Caroline Lievens

Reaction pathways of glucose during esterification: Effects of reaction parameters on the formation of humin type polymers

The formation of humin-type polymers and other products during exposure of glucose to methanol/water mixtures with methanol/water mass ratios from 10 to 0.22 in the presence of the acid catalyst Amberlyst 70 was investigated. In water-rich medium (methanol/water mass ratio: 0.22), dehydration of glucose produced 5-(hydroxymethyl)furfural (HMF), furfural, and substantial amounts of polymer. In methanol-rich medium (methanol/water mass ratio: 10), the hydroxyl and carbonyl groups of glucose, HMF or furfural were protected via etherification and acetalisation. These protections stabilized these reactive compounds and significantly lowered the polymer formation (1.43% of the glucose loaded). The polymerization of glucose and HMF was also favored at high temperatures and long residence times. Conversely, high catalyst dosage mainly accelerated the conversion of glucose to methyl levulinate. Thus, the polymerization of glucose and HMF can be suppressed in methanol/water mixtures with high methanol ratios, at low temperatures and short residence times.

Acid-Catalyzed Conversion of Xylose in Methanol-Rich Medium as Part of Biorefinery

Acid treatments of xylose have been performed in a methanol/water mixture to investigate the reaction pathways of xylose during bio-oil esterification. Xylose was mainly converted into methyl xylosides with negligible humins formed below 130 °C. However, humins formation became significant with the dehydration of xylose to furfural and 2-(dimethoxymethyl)furan (DOF) at elevated temperatures. The conversion of xylose to methyl xylosides protected the C1 hydroxyl group of xylose, which stabilized xylose and suppressed the formation of sugar oligomers and polymerization reactions. In comparison, the conversion of furfural to DOF protected the carbonyl group of furfural. However, the protection did not remarkably suppress the polymerization of furfural at high temperatures because of the shift of the reaction equilibrium from DOF to furfural with a prolonged residence time. In addition, the acid treatment of furfural produced methyl levulinate in methanol and levulinic acid in water, which was catalyzed by formic acid.

Mediating acid-catalyzed conversion of levoglucosan into platform chemicals with various solvents

Acid-catalyzed conversions of levoglucosan have been investigated in mono-alcohols, poly-alcohols, water, chloroform, toluene, acetone, N,N-dimethyl formamide, dimethyl sulfoxide and some mixed solvents, aiming to mediate conversion of sugars into platform chemicals with solvents. The mono-alcohols can stabilize soluble polymers and thus suppress formation of insoluble polymers. Water does not have such an effect, leading to lower yields of levulinic acid. Chloroform cannot effectively dissolve levoglucosan, leading to “dissolving” of levoglucosan in the catalyst and the consequent rapid polymerization. Acetone reacted with sugars, forming substantial amounts of polymer. N,N-Dimethyl formamide poisoned the acid resin catalyst, leading to negligible conversion of levoglucosan. Dimethyl sulfoxide (DMSO) mainly catalyzed the conversion of levoglucosan into 5-(hydroxymethyl)furfural (HMF), 2,5-furandicarboxaldehyde, and the sulfur ether of HMF. DMSO has a low ability to transfer protons, which helps to avoid further contact of HMF with catalytic sites and stabilizes HMF.

Understanding the stability of pyrolysis tars from biomass in a view point of free radicals

Fast pyrolysis of biomass has attracted increasing attention worldwide to produce bio-tars that can be upgraded into liquid fuels and chemicals. However, the bio-tars are usually poor in quality and stability and are difficult to be upgraded. To better understand the nature of the bio-tars, this work reveals radical concentration of tars derived from pyrolysis of two kinds of biomass. The tars were obtained by condensing the pyrolysis volatiles in 3s. It shows that the tars contain large amounts of radicals, at a level of 10(16)spins/g, and are able to generate more radicals at temperatures of 573K or higher, reaching a level of 10(19)spins/g at 673K in less than 30min. The radical generation in the tar samples is attributed to the formation of THF insoluble matters (coke), which also contain radicals. The radical concentrations of the aqueous liquids obtained in pyrolysis are also studied.

Production of value-added chemicals from bio-oil via acid catalysis coupled with liquid–liquid extraction

Sugar/sugar derivatives in bio-oil can be effectively separated from aromatics via water/chloroform extraction. Subsequent acid-treatment in methanol converts the sugars into levulinic acid/ester and the sugar derivatives into fuel additives. Further extraction with CH2Cl2/CHCl3 could efficiently separate methyl levulinate and levulinic acid from other products.

Esterification of bio-oil from mallee (Eucalyptus loxophleba ssp. gratiae) leaves with a solid acid catalyst: conversion of the cyclic ether and terpenoids into hydrocarbons.

Bio-oil from pyrolysis of mallee (Eucalyptus loxophleba ssp. gratiae) leaves differs from that obtained with wood by its content of cyclic ethers, terpenoids and N-containing organic compounds. Upgrading of the leaf bio-oil in methanol with a solid acid catalyst was investigated and it was found that the N-containing organics in the bio-oil lead to deactivation of the catalyst in the initial stage of exposure and have to be removed via employing high catalyst loading to allow the occurrence of other acid-catalysed reactions. Eucalyptol, the main cyclic ether in the bio-oil, could be converted into the aromatic hydrocarbon, p-cymene, through a series of intermediates including α-terpineol, terpinolene, and α-terpinene. Various steps such as ring-opening, dehydration, isomerisation, and aromatization were involved in the conversion of eucalyptol. The terpenoids in bio-oil could also be converted into aromatic hydrocarbons that can serve as starting materials for the synthesis of fine chemicals, via the similar processes.

