A method for extracting mannitol from kelp is characterized in that the harvested fresh kelp is cut into pieces and soaked in water twice the weight of kelp for 30-50 minutes; Adding alkali to the soaking solution to adjust the pH value, standing, floating and filtering to obtain a clear solution containing iodine and mannitol; Acidification and oxidation of clear liquid produce free iodine; Adsorbing with exchange resin to extract iodine; Adding alkali to the soaking solution after iodine extraction to adjust the pH value, evaporating, concentrating and precipitating, evaporating the feed solution to separate out salt, cooling and crystallizing, centrifuging and washing with water to obtain a mannitol semi-finished product; The semi-finished product is heated and dissolved by distilled water, decolorized by adding activated carbon, filtered to remove the activated carbon, diluted by filtrate, desalted, concentrated under reduced pressure, cooled and crystallized, centrifugally separated and dried to obtain refined mannitol. According to the invention, fresh kelp is used as a raw material for production, and a large amount of water is not needed to soak the raw material for a long time, so that the drying process of kelp is omitted, mannitol can not be crystallized and separated from the surface of kelp, the yield is improved, the production cost is reduced, and the process is simple and feasible.

Requirements:

A method for extracting mannitol from kelp is characterized in that the harvested fresh kelp is selected, accurately weighed, and then the following treatment processes are carried out: (a) soaking: chopping the weighed fresh kelp, pumping the chopped fresh kelp into a soaking pool for soaking for 30-50 minutes, and adding water which is twice the weight of the fresh kelp; (b) purification: putting the kelp soaking solution into a floating pool, adding alkali to adjust the PH value of the soaking solution to12-13, pumping air with a circulating pump, aerating and stirring for 20-30 minutes, standing for 2-3 hours, and filtering to obtain a clear solution containing iodine and mannitol; (c) Acidification and oxidation: hydrochloric acid is added into the clear solution containing iodine and mannitol, the PH value is adjusted to be between 65438 and 0.5-2, and then chlorine gas is added for oxidation, and the oxidation potential is kept between 550 and 650 millivolts, so that I- in the soaking solution is oxidized to I-2; (d) extracting iodine: passing the oxidized soaking solution containing free iodine through alkaline anion exchange resin to adsorb free iodine and extract iodine; (e) Mannitol extraction: putting the soaking solution after iodine extraction into a neutralization tank, adding alkali for neutralization, uniformly mixing with compressed air or a circulating pump, adjusting the PH value to 6.5-7, evaporating and concentrating with a three-way concentrator until the specific gravity is 65,438+/-0.2g/ml, and precipitating. The feed liquid was transferred to a single-effect concentrating tank, and evaporated under reduced pressure until the specific gravity was 1.4 ~ 1.5g/ml, most of the salt was precipitated, and mannitol remained in the solution; Naturally cooling and crystallizing the desalted solution in a crystallization tank, centrifuging to separate crude mannitol, and recrystallizing once with distilled water to obtain a mannitol semi-finished product; (f) Mannitol refining: adding 2 times of distilled water into the semi-finished product of Mannitol, heating to dissolve, adding 5% of activated carbon, heating to decolorize for 30-60 minutes, filtering to remove the activated carbon, diluting the filtrate to a specific gravity of 1.07- 1.08g/ml, desalting by ion exchange, concentrating under reduced pressure, cooling for crystallization, and centrifugal separation.