Distillation process comprising rectification for obtaining piperonyl butoxide of high purity PBO

Abstract

The present invention relates to a composition comprising piperonyl butoxide (PBO) in a concentration of 94 to 99.9% by weight, dipiperidinyl methane (DPM) in a concentration of 0.01 to 1% by weight and dipiperidinyl ether (DPE) in a concentration of 0 to 0.1% by weight, relative to the total weight of the composition, and a distillation process for obtaining the composition, the composition comprising piperonyl butoxide (PBO) in a concentration of from 94 to 99.9% by weight, dipiperidinyl methane (DPM) in a concentration of from 0.01 to 1% by weight, and dipiperidinyl ether (DPE) in a concentration of from 0 to 0.1% by weight.

Description

Technical Field

[0001] The present invention relates to a composition comprising piperonyl butoxide (PBO) and a distillation method for obtaining the composition. Background Art

[0002] The compound piperonyl butoxide, whose IUPAC name is 5-{[2-(2-butoxyethoxy)ethoxy]methyl}-6-propyl-2H-1,3-benzodioxole, also known by the acronym PBO, is a high-boiling molecule that decomposes rapidly at 300 °C (boiling point of 203 °C at 278 Pa; calculated boiling point of 400 °C at 101300 Pa).

[0003] For this reason, industrial methods for producing PBO require one or more staged evaporations to obtain the final product. The evaporation process can be carried out using different methods, such as steam flow evaporation, thin film evaporation, or simple batch evaporation.

[0004] Due to the physical properties of the product itself, the evaporation process requires harsh conditions, such as high vacuum and high temperature. The evaporation process does not allow, especially under the required conditions, effective separation of by-products from the synthesis process, which inevitably end up in the final product, thus limiting the quality of the final product.

[0005] In International Patent Application WO2021161083, a method for producing piperonyl butoxide is reported. Specifically, in Example 1c on page 21, it is stated that after separating the organic layer, PBO is obtained by distillation. The problem concerns the synthesis of various molecules derived from benzodioxole, especially sesamol and DHS, through various catalysts or their mixtures, as no details of the distillation section related to PBO are provided.

[0006] In Patent Application IN201941007564, in Example 3, regarding Step 4, it is stated that after separating the organic layer and distilling toluene under vacuum, PBO is distilled by fractional distillation, without pointing out any details about the distillation itself.

[0007] In the Chinese article "Purification of Piperonyl Butoxide by Short - Path Distillation Technology" by Xu Songlin et al. (Journal of the Chinese Society of Agricultural Engineering, Vol. 21, No. 2, February 2005), the results obtained from the distillation of PBO by two serial short - path evaporations are provided through data and graphs. In the first evaporation, the light products are removed, and the heavy products enter the second evaporator together with the target product PBO. In the second evaporator cascaded with the first evaporator, PBO is collected as the evaporation product, and the heavy by - products are collected as residues. The article reports obtaining a final PBO product with a purity of at most 96% and a yield higher than 70%. The short - path evaporation described is of course a method suitable for distilling high - boiling - point and heat - sensitive molecules, but it does not allow for effective separation of impurities, and thus high - purity products cannot be obtained with high yields.

[0008] In Chinese Utility Model CN212417044U filed in the name of Wujiang Shuguang Chemical Co., Ltd., a PBO distillation method is described. Specifically, a continuous steam - flow distillation method on a tower with staggered diaphragms is described. Specifically, this document focuses on the energy and environmental savings achievable from the recovery of condenser cooling water. Referring to Figure 1 of the reference model itself, the condenser 4 is connected to the cylinder 1. This document starts from an assumption and repeatedly reports the idea that, from an energy perspective, the existing rectification methods for producing PBO are inefficient and the rectification effect is average. See line 19 on page 1, which states that the rectification tower for producing PBO has a single function, a complex process flow, a poor rectification effect, and cannot recycle cooling water.

[0009] The present inventors have analyzed in detail the method described in this utility model and found that it involves distillation by rectification in a steam flow without indicating pressure and temperature conditions, and any organic components separated and carried by the steam inlet pipe to the top of the tower are completely condensed by the condenser (4) and completely re - introduced into the tower through the condensate return pipe (5). Therefore, the present inventors have realized that, according to the proposed scheme, any impurities that might be removed at the top (3) are condensed (4) and completely re - introduced into the process (5) and collected at the bottom together with the product (17), while the condensed steam is also introduced (18) therein, making the method itself unavailable at the level of product purification. Thus, any possible rectification effect introduced by the staggered diaphragms described in the specification is offset by the arrangement of the same devices in the distillation apparatus shown in this utility model. In the model filed in China, no data on the purity of the feed (15) and the obtained product (17) are reported, no yield is mentioned, nor any suggestions on the reflux ratio, temperature, and pressure conditions used in the distillation.

