María Atienza-Martínez

Two series of Ni and Co catalysts supported onto La-Al₂O₃ were prepared and the CO₂ hydrogenation reactions investigated. The catalytic performance was evaluated in terms of the evolution with the reaction temperature of the CO₂ conversion and product (CH₄ and CO) yields, as well as specific activities (TOF) and apparent activation energies. CH₄ was the favored product over both metals while the TOF for CH₄ formation was about three times higher for Ni than Co at 240–265 °C. Metallic particle size effects were found, with the TOF for CH₄ formation decreasing over both Ni and Co as the mean metallic size decreased. In contrast, the TOF for CO formation tended to increase at a decreasing particle size for the catalysts with the smallest Ni particle sizes. The apparent activation energies for Ni and Co were very similar and significantly decreased to values of 73–79 kJ/mol when the metallic dispersion increased. The catalysts were prepared using the all-in-one method, resulting in (poly)vinyl alcohol (PVA) being a key additive that allowed us to enhance the dispersion of Ni and Co to give very effective catalysts. This comparative study joins the few existing ones in the literature in which catalysts based on these metals operated under strictly the same reaction conditions.

In this paper, hydrochars and pyrochars were produced at 260 °C under different residence times (2 and 4 h) using anaerobic digested sewage sludge (SSL) as initial feedstock. The effect of reaction time on the fuel properties of hydrochars and pyrochars was evaluated. Moreover, the combustion kinetics of raw SSL and the derived pyrochars and hydrochars without coal blending were determined at two different air flows (20 and 90 mL/min) and compared. In the same conditions, the yield of hydrochar was significantly lower than that of pyrochar, confirming the different reaction pathways followed in each process. The results showed hydrochars have lower carbon recovery and energy yield than pyrochars, making the latter more suitable for energy purposes. The thermogravimetric combustion study showed that both thermochemical treatments increased the ignition temperature but decreased the burnout temperature, which results in higher stability during handling and storage. However, raw SSL is better for combustion than hydrochar according to the combustibility index. In addition, the kinetic study showed that the activation energy of the combustion of biochars, especially pyrochar, is lower than that of raw SSL, which is advantageous for their combustion.

A procedure to analyze sewage sludge (SS) pyrolysis liquids based on solvent fractionation has been developed. Pyrolysis liquids are separated into three different fractions: heptane soluble (Hep‐sol), dichloromethane soluble (DCM‐sol), and hydrochloric acid soluble (HCl‐sol). Diverse techniques (GC‐MS, UPLC‐TOF‐MS) were employed to qualitatively and quantitatively analyze liquid fractions to assess the potential production of value‐added chemicals. Aliphatic hydrocarbons, aliphatic nitriles, and steroids were mostly separated in the Hep‐sol fraction, phenols and fatty acids in the DCM‐sol fraction, and carboxylic acids and amides in the HCl‐sol fraction. The largest production was obtained for ammonia (10–14 kg per tonne of SS) and α‐olefins (8–9 kg per tonne of SS). The potential production of some of these value‐added chemicals from SS pyrolysis liquid was compared with their current European production. In the case of α‐olefins, 16 % of their European production could be achieved by SS pyrolysis.