CN101845038B - Method and device for processing lactide refined raffinate - Google Patents
Method and device for processing lactide refined raffinate Download PDFInfo
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Abstract
The invention relates to a method for processing lactide refined raffinate and a processing device adopting the same. The method comprises the following steps of: (1) heating and flashing lactide refined raffinate to remove heavy components containing oligomers in the refined raffinate, thereby obtaining flashing steam; (2) condensing the flashing steam to obtain a flashing condensate; (3) extracting the flashing condensate by using water as an extractant to make m-lactide blend in a liquid phase and separate out L-lactide as a solid phase, thereby forming a solid and liquid-phase system; and (4) separating the solid and liquid-phase system to obtain a wet filter cake and filtrate. The processing device comprises a flashing device, a condensation, an extraction device, a solid-liquid separation device and a melting device which are connected mutually. The invention has the advantages of reasonable process, simple device and flexible operation mode, effectively realizes the yield separation and recycling of the oligomers, the m-lactide, lactic acid and the L-lactide, improves the total yield of the L-lactide, and is mainly used for a PLA synthesis process of an indirect-polymerization two-step method.
Description
Technical field
The present invention relates to a kind of lactide refined raffinate treatment process and utilize the lactide refined raffinate treatment unit of the method, belong to chemical field, be mainly used in PLA (poly(lactic acid)) synthesis technique of indirect polymerized two-step approach.
Background technology
Poly(lactic acid) (PLA) is to take the high molecular polymer that lactic acid (LA) makes as raw material.LA can make with biomass material (as cereal such as corns), and biomass material is renewable, and the product P LA of LA is biodegradable is carbonic acid gas and water, so PLA is described as " green fiber ".
The synthetic operational path of PLA has two kinds: direct polymerization single stage method and indirect polymerized two-step approach.High molecular PLA is made by two-step approach (rac-Lactide ring-opening polymerization), and this technique generally comprises that acid by dehydrating lactic, pre-polymerization, oligopolymer depolymerization cyclisation, crude lactide are refining, rac-Lactide ring-opening polymerization and the de-master operation such as single of polymkeric substance.
Crude lactide is mainly comprised of L-rac-Lactide (left-handed), m-rac-Lactide (meso), a small amount of oligopolymer, lactic acid and water etc., wherein m-rac-Lactide is the isomers impurity of L-rac-Lactide, and under the environment of oligopolymer and water existence, easily there are thermolysis, isomerization reaction etc., therefore, crude lactide is refined and is had larger difficulty.Crude lactide is refining can adopt the methods such as rectifying, fusion-crystallization, recrystallization, extraction, to make the rac-Lactide of purity >=99.5% (wt).Fusion-crystallization generally operates near the fusing point of crystallographic component, and service temperature is low, does not need other auxiliary agents or solvent, and energy consumption is low, environmental protection, the purification that is suitable for having thermo-sensitivity and contains the crude lactide of isomers impurity.In lactide refined technique, 15～25% (wt) that the refined raffinate amount that adopts fusion-crystallization technology to produce is crude lactide, and wherein rac-Lactide concentration is 55～65% (wt), therefore, must recycle lactide refined raffinate, to improve the total recovery of rac-Lactide.
Patent CN101555243A discloses a kind of preparation method and production equipment (referring to Fig. 1) of smart rac-Lactide, wherein relates to a kind for the treatment of technology of lactide refined raffinate.This technology is that lactide refined raffinate is carried out to centrifugal thin film evaporation unit processing, the separated gas phase rac-Lactide obtaining of evaporation turns back in the condenser system of depolymerization cyclisation top, or turn back to lactide refined operation after independent condenser system condensation, and the separated residue obtaining of evaporation turns back to pre-polymerization operation, or turn back to depolymerization cyclisation operation, or judge be unfavorable for improving rac-Lactide yield because foreign matter content is too high in the situation that discarded.
