Method for manufacturing (2,2-dimethyl-1,3-dioxolan-4-yl)methanol

Abstract

The present invention relates to a method for manufacturing solketal ((2,2-Dimethyl-1,3-dioxolan-4-yl)methanol) that comprises at least the following steps: (1) milling the following reagents, called starting reagents, comprising at least: glycerol, a catalyst selected from a hard Lewis acid comprising at least one transition metal, and acetone, the molar ratio (glycerol):(acetone) being less than or equal to 0.8; preferably less than or equal to 0.7, at an ambient temperature greater than or equal to 50°C, preferably greater than or equal to 56°C, in a three-dimensional microbead mill in a liquid phase for a residence time less than or equal to 15 minutes, preferably less than or equal to 10 minutes, and in particular less than or equal to 5 minutes; (2) recovering, as output from the mill, a final composition comprising solketal and, where appropriate, one or more sub-products corresponding to the starting reagents that have not reacted and / or to 1,3-O-isopropylidene-glycerol, and (3) optionally, separating the solketal from said one or more sub-products.

Description

[0001] Description

[0002] Process for manufacturing (2,2-Dimethyl-1,3-dioxolan-4-yl)methanol

[0003] Technical field of the invention

[0004] The present invention relates to a process for manufacturing (2,2-Dimethyl-1,3-dioxolan-4-yl)methanol, also known as solkétal.

[0005] In particular, the present invention relates to a process for manufacturing solkétal, carried out by micro-milling at a certain temperature, of a starting mixture comprising at least glycerol, acetone and a particular catalyst.

[0006] State of the art

[0007] Solkétal (2,2-Dimethyl-1,3-dioxolan-4-yl)methanol, also called 1,2-0-isopropylidene-glycerol, CAS No. 100-79-8) is a molecule comprising an isopropylidene group and a hydroxymethyl group corresponding to the Chem.1 formula below.

[0008] [Chem. 1]

[0009] Solkétal is a useful compound in many fields, for example in the pharmaceutical field as a synthetic intermediate, in the field of polymers as a solvent and plasticizer (Maksimov et al., “Preparation of High Octane Oxygenate Fuel Components from Plant Derived Polyols” Pet. Chem. 51, 61-69, (2011)). Solkétal has also shown interesting properties as a fuel additive by increasing the octane rating and reducing gum formation (Mota et al., “Glycerin derivatives as fuel additives: the addition of glycerol / acetoneketal (solkétal) in gasolines”, Energy Fuels 24, 2733-2736 (2010); Silva et al., “Glycerolacetals as anti-freezing additives for biodiesel”, BioresourTechnol. 101, 6225-6229 (2010) and Garcia et al., “New class of acetal derived from glycerin as a biodiesel fuel component”, Energy Fuels 22, 4274-80 (2008)).

[0010] Generally, solkétal is prepared by acetalization from glycerol and acetone or 2,2-dimethoxypropane in acidic medium (Chem.2 below).

[0011] [Chem. 2] The acid catalyst used to carry out the synthesis reaction is usually a homogeneous catalyst such as H2SO4 or HCl, but other acids can be used, such as Lewis acids or heterogeneous acid catalysts (Talebian-Kiakalaiehef et al., "A review on the catalytic acetalization of bio-renewableglycerol to fuel additives," Front. Chem. 6, 573, (2018)). Most often the reaction is carried out in a batch reactor, although some examples demonstrate the possibility of using a continuous reactor.

[0012] Various processes for manufacturing solkétal have been proposed in the prior art.

[0013] The publication by Torres et al., "Glycerolketals: synthesis and profits in biodiesel blends," Fuel 94, 614-616, (2012), describes in particular the reaction of glycerol (10.9 mmol) in excess acetone (106 mmol) in the presence of sulfuric acid (0.10 mmol) as a homogeneous acid catalyst at 35 °C for 1 hour. After evaporation of the acetone, a saturated solution of NaHCO3 and ethyl acetate are added, and the organic phase is evaporated to yield the solketal in 80% yield. However, the use of sulfuric acid as a catalyst necessitates a neutralization and extraction step. This extraction step leads to a significant loss of solketal in the aqueous phase (on the order of 20%).

[0014] The publication by Nanda et al., “Thermodynamic and kinetic studies of a catalytic process to convert glycerol into solketal as an oxygenated fuel additive”, Fuel 117, 470-477, (2014), describes reacting glycerol (197 mmol) and excess acetone (394 mmol) in the presence of Amberlyst (1 wt%) as a heterogeneous acid catalyst in ethanol (197 mmol) at 25°C for 3.7 hours. Under these conditions, the solketal is obtained with a yield of 74%. The use of an equimolar amount of ethanol allows for the solubilization of the glycerol and acetone.

[0015] The publication by Da Silva et al., “Solvent-free heteropolyacid-catalyzed glycerol ketalization at room temperature”, RSC. Adv. 5, 44499-44506, (2015), describes reacting glycerol (9.23 mmol) in the presence of the heteropolyacid H3PW12O40 (3 mol% H2O). +) as a homogeneous acid catalyst in acetone (185 mmol) as solvent at 25°C for 2 hours. This leads to the solkétal with a yield of 82% (conversion 83%, selectivity 98%).

[0016] Document WO 2009 / 141702 describes a process for manufacturing solketal obtained by continuous flow through the reaction of glycerol and acetone at a temperature ranging from 50 to 150°C. A small amount of acetone (5 to 20 mol%) is added to each cycle at 60°C. After several hours of continuous flow (from 2 to 8 hours, typically 3 to 6 hours), the solketal is obtained.

[0017] In this reaction, acetone is first protonated, which increases its electrophilicity. The lone pair of electrons on the primary hydroxyl group of nucleophilic glycerol attacks the carbon atom of activated acetone. After deprotonation of the primary hydroxyl group of glycerol and protonation of the quaternary hydroxyl group, the lone pair of electrons on the secondary hydroxyl group of nucleophilic glycerol attacks the carbon atom, releasing a water molecule. The final step is deprotonation, releasing the acid catalyst (see Chem. 3 below). [Chem. 3]

[0018] However, the acetalization of glycerol to solketal has some drawbacks, as it generally requires the use of a significant amount of homogeneous or heterogeneous acid (amount by mass greater than 0.004% relative to the total mass of the starting compounds) and a long reaction time exceeding one hour. The major obstacle to solketal production is the low equilibrium constant. To overcome this problem, using a high acetone-to-glycerol ratio or trapping the water formed increases solketal productivity by shifting the reaction equilibrium.

[0019] Thus, these prior art processes suffer from the fact that they either have an unsatisfactory yield, or that they require a high temperature and / or a very long reaction time (which can range, for example, from 2 to 8 hours).

[0020] The publication by Amin Talebian-Kiakalaieh et al., “A review on the catalytic acetalization of bio-renewable glycerol to fuel additives”, frontiers in chemistry, November 2018, lists the many methods of catalytic acetalization of glycerol, and in particular the reaction with acetone to prepare solketal.

