(287f) Separation of Acids From Fast Pyrolysis Bio-Oils Using Nanofiltration Membranes

Bio-oil produced by fast pyrolysis is a complex mixture of acids, alcohols, sugars and other multifunctional compounds. The total acid number (TAN) of bio-oil is relatively high due to the presence of organics acids, like acetic and formic. Reducing the acid content of the bio-oil is particularly important to improve long-term stability and ease of processing. We are exploring the use of nanofiltratiom (NF) membranes to reduce TAN of bio-oils.

Initially we used single and mixed solute solutions of acetic acid and glucose as model solutions for our experiments: the effect of concentration on their retention was studied. GE Osmonics Sepa CF II cell was used for permeation experiments. The feed solution was kept around 25 °C and the membrane pressures in the experiments ranged from 5 to 20 bar. The feed flow varied from 0 to 10 L/hr.

In both the single and mixed solute experiments, the glucose retention is larger than acetic acid for all the membranes used. Glucose retention is decreased as the feed concentration is increased, in both cases, whereas acetic acid retention is not much affected by feed concentration. Compared to single solute experiments, glucose retention is decreased in the presence of acetic acid. The decrease is varied from slight to moderate from membrane to membrane. On the other hand acetic acid retention is unchanged. At transmembrane pressure of 10 bar and 0.2 M feed concentration, the retention of glucose and acetic acid are 80% and 5% respectively which makes the separation feasible.

Finally, we are currently performing NF experiments with the aqueous fraction of actual bio-oils from an industrial pyrolysis stream. The reduction in the TAN number is used to characterize the efficiency of separation.