The problem that this technology exists is:
1, in process, do not consider processing or the separation of isomer impurities m-rac-Lactide, cause the accumulation of component m-rac-Lactide in depolymerization cyclisation, lactide refined and raffinate evaporating separation device, increased the energy expenditure in process;
2, the periodic separated residue of discharge evaporation, causes the flow and the periodical change of component concentration that enter depolymerization cyclisation, lactide refined and evaporating separation device, is unfavorable for the steady running of production system.
Summary of the invention
For overcoming the defect of prior art, the invention provides a kind of lactide refined raffinate treatment process and device, the method and device can be removed the m-rac-Lactide in lactide refined raffinate effectively, to reach the abundant reuse of refined raffinate, improve rac-Lactide yield, and do not affect the steady running of production system.
The object of the invention is to be achieved through the following technical solutions:
A treatment process, it comprises the following steps: (1) heating flash evaporation lactide refined raffinate, remove the heavy component that comprises oligopolymer in described refined raffinate, obtain flash vapors; (2) flash vapors described in condensation, obtains flash distillation lime set; (3) take water as extraction agent extracts described flash distillation lime set, make m-rac-Lactide wherein incorporate liquid phase, L-rac-Lactide is separated out becomes solid phase, forms solid-liquid two-phase system; (4) solid-liquid two-phase system described in solid-liquid separation, obtains wet cake and filtrate.
The vaporization temperature of described step (1) is preferably 200～250 ℃, and evaporating pressure is preferably 5～15mmHg.
The water extraction temperature of described step (3) is preferably 10 ℃～50 ℃, and water extraction is preferably 1: 2～3: 1 than (mass ratio between extraction water and flash distillation lime set), and the residence time is preferably 10min～60min.
The heavy component that conventionally, described step (1) can be obtained returns to the utilization of depolymerization cyclisation operation.
Noncondensable gas in described step (2) can be extracted out by vacuum system.
The filtrate that described step (4) can be obtained is sent into dehydration enrichment process and is recycled water soluble organic substance wherein.
After the wet cake fusing that described step (4) can be obtained, return to the utilization of pre-polymerization operation.
In addition, can, according to the rac-Lactide isomer impurities concentration in the crude lactide making in PLA synthesis technique and the difference of oligomer concentrations, to corresponding lactide refined raffinate, adopt following different mode to process:
(1) if in the crude lactide making isomer impurities exceed standard but oligopolymer seldom, stride across described step (1) and step (2), directly enter described step (3), adopting water is that extraction agent directly extracts lactide refined raffinate;
(2) if isomer impurities does not exceed standard in the crude lactide making, after described step (1) and step (2) processing, no longer carry out the processing of step (3) and step (4), the heavy component that described step (1) is obtained returns to the utilization of depolymerization cyclization process, and the material removing after heavy component is returned to the utilization of pre-polymerization operation;
(3), if the isomer impurities concentration in the crude lactide making and oligomer concentrations are all high, carry out successively the whole process of described step (1), step (2), step (3) and step (4) and process.
A kind of lactide refined raffinate treatment unit that adopts aforesaid method, it comprises flash distillation plant, condensing works, extraction plant and equipment for separating liquid from solid, described flash distillation plant is provided with treats flash distillation material inlet, flash vapors outlet and heavy component outlet, described condensing works is provided with treats condensation material inlet, lime set outlet and noncondensable gas outlet, described extraction plant is provided with material inlet to be extracted, extraction agent import and the outlet of extraction disposed slurry, described equipment for separating liquid from solid is provided with material import to be separated, filtered solid outlet and filtrate outlet, what the flash vapors outlet of described flash distillation plant connected described condensing works treats condensation material inlet, what the lime set outlet of described condensing works connected described extraction plant treats extraction liquid import, the extraction disposed slurry outlet of described extraction plant connects the material import to be separated of described equipment for separating liquid from solid.
Described flash distillation plant preferably adopts luwa evaporator.
Preferably, in described condensing works, be provided with gas-liquid separation device, described noncondensable gas outlet connects the bleeding point of vacuum system.