[0021] Therefore, there is a need in the state of the art for new processes for manufacturing solkétal, preferably industrially exploitable, and which are alternative or improved compared to known processes.

[0022] The present invention therefore aims to provide a process for manufacturing solketal that avoids, at least in part, the aforementioned drawbacks. In particular, the present invention aims to provide a new industrially viable process for manufacturing solketal that does not require excessive heating and / or a long reaction time.

[0023] Presentation of the invention

[0024] To this end, the present invention proposes a process for manufacturing (2,2-dimethyl-1,3-dioxolan-4-yl)methanol (hereinafter referred to as solkétal) which comprises at least the following steps:

[0025] (1) the grinding of the following reagents, referred to as starting reagents, comprising at least: glycerol, a catalyst selected from a hard Lewis acid comprising at least one transition metal, and acetone, the molar ratio (glycerol):(acetone) being less than or equal to 0.8, preferably less than or equal to 0.7, at an ambient temperature greater than or equal to 50°C, preferably greater than or equal to 56°C, in a three-dimensional micro-bead mill for a residence time less than or equal to 15 minutes, preferably less than or equal to 10 minutes and in particular less than or equal to 5 minutes;

[0026] (2) the recovery at the outlet of the mill of a final composition comprising solkétal and, where applicable, one or more by-products corresponding to the unreacted starting reagent(s) and / or 1,3-O-isopropylidene-glycerol, and

[0027] (3) Optionally, the separation of the solketal from said by-product(s). The inventors have developed a process which, surprisingly and unexpectedly, allows the synthesis of solketal at a relatively low temperature (around 50°C-70°C), in a single grinding step, and in very short times (the residence time of the reagents in the mill is less than 15 minutes and is generally less than 5 minutes versus 2 to 8 hours for the process according to document WO 2009 / 141702).

[0028] As will be demonstrated in the experimental tests below, the process of the invention using a particular mill, namely a three-dimensional microbead mill, combined with particular reaction conditions (choice and molar concentration of starting reagents, reaction temperature, flow rate, etc.) makes it possible to produce solkétal with a yield generally greater than or equal to 80% and in particular greater than or equal to 99%.

[0029] The process according to the invention also has the advantages of a very low cost price (the raw materials used are widely available, non-polluting, and inexpensive) and excellent reproducibility, which further distinguishes it from processes described in the prior art. The process according to the invention also has the advantage of being able to be implemented continuously. These characteristics are important for industrial-scale application.

[0030] Furthermore, despite the numerous studies conducted on the synthesis of solkétal, none have suggested the aforementioned process and in particular a grinding step in a three-dimensional microbead mill from the starting reagents.

[0031] Other non-limiting and advantageous features of the solkétal manufacturing process according to the invention, taken individually or in all technically possible combinations, are as follows:

[0032] - the process includes a preliminary step (0) in which the starting reagents, including at least glycerol and acetone, and preferably also said catalyst, are premixed to form a starting composition;

[0033] - during the preliminary step (0), the starting composition is preheated to a temperature greater than or equal to 50°C, preferably greater than or equal to 56°C, so that the temperature during the grinding step (1) is greater than or equal to 50°C, preferably greater than or equal to 52°C and even more preferably around 56°C; - during the grinding step (1), the starting reagents and / or the starting composition is / are heated within the three-dimensional microbead mill which includes a heating device, preferably an induction heating device;

[0034] - the pressure during the grinding stage (1) ranges from 0.05 to 20 MPa, preferably from 0.08 to 0.5 MPa and is typically in the order of 0.1 MPa;

[0035] - the hard Lewis acid catalyst comprising at least one transition metal is chosen from FeC, AlC, CrC, MnSC^or one of their mixtures;

[0036] - the glycerol is anhydrous or has a water content, by mass, relative to the total mass of glycerol ranging from 0 to 10%, preferably from 0 to 5%;

[0037] - the microbeads are spherical in shape and have an average diameter ranging from 0.05 mm to 4 mm, preferably from 0.2 to 3 mm, in particular from 0.3 to 2 mm and typically in the range of 0.5 to 1 mm;

[0038] - the microbeads have a Vickers hardness measured according to EN ISO 6507-1 greater than or equal to 900 HV1, preferably ranging from 900 HV1 to 1600 HV1, typically ranging from 1000 to 1400 HV1;

[0039] - The microbeads have an actual density ranging from 2 to 15 g / cm³ 3 ;

[0040] - the grinding step (1) is carried out at an ambient temperature ranging from 50°C to 70°C, in particular from 55°C to 60°C and in general is around 56°C;

[0041] - in which the three-dimensional microbead mill comprises at least: a stationary grinding chamber of generally cylindrical shape extending along a longitudinal axis XX, said chamber being filled at least in part by said microbeads and comprising: at a first end at least an inlet for introducing said starting reagents, and at a second end, an outlet comprising a separation means suitable for evacuating only said final composition; an agitator, disposed in the stationary grinding chamber, in the form of a rod elongated along the longitudinal axis XX, said agitator being suitable for setting in motion the microbeads / said starting reagents assembly;

[0042] - in which the microbeads represent, by volume, in relation to the total volume of the stationary chamber, from 50% to 85%, preferably from 55% to 70%;

[0043] - in which the crusher operates continuously. For the remainder of the description, unless otherwise specified, the indication of a range of values ​​"from X to Y" or "between X and Y" in the present invention is understood to include the values ​​X and Y.

[0044] According to the invention, "one or more by-products" present in the final composition correspond(s) to the starting reactant(s) which did not react, such as the catalyst or glycerol (especially if the yield of the reaction is less than or equal to 99%) and, where applicable, to a co-product which may be formed during the reaction, which is Ie1,3-O-isopropylidene-glycerol.

[0045] Of course, the different features, variants and embodiments of the invention can be combined with each other in various ways as long as they are not incompatible or mutually exclusive.

[0046] Detailed description of the invention

[0047] The invention will be better understood and other objects, details, features and advantages thereof will become more apparent upon reading the following description of exemplary embodiments, with reference to the accompanying figures in which:

[0048] [Fig. 1] represents a cross-sectional view, along a cutting plane passing through the longitudinal axis XX, of a three-dimensional crusher according to a first embodiment of the invention comprising in particular an induction heating device;

[0049] [Fig. 2] represents, according to cross-sectional planes passing through the longitudinal axis XX and through the axis AA, different variants of embodiments of three-dimensional mills according to the invention, each comprising a heating device and at least one agitator possibly supporting another mixing element: (a) the agitator comprises several other mixing elements in accordance with the mill of Figure 1, (b) the agitator also comprises fingers adapted to cooperate with the other mixing elements and (c) the agitator does not comprise mixing elements and fingers;

[0050] [Fig. 3] represents a chromatogram corresponding to the synthesis of solketal from glycerol after a residence time of 1 minute (reaction time within the three-dimensional mill); and

[0051] Figure 4 shows a chromatogram corresponding to the synthesis of solketal from glycerol after a residence time of 2.37 minutes (reaction time within the three-dimensional mill). It should be noted that, in these figures, structural and / or functional elements common to the different variants may have the same reference numerals.

