| In the past, xanthan gum has been synthesized using stirred tank, bubble column, airlift or centrifugal fibrous bed fermentors. These technologies suffered from poor mixing, heat transfer, and mass transfer resulting in low productivity. Water-in-oil (W/O) multiphase cultivation technology can solve these problems and as a consequence, higher productivity is expected. But it requires the formation of fine droplets and easy phase separation to allow product recovery. To meet these requirements, new pH-sensitive polymers were created, characterized and applied to xanthan gum fermentation. The terpolymers of methacrylic acid (MAA), methoxy poly(ethylene glycol) methacrylate (MPEGMA), and lauryl methacrylate (LMA) were primarily studied here.; Polymers were synthesized with MAA: EG (ethylene glycol) repeat unit ratios of 20:1 and 1:1, respectively, to compare their behaviors at low and neutral pH. As expected from the H-bonding complexation between poly(methacrylic acid) and poly(ethylene glycol), the polymers with 1:1 MAA: EG ratio formed more stable emulsions at neutral pH and had lower surface-activity under acidic conditions. The content of the hydrophobic LMA was also varied (from 16 to 76 mol%, referred to MAA). The results indicated that the polymer with MAA:EG:LMA = 1:1:0.76 produced the finest and most stable emulsion, allowed an almost complete phase separation at pH 4, and showed no toxicity to the cells.; When the effect of two initiators (AIBN and hydrogen peroxide) was studied, AIBN gave the desirable polymer composition for more complete complexation at low pH. Polymer structure was elucidated via determination of the reactivity ratios of the monomers. The results suggested a primary structure of alternating blocks of MAA and LMA with randomly attached, lone PEG grafts. This data proposed the synthesis of polymers with methacrylate-terminated polystyrene replacing LMA which were also studied. Useful results were obtained to guide the future development.; Application of the polymeric surfactant in W/O xanthan fermentation was also evaluated. The polymer was confirmed to have the targeted properties of promoting the formation of very fine emulsions and allowing the easy phase separation at low pH. To optimize the new process, further fermentations with better control of parameters are suggested. |