[0010] The document CN202131299, applied in the name of Nanchang Yangpu Natural Spice and Essence Co., Ltd., describes a batch distillation device equipped with a test device for the purification process as an on-line test of purity. As described in the abstract, the device is designed to detect the final purity of PBO.

[0011] The fact that this document focuses on is that the methods commonly used to obtain PBO require sampling from the distillate tank and performing laborious analyses to understand whether the purity of the obtained PBO is suitable for application.

[0012] According to the reported disclosure, there are no examples explaining how to carry out the distillation step. The impurity content of the raw material PBO, the temperature and pressure conditions of the distillation step, and even the reflux ratio are not disclosed. Only the removal of the solvent of the raw material in a separate device and then feeding the compound into the boiler (1) of the distillation device are disclosed. Specifically, the system includes a boiler (1) connected to a pump (2), and the content of the boiler is recycled through a heater (3). This document reports that the content of the boiler generates high temperature at low vapor pressure via the pump (2) through the heater (3), and PBO evaporates from the liquid phase. According to this document, the PBO compound turns into a gas, reaches the top of the fractionating column (4), and condenses back into a liquid form in the condenser (5) located at the top of the column. The liquid is then further cooled in the second condenser (6) and enters a device (7) that controls its quality from here. If the purity > 95%, the green light on the device display turns on, and the liquid is directed to the collection tank (8); if the purity of the liquid in the device (7) is less than 95%, the red light on the device display turns on, and the liquid is directed back to the boiler (1) again, and the above steps are repeated.

[0013] The present inventors have studied CN202131299 in detail and noted that according to this document, piperonyl butoxide may be purified by removing the heavy by-product fractions of the raw material that accumulate in the boiler. It is well known that when the crude PBO as a raw material is heated, it not only produces heavy degradation by-product fractions but also light degradation by-product fractions. According to the detection system described in CN202131299, such light by-product fractions will inevitably accumulate at the top of the fractionating column (4) after passing through the fractionating column (4) itself, and once condensed, will reduce the purity of the collected liquid received by the device (7) after condensation in (5) and (6); this document aims to detect the final purity of PBO but does not teach how to purify PBO with very small amounts of specific impurities and their degradation products.

[0014] Therefore, it is obvious that the prior art documents do not suggest how to obtain high-purity piperonyl butoxide by distillation simply including rectification. In fact, so far, due to the inevitable introduction of pressure loss by using a rectification column, no rectification and distillation method that allows effective removal of impurities from PBO has been found to be industrially applicable. The expression "pressure loss" refers to the pressure difference between the top and the bottom of the column, which determines the temperature distribution of the column itself.

[0015] The introduced pressure loss necessarily requires a higher evaporation temperature of the product, resulting in process complication.

[0016] As mentioned above, in fact, high temperature will increase product degradation, forming more impurities, resulting in low yield and low purity. The macroscopic degradation process occurs at a temperature of about 300 °C. However, if the time is extended, a slower but non-negligible degradation process is also observed at temperatures above 240 °C.

[0017] The main impurities formed by the degradation of crude PBO are low-boiling compounds generated in the still. Among the heavy crude impurities, there are dipiperonylmethane (DPM, IUPAC name: 5,5'-methylenediylbis(6-propyl-1,3-benzodioxole)) and dipiperonyl ether (DPE, IUPAC name: 5,5'-(oxybis(methylene))bis(6-propyl-1,3-benzodioxole)), which tend to degrade at high temperatures, especially at the known temperatures of evaporation / distillation of PBO itself.

[0018] Therefore, the object of the present invention is to obtain piperonyl butoxide with high purity and high yield without using difficult-to-manage equipment, so there are no harsh production conditions.

[0019] Another object is to provide piperonyl butoxide that does not contain heavy degradation by-products and light degradation by-products that may be generated during the distillation of the high-boiling compound PBO. Summary of the Invention

[0020] The present invention achieves these objects through a preparation method of piperonyl butoxide (PBO), which allows to obtain a composition that, relative to the total weight of the composition, contains PBO at a concentration of 94% to 99.9% by weight, dipiperonylmethane (DPM) at 0.01% to 1% by weight, and dipiperonyl ether (DPE) at 0 to 1% by weight.

[0021] Accordingly, the present invention relates to a composition which, relative to the total weight of the composition, comprises PBO at a concentration of 94% to 99.9% by weight, dipiperidinylmethane (DPM) at a concentration of 0.01% to 1% by weight, and dipiperidinyl ether (DPE) at a concentration of 0 to 1% by weight.

[0022] Accordingly, the present invention allows for obtaining high-purity PBO with low concentrations of the specific impurities DPM and DPE. In fact, when the concentration of PBO in the mixture is very high, we are referring to the purity percentage.

