Maurizia Seggiani

Catalytic upgrading of pyrolytic oils over HZSM-5 zeolite: behaviour of the catalyst when used in repeated upgrading–regenerating cycles

Abstract The behaviour of HZSM-5 zeolite in the upgrading of a wood pyrolysis oil produced in the ENEL fast-pyrolysis plant located in Bastardo, Italy, was studied in repeated upgrading–regenerating cycles. The HZSM-5 zeolite performs a catalytic activity by its acidic sites that, through a carbonium ion mechanism, promote deoxygenation, decarboxylation and decarbonylation of the oil constituents, as well as cracking, oligomerisation, alkylation, isomerisation, cyclisation and aromatisation. As a consequence of the catalytic process, coke and tar were also obtained as undesirable by-products. The continued regeneration of the zeolite, consisting of removal of the coke deposits by air at 500°C, reduced the effectiveness of the catalyst in converting biomass pyrolysis oils to an aromatic product, until an irreversible deactivation was observed. By the analysis conducted on the catalyst it was possible to assess that the loss of activity is mainly connected to the disappearance of a significant amount of acidic sites, mainly the stronger ones, due to the thermal cycling to which the catalyst was submitted. Even if the regeneration was conducted at 500°C, localised raisings of temperature above 500°C due to the combustion of coke may have caused dehydroxylation of the Bronsted acid sites that predominate in zeolites activated at 500°C with formation of Lewis acid sites. Thus, the active acid sites in the upgrading reactions are presumed to be preferentially Bronsted acid sites, which were gradually deactivated by the repeated regeneration treatments.

Catalytic upgrading of pyrolytic oils to fuel over different zeolites

The upgrading of wood pyrolysis oils produced in the ENEL fast-pyrolysis plant located in Bastardo, Italy, and in the Union Fenosa fast-pyrolysis plant located in La Coruna, Spain, was studied by using HZSM-5 and H-Y zeolites in a fixed-bed laboratory scale reactor, at different temperatures and residence times. The products of the catalytic upgrading were a liquid fraction, char, coke, tar and gas. While the upgraded liquid obtained by using the HZSM-5 consisted of easily separable organic and aqueous layers, the liquid obtained by using the HY zeolite consisted of a single phase in which the organic components were either dispersed or dissolved in the water. The effect of temperature, catalyst type and residence time in the reactor on the yields of the fractions obtained (oil, char, tar, coke, gas and aqueous fraction) and on the characteristics of the upgraded oils was examined.

Brassica carinata as an alternative oil crop for the production of biodiesel in Italy: agronomic evaluation, fuel production by transesterification and characterization.

In this study, the non-food use of Brassica carinata oil for biodiesel production was investigated. B. carinata, a native plant of the Ethiopian highlands widely used as food by the Ethiopians, has recently become object of increasing interest. This is due to its better agronomic performances in areas such as Spain, California and Italy that are characterized by unfavorable environmental conditions for the cultivation of Brassica napus (by far the most common rapeseed cultivated in continental Europe). The agronomic performance and the energetic balance described here confirmed that B. carinata adapted better and was more productive both in adverse conditions (clay- and sandy-type soils and in semi-arid temperate climate) and under low cropping system when compared with B. napus. The biodiesel, produced by transesterification of the oil extracted from the B. carinata seeds, displayed physical–chemical properties suitable for the use as diesel car fuel. A comparison of the performance of B. carinata oil-derived biodiesel with a commercial biodiesel and petroleum diesel fuel was conducted as regards engine performance, regulated and unregulated exhaust emissions. These results make B. carinata a promising oil feedstock for cultivation in coastal areas of central-southern Italy, where it is more difficult to achieve the productivity potentials of B. napus, and could offer the possibility of exploiting the Mediterranean marginal areas for energetic purposes.

Modelling and simulation of time varying slag flow in a Prenflo entrained-flow gasifier

A slag building simplified model has been developed to simulate the time varying phenomena connected to the slag accumulation and flow on the walls of a Prenflo coal gasifier. For this purpose this model has been integrated with a three-dimensional code which provides the temperature and concentration profiles of the gas phase within the gasifier. The integrated models have been used to evaluate the effects of changes of the gasifier operating conditions on the slag behaviour.

Empirical correlations of the ash fusion temperatures and temperature of critical viscosity for coal and biomass ashes

Empirical correlations have been derived by regression analysis to calculate the ash fusion temperatures under reducing conditions and the temperature of critical viscosity from the ash chemical composition. The data-base used in this work includes about 300 ash samples from coals of different sources and biomasses. The standard deviation, σ, for these equations are generally about 45–80°C. These fall within the experimental errors of the measurements. These correlations: (1) provide a tool for calculating the thermal properties of the ash from its chemical composition; (2) provide a method to predict the effect of adding minerals (such as CaO) normally used to modify the slag behaviour.

