Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1999-09-07
2001-11-06
Phasge, Arun S. (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S541000, C205S431000
Reexamination Certificate
active
06312578
ABSTRACT:
The present invention relates to a process for extracting, by electrodialysis, a compound comprising at least protonatable amine functions from a liquid medium.
The invention relates more particularly to a process for extracting and separating at least the monomers comprising protonatable amine functions from a medium originating from the hydrolysis of polyamides.
Synthetic materials, and among these polymers containing amide functions such as polyamides and more particularly polyamide 6.6 or polyamide 6, are increasingly being used to make varied articles such as textile fibres, technical industrial yarns, filaments or moulded articles such as components for electricity, electronics or motor vehicles. These synthetic materials are generally used in the form of compositions comprising, in addition to the synthetic material, various additives for, for example, increasing their thermal stability, or their stability to radiation, or for improving their mechanical, electrical or electrostatic properties, dyes and pigments. These additives are of very varied nature and can be either organic or inorganic compounds.
In addition, in particular for the preparation of moulded articles, the compositions comprise fillers, often inorganic fillers, such as glass fibres, talc, clay, etc.
The materials thus produced can be destroyed after use. One of the standard methods of destruction is incineration, which allows the energy to be recovered. However, it is also proposed to recycle these materials.
In point of fact, one of the current preoccupations lies in the recycling of the products obtained from natural sources in order, on the one hand, to slow down the depletion of these sources, and, on the other hand, to reduce the volume of waste in nature.
Thus, processes for depolymerizing polyamides have been proposed. One of the processes consists in carrying out a hydrolysis in acidic, neutral or basic medium of the polyamide in order to obtain either oligomers with a low degree of polymerization, or salts. The hydrolysis process applies in particular to the depolymerization of PA 6-type polyamides, i.e. polyamides obtained by homopolycondensation of an amino acid or of a lactam.
In the case of PA 6.6-type polyamides, i.e. polyamides obtained by polymerization between diamine and a diacid, the hydrolysis must be carried out in alkaline medium in order to obtain total depolymerization. In the case of a hydrolysis in neutral medium, the hydrolysate medium contains a mixture of oligomers with a different degree of polymerization generally of between 2 and 40, and more specifically between 2 and 20.
Hydrolysis in alkaline medium presents a major drawback since it is necessary, in order to recover the acidic monomer, for example the adipic acid, to react the adipate formed with an acid, for example nitric acid. This process thus consumes product (acid) and generates an effluent (alkaline salts). In order to overcome this problem, an electrolytic process for converting the adipate salt into adipic acid has been proposed in International patent applications WO 93/25299, WO 93/25514 and WO 93/25513.
French patent applications FR 95/08916 and FR 95/08917 have also proposed a process for thermally hydrolysing polyamides in neutral medium, and then converting the oligomers thus obtained into amine, acid or amino acid monomers or into amine salts by enzymatic hydrolysis. These compounds dissolved in the hydrolysis medium can be extracted and separated by various processes such as crystallization, precipitation or distillation. However, these conventional extraction and purification processes have low yields and are not very selective.
One of the aims of the present invention is to propose a process for selectively separating the various compounds produced, and in particular compounds comprising at least one protonatable amine function.
To this end, the invention proposes a process for extracting from a liquid medium a compound comprising at least one protonatable amine function, characterized in that it consists in protonating the amine function(s) by adjusting the pH of the medium and in separating the compounds by passing them through a cationic membrane under the effect of an electric current.
Thus, the electrodialysis elemental cell for carrying out the invention comprises a cationic membrane arranged between two electrodes.
According to another characteristic of the invention, the pH of the solution is determined and adjusted so as to correspond to the isoelectric point or to the pKa of the compound to be extracted by passing it through the cationic membrane, and more advantageously to the pKa of the amine to be separated.
The term “isoelectric point” will be used when the compound to be extracted comprises several positively and negatively ionizable functions, respectively, such as amine functions and acid functions.
Thus, the process of the invention makes it possible to separate different compounds contained in a liquid medium by selective extraction of one of the compounds, or by carrying out a separation in several steps with extraction of a compound at each step with modification of the pH of the liquid medium between each step in order to adapt it to the isoelectric point or pKa of the compound to be extracted in the said step.
In one preferred embodiment of the invention, in particular when the liquid medium comprises monomers produced by the depolymerization of polyamides, the elemental electrodialysis cell advantageously comprises a cationic membrane and an anionic membrane.
Thus, this cell comprises a dilution compartment D into which the liquid medium to be treated is fed, and two concentration compartments (C
+
, C
−
) in which the compounds extracted from the liquid medium and crossing the cationic and anionic membranes, respectively, under the effect of the electric current, are concentrated. When cells are mounted in electrical series, the compartment C
+
of one cell will also form the compartment C
−
of the adjacent cell in the series, and vice versa for the compartment C
−
. Consequently, for greater clarity, all the concentration compartments will be referred to as C, without distinction of signs.
In point of fact, the process of the invention finds a preferential application in the separation and recovery of the monomers produced by a process of depolymerizing polyamides.
Thus, the hydrolysis of polyamide in neutral medium leads to an aqueous solution of diamine, diacid and/or amino acid monomers depending on the nature of the polyamides treated, as well as oligomers with a degree of polymerization of, for example, between 2 and 40.
The treatment of such a solution by the process of the invention makes it possible to extract and separate the diamine and diacid monomers from the oligomers and amino acids.
However, in order to improve the depolymerization yield and to convert the oligomers into monomers, the aqueous solution described above is subjected to an enzymatic hydrolysis.
Examples of enzymatic hydrolysis of polyamide oligomers, and more particularly of polyhexamethylene adipamide (PA 6.6) oligomers are described in French patent applications No. 95 08916 and No. 95 08917, the texts of which are incorporated into the present invention.
Briefly, the processes described consist in carrying out a thermal hydrolysis of polyamides in neutral medium, and then in treating this hydrolysate with enzymes known as “amidases”. These enzymes are, for example, the one (PAM I) expressed by the
E. coli
strain containing the plasmid PXL 2564 filed at the National Collection of Culture and Microorganisms under No. I 1495, on Nov. 29, 1994, the enzyme produced by the strain nyl-B described in Kinoshita et al. (Eur. J. Biochem 116, 547-551, 1981), the amidase (PAM II) expressed by the strain Comonas acidovorans filed at the National Collection of Cultures and Microorganisms under No. I 1522 of Jan. 4, 1995.
The solution recovered after enzymatic hydrolysis contains only amine salts and/or diamine and diacid monomers, lactams or amino acids depending on the nature
Canivenc Edith
Horbez Dominique
Burns Doane Swecker & Mathis L.L.P.
Phasge Arun S,.
Rhodia Fiber & Resin Intermediates
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