JP2010168415A - Apparatus and method for recovering lactide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and method for recovering lactide from a lactic acid polymer composition containing aluminum hydroxide. <P>SOLUTION: The apparatus for recovering lactide includes a temperature controllable cylinder and a screw rotatably disposed inside of the cylinder for transporting the lactic acid polymer composition supplied from one end of the cylinder and releasing the same from the other end thereof. The cylinder is provided with vent sections at least three locations in a longitudinal direction of the cylinder for taking out a volatile component from the cylinder to the outside. Any of the vent ports of the vent sections is, via piping, connected to a cooling trap which is vacuum sucked by a vacuum generating source. The apparatus is designed such that lactide is vacuum sucked from the vent section downstream of the cylinder while water is vacuum sucked from the vent section upstream of the cylinder. The recovery method of lactide uses the apparatus. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to water generated from aluminum hydroxide by decomposing a polylactic acid component into lactide from a lactic acid polymer or a resin composition containing lactic acid polymer and aluminum hydroxide, or a composition containing an alkaline earth metal compound. The present invention relates to a lactide recovery device for separately recovering lactide and lactide, and a lactide recovery method using the recovery device.

In recent years, there has been a demand for recycling of flame retardant resin compositions used as parts in accordance with the movement of recycling household appliances, IT devices, and automobiles. Lactic acid polymers, which are plastics derived from renewable resources, will be used for home appliances, IT and automobile parts for the purpose of suppressing carbon dioxide generation, and their recycling will be necessary in the future. Therefore, for that purpose, development of a technique for making a resin composition containing a lactic acid polymer flame retardant and a technique for decomposing and recovering the lactic acid polymer as a raw material is desired.

So far, various catalysts have been found when recovering raw material lactide by thermal decomposition of lactic acid polymer. For example, as a method for recovering high purity lactide from high molecular weight lactic acid polymer, alkaline earth metal compound Japanese Patent Application Laid-Open No. H10-228561 discloses a method of using a catalyst as a catalyst. Patent Document 2 discloses that, for lactide recovery from high molecular weight polylactic acid, an alkaline earth metal, for example, magnesium oxide, functions as a catalyst that gives high optical purity lactide.

On the other hand, in order to make a lactic acid polymer flame-retardant, a method using a safer metal hydroxide such as aluminum hydroxide as a flame retardant is already known in several documents (Patent Document 3). Or 4). However, since flame retardancy aims to suppress the combustion of lactic acid polymer and thermal decomposition at high temperature, the policy to recover lactide as raw material by depolymerization of lactic acid polymer in the flame retardant composition It has not been studied in the past. In recent years, when aluminum hydroxide, which is a metal hydroxide flame retardant, is used, it has been found that aluminum hydroxide itself also acts as a depolymerization catalyst for lactic acid polymers (Non-patent Document 1). The present inventors have also proposed a chemical recycling technique for a lactic acid polymer composition containing a metal hydroxide such as aluminum hydroxide as flame retardant (Patent Document 5).

However, since aluminum hydroxide needs to be added in a large amount in order to exhibit sufficient flame retardancy, when a lactic acid polymer composition containing aluminum hydroxide is heated, a large amount of water is generated, and the water is generated by the lactic acid polymer. A new problem has been found in that it is mixed with lactide generated by thermal decomposition of bismuth and reacts with lactide to reduce its optical purity. No countermeasure technology for this problem has been disclosed yet. Therefore, in order to recover lactide with higher yield and higher purity, there has been developed a method for effectively separating water and lactide generated from aluminum hydroxide and recovering higher purity lactide with higher yield. It is desired.

International Publication No. 2003/91238 Pamphlet JP 2008-231048 A JP 2003-192929 A JP 2004-075752 A International Publication No. 2005/105775 Pamphlet

Nishida, Sakai, Mori, Daiyagi, Shirai, Endo "Industrial & Engineering Chemistry Research, Vol. 44, No. 4, 1433-1437 (2005)"

An object of the present invention is to provide a lactide recovery apparatus capable of separately sucking and recovering water derived from aluminum hydroxide and lactide derived from a lactic acid polymer from a lactic acid polymer composition containing aluminum hydroxide, and a lactide recovery method using the same. Is to provide.

