EP2616419A1

EP2616419A1 - Process for purifying crude glycerol

Info

Publication number: EP2616419A1
Application number: EP11754390.0A
Authority: EP
Inventors: Sergio Mastroianni
Original assignee: Rhodia Operations SAS
Current assignee: Rhodia Operations SAS
Priority date: 2010-09-15
Filing date: 2011-09-07
Publication date: 2013-07-24
Also published as: FR2964657B1; BR112013005946A2; CN103097327A; US20130165699A1; FR2964657A1; WO2012034904A1

Abstract

The present invention relates to a process for purifying crude glycerol obtained from raw materials such as the glycerol obtained during the manufacture of biodiesel or the glycerol obtained during conversions of fats or oils. The invention aims in particular to dissolve the glycerol in an organic solvent and to form an insoluble phase comprising the salts of the crude glycerol.

Description

PROCESS FOR PURIFYING RAW GLYCEROL

The present invention relates to a process for purifying crude glycerol obtained from raw materials such as glycerol obtained during the manufacture of biodiesel or glycerol obtained during transformations of fats or oils. The invention aims in particular to dissolve glycerol in an organic solvent and form an insoluble phase comprising the salts of crude glycerol.

PRIOR ART

Glycerol, 1,2,3-propanetriol, is present in combination form in vegetable and animal oils and fats. It is especially present in the form of triglycerides combined with fatty acids such as stearic, oleic, palmitic and lauric acids. The most common industrial process for obtaining glycerol from vegetable and animal oils and fats involves saponification reactions, high pressure hydrolysis and transesterification with alcohols, such as ethanol or methanol.

Glycerol is also a by-product of biodiesel which is generally obtained by the transesterification of glycerides with short chain alcohols, for example methanol or ethanol. The transesterification reaction is catalyzed by an acid or a base, depending on the characteristics of the oils and / or greases used. After the transesterification reaction, the resulting esters are separated from excess reactants, catalyst and by-products by a two-step process. First, the glycerol is separated by decantation or centrifugation, then the soaps, the catalyst and alcohol residues are removed by washing with water and bubbling or using magnesium silicate with filtration. The significant production of biodiesel as an alternative to fossil fuels is accompanied by a high production of by-product glycerol. According to the manufacturing processes, the crude glycerol obtained comprises impurities which involve numerous and complex treatment steps. For this purpose, it is particularly known to purify the crude glycerol by distillation, operating under particular conditions so as not to alter the glycerol which decomposes at temperatures of 170-180 ° C. and which can polymerize and generate impurities. Such a purification process is therefore not interesting at the industrial level.

There are thus a number of complex techniques that have been developed in the past to purify glycerol while avoiding decompositions or other unwanted reactions. For example, US Pat. No. 4,655,879 describes a very laborious crude glycerol purification process which involves a large number of steps in which the crude glycerol is first alkalinized in the presence of air for oxidation, and then distilled at high temperatures under reduced pressure. Since the glycerol obtained has an undesired color, it is also necessary to carry out additional treatment with activated charcoal.

US Patent 4,990,695 describes the purification of crude glycerol with a combination of operations such as pH adjustment in a range of 9 to 12, heating the medium to 100 ° C, microfiltration and then ultrafiltration. The glycerol obtained is then distilled, optionally after treatment with ion exchange compounds.

The prior art also knows other complex methods such as electro-deionization, phosphoric acid treatment or sulfuric acid which require several constraining steps of separation.

It is thus sought the development of a simple and industrial process for the purification of glycerol from crude glycerol which is inexpensive and in usual conditions of temperature and pressure; to obtain purified glycerol having a suitable quality for a number of applications, while avoiding the disadvantages mentioned above. INVENTION

It has now been demonstrated that it was possible to purify crude glycerol by a process that is simple to implement, effective and that, moreover, does not alter glycerol or its color. This process consists in adding to the crude glycerol an amount of organic solvent which will dissolve the glycerol and thus form an insoluble phase consisting of a heterogeneous mixture of salts and some organic compounds. This insoluble phase will then be separated from the liquid medium and finally the solvent will be separated from the purified glycerol. Such a method has many advantages. Indeed, this process allows excellent purification and separation of glycerol regardless of the type of crude glycerol used. In particular, a purity greater than 95%, preferably greater than 97%, of glycerol containing very small amounts of residual salts is obtained; and the solvent used can be perfectly recycled.