[0023] Without being bound by any theory and contrary to what is reported in the literature, the inventors believe that they have successfully obtained PBO of such high purity and with such low contents of DPE and DPM thanks to a distillation method that includes vacuum distillation, which allows for the withdrawal of the heavy and light by-products generated during the distillation of PBO and ensures obtaining a composition which, relative to the total weight of the composition, comprises PBO at a concentration of 94% to 99.9% by weight, dipiperidinylmethane (DPM) at a concentration of 0.01% to 1% by weight, and dipiperidinyl ether (DPE) at a concentration of 0 to 1% by weight. At the same time, the method of the present invention allows for a distillation yield of greater than 85%.

[0024] In fact, as is known in the prior art, when obtaining high-purity PBO from a distillation process, the use of drastic process conditions simultaneously results in a low distillation yield, which makes the method unattractive from an industrial perspective.

[0025] Accordingly, in another aspect, the present invention relates to a distillation method for preparing a composition comprising PBO according to the present invention, the method comprising one or more distillation steps of a crude product comprising PBO in a distillation apparatus equipped with rectification, the distillation apparatus equipped with rectification comprising at least one distillation column, each distillation column in the at least one distillation column independently comprising at least a theoretical stage equal to or greater than 1 and a reflux ratio in the range of 0.5:1 to 15:1, wherein the one or more distillation steps are carried out under vacuum conditions.

[0026] The distillation method of the present invention also allows for obtaining a distillation yield of higher than 85%.

[0027] Advantageously, the distillation method is carried out under vacuum conditions, preferably at the maximum vacuum allowed by the best available technology on the market, preferably at a pressure equal to or lower than 4000 Pa, more preferably equal to or lower than 2000 Pa, still more preferably at a pressure in the range of 1500 Pa to 10 Pa.

[0028] The crude product containing PBO of the method of the present invention, i.e., the raw material, preferably is a product containing PBO at a concentration of greater than or equal to 75%, preferably greater than or equal to 83%, more preferably greater than or equal to 90%. The crude PBO product raw material as a composition containing PBO and impurities has a content of DPM and DPE higher than 1% relative to the total amount of the total composition. After the distillation method of the present invention, relative to the total weight of the composition, the final composition contains PBO at a concentration of 94% to 99.9% by weight, dipiperidylmethane (DPM) at 0.01% to 1% by weight, and dipiperidyl ether (DPE) at 0 to 1% by weight.

[0029] In a preferred aspect of the present invention, the distillation apparatus operates continuously.

[0030] In other advantageous aspects of the present invention, one or more distillation columns of the distillation apparatus include / contain internal condensers, which allow for a reduction in the system pressure drop, thus ensuring a lower process temperature, which is important for limiting the thermal degradation of the product. Without being bound by any theory, the inventors believe that the presence of the internal condenser allows for the selective removal and condensation of only the desired photodegradation by-product fraction in the distillate through temperature control. Considering that the liquid of the internal reflux is not "subcooled" and reintroduced by a pump, but remains at the temperature of the distillation stage, this advantageously saves a large amount of energy.

[0031] In fact, in a preferred embodiment, one or more distillation columns of the distillation apparatus include / contain an external reboiler, which allows for a reduction in the contact time of the product with the hotter wall portions of the distillation apparatus. This minimizes the thermal stress of the product, thereby reducing degradation. The lower product decomposition, combined with the separation introduced by the distillation apparatus equipped with rectification, results in a higher product quality and yield. In an even more preferred embodiment, the choice of external heating (always operating at full load) is combined with the level control in the apparatus, which avoids the formation of potentially dangerous hot spots.

[0032] In the preferred and advantageous aspects of the present invention, the method of the present invention is continuous and allows for very precise and reproducible control of the final product. In fact, at the same productivity, compared with the batch method, this method has a shorter average residence time at high temperatures. In addition, the continuous distillation method is easier to manage operationally (fewer unitary operations due to no transient processes to manage), and at the same productivity, results in a smaller size and fewer equipment (cheaper and less maintenance) than the batch method, and is more efficient from an energy perspective (it allows for easy energy recovery by preheating the inlet vapor stream with the outlet vapor stream of the cooler). This continuous method also allows for a low residence time of the product, which results in a minimization of the formation of degradation by-products.

[0033] In other preferred aspects of the present invention, the selection of the high-efficiency packing and the associated liquid distribution system make it possible to maximize the theoretical number of distillation stages while minimizing the pressure drop.

[0034] With the aid of the figures shown in the drawings, other features and advantages of the present invention will become apparent from the following detailed description provided as a non-limiting example. Detailed Description

[0035] The present invention relates to a composition which, relative to the total weight of the composition, comprises PBO in a concentration of 94% to 99.9% by weight, dipiperidinylmethane (DPM) in a concentration of 0.01% to 1% by weight and dipiperidinyl ether (DPE) in a concentration of 0 to 1% by weight.

