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Dissertation zugänglich unter
Enhancement of Chemical Products in Bio-Crude-Oil from Lignocellulosic Residues – Effects of Biomass Type, Temperature, Pre-treatment and Catalyst
Verbesserung von chemischen Produkten in Bioölen aus lignocellulosischen Reststoffen - Einfluss von Art der Biomasse, Temperatur, Art der Vorbehandlung und Katalysatoren
Azeez, Mayowa Akeem
Dokument 1.pdf (5.774 KB)
Biomasse, Lignocellulose , Chemische Analyse , Pyrolyse-Gaschromatographie , Katalysator , Chemometrie
Freie Schlagwörter (Englisch):
biomass , chemical analysis , pyrolysis gas chromatography , catalyst , chemometry
Odermatt, Jürgen (PD Dr. habil.)
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
Thermochemical conversion of various lignocellulosic wastes (beech, spruce, iroko and albizia sawdust and corncob), obtained from Africa and Europe, at 500°C in a fluidised bed reactor produced pyrolysate, char and mixture of non-condensable gases. The pyrolysate otherwise known as bio crude oil (BCO) contains over 85 chemical products.The concentrations of many of these products were found low in BCO, thereby impairing their separation.
Comparison of chemical products in BCOs from various lignocelluloses showed significant amounts of chemical products such as 4-vinyl phenol, 4-vinyl guaiacol and acetic acid in corncob. The largest amount of levoglucosan, an anhydrosugar, was obtained in BCO of spruce. This is an indication that the composition of pyrolysis products in BCO is feedstock specific. Generally, the African biomasses yielded lesser pyrolysate owing to catalytic effects of high metal content present in the samples. The chemical compositions of BCOs from similar wood types (iroko, albizia and beech) largely correspond.
In order to improve the yield of individual chemical products in pyrolysates of different samples, parametric influence of pyrolysis temperature was employed. The result of this analysis carried out using an analytical pyrolysis unit showed that the possibility of efficiently producing volatile chemical products at temperature below the optimum value of 450-550°C is remote. It compromises the yield and the purity of individual chemical products. Conversions at temperatures above 600-700°C produced several benzyl and phenyl products mostly derived from lignocellulose lignin macromolecule. However, their concentrations were very low and may prove uneconomical to extract from several tens of products with higher fractions (mostly holocellulose derived products). Based on these observations, the best practice of fast pyrolysis at optimum temperature still stands as the best option to obtain high yields of chemical products.
The application of samples pretreatment such as water and dilute acid washing, to ameliorate the effect of indigenous mineral contents in feedstock on the pyrolysate yield, revealed that dilute acid washing is more effective than the former. Divalent ions were more easily removed than the monovalent ion, while larger fraction of these metals in both African hardwoods remains unaffected by any of the washing options. The removal of these ubiquitous minerals in feedstock alters the pyrolysis decomposition reaction pathway. The impregnation of calcium and sodium ions in water-washed samples showed that these alkali and alkaline earth metals are specific in their influences on the pyrolysate composition. While Ca2+ enhanced the formation of high molecular products from holocellulose, the presence of sodium slightly promoted formation of 4-vinyl phenol and 4-vinyl guaiacol from lignin macromolecule.
It was noted that the impregnation of Ca2+ into lignocellulose promotes the cyclization of holocellulose-derived products leading to the substantial increase in cyclic compounds (up to order of 1 in some products especially levoglucosan). The production of compounds such as levoglucosan, furfural, 5-(hydroxymethyl)-2-furaldehyde, 2-hydroxymethyl-5-hydroxy-pyran-4-one at the expense of low molecular weight products will limit the number of chemical products in pyrolysate and facilitate separation processes. And specific cyclic compounds can then be carefully converted to more valuable chemical products.
The application of zeolite catalysts is another strategic option in modifying nature and yields of chemical products from thermochemical conversion of lignocellulose.Investigations using zeolite catalysts showed that the nature of the active site on zeolites and the alumina to silica ratio play most important roles, in addition to method of sample preparation. The use of acidic zeolites in a way similar to the operation in fluidized catalytic cracking (FCC) unit induced a very high concentration of levoglucosan and furfural owing to effective depolymerisation of the cellulose and hemicellulose unit occasioned by high cleavage of glycosidic bonds. The close interactions between sample particles and the zeolite surface area might have contributed to this dramatic effect via protonation.