Described extraction plant preferably adopts extraction kettle, describedly treat that extraction liquid import and described extraction agent import are separately positioned on top and/or the top of described extraction kettle, described extraction disposed slurry outlet is arranged on bottom or the bottom of described extraction kettle, in described extraction kettle, is provided with agitator.
On the extraction disposed slurry outlet of described extraction plant and the connecting tube between the material import to be separated of described equipment for separating liquid from solid, generally should be provided with pump, the whizzer that described equipment for separating liquid from solid can adopt solid-liquid separation to use, described filtered solid outlet can connect melting pot by material transport mechanism conventionally, and described filtrate outlet can connect filtrate tank conventionally.
The invention has the beneficial effects as follows: the present invention utilizes isomer impurities m-rac-Lactide than being easier to water-soluble and being hydrolyzed L-rac-Lactide and being difficult to be dissolved in the principle in water, the mode extracting by water is separated m-rac-Lactide, thereby avoided the accumulation of m-rac-Lactide in system and a large amount of consumption of energy in treating processes, according to applicant's experiment, adopt after the present invention, the clearance of isomer impurities m-rac-Lactide can reach 90%～95%; Because can returning in the corresponding operation of PLA synthesis system, the various materials of separating by each steps such as flash distillation, condensation, water extraction, solid-liquid separation carry out reuse, reduced material quantity discharged, greatly improved the total recovery of rac-Lactide, according to applicant's experiment, adopt after the present invention, the total recovery of L-rac-Lactide compared with the existing technology can improve 5%～10%; Because treatment system can realize continuous work, can guarantee the steady running of whole PLA synthetic system; Owing to adopting water in extraction, be extraction agent, extraction conditions is gentle, easily realizes through engineering approaches, is conducive to process simplification, reduces production costs.
Accompanying drawing explanation
Fig. 1 is the process flow sheet that in CN101555243A, lactide refined raffinate is processed.
Fig. 2 is the process flow sheet that lactide refined raffinate of the present invention is processed.
Embodiment
Referring to Fig. 2, lactide refined raffinate treatment process provided by the invention and the lactide refined raffinate treatment unit that utilizes described method, effectively oligopolymer, m-rac-Lactide and L-rac-Lactide are separated from each other and can return respectively in the synthetic suitable operation of PLA and be used, reach the abundant recycling of refined raffinate and the object of minimizing discharge of materials, effectively improved L-rac-Lactide yield, and can not have a negative impact to the steady running of PLA synthesis system, possess good suitability.
First the present invention carries out heating flash evaporation to lactide refined raffinate in flash distillation plant, flash distillation plant can adopt luwa evaporator and other flashing apparatuss, a kind of preferably luwa evaporator wherein, luwa evaporator heat transfer coefficient is large, evaporation capacity is high, is adapted to especially the flash distillation operation of raffinate in the present invention.Under existing PLA synthetic technology, the content of sending into rac-Lactide in the refined raffinate of flash distillation plant can reach 55～65% (wt), m-rac-Lactide wherein, L-rac-Lactide and other separating substances of different nature need be come, to carry out respectively different recyclings, to be used.Owing to conventionally containing certain oligopolymer in raffinate, vaporization temperature in flash distillation operation can be controlled at 200 ℃～250 ℃, such as 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃ or 250 ℃, evaporating pressure can be controlled at 5mmHg～15mmHg, such as 5mmHg, 7mmHg, 9mmHg, 11mmHg, 13mmHg or 15mmHg.Conventionally, flash distillation plant is provided with treats flash distillation material inlet, flash vapors outlet and heavy component outlet, under above-mentioned processing parameter, oligopolymer in raffinate etc. form heavy component, from the heavy component outlet of flash distillation plant bottom, discharge, separate heavy component and can return to depolymerization cyclisation operation oligopolymer is wherein used, the flash vapors that contains m-rac-Lactide and L-rac-Lactide etc. is discharged from the flash vapors outlet at flash distillation plant top, by pipeline, be transported to and in condensing works, carry out condensation process.
