Stabilising mannose using sodium dithionite at alkaline conditions

Abstract

The kraft process remains the dominant chemical pulping process but still struggles with extensive hemicellulose degradation. Such degradation has previously been mitigated through the use of anthraquinone; but due to it recently being found to have carcinogenic properties, anthraquinone is now being phased out. One alternative, sodium dithionite, was initially investigated in the 1950s but was found to be unviable. The present study investigated whether sodium dithionite could be made viable through the use of different processing parameters, using mannose as a model compound and measuring the yield of mannitol in the various systems using gas chromatography with flame ionization detection (GC-FID) and nuclear magnetic resonance (NMR). Alkalinity was found to be crucial; at pH 14 as well as pH 7, dithionite indeed proved unviable, but if pH was kept at either 8 or 10 significant reduction was seen to occur. The best results were obtained at pH 10 when a lower temperature (70°C) was used to compensate for alkaline degradation of the mannose reactant.

Pretreatment with Sodium Methyl Mercaptide Increases Carbohydrate Yield during Kraft Pulping

“…(iii) They should be reducing, avoiding the formation of unsaturated bonds that can undergo further peeling. 13 Although sodium borohydride is commonly used, it is expensive and adds the nonprocess element boron to the reaction conditions. 12 Recently, sodium dithionite was investigated but was unsuccessful in stabilizing mannose under kraft pulping conditions.…”

“…12 Recently, sodium dithionite was investigated but was unsuccessful in stabilizing mannose under kraft pulping conditions. 13 Sodium methyl mercaptide can be prepared by dissolving methyl mercaptan gas in an aqueous solution of sodium hydroxide (Scheme 1).…”

“…(ii) They should avoid nonprocess elements (i.e., include only H, C, O, S, and Na). (iii) They should be reducing, avoiding the formation of unsaturated bonds that can undergo further peeling . Although sodium borohydride is commonly used, it is expensive and adds the nonprocess element boron to the reaction conditions .…”