FR2763939A1 - Method of obtaining cuts of methyl esters of long chain fatty acids - Google Patents

Abstract

Procedure for obtaining a cut of methyl esters of 11-20 C fatty acids (esterols) having a cloud point of <= 5 deg C comprises contacting the liquid esterol mixture, adjusted to a temperature slightly above its initial cloud temperature, with a cold surface which has first been adjusted to a temperature just below the melting point of the esterol and then held at a temperature of several degrees below the melting temperature of the esterol for a period sufficient to deposit a crystalline phase representing about 5 % of the initial weight of the esterol mixture onto the cold surface.

Description

 The present invention relates to the purification of heavy methyl ester slices from thermal cracking of the methanolysis product of castor oil.

Esterols are produced industrially as mixtures of methyl esters of C11-C20 acids, the following table giving an overview of the average composition:

<tb> II <SEP> I <SEP> n
<tb><SEP> Compounds <SEP>% <SEP> mass
<tb><SEP> ricinoleate <SEP> of <SEP> methyl <SEP><<SEP> 5
<tb><SEP> linoleate <SEP> of <SEP> methyl <SEP> 30 <SEP> - <SEP> 35
<tb><SEP> oleate <SEP> of <SEP> methyl <SEP> 20 <SEP> - <SEP> 35
<tb><SEP> stearate <SEP> of <SEP> methyl <SEP><10<SEP> (5 <SEP> - <SEP>?) <SEP>
<tb><SEP> palmitate <SEP> of <SEP> methyl <SEP><10<SEP> (5 <SEP> - <SEP>?) <SEP>
<tb><SEP> dihydroxystearate <SEP> of <SEP> methyl <SEP> traces
<tb><SEP> arachidate <SEP> of <SEP> methyl <SEP><10
<tb><SEP> linolenate <SEP> of <SEP> methyl <SEP><5
<tb><SEP> undecanoate <SEP> of <SEP> methyl <SEP><5
<tb> whose valuation depends on their cloud point. The cloud point of direct ester sterols is around 11 ° C. It is certainly possible to lower this cloud point by adding diesel additives, the effect obtained is very limited (lowering of two or three degrees) and the Fixed trouble points are still too high to prevent any incidents of bulk storage of these products.

 Fractionation of fat by crystallization is a known technique and used for their purification, in particular crystallization in a molten medium, that is to say without solvent. It is a process whose advantages are known, a reduced energy cost and the simplicity of its implementation, but also the disadvantages, a lack of selectivity and the difficulty of access to very pure crystalline fractions. But the problem to solve is not here obtaining pure species from an esterol, but obtaining what remains a cup, with an improved cloud point. What has been found is that the cloud point of esterol was strongly affected by the presence of saturated esters, such as palmitate and methyl stearate, species whose respective melting points are 63 and 70 ° C. It was found, and this is the basis of the invention, that the separation of a small portion of these compounds was sufficient to cause a very significant lowering of the cloud point.

 The invention is thus a process for obtaining, without resorting to the addition of additives, a cloud point esterol which is equal to or lower than 6 ° C., which method consists in applying to the esterol a crystallization in a molten medium. in order to remove about 5% of the total mass by crystallization, there is always a possibility of lowering the cloud point of the esterol thus obtained by one to two degrees by adding from 100 to 1,000 ppm of a commercial gasoil point lowering additive.

 In order to carry out the process according to the invention, the liquid esterol, taken at a temperature slightly above its cloud temperature, is brought into contact with, in practice, a temperature of between 12 ° C. and 40 ° C., with a cold wall. first brought to a temperature much lower than the melting temperature of the esterol, in practice between -10 "to +10 C. It is the nucleation phase, during which the crystallization of the heavy parts of the esterol, which lasts only fifteen minutes. After which, the temperature of the cold wall rose a few degrees below the melting temperature of the esterol and maintained at this temperature throughout the duration of the crystallization. At the end of the operation, the remaining liquid phase is withdrawn and the crystallized portion recovered by melting.

 This contacting can be carried out either by static crystallization, during which the crystallized portion is deposited on a cold wall immersed in molten esterol, or by dynamic crystallization, during which the molten sterol circulates by gravity on a cold wall which retains the crystallized fraction.

 The following nonlimiting examples will make the invention better understood.

 Example 1: Purification of an esterol by static crystallization

 The equipment (see FIG. 1) consists of a jacketed reactor (1), with its inlet and outlet (2) of thermostatic fluid and provided with temperature control probes (3) made of glass or stainless steel. It is provided with a central tube with a double jacket (4) cooled by the circulation (5) of a coolant (for example Gilotherm DR oil) and which constitutes the cold wall on which the crystallized fraction is deposited. At its base, an evacuation device (6) for recovering molten products.

 A reactor is filled with an esterol, whose cloud point is 11 ° C., and its temperature is set at 120 ° C. It then constitutes the molten medium (7). The central tube is cooled (wall temperature to +4 ° C) until the first crystals (8) appear, then the temperature of the cold wall is raised to + 6 ° C, and the system is maintained. the state until 5% of the mass of the esterol is crystallized. The cold wall is then supercooled and the 95% of the mass which remains liquid is quickly emptied, the supercooling being intended to prevent any separation of the crystallized part at the time of emptying.

 A liquid esterol with a cloud point measured at 6 ° C. is thus obtained.

 The crystallized part is separated by melting of its support, possibly used as stearin, more generally incinerated.

Example: Purification of an esterol by dynamic semi-continuous crystallization
The purification device (see FIG. 2) consists here of the reactor of example 1, furthermore equipped with a feed system (9) comprising a pump and a dispensing head by which the esterol is previously melted and maintained. Liquid at 12 ° C melted is directed to the top of the cooled tube and flows along its wall.The temperature of the cane is at the beginning of the operation brought to -2 C to start nucleation, then set to 6 "C until the end of the diet.

 The tube is covered with crystallized estérol, while the liquid part flows at the foot of the cooling rod and is directly withdrawn as a finished product by the bung (6). This liquid part is an esterol whose cloud point is 5-60C.

 It is obviously possible to repeat the operation on the recovered esterol to further lower the cloud point.

Claims (3)

 1. Process for obtaining methyl ester fractions of C1 fatty acids C20 (esterols) with a lower cloud point or at most equal to 5 ° C., characterized in that the liquid esterol, taken at a temperature slightly above its initial cloud temperature, is brought into contact with a cold wall firstly brought to a temperature much lower than the melting temperature of the esterol, and then kept at a temperature a few degrees lower than the melting temperature of the esterol for a time sufficient for it to deposit on this cold wall a crystallized phase representing approximately 5% of the initial mass of the esterol.  2. Method according to claim 1, characterized in that the crystallized phase is deposited on a cold wall immersed in the molten esterol.  3. Method according to claim 1, characterized in that the molten sterol flows by gravity on a cold wall which retains the crystallized phase.