Microfiltration of Lignocellulosic Hydrolyzates Using Dead End Filtration to Separate Lignin

Microfiltration of lignocellulosic hydrolyzates using dead end filtration to separate lignin and other inhibitors

B. Bhayani, B.V. Ramarao

Department of paper & Bioprocess engineering, SUNY ESF

In the production of biofuels from lignocellulosics, the biomass is first extracted using dilute mineral acids or hot water. This hemicellulose rich oligomers are hydrolyzed under treatments at higher temperature and pressure to yield sugar monomers which are fermented into biofuels such as ethanol, biobutanol or bioplastics.  The initial treatment with either dilute acids or hot water also allows some of the lignin to pass in particulate, colloidal or dissolved forms into the sugar solution. Lignin and other phenolic compounds derived from it are strongly inhibitory to microbial fermentation processes. They also adhere to polymeric membranes, carbohydrates and other surfaces, fouling separation membranes. Their removal from the liquor stream not only facilitates downstream separations but improves the fermentation profiles of the resulting sugar hydrolyzates. Therefore, methods to separate lignin from liquors and hydrolyzates form valuable additional operations in the biorefineries.

A new approach has been developed which can separate inhibitory components from the extracts based on the fact that reduction of temperature of the biomass hydrolyzates can result in the native agglomeration and separation of lignin containing solids by simple settling and/or filtration which thus can result in large increases in separation efficiencies for hydrolyzates. By filtering the extracts at lower temperature (10ºC) it is possible to obtain higher flux rate than at higher temperatures (20ºC).  As shown in Figure 1 and Figure 2, the cumulative flow for extracts at 10ºC is higher than the extracts at 20ºC at two different pressures. The turbidity of permeate for any given combination of pressure and temperature was less than 10 NTU. It has been hypothesized that the natural flocculation tendency of extracts increases with decreasing temperature.

In addition to the temperature, the effect of addition of a flocculent (Polyethylene oxide, PEO) has been investigated. Substantial enhancement in filtrate flux upon addition of 20 ppm of PEO as seen in Figure 3 is observed.