Described condensing works is provided with treats condensation material inlet, lime set outlet and noncondensable gas outlet, what the flash vapors outlet of flash distillation plant connected condensing works by pipeline treats condensation material inlet, flash vapors is from treating that condensation material inlet enters condensing works, through condensation, rac-Lactide in flash vapors, lactic acid and other organic components are condensed into liquid phase, form flash distillation lime set, from lime set outlet, discharge and send into extraction plant by pipeline, noncondensable gas can be drawn out of from noncondensable gas outlet by vacuum system.
Impurity in described flash distillation lime set mainly comprises m-rac-Lactide and lactic acid, in order further to remove these impurity, to entering the described flash distillation lime set of extraction kettle, extracts.Because isomer impurities m-rac-Lactide ratio is easier to be dissolved in water and is hydrolyzed, L-rac-Lactide is difficult to be dissolved in water, therefore by water, extracts, and isomer impurities m-rac-Lactide is dissolved in water, and lactic acid is also soluble in water simultaneously, forms liquid phase.Overwhelming majority L-rac-Lactide, with solid separation, has formed solid-liquid two-phase system in extraction kettle, by follow-up solid-liquid separation, just L-rac-Lactide can be separated with m-rac-Lactide and lactic acid.
Described extraction plant can adopt extraction kettle, extraction tower or other suitable extraction equipments, described in the housing top of described extraction plant can be provided with, treats extraction liquid import and extraction agent import, and bottom can be provided with described extraction disposed slurry outlet.Described extraction agent adopts the water at low temperature of optimal temperature, and the temperature of described extraction can be 10 ℃～50 ℃, such as 10 ℃, 20 ℃, 30 ℃, 40 ℃ or 50 ℃; Water extraction can be 1: 2～3: 1 than (extraction water is with the mass ratio of flash distillation lime set) conventionally, such as 1: 2,1: 1,3: 2,2: 1,5: 2 or 3: 1, the residence time can be 10min～60min, such as 10min, 20min, 30min, 40min, 50min or 60min, to reach good effect of extracting.Described flash distillation lime set enters extraction kettle from the extraction liquid import for the treatment of of described extraction kettle, extraction agent import (being water at low temperature import) as the water at low temperature of extraction agent by described extraction kettle enters extraction kettle, and described solid-liquid two-phase system (extraction disposed slurry) can be discharged from the extraction disposed slurry outlet of described extraction kettle.
For described solid-liquid two-phase system is carried out to solid-liquid separation, described solid-liquid two-phase system enters equipment for separating liquid from solid after discharging from the extraction plants such as described extraction kettle.On the connecting tube of described extraction plant and equipment for separating liquid from solid, pump is set, by pump, described extraction disposed slurry is transported to described equipment for separating liquid from solid.
Described equipment for separating liquid from solid can adopt prior art or the other technologies of any suitable, such as rotary drum filter-press etc., these equipment for separating liquid from solid are typically provided with material import to be separated, filtered solid outlet and filtrate outlet, extraction disposed slurry can be separated into the filter cake that contains L-rac-Lactide and the filtrate of containing m-rac-Lactide, lactic acid.Described wet cake can be discharged and send into melting appartus by the material transport mechanism of suitable structure from filtered solid outlet, and described filtrate can be discharged and send into Filtrate collection device by modes such as pipelines from described filtrate outlet.
In the wet cake that described equipment for separating liquid from solid produces, comprise most L-rac-Lactide, in order to realize the reuse of these L-rac-Lactides, wet cake further need to be melted, therefore, wet cake is admitted to melting appartus and melts after the filtered solid outlet of described equipment for separating liquid from solid is discharged, and the pre-polymerization operation that the wet cake after fusing can be sent into PLA synthesis system by the mode of the adaptations such as pipeline is used.Described melting appartus can adopt prior art or the other technologies of any suitable, for example, possess the melting pot of heating unit, and described melting appartus inside can be provided with agitator to improve fusing effect.