The present invention thus relates to a crude glycerol purification process comprising at least the following steps:

(a) in the presence of crude glycerol and at least one organic solvent comprising from 1 to 10 carbon atoms and comprising at least one ketone, aldehyde, alcohol, acetal and / or ketal function, so as to form a liquid phase comprising glycerol dissolved in the solvent (s) and also forming an insoluble phase;

(b) separating the insoluble phase and the liquid phase;

(c) separating the solvent and glycerol from the liquid phase; and

(d) recovery of glycerol. The insoluble phase is generally a heterogeneous dispersed phase in the majority phase and is in the form of a precipitate. The process of the invention can be carried out continuously or discontinuously. The steps mentioned can be performed successively and one after the other or not. Each of the steps of the process can be carried out continuously or discontinuously. Preferably, the method according to the invention is implemented by the strict succession of steps a), b), c) and d) without performing an intermediate or additional step. In particular and advantageously, said liquid phase comprising the dissolved glycerol formed during said step a) is not subjected, in itself, to any other treatment than the separation of said step c) during which the glycerol is separated from the solvent.

The crude glycerol is preferably obtained from renewable raw materials, in particular the crude glycerol is obtained during the manufacture of biodiesel or obtained during the transformation of fats or oils, particularly animal or vegetable fats or oils. The crude glycerol is generally obtained by saponification reaction, transesterification and / or hydrolysis of animal or vegetable fats or oils.

The crude glycerol generally comprises from 5 to 95% by weight of glycerol, in particular from 40 to 90% by weight of glycerol and more particularly from 60 to 90% of glycerol. Crude glycerol also includes inorganic salts, glycerides, water and other organic compounds.

The crude glycerol may optionally be treated for the process of the invention, in particular for example by adjusting the pH, filtration or distillation. It is thus possible to filter the crude glycerol to remove insoluble organic material and / or distill it generally at temperatures between 100 and 120 ° C at atmospheric pressure to remove water and volatile compounds. Part or all of the water contained in the crude glycerol can also be evaporated before glycerol is dissolved in the solvent.

Step a) of the process according to the invention aims at dissolving glycerol in the organic solvent and forming an insoluble phase comprising the salts of crude glycerol. One or more solvents can be used. The solvent according to the invention may in particular be a ketone, an alcohol, an aldehyde, an acetal and / or a ketal. Acetals are obtained by nucleophilic addition of an alcohol to an aldehyde in an acidic medium, followed by removal of water. The ketals are obtained by the same type of reaction performed on ketones.

The ketones preferentially used are acetone, cyclohexanone, methyl cyclohexanone, cyclopentanone, methyl cyclopentanone and methyl isobutyl ketone (MIBK). The preferred aldehydes are formaldehyde, acetaldehyde and furfuraldehyde. The alcohols preferentially used are ethanol, methanol and isopropanol. The ketals and acetals are preferably dioxonals such as 2,2-dimethyl-1,3-dioxolane 4 methanol (solketal) for example. An organic solvent mixture such as a mixture of alcohol and ketone, particularly a mixture of acetone and ethanol, is particularly preferred.

In step a), no catalyst capable of catalyzing a reaction between the glycerol and the organic solvent or solvents of the medium, especially an esterification catalyst, will be used.

Step a) can last between 2 minutes and 1 hour. It can be carried out at a temperature of between 10 and 100 ° C., in particular between 20 and 50 ° C. The pH during this step can be between 6 and 12, preferably between 7 and 12.

The mass ratio between the crude glycerol and the solvent (crude glycerol / solvent) is in particular a function of the solubility of glycerol in said solvent, and for example preferably between 1/1 and 1/50, more preferably between 1/1 and 1/25.

Step b) aims at the separation of the precipitate obtained in step a) from the liquid phase comprising the solvent and the dissolved glycerol. In particular, filtration, decantation or centrifugation can be carried out. Step c) is aimed at separating the solvent and the glycerol which is dissolved in the solvent. In particular, evaporation or distillation can be carried out for this purpose.

