Daniel Montané

Steam reforming model compounds of biomass gasification tars: conversion at different operating conditions and tendency towards coke formation

The purification of biomass-derived syngas via tar abatement by catalytic steam reforming has been investigated using benzene, toluene, naphthalene, anthracene and pyrene as surrogated molecules. The effects of temperature and steam-to-carbon ratio on conversion, and the tendency towards coke formation were explored for each model compound. Two commercial nickel-based catalysts, the UCI G90-C and the ICI 46-1, were evaluated. The five tar model compounds had very different reaction rates. Naphthalene was the most difficult compound to steam reform, with conversions from 0.008 gorg_conv/gcat min (790 °C) to 0.022 gorg_conv/gcat min (890 °C) at an S/C ratio of 4.2. The most reactive compound was benzene, with a conversion of 1.1 gorg_conv/gcat min at 780 °C and an S/C ratio of 4.3. The tendency towards coke formation grew as the molecular weight of the aromatic increased. The minimum S/C ratio for toluene was 2.5 at a catalyst temperature of 725 °C, and for pyrene at 790 °C ,it was 8.4. In general, catalyst temperatures and S/C ratios need to be higher than for naphtha in order to prevent the formation of coke on the catalyst.

High-temperature dilute-acid hydrolysis of olive stones for furfural production

Abstract We studied the production of furfural by acid hydrolysis of olive stones, which in Spain are an abundant lignocellulosic residue derived from the production of olive oil. We focused on the hydrolysis in dilute sulfuric acid (0.05 to 0.250 mol l −1 ), at high temperature (220–240°C), and short reaction times, of a few minutes at the most. The experimental study was performed in a tubing-bomb reactor system that approximately reproduces the temperature profiles obtained in a continuous tubular reactor. We obtained maximum furfural yields ranging from 50% to 65% of the potential depending on acid concentration and temperature.

Fractionation of Wheat Straw by Steam-Explosion Pretreatment and Alkali Delignification. Cellulose Pulp and Byproducts from Hemicellulose and Lignin

Abstract The fractionation of wheat straw was studied using a two-stage process based on an hydrolytic pretreatment followed by alkali delignification. The hydrolytic pretreatment was performed by steam explosion. Straw was steamed at temperatures comprised between 205 and 230°C for 2 min. The steamed straw was washed with hot water to yield a solution rich in hemicellulose-derived mono- and oligosaccharides. The washed fiber was delignified by alkali at 160°C for 60 min using a NaOH load of 20%. The alkali-soluble lignin was recovered by filtration after acidification of the black liquor. The delignified pulp was screened and bleached to produce viscose-grade cellulose. The optimization of the pretreatment conditions led to the following results at a pretreatment severity of log(R0) = 3.80: yield of viscose-grade cellulose = 70% of the potential; lignin recovery = 70% of the Klason lignin present in the untreated straw; hemicellulose sugars = 55% of the potential, recovered as molasses.

Exploring iron-based multifunctional catalysts for Fischer-Tropsch synthesis: a review.

The continuous increase in oil prices together with an increase in carbon dioxide concentration in the atmosphere has prompted an increased interest in the production of liquid fuels from non-petroleum sources to ensure the continuation of our worldwide demands while maximizing CO(2) utilization. In this sense, the Fischer-Tropsch (FT) technology provides a feasible option to render high value-added hydrocarbons. Alternative sources, such as biomass or coal, offer a real possibility to realize these purposes by making use of H(2)-deficient or CO(2)-rich syngas feeds. The management of such feeds ideally relies on the use of iron catalysts, which exhibit the unique ability to adjust the H(2)/CO molar ratio to an optimum value for hydrocarbon synthesis through the water-gas-shift reaction. Taking advantage of the emerging attention to hybrid FT-synthesis catalysts based on cobalt and their associated benefits, an overview of the current state of literature in the field of iron-based multifunctional catalysts is presented. Of particular interest is the use of zeolites in combination with a FT catalyst in a one-stage operation, herein named multifunctional, which offer key opportunities in the modification of desired product distributions and selectivity, to eventually overcome the quality limitations of the fuels prepared under intrinsic FT conditions. This review focuses on promising research activities addressing the conversion of syngas to liquid fuels mediated by iron-based multifunctional materials, highlights their preparation and properties, and discusses their implication and challenges in the area of carbon utilization through H(2)/CO(+CO(2)) mixtures.

Synthesis and characterization of carboxymethylcelluloses (CMC) from non-wood fibers I.Accessibility of cellulose fibers and CMC synthesis

This paper explores the production of carboxymethylcellulose (CMC) fromseveral bleached cellulose pulps obtained from non-wood species. The chemicalcomposition (α-cellulose, hemicellulose and lignin content), the degreeofswelling, viscosity, solubility in concentrated NaOH and crystallinity ofsoda/AQ cellulose pulps from abaca, jute, sisal, linen and Miscanthussinensis were determined. The pulps were carboxymethylated by one andtwo successive reaction steps in aqueous medium under identical conditions. Thedegree of substitution (DS) of CMC was found to be dependent upon the source ofthe cellulose pulp, but generally it was close to 1 with one etherificationtreatment and around 2 after the second. The molar mass of CMC was found to bedependent on the initial intrinsic viscosity of the cellulose pulp. The weightaverage molar mass of our CMCs ranged from 1.5 × 105 to2.8 × 105. Increasing the DS up to 2 improved the CMC solubility, butviscosity slightly decreased due to a slight degradation of the polymer.

