Sodium gluconate synthesis from oil palm frond: Optimization of neutralisation and purity enhancement through low-pressure nanofiltration

Sodium gluconate (SG) is a widely utilised organic salt within the construction sector, mainly employed as a cement additive and metal chelate. Using holocellulose-rich biomass such as oil palm frond (OPF) enables the sustainable production of SG. The present investigation was undertaken as an initial study into the independent neutralisation and separation of SG from other impurities utilising low-pressure nanofiltration. The experimental conditions for the neutralisation study involved varying the reaction temperature and the molar ratio of NaOH to Gluconic Acid (GA) to assess the quantity of SG produced. Subsequently, a separation experiment was conducted employing low-pressure nanofiltration, wherein the variables of membrane type, inlet gas pressure, and filtration time were systematically varied. The evaluation of nanofiltration performance in the separation of SG under the parameters mentioned earlier was conducted. According to the neutralisation investigations, the reaction temperature and excess NaOH had no significant effect on the accumulated mass of SG. The maximum quantity of SG generated across all GA: NaOH ratios was 281.270 mg due to the presence of other organic acids produced during the fermentation. The NF245 membrane exhibited higher rejection and recovery rates, indicating a superior selectivity towards SG compared to the NF270 membrane. Increased pressure led to higher flux, concentration, and rejection while reducing the SG recovery. A 90-min filtration of OPF hydrolyzate fermentation broth (OPFHFB) using an NF270 membrane at 9 bar led to a recovery of 97.35 %. Additionally, this process resulted in a 16 % (w/w) increase in the SG content.