Patent GB-815358-A (GB)
Title: A process for the manufacture of derivatives of polysaccharides, more particularly of starch, by a dry process
IPC: C08B31/00
Filed: 1957-06-25
Abstract: <PICT:0815358/III/1> Apparatus suitable for use in etherifying, esterifying or acetalizing polysaccharides by maintaining starch in a fluidized bed with a gas in the presence of a catalyst (see Group IV (a)) comprises, as shown, a conveyer 1 through which the polysaccharide is supplied to traverse zones 2, 6, 9, 10 and 11, the last three of which are accommodated in a common space, via overflows 21.  In each of the zones the polysaccharide is maintained in a dense phase fluidized condition by streams of gas from fans 3, 8 and 12. Nitrogen, CO2, air or superheated steam is used.  The control mechanisms 22 control the rate of flow of the polysaccharide between beds, the height of the bed and the residence time in the various zones.  The temperature in the zones is controlled by heating elements 19 surrounding the zones and 20 located in the fluidized bed.  In zone 2 the stream of gas, which may be heated, serves to predry the polysaccharide.  In zone 6 the catalyst is added via conduit 16 and/or 7.  The etherifying, esterifying or acetalizing agent is introduced via conduit 18 and/or 17.  Cyclones 4, 13 and 14 remove the polysaccharide entrained in the gas streams and the gases containing catalyst or reagent may be recirculated to the fans by conduits 23 and 24.  The polysaccharide product is removed from the apparatus via the conveyer 15.ALSO:<PICT:0815358/IV (a)/1> Polysaccharide derivatives are manufactured in a dry state by reacting the polysaccharide in a dense phase fluidized condition with an etherifying, esterifying or acetalizing agent, in the presence of a catalyst.  Suitable fluidizing gases are air, nitrogen, carbon dioxide, superheated steam or mixtures thereof. The polysaccharides may be native starches, such as potato starch, corn starch, cassava starch, wheat starch, sago starch, waxy starches or starches modified by heat, acids, or oxidants, such as dextrin or thin boiling starch, amylose, amylopectin, partially etherified, esterified or acetalized starches, wheat, rye or cassara flour, cellulose, gums such as Arabic, karaya, shiraz, tragacanth, carob, tamarind, guar, or konyak, pectin, alginates, insulin and their derivatives.  It may be desirable to pre-dry the starting materials or to add tricalcium phosphate, magnesia or other oxides, or inorganic or organic silicon compounds to increase the mobility of the polysaccharide.  The etherifying agents may be compounds containing reactive halogen (e.g. alkyl halides, halogen fatty acids, halohydrins or haloalkylsulphonic acids), epoxy compounds (e.g. ethylene oxide, glycidol or epichlorohydrin), unsaturated compounds (e.g. ethylene sulphonic acids or acrylonitrile), alkyl sulphates, diazomethane, or ethylene imine, methylol urea, methylol melamines or phenol or resorcinol formaldehyde pre-condensates.  The esterifying agents may be acid anhydrides of mono or polybasic acids, organic or inorganic acid chlorides, lactones (e.g. propiolactone), phosphates, ketenes or isocyanates.  The acetalizing agents comprise reactive aldehydes and ketones (e.g. formaldehyde, propionaldehyde, butyraldehyde or glyoxal) or products capable of splitting off aldehyde (e.g. paraformaldehyde or hexamethylene tetramine).  The etherifying, esterifying or acetalizing agent may be added prior to or during the treatment in fluidized condition. In the latter case the agent is preferably added in gaseous or vapour form.  The catalyst may be added prior to, simultaneously with or after the addition of the above agents.  Suitable catalysts are alkali hydroxides, alkaline earth hydroxides, organic compounds having an alkaline reaction, such as primary, secondary and tertiary amines, quaternary ammonium compounds, pyridine or urea.  Acid catalysts, such as inorganic acids, organic acids and acid anhydrides may also be used.  The process may be carried out continuously or batchwise.  The reaction temperature preferably ranges between room temperature and 200 DEG C. Elevated temperatures are provided by heating elements in and/or around the reaction space containing the fluidized bed.  The conversions may take place at atmospheric or increased pressure. The reaction apparatuses may comprise more than one fluidized bed, arranged in tiers or side by side.  In a suitable apparatus shown in the Figure, the polysaccharide introduced at 1 flows via overflows 21 successively through zones 2, 6, 9, 10 and 11 in which it is fluidized by gases from fans 3, 8 and 12.  The temperature is controlled by heating elements 19 and 20.  The polysaccharide is pre-dried by the gases in zone 2, catalyst is introduced in zone 6 and reaction takes place in zones 9, 10 and 11 with the etherifying, esterifying or acetalizing agent incorporated in the gas stream from fan 12, the product being removed at 15.  Alternatively the said agent may be introduced in zone 6 and catalyst in zones 9, 10 and 11. The gas streams containing catalyst or agent may be recirculated. The polysaccharide entrained in the gas stream is removed by cyclones and may be recycled.  In examples: (1) potato starch is fluidized in nitrogen, aqueous potassium hydroxide and ethylene oxide are introduced at 45 DEG  C. and after 2 hours the product is neutralized with a powdered organic acid; (2) carob gum mixed with potassium hydroxide is fluidized with air and nitrogen at 45 DEG  C. and ethylene oxide is introduced over 2 hours at 1-2 atmospheres, and after a total time of 3 hours the product is neutralized with a solid acid, e.g. citric acid; (3) the starch ether of (1) is mixed with ethyl-alcoholic hydrochloric acid and fluidized in air and nitrogen, the temperature being raised to 150 DEG  C. in 2 hours; (4) cassava starch is impregnated with phosphoric acid, mixed with silica gel and fluidized in nitrogen, whereupon ketene is introduced at room temperature and after three hours the starch acetate product is neutralized with ammonia; (5) corn starch containing sodium hydroxide and tricalcium phosphate is fluidized in air and reacted with epichlorhydrin at 50-60 DEG  C.; (6) potato starch is fluidized in air and a mixture of sodium monochloroacetate and caustic soda solution is sprayed into the bed, the temperature is raised to 100 DEG  C. for 30 minutes to form a carboxymethyl ether of starch; (7) cassava starch is mixed with sodium hydroxide and magnesia, fluidized with nitrogen, and reacted with formalin at 60 DEG  for three hours giving a hydroxymethylether of starch; (8) corn starch containing dimethylolurea is fluidized with air after mixing with silica gel, and is treated with hydrogen chloride for 1 hour at 80 DEG  C. and then neutralized with ammonia.