Separation Of Lignin Degradation Products

Lignin is a natural renewable aromatic macromolecular polymer and its content is second to cellulose in nature. Aromatic compounds which are obtained via lignin deploymeriazation not only are important chemical raw materials, but also can be converted to liquid fuel by hydrodeoxygenation. The oligomers in lignin degradation products can be used to produce low-value products, such as resin and so on. In order to fully and effectively utilize the lignin degradation products, it’s necessary to separate aromatic compounds and oligomers from lignin degradation products. In addition, lignin also can be converted to bio-oil via liquefaction or pyrolysis. However, the organic solvents used to extract bio-oil are generally toxic, flammable and volatile. It’s necessary to find other ways for extraction.Two-step separation of lignin oxidative degradation products was studied. Firstly, Sephadex G-10 gel column chromatography was used to separate oligomers and aromatic compounds. Effects of pH and flow rate of mobile phase and injection volume on the separating performance were investigated. It is found that alkaline mobile phase favor good recovery of aromatic compounds. Moreover, high flow rate of mobile phase or large injection volume will reduce the separation effect. The optimized process variables for the separation of lignin oxidative degradation products is 10.5 of p H, 0.5 mL/min of flowrate and 2 mL of injection volume. Under such conditions, an oligomer fraction with large molecular weight and an aromatic fraction with 78.1% of aromatic compounds content were obtained. Secondly, the aromatic fraction was further separated by silica gel column chromatography. When using ethyl acetate as the mobile phase, 60-100 mesh silica gel after activation for 1 h as the stationary phase and the sample volume was 5 mL, the content of aromatic compounds could reach 99.8% and the recovery of aromatic compounds was above 97%. After being washed and dried, silica gel can be recycled. And the content of aromatic compounds could reach 96.6% using the recycled silica gel.A new technology of salting-out extraction was used to separate bio-oil from liquefaction products of lignin. The effects of the kind and dosage of inorganic salt, equilibrium time and temperature on the yields of bio-oil from products of lignin liquefaction and its salt content were investigated. It is found that extraction effect is facilitated by saturated MnSO4 as salting-out agent. The yield of bio-oil is up to 52.47 % and salt content of oil is 2.76 % under the conditions of 1:1 of volume ratio of oil to water, 10 min of equilibrium time, and 80 ℃ of extraction temperature, whereas the yield of oil is 51.53% by using ethyl acetate extraction, which is less than that by salting-out extraction. This work provides a low-cost, safe, and green approach to separating bio-oil from the liquefaction products of lignin.