Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B3/00—Preparation of cellulose esters of organic acids
  • C08B3/06—Cellulose acetate, e.g. mono-acetate, di-acetate or tri-acetate
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B17/00—Apparatus for esterification or etherification of cellulose
  • C08B17/02—Apparatus for esterification or etherification of cellulose for making organic esters of cellulose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B31/00—Preparation of derivatives of starch
  • C08B31/02—Esters
  • C08B31/04—Esters of organic acids, e.g. alkenyl-succinated starch

Definitions

• the invention relates to a process for the continuous acetylation of polysaccharides.
• the process of acetylation of polysaccharides has long been known.
• the polysaccharide to be reacted is conventionally contacted with a mixture of acetic anhydride and anhydrous acetic acid and other additives in a stirred tank.
• the acetic anhydride reacts with the polysaccharide to polysaccharide (s) acetate and acetic acid.
• the acetic acid is instant
• Polysaccharide is usually fully acetylated, which is a partial acetylation but also possible according to the invention.
• the polysaccharide is inoculated with the aid of a catalyst.
• the catalyst is usually a strong acid.
• Added additives often have the role of the plasticizer of the polysaccharide, these usually react with and the reaction products can then be plasticizer of the polysaccharide (s) acetate.
• the activity of the catalyst increases with the temperature.
• the catalyst alters the polysaccharide and produces shorter molecules.
• the process is therefore characterized by accurate catalyst dosing and temperature control because the reaction is highly exothermic.
• this temperature control can be carried out by gradually adding the supercooled liquid reactants and the catalyst to the polysaccharide mass. Likewise, part of the heat can be dissipated through the cooling jacket of the stirred tank. This process is very slow due to the poor mixing performance of the stirred tank and the boiler must have a very large volume to accommodate the initially very light polysaccharide (low bulk density).
• GB 969 711 shows a process for the continuous acetylation of amylose. there the process is run at a certain temperature and at a certain pressure.
• the object of the invention is to find a continuous process and corresponding devices which make it possible to complete the acetylation with the lowest possible residence time in the reaction space with a high degree of conversion, in order at the same time to keep the production costs of the reactor small and the catalyst exposure time short. so that unwanted side reactions are suppressed.
• the polysaccharide and a portion of the liquid educts are premixed in an upstream unit and fed as a suspension to a continuous reactor, which is for example a mixing kneader, by means of a suitable conveying member in the process space of the reactor in which it is under a set pressure which corresponds to the boiling point of the acetic acid at the desired process temperature.
• a continuous reactor which is for example a mixing kneader
• the acetic acid and partially also the acetic anhydride therefore evaporates in parts, thus depriving the reactor of excess energy from the exotherm and being withdrawn through one or more bridgehead mounted on the reactor, condensed, and the process along with the liquid reactants and catalyst completely or partially recycled.
• This process creates a local dilution of the mixture in the recycle or feed zone, which favors the suspension of the polysaccharide in the feed zone, which in turn accelerates the reaction since the acetic anhydride gets easier access to the polysaccharide.
• the entry member into the process space according to the invention is a lock.
• Process space is metered, but the polysaccharide is previously suspended in sufficient amount of anhydrous acetic acid. Then it is pumped into a continuous sieve centrifuge or granulator operating under the same pressure conditions as in the reactor or the excess
• Acetic acid is separated again.
• the solid-acetic acid suspension is then pumped directly into the reactor or falls into it by gravity.
• Another advantage of this invention relates to the cooling of the condensate. It can be done by tempered cooling water, while the conventional process, the liquids must be overcooled or added as a solid to compensate for the exothermic energy.
• the process according to the invention allows by targeted recycling only parts of the acetic acid or by a downstream flash to adjust the residual content of acetic acid in Polysaccharidazetats.
• the partial stream not returned to the reactor can be reused directly in the premix.
• the process of the invention also allows to adjust the residual content of the polysaccharide acetate to acetic acid as desired. If too much acetic acid is present, a partial stream or the entire stream of the condensate is withdrawn from the recirculation and discharged separately. Since this substream is anhydrous, it can be reused directly or after conversion to acetic anhydride.
• the process according to the invention for the continuous acetylation of polysaccharide begins in a premixer 1, followed by a centrifuge 2. Thereafter, the product passes into a reactor 3, from which in turn the product is transferred via a flash 7 in a Vakuumausdampfer 8, from which then the final product is discharged.
• the starting materials or parts of the educts are continuously metered into the premixer 1 and homogeneously mixed there. Excess acetic acid may be mechanically separated in the case of using a centrifuge or otherwise. However, it is also possible that the suspension from the premixer 1 is pumped directly into the reactor 3 or falls into the reactor 3 via a vacuum lock.
• split metered portion further fractions of the split educts are fed directly to the reactor 3 continuously.
• This may be a catalyst, acetic anhydride or other additives.
• Acetic anhydride which is condensed in a condenser 4 and partly 5 or completely returned to the reactor or discharged at 6.
• the exhaust stream may be connected to a vacuum system, to control the product temperature (evaporation temperature) in the reactor.
• the polysaccharide acetate is introduced via flash 7 into a vacuum steamer 8 in which the residual acetic acid and acetic anhydride are removed. Is discharged polysaccharide.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Biochemistry (AREA)
• Materials Engineering (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2008
  • 2008-07-29 DE DE102008035401A patent/DE102008035401B4/de not_active Expired - Fee Related
• 2009
  • 2009-07-27 BR BRPI0916587A patent/BRPI0916587A2/pt not_active IP Right Cessation
  • 2009-07-27 CN CN2009801319026A patent/CN102124033A/zh active Pending
  • 2009-07-27 EP EP09777447A patent/EP2310420A1/de not_active Withdrawn
  • 2009-07-27 JP JP2011520371A patent/JP2011529510A/ja active Pending
  • 2009-07-27 US US13/056,326 patent/US20110213140A1/en not_active Abandoned
  • 2009-07-27 WO PCT/EP2009/005412 patent/WO2010012430A1/de active Application Filing

Non-Patent Citations (1)

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