Elsa Weiss-Hortala

Agro-industrial waste to solid biofuel through hydrothermal carbonization

In this paper, the use of grape marc for energy purposes was investigated. Grape marc is a residual lignocellulosic by-product from the winery industry, which is present in every world region where vine-making is addressed. Among the others, hydrothermal carbonization was chosen as a promising alternative thermochemical process, suitable for the treatment of this high moisture substrate. Through a 50 mL experimental apparatus, hydrothermal carbonization tests were performed at several temperatures (namely: 180, 220 and 250 °C) and residence times (1, 3, 8 h). Analyses on both the solid and the gaseous phases obtained downstream of the process were performed. In particular, solid and gas yields versus the process operational conditions were studied and the obtained hydrochar was evaluated in terms of calorific value, elemental analysis, and thermal stability. Data testify that hydrochar form grape marc presents interesting values of HHV (in the range 19.8-24.1 MJ/kg) and physical-chemical characteristics which make hydrochar exploitable as a solid biofuel. In the meanwhile, the amount of gases produced is very small, if compared to other thermochemical processes. This represents an interesting result when considering environmental issues. Statistical analysis of data allows to affirm that, in the chosen range of operational conditions, the process is influenced more by temperature than residence time. These preliminary results support the option of upgrading grape marc toward its energetic valorisation through hydrothermal carbonization.

Hydrothermal carbonization of off-specification compost: A byproduct of the organic municipal solid waste treatment

The possibility to apply the hydrothermal carbonization (HTC) process to off-specification compost (EWC 19.05.03) at present landfilled was investigated in this work. The aim was to produce a carbonaceous solid fuel for energy valorization, with the perspective of using HTC as a complementary technology to common organic waste treatments. Thus, samples of EWC 19.05.03 produced by a composting plant were processed through HTC in a batch reactor. Analytical activities allowed to characterize the HTC products and their yields. The hydrochar was characterized in terms of heating value, thermal stability and C, H, O, N, S and ash content. The liquid phase was characterized in terms of total organic carbon and mineral content. The composition of the gas phase was measured. Results show that the produced hydrochar has a great potentiality for use as solid fuel.

The effect of temperature and heating rate on char properties obtained from solar pyrolysis of beech wood

Char samples were produced from pyrolysis in a lab-scale solar reactor. The pyrolysis of beech wood was carried out at temperatures ranging from 600 to 2000°C, with heating rates from 5 to 450°C/s. CHNS, scanning electron microscopy analysis, X-ray diffractometry, Brunauer-Emmett-Teller adsorption were employed to investigate the effect of temperature and heating rate on char composition and structure. The results indicated that char structure was more and more ordered with temperature increase and heating rate decrease (higher than 50°C/s). The surface area and pore volume firstly increased with temperature and reached maximum at 1200°C then reduced significantly at 2000°C. Besides, they firstly increased with heating rate and then decreased slightly at heating rate of 450°C/s when final temperature was no lower than 1200°C. Char reactivity measured by TGA analysis was found to correlate with the evolution of char surface area and pore volume with temperature and heating rate.

Glycerol and bioglycerol conversion in supercritical water for hydrogen production

Catalytic transesterification of vegetable oils leads to biodiesel and an alkaline feed (bioglycerol and organic residues, such as esters, alcohols…). The conversion of bioglycerol into valuable organic molecules represents a sustainable industrial process leading to the valorization of a renewable organic resource. The physicochemical properties in the supercritical domain (T>374°C, P>22.1 MPa) transform water into a solvent for organics and a reactant favouring radical reactions. In this context, the conversion of bioglycerol in supercritical water (SCW) into platform molecules and/or high energetic gases (hydrogen, hydrocarbons) could represent an interesting valorization process. The reported research results concern the conversion of bioglycerol compared to pure glycerol. The experiments have been done in batch autoclaves (5 ml and 500 ml stirred). Solutions of pure (5 or 10 wt%) and crude (3.5 wt%) glycerol have been processed with or without catalyst (K2CO3 1.5 wt%) in the range of 450–600°C. The molecular formula of bioglycerol was determined as C4.3H9.7O1.8Na0.1Si0.08. Glycerol was partially decomposed in the batch systems during the heating (42% before reaching 420°C) and some intermediates (propanediol, ethylene glycol …) were quantified, leading to a proposition of a reaction pathway. Acrolein, a valuable platform molecule, was mainly produced in the absence of catalyst. No solid phase was recovered after SCW conversion of pure and bioglycerol in batch reactors. The optimal parameters for gasification were 600°C, 25 MPa for bioglycerol and 525°C, 25 MPa, for pure glycerol. In these operating conditions, 1 kg of pure or bioglycerol leads to 15 and, respectively, 10 mol of hydrogen. Supercritical water gasification of crude glycerol favoured the generation of light hydrocarbons, while pure glycerol promoted H2 production. SCW conversion of glycerol (pure and crude) allows to obtain simultaneously energetic gases (respectively 2600 and 4000 kcal/kg glycerol) and valuable platform molecules.