[0036] Thus, the present invention allows for obtaining high-purity PBO with low concentrations of the specific impurities DPM and DPE.

[0037] The composition comprises PBO in a concentration range of 94% to 99.9% by weight, preferably 96% to 99% by weight.

[0038] Relative to the weight of the composition, the composition of the present invention comprises 0.01% to 1% by weight, preferably 0.01% to 0.5% by weight, more preferably 0.01% to 0.1% by weight of dipiperidinylmethane (DPM).

[0039] Relative to the total weight of the composition, the composition of the present invention comprises 0 to 1% by weight, preferably 0.01% to 0.5% by weight, more preferably 0.01% to 0.1% by weight of dipiperidinyl ether (DPE).

[0040] Thus, in another aspect, the present invention relates to a distillation method for preparing a composition comprising PBO according to the present invention, the method comprising subjecting a crude product comprising PBO to one or more distillation steps in a distillation apparatus equipped with rectification, the distillation apparatus equipped with rectification comprising at least one distillation column, each distillation column in the at least one distillation column independently comprising a theoretical number of stages equal to or greater than 1 and a reflux ratio in the range of 0.5:1 to 15:1, wherein the one or more distillation steps are carried out under vacuum conditions.

[0041] In the present invention, when using the terms:

[0042] - "theoretical number of stages" means the theoretical number of trays of one or more columns of a distillation apparatus equipped with rectification calculated according to any method known in the art.

[0043] - "distillation step" means the number of steps carried out in a distillation apparatus equipped with rectification;

[0044] - "The crude product containing PBO" refers to the starting crude product that contains PBO and contains impurities DPE and / or DPM with a content higher than 1%. Preferably, the crude product contains PBO with a concentration greater than or equal to 75%, preferably greater than or equal to 83%, more preferably greater than or equal to 90%, and the content of DPM and DPE is higher than 1% and lower than or equal to 4%, still more preferably higher than 1% and lower than or equal to 3%, and even more preferably higher than 1% and lower than or equal to 2%.

[0045] - "Under vacuum conditions" means at a pressure lower than atmospheric pressure.

[0046] - "Degradation of the product" or "degradation of the crude product" or "degradation of the crude impurities" refers to the degradation of PBO and the degradation of impurities (including DMP and DPE).

[0047] Relative to the crude product containing PBO, the distillation method of the present invention also allows obtaining a distillation yield greater than 85%, preferably a distillation yield of 90% to 98%.

[0048] The crude product of PBO is obtained according to any method known in the art.

[0049] According to the present invention, the crude product containing PBO contains PBO with a concentration greater than or equal to 75%, preferably greater than or equal to 83%, more preferably greater than or equal to 90%. Relative to the total amount of the total composition, the content of DPM and DPE as the raw material of the crude PBO product of the composition containing PBO and impurities is higher than 1%. After the distillation method of the present invention, relative to the total weight of the composition, the final composition contains PBO with a concentration of 94% to 99.9% by weight, dipiperidylmethane (DPM) with a content of 0.01% to 1% by weight, and dipiperidyl ether (DPE) with a content of 0 to 1% by weight.

[0050] Advantageously, the distillation method is carried out under vacuum conditions, preferably under the maximum vacuum allowed by the best available technology on the market, preferably at a pressure equal to or lower than 4000 Pa, more preferably equal to or lower than 2000 Pa, and still more preferably at a pressure of 1500 Pa to 10 Pa.

[0051] According to the present invention, the method is carried out by a distillation device equipped with rectification, and the rectification device includes at least one distillation column, preferably 1 to 3 distillation columns, and these distillation columns each independently include at least 1, preferably 1 to 30 theoretical plates and a reflux ratio in the range of 0.5:1 to 15:1.

[0052] According to a preferred embodiment, the rectification device is a single rectification column or a series of rectification columns, preferably 2 - 3 rectification columns, which can operate in series or continuously, that is, operate simultaneously in a cascaded manner.

[0053] Distillation can be carried out in many different ways, and the possible combinations increase with the increase in the number of columns.

[0054] For example, the crude product can be fed into the first column, and the light by-products can be discharged from the first column. The composite PBO containing the heavy by-products is discharged from the bottom of the column still, and then the composite PBO is fed into the second column. The light degradation by-products come out from the top of the second column, the high-purity PBO is withdrawn from the side, and the heavy by-products come out from the bottom of the column.

[0055] For the same scheme with two columns, for example, by changing the process parameters, the heavy by-products can come out from the bottom of the first column, while the PBO containing the light products and part of the DPM are at the top. Then the PBO containing the light substances and part of the DPM can be fed into the second column, where the light / degradation by-products will come out from the top, the high-purity PBO is withdrawn from the side, and the DPM comes out from the bottom.

