Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B30/00—Preparation of starch, degraded or non-chemically modified starch, amylose, or amylopectin
  • C08B30/12—Degraded, destructured or non-chemically modified starch, e.g. mechanically, enzymatically or by irradiation; Bleaching of starch
  • C08B30/16—Apparatus therefor
• • 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
• • 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
  • C08B31/08—Ethers
  • C08B31/12—Ethers having alkyl or cycloalkyl radicals substituted by heteroatoms, e.g. hydroxyalkyl or carboxyalkyl starch

Definitions

• modified starch products such as starch ethers and starch esters
• starch ethers and starch esters are often used as additive in the food and paper industry.
• applications of inter alia hydroxypropyl starch are the use as additive in textile printing and as size for corrugated board.
• the production of modified starch with a low molar substitution is done on an industrial scale by reaction of a suitable reagent, for instance ethylene oxide, propylene oxide or vinyl acetate, in an aqueous slurry of starch.
• the invention contemplates providing a solution to one o more of these problems and is partly based on the insight th the problem of poor reproducibility and homogeneity of the product can be obviated at least partly by distributing the added lye homogeneously in the slurry.
• the invention accordingly relates to a method for continuously modifying starch, wherein a suspension of starc granules (slurry) in an aqueous liquid is heated to a temperature at which still no gelatinization occurs, then ly and reagent are continuously fed to the suspension, with the lye and optionally also the reagent being distributed homogeneously in the slurry, whereafter by means of electromagnetic radiation the mixture is further heated to temperature desired for complete gelatinization and the modification and the mixture is fed to a reactor section provided with static mixing elements.
• the invention is based on the surprising insight that b special combination of measures the objects of the inventio can be realized. Of importance in this combination is first the preheating of the suspension of starch particles to a temperature at which still no gelatinization occurs. Preferably, this preheating is effected to a temperature which is not more than 15, preferably not more than 10 and more particularly not more than 5°C below the temperature at which gelatinization will occur.
• a second aspect of the invention is concerned with the homogeneous feed of lye, which means that the lye is uniformly distributed throughout the entire slurry in a shortest possible period of time, while in the liquid substantially no concentration gradient of the supplied component over the cross section of the space arises.
• the modifying reagent often an alkene oxide or vinyl acetate, preferably ethylene oxide and/or propylene oxide, is added simultaneously with the lye or prior thereto.
• this addition is also effected homogeneously, although this seems to be less critical.
• a third aspect of the invention is concerned with the homogeneous heating of the continuously gelatinizing mixture by means of electromagnetic radiation, in short, with a magnetron.
• Heating the continuously gelatinizing mixture with a magnetron leads to a highly uniform rise in temperature, so that the viscosity of the mixture over a cross section of the reactor remains the same. This prevents any substantial spread in the residence time due to differences in viscosity.
• Other methods of heating entail the problem that the non-uniform distribution of the heat, for instance due to a gradient over the cross section of the reactor, gives rise to large viscosity differences, as a consequence of which parts of t reactor content "shoot through" while other parts linger fo long time. The result is a marked difference in product quality in the reactor output.
• modified starch which satisfies the conditions in the introduction. More particularly, a homogeneous and reproducible product of a low sodium hydroxide (lye) conten is obtained.
• the various process conditions can be chosen by the skilled person, depending on the final products actually desired.
• the nature of the substitution and the degree of substitution partly determine the process conditions, such as the amount of lye, the preheat temperature, and so forth.
• these variables also depend on the amount of starch in the suspension, which may for instance be between 10 and 45% by weight.
• the lye solution preferably with a concentration of from 0.05 to 5 molar, is to be adde homogeneously, it being sufficient to use a concentration o maximally 300 mol/m 3 slurry.
• This can be effected with advantage by feeding the lye and optionally also the alkene oxide to the slurry in a tubular reactor segment using one or more supply tubes which are arranged axially in the tubular reaction segment, and which supply tubes are provided with radial outlet openings.
• Heating of the mixture is effected to a temperature which will be dependent on the degree of substitution and on the nature of the substituent, as well as on the amount of lye. It is noted that the supplied lye not only (partly) effects the gelatinization, but can also catalyze the modification reaction, for instance the etherification or the esterification reaction. Preferably, heating is effected to a temperature between 60 and 120°C, whereafter the heated mixture reacts further in the section of static mixing elements.
• a reactor is depicted which is suitable for the practise of the method according to the invention.
• the reactor 1. is provided with a supply for the starch slurry 2, which slurry is mixed in mixing chamber 3 with reagent and lye. These are supplied via feed lines 4 and 5. It is of great importance in this connection that the feed of lye via line 5 takes place uniformly throughout the liquid. According to the invention, this can be achieved by providing the feed line 5 at the end thereof with radial openings, indicated by arrow 6. After passing the mixing chamber, the gelatinizing slurry enters reactor section 7, which is provided with static mixing elements 8, for instance SMX ® elements.
• the slurry is further heated to the temperature desired for the complete gelatinization and modification, by means of electromagnetic radiation generated with microwave unit 9.
• the reaction can be continued further in react segments (not shown) provided with static mixing elements, whereafter finally the modified starch can be discharged fr the reactor and be processed further into a form that is suitable for sale and/or be stored.
• a slurry consisting of 34.8% by weight of starch granul in water was fed at a flow rate of 3.07xl0" 3 kg/s to a reac as depicted in the drawing.
• This slurry had been heated in preheating unit (not shown in the drawing) to a temperature 57°C.
• preheating unit not shown in the drawing
• 0.21 g/s propylene oxide and 0. g/s of a 4 molar lye solution were continuously added to th slurry.
• the resultant highly viscous liquid was then heated a temperature of 90°C in the mixing section 8 by means of t microwave unit 9. After a residence time of 300 s in the reactor section of the reactor, which was also maintained a

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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)
• Crystallography & Structural Chemistry (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)

Applications Claiming Priority (3)

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• 1994
  • 1994-08-31 NL NL9401412A patent/NL9401412A/nl not_active Application Discontinuation
• 1995
  • 1995-08-25 WO PCT/NL1995/000283 patent/WO1996006866A1/en not_active Application Discontinuation
  • 1995-08-25 AU AU32319/95A patent/AU3231995A/en not_active Abandoned
  • 1995-08-25 EP EP95928638A patent/EP0778850A1/en not_active Withdrawn

Non-Patent Citations (1)

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