Purification of triazabicyclo-decene (TBA)

Abstract

In accordance with an example aspect of the present invention, there is provided a method for separating mTBD from a sample comprising mTBD and TBD, where the method comprises the steps of filtering the sample and subsequently distilling the sample.

Description

Technical Field

[0001] The present invention relates to the purification of guanidine bases. More specifically, the present invention relates to the purification of 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (mTBD). Background Art

[0002] Ioncell technology can be used to convert cellulose fibers derived from, for example, old textiles, pulps, or old newspapers into fibers that can be used, for example, to produce new knitted and woven garments. The Ioncell process uses ionic liquids to dissolve cellulose and then converts it into fibers using dry-jet wet spinning technology (Elsayed et al.).

[0003] Ionic liquids are a type of liquid salt. An ionic liquid suitable for the Ioncell process is mTBD, which is a bicyclic strong guanidine base. It forms an ionic liquid when in contact with certain acids.

[0004] TBD is an impurity in mTBD formulations. TBD has the potential to form solid particles in the Ioncell process and also increases the melting point of the resulting ionic liquid. For these reasons, the TBD content of mTBD formulations should be reduced as much as possible before the ionic liquid is produced. In addition, the hydrolysis products of mTBD should be removed from the mTBD formulations used in the Ioncell process. The removal of hydrolysis products is crucial for the subsequent use of the formulation in cellulose dissolution.

[0005] The cost of mTBD superbase containing TBD is significantly lower than that of pure mTBD formulations. However, to our knowledge, there is currently no simple and cost-effective method for purifying mTBD from formulations containing TBD. Summary of the Invention

[0006] The present invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0007] According to a first aspect of the present invention, there is provided a method for separating mTBD from a sample comprising mTBD and TBD, wherein the method comprises the steps of: filtering the sample and then distilling the sample.

[0008] The present invention is based on a new discovery that mTBD and TBD can be separated based on the difference in their vapor pressures. This is surprising because the structures of these two compounds are very similar, and thus those skilled in the art would not expect distillation to be a viable strategy for separating these compounds. In addition, the molar mass of TBD is lower than that of mTBD, and more surprisingly, TBD has a much lower vapor pressure. This makes it possible to obtain very pure mTBD by distillation. Description of the Drawings

[0009] Figure 1 Shows the composition of the samples taken during distillation. The y-axis represents the mass-% (%) of the components calculated from the total mass of the sample, the x-axis represents the cumulative mass (g) of the distillate, the black line represents mTBD, the grey line represents H-mTBD-2, and the dashed line represents H-mTBD-1.

[0010] Figure 2 Shows the solid-liquid equilibrium of TBD and mTBD measured by differential scanning calorimetry. The y-axis represents temperature (K), and the x-axis represents the TBD equilibrium. The lines in the figure represent the ideal equilibrium, the circles represent pure mTBD, the x represents the differential scanning calorimetry measurement results, and the triangles represent the room temperature solubility of TBD in mTBD.

[0011] Figure 3 Shows a schematic setup diagram of the batch column used in the examples. 1. Heater, 2. Round-bottom flask, 3. Vigreaux column, 4. Distillate reflux controller, 5. Condenser, 6. Additional distillate condenser, 7. Round-bottom flask for collecting distillate fractions, 8. Vacuum line, 9. Liquid nitrogen trap, 10. Vacuum control valve, T temperature probe, P pressure transducer.

[0012] Figure 4 Shows the temperature curve of the distillation column. The y-axis represents temperature (°C), the x-axis represents time (min), the line represents the reboiler temperature, and the dashed line represents the column top temperature.

[0013] Figure 5 Shows the pressure of the distillation column. The y-axis represents pressure (mbar), and the x-axis represents time (min).

[0014] Figure 6 Shows the vapor pressures of mTBD and TBD. The y-axis represents vapor pressure (Pa), the x-axis represents temperature (°C), the circles represent the mTBD vapor pressure measured by Baird et al. (2019), the triangles represent the measured mTBD vapor pressure, the squares represent the measured TBD vapor pressure, and the line represents the TBD correlation. Detailed Description of the Invention

[0015] In this context, the abbreviation "TBD" refers to 1,5,7-triazabicyclo[4.4.0]dec-5-ene, which has a CAS number of 84030-20-6. The abbreviations "m-TBD" and "mTBD" refer to 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, which has a CAS number of 5807-14-7. The abbreviation H-mTBD-1 refers to 1-[(3-methylamino)propyl]-1,3-diazinan-2-one. The abbreviation H-mTBD-2 refers to 1-[(3-amino)propyl]-3-methyl-1,3-diazinan-2-one. H-mTBD-1 and H-mTBD-2 are hydrolysis products of mTBD.

