Studies On Simultaneous Reaction-Separation Process For Alginate Production

Recently, alginate production has been a mature industry in the world. Howeverthe high water consumption associated with high waste water producing, and highsodium carbonate consumption have been the critical problem to be solved to satisfythe requirements for modern industry with green, cost-effective. This work aimedsuch technical problems and investigated the dissolution kinetics of Laminariadigitata, and then based on the fact that high viscosity of dissolved solution preventsthe filtration, causing quantity of water addition for dilution, simultaneousreaction--separation was induced in the alginate extraction to improve the process.At first, as the dissolution principle of Laminaria japonica is the substitution of(Ca, Fe, Mg, Al) ions by sodium ion. Thus the contents of Ca, Fe, Mg, Al inLaminaria japonica was determined first to calculate the theoretical amount ofsodium carbonate. The results shown that the main ions was Ca，and then wasmagnesium. The theoretical amount of sodium carbonate to substitute all the highvalue metal ions was103.6gram per kg Laminaria japonica, which corresponding to0.25tons sodium carbonate producing1tons alginate. The dissolution kinetics ofsodium alginate extracted from Laminaria japonica and its influence factors includingreaction temperature， concentration of Na2CO3， stirring rate and size of algae piecewere investigated. The results have shown that with the increases of reactiontemperature，concentration of Na2CO3，stirring rate and the decrease of block size ofLaminaria japonica piece，the dissolution rate was increased obviously. Both therecovery rate of sodium alginate and quality，especially the viscosity of the productfrom Laminaria japonica were also evaluated. An optimal dissolution condition wasdetermined as follows：0.5%Na2CO3concentration，60℃of digestion temperature， 200r/min of stirring rate and20mm of the size of algae piece. In this condition， theproduct recovery rate could reach more than22%，and the viscosity of sodiumalginate products was greater than20000mPa.s. The results offered the theoreticalfoundation of the optimized process for alginate extraction.The main step in the extraction protocol used in the alginate industry is that of abatch process for alkaline extraction，which contains a series of steps. In this paper，anew extraction technology for alginate was proposed. The possibility of extracting bysimultaneous reaction--separation extraction was investigated. The optimal conditionwas determined as follows: adding300mL of a0.5%Na2CO3solution in thebeginning， adding100mL1%Na2CO3solution every15min in the process. Thealginate recovery of95%is achieved in this condition. Compared with the traditionalprocess，the water consumption reduces27%and the time reduces12h, while theviscosity of sodium alginate products increase3000mPa.s. The results have shownthat the process appeared to be more efficient than the batch process for the alkalineextraction of alginate. The alginate was separated from impurities in the extractionprogress to avoid the difficulty of the follow-up separation by filtration. Moreover，reaction separation extraction has the advantage of being a continuous process. Thismakes the reaction separation extraction process for alginate extraction interestingeconomically.In order to further reduce the sodium and water consumption，homogeneouspretreatment way in the reaction--separation integrated process was applied. Theeffect of homogeneous pretreatment on extraction yield and alginate productivity andviscosity was investigated. It shows that an optimal condition was determined asfollows:20s of dealing the Laminaria japonica with300mL of a0.5%Na2CO3solution，every15min of adding proper volume and1%Na2CO3solution. At which,water consumed reduced27%, and sodium carbonates reduced12%，the total reactiontime was shortened12hours, and the alginate recovery rate increased4%. Comparedwith the traditional process，reaction--separation integrated process with homogenouspretreatment would be an good choice for alginate extraction.