Luís S. Lobo

Effect of coal pre-treatment with swelling solvents on coal liquefaction

Pre-treatment of coal with swelling solvents may enhance coal porosity and thus facilitate catalyst action. The yields of products obtained by coal liquefaction were very much dependent on the type of swelling solvent used. Those studied included ethanol, tetrahydrofurane (THF) and tetrabutylammonium hydroxide (TBAH). After this treatment coal was liquefied using ZnCl2 as catalyst, both alone and mixed with Fe2O3 or ICI 41-6 (Co–Mo). When ethanol was used, the highest coal conversion was obtained, although this solvent had the lowest swelling ratio, probably because a better catalyst impregnation was achieved. On the other hand, although the swelling ratio of TBAH was the greatest, lower overall coal conversions and higher oils yields were observed. In an attempt to interpret these results, coal structure before and after swelling pre-treatment was also studied using SEM.

Uncatalysed and MoO3-catalysed carbon-oxygen reaction: A kinetic study

Abstract A kinetic study was made of the reaction of activated carbon with oxygen, uncatalysed and catalysed by MoO 3 , using a microbalance to record the loss of weight as a function of time. Orders and activation energies were measured. MoO 3 was found to be a moderate catalyst for this reaction. The effect of loading on reactivity is linear for low loadings and shows saturation above 2.5 wt%. It is proposed that this type of reaction, involving three phases and two interfaces, can be explained by surface catalysis at the gas/catalyst interface with continuous diffusion of carbon atoms through the catalyst.

Study of CO2 gasification of activated carbon catalysed by molybdenum oxide and potassium carbonate

Abstract A kinetic study is made of the reaction of activated carbon gasification by CO 2 catalysed by MoO 3 and K 2 CO 3 , using a microbalance to record the loss of weight as a function of time. Orders and activation energies were measured. MoO 3 is found to be a good catalyst at low temperatures and moderate pressures. The effect of loading on reactivity shows saturation above ≈ 0.3 wt %. The catalytic effect of the mixture MoO 3 /K 2 CO 3 is found to be slightly above the effect expected by the addition of the separate effects of the two catalysts. A brief reference is made to the possible mechanism for these reactions.

The effect of catalysts blending on coal hydropyrolysis

Abstract The effect of several catalysts on coal hydropyrolysis efficiency was studied, having selected catalysts with different characteristics and behaviours. For the experimental conditions used Fe 2 O 3 and ICI 41-6 showed selectivity towards lighter fractions, whilst ZnCl 2 led to the highest coal conversion and to the greatest preasphaltenes yields. These results suggested the use of mixtures of catalysts. The heavier molecules of asphaltenes produced as a result of ZnCl 2 action could then be converted into lighter fractions by the action of a selective catalyst. Coal hydropyrolysis tests were undertaken using ZnCl 2 mixed with Fe 2 O 3 or ICI 41-6. These mixtures of catalysts led to increased conversions and higher product yields. The best results were obtained in the presence of ZnCl 2 mixed with Fe 2 O 3 . In an attempt to interpret these results, coal structure before and after swelling pre-treatment was also studied using SEM.

N2O formation during coal combustion in fluidised beds - is it controlled by homogeneuous or heterogeneous reactions?

Abstract This paper discusses the results of the experimental work undertaken to determine the N 2 O and NO emissions from fluidised bed combustion. First, studies were carried out to measure the amounts of both NO and N 2 O formed during the combustion of bituminous coals and that chars prepared from the same coals. Second, the combustion of the volatiles released during the devolatilisation of coals was investigated and the N 2 O and NO emissions were measured. The analysis of HCN and NH 3 in volatiles was also undertaken. From our results, a better understanding of the issue of homogeneous reactions versus those of heterogeneous for the formation of N 2 O is achieved.

Catalytic carbon formation: clarifying the alternative kinetic routes and defining a kinetic linearity for sustained growth concept

Understanding stable carbon formation mechanisms requires isothermal kinetic studies. Distinguishing preliminary solid-state changes from the prevailing steady-state (sustained) carbon formation route is essential. The three alternative kinetic routes for carbon formation are clarified: dual catalyst route, gas phase pyrolysis and hybrid route—a combination of the two previous ones. When kinetic linearity is observed in a reaction involving catalytic formation or gasification of a solid, this is evidence that only a steady-state carbon diffusion process is operating obeying Fick’s 1st law in a stable geometry. Fick’s 2nd law rules in the initial transition stage, involving nucleation and solid-state reaction processes. Catalyst duality is discussed, considering the roles played by the two distinct surface regions between which the bulk carbon flux is maintained during steady-state reaction.

THE CONTROL OF THE EMISSIONS OF N 2 O AND NO DURING COMBUSTION OF COALS IN FLUIDISED BED SYSTEMS

Experimental studies were carried out to investigate the effect of the heterogeneous reaction between char and N2O. The chars were prepared at different temperatures and heating rates in a fluidised bed. They were then burned in a fluidised bed and the emissions of NO and N2O were recorded. Elemental analysis showed different degrees of the retention of coal-N during devolatilisation. A thermogravimetric analysis system (TGA) was used to determine the reactivity of chars to N2O. Correlation between isothermal reactivities and emissions of NO and N2O from the combustion of chars were consequently obtained. The results confirm the importance of the reaction of N2O and char and the dependence on the type of coal.

Fouling from Light Hydrocarbons on Metal Surfaces

Fouling from hydrocarbons on metal surfaces is an important problem and occurs in many and diverse industrial situations. In some cases, hydrocarbon mixtures contain significant amounts of inorganic matter (eg. sulfur and organo-metallic compounds) and particles in suspension. This may give rise to combined and complex fouling processes. In this paper we deal with mechanisms of fouling from hydrocarbons only.