Effect of Functional Groups on Autothermal Partial Oxidation of Bio-oil. Part 2: Role of Homogeneous and Support-Mediated Reactions

Abstract

This work aims to clarify preferred chemical routes in an autothermal system by investigating individually two-carbon molecules containing the functional groups found in bio-oil. In part 2, conversion and selectivity to major compounds are compared in the presence and absence of R-Al 2 O 3 support and oxygen. Oxygen significantly increases conversion, even at feed rates insufficient to sustain autothermal operation. In general, below 450 °C, homogeneous reactions in the absence of oxygen are insignificant for all molecules; in the presence of oxygen, the reaction onset temperature is somewhat lower. The role of the R-Al 2 O 3 support appears to be a combination of improved heat transfer and the radical quenching ability of the foam structure. Acid catalysis appears minor compared to these other functions. With no O 2 co-feed, acids, ethers, and aldehydes appear to be more stable than alcohols and esters. With O 2 co-feed, acids and ethers may be less reactive in the gas phase than the other functionalities studied. Implications for autothermal systems are discussed.

Effect of Functional Groups on Autothermal Partial Oxidation of Bio-oil. Part 1: Role of Catalyst Surface and Molecular Oxygen

“…The relative contribution of homogeneous chemistry is discussed in part 2 (10.1021/ef200456m). Production of CO 2 is not significantly correlated to any of the other products ( R ≤ 0.70) and, thus, may occur via a parallel channel. CO 2 may be formed homogeneously or on different index planes of the Pt surface at stepped or defect sites …”

“…While the Pt surface appears to be particularly efficient at dissociating surface methyl groups in the autothermal experiments (as evidenced by the consistently low selectivity to CH 4 in those experiments), the lack of surface oxygen in the O 2 -free experiments may allow for CH 4 to form on the surface as well. It is therefore difficult to discern the relative contributions of surface and gas phase decomposition of acetaldehyde in the absence of oxygen, although results from part 2 (10.1021/ef200456m) suggest that homogeneous chemistry of acetaldehyde in the absence of O 2 may be minor . Selectivity to CH 4 slightly lags selectivity to CO as the temperature increases, but it is difficult to interpret this phenomenon as an effect of surface decomposition of acetaldehyde followed by further reaction of the methyl group or simply that, at higher temperatures, there is sufficient energy to sever the C–C bond of ethylene glycol in a Pt-catalyzed complex.…”

Kinetic Modeling of Pt-Catalyzed Glycolaldehyde Decomposition to Syngas

“…Recent advancements in computer-aided catalyst design have increased the motivation for fundamental computational kinetic studies on the catalytic chemistry of these biomass-derived oxygenates. − Because of the complex diversity of oxygen functional groups in biomass-derived oils, optimized catalysts not only need to be tailored to specific functional groups but also to specific molecules that contain multiple oxygen functional groups. ,− Specifically, glycolaldehyde (HOCH 2 CHO) is well suited as a probe molecule for more complex biomass derivatives due to the 1:1 oxygen:carbon ratio and the presence of both alcohol and aldehyde functionality, similar to that of C6 sugars . The relatively small size of this molecule, and its moderate number of reactive intermediates (C 2 H x O 2 ), makes it reasonably suited for in-depth computational studies.…”

Role of Potassium and Phosphorus in Catalytic Partial Oxidation in Short Contact Time Reactors

“…Also, phosphorus increased ethylene selectivities in both the doped and transient experiments with ethanol as a result of its acidic nature. Since phosphorus is a strong reforming poison, there is increased homogeneous chemistry of ethanol, which has been shown to produce ethylene at temperatures typically observed during CPO . Thus, both homogeneous and phosphorus-catalyzed heterogeneous chemistries contribute to increased ethylene formation.…”

“…Since phosphorus is a strong reforming poison, there is increased homogeneous chemistry of ethanol, which has been shown to produce ethylene at temperatures typically observed during CPO. 27 Thus, both homogeneous and phosphoruscatalyzed heterogeneous chemistries contribute to increased ethylene formation. In the third set of tranient experiments with phosphorus-doped ethanol, water selectivities increased as a result of a combination of the reduced water-gas shift, reduced steam reforming, and increased ethanol dehydration to ethylene.…”