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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 6/14/2015 Publication Date: 6/14/2015 Citation: Jackson, M.A., Vermillion, K., Peterson, S.C. 2015. Hydrogenation of biomass extracts for production of chemicals concurrently from sugars and lignin [abstract]. North American Catalysis Society. p. 1. Interpretive Summary: Technical Abstract: The efficient conversion of biomass to commodity or specialty chemicals is critical to the success of the biorefinery concept. Biomass consists largely of the three interwoven polymers cellulose, hemicellulose, and lignin [1]. A key step toward utilization is the pretreatment of biomass which includes such methods as steam explosion, AFEX, supercritical water extraction, and acid or alkaline soaking, all with the aim of disentangling and depolymerizing these biopolymers. The separation of the components then allows for the upgrading to chemicals. Currently, this means fermentation of the glucose hydrolyzed from cellulose to second generation ethanol [2]. Isolated lignin is oftentimes burned to power the facility; however it holds great promise as a source of biobased aromatic chemicals. This poster describes our efforts to cleave aromatics from lignin during the hydrogenation of glucans and xylans. Switchgrass was milled in a planetary ball mill using 3 mm YSZ balls in a ball-to-biomass mass ratio of either 40 or 100. Milling was for a total of 12 h at 500 rpm reversing the direction every 3 h with a rest period of 6 min at each change of direction. Extractions were performed in a flow cell on 2 g samples using either water or 25 mM KOH at 160° flowing at 1.5 ml/min. for a total of 50 ml. A back pressure regulator maintained pressure at 1.3 MPa. The hydrolysate was then hydrogenated over various heterogeneous catalysts in a stirred reactor at 160° and 7 MPa H2. The post-reaction solution was then analyzed for sugars following NREL LAP methods [3]. Aromatic products were separated from sugars and small organics using C18 solid phase extraction. The eluted products were then analyzed by GCMS. Further characterization of the hydrolysate and reaction solution was done using HSQC, HMBC, and COSY nmr techniques. Catalysts were prepared by wet impregnation of RhCl3 or PdCl2 onto commercial silica-alumina (SA), Beta and HZSM-5 zeolites, homemade Mg-Al hydrotalcites, and zirconia. These were characterized for surface texture by N2-adsorption, XRD, and EDS. Switchgrass that is ball-milled at a ball:biomass of 100 yields a powder that can be hydrolyzed by hot compressed water with 67% of the mass in the hydrolysate. This number can be increased to 75% by using 25 mM KOH as the hydrolysis solution. Hydrogenation of this solution yields products originating in lignin, glucans, and xylans. Pd/SA produces aromatic derivatives of propanoic and acetic acids where the aromatics are phenol, guaicyl-, and syringyl-substituents. These are seen in the figure as H-, G-, S-lignin. The methoxy substituent of G- and S- lignin can be seen as well. The narrowing of this signal at 55 ppm in the C nmr after hydrogenation indicates that a wide range of similar lignin components has been reduced to just a few. The same thing can be seen in the aromatic region. Rh/AlOx produces the same aromatic acids but is better at converting sugars both through hydrogenation to C5 products and hydrogenolysis to acetol and hydroxybutanone. |
