Resumen de Sucrose crystallization by secondary nucleation
E. R. Asquieri, E. M. de Assis, G. E. Serra
The dissolution of sucrose ¡ti a 75 to 85% (w/w) (0/(, ethanol ni/ni) liydro alcoholic solution, permits an casy obtention of solutions with a hifli coctficient of super saturation due to the low solubility of sucrose in ctlia-nol. Furthermore, the rate oí' secondary nucleation is Iii2,---her in solutions with high coefficients of super satura-tion and this favors a high yield of crystal foririation. To dernonstrate the oecurrence of the secondary ¡in-cleation of sucrose, this SUgar was dissolved in a 80"/(, (w/w) hydro alcoliolic solution (ethanol). Sucrose p.a. was used in different quantitics for the preparation of the hydro alcoliolic solutions, with coeffi-cients of super saturation viirying from 1.0 to 9.0. The sucrose is diluted in distilled water, and this solution was mixed with the adeqUate amount of 93.8 % % (w/w) ethanol to obtain 300g of 80 % % (w/w) solution (it is impossible to dilute sucrose in a 80 % (w/w) solution). To induce the secondary nucleation of sucrose , seeding was perfórmed by the introduction of 100 nia of seed crystals (0.037 to 0.044miii). The seed was introduced into the Becker containin~ the solution that was bein- ma, itated, and this agitation was ¡Tiaintained for 60 i-ninLl-tes, guarantecin- cortiplete nueleation. The precipitated was dried at 40 'C, until a constant weight was reaclied. The working teniperature for nucleation was 30 'C. The results show that when a coefficient oí" super saturation of 8.0 is reached, the yicld of the suerose obtained by secondary nueleation, reaclies its maxi-Inum, with the precipitation of 82.9% of the suerose. Attention niust be drawn to the fact that the nuclea-tion yicld depends on the solution's alcobolic degree. This nicans that the alcoliolic degree interferes in the yield because of the different solubility of suerose. The solubility of suerose in a 80% (w/w) hydro al-coholic solution, at 30 'C, is 2.58g per 100g of the solvent. The tlicoretie maxiiiiiii---n yicld of sucrose mi-cleation shotild therefore be 89.75% of the sucrose pre-sent. Howevci-, the yicld obtained was 82.9%, irteaning that the efficiency of the process was 92.3%. The process, performed in the laboratory, for secon-dary nucleation of suerose in a 80% (w/w) hydro alco-holic solution, with a SUCfOSC COCffiCiCi1t Of SUper satLI-ration equal to 8.0, permits the production of precipitated amorphous suerose, with a yicid of 82.9%.
