Progress and recent trends in biofuels

Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.

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Heterogeneous Catalyst Deactivation and Regeneration: A Review

A critical review of the kinetics and selectivity of the Fischer–Tropsch synthesis (FTS) is given. The focus is on reaction mechanisms and kinetics of the water–gas shift and Fischer–Tropsch (FT) reactions. New developments in the product selectivity as well as the overall kinetics are reviewed. It is concluded that the development of rate equations for the FTS should be based on realistic mechanistic schemes. Qualitatively, there is agreement that the product distribution is affected by the occurrence of secondary reactions (hydrogenation, isomerization, reinsertion, and hydrogenolysis). At high CO and H2O pressures, the most important secondary reaction is readsorption of olefins, resulting in initiation of chain growth processes. Secondary hydrogenation of α-olefins may occur and depends on the catalytic system and the process conditions. The rates of the secondary reactions increase exponentially with chain length. Much controversy exists about whether these chain-length dependencies stem from differe...

Kinetics and Selectivity of the Fischer–Tropsch Synthesis: A Literature Review

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Studies in Surface Science and Catalysis

Lower olefins are key building blocks for the manufacture of plastics, cosmetics, and drugs. Traditionally, olefins with two to four carbons are produced by steam cracking of crude oil-derived naphtha, but there is a pressing need for alternative feedstocks and processes in view of supply limitations and of environmental issues. Although the Fischer-Tropsch synthesis has long offered a means to convert coal, biomass, and natural gas into hydrocarbon derivatives through the intermediacy of synthesis gas (a mixture of molecular hydrogen and carbon monoxide), selectivity toward lower olefins tends to be low. We report on the conversion of synthesis gas to C(2) through C(4) olefins with selectivity up to 60 weight percent, using catalysts that constitute iron nanoparticles (promoted by sulfur plus sodium) homogeneously dispersed on weakly interactive α-alumina or carbon nanofiber supports.

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Supported Iron Nanoparticles as Catalysts for Sustainable Production of Lower Olefins

The effects of potassium and copper promotion on the activity and selectivity of precipitated iron catalysts for Fischer--Tropsch synthesis (FTS) were studied in a fixed bed reactor at 148 MPa and 235--265{degrees} C using synthesis gas with a H{sub 2}/CO = 1 molar feed ratio It was found that both potassium and copper increase the catalyst activity for FTS and the water gas shift reaction Potassium promotion ({approximately} 02--1 wt %) results in an increase in the average molecular weight of hydrocarbon products and suppression of secondary reactions (olefin hydrogenation and isomerization of 1-alkenes to 2-alkenes) Copper promotion ({approximately} 3 wt %) has a similar effect on the hydrocarbon distribution, but it enhances slightly the secondary reactions The activity of doubly promoted (100 Fe/3 Cu/{ital x}K, {ital x} = 02 or 05) catalysts was higher than that of singly promoted catalysts and was independent of potassium loading, whereas their selectivity behavior was strongly influenced by their potassium loading Product selectivities on the 100 Fe/3 Cu/02 K catalyst were similar to those of the 100 Fe/3 Cu catalyst, whereas selectivities of the 100 Fe/3 Cu/05 K catalyst were similar to those obtained in tests with the 100 Fe/05 K catalyst

Promoter effects on precipitated iron catalysts for Fischer-Tropsch synthesis

Activation studies with a precipitated iron catalyst for Fischer-Tropsch synthesis. I. Characterization studies

This paper reports on the influence of silica and alumina binders (supports) on the activity and product selectivity of precipitated iron catalyst for Fischer-Tropsch synthesis (FTS) that was studied in a fixed bed reactor at 1.5-3.0 MPa and 220-250{degrees} C, using synthesis gas with H{sub 2}/CO = 1 M feed ratio. Both the FTS and the water gas shift activity decreased with increasing support content. The catalyst deactivation rate decreased with catalysts containing 24 and 100 g of SiO{sub 2} per 100 g of Fe. Secondary reaction (olefin hydrogenation and isomerization) increased with increasing silica content. Hydrocarbon selectivities improved (less gaseous hydrocarbons) with the addition of support, except for the catalyst containing 24 SiO{sub 2}/100Fe. The results were interpreted in terms of interactions between potassium and/or iron with supports.

Binder/support effects on the activity and selectivity of iron catalysts in the Fischer-Tropsch synthesis

The kinetics of the Fischer-Tropsch (FT) and water-gas shift (WGS) reactions were studied in a stirred tank slurry reactor, using a 100 Fe/0.3 Cu/0.2 K catalyst and a commercial catalyst, Ruhrchemie LP 33/81. The 100 Fe/0.3 Cu/0.2 K catalyst was more active than the Ruhrchemie catalyst for both reactions. FT kinetics which accounted for water inhibition was the best of the rate forms considered for the 100 Fe/0.3 Cu/0.2 K catalyst. First order in H2 kinetics was sufficient for the Ruhrchemie catalyst, probably due to the low conversions obtained during the test of this catalyst. WGS kinetics, which included product inhibition, were also studied for each catalyst.

Dragomir B. Bukur

Papers

Promoter effects on precipitated iron catalysts for Fischer-Tropsch synthesis

Activation studies with a precipitated iron catalyst for Fischer-Tropsch synthesis. I. Characterization studies

Binder/support effects on the activity and selectivity of iron catalysts in the Fischer-Tropsch synthesis

Reaction kinetics over iron catalysts used for the fischer-tropsch synthesis

Activation studies with a precipitated iron catalyst for Fischer-Tropsch synthesis. II. Reaction studies