In order to solve the above problems, a lactide recovery apparatus of the present invention is an apparatus for recovering lactide from a lactic acid polymer composition containing aluminum hydroxide, and includes a temperature-adjustable cylinder and one end of the cylinder. A screw rotatably disposed inside the cylinder for transferring the supplied lactic acid polymer composition and discharging it from the other end, and the cylinder has a vent for taking out volatile components from the cylinder; There are at least three portions in the longitudinal direction of the cylinder, and the vent ports of the vent portion are all connected via a pipe to a cooling trap that is vacuum-sucked by a vacuum generation source. It is configured so that moisture can be vacuum-sucked from the upstream vent part and lactide from the downstream vent part.

The method for recovering lactide according to the present invention is provided in a rotatable manner inside the cylinder for transferring a temperature-adjustable cylinder and a polymer composition supplied from one end of the cylinder and discharging it from the other end. The cylinder is provided with at least three vent portions in the longitudinal direction of the cylinder for taking out volatile components from the cylinder, and all the vent ports of the vent portion generate a vacuum. A lactic acid polymer composition containing aluminum hydroxide is supplied to a recovery device connected via a pipe to a cooling trap that is vacuumed by a source, and the temperature of the cylinder and the degree of vacuum (decompression) of the vent port are adjusted. On the other hand, water is collected from the upstream vent port and lactide is collected by vacuum suction from the downstream vent port.

According to the present invention, when lactide is recovered by thermal decomposition from a composition containing aluminum hydroxide and a lactic acid polymer or a composition containing an alkaline earth metal compound, water generated by a dehydration reaction of aluminum hydroxide. This can avoid the adverse effects caused by the hydrolysis of lactide, etc., such as a decrease in yield and a decrease in optical purity, and it is possible to efficiently recover higher purity lactide. According to the present invention, water is sucked from the vent port on the upstream side (polymer composition supply side) of the cylinder of the recovery device, and lactide is vacuum sucked from the vent port on the downstream side (discharge side of the decomposition product). However, it is possible to vacuum-suck water from the first vent port and lactide from the second and subsequent vent ports, counting from the upstream side.

FIG. 1 is a schematic view for explaining a lactide recovery apparatus and recovery method of the present invention.

Hereinafter, the present invention will be described with reference to FIG. The recovery device of the present invention is basically like a screw extruder, and rotates a temperature-adjustable cylinder 1, two screws 2 rotatably arranged in the cylinder, and two screws. And a rotational drive mechanism (not shown) including a motor and a speed reducer. There may be one screw. The temperature of the cylinder can be adjusted by suitable heating means (not shown). A hopper 3 is arranged on the most upstream side of the cylinder, and sequentially from the hopper toward the downstream side, a first vent part 4, a second vent part 5, a third vent part 6, and a further vent part 7, And a die 8 is provided. The raw lactic acid polymer composition supplied from the hopper 3 at one end of the cylinder is transferred by the rotation of the screw, a decomposition reaction occurs in the middle thereof, and the remaining portion of the decomposition product is discharged from the die 8 at the other end. In FIG. 1, four vent portions are provided in the longitudinal direction of the cylinder, but in the recovery device of the present invention, at least three vent portions are required, and three or four are preferable.

Each vent port 4a, 5a, 6a, 7a of vent parts 4, 5, 6, 7 leads to a recovery part (not shown) consisting of a cooling trap, a receiver, and a decompression device via a pipe, Moisture, which is the main recovered material from the first vent port, is recovered by an independent recovery unit. The second and subsequent vent ports are connected to an independent recovery unit composed of the same system, and have a structure in which mixing with moisture is suppressed. The recovery unit including the cooling trap, the receiver, and the pressure reducing device is a normal unit including a cooling trap and a receiver that are vacuumed by a vacuum generation source such as a vacuum pump.