Fibrous NiO/CeO2 nanocatalysts for the partial oxidation of methane at microsecond contact times

To maximize syngas yield by the catalytic partial oxidation of methane, fibrous NiO/CeO2 nanocatalysts were synthesized by a one-step template process for the catalytic reaction at microsecond contact times. High conversion performances at high gas hourly space velocities (∼107 h−1) indicate potential applications in gas conversion industry.

An Alternative Quality Control Technique for Mineral Chemistry Analysis of Portland Cement-Grade Limestone Using Shortwave Infrared Spectroscopy

Shortwave infrared (SWIR) spectroscopy can be applied directly to analyze the mineral chemistry of raw or geologic materials. It provides diagnostic spectral characteristics of the chemical composition of minerals, information that is invaluable for the identification and quality control of such materials. The present study aims to investigate the potential of SWIR spectroscopy as an alternative quality control technique for the mineral chemistry analysis of Portland cement-grade limestone. We used the spectroscopic (wavelength position and depth of absorption feature) and geochemical characteristics of limestone samples to estimate the abundance and composition of carbonate and clay minerals on rock surfaces. The depth of the carbonate (CO3) and Al-OH absorption features are linearly correlated with the contents of CaO and Al2O3 in the samples, respectively, as determined by portable X-ray fluorescence (PXRF) measurements. Variations in the wavelength position of CO3 and Al-OH absorption features are related to changes in the chemical compositions of the samples. The results showed that the dark gray and light gray limestone samples are better suited for manufacturing Portland cement clinker than the dolomitic limestone samples. This finding is based on the CaO, MgO, Al2O3, and SiO2 concentrations and compositions. The results indicate that SWIR spectroscopy is an appropriate approach for the chemical quality control of cement raw materials.

Influence of Monomer Connectivity, Network Flexibility, and Hydrophobicity on the Hydrothermal Stability of Organosilicas

It is generally assumed that the hydrothermal stability of organically modified silica networks is promoted by high monomer connectivity, network flexibility, and the presence of hydrophobic groups in the network. In this study a range of organosilica compositions is synthesized to explore the extent to which these factors play a role in the hydrothermal dissolution of these materials. Compositions were synthesized from hexafunctional organically bridged silsesquioxanes (OR1)3Si–R–Si(OR1)3 (R = −CH2–, –C2H4–, –C6H12–, –C8H16–, –p-C6H4–; R1 = −CH3, –C2H5), tetrafunctional (OEt)2Si(CH3)–C2H4–Si(CH3)(OEt)2 and Si(OEt)4, trifunctional silsesquioxanes R′-Si(OMe)3 (R′=CH3, n-C3H7, cyclo-C6H11, phenyl), and bifunctional Si(i-C3H7)2(OMe)2. The bond strain, connectivity and hydroxyl concentration of all networks were estimated using 29Si cross-polarized magic angle spinning nuclear magnetic resonance and Fourier-transform infrared spectroscopy. The hydrophilicity was characterized by monitoring the water uptake of the materials in moisture treatments with thermogravimetric analysis, differential scanning calorimetry, and Fourier-transform infrared spectroscopy. The resistance of each network against hydrothermal dissolution in a water/1,5-pentanediol mixture at 80 °C and pH 1, 7, and 13 was analyzed with inductively coupled plasma optical emission spectroscopy and X-ray fluorescence. Bond strain appears to significantly increase the tendency to dissolve under hydrothermal conditions. The stabilizing influences of increased connectivity and hydrophobicity were found to be weak.

Using Color, Texture and Object-Based Image Analysis of Multi-Temporal Camera Data to Monitor Soil Aggregate Breakdown

Remote sensing has shown its potential to assess soil properties and is a fast and non-destructive method for monitoring soil surface changes. In this paper, we monitor soil aggregate breakdown under natural conditions. From November 2014 to February 2015, images and weather data were collected on a daily basis from five soils susceptible to detachment (Silty Loam with various organic matter content, Loam and Sandy Loam). Three techniques that vary in image processing complexity and user interaction were tested for the ability of monitoring aggregate breakdown. Considering that the soil surface roughness causes shadow cast, the blue/red band ratio is utilized to observe the soil aggregate changes. Dealing with images with high spatial resolution, image texture entropy, which reflects the process of soil aggregate breakdown, is used. In addition, the Huang thresholding technique, which allows estimation of the image area occupied by soil aggregate, is performed. Our results show that all three techniques indicate soil aggregate breakdown over time. The shadow ratio shows a gradual change over time with no details related to weather conditions. Both the entropy and the Huang thresholding technique show variations of soil aggregate breakdown responding to weather conditions. Using data obtained with a regular camera, we found that freezing–thawing cycles are the cause of soil aggregate breakdown.