[0056] Thus, in embodiments comprising more than one column, the method according to the invention provides at least one distillation step under vacuum conditions.

[0057] In a preferred and advantageous embodiment, the distillation method is carried out in a distillation apparatus equipped with rectification, which distillation apparatus comprises a single distillation column.

[0058] The rectification apparatus comprises at least one, preferably 1 to 30 theoretical plates, and the reflux ratio of the same distillation apparatus is from 0.5:1 to 15:1.

[0059] The theoretical plates are preferably from 5 to 25, more preferably from 9 to 20.

[0060] Without being bound by any theory, the inventors believe that a distillation apparatus equipped with rectification having more than 30 plates will allow the obtaining of high-purity PBO, but the yield is too low; while less than 1 plate will not allow the sufficient purification of one or both of the DPE and DPM impurities from the product.

[0061] According to a preferred invention, when the theoretical plates are almost or equal to 30, in order to avoid an increase in the boiling point due to the pressure drop and cause PBO degradation, the distillation method comprises a plurality of distillation stages, preferably 2 or 3 distillation stages.

[0062] In the method of the present invention, the distillation apparatus equipped with rectification comprises at least 1 distillation column, preferably 1 to 3 distillation columns, and these distillation columns each independently comprise a reflux ratio of 0.5:1 to 15:1. Preferably, the reflux ratio is from 3:1 to 10:1, more preferably from 4:1 to 8:1.

[0063] The distillation apparatus includes a still, preferably in the form of a reactor heating system with heat transfer oil, or a boiler external to at least one distillation column. The boiler is within a temperature range of 170 °C to 270 °C, preferably 190 °C to 260 °C, more preferably 200 °C to 250 °C, to allow the distillation of PBO.

[0064] Advantageously, according to the present invention, when the number of stages of one or more columns of a distillation apparatus equipped with rectification is greater than 9, the distillation of crude PBO can preferably be carried out in a single stage. Conversely, if the number of stages is less than 9, advantageously, the distillation method contemplates more than one distillation stage, where the product of the previous distillation is used as the feedstock for the subsequent distillation.

[0065] In a preferred aspect of the present invention, the distillation apparatus operates continuously.

[0066] The distillation method also preferably provides for the use of condensers and / or reboilers for each distillation column (internal and external).

[0067] In other advantageous aspects of the present invention, one or more distillation columns of the distillation apparatus include / contain an internal condenser, which allows a reduction in the system pressure drop and ensures a lower process temperature, which is important for limiting the thermal degradation of the product / crude impurities. Without being bound by any theory, the inventors believe that the presence of the internal condenser allows the selective removal and condensation of only the desired light fraction in the distillate by temperature control. Considering that the liquid of the internal reflux is not "sub-cooled" and re-introduced by a pump, but remains at the temperature of the distillation stage, this advantageously saves a large amount of energy.

[0068] In fact, in a preferred embodiment, one or more distillation columns of the distillation apparatus include / contain an external reboiler, which allows a reduction in the contact time of the product with the hotter wall parts of the distillation apparatus. This minimizes the thermal stress on the product / crude impurities, thus reducing degradation. The reduced product decomposition, combined with the separation introduced by the distillation apparatus equipped with rectification, results in a higher product quality and yield. In an even more preferred embodiment, the choice of external heating (always operating at full load) is combined with the level control in the apparatus, which avoids the formation of potentially dangerous hot spots.

[0069] A distillation apparatus equipped with rectification can include at least 1 to 3 or more distillation columns, the sizes of which are designed to have an optimal reflux under process conditions.

[0070] The internal reflux can preferably be varied within a specified range by changing the temperature of the outlet steam, the feed rate, the feed temperature, and the heat supplied to the external reboiler (if present).

[0071] In fact, in a preferred embodiment, the distillation apparatus of the present invention comprises at least one distillation column, preferably 1 - 3 distillation columns, which independently of one another comprise an external reboiler that allows reducing the contact time of the product with the hotter wall portions of the distillation apparatus. This minimizes the product / crude impurity thermal stress, thereby reducing degradation. The reduced product / crude impurity decomposition, combined with the separation introduced by the distillation apparatus equipped with rectification, results in obtaining a higher product quality and yield. In an even more preferred embodiment, the choice of external heating (always operating at full load) is combined with the level control in the apparatus, which avoids the formation of potentially dangerous hot spots.

[0072] Without being bound by any theory, the inventors believe that the use of an internal condenser and / or an external reboiler is an advantageous aspect as it allows reducing the pressure drop and minimizing the degradation of the product / crude impurities.

