• Energy Research

This study looked at the potential synergy of co-pyrolysis of residual lignocellulosic biomass in the form of olive stone with low-density polyethylene in the absence/ presence of solid acid catalyst in a bench scale continuous bubbling fluidised bed reactor. Despite the catalyst lowering the pyrolytic oil yield, there was significant transition in the class of hydrocarbon derivatives formed with catalytic co-pyrolysis yielding much more deoxygenated hydrocarbons in contrast to the product class from the inert sand bed. .-alumina performed much better improving the H/C molar ratio of bio-oil by ~20% over the inert bed co-pyrolysis experiment, both the .-alumina and HZSM-5 catalyst significantly lowered the O/C molar ratio of bio oil recovered. The product stream from both catalysts was relatively high in polycyclic aromatic hydrocarbons (PAHs)due to the strong acid catalysed reactions which promotes strong aromatisation. Proceedings of the 29th European Biomass Conference and Exhibition, 26-29 April 2021, Online, pp. 817-823

Recently the use of lignocellulosic feedstock as source of fermentable sugars has been extensively investigated in order to develop biorefinery processes to produce liquid biofuels and bio-commodities. In particular, second generation biofuels have been proposed as the result of the conversion of sugars from residual biomass such as agriculture and food industry by-products. An example of liquid biofuel produced through sugar-based biorefinery is bio-butanol [1]. The possibility to produce butanol from low cost feedstocks, such as lignocellulosic food wastes, has been recently explored [2]. This process, as well as all the second generation biorefinery processes, asks for physical or chemical pretreatments of the lignocellulose (e.g., acid hydrolysis, alkaline wet oxidation and steam explosion) in order to mitigate the hindrance effect of lignin that limits the accessibility of carbohydrates to the hydrolytic enzymes. Despite the progress made in developing innovative biomass delignification processes [3], some drawbacks still exist that need to be faced. Further efforts are therefore needed in order to identify biomass pretreatments that are able to break up the lignocellulosic structure, to decrease the cellulose crystallinity, and at the same time to provide a high hemicellulose recovery while limiting the formation of inhibitory compounds [4]. Moreover, most of the pretreatment processes requires large water, solvents or energy consumption and are typically implemented at large scale as first operation in the biorefinery sites. More versatile processes that might be locally applied for distributed production and collection of lignocellulosic feedstock are required in order to develop 'intermediate' carbon vectors in the form of stable and ready-to-use resources. To this aim, the investigation of mild thermochemical processes such as torrefaction can offer wide opportunities. Torrefaction is a mild thermo-chemical treatment where biomass is heated in an inert environment up to a temperature ranging between 200 and 300 °C. It is characterized by low particle heating rate (< 50 °C/min) and a relatively long reactor residence time (5 -120 min) [5]. Even though, so far, torrefaction has been mostly adopted as a biomass pretreatment technology for thermochemical conversion pathways (i.e. combustion, pyrolysis and gasification), there are evidence in the pertinent literature [6] that torrefied feedstocks can be enzymatically hydrolyzed for lignocellulosic bioethanol production. Brachi et al. (2017) [7] have also found that torrefaction promote the conversion of crystalline cellulose into an amorphous state, the latter being more susceptible to the enzymatic hydrolysis than the former. Among the other effects, torrefaction improves the grindability of fibrous materials [5], which may reduce the energy demand for grinding the feedstock before hydrolysis, and turned out to be a suitable pretreatment to improve the fuel properties of lignin residues resulting from enzymatic hydrolysis [8]. In the light of the abovementioned benefits, the potential of combining biomass torrefaction with enzymatic hydrolysis for lignocellulosic butanol and isopropanol production has been preliminary investigated in the present paper by using coffee silverskin as a feedstock. In more details, thermogravimetric runs and lab-scale fixed bed torrefaction tests have been carried out to identify the process temperature, which allows minimizing the content of lignin in the torrefied solid, while preserving the original amount of cellulose and hemicellulose. The basic idea is to exploit the different thermal stability and reactivity that hemicellulose, cellulose and lignin exhibit because of their different composition and structure.