In the present invention, the lactic acid polymer composition containing aluminum hydroxide is supplied from the hopper 3 of the recovery device of FIG. 1 and is gradually transferred to the other end by the rotation of the screw. In the present invention, the lactic acid polymer composition containing aluminum hydroxide is first heated at a temperature of less than 220 to 270 ° C., for example, while being transferred through the cylinder, and the dehydration reaction of aluminum hydroxide proceeds to generate generated moisture. Is preferentially vaporized from the first vent port 4a controlled under a reduced pressure of 10 kPa or more, cooled in a cooling device (not shown) temperature controlled to 50 ° C. or less, and liquefied or solidified to be recovered. . At this time, if the cylinder temperature is 220 ° C. or lower, the dehydration reaction of aluminum hydroxide does not proceed effectively, and if it is 270 ° C. or higher, the thermal decomposition of the lactic acid polymer proceeds and lactide is generated. Absent. A more preferable temperature range during this period is a temperature range of 245 to 265 ° C, and a more preferable vacuum (decompression) range of the vent port is 15 kPa or more.

Next, in the zone after the second vent port 5a, the lactic acid polymer composition is heated and decomposed at a temperature of 270 to 330 ° C., and the generated lactide is vented 6a after the second vent port 5a under a reduced pressure of 10 kPa or less. , 7a is volatilized and discharged. The discharged lactide is cooled and solidified and recovered in a cooling device whose temperature is controlled at 50 ° C. or lower. At this time, water generated from the aluminum hydroxide is volatilized at the same time, but under a reduced pressure of 10 kPa or less, it is not cooled and liquefied or solidified in the cooling device, and is discharged as it is, so that it is effectively separated from lactide. . The produced aluminum oxide and other decomposition products are discharged from the die 8.

However, when a large amount of water is generated, lactide and water react in the process of volatilization / discharge / recovery, and lactic acid and oligomers are easily generated as hydrolysis products. Accordingly, in the present invention, a technique for first discharging and separating the water generated and volatilized at a lower temperature is disclosed, whereby the reaction between lactide and water is reduced, and higher purity lactide is higher. Recovered in yield.

In the present invention, the lactic acid polymer means a polymer (homopolymer or copolymer) containing a lactic acid ester structure as a basic unit as a main component as described below, and the lactic acid polymer composition means such a polymer and others. The resin component or various additives and the like. As the lactic acid polymer composition, if the lactic acid polymer component is 10% by weight or more, selective chemical recycling is possible without any problem. However, considering practical operation efficiency, the lactic acid polymer composition is preferably 20% by weight or more.

In the present invention, the lactic acid polymer is a polymer having a lactic acid ester structure as a basic unit, and in particular, the L- or D-lactic acid ester structure unit is 90% or more, preferably 95% or more, more preferably 98% of all units. The above polymer. As components other than the L- or D-lactic acid ester structural unit, there may be a copolymer component unit derived from lactones, cyclic ethers, cyclic amides, cyclic acid anhydrides and the like copolymerizable with lactide. Is possible. Suitable copolymerization components include lactones such as caprolactone, valerolactone, β-butyrolactone, and baradioxanone; cyclic ethers such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, phenylglycidyl ether, oxetane, and tetrahydrofuran; cyclic amides such as ε-caprolactam; cyclic acid anhydrides such as succinic anhydride and adipic anhydride.

Furthermore, as initiator components, alcohols, glycols, glycerols, other polyhydric alcohols, carboxylic acids, polycarboxylic acids, phenols, etc. are used as units that can coexist in the lactic acid polymer of the present invention. It is done. Specific examples of suitably used initiator components include ethylhexyl alcohol, ethylene glycol, propylene glycol, butanediol, polyethylene glycol, polypropylene glycol, polyvinyl alcohol, glycerin, octylic acid, lactic acid, glycolic acid and the like.

In the present invention, when the lactic acid polymer composition containing aluminum hydroxide is thermally decomposed, an alkaline earth metal compound may be used in combination as a decomposition catalyst in order to accelerate the heat decomposition. The alkaline earth metal compound used in the present invention need not be special. Commonly known alkaline earth metal compounds include calcium compounds, magnesium compounds, barium compounds, and the like, and oxides, hydroxides, carbonates, salts with organic acids, and the like are preferably used. A mixture of these may also be used. Preferably, a calcium compound and a magnesium compound are preferably used because of their availability. More preferably, magnesium oxide is suitably used from the viewpoint of the thermal decomposition reaction selectivity.