[0073] In a preferred and advantageous aspect of the present invention, the method of the present invention is continuous and allows for a very precise and reproducible control of the final product. In fact, for the same productivity, compared to the batch method, this method has a shorter average residence time at high temperatures. Additionally, the continuous distillation method is easier to manage operationally (fewer individual operations as there are no transient processes to manage), and for the same productivity, results in a smaller size and fewer equipment (cheaper and less maintenance) compared to the batch method, and is more energy - efficient from an energy perspective (it allows for easy energy recovery by pre - heating the inlet stream with the cooled outlet vapor stream). This continuous method also allows for a low residence time of the product / crude impurities, which results in minimizing the formation of degradation by - products.

[0074] In other preferred aspects of the present invention, the distillation apparatus comprises at least 1 distillation column, preferably 1 to 3 distillation columns with high - efficiency packing, with a related liquid distribution system, thereby advantageously minimizing the load loss.

[0075] Also in this case, the reduced pressure drop allows for a lower process temperature, which limits the degradation of the product / crude impurities.

[0076] According to the present invention, the distillation method of the present invention, the distillation apparatus, preferably at least one distillation column, may preferably comprise a withdrawal system for heavy degradation impurities and light degradation impurities, said withdrawal system comprising - a final product withdrawal pump, a bottom product withdrawal pump, preferably connected to a bottom product collection tank and a top product collection tank respectively.

[0077] Therefore, in other aspects, the present invention relates to the composition of the present invention obtainable from the distillation method of the present invention.

[0078] The present invention will be further described in the following experimental section, which is for illustrative purposes only and not for limitation. The experimental section reports examples of the application of the method of the present invention to different raw materials and the impact of the method on the final product.

[0079] Experimental Section

[0080] Example 1

[0081] Obtain 97% PBO, 0.7% DPM and 0.1% DPE (laboratory batch; reflux ratio of 10:1; number of stages is 2)

[0082] Place 499 g of the crude PBO product with a titration degree of 86% w / w in a 1-liter four-necked flask.

[0083] The flask is equipped with a distillation column (h 50 mm × d 25 mm, equipped with 10 cm of Sulzer EX packing) connected to the top of the column, and an oil pump is set up for high-vacuum distillation. The system is equipped with vacuum and temperature measurement points at the top and bottom of the column.

[0084] Heat the system using a heating plate through an aluminum hood.

[0085] Stir the bottom of the flask with a magnetic stir bar.

[0086] Measure the vacuum degree using a capacitance cell and a digital reader.

[0087] Start the magnetic stirring, bring the system to the maximum pump vacuum, and start heating by setting the plate temperature to 250 °C. Start collecting fractions under the conditions shown in Table 1 below. This distillation step is carried out under vacuum conditions.

[0088] Table 1

[0089] g ℃ ℃ Pa Pa Bottoms Top Bottoms Top Fraction 1 10.35 119-228 114-165 170-300 80 Fraction 2 405.3 228-231 165-168 310-510 80

[0090] Once the collection of fraction 2 is completed, stop the distillation.

[0091] There are 83.5 g of heavy by-products remaining in the flask.

[0092] The system is operated with the distillate collection valve partially open to obtain a reflux ratio of 10:1. The separation stage number is 2.

[0093] Table 5 below shows the composition of the input crude product and the composition of the output product. The distillation step is carried out under vacuum conditions.

[0094] Table 2

[0095]

[0096]

[0097] The distillation yield based on PBO is 91.5%.

[0098] Example 2

[0099] Obtain 97% PBO, 0.5% DPM and 0.05% DPE (laboratory batch; reflux ratio of 10:1; number of stages is 3)

[0100] Place 500 g of the crude PBO product with a titre of 86% w / w in a 1-litre four-necked flask.

[0101] The flask is equipped with a distillation column (h 50 mm × d 25 mm, equipped with 15 cm of Sulzer EX packing) connected to the top of the column, and an oil pump is set up for high-vacuum distillation. The system is equipped with vacuum and temperature measurement points at the top and bottom of the column.

[0102] Heat the system using a heating plate through an aluminium hood.

[0103] Stir the bottom of the flask using a magnetic stir bar.

[0104] Measure the vacuum using a capacitance cell and a digital reader.

[0105] Switch on the magnetic stirrer, bring the system to maximum pump vacuum and start heating by setting the plate temperature to 250 °C. The distillation step is carried out under vacuum conditions.

[0106] Start collecting fractions under the conditions shown in Table 4 below.

[0107] Table 3

[0108] g ℃ ℃ Pa Pa Bottoms Top Bottoms Top Fraction 1 13.5 117-225 115-165 150-420 110 Fraction 2 398 225-232 165-168 420-750 120

[0109] Once fraction 2 has been collected, stop the distillation.

[0110] 88 g of heavy by-products remain in the flask.

[0111] The system is operated with the distillate collection valve partially open to obtain a reflux ratio of 10:1. The number of separation stages is 3.

