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There are two basic forms of devolatilization to a vacuum. In foam devolatilization, bubbles inside the polymer solution nucleate and grow, finally bursting and releasing their volatile content to the surroundings. This requires sufficient vapor pressure. If possible, this is a very efficient method
218:
Co-rotating twin screw extruders: The polymer solution is brought into a co-rotating twin screw extruders, where it is subjected to shear and mechanical energy input and where vapors are drawn off. This type of machine allows different pressures in different zones. An advantage is the self-cleaning
188:
Falling strand devolatilizers: Polymer is partitioned into many individual strands which fall down in a vacuum chamber. Diffusion moves volatiles into the gas phase, which are then collected via a vacuum system. This is usually the last stage of a devolatizing process, when vapor pressure is
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167:
Film devolatilization occurs when there is no longer sufficient vapor pressure to generate bubbles, and requires on sufficient surface area and good mixing. In this case, stripping agent such as nitrogen may be added to the polymer to induce improved mass transfer through bubbles.
119:. Because of the low diffusion coefficients of volatiles in polymers, this can be the rate-determining step. This effect can be enhanced by higher temperatures or by small diffusion lengths due to its higher
102:
of volatiles needs to be higher in the polymer than in the other phase for them to leave the polymer. In order to design such a process, the activity needs to be calculated. This is usually done via the
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228:: Polymer solution is brought into a single large vessel, where a rotor agitates the product and creates surface renewal. Only a single pressure level is possible in these machines.
39:, may cause bad sensory properties such as an unpleasant smell or worsen the properties of the polymer. It may also be desirable to recycle monomers and solvents to the process.
19:, also known as polymer degassing, is the process of removing low-molecular-weight components such as residual monomers, solvents, reaction by-products and water from polymers.
31:
reaction, many polymers still contain undesired low-molecular weight components. These component may make the product unusable for further processing (for example, a
208:: A polymer solution is preheated and brought into a separator, where pressure below the vapor pressure of the solution leads to a part of the volatiles evaporating.
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Devolatilization can be carried out when a polymer is in the solid or liquid phase, with the volatile components going into a liquid or gas phase. Examples are:
107:. This effect can be enhanced via higher temperatures or lower partial pressure of the volatile component by applying an inert gas or lower pressure.
386:, "Continuous process for the extraction of monomers and oligomers from highly polymerized caprolactam granules", published 1968-03-19
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629:
354:
Winkelmann, H; Liebhold, J (2006). "Wirtschaftliches
Aufbereiten von ungetrocknetem PET auf gleichläufigen Zweischneckenextrudern ZE".
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Devolatilizers for polymer melts are classified as static or moving, also called "still" and "rotating" in the literature.
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It is usual for different types of devolatilization steps to be combined to overcome limitations in the individual steps.
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Higher temperatures can also affect the chemical stability of the polymer and thus its use properties. If a polymer's
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Single-screw extruders: In principle similar to co-rotating twin screw extruders, without the self-cleaning action.
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into a separator. Polymer is collected at the bottom, vapor is collected via a vacuum system and condensers.
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also occurs during devolatilization, limiting the temperature and residence time available for the process.
195:: Polymer falls down vertical walls, volatiles diffusing on the side that is not in contact with the walls.
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In order to be removed from the polymer, the volatile components need to travel to a phase boundary via
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Because polymers and polymer solutions often have a very high viscosity, the flow in devolatilizers is
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is exceeded, it will partially revert to its monomers, destroying its usability. More generally,
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Lechner, F (2006). "Entgasen von
Polymerschmelzen mit gleichläufigen Doppelschneckenextrudern".
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Diener, A; Kunkel, R (2006). "Kontinuierliche
Eindampfung und Entgasung von Polymerschmelzen".
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Dohrn, R; Pfohl, O (2006). "Entfernen von FlĂĽchtigen aus
Polymeren: Physikalische Grenzen".
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Rust, H (2006). "Trocknung und
Aufbereitung von PET mit dem Planetwalzenextruder".
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Becker, D; Pfeiffer, A (2006). "Devolatilization on single-screw extruders".
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Aufbereitungstechnik 2006 - Entgasungsprozesse in der Aufbereitungstechnik
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Aufbereitungstechnik 2006 - Entgasungsprozesse in der Aufbereitungstechnik
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Tube evaporators: A boiling polymer solution flows downward in a vertical
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can also involve removal of water and volatile degradation products.
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and subjected to shear at longer residence times than in an
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Large-volume kneaders: A polymer solution is brought into a
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König, T; Kohlgrüber, K (2006). "Entgasung von Polymeren".
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cannot directly be used for plastics processing), may be
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because the volatiles only need to diffuse a short way.
405:, "Polymer treatment", published 2006-09-28
252:and suspensions, for example in the production of
573:Co-Rotating Twin-Screw Extruders: Applications
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558:Strömungssieden hochviskoser Polymerlösungen
428:. New York: Reinhold Publishing Corporation.
55:Solid polymer, liquid phase: Extraction of
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248:Removal of monomers and solvents from
73:Liquid polymer, gas phase: Removal of
62:Solid polymer, gas phase: Removal of
7:
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560:(PhD thesis). Universität Bochum.
184:Static devolatilizers include:
27:When exiting a reactor after a
159:Foam vs. film devolatilization
1:
507:Gestring, Ingo (2002-11-11).
200:shell and tube heat exchanger
105:Flory–Huggins solution theory
89:Physical and chemical aspects
70:via air or nitrogen in silos.
571:KohlgrĂĽber, Klemens (2021).
660:Verein Deutscher Ingenieure
606:Verein Deutscher Ingenieure
533:Verein Deutscher Ingenieure
481:Verein Deutscher Ingenieure
445:Verein Deutscher Ingenieure
360:Verein Deutscher Ingenieure
331:Verein Deutscher Ingenieure
219:action of those extruders.
59:from polyamides with water.
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296:Albalak, Ramon J. (1996).
137:heat transfer coefficients
632:. List AG. Archived from
424:Teach; Kiessling (1960).
298:Polymer devolatilization
17:Polymer devolatilization
193:Falling film evaporator
556:Liesenfelder, Ulrich.
510:Entgasen von Polymeren
226:Wiped-film evaporators
100:thermodynamic activity
213:Moving devolatilizers
180:Static devolatilizers
690:Chemical engineering
233:large-volume kneader
695:Process engineering
153:polymer degradation
149:ceiling temperature
47:Basic process types
630:"Devolatilization"
577:Carl Hanser Verlag
143:Chemical stability
586:978-1-56990-781-8
206:Flash evaporators
135:, leading to low
41:Plastic recycling
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426:Polystyrene
384:US 3374207A
81:via vacuum.
79:polystyrene
57:caprolactam
684:Categories
640:2021-08-22
260:References
23:Motivation
117:diffusion
111:Diffusion
700:Polymers
237:extruder
64:ethylene
133:laminar
75:styrene
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