[0052] The inventors focused on developing a new solkétal manufacturing process suitable for implementation on an industrial scale in a very short time.

[0053] Thus, the present invention relates to a process for manufacturing (2,2-dimethyl-1,3-dioxolan-4-yl)methanol (hereinafter referred to as solkétal) which comprises at least the following steps:

[0054] (1) the grinding of the following reagents, referred to as starting reagents, comprising at least: glycerol and a catalyst selected from a hard Lewis acid comprising at least one transition metal (hereinafter referred to as "the catalyst"), with acetone, the molar ratio (glycerol): (acetone) being less than or equal to 0.8; preferably less than or equal to 0.7, at an ambient temperature greater than or equal to 50°C, preferably greater than or equal to 56°C, in a three-dimensional micro-bead mill for a residence time less than or equal to 15 minutes, preferably less than or equal to 10 minutes and in particular less than or equal to 5 minutes;

[0055] (2) the recovery at the outlet of the mill of a final composition comprising solkétal and, where applicable, one or more by-products corresponding to the unreacted starting reagent(s) and / or 1,3-O-isopropylidene-glycerol, and

[0056] (3) optionally, the separation of the solketal from said by-product(s).

[0057] Generally, the process includes a preliminary step (0) in which the starting reagents, including at least glycerol and acetone and preferably the catalyst, are premixed to form a starting composition.

[0058] In particular, the process according to the invention makes it possible to carry out the following synthesis (Chem 4):

[0059] [Chem. 4]

[0060] The "acid" compound here represents the catalyst according to the invention, namely a hard Lewis acid catalyst comprising at least one transition metal. A "hard Lewis acid" according to the invention is understood to be a Lewis acid whose electron-accepting center is weakly polarizable. The hardness criterion for an acid is notably defined in the Hard and Soft Acid and Base (HSAB) principle, which is known to those skilled in the art. Hard acids include, for example, iron(III), chromium(IV), aluminum(III), manganese(II), etc. Iron(II) and copper(II) are known to be intermediate metallic acids, and copper(I) is a soft acid.

[0061] Therefore, according to the process of the invention and unlike prior art processes such as the process of document WO 2009 / 141702, the equilibrium of the reaction is shifted towards the formation of solketal; there is no need to trap water or to use a large acetone-glycerol ratio to shift the equilibrium constant of the reaction and thus increase the productivity of solketal.

[0062] If the reaction is not complete and the solketal yield is greater than or equal to 80% (this depends in particular on the reaction parameters, such as the molar proportions of the starting reactants, for example acetone, and / or the temperature during the grinding step), 1,3-O-isoprolylidene-glycerol may also be formed as a by-product (Chem 5):

[0063] [Chem. 5]

[0064] To better understand the process which is the subject of the invention, a three-dimensional microbead mill capable of enabling the synthesis of solkétal, and thus forming part of the invention, will first be described below with reference to figures 1 and 2.

[0065] As illustrated in Figures 1 and 2, the three-dimensional crusher 100 comprises at least one stationary crushing chamber 1 having a wall 7 of generally cylindrical shape which encloses an interior 8.

[0066] Wall 7 extends along a longitudinal axis XX, advantageously horizontal.

[0067] This stationary grinding chamber 1 is configured to receive and mix at least the starting reagents, namely glycerol, acetone, and the catalyst, or, where applicable, the starting composition (a particular embodiment where the starting reagents are pre-mixed). This stationary grinding chamber 1 is partially filled with at least grinding media 6, such as microbeads 6, which will allow the grinding and mixing of the reagents in an intensive and efficient manner.

[0068] Stationary chamber 1 includes, at a first end 2 (upstream), an inlet 4 which opens into the stationary grinding chamber 1 and which is used to introduce the starting reagent(s) or the starting composition.

[0069] This inlet 4 can also be used to introduce the microbeads 6 before the implementation of the crusher 100. As will be seen below, the size and nature of the microbeads 6 can vary slightly.

[0070] The grinding chamber 100 includes, at a second end 3 (downstream), an outlet 5 which leads to the outside and which is configured to evacuate the final composition formed in the stationary grinding chamber 1.

[0071] Outlet 5 generally includes a means of separation (not shown), such as a sieve or a grid, adapted to evacuate only the final composition and to retain consequently the microbeads 6 when the grinder 100 is in operation.

[0072] In particular, inlet 4 is generally connected to at least one pump, for example a peristaltic pump (not shown). This pump or these pumps allow(s) the starting reagent(s) or the previously prepared starting composition to be brought into the stationary grinding chamber 1.

[0073] The starting reagents or the initial composition can, for example, be contained in a vessel, such as a tank. The pump also allows, during the operation of the three-dimensional mill 100, the delivery of the starting reagents or the initial composition at a specific, adjustable flow rate, hereafter referred to as the "flow rate." This flow rate also creates a current in the stationary chamber 1, which carries these starting reagents and / or this initial composition from the inlet 4 to the outlet 5.

[0074] The three-dimensional crusher 100 also includes an agitator 10 which has an elongated rod 11 along the longitudinal axis XX and which extends mainly around the first end 2 to beyond the second end 3 of the stationary chamber 1.

[0075] This elongated rod 11 extends advantageously coaxially to the aforementioned longitudinal axis XX. This agitator 10 is particularly capable of pivoting so as to set in motion, in addition to the aforementioned flow rate, the grinding body 6 and the starting reagents / initial composition.

[0076] In particular, the agitator 10 is configured to rotate about itself, along the longitudinal axis XX, via an elongated rod 11 (or rotating shaft), to impart a vortex motion to the initial mixture within the stationary chamber 1 and thus perform an intense mixing between this initial mixture and the microbeads 6 present in the chamber 1 along the internal surface of the wall 7 of this chamber 1.

[0077] In particular, the agitator 10 via its elongated rod 11 can have a rotation speed greater than or equal to 100 revolutions per minute, advantageously greater than or equal to 1000 revolutions per minute (rpm), preferably greater than or equal to 2000 revolutions per minute and typically greater than or equal to 2500 revolutions per minute.

[0078] For the purposes of the invention, "a rotational speed greater than or equal to 100" includes the following values: 100; 150; 200; 250; 300; 350; 400; 450;

[0079] 500; 550; 600; 650; 700; 750; 800; 850; 900; 950; 1000; 1100; 1200; 1300;

[0080] 1400; 1500; 1600; 1700; 1800; 1900; 2000; 2100; 2200; 2300; 2400; 2500;

[0081] 2600; 2700; 2800; 2900; 3000; 3100; 3200; 3300; 3400; 3500; 3600; 3700;

[0082] 3800; 3900; 4000, 4500; 5000; 5500; 6000; etc., or any intervals between these values.