[0112] Table 5 below shows the composition of the input crude and the output product.

[0113] Table 4

[0114] % w / w % a / a Feed Distillate PBO 86 97.00 DPM 1.99 0.5 DPE 1.71 0.05

[0115] The distillation yield based on PBO is 89.7%.

[0116] Example 3

[0117] Obtain 96.4% PBO, 0.35% DPM and 0% DPE (laboratory batch operation; reflux ratio of 10:1; number of stages is 5)

[0118] Place 505.2 g of crude PBO product with a titration of 83% w / w in a 1-liter four-necked flask.

[0119] The flask is equipped with a distillation column connected to the top of the column (h 50 mm × d 25 mm, equipped with 20 cm of Sulzer EX packing), and an oil pump is set up for high-vacuum distillation. The system is equipped with vacuum and temperature measurement points at the top and the bottom of the column.

[0120] Heat the system using a heating plate through an aluminum hood.

[0121] Stir the bottom of the flask with a magnetic stir bar.

[0122] Measure the vacuum using a capacitance cell and a digital reader. The distillation step is carried out under vacuum conditions.

[0123] Turn on the magnetic stirring, bring the system to the maximum pump vacuum, and start heating by setting the plate temperature to 250°C. Start collecting fractions under the conditions shown in Table 4 below.

[0124] Table 5

[0125] g ℃ ℃ Pa Pa Bottoms Top Bottoms Top Fraction 1 30.3 121-228 85-167 560-820 170 Fraction 2 384.66 228-232 167-174 900 170

[0126] Once the collection of fraction 2 is complete, stop the distillation.

[0127] There are 87.5 g of heavy by-products remaining in the flask.

[0128] The system is operated with the distillate collection valve partially open to obtain a reflux ratio of 10:1. The number of separation stages is 5.

[0129] Table 5 below shows the composition of the input crude product and the output product.

[0130] Table 6

[0131] % w / w % a / a Feed Distillate PBO 83 96.4 DPM 1.6 0.35 DPE 0.62 0

[0132] The distillation yield based on PBO is 88.5%.

[0133] Laboratory tests show that it is possible to obtain the desired product under the said conditions.

[0134] Example 4

[0135] Obtained 97.6% PBO, 0.09% DPM and 0% DPE (laboratory batch operation; reflux ratio of 2:1; number of stages is 10)

[0136] 1205 g of crude PBO product with a titration of 94.9% w / w was placed in a 2-liter four-necked flask.

[0137] The flask was equipped with a distillation column (h 55 mm × d 43 mm, equipped with 50 cm of Sulzer type DX packing) connected to the top of the column, and an oil pump was set up for high-vacuum distillation. The system was equipped with vacuum and temperature measurement points at the top and bottom of the column.

[0138] A reflux management system with a timing valve was set at the top, which allowed adjustment of the collection time and reflux time.

[0139] The system was heated by a heating mantle connected to a potentiometer to control the supplied power.

[0140] The vacuum was measured using a capacitance cell and a digital reader.

[0141] The system was brought to the maximum vacuum allowed by the oil pump, and heating was started by operating the potentiometer.

[0142] Under the conditions shown in Table 7 below, fractions were collected at a reflux:collection ratio of 2:1 (reflux 10″: collection 5″).

[0143] Table 7

[0144]

[0145]

[0146] Once the collection of fraction 2 was completed, the distillation was stopped.

[0147] 99 g of heavy by-products remained in the flask.

[0148] The system was operated at a reflux ratio of 2:1. The number of separation stages was 10.

[0149] Table 8 below shows the composition of the input crude product and the composition of the output product.

[0150] Table 8

[0151]

[0152] The distillation yield was 89.2%.

[0153] Example 5

[0154] Obtain 99% PBO, 0.03% DPM and 0% DPE (continuous industrial column; reflux ratio of 4:1; number of stages is 20)

[0155] The continuous distillation system consists of the following:

[0156] - Crude feed tank;

[0157] - Metering pump for feeding the crude into the column;

[0158] - Crude feed preheating system;

[0159] - Rectifying column with 20 theoretical plates, equipped with an internal condenser, a side feed port, a light product draw-off port, a heavy product draw-off port and a product side draw-off port;

[0160] - Top product post-condenser;

[0161] - External bottom reboiler heated with heat transfer oil;

[0162] - Bottom / external reboiler circulation pump;

[0163] - Final product draw-off pump;

[0164] - Final product collection tank;

[0165] - Bottom product draw-off pump;

[0166] - Bottom product collection tank;

[0167] - Top product collection tank;

[0168] - Pressure and temperature sensors (located at the bottom of the column, the feed port, the product draw-off ports and the top of the column);

[0169] - High-efficiency vacuum pump and booster;

[0170] - Heat transfer oil circuit.