To promote the integration between solar-driven torrefaction, Power-to-Gas, and Chemical Looping Combustion (CLC) systems, this work numerically analyzes the performances of a novel process layout. Several agro-industrial residues were considered as fuels. CuO supported on zirconia and Ni supported on alumina were considered as oxygen carrier and methanation catalyst, respectively. Torrefied samples were purposely obtained by means of experimental runs carried out for 30 min at 300 °C in a lab-scale fixed bed reactor under a nitrogen atmosphere. Under the adopted conditions it was attained an increase in the lower heating values (LHV) of the selected feedstocks by about 14-49 %, depending on the different composition and reactivity of the parent biomass. Based on these data, it was estimated that, with respect to 10 kg h-1 torrefied biomass fed to the CLC system, a total thermal power production in the range of 28-58 kW can be achieved. CO2 conversion degrees of above 98 % were evaluated for the methanation unit in all considered scenarios. Considering different locations in Italy, PV field sizes ranging from 45 m2 up to 1392 m2 were evaluated for the solar-driven torrefaction unit. Wider sizes were calculated for the hydrogen production one, ranging from 3366 m2 up to 5598 m2. Eventually, an electric energy storage efficiency of around 16 % was assessed for the proposed layout. Finally, it was found that moving from the adopted torrefied feedstocks to the produced gaseous fuel, an increase in the LHV by about 44-55 % can be attained, while concurrently, CO2 emissions are favorably decreased by 98 %.

Crude bio-oil obtained from fast pyrolysis of biomass and wastes is typically characterised by the presence of high levels of oxygenated compounds, which are mainly responsible for its unfavourable characteristics (e.g., low heating value, high acidity, and poor storage stability). In order to overcome this drawback and favourably produce drop-in fuels, the fast pyrolysis of olive stone (OS), has been studied by giving particular attention to the exploration of operating conditions (i.e. pyrolysis temperature) and strategies (i.e. catalytic pyrolysis and co-pyrolysis) suitable to promote efficient de-oxygenation of bio-oils and improve the quality of the product streams. Steady state fast pyrolysis tests were performed in a bench scale fluidized bed reactor (gas residence time ~1s). Pyrolysis tests were carried out at 500 °C and 600 °C by using either inert sand or ?-alumina catalyst as bed material. Outcomes from the non-catalytic and the catalytic co-pyrolysis of low-density polyethylene (LDPE) and OS (plastic-to-biomass ratio of 20/80) at two different temperatures (500 and 600 °C) are also presented. Preliminary findings highlight that the co-processing of LDPE and OS under non-catalytic conditions stands out for the formation of long-chain aliphatic hydrocarbons in the form of both liquid paraffins and wax deposits, which are well-known to be the primary products evolved from the pyrolysis of polyolefins. The addition of ?-alumina catalyst significantly affects both the distribution and the quality of the pyrolytic products (char, bio-oils, and gas). Under catalytic co-pyrolysis conditions, a marked reduction in the yield of bio-liquid is observed, compensated by a remarkable improvement in its quality, particularly in terms of the formation of light mono-aromatics and a marked decrease in the total amount of the oxygenated compounds. On the downside, however, a significant increase in the production of polycyclic aromatic hydrocarbons (PAHs) is detected. Remarkable benefits are also detected by increasing the co-pyrolysis temperature to 600 °C, particularly in terms of content of oxygenated compounds in the bio-oils, as well as in terms of PAHs and water formation, which decreased considerably. Altogether, preliminary findings of this study suggest that further research efforts are required in order to improve the process performance, for example by optimizing the operating conditions as well as the physicochemical properties of catalysts.

