(117f) Ion-Exchange Equilibrium and Fixed-Bed Performance of the System Vanillin/Naoh-Amberlite Ir 120h

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is one of the most common aromatic molecules used in the food, pharmaceutical and cosmetic industries. There are two commercial types of vanillin, industrial vanillin obtained by chemical synthesis from guaiacol or black liquors from paper industry and a vanilla extract obtained by the ageing and alcoholic extraction of the pod of tropical Vanilla orchid (principally Vanilla planifolia Andrews, syn. V. fragrans (Salisb. Ames) [1,4,5]. The world market consists of around 1800 tons of pods, with the market price approximately $1200-$4000 per kilo, while industrial vanillin is around 12,000 tons and a market price is bellowing $15 per kilo [6,7]. That means vanilla extract is 250 times more expensive than synthetic vanillin, because of the complexity of the culture and tedious ageing process [5]. Nowadays, approximately 50% of the worldwide production of industrial vanillin is used by the chemical and pharmaceutical industries for the production of herbicides, antifoaming agents, household products or drugs. [1-3]. The antioxidant and antimicrobial properties are applied in use of vanillin as a food preservative [4,8,9]. It exhibits the activity against both Gram-positive and Gram-negative food-spoilage bacteria and also shows antimutagenic effect, for instance, as a suppressor of chromosomal damages [10-13]. The raw material for vanillin production can be any lignin-containing substance but pulp and paper industries still remain the main source of lignin [14]. The Kraft pulping process of wood delignification represents 2/3 of the production of lignin (30 million tons of Kraft lignin/year), and the remaining comes from sulfite process [15].The Kraft process is a method for cooking wood where a mixture of sodium hydroxide and sodium sulfite is used. Most of the studies of vanillin production were carried out with lignin from waste sulfite liquors. It has been well known since 1920s that lignin heated under reflux conditions for long times in the presence of active alkali produces maximum yield of vanillin [16,14] and this fact is still of theoretical interest from the point of view of lignin chemistry [17]. During the oxidation process, in addition of vanillin also other reaction products are formed such as oxidized lignin, acetovanillone, dehydrodivanillin, guaiacol, p-hydroxibenzaldehyde, and aromatic acids. The isolation of vanillin from oxidized solution is an important stage in vanillin production. The concentration of vanillin in solution cannot be significantly increased by evaporation because of the high solids content as well the vanillin is present as sodium vanillate, which is difficult to extract. Vanillin can be extracted from the solution with suitable solvents such as benzene or toluene after acidification of the liquor [18]. Disadvantage of this method is that a large amount of acidic solution is required for neutralization and also the precipitation of the lignin complicates the extraction and causes loss of vanillin [18]. The Lignin precipitation can be avoided by extraction of sodium vanillate from the alkaline solution, for instance with n-butyl alcohol or isopropyl alcohol [19, 20]. However, the limited solubility of sodium vanillate in organic solvents is a disadvantage of this process. In 1971 Craig and Logan provided an experiment using weak cation-exchange resins in acid form for vanillin isolation. The alkaline solution is eluted through the column filled with such a resin, sodium vanillate and other phenolates are converted into a phenolic form [21]. This last mentioned method we have find very interesting because can represents low cost and efficient process to obtain vanillin from reaction mixture. This idea became the main goal of the work we are presenting here. The ion-exchange equilibrium for Na+/ H+ ions as a relationship between fractions of the ions in the liquid phase and in the solid phase have been investigated. The alkalinity of vanillin was adjusted by adding sodium hydroxide to the solution which leads to vanillate formation. The sulphonic resin Amberlite IR 120H+ (strong cationic) has been used as the ion-exchanger. The studied ion-exchange process is accompanied by neutralization reaction, which leads to formation of inert water. As well, the reaction between vanillin and sodium hydroxide takes place and can be written as: , where VH is vanillin and V- is vanillate anion. The set of batch experiments (uptake curves) were evaluated in order to obtain the concentration behavior of the H+,Na+ , vanillin, vanillate species and pH according the time till equilibrium between liquid and solid phase is established. The fixed bed ion-exchange performance of Na+, H+ ions, vanillin and vanillate was studied in a laboratory scale by using the glass column with jacket (150 × 20 mm, I.D.) in order to investigate the influence of alkalinity on the ion-exchange process. The mathematical model has been developed and applied for studied system. Since a vigorous agitation of the solid/liquid system is maintained in the batch operation, as well high flow rate in column operations, external mass transfer was assumed neglected. In this ion-exchange process involving reaction, the mathematical model considers that the rate is controlled by diffusion within particle ? particle-diffusion control. The Nernst-Planck equation was applied for the fluxes of the ionic species.

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