Hydrothermal liquefaction of blackcurrant pomace and model molecules: understanding of reaction mechanisms

Hydrothermal liquefaction (HTL) refers to the conversion of carbonaceous resources into oily substances in hot pressurized liquid water. During this process, constitutive biomass molecules decompose into thousands of organic compounds, following complex reaction mechanisms. The chemistry behind HTL processes is highly complex and still poorly understood to date, in spite of many research efforts. After a detailed analysis of a wet bioresource, blackcurrant pomace, a selection of representative model compounds was subjected to hydrothermal liquefaction conditions (300 C, 60 min), either alone or as binary, ternary and quaternary mixtures: glucose, xylose, and microcrystalline cellulose were chosen to represent carbohydrates; guaiacol and alkali lignin for native lignin; glutamic acid for proteins; and linoleic acid for lipids. The results show that the reaction products mainly arise from degradation of individual compounds. The main reactions that can be identified are decarboxylation, dehydration, and condensation reactions producing heavy compounds found in the bio oil and the char. Some binary interactions have been identified such as the Maillard reaction between carbohydrates and proteins, and also a strong interaction between carbohydrates and lipids for bio oil formation. Comparative experiments showed that HTL of the real resource (blackcurrant pomace) could be qualitatively represented by model mixtures, in terms of the molecular composition of the products, especially when model fibres were used. The quantitative representativeness of the simulating monomers is lower than that obtained by using model polymers.

Synthesis, characterization, and thermo-mechanical properties of copper-loaded apatitic calcium phosphates

Copper is well known as a classical transition metal used in heterogeneous catalysis. In this study, copper-loaded apatitic calcium phosphates were prepared using incipient wetness impregnation (IWI) and ionic exchange (IE) methods. The interaction between copper precursor (copper nitrate trihydrate, Cu(NO3)2∙3H2O) and apatitic calcium phosphate (CaP) depended strongly on the preparation method and the content of copper-loaded. Using IE, copper(II) cations (Cu2+) were incorporated in the apatitic structure of CaP. The content of copper(II) cations seemed to be limited at about 2.2 wt.%. Calcination at 400 °C had no influence on the solids obtained by the IE method. Using IWI, the deposition of a theoretical copper content of 2 wt.% led to the incorporation of copper(II) cations in the apatitic structure of CaP by IE with Ca2+, despite the low quantity of aqueous solvent used. Therefore the resulting product was similar to that obtained by IE. When the theoretical copper content rose to 20 wt.%, the entire amount of copper precursor molecules were largely deposited, which resulted in the formation of copper oxide particles (CuO) after air calcination at 400 °C. Thermo-mechanical analysis study showed that the presence of copper oxide did not modify the thermal shrinkage of the initial calcium phosphate. On the other hand, thermal shrinkage was much more important in the case of CaP substituted with copper(II) cations.

Life cycle assessment of pyrolysis, gasification and incineration waste-to-energy technologies: Theoretical analysis and case study of commercial plants

Municipal solid waste (MSW) pyrolysis and gasification are in development, stimulated by a more sustainable waste-to-energy (WtE) option. Since comprehensive comparisons of the existing WtE technologies are fairly rare, this study aims to conduct a life cycle assessment (LCA) using two sets of data: theoretical analysis, and case studies of large-scale commercial plants. Seven systems involving thermal conversion (pyrolysis, gasification, incineration) and energy utilization (steam cycle, gas turbine/combined cycle, internal combustion engine) are modeled. Theoretical analysis results show that pyrolysis and gasification, in particular coupled with a gas turbine/combined cycle, have the potential to lessen the environmental loadings. The benefits derive from an improved energy efficiency leading to less fossil-based energy consumption, and the reduced process emissions by syngas combustion. Comparison among the four operating plants (incineration, pyrolysis, gasification, gasification-melting) confirms a preferable performance of the gasification plant attributed to syngas cleaning. The modern incineration is superior over pyrolysis and gasification-melting at present, due to the effectiveness of modern flue gas cleaning, use of combined heat and power (CHP) cycle, and ash recycling. The sensitivity analysis highlights a crucial role of the plant efficiency and pyrolysis char land utilization. The study indicates that the heterogeneity of MSW and syngas purification technologies are the most relevant impediments for the current pyrolysis/gasification-based WtE. Potential development should incorporate into all process aspects to boost the energy efficiency, improve incoming waste quality, and achieve efficient residues management.