Paul J Dauenhauer

Revealing pyrolysis chemistry for biofuels production: Conversion of cellulose to furans and small oxygenates

Paul J. Dauenhauer et al. — Tue, 26 Jun 2012 12:36:18 PDT

Biomass pyrolysis utilizes high temperatures to produce an economically renewable intermediate (pyrolysis oil) that can be integrated with the existing petroleum infrastructure to produce biofuels. The initial chemical reactions in pyrolysis convert solid biopolymers, such as cellulose (up to 60% of biomass), to a short-lived (less than 0.1 s) liquid phase, which subsequently reacts to produce volatile products. In this work, we develop a novel thin-film pyrolysis technique to overcome typical experimental limitations in biopolymer pyrolysis and identify α-cyclodextrin as an appropriate small-molecule surrogate of cellulose. Ab initio molecular dynamics simulations are performed with this surrogate to reveal the long-debated pathways of cellulose pyrolysis and indicate homolytic cleavage of glycosidic linkages and furan formation directly from cellulose without any small-molecule (e.g., glucose) intermediates. Our strategy combines novel experiments and first-principles simulations to allow detailed chemical mechanisms to be constructed for biomass pyrolysis and enable the optimization of next-generation biorefineries.

Aerosol Generation by Reactive Boiling Ejection of Molten Cellulose

Paul J. Dauenhauer et al. — Tue, 26 Jun 2012 12:32:05 PDT

The generation of primary aerosols from biomass hinders the production of biofuels by pyrolysis, intensifies the environmental impact of forest fires, and exacerbates the health implications associated with cigarette smoking. High speed photography is utilized to elucidate the ejection mechanism of aerosol particles from thermally decomposing cellulose at the timescale of milliseconds. Fluid modeling, based on first principles, and experimental measurement of the ejection phenomenon supports the proposed mechanism of interfacial gas bubble collapse forming a liquid jet which subsequently fragments to form ejected aerosol particles capable of transporting nonvolatile chemicals. Identification of the bubble-collapse/ejection mechanism of intermediate cellulose confirms the transportation of nonvolatile material to the gas phase and provides fundamental understanding for predicting the rate of aerosol generation.

Kinetics and reaction chemistry for slow pyrolysis of enzymatic hydrolysis lignin and organosolv extracted lignin derived from maplewood

Paul J. Dauenhauer et al. — Tue, 26 Jun 2012 12:26:08 PDT

The kinetics and reaction chemistry for the pyrolysis of Maplewood lignin were investigated using both a pyroprobe reactor and a thermogravimetric analyser mass spectrometry (TGA-MS). Lignin residue after enzymatic hydrolysis and organosolv lignin derived from Maplewood were used to measure the kinetic behaviours of lignin pyrolysis and to analyse pyrolysis product distributions. The enzymatic lignin residue pyrolyzed at lower temperature than that of organosolv lignin. The differential thermogravimetric (DTG) peaks for pyrolysis of the enzymatic residue were more similar to the DTG peaks for pyrolysis of the original Maplewood than DTG of the organosolv lignin. The condensable liquid volatile products were collected from a Pyroprobe reactor with a liquid nitrogen trap. The primary monomeric phenolic compounds were guaiacol, syringol, and vanillic acid. However, only 14–36 carbon% of the sample could be detected by GC-MS. Over 60 carbon% of the condensable products were heavy tar molecules that are not detectable by GC-MS. These heavy tar molecules are the primary products from pyrolysis of lignin. Intermediate solid samples were also collected at various pyrolysis temperatures and characterized by elemental analysis, FT-IR, DP-MAS 13C NMR, and TOC. The methoxy groups and ether linkages decreased and the non-protonated aromatic carbon–carbon bonds increased in the solid residues as the pyrolysis temperature increased. The carbon content of the initial lignin feed (derived from enzymatic hydrolysis) and the solid polyaromatics residue (obtained at 773 K) was 58 wt% and 74 wt% respectively. This polyaromatic residue contained about 69 wt% of the original lignin feed. The solid polyaromatics undergo further slow decomposition accompanied by a constant release of carbon dioxide as the pyrolysis reaction continues. The pyrolysis of the enzymatic lignin residue was modelled by two reactions in series. In the first pyrolysis step the lignin was decomposed with an apparent activation energy of 74 kJ mol−1 and a heat of reaction of −8,780 kJ kg−1. The second pyrolysis step had an apparent activation energy of 110 kJ mol−1 and a heat of reaction of −2,819 kJ kg−1. Lignin pyrolysis has lower activation energies and higher heats of reaction than cellulose pyrolysis.

Improved utilization of biomass-derived carbon by millisecond co-processing with hydrogen rich feedstocks

Paul J. Dauenhauer et al. — Tue, 26 Jun 2012 11:13:54 PDT

A reactor capable of improving the utilization of biomass-derived carbon during thermochemical conversion to synthesis gas is demonstrated experimentally. By co-processing hydrogen-deficient biomass (H/C[similar]2) with hydrogen-rich feedstocks (H/C≥4) through catalytic partial oxidation, 100% of the fuel carbon atoms fed to the reactor can be converted to CO.

Reactive Boiling of Cellulose for Integrated Catalysis through a Liquid Intermediate

Paul J. Dauenhauer et al. — Tue, 26 Jun 2012 11:06:12 PDT

Advanced biomass processing technology integrating fast pyrolysis and inorganic catalysis requires an improved understanding of the thermal decomposition of biopolymers in contact with porous catalytic surfaces. High speed photography (1000 frames per second) reveals that direct impingement of microcrystalline cellulose particles (300 μm) with rhodium-based reforming catalysts at high temperature (700 °C) produces an intermediate liquid phase that reactively boils to vapors. The intermediate liquid maintains contact with the porous surface permitting high heat transfer (MW m−2) generating an internal thermal gradient visible within the particle as a propagating wave of solid to liquid conversion. Complete conversion to liquid yields a fluid droplet on the catalyst surface exhibiting a linear decrease in droplet volume with time leaving behind a clean surface absent of solid residue (char). Under specific interfacial conditions, conversion with large cellulosic particles on the length-scale of wood chips (millimeters) occurs continuously as generated liquid and vapors are pushed into the porous surface.

Millisecond Autothermal Steam Reforming of Cellulose for Synthetic Biofuels by Reactive Flash Volatilization

Paul J. Dauenhauer et al. — Tue, 26 Jun 2012 11:01:40 PDT

Three biomass-to-liquid process steps (volatilization of cellulose, tar-cleaning of organic products, and water-gas-shift of the gaseous effluent) have been integrated into a single autothermal catalytic reactor for the production of high quality synthesis gas at millisecond residence times ([similar]30 ms). Particles of cellulose ([similar]300 μm) were directly impinged upon the hot, catalytic bed of Rh–Ce/γ-Al2O3 catalyst on 1.3 mm α-Al2O3 spheres in the presence of O2, N2, and steam in a continuous flow fixed-bed reactor at 500–1100 °C. Complete conversion to gases was observed for all experimental parameters including N2/O2, S/C, the total flow rate of cellulose, and the fuel-to-oxygen ratio (C/O). The addition of steam increased the selectivity to H2 and decreased the selectivity to CO in agreement with water-gas-shift equilibrium. Optimal conditions produced a clean gaseous effluent which exhibited [similar]80% selectivity to H2 at a synthesis gas ratio of H2/CO = 2.3 with no dilution from N2 at a fuel efficiency of [similar]75%. Carbon-free processing was explained by relating the domain of experimental parameters to the thermodynamic prediction for the formation of solid carbon, CS.