00155] Figure 4: X-ray diffraction patterns of calcium carbonate with a treated surface thermally activated at different temperatures and at different times of thermal activation.

[00156] Figure 5: (a) SEM micrograph of SRCC before calcination, (b) SEM micrograph of SRCC calcined at 900°C for 3 hours in a Nabertherm oven model Le 6/11, Nabertherm GmbH, Lilienthal , Germany.

[00157] Figure 6: (a) SEM micrograph of GNCC before calcination, (b) SEM micrograph of GNCC calcined at 900°C for 3 hours in a model oven from Nabertherm Le 6/11, Nabertherm GmbH, Lilienthal , Germany.

[00158] Figure 7: (a) NMR spectrum of sunflower oil; b) NMR spectrum of the transesterification product obtained with GNCC calcined at 900°C.

[00159] Figure 8: Crude glycerol obtained using: 1) KOH, 2) NaOH, 3) calcined GNCC and 4) calcined SRCC as catalysts, 5) is pure glycerol.

Examples

[00160] The scope and interest of the invention can be better understood based on the following examples, which are intended to illustrate embodiments of the present invention.

(A) Analytical methods

[00161] All parameters defined throughout this document and those mentioned in the following examples are based on the following measurement methods:

Particle size distribution

[00162] To determine particle size distribution based on volume, a Malvern Mastersizer 2000 Laser Diffraction System is used. The raw data obtained by measurement is analyzed using Fraunhofer theory and Malvern Application Software 5.60. In general, measurement is performed with an aqueous dispersion with the exception of surface-treated calcined calcium carbonate which is measured in a dry state (< 0.5% by weight of total moisture based on total sample weight) and at a pressure of 400 kPa. The particle size distribution determined based on weight can correspond to the particle size determined in the volume if the density of all particles is equal.

[00163] Any particle size distribution based on weight is measured by the sedimentation method, which is an analysis of sedimentation behavior in a gravimetric field. The measurement was made with a SedigraphTM 5120 from Micromeritics Instrument Corporation, USA. The method and instrument are known to those skilled in the art and are commonly used to determine particle size distributions of, e.g. e.g., fillers (fillers) and pigments. The measurement was carried out in an aqueous solution of 0.1 wt% Na4P2O7. Samples were dispersed using a high-speed shaker and supersonicated.

X-ray diffraction (XRD)

[00164] XRD experiments are performed on the samples using rotating PMMA support rings. The samples are analyzed with a Bruker D8 Advance powder diffractometer following Bragg's law. This diffractometer consists of a 2.2 kW X-ray tube, a sample holder, a 3-3 goniometer and a VÂNTEC-1 detector. Nickel-filtered Cu-Kα radiation is used in all experiments. Profiles are recorded in tables automatically using a scan speed of 0.7° per minute in 23 minutes. The resulting powder diffraction pattern can be easily classified by mineral content using the DIFFRACsuite EVA and SEARCH software packages, based on in reference standards from the ICDD PDF 2 database.

[00165] Quantitative analysis of diffraction data refers to the determination of quantities of different phases in a multi-phase sample, and was performed using the DIFFRACsuite TOPAS software package. In detail, quantitative analysis makes it possible to determine structural characteristics and phase proportions with quantifiable numerical precision from the experimental data itself. This involves modeling the entire diffraction pattern using the Rietveld approach such that the calculated pattern(s) duplicate the experimental pattern.

[00166] Unless otherwise indicated, activated solids were temporarily stored in round-bottom flasks, purged with an inert atmosphere (e.g., N2) until XRD measurement was performed.

Specific surface area

[00167] The specific surface area (in m2/g) of surface-treated calcium carbonate or other materials is determined by the BET method (using nitrogen as adsorption gas), which is well known to those skilled in the art (ISO 9277 :2010). The total surface area (in m2) can be obtained by multiplying the specific surface area and the mass (in g) of the corresponding sample. To perform the measurement on thermally activated solids, precautions similar to those described above for X-ray diffraction were taken.

Scanning electron microscope (SEM)

[00168] SEM images were produced using the field emission scanning electron microscope (FESEM) Zeiss Sigma VP from Carl Zeiss Microscopy GmbH, Jena, Germany.

Nuclear Magnetic Resonance Spectroscopy (NMR Spectroscopy)

[00169] Samples were distinguished using a Bruker 300 MHz Avance 300 Spectrometer. Specific weights of samples were solubilized in diclomethane-d2 before analysis.

