• Energy Research

Abstract Pressure swing adsorption (PSA) is an interesting technology for biogas upgrading, due to compactness of the equipment, low energy requirements, low capital cost, and safety and simplicity of operation. Unfortunately, some shortcomings penalize its diffusion in comparison with other technologies; in particular, conventional PSA has a low methane recovery and cannot compete in this field with other processes such as amine scrubbing; furthermore, it produces an off gas stream with a significant methane content, which requires further treatment to avoid the emission of residual methane into the atmosphere. In this framework, this study focuses on the feasibility of a PSA based separation process able to obtain a biomethane stream suitable to be injected in the natural gas grid (CO 2 2 stream (CO 2 > 99%). The proposed process uses Zeolite 5A as adsorbent material in two PSA units; the biogas is fed to the first unit which produces biomethane; the off gas of the first unit is sent to a second PSA unit which separates carbon dioxide from a residual gas stream, recycled to the first to enhance methane recovery. A dynamic non-isothermal model, based on the linear driving force approximation, is employed to demonstrate the technological feasibility of the separation units and to assess the performance of the whole process. In particular a methane recovery greater than 99% can be obtained with energy consumption of about 1250 kJ per kg of biomethane.

The applicability of a sequencing batch two phase partitioning bioreactor (TPPB) to the biodegradation of a highly toxic compound, 2,4-dichlorophenol (DCP) (EC(50)=2.3-40 mgL(-1)) was investigated. A kinetic study of the individual process steps (DCP absorption into the polymer, desorption and biodegradation) was performed and, based on favourable absorption/desorption characteristics (DCP diffusivity of 6.6×10(-8)cm(2)s(-1)), the commercial polymer Tone P787 (Dow Chemical), was utilized as the sequestering phase for TPPB operation. Batch kinetic biodegradation tests were performed in both single- and two-phase modes, and the Haldane equation kinetic parameters were estimated (k=1.3×10(-2) mgDCP mgVSS(-1)h(-1), K(I)=35 mgDCPL(-1) and K(s)=18 mgDCPL(-1)), confirming the highly toxic nature of DCP. Consistent with these findings, operation of the single-phase system showed that for an initial DCP concentration of 130 mg L(-1) the biomass was completely inhibited and DCP was not degraded, while the two-phase system achieved near-complete DCP removal. In sequencing batch mode the TPPB had a removal efficiency of 91% within 500 min for a feed of 320 mg L(-1), which exceeds the highest concentration previously degraded. These results have confirmed the effectiveness of the use of small amounts (5%, v/v) of inexpensive commercial polymers as the partitioning phase in TPPB reactors for the treatment of a highly toxic substrate at influent loads that are prohibitive for conventional single-phase operation, and suggest that similar detoxification of wastewater influents is achievable for other target cytotoxic substrates.

In this paper, a comparison is provided between liquid-liquid and liquid-solid partitioning systems applied to the removal of high concentrations of 4-nitrophenol. The target compound is a typical representative of substituted phenols found in many industrial effluents while the biomass was a mixed culture operating as a conventional Sequencing Batch Reactor and acclimatized to 4-nitrophenol as the sole carbon source. Both two-phase systems showed enhanced performance relative to the conventional single phase bioreactor and may be suitable for industrial application. The best results were obtained with the polymer Hytrel™ which is characterized by higher partition capability in comparison to the immiscible liquid solvent (2-undecanone) and to the polymer Tone™. A model of the two systems was formulated and applied to evaluate the relative magnitudes of the reaction, mass transfer and diffusion characteristic times. Kinetic parameters for the Haldane equation, diffusivity and mass transfer coefficients have been evaluated by data fitting of batch tests for liquid-liquid and liquid-solid two phase systems. Finally, preliminary results showed the feasibility of polymer regeneration to facilitate polymer reuse by an extended contact time with the biomass.

The manganese-ferrite thermochemical cycle developed by ENEA for hydrogen production, whose maximum temperature level lays in the range 750-800 C, has a high potential for coupling with the solar source using conventional structural materials. As a first step for the on sun feasibility validation of the cycle, an experimental survey of the thermal performance of a receiver-reactor designed by ENEA, to be powered by a solar furnace (1 kW), has been carried out in the absence of a reaction. The temperature distribution over the reactor chamber as a function of solar irradiation has been measured and the thermal inertia of the system has been evaluated. The experimental results confirm that the reactor temperature and inertia are compatible with the manganese-ferrite cycle and other cycles operating at moderate temperatures. In order to set the basis for the evaluation of this and other similar prototypes, a finite element model (FEM) has been developed to describe the thermofluidodynamic behavior of the reactor. Good agreement between calculated and experimental data has been obtained; therefore this model will be improved and extended to describe both the hydrogen and oxygen releasing reactions of the manganese-ferrite cycle, with the aim of optimizing the reactor design.

AbstractThis paper presents a project named CoMETHy (Compact Multifuel-Energy to Hydrogen converter) co-funded by the European Commission under the Fuel Cells and Hydrogen Joint Undertaking (FCH JU). The project is developing an innovative steam reformer for pure hydrogen production to be powered by Concentrating Solar Power (CSP) plants using molten salts as heat transfer fluid. Due to the limitations in the molten salts maximum operating temperature of 550°C, the reformer should operate at lower temperatures than conventional steam reforming processes. This implies the development of an innovative system, involving different R&D topics presented in this paper.

The present study has provided a comparison between a conventional ex situ method for the treatment of contaminated soil, a soil slurry bioreactor, with a novel technology in which a contaminant is rapidly and effectively removed from the soil by means of absorptive polymer beads, which are then added to a two-phase partitioning bioreactor (TPPB) for biodegradation of the target molecule. 4-nitrophenol (4NP) was selected as a model contaminant, being representative of a large class of xenobiotics, and the DuPont thermoplastic Hytrel™ 8206 was utilized for its extraction from soil over ranges of soil contamination level, soil moisture content, and polymer:soil ratios. Since the polymers were able to rapidly (up to 77% and 85% in 4 and 24h respectively) and selectively remove the contaminant, the soil retained its nutrient and microflora content, which is in contrast to soil washing which can remove these valuable soil resources. After 4h of reaction time, the TPPB system demonstrated removal efficiency four times higher (77% vs 20%) than the slurry system, with expected concomitant savings in time and energy. A volumetric removal rate of 75 mg4NPh(-1) L(-1) was obtained in the TPPB, significantly greater than the value of 1.7 obtained in the slurry bioreactor. The polymers were readily regenerated for subsequent reuse, demonstrating the versatility of the polymer-based soil treatment technology.