From biomass to fuels : hydrotreating of oxygen-containing feeds on a CoMo/Al<sub>2</sub>O<sub>3</sub> hydrodesulfurization catalyst

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dc.contributor Aalto-yliopisto fi
dc.contributor Aalto University en Viljava, Tuula-Riitta 2012-02-13T12:31:47Z 2012-02-13T12:31:47Z 2001-11-30
dc.identifier.isbn 951-22-5912-5
dc.identifier.issn 1235-6840
dc.description.abstract Biomass is a renewable alternative to fossil raw materials in the production of liquid fuels and chemicals. Liquefied biomass contains an abundance of oxygen-containing molecules that need to be removed to improve the stability of the liquids. A hydrotreating process, hydrodeoxygenation (HDO), is used for the purpose. Hydrodeoxygenation is similar to the hydrodesulfurization (HDS) process used in oil refining, relying upon a presulfided CoMo/γ-Al2O3 catalyst. The stability of the sulfided catalyst is critical in HDO because biocrudes usually do not contain the sulfur compounds needed to maintain the sulfidation of the catalyst. The aim of this work was to examine the role of sulfur in maintaining the activity of the HDO catalyst. Sulfur was introduced as an organic sulfur-containing co-reactant or as a sulfur substituent in an oxygen-containing reactant molecule as a way of simulating mixed feeds composed of biocrudes and conventional crudes, or it was introduced as a low molecular weight sulfiding agent. In addition, the stability of the sulfided catalyst against changes in the feed composition was studied to find out whether the activity of the catalyst could be maintained by carrying out HDO alternately with HDS. Simultaneous HDO and HDS was studied in a batch reactor with model compounds having a sulfur-containing (mercapto or methylmercapto) and an oxygen-containing (hydroxyl or methoxy) substituent in the same molecule, and with binary mixtures of mono-substituted benzene compounds. In both cases, the reactions of the oxygen-containing substituents were strongly suppressed as long as a sulfur-containing functionality was present. HDS reactions of mercapto and methylmercapto groups were either enhanced or retarded in the presence of oxygen-containing functionality. HDS was enhanced when the oxygen-containing substituent was located in para-position to the sulfur substituent thereby increasing the electronegativity of the sulfur atom and thus facilitating the adsorption of the reactant on the active site of the catalyst. Otherwise, the HDS rate declined due to strong competitive adsorption of the oxygen-containing compounds on the active sites of the catalyst, and due to the formation of less reactive sulfur compounds via methyl transfer from the methoxy groups to sulfur. In conclusion, simultaneous hydrotreating of sulfur- and oxygen-containing feeds leads to strong suppression of oxygen removal reactions and usually also to a decrease in the efficiency of sulfur removal. The effect of low molecular weight sulfiding agents, H2S and CS2, on HDO of phenol and anisole was studied first in a batch and then in a flow reactor to see whether the addition of sulfiding agents might improve the stability of the presulfided catalyst without decreasing the rate and without affecting the selectivity of HDO. The HDO rate of phenol decreased noticeably in the presence of CS2 in the batch reactor, and the selectivities of the HDO reaction paths were changed: the hydrogenation-hydrogenolysis route was less sensitive to the sulfur compound than was the CArom-O hydrogenolysis path. At higher concentrations of the sulfiding agent, also the hydrogenation route became inhibited. With anisole, there was an increase in the rate of demethylation to phenol, but oxygen removal was virtually unaffected. In the flow reactor studies, the formation of hydrogenated HDO products of phenol remained constant up to the highest concentration of H2S in the feed, but a dramatic decrease in the yield of the aromatic reaction product occurred already at low concentrations of H2S. Selective inhibition of one of the HDO paths confirmed the presence of at least two kinds of active sites on the catalyst. This means that addition of an inhibitor can be used to adjust the product distribution of HDO in process scale. However, the presulfided catalyst deactivated with time on stream also in the presence of sulfiding agents. Finally, the stability of the presulfided catalyst against changes in the feed composition was studied in a flow reactor. HDO of phenol and HDS of benzothiophene were carried out alternately in periods of four to eight hours. In this way, the deleterious effect of the competition of HDO and HDS was almost totally avoided and the stability of the catalyst during HDO was improved. The lengths of the HDO and HDS periods now need to be optimized. en
dc.format.extent 48, [66]
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher Helsinki University of Technology en
dc.publisher Teknillinen korkeakoulu fi
dc.relation.ispartofseries Industrial chemistry publication series / Helsinki University of Technology en
dc.relation.ispartofseries 11 en
dc.relation.haspart Viljava, T.-R. and Krause, A.O.I., Hydrogenolysis reactions in a batch reactor. Effect of mass balance inaccuracies on the kinetic parameters, Appl. Catal. A: General, 135 (1996), pp. 317-328.
dc.relation.haspart Viljava, T.-R. and Krause, A.O.I., Hydrotreating of compounds containing both oxygen and sulfur: Effect of para-hydroxyl substituent on the reactions of mercapto and methylmercapto groups, Appl. Catal. A: General, 145 (1996), pp. 237-251.
dc.relation.haspart Viljava, T.-R. and Krause, A.O.I., Hydrotreating of compounds and mixtures of compounds having mercapto and hydroxyl groups, Stud. Surf. Sci. Catal., 106 (1997), pp. 343-352.
dc.relation.haspart Viljava, T.-R., Saari, E.R.M. and Krause, A.O.I., Simultaneous hydrodesulfurization and hydrodeoxygenation: Interactions between mercapto and methoxy groups present in the same or in separate molecules, Appl. Catal. A: General, 209 (2001), pp. 33-43.
dc.relation.haspart Viljava, T.-R., Komulainen, S., Selvam, T. and Krause, A.O.I., Stability of CoMo/Al<sub>2</sub>O<sub>3</sub> catalysts: Effect of HDO cycles on HDS, Stud. Surf. Sci. Catal., 127 (1999), pp. 145-152.
dc.relation.haspart Viljava, T.-R., Komulainen, S. and Krause, A.O.I., Effect of H<sub>2</sub>S on the stability of CoMo/Al<sub>2</sub>O<sub>3</sub> catalysts during hydrodeoxygenation, Catal. Today, 60 (2000), pp. 83-92.
dc.subject.other Energy en
dc.subject.other Biotechnology en
dc.title From biomass to fuels : hydrotreating of oxygen-containing feeds on a CoMo/Al<sub>2</sub>O<sub>3</sub> hydrodesulfurization catalyst en
dc.type G5 Artikkeliväitöskirja fi
dc.description.version reviewed en
dc.contributor.department Department of Chemical Technology en
dc.contributor.department Kemian tekniikan osasto fi
dc.subject.keyword hydrotreating en
dc.subject.keyword hydrodeoxygenation en
dc.subject.keyword hydrodesulfurization en
dc.subject.keyword biomass en
dc.subject.keyword CoMo catalysts en
dc.identifier.urn urn:nbn:fi:tkk-003125
dc.type.dcmitype text en
dc.type.ontasot Väitöskirja (artikkeli) fi
dc.type.ontasot Doctoral dissertation (article-based) en
dc.contributor.lab Laboratory of Industrial Chemistry en
dc.contributor.lab Teknillisen kemian laboratorio fi

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