[0083] In particular, the rotation speed of the agitator 10 is greater than or equal to 1500 rpm, advantageously greater than or equal to 1600 rpm, in particular greater than or equal to 1800 rpm and typically greater than or equal to 2400 rpm.

[0084] In general, the agitator 10 has a rotation speed ranging for example from 1500 rpm to 5000 rpm, in particular from 1550 rpm to 4500 rpm, preferably from 1600 rpm to 4000 rpm and typically from 2400 to 3200 rpm.

[0085] Preferably, the peripheral speed of the agitator is greater than or equal to 6 m / s, in particular greater than or equal to 8 m / s.

[0086] According to the invention, a peripheral speed of the agitator greater than or equal to 6 m / s includes the following values ​​or any interval between these values: 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20, etc.

[0087] In general, the peripheral speed of the agitator ranges from 7 m / s to 20 m / s, preferably from 8 m / s to 16 m / s. By "peripheral speed of the agitator", we mean the rotational speed multiplied by the circumference of the agitator disc.

[0088] The rotation speed will be adjusted by a person skilled in the art according to the three-dimensional crusher used (laboratory crusher or industrial crusher).

[0089] For example, a three-dimensional mill marketed by the company WAB (Willy A. Bachofen SARL) of type AP05 has an agitator with the following characteristics: for a frequency of 80 Hz, a speed of 4800 revolutions per minute and a peripheral speed of 16.0 m / s; while a mill of type AP2, for a frequency of 70.8 Hz, has a speed of 2730 revolutions per minute and a peripheral speed of 16.0 m / s. In order to improve this mixing, the agitator 10, as well as the internal surface of the inner wall 7 of the chamber 1, can have various possible configurations represented for example in Figure 2.

[0090] According to a first configuration illustrated in figure 2a, the agitator 10 includes, along its elongated stem 11, "rotating" mixing elements 22, 26, arranged perpendicularly to it.

[0091] As will be described later, a mixing element 22 (called "first mixing element") can also correspond to a susceptor of the heating means 20 according to the invention and is thus different from the other mixing elements 26 (called "other mixing elements").

[0092] This first mixing element 22, as well as the other mixing elements 26, can correspond to the mixing elements described in US document 5 597 126.

[0093] In particular, they may include at least two parallel circular discs, configured to set in motion the grinding bodies 6 (microbeads).

[0094] The number of these mixing elements 22, 26 within the grinding chamber 1 can vary from 2 to 8, preferably from 2 to 5.

[0095] These mixing elements 22, 26 allow, on the one hand, for improved grinding of the starting reagents and / or the starting composition by further stirring the microbeads 6 and, on the other hand, for accelerated reaction time.

[0096] According to a second configuration illustrated in Figure 2b, the agitator 10 can also include, along its stem 11, one or more "rotating" mixing elements 22, 26 which are further able to cooperate with "fixed" fingers 28, arranged perpendicularly to the internal wall 7 of the chamber 1.

[0097] A finger 28 notably takes the form of a ring which extends perpendicularly from wall 7.

[0098] For this configuration, the mixing elements 22, 26 and the fingers 28 are arranged in a staggered fashion, namely the mixing elements 22, 26 and the fingers 28 are arranged alternately in chamber 1.

[0099] The fingers 28 thus form counter-fingers, each arranged between two mixing organs 22, 26.

[0100] In addition, the thickness of the rod 11 is increased compared to the previous configuration (figure 2a) so that the periphery of the mixing members 22, 26 is close to the inner wall 7 and that of the fingers 28 is close to the periphery of the agitator rod 10.

[0101] Thus, in this configuration, the volume of the chamber is reduced compared to the previous configuration, consequently allowing better mixing between the starting reagents and / or the starting composition, the microbeads 6 and the internal wall 7 of chamber 1.

[0102] According to a third configuration, the volume of chamber 1 can be further reduced as illustrated in figure 2c.

[0103] According to this mode, the agitator 10 has an external diameter slightly smaller than the internal diameter of the chamber 1, thus forming a small-volume annular chamber 12 located between the external wall of the agitator 10 and the internal wall 7 of the chamber 1. The microbeads (not shown) are arranged in this annular chamber 12. During the operation of this third configuration, the starting reagents and / or the starting composition are introduced through the inlet 4 at a certain flow rate, which then travels through the annular chamber 12 to the outlet 5, while being stirred by the microbeads 6.

[0104] The geometry of the grinding chamber 1 and the agitator 10 can be adjusted by those skilled in the art according to the desired yield and reaction time. For example, the grinding chamber 1 may also include an accelerator to improve the grinding of the initial mixture. Since this accelerator is known to those skilled in the art, it will not be described in detail below. Generally, the stationary chamber has a diameter of 75 mm to 300 mm and a length of 80 mm to 900 mm, and the agitator 10 has a diameter of 65 mm to 260 mm. Thus, the volume of the grinding chamber can vary from 0.35 L to 600 L, preferably from 0.35 L to 400 L, and typically from 0.35 L to 62 L.

[0105] For the purposes of the invention, "a volume of the stationary chamber 1 ranging from 0.35 L to 600 L" includes the following values: 0.35; 0.5; 0.8; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 15; 20; 25; 30; 35; 40; 45; 50; 55; 60; 65; 70; 80; 85; 90; 100; 110; 120; 130; 140; 150; 160; 170; 180; 190; 200; 210; 220; 230; 240; 250; 260; 270; 280; 290; 300; 350; 400; 450; 500; 550; 600, or any intervals between these values.

[0106] Preferably, the microbeads 6 housed in the grinding chamber 3 of the mill 1 during its operation are substantially spherical in shape and have an average diameter less than or equal to 5 mm, generally ranging from 0.05 mm to 4 mm, preferably from 0.2 to 3 mm, in particular from 0.3 to 2 mm, and typically in the range of 0.5 to 1 mm. Preferably, the diameter of the microbeads is less than or equal to 1 mm and is typically in the range of 0.05 mm to 1 mm.

[0107] They are preferably chosen from microbeads with high hardness and relatively good resistance to abrasion.

[0108] In particular, microbeads 6 have a Vickers hardness measured according to EN ISO 6507-1 (2005) greater than or equal to 900 HV1, preferably ranging from 900 HV1 to 1600 HV1, typically ranging from 1000 to 1400 HV1 and especially ranging from 110 to 1300 HV1.

[0109] For the purposes of the invention, "a Vickers hardness greater than or equal to 900 HV1" includes the following values: 900; 910; 920; 930; 940; 950; 960; 970; 980; 990; 1000; 1010; 1020; 1030; 1040; 1050; 1060; 1070; 1080; 1090; 1000; 1110; 1120; 1130; 1140; 1150; 1160; 1170; 1180; 1190; 1200; 1300; 1400; 1500; 1600; 1700; etc., or any intervals between these values.