[0171] Charge 1200 kg of 91.9 wt% crude PBO to the bottom of the column, bring the system to the maximum vacuum allowed by the pump, start the system, set the boiler temperature to 240 °C and the internal top condenser to 120 °C.

[0172] Once stable conditions are reached, feed the crude at a flow rate of 180 kg / h (200 °C) using a pump; simultaneously, start collecting the product from the side draw-off port (draw-off from the side of the column at 190 °C) at a flow rate of 163 kg / h using the respective pumps, and collect the residue from the bottom at a flow rate of 12 kg / h (221 °C).

[0173] At a temperature of 120 °C, the removal rate of the top fraction leaving the condenser is 5 kg / h. The top pressure is equal to 280 Pa and the bottom pressure is equal to 900 Pa.

[0174] The system operates at a reflux ratio of 4:1 and 20 stages.

[0175] The system is continuously used for 7.5 h to obtain 1222.5 kg of high-purity product, 37.5 kg of top by-product, and 90 kg of bottom by-product.

[0176] Table 9 below shows the composition of the input crude and the composition of the output product taken from the side of the column.

[0177] Table 9

[0178] % w / w % a / a Feed Distillate PBO 91.9 98.9 DPM 2.87 0.03 DPE 2.21 0

[0179] The distillation yield is 97.4%.

[0180] The creation and adoption of the technical solution for the designed distillation system incorporating continuous rectification make it possible to obtain the desired results.

Claims

1. A composition which, relative to the total weight of the composition, comprises PBO at a concentration of 94% to 99.9% by weight, dipiperidinylmethane (DPM) at a concentration of 0.01% to 1% by weight, and dipiperidinyl ether (DPE) at 0 to 1% by weight.

2. The composition according to claim 1, wherein the composition comprises PBO at a concentration of 94% to 99.9% by weight, preferably 96% to 99% by weight.

3. The composition according to claim 1 or 2, wherein, relative to the weight of the composition, dipiperidinylmethane (DPM) is in the range of 0.01% to 0.5%, preferably 0.01% to 0.1%.

4. The composition according to any one of claims 1 to 3, wherein, relative to the total weight of the composition, dipiperidinyl ether (DPE) is in the range of 0.01% to 0.5%, preferably 0.01% to 0.1%.

5. A distillation method for preparing a composition comprising PBO according to any one of claims 1 to 4, which comprises subjecting a crude product containing PBO to one or more distillation steps in a distillation apparatus equipped with rectification, the distillation apparatus equipped with rectification comprising at least one distillation column, each of the at least one distillation columns independently comprising a theoretical stage number equal to or greater than 1 and a reflux ratio of 0.5:1 to 15:1, wherein the one or more distillation steps are carried out under vacuum conditions.

6. The method according to claim 5, wherein the final distillation yield is greater than or equal to 85%, preferably 90% to 98%, relative to the crude product containing PBO.

7. The method according to claim 5 or 6, wherein the one or more distillation steps of the distillation method are each independently carried out under a degree of vacuum equal to or lower than 4000 Pa, preferably equal to or lower than 2000 Pa, more preferably in the range of 1500 Pa to 10 Pa.

8. The method according to any one of claims 5 to 7, wherein the rectification apparatus comprises a single distillation column.

9. The method according to any one of claims 5 to 7, wherein the rectification apparatus comprises 2 to 3 distillation columns operating in series or continuously.

10. The method according to any one of claims 5 to 9, wherein the rectification apparatus comprises at least one distillation column, each of the at least one distillation columns independently comprising 5 to 25, preferably 9 to 20, theoretical stages.

11. The method according to any one of claims 5 to 10, wherein the distillation apparatus equipped with rectification comprises at least one distillation column, each of the at least one distillation columns independently comprising a reflux ratio of 3:1 to 10:1, preferably 4:1 to 8:

1.

12. The method according to any one of claims 5 to 11, wherein the distillation apparatus comprises a boiler at a temperature of 170 °C to 270 °C, preferably 190 °C to 260 °C, more preferably 200 °C to 250 °C, to allow PBO to be distilled.

13. The method according to any one of claims 5 to 12, wherein the distillation apparatus operates continuously.

14. The method according to any one of claims 5 to 13, wherein the distillation method further provides for the use of an internal condenser and / or an external reboiler for each distillation column.

15. The method according to any one of claims 5 to 14, wherein the distillation apparatus, preferably the at least one distillation column, may include a withdrawal system for heavy degradation impurities and light degradation impurities, the withdrawal system including a final product withdrawal pump and a bottom product withdrawal pump, preferably connected to a bottom product collection tank and a top product collection tank, respectively.

16. A composition comprising PBO according to any one of claims 1 to 4, obtained by the distillation method according to claims 5 to 15.

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