Ion Exchange Processes

Another direct method to recover vanillin from the oxidized liquor is based on adsorption and ion exchange principles. Using a strong sulfonic acid resin in its Na+ form, sodium vanillate can be separated from lignosulfonates, sodium hydroxide and sodium carbonate, which are eluted first [166, 167]. This treatment should be performed between oxidation and extraction steps in vanillin production showing as main advantages the separation of around 80% of dry matter, lignin, and sodium from vanillin reactor effluent and the smaller quantity of acid needed to neutralize the vanillin fraction when compared to other processes. Moreover, the ion exchange resin does not require regeneration step and the lignin and the sodium can be returned to the chemical recovery of the pulp mill without any neutralization [166].

The process patented by Logan [168] reported weak ion exchange resins in acid form for vanillin isolation. In this case, the sodium vanillate and other phenolates contained in the alkaline oxidized solution were converted into a phenolic form. This is one of the steps in designed cyclic recovery of vanillin. This invention describes the suitable treatment for vanillin reactor effluent where any type of weak cationic resin may be used since it accepts sodium ion from the sodium hydroxide solution and also can be regenerated back to the hydrogen form. This particular method applying a strong cationic resin in H+ form was also studied in detail by Zabkova et al. [134] including the influence of the alkalinity and con­centration of the vanillin solution on the ion exchange process. The presence of a buffer system comprising of vanillin/vanillate in the ion exchange process affects the expected rectangular behavior of isotherm in ion exchange coupled with neutralization reaction. Recently, non-polar macroporous resins have been applied for separating vanillin and syringaldehyde from oxygen delignification spent liquor [137]. It was verified that adsorption equilibrium constant decreased remarkably with the increasing pH due to the acid dissociation of the aromatic aldehydes, since ionic species are not adsorbed by these resins. The recoveries of vanillin and syringaldehyde were 96.2 and 94.7%, respectively [137].

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