[0110] Advantageously, they exhibit a high actual density. In general, the microbeads according to the invention have an actual density greater than or equal to 2 g / cm³. 3 , in particular ranging from 2 to 15 g / cm² 3 , preferably from 3 to 12 g / cm³ 3 , and typically from 4 to 10 g / cm³ 3 .

[0111] Thus, the microbeads according to the invention can be ceramic microbeads (zirconium oxide ZrÜ2, zirconium silicate ZrSiC); steel microbeads, tungsten carbide microbeads, glass microbeads or one of their combinations.

[0112] Preferably, the microbeads are made of ceramic because they do not generate pollution through wear. In particular, the microbeads are made of zirconium oxide.

[0113] Optionally, zirconium oxide microbeads can be stabilized by another oxide, such as cerium oxide, yttrium oxide and / or silicon.

[0114] By way of example, the following compositions, summarized in Table 1 below, are suitable for forming the microbeads according to the invention: [Table 1]

[0115] Generally, the microbeads 6 suitable for the invention are not made of glass or exclusively of glass.

[0116] In particular, the microbeads 6 represent, by volume, in relation to the total volume of the stationary chamber 2, from 50% to 85%, preferably from 55% to 70%. For the purposes of the invention, "a volume of 50 to 85%" includes the following values: 50; 55; 60; 65; 70; 75; 80; 85; etc., or any intervals between these values.

[0117] The solketal synthesis reaction is carried out hot, i.e. at a temperature greater than or equal to 50°C, preferably greater than or equal to 52°C and ideally greater than or equal to 56°C in order to obtain a better yield.

[0118] Indeed, the boiling point of acetone is 56.05°C at atmospheric pressure. Therefore, advantageously, the reaction temperature within the mill is around 56°C.

[0119] According to a first embodiment, in order to obtain this temperature of at least 50°C and preferably 56°C, the starting reagents and / or the starting composition are preheated. Thus, it is not necessary to heat or have a heating device within or around the three-dimensional microbead mill.

[0120] For example, according to this embodiment, during the preliminary step (0), the starting composition is heated to a temperature greater than or equal to 50°C, preferably greater than or equal to 56°C, so that the temperature during the grinding step (1) is greater than or equal to 50°C, preferably greater than or equal to 56°C.

[0121] Indeed, since the residence time of the starting reagents or the starting composition within the mill is very short (generally less than or equal to 5 minutes, preferably less than or equal to 2 minutes), heating the starting reagents and / or the starting composition is sufficient.

[0122] However, this embodiment requires special attention, particularly when starting the reaction when the crusher is cold or when changing the flow rate.

[0123] According to a second embodiment, which can be combined with the first, a temperature of at least 50°C and ideally 56°C can be reached in the three-dimensional crusher.

[0124] For this purpose, during the grinding step (1), the starting reagents and / or the starting composition are heated within the three-dimensional micro-bead mill, which includes at least one heating device, preferably at least one induction heating device 20. This embodiment has the advantage of a more precise reaction temperature, regardless of the flow rate or temperature of the starting reagents / starting composition at the mill inlet (better heating of the flow forming the starting mixture). This embodiment is also particularly well-suited to an embodiment where several successive grindings are performed on the same mixture.

[0125] For example, and as shown in Fig. 1, the induction heating device(s) 20 are integrated inside the stationary grinding chamber 1 and allow heating of at least one area of ​​said stationary grinding chamber 1.

[0126] According to one feature of the invention, the induction heating device(s) 20 are located at the entrance of chamber 1, i.e. in the vicinity of the first end 2 so as to be able to heat the initial mixture flow (starting reactants / starting composition) as soon as it is introduced and to enable and / or activate consequently the chemical synthesis of the solketal.

[0127] According to a preferred embodiment of the invention, the induction heating device 20 is supported by at least a part of said agitator 10, enabling the induction heating device 20 to be set into rotation around the longitudinal axis XX.

[0128] Generally, the induction heating device 20 includes:

[0129] - at least one inductor 21, capable of generating a magnetic field, and

[0130] - at least one electrically conductive susceptor 22, which is coupled to said inductor 21 and which is capable of being heated by it 21.

[0131] In particular, the inductor 21 is a coil or solenoid having turns surrounding a part of said rod 11 of the agitator 10, advantageously an upstream section located on the side of the first end 2 as shown in Figure 1.

[0132] The inductor 21 is particularly capable of generating a magnetic field, which will allow the heating of the conductive materials in its environment, and in particular the susceptor 22 to which it is coupled. Indeed, the susceptor 22, which is electrically conductive, is capable of capturing the magnetic field emitted by the inductor.

[0133] The coil and susceptor assembly can be rotated by the rod 11.

[0134] The other mixing elements 26 which are different from the first mixing element 22, namely they are not necessarily electrically conductive, can in particular be made of chrome cast iron or zirconium oxide type ceramic.

[0135] Referring to Figure 1, this first mixing element 22 generally comprises a base attached to the rod 11 of the agitator 10. Preferably, the inductor 21 is implanted at the level of this base.

[0136] Generally, the induction heating device 20 is connected to an alternating current generator disposed outside said grinding chamber 1 by means of at least one current supply means 27 which is coaxial with the rod 11 of the agitator 10.

[0137] In particular, the generator can have a power output ranging from 5 to 15 kW, and preferably 10 kW, with a frequency ranging, for example, from 17 to 200 kHz. It includes a capacitor bank that can be connected in parallel or in series. For example, an ID Partner series generator, reference IX3600, model P08010, is suitable for constructing the crusher according to the invention.

[0138] In general, the stationary grinding chamber 1 incorporates a magnetic screen 23 disposed between said inductor 21 and said rod 11 of the agitator 10, so as to direct the heating towards the initial mixture.

[0139] Indeed, it is possible that the agitator 10 or its rod 11 is made of electrically conductive material and thus, in order to avoid any overheating of the agitator 10, it is preferable to protect the agitator 10 or at least the part of the rod 11 which is surrounded by the inductor 21.

[0140] This magnetic screen 23 also has the advantage of directing the magnetic field emitted by the coil 21 to the first mixing element 22 so that all the power is concentrated outside the inductor and in particular not directed towards the rod 11. Thus the heating area is restricted to the outer periphery of the rod 11 and particularly concentrated on the first mixing element 22.

[0141] Such a grinder incorporating a heating device is described in particular in application FR 18 54592.

[0142] As mentioned above, it is possible to combine the first and second embodiments. Thus, according to a third embodiment, a temperature of at least 50°C and ideally 56°C is achieved by combining preheating according to the first embodiment and internal heating of the mill according to the second embodiment. For example, the three-dimensional liquid-phase microbead mill suitable for carrying out the process according to the invention may correspond to mills marketed by companies such as WAB, Dyno-Mill range: Multi Lab, ECM and KD, NETZCH, or Alpine Hosokawa, for example, Agitated Media Mill AHM, or to these types of mills in which a heating device as described above has been integrated.