By coexisting aluminum hydroxide with alkaline earth metal compounds such as magnesium oxide and calcium oxide, the thermal decomposition temperature of the lactic acid polymer can be lowered, and the anti-racemization effect of aluminum hydroxide is more effective. To express. The particle size of the alkaline earth metal compound to be used is preferably 0.01 to 50 μm, and the mixing amount is preferably 0.01 to 10 parts by weight, more preferably 0. 2 to 5 parts by weight.

When, for example, magnesium oxide or calcium oxide is used as a thermal decomposition catalyst in the lactic acid polymer composition containing aluminum hydroxide, the composition containing only aluminum hydroxide is thermally decomposed in a lower temperature range. However, it is a preferred method for recovering higher purity lactide. For example, in the case of magnesium oxide, a range of 270 to 300 ° C. is suitable.

As described above, the method of the present invention heats a composition containing aluminum hydroxide and a lactic acid polymer, or another general-purpose resin or an alkaline earth metal compound, in a cylinder of a recovery device like a screw extruder, By converting aluminum hydroxide to aluminum oxide and lactic acid polymer to lactide, effectively separating the volatilized lactide and water under controlled pressure conditions, and recovering them by cooling or liquefying is there.

The thermal decomposition method of the lactic acid polymer or the composition thereof is not particularly limited to those properties, and arbitrarily set conditions of the recovery device, that is, the temperature, the degree of vacuum, the number of rotations of the screw, the amount of general-purpose resin, and water The amount of aluminum oxide and the like can be adjusted. Moreover, this thermal decomposition reaction can employ | adopt either a batch type or a continuous type.

Thermal decomposition of the lactic acid polymer or composition thereof requires heating at a temperature of 270 to 330 ° C. When the thermal decomposition temperature is higher than 330 ° C., the racemization of lactide is promoted and the yield decreases. On the other hand, when the thermal decomposition temperature is lower than 270 ° C., a dehydration reaction occurs, but the thermal decomposition reaction of the lactic acid polymer or its composition does not proceed effectively.

The degree of vacuum (decompression) at the vent port of the vent part is set to a pressure condition equal to or lower than the saturated vapor pressure of lactide at the thermal decomposition temperature. The lower the pressure, the lower the distillation temperature, which is preferable. However, if the distillation temperature is too low, the distilled lactide solidifies and clogs the recovery device, so the degree of vacuum is higher than the lactide solidification temperature. It is preferable to adjust the degree of decompression at the thermal decomposition temperature so as to be.

The screw rotation speed is not particularly limited, but is generally within a range of 100 to 400 rpm. If the rotation exceeds 400 rpm, the adverse effect of local heat generation tends to occur, and if it is 100 rpm or less, the recovery amount tends to decrease. More preferably, the screw rotation is preferably adjusted at 150 to 200 rpm.

The thermal decomposition time can be arbitrarily set depending on the screw rotation speed, the processing amount, the degree of decompression, the property of the lactic acid polymer or the composition thereof, and the amount of aluminum hydroxide to be used. Therefore, it is preferable to carry out in a shorter time.

Moreover, about aluminum hydroxide in this invention, the aluminum hydroxide used with a flame retardant can be used without a restriction | limiting at all. Among these, a particle diameter of 0.1 to 50 μm is particularly preferable because it is effective for the decomposition reaction of the lactic acid polymer.

Further, the recovery device of the present invention is most effectively used as a continuous screw extruder.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

(1) Method for Analyzing Lactide Component Analysis of a lactide component can be performed by gas chromatography and ¹ H-NMR method. A specific measurement method is exemplified as follows.

The gas chromatograph (GC) analysis was performed using Shimadzu GC-2014 equipped with a Varian cyclodextrine-β-236M-19 capillary column (0.25 mm × 50 m), and the carrier gas was helium, injector, and column temperature. Perform at 220 and 150 ° C. isothermally. About 3 mg of a sample is dissolved in 1 mL of acetone, and 1 μL of the solution is injected from an injector to perform measurement. L, L-lactide, meso-lactide, and D, D-lactide were detected as independent peaks at retention times of 8.15, 6.25, and 8.58 minutes, respectively, and the composition ratio was calculated from the peak area. Is done.