(B) Examples

[00170] The following examples should not be interpreted in any way as limitations on the scope of the claims.

Comparative example 1 - CE1

[00171] A first comparative test was carried out in a 250 mL round bottom flask using a commercial sunflower oil (M Classic sunflower oil from Migros) and anhydrous methanol (for HPLC > 99.9% from Sigma Aldrich) and pellets of NaOH (ACS reagent >97% from Sigma Aldrich) as homogeneous base catalyst. In this process, an oil/methanol weight ratio of 2:1 and an oil/NaOH weight ratio of 170:1 were used. First, anhydrous methanol was mixed with the NaOH pellets at 30°C for 30 minutes. At the same time, in another round-bottom flask, the vegetable oil was also heated to 30°C and, after 30 minutes, the vegetable oil was added to the methanol/NaOH mixture, drop by drop. Furthermore, the temperature was gradually increased to 50°C. At the end of the addition, the temperature of the entire mixture was increased to 60°C and maintained for 2 to 3 hours.

[00172] At the end of the process, the reaction was stopped, methanol was evaporated under vacuum at 50°C/25 mbar for a period of time of 15 to 20 minutes. Finally, the mixture was transferred to a separating funnel in order to separate the phases obtained (see Figure 1a). The upper lighter phase corresponds to the transesterification product, the lower heavy phase contains the crude glycerol.

Comparative example 2 - CE2

[00173] A catalytic evaluation analogous to that for CE1 was carried out using KOH as a base source, in which the oil/KOH weight ratio was 119:1.

Comparative example 3 - CE3 Catalyst preparation and activation

[00174] A conventional ground natural calcium carbonate (GNCC) was obtained by wet grinding and spray drying Carrara marble. The ground calcium carbonate had a specific surface area of 4 m2/g and d50(p) of 1.6 μm.

[00175] The ground calcium carbonate was calcined to activate the catalyst. Different thermal activation conditions (i.e., temperatures and activation time) were employed. After activation, solids were then distinguished using X-ray diffraction (XRD) as well as BET techniques and SEM imaging (see Figure 2, Figure 3 and Figure 6). By using the last two techniques, an idea about the chemical composition and surface of the solids is provided.

[00176] Thermal activation of GNCC at different temperatures showed that a heat treatment of at least 700°C is preferred to achieve full calcination. Furthermore, the results demonstrate, e.g. e.g., a clear increase in surface area from 4 m2/g to 14 m2/g and the formation of micropores of the mineral activated at 900°C for 2 hours.

Heterogeneous catalysis assays

[00177] The transesterification carried out with this heterogeneous catalyst is analogous to the protocol presented in CE1.

[00178] 0.75 g of the activated catalyst prepared above was placed in a round-necked flask, then purged with N2 for about 10 minutes. 25 g of anhydrous methanol was added to the catalyst, stirred, then once again the system was purged with N2 to eliminate any traces of air. The mixture was heated to 30°C and stirred for 30 minutes. 50 g of sunflower oil (Migros M Classic sunflower oil) was heated in another round-bottom flask at 30°C for 30 minutes. After 30 minutes, the heated oil was added to the catalyst/methanol mixture and then the mixture was progressively heated to 50°C. At the end of the addition, the entire catalyst/methanol/vegetable oil mixture was heated to 60°C and maintained at that temperature for 2 to 3 hours. At the end of the process, methanol was evaporated under vacuum at a temperature of 50°C/25 mbar for approximately 15 to 20 minutes. Then, the solid was separated by filtration using Whatman grade 589/1 filter paper.

Example of the invention - EX1 Preparation and activation of the catalyst

[00179] In an exemplary test, a surface treated calcium carbonate (SRCC) was obtained as follows: 10 liters of an aqueous suspension of ground marble were prepared in a mixing vessel, adjusting the solids content to 10% by weight , based on the total weight of the aqueous suspension. Ground marble was obtained from Hustadmarmor, Norway, and had d9o(p) less than 2 μm. An aqueous solution containing 30% by weight of phosphoric acid was prepared while another solution was prepared containing 5% by weight of citric acid. While the suspension was mixed, 1.60 kg of the phosphoric acid solution was added to said suspension over a period of 10 minutes and at a temperature of 70°C. Furthermore, starting 2 minutes after the addition of phosphoric acid began, 0.05 kg of the citric acid solution was added to the paste. Finally, after adding the phosphoric acid, the paste was stirred for another 5 minutes before being removed from the container. The solid obtained was then filtered and dried.