In described filtrate, contain the water-soluble organic components such as m-rac-Lactide and lactic acid, in order to reach the recycling of these organic components, filtrate can be collected in Filtrate collection device after described equipment for separating liquid from solid is discharged, to continue to send into the synthetic dehydration enrichment process of PLA, is used.Described Filtrate collection device can adopt prior art or other technologies arbitrarily, for example filtrate tank, reservoir or other suitable equipment.
Technical process of the present invention is: from the lactide refined raffinate of PLA synthesis system, be admitted to the flash distillation plants such as luwa evaporator and carry out heating flash evaporation, the flash vapors obtaining discharges and sends in condenser from the flash vapors outlet of described luwa evaporator, flash distillation in luwa evaporator removes thing heavy components such as () oligopolymer and discharges and collect through the heavy component outlet of described luwa evaporator, the flash vapors that enters described luwa evaporator condenser is condensed, m-rac-Lactide wherein, L-rac-Lactide and lactic acid enter liquid phase, form lime set, noncondensable gas is extracted out by the vacuum system being connected with described luwa evaporator condenser, lime set is further admitted to extraction kettle, adopt water extraction herein, in described water extraction still, m-rac-Lactide and lactic acid dissolution become liquid phase in water, L-rac-Lactide is insoluble in water and is precipitated and becomes solid phase, thereby form solid-liquid two-phase system, for L-rac-Lactide is carried out effective separated with major impurity (comprising m-rac-Lactide and lactic acid), described solid-liquid two-phase from the extraction disposed slurry outlet of described water extraction still discharge and by pump delivery to whizzer, through solid-liquid separation, obtain wet cake and filtrate, separated wet cake contains a large amount of L-rac-Lactides, being admitted to melting pot melts with standby, separated filtrate is contained a large amount of organic components, liquor collecting device (filtrate tank) is collected with reuse after filtration.
Can select part processing step wherein to process accordingly, and omit wherein unwanted step according to the rac-Lactide isomer impurities concentration in the crude lactide making in PLA synthesis technique and the difference of oligomer concentrations, for example:
(1) if in the crude lactide making isomer impurities exceed standard but oligopolymer seldom, contained oligopolymer has a negative impact can to operation, yield and the quality product of PLA synthesis system, can stride across described step (1) and step (2), directly enter described step (3), adopting water is that extraction agent directly extracts lactide refined raffinate;
(2) if isomer impurities does not exceed standard in the crude lactide making, contained m-rac-Lactide has a negative impact can to operation, yield and the quality product of PLA synthesis system, after described step (1) and step (2) processing, no longer carry out the processing of step (3) and step (4), the heavy component that described step (1) is obtained returns to the utilization of depolymerization cyclization process, and the material removing after heavy component is returned to the utilization of pre-polymerization operation;
(3) if the isomer impurities concentration in the crude lactide making and oligomer concentrations are all high, operation, yield and/or quality product that not separating meeting affect PLA synthesis system have a negative impact, and should carry out successively the whole process of described step (1), step (2), step (3) and step (4) and process.
Claims (2)
1. a lactide refined raffinate treatment process, is characterized in that comprising the following steps: (1) heating flash evaporation lactide refined raffinate, remove the heavy component that comprises oligopolymer in described refined raffinate, and obtain flash vapors, flash distillation plant adopts luwa evaporator, (2) flash vapors described in condensation, the rac-Lactide in flash vapors, lactic acid and other organic components are condensed into liquid phase, form flash distillation lime set, obtain flash distillation lime set, (3) take water as extraction agent extracts described flash distillation lime set, make m-rac-Lactide wherein incorporate liquid phase, L-rac-Lactide is separated out becomes solid phase, forms solid-liquid two-phase system, (4) solid-liquid two-phase system described in solid-liquid separation, obtain wet cake and filtrate, the heavy component that described step (1) is obtained returns to the utilization of depolymerization cyclisation operation, noncondensable gas in described step (2) is extracted out by vacuum system, the filtrate that described step (4) is obtained is sent into dehydration enrichment process and is recycled water soluble organic substance wherein, after the wet cake fusing that described step (4) is obtained, return to the utilization of pre-polymerization operation, the vaporization temperature of described step (1) is 200～250 ℃, evaporating pressure is 5～15mmHg, the water extraction temperature of described step (3) is 10 ℃～50 ℃, water extraction is than being 5:2～1:1, the residence time is 10 min～60min,
The clearance of isomer impurities m-rac-Lactide reaches 90%～95%, and treatment system realizes continuous work, guarantees the steady running of whole PLA synthetic system.