^{For 1} HNMR measurement, INOVA300 manufactured by JEOL is used, deuterated chloroform (CDCl ₃ ) is used as a solvent, and the signal of tetramethylsilane is measured as a reference value (0 ppm) of chemical shift δ. L, L / D, D-lactide and meso-lactide are detected as doublet peaks independent of 1.68 and 1.72 pm, respectively, and the composition ratio is calculated from the integrated intensity ratio of the peaks.

(2) How to determine the lactide recovery rate (%)
In the collection flask connected to each bend port of the collection apparatus (having three vent parts) as shown in FIG. 1, the weight of solid or liquid lactide collected within a certain time is weighed. The recovery rate can be calculated based on the following equation from the comparison with the weight of the polylactic acid introduced into the recovery device within the same time.

Lactide recovery rate (%) = (weight of recovered lactide / weight of supplied polylactic acid) × 100

(3) How to determine the water recovery rate (%)
Aluminum hydroxide undergoes a dehydration reaction by heating and changes to aluminum oxide (alumina). The theoretical weight loss at that time is 34.6%. However, although the weight loss reaches a theoretical value by heating up to 600 ° C., it does not reach the theoretical value in the temperature range during chemical recycling. Therefore, the weight loss value in the actual chemical recycling temperature range is obtained by thermogravimetry. Thermogravimetric results confirm that aluminum hydroxide exhibits a 28.4% weight loss during heat treatment up to 265 ° C and a 30.5% weight loss during heat treatment up to 330 ° C. . Therefore, considering the chemical recycling process in the temperature range up to 330 ° C, the maximum value of moisture generated from the aluminum hydroxide used in this process is 30.5%, and the amount of moisture vaporized and recovered within a certain time The recovery rate can be calculated based on the following formula from comparison with the weight of aluminum hydroxide supplied to the recovery device within the same time.

Moisture recovery rate (%) = (weight of recovered water / (weight of supplied aluminum hydroxide × 0.305)) × 100

[Examples 1-2]
Polylactic acid (L-form = 99.1% ee, melting point 160-175 ° C., manufactured by Unitika Ltd.), polypropylene (Nippon Polypropylene Co., Ltd. FY-6: MFI = 1) in the proportions (parts by weight) shown in Table 1. 7) Powder composition of a composition made of aluminum hydroxide (B1403 manufactured by Nippon Light Metal Co., Ltd .: particle size 2 μm), put this into a hopper of a recovery device having three vent parts, and rotational speeds of 150 and 200 rpm And kneading using a twin screw. The zone up to the first vent part was heated at a temperature of 245 to 265 ° C., and the water generated by the dehydration reaction of aluminum hydroxide was vaporized under a reduced pressure of 15 kPa from the first vent port. Vaporized water vapor was guided to a cooling device directly connected to the first vent port and controlled to a temperature of 50 ° C. or lower, and recovered by cooling or solidifying.

On the other hand, the composition in the recovery device is sent to a heating zone having a second vent part, and the composition is heated at a predetermined temperature within a range of 299 to 303 ° C. in the zone of the second vent part to the third vent part. The polylactic acid component was converted to lactide. The produced lactide volatilized from the second and third vent ports whose pressure was adjusted under a reduced pressure of 2.4 to 3.3 kPa. The volatilized lactide was directly connected to the second and third vent ports and guided into a cooling device controlled to a temperature of 50 ° C. or lower, and cooled and solidified to be recovered as high-purity lactide.

Table 2 shows the products recovered in 10 minutes after lactide started to distill. When the product was analyzed, the amount of water recovered from the first vent port was 27.0 and 36.0%. The recoveries of lactide recovered from the second vent port and the third vent port were 69.0 and 74.7%.

The composition of the collected lactide was analyzed using a gas chromatographic method. The results are shown in Table 3. The purity of the recovered L, L-lactide was 91.1% (second vent port) and 93.6% (third vent port) in Example 1, and 97.2% (second vent) in Example 2. ) And 92.2% (third vent port). Moisture that volatilized simultaneously with lactide from the second and third vent ports was discharged without being liquefied or solidified in the cooling device due to a high degree of vacuum, and separated from lactide.