[00180] A surface-treated calcium carbonate, prepared in a similar way, with a specific surface area of 135 m2/g, d50(vol) of 6.2 μm and d98(vol) of 12.8 μm was used in the tests following.

[00181] The surface treated calcium carbonate (SRCC) was calcined to activate the catalyst. Different thermal activation conditions (i.e., temperatures and activation time) were employed. After activation, solids were then distinguished using X-ray diffraction (XRD) as well as BET techniques and SEM imaging (see Figure 3, Figure 4 and Figure 5).

[00182] Thermal activation of GNCC at different temperatures showed that a heat treatment of at least 700°C is preferred to achieve the desired activity.

[00183] As is evident from Figure 3, the surface area of surface-treated calcium carbonate as a function of temperature contrasts starkly with that of ground natural calcium carbonate, as its surface area has decreased as a function of conditions. thermal activation. In fact, the surface area decreased from 135 m2/g in the fresh sample to 15 m2/g after activation for 2 hours at 900°C. However, as can be seen from Figure 5, the surface structure of surface-treated calcined calcium carbonate (SRCC) is comparable to that of surface-treated calcium carbonate before calcination.

Heterogeneous catalysis assays

[00184] A procedure identical to that described in CE3 was used in tests with the catalyst prepared from surface-treated calcium carbonate.

(C) Catalyst performance assessment

[00185] When indicated below, all yields of transesterification products were calculated based on 1H-NMR spectra and normalized.

Homogeneous catalysts

[00186] Using NaOH or KOH, the presence of the transesterification product was confirmed by proton nuclear magnetic resonance (1H-NMR), since no signals were observed from the vegetable oil, which confirms its total conversion. The high yields of transesterification products were also confirmed by analyzes certified in accordance with EN 14103. A difference could be observed in the physical appearance of the raw glycerol. In the case of NaOH, the crude glycerol is less viscous when compared to a more viscous crude glycerol obtained in the case of KOH (see Figure 1b and Figure 1c).

Heterogeneous catalysts

[00187] The evaluation of calcined GNCC as a transesterification catalyst demonstrated that catalysts activated at temperatures above 700°C were more efficient, since full conversion could be observed in this case.

[00188] The performance of SRCC as a transesterification catalyst was investigated in a similar way. Analysis demonstrated that full conversion was possible with SRCC activated at 900°C and 700°C, respectively.

[00189] The comparison in catalytic performance of calcined GNCC and calcined SRCC can be summarized as follows:

[00190] 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.

[00191] Furthermore, a comparison of the crude glycerol phases shows that the glycerol obtained using calcined SRCC is clearer than that obtained using calcined GNCC or conventional catalysts (see Figure 8). This fact suggests that the crude glycerol obtained using calcined SRCC has a higher purity than that obtained using calcined GNCC or NaOH/KOH.

Claims (19)