[0016] In this context, the term "ionic liquid" refers to a salt that exhibits liquid properties at room temperature. Such substances are also known as liquid electrolytes, ionic melts, ionic fluids, molten salts, liquid salts, or ionic glasses. Ordinary liquids are mainly composed of electrically neutral molecules, while ionic liquids are mostly composed of ions.

[0017] Unless otherwise specified herein or the context clearly indicates otherwise, any percentages mentioned herein are expressed as weight percentages based on the total weight of the corresponding composition.

[0018] Unless otherwise specified, the properties measured or determined in the experiments herein are measured or determined at room temperature. Unless otherwise specified, room temperature is 25 °C. Unless otherwise specified, the properties measured or determined in the experiments herein are measured or determined at atmospheric pressure.

[0019] As used herein, the term "about" refers to the actual given value and also to an approximation of such a given value that a person of ordinary skill in the art would reasonably infer, including approximations due to experimental and / or measurement conditions for such a given value. Introduction paragraph - Explain the core of the invention in one paragraph and provide an executive summary of the overall content of this application.

[0020] The present disclosure relates to a method for separating mTBD from a sample comprising mTBD and TBD. The method comprises the steps of filtering the sample, followed by distilling the sample.

[0021] Filtration can be carried out by applying the sample to a filtration medium and collecting the fluid that passes through. The filtration medium can be any medium suitable for separating solid matter from liquid, such as filter paper or a filter membrane. In one exemplary setup, filter paper is placed on a glass funnel and pre-wetted, the sample is applied to the pre-wetted filter paper, and the fluid that passes through the filter paper and contains mTBD is collected. The filter cake formed on top of the filter paper includes TBD. In some embodiments, the filter cake can be collected as the TBD-rich fraction. After the sample has passed through, the filtration medium can be washed to recover any sample remaining in the filtration medium. A washing solution is applied to the filtration medium, and the fluid that passes through is collected as the wash fraction and can be combined with the sample collected after filtration. Filtration can be carried out, for example, by gravity filtration or vacuum filtration.

[0022] In some preferred embodiments, the TBD content of the sample is 5 mol% or less, such as 3 mol% or less, 2 mol% or less, calculated from the total number of moles of mTBD and TBD in the sample after filtration. In some instances, according to the solid-liquid equilibrium behavior of TBD ( Figure 2 ), the TBD concentration can be further reduced by lowering the storage temperature of the sample. Preferably, the storage temperature ranges from 16 °C to 25 °C, such as 16 °C to 20 °C. In some embodiments, the filtration step can be carried out at a temperature ranging from 10 to 30 °C. Preferably, the temperature can be between 12 - 25 °C, most preferably between 16 - 20 °C. At higher temperatures, more TBD dissolves in the mTBD solution ( Figure 2 ). Therefore, a lower temperature is beneficial for separating TBD from the mTBD solution. At temperatures below 16 °C, the sample containing mTBD may enter a supercooled state.

[0023] The setup of the distillation apparatus can be simple and includes a flask for containing the substance to be distilled, a heater, and a reflux column. However, more complex apparatuses are generally used, which are known in the art. One exemplary setup includes a reboiler flask, a column / tower and column / tower packing, and a condenser with a reflux controller. Another exemplary setup is as Figure 3As shown, and including 1. a heater, 2. a round-bottom flask, 3. a Vigreux column, 4. a distillate reflux controller, 5. a condenser, 6. an additional distillate condenser, 7. a round-bottom flask for collecting distillate fractions, 8. a vacuum line, 9. a liquid nitrogen cold trap, 10. a vacuum control valve, T a temperature probe, P a pressure transducer. Thus, the device can be a batch distillation column / tower, a continuous distillation column / tower, a short-path distillation unit, a thin-film evaporator, or any combination thereof. The thin-film evaporator can be selected from the group including the following: a batch evaporator, a natural circulation evaporator, a forced circulation evaporator, a horizontal tube evaporator, a long tube vertical evaporator, a short tube vertical evaporator, a falling film evaporator, a rising film evaporator, a rising / falling film evaporator, a rotary thin-film evaporator, and a gasketed plate evaporator.

[0024] The distillation apparatus is generally operated by introducing the feed into a reboiler flask and connecting the flask to the column. After heating begins, the distillate fraction is removed from the top of the column and fed into a round-bottom flask. In a batch distillation process as used herein, the first 1-2 fractions generally contain water and are therefore preferably discarded. However, subsequent fractions, such as fractions 3-7, mainly consist of mTBD and are therefore collected as product fractions.