In step c) it is also possible to separate the water contained in the crude glycerol.

The evaporation will include the passing of the organic solvent (s) in the gaseous state so as to recover the glycerol in the liquid state.

To carry out the distillation, one or more distillation columns can be used. In particular, the different compounds can be distilled on the same distillation column by varying the temperature, and possibly the pressure; for example proceed to the distillation of the organic solvent, then an increase in the temperature to distill the glycerol. Temperatures between 60 and 190 ° C are usually used and pressures between 2 and 1000 mbar are used.

The purified glycerol is then obtained and can be used in various applications requiring a high purity level.

A specific language is used in the description so as to facilitate understanding of the principle of the invention. It should nevertheless be understood that no limitation of the scope of the invention is envisaged by the use of this specific language. In particular, modifications, improvements and improvements may be considered by a person familiar with the technical field concerned on the basis of his own general knowledge.

The term and / or includes the meanings and, or, as well as all other possible combinations of elements connected to this term. Other details or advantages of the invention will emerge more clearly in the light of the examples given below solely for information purposes.

EXPERIMENTAL PART

Example 1

The commercially available crude glycerol has the following composition: 79.3% by weight of glycerol, 15.8% by weight of water, 1.61% by weight of Na + and 2.56% by weight of Cl-. 120.2 g of crude glycerol are added at room temperature to 2464 g of acetone. The mixture is stirred for 15 minutes until dissolution of the glycerol in acetone and formation of an insoluble phase. The liquid phase is filtered using a PTFE filter with a pore diameter of 0.2 μm; then the solvent and the water are evaporated under vacuum at a temperature of 60 ° C and a pressure of 0.3 bar absolute.

88.93 g of purified glycerol, comprising 97.5% by weight of glycerol, are then recovered. Example 2

150.8 g of crude glycerol are added at room temperature to 91.3 g of ethanol and 1754.3 g of acetone. The mixture is stirred for 20 minutes until dissolution of glycerol in acetone and formation of an insoluble phase. The liquid phase is filtered using a PTFE filter with a pore diameter of 0.2 μm; then the solvent is evaporated under vacuum at a temperature of 75 ° C and a pressure of 0.3 bar absolute.

106.7 g of purified glycerol, comprising 98.3% by weight of glycerol, are then recovered.

Claims

1. A process for purifying crude glycerol comprising at least the following steps:

(a) in the presence of crude glycerol and at least one organic solvent comprising from 1 to 10 carbon atoms and comprising at least one ketone, aldehyde, alcohol, acetal and / or ketal function, so as to form a liquid phase comprising glycerol dissolved in the solvent (s) and also forming an insoluble phase in the form of a precipitate;

(b) separating the insoluble phase and the liquid phase;

(c) separating the solvent and glycerol from the liquid phase; and

(d) recovery of glycerol.

2. Method according to claim 1, characterized in that the crude glycerol comes from renewable raw materials.

3. Method according to claim 1 or 2, characterized in that the crude glycerol is obtained during the manufacture of biodiesel or during the transformation of fats or oils, particularly animal or vegetable fats or oils.

4. Process according to any one of the preceding claims, characterized in that the ketone is chosen from the group comprising acetone, cyclohexanone, methyl cyclohexanone, cyclopentanone, methyl cyclopentanone and methyl isobutyl ketone.

5. Process according to any one of the preceding claims, characterized in that the aldehyde is chosen from the group comprising formaldehyde, acetaldehyde and furfuraldehyde.

6. Process according to any one of the preceding claims, characterized in that the alcohol is chosen from the group comprising ethanol, methanol and isopropanol.

7. Process according to any one of the preceding claims, characterized in that the ketal or the acetal is a dioxolane.

8. Process according to any one of the preceding claims, characterized in that the mass ratio between the crude glycerol and the solvent (crude glycerol / solvent) is between 1/1 and 1/50.

9. Method according to any one of the preceding claims, characterized in that the separation of step b) is carried out by filtration.

10. Process according to any one of the preceding claims, characterized in that the separation of step c) is carried out by evaporation.