[0143] The manufacturing process according to the invention will now be described more explicitly below.

[0144] In particular, we will describe in more detail below the embodiment including the preliminary step (0) of preparing the starting composition, although this step is not limiting to the invention. Indeed, as already mentioned, the starting reagents can be introduced directly into the mill 100.

[0145] Thus, advantageously, the manufacture of solkétal according to the invention may include (0) a preliminary step of preparing the starting composition. Indeed, it is generally easier from a practical point of view to prepare the starting composition comprising the various starting reagents in the required proportions. Optionally, the catalyst according to the invention may be added subsequently in the three-dimensional mill 100.

[0146] Thus, glycerol is mixed with acetone in a molar ratio (glycerol:acetone) less than or equal to 0.8, preferably less than or equal to 0.7.

[0147] According to the invention, a molar ratio (glycerol:acetone) less than or equal to 0.8 includes the following ratios and all intervals between these values: 0.8; 0.7; 0.6; 0.5; 0.4; 0.3; 0.2; 0.1, etc.

[0148] In particular, the molar ratio is also greater than or equal to 0.1, preferably greater than or equal to 0.2 and typically greater than or equal to 0.3, such as for example in the order of 0.5.

[0149] Typically, the molar ratio (glycerol:acetone) is around 0.5. Unlike prior art processes, it is not necessary to have a large excess of acetone in order to carry out the synthesis of solkétal according to the invention.

[0150] The starting composition is conventionally prepared by mixing the starting reagents, namely at least acetone and glycerol, and preferably the catalyst, in a suitable device, such as a container or tank, equipped with a stirring system (such as a magnetic stirrer, stirring paddles, etc.). The device and the stirring system can be adapted by a person skilled in the art according to the quantity of solketal to be produced.

[0151] As indicated above, glycerol and acetone are mixed to carry out the following reaction:

[0152] [Chem. 4]

[0153] It is well known that the viscosity of glycerol decreases very rapidly with temperature, but also with water content. Therefore, preferably, the glycerol used in the process of the invention is anhydrous or has a water content, by mass, relative to the total mass of glycerol, ranging from 0 to 10%, preferably ranging from 0 to 5%.

[0154] According to the invention, glycerol comprising a quantity of water from 0 to 10% includes the following values ​​or any intervals between these values: 0; 1; 2; 3; 4; 5; 6; 7; 8; 9 or even 10%.

[0155] The viscosity of glycerol can, according to techniques known to those skilled in the art, such as using a vibrating blade viscometer, be measured before carrying out the process according to the invention and in particular the grinding step (1).

[0156] The glycerol suitable for the present invention is in liquid form. Glycerol with CAS number 56-81-5, sold for example by Mon-droguiste.com, with a purity of 99.5% or higher, is suitable for carrying out the process of the invention.

[0157] The acetone suitable for the present invention is in liquid form. Acetone with CAS number 67-64-1, marketed for example by Mon-droguiste.com, with a purity of 99.5% or higher, is suitable for carrying out the process of the invention.

[0158] Preferably, acetone and glycerol have a high purity, generally greater than or equal to 90%, particularly greater than or equal to 95% and typically greater than or equal to 99%, or even greater than or equal to 99.9%.

[0159] The catalyst suitable for the process according to the invention is selected from a hard Lewis acid (doublet acceptor) comprising at least one transition metal. In particular, the transition metal is selected from iron, aluminum, manganese, or chromium. By way of example, the catalyst according to the invention may be selected from: FeCb such as FeCl3.6H2O, AlC, CrCb, MnSC, or a mixture thereof.

[0160] The catalyst represents, by mass, relative to the total mass of the starting composition composed of acetone, glycerol and catalyst, from 0.02% to 1%, preferably from 0.03% to 0.08% and typically from 0.03% to 0.05%, such as 0.044%.

[0161] Once the starting composition is prepared, it is brought to the three-dimensional micro-bead mill 100, usually via the adjustable-flow peristaltic pump through inlet 4. The peristaltic pump allows the starting composition to continue mixing before entering stationary chamber 1. In addition, as previously indicated, this pump allows the starting composition to be introduced into chamber 1 with a controlled flow rate.

[0162] Generally, the starting composition is introduced at a flow rate of 5 to 130 L / h, preferably 10 to 100 L / h and typically 10 to 90 L / h.

[0163] According to the invention, a "flow rate from 5 to 130 L / h" includes the following values ​​and all intervals between these values: 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 35; 40; 45; 50; 55; 60; 65; 70; 75; 80; 85; 90; 95; 100; 105; 110; 115; 120; 125; 130.

[0164] Once the starting composition is introduced into chamber 1, the grinding step (1) begins.

[0165] Under the effect of the current created by the flow rate, the starting composition travels through the stationary chamber 1 from the inlet 4 to the outlet 5, while being set in motion by the agitator 10 which allows intense mixing of this composition with the microbeads and, where applicable, with the discs 22; 26, the fingers 28, etc., along the inner wall of the chamber 1.

[0166] The rotation speed of the agitator can, for example, vary from 10 to 150 Pi rad / s, preferably from 40 to 100 and in particular from 60 to 70 Pi rad / s and is in particular at least 60 Pi rad / s as well as 63 Pi rad / s.

[0167] According to the invention, a rotational speed ranging from 10 to 150 Pi rad / s includes the following values ​​and all intervals between these values: 10; 20; 30; 40; 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100; 110; 120; 130; 140; 150. The departure suspension time is less than or equal to 15 min.

[0168] According to the invention, a residence time of less than or equal to 15 minutes includes the following values ​​and all intervals between these values: 15 min; 10 min; 11 min; 10 min; 9 min; 8 min; 7 min; 6 min; 5 min; 4 min; 3 min; 2 min; 1 min; 55 sec; 50 sec; 45 sec; 40 sec; 35 sec; 30 sec; 25 sec; 20 sec; 15 sec; 10 sec; 5 sec, etc.

[0169] Preferably, the residence time in the grinder is less than or equal to 10 minutes, and in particular ranges from 30 seconds to 8 minutes and especially from 50 seconds to 5 minutes.

[0170] It is indeed inherent to the apparent volume of the balls and the flow rate. For example, if the total apparent volume of the balls is 270 cm³ 3 (beads with an apparent density of 3.7 g / cm³) 3 and that the suspension introduction flow rate is 45 L / h, or 12.45 cm 3 / s, then the residence time of the suspension in chamber 1 is estimated to be approximately 22 seconds. Therefore, the residence time can be advantageously adjusted, for example by controlling the apparent density of the microbeads, as well as the flow rate.

[0171] The term "apparent volume" refers to the volume of the microbeads, including the interstitial air between them. Apparent density is the ratio of the mass of the microbeads to the apparent volume.