In this study, the integration between anaerobic digestion and Power-to-Gas system is proposed and numerically investigated. The rationale behind the proposed layout is that direct conversion of biogas CO2 content to CH4 without its prior separation increases biomethane yield and reduces to nearly zero carbon dioxide emissions from biogas cleaning/upgrading process. Detailed design of a methanation unit composed of multistage adiabatic reactors is presented by combining a thermodynamic equilibrium analysis carried out by means of the Aspen plus(TM) software and process simulations at steady state (including kinetic modelling) implemented in MATLAB. The performances of the proposed layout are benchmarked against those of conventional biogas upgrading techniques in terms of methane losses and purity and CO2 recovery. The proposed system not only equals conventional technologies with respect to produced methane purity (95%) but also outperforms them with respect to CH4 losses (~0%) and CO2 recovery (>97%).

This work numerically analyzes an innovative process layout considering a torrefaction processes followed by chemical looping combustion of biomass waste, solar hydrogen, and carbon methanation. System performances were evaluated by considering several agro-industrial residues (i.e., sugar beet pulp from sugar production, grape marc from winemaking and olive pits from olive oil production) as fuels, CuO supported on zirconia as oxygen carrier, and Ni supported on alumina as methanation catalyst. The torrefaction pre-treatment was proposed for upgrading the properties, namely heating values, moisture content as well as hydrophobicity, and storability, of the selected biomasses. To this aim, experimental runs were performed at 300 °C and 30 min in a lab-scale fixed bed reactor under an inert atmosphere of nitrogen. The study was complemented with an extensive investigation on fuel properties (i.e., ultimate analysis, proximate analysis, calorific values determination) of both the untreated and the torrefied samples, which provides useful input data for modelling their conversion processes. By considering that only electric energy from renewable sources is used, the capability of the proposed process to be used as an energy storage system was eventually assessed.

The kinetics of the thermal decomposition of tomato peel residues under nitrogen atmosphere was studied by non-isothermal thermogravimetric analysis in the heating rate range 2-40 °C/min. Due to the complexity of the kinetic mechanism, which implies simultaneous multi-component decomposition reactions, an analytical approach involving the deconvolution of the overlapping decomposition steps from the overall differential thermogravimetric curves (DTG) and the subsequent application of model-free kinetic methods to the separated peaks was employed. Two freely available Matlab functions, which adopt a non-linear optimization algorithm to decompose a complex overlapping-peak signal into its component parts, were used. Different statistical functions (i.e., Gaussian, Voigt, Pearson, Lorentzian, equal-width Gaussian and equal-width Lorentzian) were tested for deconvolution and the best fits were obtained by using suitable combinations of Gaussian and Lorentzian functions. For the kinetic analysis of the deconvoluted DTG peaks, the Friedman's isoconversional method was adopted, which does not involve any mathematical approximation. The reliability of the derived kinetic parameters was proved by successfully reproducing two non-isothermal conversion curves, which were recorded at a heating rate of 60 °C/min and 80 °C/min and not included in data set used for the kinetic analysis. Seven pseudocomponents were identified as a result of the deconvolution procedure and satisfactorily associated with the main constituents of the investigated tomato peels.

Currently a great emphasis is being placed on simplification and cost reduction in the production process of methanol from renewable biomass sources. The experimental results obtained in this work, using a pre-pilot fluidized bed gasifier, demonstrate that the co-gasification of regional biomass residues with PET (polyethylene terephthalate) or tyre wastes may be regarded as a useful strategy to achieve the above goals. In fact, the product gas composition resulting from the presence of the aforesaid polymeric wastes in the fuel blend is such that the gas from the steam reforming unit does not need to be further conditioned in a water-gas shift reactor; the sole carbon dioxide capture process is sufficient to meet the requirements for the downstream methanol production. No significant differences in gas composition were observed moving from the PET to tyre-based pellets, but penalties were noted for the latter concerning tar and particulate generation.