C. Berrueco

Fluidized bed thermal degradation products of HDPE in an inert atmosphere and in air–nitrogen mixtures

Abstract Different processes involving thermal decomposition such as incineration, pyrolysis, gasification or co-combustion are becoming important for energy generation using plastic wastes as combustible materials. The thermal degradation of the material, the product distribution and consequently the economics of the process are strongly influenced by the experimental conditions used. In this work, the thermal degradation of high-density polyethylene (HDPE) has been carried out using a fluidized bed reactor under different temperature conditions. Two types of experiments have been performed, pyrolysis experiments, in which nitrogen has been used as inert gas, and gasification experiments, meaning that the thermal decomposition has been carried out in a nitrogen–air mixture with low oxygen concentration. The influence of the operating parameters on the product distribution and gas composition has been investigated using GC and MS/GC for the analysis of the gas, wax and oil fractions obtained. The results obtained show a widely differing product yield in both processes. The main objective of the paper is a comparison of pyrolysis and gasification in terms of the generation of products of high heating value, and the energy requirements for the thermal degradation and production of residues and polyaromatic compounds. An optimum interval of operation temperatures is suggested in order to obtain high yield to gases of high heating values and low yield to PAHs.

Effect of temperature and pressure on characteristics and reactivity of biomass-derived chars

This study evaluates the influence of pyrolysis temperature (350-450°C) and pressure (0.1-2.0MPa) on product yields and char properties. Spruce chars were produced under slow pyrolysis conditions in a fixed bed reactor. Special attention was devoted to the study of the oxidation reactivity of the produced chars, and its relationship with the evaluated char properties. The obtained results showed that the effect of the pyrolysis condition on char production and in particular on the mechanism of secondary char formation strongly influenced the char reactivity. Additionally it has been observed that the interval of temperature between 350 and 450°C may be key in the mechanism of tar repolymerization. The information provided in this study is of great interest for the determination of optimal operation conditions and the design of new gasification concepts or the development of bioenergy carriers via pyrolysis technologies.

The detection of high-mass aliphatics in petroleum by matrix-assisted laser desorption/ionisation mass spectrometry†

RATIONALE The development of simplified procedures for isolating high-mass alkanes present in crude oils is described. The new procedures, which bypass the sample recovery step with hot toluene in the conventional alkane-isolation procedure, also provide an effective sample preparation route, prior to analysis by matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS). METHODS Urea-alkane adducts are formed by mixing sample and urea solutions on chromatographic paper or silica-coated plates. Unreacted hydrocarbons are removed by developing the plates with chloroform. In a second development with water, adducts are broken up in situ and the liberated urea removed, leaving bands of isolated alkanes behind. For MALDI-MS, strips of paper/plates, carrying the isolated alkanes, are fixed on metal target plates. The samples are treated with matrix (AgNO(3)) and analysed by MALDI-MS. RESULTS The observed signal represents silver ion adducts of the isolated alkanes. Silver appears to work without much fragmentation and to generate whole silver adduct ions. Much improved MALDI-MS detection sensitivity and a wider range of masses was observed when samples were ablated from paper/plate surfaces, than by ablation from bulk samples spread over a smooth surface--the conventional method. Chromatographic paper gave better resolution and a broader range of masses than silica-coated plates. CONCLUSIONS The analytical sequences have been confirmed using standard alkanes (C(20)-C(60)) and Polywax. The proposed procedures enhanced the sensitivity and detection range of the MS analysis. The method was useful in detecting n-alkanes to m/z 1500 (C(100)) and required relatively small quantities of sample and reagents. It provides a promising qualitative analysis route for the rapid isolation and reliable determination of alkanes in crude oils.

Synthetic natural gas by direct CO2 hydrogenation on activated takovites: effect of Ni/Al molar ratio

Takovite-derived mixed oxides in Ni/Al molar ratios from 1 to 3 have been used as catalysts in hydrogenation of CO2 to CH4. The catalysts were characterized by XRD, BET, TEM, TGA, and H2-TPR, and monitored by in situ DRIFTS under reaction conditions. The catalytic performance for the CO2 methanation has been investigated in a fixed-bed reactor at the temperature range from 225 to 400 °C and pressures of 10.0 and 1.0 bar(g). Takovite decomposition leads to the formation of a NiO phase containing Al ions and a nickel-containing alumina phase (Ni-deficient spinel). The percentage of spinel increases upon decreasing the Ni/Al ratio, and consequently, a lower amount of metallic nickel after subsequent reduction is achieved. All catalysts were partially reduced upon time on stream, leading to the formation of small Ni0 crystallites (ca. 3 nm) dispersed on a NiAl2O4 matrix. The most active and selective catalyst was the one with a Ni/Al ratio of 2, which was also very stable after a 500 h lifetime test at atmospheric pressure and 275 °C.

Transformation of lignin from bioethanol production for phenol substitution in resins

The main objective of biorefineries is the efficient conversion of lignocellulosic materials into valuable products. Lignin, a major abundant polymer not sufficiently exploited, is considered to be a promising substitute of phenol in phenol–formaldehyde resin synthesis. In this study, a lignin sample from a bioethanol production plant was modified under different experimental conditions by a depolymerisation treatment. The modification was intended to enhance the reactivity of lignin by increasing its functionality. The structural changes were studied with several characterisation techniques including size exclusion chromatography, Fourier transform infrared spectroscopy and nuclear magnetic resonance. The lignin reactivity towards formaldehyde was determined with a formaldehyde reactivity test. From the characterisation results of the reacted lignins, it was concluded that increasing the severity of the depolymerisation treatment (i.e. higher temperature, reaction time and catalyst content) resulted in an increase in active functional groups. Consequently, lignins depolymerised at more severe conditions were more reactive towards formaldehyde reaction. Due to their improved reactivity, the treated lignins could be successfully used as substitutes of phenol, converting them into a highly value-added product. An estimation of the cost of the proposed process is provided.