2. a lactide refined raffinate treatment unit that utilizes method described in claim 1, it is characterized in that comprising flash distillation plant, condensing works, extraction plant and equipment for separating liquid from solid, described flash distillation plant is provided with treats flash distillation material inlet, flash vapors outlet and heavy component outlet, described condensing works is provided with treats condensation material inlet, lime set outlet and noncondensable gas outlet, described extraction plant is provided with material inlet to be extracted, extraction agent import and the outlet of extraction disposed slurry, described equipment for separating liquid from solid is provided with material import to be separated, filtered solid outlet and filtrate outlet, what the flash vapors outlet of described flash distillation plant connected described condensing works treats condensation material inlet, what the lime set outlet of described condensing works connected described extraction plant treats extraction liquid import, the extraction disposed slurry outlet of described extraction plant connects the material import to be separated of described equipment for separating liquid from solid, the heavy component that described flash distillation plant is obtained returns to the utilization of depolymerization cyclisation operation, noncondensable gas in described condensing works is extracted out by vacuum system, the filtrate that described equipment for separating liquid from solid is obtained is sent into dehydration enrichment process and is recycled water soluble organic substance wherein, after the wet cake fusing that described equipment for separating liquid from solid is obtained, return to the utilization of pre-polymerization operation, described flash distillation plant adopts luwa evaporator, in described condensing works, be provided with gas-liquid separation device, described noncondensable gas outlet connects the bleeding point of vacuum system, described extraction plant adopts extraction kettle, describedly treat that extraction liquid import and described extraction agent import are separately positioned on top and/or the top of described extraction kettle, described extraction disposed slurry outlet is arranged on bottom or the bottom of described extraction kettle, in described extraction kettle, be provided with agitator, the extraction disposed slurry outlet of described extraction plant and the connecting tube between the material import to be separated of described equipment for separating liquid from solid are provided with pump, the whizzer that described equipment for separating liquid from solid adopts solid-liquid separation to use, described filtered solid outlet connects melting pot by material transport mechanism, described filtrate outlet connects filtrate tank.
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| CN111548339A (en) * | 2020-04-10 | 2020-08-18 | 深圳光华伟业股份有限公司 | Process for preparing glycolide from glycollate |
| CN111693559B (en) * | 2020-06-22 | 2022-04-01 | 中国核动力研究设计院 | Vapor droplet mass flow separation measuring device and method for gas-phase mixture |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1112559A (en) * | 1993-12-08 | 1995-11-29 | 株式会社武藏野化学研究所 | Method for purification of lactide |
| CN101555243A (en) * | 2008-04-11 | 2009-10-14 | 株式会社日立工业设备技术 | Manufacturing method and device of cyclic refined lactic acid dimmer and manufacturing method and device of polylactic acid |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1112559A (en) * | 1993-12-08 | 1995-11-29 | 株式会社武藏野化学研究所 | Method for purification of lactide |
| CN101555243A (en) * | 2008-04-11 | 2009-10-14 | 株式会社日立工业设备技术 | Manufacturing method and device of cyclic refined lactic acid dimmer and manufacturing method and device of polylactic acid |
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Effective date of registration: 20170203 Address after: 100007 Beijing, Dongzhimen, North Street, No. 9, No. Patentee after: China National Petroleum Corporation Patentee after: China Kunlun Engineering Co., Ltd. Address before: 100007 Beijing, Dongzhimen, North Street, No. 9, No. Patentee before: China National Petroleum Corporation Patentee before: China Textile Industrial Engineering Institute |