[0025] In some embodiments, the TBD present in the sample can precipitate, and the precipitate can be removed before distillation. For example, precipitation can be achieved by reducing the solution temperature to a temperature below room temperature, such as in the range of 12-25 °C or 16-20 °C. Preferably, the precipitate can be removed by filtration or decantation. In some embodiments, the temperature during precipitate removal is 10-30 °C, preferably 12-25 °C, and most preferably 16-20 °C. The precipitation of TBD will reduce the TBD concentration in the sample and ultimately result in more efficient sample purification.

[0026] In some embodiments, the pressure during distillation can be below 101.325 kPa. Preferably, the pressure during distillation can be 1-10 kPa, preferably 1-5 kPa, and most preferably 2-2.5 kPa. At reduced pressure, water cannot condense and is transferred to a trap. In addition, the hydrolysis products of mTBD, namely H-mTBD-1 and H-mTBD-2, are also directed to the trap at reduced pressure. Thus, reducing the pressure during distillation will increase the purity of the mTBD preparation.

[0027] In other embodiments, the sample is dried before distillation, one purpose of which is to reduce the formation of unwanted by-products by reacting with water. In the presence of water, mTBD hydrolyzes to H1-mTBD and H2-mTBD, reducing its ability to dissolve cellulose. In addition, the drying step reduces the water content in the ionic liquid. Excessive water in the ionic liquid reduces the ability of the ionic liquid to dissolve cellulose. Therefore, the drying step can improve the purity of mTBD. The drying is preferably carried out by stripping the sample with an inert gas such as nitrogen, heating, evaporation, freeze-drying, or a combination thereof.

[0028] It should be understood that the disclosed embodiments of the present invention are not limited to the specific structures, process steps, or materials disclosed herein, but extend to their equivalents as would be recognized by those of ordinary skill in the relevant art. It should also be understood that the terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting.

[0029] The mention of one embodiment or an embodiment throughout the specification means that the specific features, structures, or characteristics described in connection with that embodiment are included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment" or "in an embodiment" appearing throughout this specification do not necessarily all refer to the same embodiment.

[0030] As used herein, for convenience, a plurality of items, structural elements, constituent elements, and / or materials may be presented in a common list. However, these lists should be interpreted as if each member of the list was individually identified as a separate and unique member. Thus, no single member of such a list should be construed as being in fact equivalent to any other member of the same list, solely based on their appearance in a common group, without an indication to the contrary. In addition, various embodiments and examples of the present invention, along with alternatives for various components thereof, may be mentioned herein. It should be understood that such embodiments, examples, and alternatives should not be construed as being in fact equivalents of one another, but rather as being separate and autonomous representations of the present invention.

[0031] In addition, in one or more embodiments, the described features, structures, or characteristics may be combined in any suitable manner. In the following description, numerous specific details, such as examples of length, width, shape, etc., are provided to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the relevant art will recognize that the present invention may be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring various aspects of the present invention.

[0032] While the foregoing examples illustrate the principles of the present invention in one or more specific applications, it will be apparent to those of ordinary skill in the art that various modifications can be made in form, usage, and implementation details without the exercise of creativity and without departing from the principles and concepts of the invention. Accordingly, the invention is not intended to be limited except as set forth in the claims below.

[0033] The verbs "comprise" and "include" are used in this document as open-ended limitations that neither exclude nor require the presence of unrecited features. Unless otherwise expressly stated, the features recited in dependent claims may be freely combined with one another. In addition, it should be understood that the use of "a" or "an" throughout this document, i.e., the singular form, does not exclude the plural form.

[0034] Experimental Section

[0035] The sample contained a mixture of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (mTBD). The column was a single-section setup with internals of type A3-1000 Montz packing (7x80 mm). The column had a diameter of DN25, was coated with silver, and had vacuum insulation, viewing strips, and an external expansion bellows. The packed height was 560 mm, and the total height was approximately 690 mm. The absolute pressure on the column side was set to Pabs, distcol = 21 mbar. The target pressure inside the column was 20 - 25 mbar. The reboiler used was of the 320W Barnstead Electrothermal EMA stirred heating mantle type. The reboiler was operated at a setting of 5 / 10. Thus, the heating power was 5 / 10 * 320W = 160W. The reflux ratio RD = 2 was kept constant throughout the distillation cycle. The schematic setup of the instrument is as Figure 3 shown.