[Comparative Examples 1-2]
For Examples 1 and 2, the first vent port for selectively removing moisture was blocked, and lactide and moisture were simultaneously recovered using only the second vent port and the third vent port. The operating conditions are shown in Table 1, and the products recovered in 10 minutes after the start of the distillation of lactide are shown in Table 2. As a result, the yields of lactide recovered from the second vent port and the third vent port were 42.6% and 56.8%. The composition of the collected lactide was analyzed using a gas chromatographic method, and the results are shown in Table 3.

The purity of the recovered L, L-lactide was 78.7% (second vent port) and 80.4% (third vent port) in Comparative Example 1, and 78.3% (second vent) in Comparative Example 2. Mouth) and 82.5% (third vent mouth). At this time, a low recovery rate and a low L, L-lactide purity were obtained as shown in Tables 2 and 3 in spite of setting a high pressure reduction condition of 3.6 kPa. This is because a large amount of water discharged simultaneously with lactide reacted with lactide during the discharge process.

[Examples 3 to 4]
With respect to the conditions of Examples 1 and 2, 0.14 parts by weight of magnesium oxide (particle diameter 4 μm) was further added to recover lactide from the polylactic acid / polypropylene / aluminum hydroxide composition. Tables 1 to 3 show the test conditions, the lactide and water recovery ratios, and the composition ratio of the obtained lactide. As a result of the chemical recycling test carried out at a screw rotational speed of 150 (Example 3) and 200 rpm (Example 4), the amount of water recovered from the first vent port was 22.3% and 28.0%. The recovery rates of lactide recovered from the second vent port and the third vent port were 82.3% and 93.0%, which were higher than those obtained with aluminum hydroxide alone.

The purity of the recovered L, L-lactide was 92.4% (second vent port) and 86.0% (third vent port) in Example 3, and 94.1% (second vent) in Example 4. Mouth) and 90.0% (third vent port), and high L, L-lactide purity almost the same as in Examples 1 and 2 using only aluminum hydroxide as the decomposition catalyst was obtained. The water volatilized simultaneously with the lactide from the second and third vent ports is discharged without being cooled or liquefied or solidified in the cooling device and separated from the lactide in the cooling device because of the high degree of decompression, as in Examples 1-2. It was.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Screw 3 Hopper 4 1st vent part 5 2nd vent part 6 3rd vent part 7 4th vent part 8 Die

Claims (3)

An apparatus for recovering lactide from a lactic acid polymer composition containing aluminum hydroxide, wherein the apparatus transfers a temperature-adjustable cylinder and the lactic acid polymer composition supplied from one end of the cylinder to the other end. And a screw that is rotatably disposed inside the cylinder, and the cylinder is provided with at least three vent portions for taking out volatile components out of the cylinder in the longitudinal direction of the cylinder. Each of the vent ports of the vent part is connected to a cooling trap that is vacuum-sucked by a vacuum generation source through a pipe, and moisture is supplied from the upstream vent part of the cylinder to the downstream side. An apparatus for recovering lactide, characterized in that lactide can be vacuumed from the vent. A temperature-adjustable cylinder, and a screw rotatably disposed inside the cylinder for transferring a polymer composition supplied from one end of the cylinder and discharging it from the other end. At least three vent parts are provided in the longitudinal direction of the cylinder for taking out volatile components out of the cylinder, and all the vent ports of the vent part are connected to a cooling trap that is vacuumed by a vacuum generation source. The lactic acid polymer composition containing aluminum hydroxide is supplied to the recovery device connected via the control port, and moisture is supplied from the upstream vent port while adjusting the temperature of the cylinder and the degree of vacuum (decompression) of the vent port. A method for recovering lactide, wherein the lactide is recovered by vacuum suction from a downstream vent port. The lactide polymer composition according to claim 2, wherein the lactic acid polymer composition containing aluminum hydroxide contains 0.01 to 10 parts by weight of at least one alkaline earth metal compound with respect to 100 parts by weight of the lactic acid polymer. Collection method.

Images