[0172] Preferably, the apparent volume of the microbeads ranges from 250 mL to 450 mL, preferably from 300 mL to 400 mL, and is typically from 330 mL to 360 mL. This apparent volume of the microbeads is suitable, for example, for a three-dimensional mill comprising a stationary chamber 1 of 500 mL.

[0173] Furthermore, by playing with the size of the microbeads and the flow rate, the synthesis of solketal can be improved.

[0174] Preferably, the pressure during the grinding step (1) ranges from 0.05 to 20 MPa, preferably from 0.08 to 0.5 MPa and is typically in the order of 0.1 MPa.

[0175] The grinding stage can be carried out continuously or discontinuously in one or more passes (pendulum or recirculating mode). When carried out discontinuously, the number of passes of the initial composition can be from 1 to 10, preferably from 1 to 5 (i.e., after a first pass, the final composition is recovered at outlet 6 and reintroduced, by means of the pump, into chamber 1 via inlet 4 to allow a second pass). In particular, the number of passes of the initial suspension is 1.

[0176] Indeed, the inventors noticed that a single pass through the micro-bead mill, despite a very short residence time, made it possible to obtain at the output 5 a final composition consisting mainly of solkétal.

[0177] Therefore, this grinding step is preferably carried out in continuous mode.

[0178] Advantageously, this grinding stage takes place at a temperature greater than or equal to 50°C, namely most often at a temperature greater than or equal to 56°C, which is the synthesis temperature of solketal, in order to obtain a better yield.

[0179] Once the grinding step has been completed, (1) the final composition is recovered at the outlet 5 of the mill 100. This final composition may include traces of the starting reagents which have not reacted, such as for example the catalyst or even a by-product, 1,3-O-isopropylidene-glycerol if the reaction temperature or the concentrations of the starting reagents were not in the ideal reaction ranges.

[0180] The process according to the invention makes it possible to obtain a solketal yield greater than or equal to 80%, preferably greater than or equal to 85% and in particular greater than or equal to 90%.

[0181] In general, the process according to the invention makes it possible to obtain a solketal yield greater than or equal to 99% (optimized experimental conditions).

[0182] As is known, solketal can be separated from the reaction mixture (from the initial reactions and / or the initial composition, or even from any other by-products formed) by methods well known to those skilled in the art. These methods may include, for example, extraction, evaporation of the solvent (acetone), or distillation.

[0183] Solketal can also be purified, if necessary, using techniques well known to those skilled in the art, such as distillation, silica gel column chromatography, or high-performance liquid chromatography (HPLC). EXAMPLES

[0184] The description of the tests below is given as a purely illustrative and non-limiting example.

[0185] Raw materials For the tests, the starting raw materials are:

[0186] Glycerol (Fluorochem, Hadfield, UK) Batch FCB019493 FeCl3.6H2O (Fluorochem, Hadfield, UK) Batch FCB048596 Acetone >99% (Sigma-Aldrich, Steinheim, Germany), Batch #STBJ2303 Mill according to the invention The tests were carried out in a three-dimensional micro-bead mill

[0187] Dynomill ECM AP-05 from Willy A. Bachofen AG (WAB), which contains 1.235kg of microbeads, and which has been adapted to include a heating device 20 according to the invention as shown in Figure 1. Namely, the mill includes a heating device positioned at the entrance of the stationary chamber, and the first mixing element acts as a susceptor (patent FR18 54592).

[0188] In particular, the heating device has the following characteristics: [Table 2]

[0189] The microbeads are made of zirconium oxide and have a diameter of 0.5 mm. The characteristics of the microbeads used for the tests are summarized in Table 3 below:

[0190] [Table 3]

[0191] The 0.5mm microbeads are notably marketed under the brand name Zirmil® Y Ceramic Beads by the company Saint-Gobain.

[0192] The grinding chamber of the mill has a capacity of 514 mL and is filled, in volume, relative to its total volume and depending on the tests, with 167 or 334 mL of the microbeads described above.

[0193] During operation, the microbeads are agitated by an agitator at a rotational speed that can vary from 6 to 8 m / s, depending on the example. The agitator also includes chrome-plated cast iron mixing discs.

[0194] General implementation procedure according to the invention (3 ème method of implementation)

[0195] Preparation of the starting composition with preheating:

[0196] A mixture of glycerol (425.0 g, 4.62 mol), catalyst, and acetone (5.54 mol, 6.93 mol, 9.24 mol, or 13.86 mol) is stirred magnetically and vigorously at 25°C, 40°C, or 56°C in a 1-liter, three-necked, round-bottom flask equipped with a condenser (experimental conditions are shown in Table 4). In particular, the starting composition of Example 10 in Table 4 is preheated to 40°C and that of Example 14 to 25°C, while the compositions of the other examples are preheated to 56°C.

[0197] Introduction to the three-dimensional crusher:

[0198] The reaction medium is pumped using a peristaltic pump at a flow rate of 14 L / h or 42 L / h, and the flow is introduced into the Dynomill ECM AP-05 three-dimensional mill described above, which may or may not be preheated depending on the example. Specifically, the heating device 20 is not activated for example 14, or is used to heat the mixture to a temperature of 40°C for example 10, and to a temperature of 56°C for the other examples in Table 4.

[0199] After a certain period of residence in the grinder, the reaction medium is analyzed as described below.

[0200] Sample analysis

[0201] The analysis of the molecules resulting from the reaction was carried out by gas chromatography with a Hewlett Packard brand chromatograph (14009 Arcade, New York, United States). The system consists of a manual injection system equipped with a septum (SPI), a Supelco 2-8047-U capillary column (15m x 0.25mm id and 0.25 pm film thicknesses, Alltech Part No. 31163-01), a furnace, a flame ionization detector (FID, 70 eV, 300 mA, and 250 °C) and a data acquisition system.

[0202] Sample preparation

[0203] For each sample, the reaction medium (50 pL) and an n-decane-acetone solution (0.009 M in acetone) are mixed.

[0204] Calibration

[0205] Calibration is performed by injecting several solutions containing solketal at varying concentrations (3.65 x 10 4 M - 4.5625x10 5M) and the n-decane solution (0.009 M in acetone) - acetone at a fixed concentration.

[0206] Solketal (50 pL) and an n-decane-acetone solution (1:1, v / v) are mixed, resulting in a solketal concentration of 3.65 x 10⁻³ 4 M and an n-decane concentration of 0.009 M. A fraction of this mixture (50 pL) is diluted with an n-decane-acetone solution (50 pL, 1:1, v / v) and represents a solkétal concentration of 1.825 x 10 4 M and an n-decane concentration of 0.009 M. A fraction of this mixture (50 pL) is diluted with an n-decane-acetone solution (50 pL, 1:1, v / v) and represents a solkétal concentration of 9.125 x 10 5 M and an n-decane concentration of 0.009 M. A fraction of this mixture (50 mIU) is diluted with an n-decane-acetone solution (50 mIU, 1:1, v / v) and represents a solkétal concentration of 4.5625 x 10⁻³ 5 M and an n-decane concentration of 0.009 M. Sample analysis

[0207] The carrier gas used is hydrogen at a flow rate of 1 mL / min 1 The samples (2 µL) are manually injected using a septum injector (SPI). The injector temperature is set to 250°C with a furnace temperature of 70°C for 1 min and a temperature ramp rate of 20°C / min. _1 up to a temperature of 250 °C for 10 min.