[0036] Track the temperature during distillation ( Figure 4 ). These temperatures were obtained by two temperature probes, one located in the bottom flask ( Figure 4 solid line in Figure 4 ), at the base of the distillation column ( Figure 5 dashed line in Figure 5 ), and the other at the top of the column. In addition, the pressure during distillation (

[0037] ) was also tracked. Two distinct pressure peaks were caused by the removal of the distillate fraction (

[0038] ) The m-% after distillation was 91.1, and the m-% loss calculated from the mass of the original sample was 2.8.

[0038] After observing that the temperature of the column was relatively stable, the distillation was started at total reflux. Then the reflux ratio was set to 2 for continuous distillation, and the fractions collected are shown in Table 1.

[0039] Table 1. Details of the distilled fractions collected. Btm = bottom fraction.

[0040]

[0041] The fractions were analyzed by NMR to determine the components and composition present. DMSO was used as the solvent, and the 1H NMR isotopes of the chemical substances were used for the analysis. The results obtained from the analysis are shown in Table 2. 1 H NMR isotopes for analysis. The results obtained from the analysis are shown in Table 2.

[0042] Table 2. NMR analysis results

[0043]

[0044] Figure 1 Showed how the distillate composition changed over time. It was observed that most of the impurities could be removed at the beginning of the distillation, and pure mTBD could be obtained through the distillation process starting from the third distillation fraction.

[0045] The amount of pure mTBD collected could be further increased. The amount of the first distillation fraction collected could be increased. It was observed that the impurities mainly existed at the beginning of the distillation, and by increasing the volume of the distillate collected initially, the impurities present in the subsequent fractions should decrease. Alternatively, the number of fractions collected could be increased, and at the same time, the volume collected per fraction at the beginning of the distillation could be decreased.

[0046] The first two fractions contained small amounts of water and hydrolysis products. Under reduced pressure distillation, the water could not be condensed and was transferred to the collector together with the hydrolysis products. The distillate fractions 3 to 7 were very pure mTBD.

[0047] The results obtained were verified by determining the vapor pressure of TBD, which was significantly lower than the vapor pressure of mTBD ( Figure 6 ).

[0048] If deemed necessary, the sample could be dried before distillation. The water in the sample tended to produce hydrolysis products of mTBD, especially at elevated temperatures. Therefore, removing the excess water could be beneficial for increasing the yield of pure mTBD. In addition, in some cases, it was necessary to remove the water from the system before the vacuum pump could be used to prevent damage to the pump.

[0049] Citations

[0050] Non-patent literature

[0051] Zachariah Steven Baird,Artur Dahlberg,Petri Uusi-Kyyny,Nahla Osmanbegovic,Joanna Witos,Jussi Helminen,Daniel Cederkrantz,Paulus Ville Alopaeus,Ilkka Susanne K. Wiedmer,Herbert Sixta,Physical Properties of 7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (mTBD) International Journal of Thermophysics,Volume 40,Issue 71 July 2019 Article number 71.DOI 10.1007 / s10765-019-2540-2

[0052] Sherif Elsayed,Jussi Helminen,Sanna Hellsten,Chamseddine Guizani,Joanna Witos,Marja Rissanen,Antti H. Paulus Pauliina Varis,Susanne K. Wiedmer,Ilkka and Herbert Sixta.Recycling of Superbase-Based Ionic Liquid Solvents for the Production of Textile-Grade Regenerated Cellulose Fibers in the Lyocell Process,ACS Sustainable Chem.Eng.2020,8,37,14217-14227

[0053] https: / / doi.org / 10.1021 / acssuschemeng.0c07773。

Claims

1. A method for separating mTBD from a sample comprising mTBD and TBD, wherein, The method comprises the following steps: filtering the sample, and subsequently distilling the sample.

2. The method according to any one of the preceding claims, wherein, The temperature during filtration is 10 - 30 °C, preferably 12 - 25 °C, and most preferably 16 - 20 °C.

3. The method according to any one of the preceding claims, wherein, The TBD in the sample precipitates, and the precipitate is removed before distillation, preferably by filtration or decantation.

4. The method according to any one of the preceding claims, wherein, The pressure during distillation is below 101.325 kPa.

5. The method according to any one of the preceding claims, wherein, The pressure during distillation is 1 - 10 kPa, preferably 1 - 3 kPa, and most preferably 2 - 2.5 kPa.

6. The method according to any one of the preceding claims, wherein, The distillation apparatus is a batch distillation column / tower, a continuous distillation column / tower, a short-path distillation unit, a thin-film evaporator, or any combination thereof.

7. The method according to any one of the preceding claims, wherein, The sample is dried before distillation.

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