Process for preparing high-purity L-arabinose by using arabic gum as raw material

A process for preparing high-purity L-arabinose from gum arabic, the process comprising the following steps:

• (1) adding dissolved gum arabic into an inorganic acid to form a mixed solution, controlling pH value of the solution at 0.2˜1, undertaking hydrolysis reaction at the temperature of 70˜100° C., after the reaction, neutralizing the hydrolysate by adding an alkali aqueous solution to reach pH of about 4˜7 and obtaining the neutralized hydrolysate containing L-arabinose;
• (2) adding the hydrolysate of step (1) to a fixed bed equipped with an adsorbent A continuously, collecting an effluent that passes through the adsorbent A to form a decolored solution;
• (3) passing the decolored solution of step (2) through a microporous membrane of a drainage to obtain a pretreatment solution, then desalinating the pretreatment solution by electrodialysis to obtain a desalination solution;
• (4) passing the desalination solution of step (3) through a fixed bed equipped with an adsorbent B continuously under room temperature, collecting an effluent that passes through the adsorbent B, obtaining a supersaturated syrup by concentrating the effluent that passes through the adsorbent B under reduced pressure at 45˜60° C.;
• and
• (5) crystallizing the supersaturated syrup and obtaining white powder of L-arabinose after drying;
• wherein the adsorbent A is one of granular activated carbon, non-polar macroporous polystyrene adsorption resin, weak polar macroporous polystyrene adsorption resin, non-polar macroporous acrylic adsorption resin, weak polar macroporous acrylic adsorption resin, non-polar gel-type polystyrene adsorption resin, weak polar gel-type polystyrene adsorption resin, weak polar gel-type polystyrene acid adsorption resin, non-polar gel-type acrylic adsorption resin and weak polar gel-type acrylic adsorption resin;
• wherein the process of the electrodialysis consists of the steps of:
• circulating the pretreatment solution in concentrated solution chamber and pure water in diluted solution chamber of an electrodialysis instrument respectively through electrode chamber that contains Na2SO4 as polar water and desalinating for 2˜5 hours under constant voltage and velocity;
• wherein the adsorbent B is one of non-polar macroporous polystyrene adsorption resin, non-polar macroporous acrylic adsorption resin, non-polar gel-type polystyrene acid adsorption resin, non-polar gel-type acrylic adsorption resin, granular activated carbon, and silica gel bonded with C18 or C30;
• wherein the process of the crystallization comprises the steps of:
• dissolving the supersaturated syrup of step (4) in alcohol, cooling the temperature to ambient temperature, inducing crystallization by adding some L-arabinose, filtering after crystallizing for 24˜72 hours, and obtaining pure L-arabinose with purity of 98% or higher after drying in a vacuum oven at 50˜60° C.;
• the alcohol is methanol or ethanol, the ratio of alcohol volume to the supersaturated syrup by weight is (6˜10) L:
• 1 kg, the cooling rate is 0.2˜3° C./min and crystallization temperature range is -5˜10° C.;
• wherein the inorganic acid is sulfuric acid, hydrochloric acid, phosphoric acid or mixture of two thereof and molar concentration of H+is 1˜6 mol/L;
• wherein the hydrolysis time is 1˜5 hours;
• wherein decolorization temperature of step (2) is 20˜55° C. and flow rate is 0.5˜3 bed volume/hour;
• wherein the mass concentration of Na2SO4 is 3% -˜8% and the volume ratio of the pretreatment solution and pure water is 1:
• 1˜3;
• and
• wherein the desalination conditions are as follows:
• operating voltage is 20˜30 V and the solutions flow rate is 10˜30 L/hours.