[0208] The qualitative analysis of the compounds was performed by comparing their retention times with pure standards (acetone, n-decane, solketal, glycerol). The retention time of acetone was 0.417 min, and the retention times of n-decane, solketal, and glycerol were 1.33 min, 2.36 min, and 3.61 min, respectively. The qualitative analysis of the compounds was based on the calibration curve.

[0209] reaction conditions used and results

[0210] [Table 4]

[0211]

[0212] * The agitator's agitation speed here corresponds to its peripheral speed (linear speed in m / s). For the AP05 type mill, with an agitator diameter of 6.5 cm, a peripheral speed of 8 m / s corresponds to 2400 rpm. The peripheral speed is calculated by multiplying the rotational speed by the circumference of the agitator disc. As mentioned above, the optimal agitation speed will depend on the type of mill used (laboratory mill, as in these examples, or industrial mill).

[0213] As can be seen, the process according to the invention makes it possible to obtain very high yields depending in particular on the experimental conditions (non-arbitrary choice of catalyst, advantageously temperature of 56°C, volume of microbeads, concentration of acetone, etc.).

[0214] Example 13 shows, for example, that a residence time of less than 2 min (1.85 min) with a flow rate of 42 L / h does not allow for a solkétal yield of 99% (but 68%), whereas example 2 shows that a residence time of 1.8 min with a flow rate of 14 L / h and a larger quantity of acetone (13.86 mol versus 9.24 mol for example 11) allows for a yield of 99%.

[0215] In general, the inventors have found that the longer the residence time within the stationary chamber of the crusher, the better the yield.

[0216] It also appears that the choice of catalyst is important and that a Lewis hard acid catalyst comprising at least one transition metal such as FeC, AlC, CrC, MnSC or one of their mixtures makes it possible to obtain very good yields, unlike the other catalysts tested.

[0217] Also, Figures 3 and 4, corresponding to Example 3, show that after a residence time of 1 minute (Figure 3), the process according to the invention allows the synthesis of solketal (retention time of 2.356 minutes), but that glycerol also remains in the final composition (retention time of 3.607 minutes); whereas with a residence time of 2.37 minutes (Figure 4), the peak corresponding to glycerol is no longer observed. Thus, the reaction is complete and has yielded solketal.

[0218] Naturally, the process parameters (concentration of starting reagents, flow rate, etc.) can be optimized to achieve continuous solketal synthesis, i.e., in a single pass. For example, using a lower flow rate increases the residence time of the starting reagents / initial composition in the grinding chamber, thus increasing the solketal yield in a single pass.

Claims

A method for preparing solketal ((2,2‑dimethyl-1,3-dioxolan-4-yl)methanol) comprising at least one of the following steps:(1) milling the following reactants, referred to as initial reactants, comprising at least: glycerol, a catalyst selected from a hard Lewis acid containing at least one transition metal, and acetone, the glycerol:acetone molar ratio being less than or equal to 0.8, at an ambient temperature greater than or equal to 50 °C, in a three-dimensional mill with microbeads in liquid phase for a residence time of less than or equal to 15 minutes,(2) collecting, at the outlet of the mill, a final composition comprising the solketal and, where applicable, one or more by-products corresponding to one or more of the following compound(s): unreacted initial reactant(s), 1,3‑O‑isopropylideneglycerol and mixture threof.The method of preparation according to claim 1, characterized in that it comprises the following step (3) of separating the solketal from said by-product(s).The method of preparation according to Claim 1 or 2, wherein the temperature during the milling step (1) is greater than or equal to 56 °C.The method of preparation according to Claim 1 or 2, wherein the residence time during the milling step (1) is less than or equal to 10 minutes.The method of preparation according to Claim 4, wherein the residence time during the milling step (1) is less than or equal to 5 minutes.The method of preparation according to claim 1 or 2, comprising a preliminary step (0) wherein the initial reactants, including at least glycerol and acetone are premixed to form an initial compositionThe method of preparation according to Claim 6, wherein, during the preliminary step (0), the initial composition is preheated to a temperature greater than or equal to 50 °C so that the temperature during the milling step (1) is greater than or equal to 50 °C.The method of preparation according to Claim 7, wherein, during the preliminary step (0), the initial composition is preheated to a temperature greater than or equal to 56 °C, so that the temperature during the milling step (1) is greater than or equal to 56 °CThe method of preparation according to claim 1 or 2, wherein, during the milling step (1), the initial reactants are heated inside the three-dimensional mill with microbeads, which includes a heating deviceThe method of preparation according to claim 9, wherein said heating device is an induction heating deviceThe method of preparation according to claim 1 or 2, wherein the pressure during the milling step (1) is within a range from 0.05 to 20 MPa.The method of preparation according to claim 1 or 2, wherein the hard Lewis acid catalyst containing at least one transition metal is chosen from: FeCl3, AlCl3, CrCl3, MnSO4 or a mixture thereof.The method of preparation according to claim 1 or 2, wherein the glycerol is anhydrous or has a water content by mass, relative to the total mass of the glycerol, within a range from 0 to 10%The method of preparation according to claim 1 or 2, wherein the microbeads are spherical in shape and have an average diameter within a range from 0.05 mm to 4 mm.The method of preparation according to claim 14, wherein the microbeads are spherical in shape and have an average diameter within a range from 0.2 to 3 mmThe method of preparation according to claim 1 or 2, wherein the microbeads have a Vickers hardness, measured in accordance with standard EN ISO 6507-1, greater than or equal to 900 HV1.The method of preparation according to claim 1 or 2, wherein the microbeads have real volumic mass within a range from 2 to 15 g / cm3.The method of preparation according to claim 1 or 2, wherein the three-dimensional mill with microbeads comprises at least:- a stationary mill chamber generally cylindrical in shape, extending along a longitudinal axis XX, said chamber being filled, at least in part, with said microbeads and comprising: at one end at least one inlet used to introduce said initial reactants and, at the other end, an outlet comprising a separation means capable of discharging only said final composition formed in said chamber; and- an agitator arranged in the stationary mill chamber and taking the form of a rod extending along the longitudinal axis XX, said agitator being capable of setting in motion the totality of the microbeads / initial reactants.The method of preparation according to Claim 18, wherein the microbeads constitute by volume 50% to 85%of the total volume of the stationary chamberThe method of preparation according to Claim 19, wherein the microbeads constitute by volume 55% to 70%, of the total volume of the stationary chamberThe method of preparation according to claim 1 or 2, wherein the mill operates continuously.

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