1. Method for transesterification of carboxylic acid esters by heterogeneous catalysis, wherein the method comprises the following steps: (a) providing a substrate comprising a first carboxylic acid ester; (b) provide a first alcohol; (c) providing a catalyst; 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 ; characterized in that the catalyst comprises surface-treated calcined calcium carbonate, wherein the surface-treated calcium carbonate is a reaction product of a mineral containing ground natural calcium carbonate (GNCC) or precipitated calcium carbonate (PCC) with carbon dioxide and one or more H3O+ ion donors and wherein the carbon dioxide is formed IN SITU by treatment with H3O+ ion donors and/or is supplied by an external source. 2. Method according to claim 1, characterized in that the substrate is a fat or a fatty oil, preferably a vegetable oil, more preferably the substrate is selected from the group consisting of canola oil, seed oil cottonseed oil, coconut oil, corn oil, hazelnut oil, linseed oil, mustard seed oil, olive oil, palm oil, peanut oil, rapeseed oil, rice bran oil, safflower oil , sesame oil, soybean oil, sunflower oil, tigernut oil, tung oil and mixtures thereof and, most preferably, the substrate is sunflower oil. 3. Method according to claim 1 or 2, characterized in that the first carboxylic acid ester is a triglyceride. 4. Method according to any one of claims 1 to 3, characterized in that the first alcohol is a monohydric alcohol, preferably a C1-C5 monohydric alcohol, more preferably a C1-C3 monohydric alcohol, even more preferably methanol or ethanol and, most preferably, methanol. 5. Method according to any one of claims 1 to 4, characterized by the fact that the catalyst has: (i) d5O(VOI) between 1 and 75 μm, preferably from 1.5 to 50 μm, more preferably from 2 to 30 μm and, most preferably, 3 to 15 μm; and/or (ii) D98(vol) between 2 and 150 μm, preferably from 5 to 120 μm, more preferably from 8 to 80 μm and, most preferably, from 10 to 30 μm. 6. Method according to any one of claims 1 to 5, characterized in that the catalyst has a specific surface area between 1 and 200 m2/g, preferably from 5 to 120 m2/g and, most preferably, from 10 at 100 m2/g, measured using nitrogen and the BET method according to ISO 9277:2010. 7. Method according to any one of claims 1 to 6, characterized by the fact that the surface-treated calcium carbonate has: (i) D50 (vol) between 0.5 and 50 μm, preferably from 1 to 30 μm, more preferably 1.5 to 20 μm and most preferably 2 to 12 μm; and/or (ii) D98(vol) between 1 and 120 μm, preferably from 2 to 100 μm, more preferably from 5 to 50 μm and, most preferably, from 8 to 25 μm. 8. Method according to any one of claims 1 to 7, characterized in that the surface-treated calcium carbonate has a specific surface area between 15 and 200 m2/g, preferably 25 to 180 m2/g and, the more preferably, from 30 to 150 m2/g, measured using nitrogen and the BET method in accordance with ISO 9277:2010. 9. Method according to any one of claims 1 to 8, characterized by the fact that: (i) the mineral containing ground natural calcium carbonate is selected from the group consisting of marble, chalk, dolomite, limestone and mixtures thereof same; and/or (ii) the precipitated calcium carbonate comprises mineralogical crystalline forms of aragonite, vaterite or calcite or mixtures thereof. 10. Method according to any one of claims 1 to 9, characterized in that the catalyst can be obtained by partial or total calcination of calcium carbonate with a treated surface. 11. Method according to any one of claims 1 to 10, characterized by the fact that the catalyst can be obtained by calcining surface-treated calcium carbonate, wherein the calcination is carried out: (i) at a calcination temperature of at least 650°C, preferably at least 680°C and most preferably at a temperature of 700 to 950°C; and/or (ii) in a calcination time of at least 5 minutes, preferably at least 0.25 hours, more preferably at least 0.5 hours and, most preferably, in a calcination time of 1 to 3 hours. 12. Method according to any one of claims 1 to 11, characterized by the fact that, in step (d), the first alcohol is used as a reaction medium, preferably said first alcohol is used in molar excess with respect to the first carboxylic acid ester. 13. Method according to any one of claims 1 to 12, characterized by the fact that, in step (d), the catalyst is used in an amount between 0.01 to 20% by weight, preferably 0.1 to 10 % by weight, and most preferably from 0.5 to 5% by weight, based on the total weight of the substrate. 14. Method according to any one of claims 1 to 13, characterized by the fact that, in step (d), the alcohol and the catalyst are brought into contact in a first step and the substrate is then added in a second step. 15. Method according to any one of claims 1 to 14, characterized by the fact that step (d) is carried out at a temperature of at least 20°C, preferably at least 25°C and, most preferably, at a range between 30 and 80°C. 16. Method according to any one of claims 1 to 15, 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. Use of the method as defined in any one of claims 1 to 16, characterized by the fact that it is in the production of fuel or fuel components. 18. Transesterification catalyst, characterized in that it comprises surface-treated calcined calcium carbonate, wherein the surface-treated calcium carbonate is a reaction product of a material containing ground natural calcium carbonate (GNCC) or calcium carbonate precipitate (PCC) with carbon dioxide and one or more H3O+ ion donors and in which the carbon dioxide is formed IN SITU by treatment with H3O+ ion donors and/or is supplied by an external source. 19. Use of catalyst, characterized in that the catalyst comprises surface-treated calcined calcium carbonate, wherein the surface-treated calcium carbonate is a reaction product of a material containing ground natural calcium carbonate (GNCC) or carbonate of precipitated calcium (PCC) treated with carbon dioxide and one or more H3O+ ion donors and in which the carbon dioxide is formed IN SITU by treatment with H3O+ ion donors and/or is supplied by an external source, such as catalyst in a transesterification reaction.