Life cycle inventory analysis of hydrogen production by the steam-reforming process: comparison between vegetable oils and fossil fuels as feedstock

A life cycle inventory analysis has been conducted to assess the environmental load, specifically CO2 (fossil) emissions and global warming potential (GWP), associated to the production of hydrogen by the steam reforming of hydrocarbon feedstocks (methane and naphtha) and vegetable oils (rapeseed oil, soybean oil and palm oil). Results show that the GWPs associated with the production of hydrogen by steam reforming in a 100 years time frame are 9.71 and 9.46 kg CO2-equivalent/kg H2 for natural gas and naphtha, respectively. For vegetable oils, the GWP decreases to 6.42 kg CO2-equivalent/kg H2 for rapeseed oil, 4.32 for palm oil and 3.30 for soybean oil. A dominance analysis determined that the part of the process that has the largest effect on the GWP is the steam reforming reaction itself for the fossil fuel-based systems, which accounts for 56.7% and 74% of the total GWP for natural gas and naphtha, respectively. This contribution is zero for vegetable oil-based systems, for which harvesting and oil production are the main sources of CO2-eq emissions.

Fractionation of residual lignocellulosics by dilute-acid prehydrolysis and alkaline extraction: Application to almond shells

Abstract A two-stage process based on a hydrolytic pretreatment and an alkali extraction was applied to the fractionation of almond shells into cellulose, pentosan and lignin. Autohydrolysis and dilute-acid hydrolysis were studied as pretreatment methods in two different reactor configurations: an isothermal plug-flow reactor and a stirred, non-isothermal, batch autoclave. Yield and composition of the pulps resulting from the hydrolytic pretreatment were equivalent for both reactors when compared through the reaction severity concept. In this approach, pretreatment severity is quantified by R OH , a semi-empirical parameter that comprises the effect of temperature, time and acid concentration used during the pretreatment into a single reaction ordinate. Results showed that a pretreatment severity of log 10 R OH =4.3 was the optimal to maximize pentosan recovery, with 66% of the potential yield. At this severity, lignin obtained was 64% of the potential yield and 9% of the initial cellulose was degraded. Viscosity average degree of polymerization of the α-cellulose remaining in the pulp was reduced to 500 at this severity. Lignin recovery increased with severity to a value of 82% at log 10 R OH =4.7, allowing a better separation of the cellulose and the lignin, but also producing a higher depolymerization of the α-cellulose. Polydispersity of the α-cellulose also decreased with the severity increase, from 6.3 at log 10 R OH =4.0 to a value of 3.4 at log 10 R OH =4−7.

The fractionation of almond shells by thermo-mechanical aqueous-phase (TM-AV) pretreatment

The fractionation of almond (Prunes amygdalus) shells using an aqueous phase thermo-mechanical pretreatment is the main goal in the present work. Almond shells are an abundant agricultural waste in the Mediterranean regions with an estimated world production of 550,000 Tm yr−1. The solubilization profile, the pretreated fiber composition and the yield of the xylan recovered in the aqueous phase have been studied as a function of the pretreatment severity. Two different models have been used to describe the xylan solubilization kinetics: a pseudo-kinetic model and a model based on the generalized severity factor. The results of xylan solubilization and recovery are in concordance with those reported for hardwood. It has also been found that under certain operational conditions and reactor configurations, the reaction rate may not be under kinetic control due to poor stirring of the lignocellulosic-aqueous slurry.

Synthesis and characterization of carboxymethylcelluloses from non-wood pulps II. Rheological behavior of CMC in aqueous solution

This paper concerns the rheological behavior of carboxymethylcelulloses(CMC) derived after one and two successive steps from different non-woodbleached cellulose pulps. CMC rheological characterization was achieved in0.1M NaCl solution, as a function of polymer concentration. Theevidence of a critical concentration (C* < 1 g/L) is discussedfromsteady shear and dynamic experiments. Rheological properties of the CMC werefound to depend on the cellulose source reactivity and on their degree ofsubstitution (DS). Higher molecular weight of initial cellulose was accompaniedby higher apparent intrinsic viscosity of the CMC produced. Depending on theCMCconcentration and on the degree of etherification, the system behaves as asolution or as a gel. In the case of abaca CMC sample, it is shown that afteronly one step of chemical modification and above a polymer concentration of20 g/L, the system behaves as a gel. The gel behavior was studied asafunction of temperature. In the temperature range from 25 to 45°C, the rheological behavior was found to remain almostconstant due to the existence of dispersed swollen aggregates. This unusualcharacteristic represents an advantage for applications such as oil recovery inthe petroleum industry, where viscosity of the recovered fluid should not diminishwith temperature.

Fractionation of Wheat Straw via Steam-Explosion Pretreatment. Characteristics of the Lignin Obtained by Alkali Delignification of the Steamed Straw

Lignin was produced from wheat straw via a fractionation process based on a steam explosion pretreatment followed by an alkali delignification stage. The yield and chemical composition of the resulting lignin samples were related to the conditions of the pretreatment stage. Temperature and time were grouped into a single reaction ordinate, R 0 , by using the reaction severity concept. Increasing the severity of the pretreatment causes the lignin yield to increase in the severity range studied, from log 10 R 0 = 3.39 to 4.13. The methoxyl and aliphatic alcohol contents decreased as the pretreatment because more severe. The apparent molecular weight distribution (polystyrene-equivalent) was bimodal for all the samples. The yield of the alkali-extracted lignin obtained at the optimum severity for hemicellulose and cellulose recovery (log 10 R 0 = 3.80) was 70.5% of the Klason lignin in wheat straw, while the C-9 structure calculated for this material was C 9 H 7.08 O 2.40 N 0.09 (OCH 3 ) 0.81 (OH) 1.05 (COCH 3 ) 0.005