Recovery of vanadium from heavy oil and Orimulsion fly ashes

This work concerns a three-step process for the recovery of vanadium from heavy oil and Orimulsion combustion fly ashes. This consisted of acid leaching, oxidation and precipitation of the vanadium pentoxide, followed by washing of the precipitate. Preliminary tests were conducted to investigate the effect of some operating parameters for the various steps of the process. After these preliminary tests, the recovery of vanadium from the fly ash samples was performed on a laboratory scale and the overall yield of the process was determined. By washing the precipitate, it was possible to reduce the concentration of the impurities and to allow its use for the production of ferrovanadium alloys.

Mercury removal from geothermal exhaust gas by sulfur-impregnated and virgin activated carbons

Sulfur-impregnated and virgin activated carbons have been used in a laboratory scaled fixed-bed reactor to investigate their capability of removing mercury vapours from a gas mixture containing H2S, O2 and moisture that is representative of the exhaust gas emissions of the geothermal power plants of the Monte Amiata field in Italy. The observed deposition of sulfur from H2S oxidation on the carbonaceous matrix increases the mercury scavenging capacity of the commercial sulfur-impregnated activated carbon and makes virgin activated carbon capable of adsorbing mercury vapours by the formation of HgS contextually to the deposition of sulfur, achieving a mercury adsorption capacity comparable to the commercial sulfur-impregnated activated carbon. This result suggests that the extremely economic virgin activated carbon can be used in this specific application, provided that a suitable carbonaceous matrix is selected to achieve a sulfur deposition rate that can guarantee a high mercury adsorption capacity.

Recovery of vanadium from a previously burned heavy oil fly ash

Abstract The recovery of vanadium from heavy oil fly ash having a high carbon content was performed using a four-step process consisting of a preliminary burning in order to reduce the carbonaceous fraction, followed by an acid leaching and an oxidative precipitation of vanadium pentoxide. The preliminary burning was conducted in the temperature range 650 to 1150 °C, below the initial deformation temperature (IDT) of the fly ash. The temperature of the preliminary burning step was revealed to be a significant parameter. Above 950 °C various phenomena (fusion, volatilisation of V, formation of V–Ni refractory compounds) occurred that adversely affected the recovery of vanadium. The burning temperature of 850 °C was found to be the best as a result of the trade-off between the overall vanadium recovery yield (83%) and the V2O5 weight percentage in the precipitate (84.8%).

Effect of sewage sludge content on gas quality and solid residues produced by cogasification in an updraft gasifier.

In the present work, the gasification with air of dehydrated sewage sludge (SS) with 20 wt.% moisture mixed with conventional woody biomass was investigated using a pilot fixed-bed updraft gasifier. Attention was focused on the effect of the SS content on the gasification performance and on the environmental impact of the process. The results showed that it is possible to co-gasify SS with wood pellets (WPs) in updraft fixed-bed gasification installations. However, at high content of sewage sludge the gasification process can become instable because of the very high ash content and low ash fusion temperatures of SS. At an equivalent ratio of 0.25, compared with wood pellets gasification, the addition of sewage sludge led to a reduction of gas yield in favor of an increase of condensate production with consequent cold gas efficiency decrease. Low concentrations of dioxins/furans and PAHs were measured in the gas produced by SS gasification, well below the limiting values for the exhaust gaseous emissions. NH(3), HCl and HF contents were very low because most of these compounds were retained in the wet scrubber systems. On the other hand, high H(2)S levels were measured due to high sulfur content of SS. Heavy metals supplied with the feedstocks were mostly retained in gasification solid residues. The leachability tests performed according to European regulations showed that metals leachability was within the limits for landfilling inert residues. On the other hand, sulfate and chloride releases were found to comply with the limits for non-hazardous residues.

Preparation of activated carbons from heavy-oil fly ashes

The use of heavy oil fly ash with high ash content (45 wt.%) as a precursor for the preparation of activated carbons has been investigated. The raw fly ash and the fly ash with lower ash content, obtained by a HCl/HF washing treatment, have been pyrolyzed at 900 degrees C and then activated with CO(2) in the temperature range of 800-900 degrees C for different times. The activated carbons have been characterised as regards the surface area and the pore volume. The evolution of the porosity has been related to the burn-off degree.