Volume 13, Issue 2 - Special Issue: The 4th International Congress on Green Process Engineering (GPE2014), Guest Editor: Martine Poux

The aim of this work is to identify solid sorbents for CO 2 capture for coal and biomass syngas conditioning and cleaning by means of a sorption-enhanced reaction process. Hydrotalcite-like compounds (HTlcs) were synthesized with and without K 2 CO 3 impregnation. Samples were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) porosimetry after synthesis and after capture tests, respectively. Sorption and desorption tests were performed in a fluidized bed reactor, under cyclic conditions, at two different temperature levels: 350/450°C and 600/700°C. At low temperature only the Mg–Al HTlcs K promoted samples showed stability and sorption capacity comparable with literature values. On the other hand, results at high temperature indicate that the mixed Mg-Ca-Al HTlcs samples exhibit the best behavior with the highest sorption capacity (1.7 mmol CO2 /g) almost stable over 5 sorption/regeneration cycles; furthermore, addition of steam allowed increasing their reactivity by 70% compared to the dry value. This type of sorbent could be a promising candidate to prepare a bifunctional sorbent–catalyst for sorption-enhanced processes, taking place directly in the fluidized bed gasifier, or downstream the reactor for adjustment of gas composition before further conversion in gaseous energy carriers.

In spite of good performances of the membrane bioreactor (MBR) process, permeate from it can still contain refractory pollutants that have to be removed before water reuse or discharge. The present study is an attempt to combine the advantages of two well-known technologies, which are nanofiltration (NF) and electrochemical oxidation (EO) to treat MBR effluent from hospital wastewater. The concept is based on a preconcentration of micropollutants with a reduction of the wastewater volume by NF and treatment of the NF retentate by oxidation. During filtration process the rejection of ciprofloxacin, as a target molecule, reached beyond 97%. Then the NF retentate was treated by EO using a boron-doped diamond anode (BDD). Galvanostatic electrolyses showed that this anode is efficient to mineralize not only ciprofloxacin but also all the micropollutants and organics contained in MBR effluent. The results demonstrated that rapid mineralization occurred: the removal of total organic carbon and chemical oxygen demand (COD) reached 97% and 100%, respectively, in our conditions in 300 min maximum. The specific energy consumption for the total removal of COD was calculated to be 50 kW h kg ˗1 COD.

The overall aim of this research was to apply a hybrid constructed soil filter for sewage treatment. A hybrid constructed soil filter is an ecological process used for decentralized sewage treatment in villages, small towns or scattered residential areas. Sewage is firstly treated by conventional physicochemical or biological treatment and then allowed to infiltrate through aerated unsaturated zone wherein it gets purified through processes such as filtration, adsorption, chemical reaction and biodegradation. This system has demonstrated a consistent capacity to remove organic matter and nitrogen. Experimental results have shown that under hydraulic load rates of 0.22 m 3 /m 2 · h and organic load rates ranging from 47 to 156 g COD/m 2 · h, mean removal efficiencies of 89% for COD, 99% for BOD 5 , 86% for suspended solids and 52% for total nitrogen can be achieved using an hybrid constructed soil filter. Compared to the conventional activated sludge process, this technology has many advantages, such as simple construction, low operation and maintenance costs, as well as a simple operation.

Intensification process by the use of microwave heating was investigated by testing two catalyst configurations on the selective styrene oxidation for benzaldehyde production. The oxidation reaction was studied over Co-ZSM-11 and Fe-ZSM-11 catalysts. Their catalytic activity was evaluated by using these catalysts in two different forms: compacted pellets and fine particles. Thus, two reaction systems were studied under microwave: a batch system with fine particles in suspension (system 1) and a recirculating batch liquid through a fixed bed system comprising the compact catalyst pellets (system 2). Despite a better microwave interaction with the catalyst in the pellet form, the fixed bed configuration did not lead to a significant intensification of the process. At 60°C, the styrene molar conversions by using Co-ZSM-11 catalyst were found to be 33% and 3% for systems 1 and 2, respectively. With fine particles, the catalytic activity was higher since the styrene oxidation was able to occur without significant internal diffusional resistance of the reagents toward the active acid sites of the zeolite structure.

In this work, a gas containing CO 2 and SO 2 at the usual concentrations on the coal combustion flue gas reacted with calcium hydroxide to evaluate and quantify the influence of SO 2 on the CO 2 capture and vice versa. This influence was quantified with a continuous gas analyzer and by thermogravimetry (TG). Results show that the CO 2 retained increases in general as its concentration does and decreases as the SO 2 concentration increases. A similar behavior was found for the SO 2 retention at different CO 2 concentrations being more relevant the influence of the presence of SO 2 on the CO 2 capture than the opposite one. Results suggest that for a high CO 2 capture, SO 2 should be eliminated previously. With respect to the reaction process it was found that the desulfurization product clearly identified was CaSO 3 ·½H 2 O; in the reaction between Ca(OH) 2 and CO 2 , CaCO 3 is mainly obtained, the complex CaO·CO 2 being another possible product synthesized in low amount. Gas analyzer shows that SO 2 and CO 2 react simultaneously and that a part of the CaCO 3 reacts with the SO 2 and releases CO 2 . Sulfation values calculated by TG and from the gas analyzer are very similar but the amount of CO 2 captured is not possible to know clearly by TG due to the synthesis and decomposition of CaCO 3 during the process. The study of the evolution of the sorbent porosity in the process reveals that the presence of both acid gases produces a lower blockage of the pores than when only one gas is present probably due to the generation of new pores in the reaction of CaCO 3 and SO 2 .

Extraction of lactic acid from its aqueous solution was carried out at 30.0°C in a mixed solvent electrolyte system containing water, 1-butanol and ammonium sulfate ((NH 4 ) 2 SO 4 ). The salt appeared to reduce mutual solubility between water and 1-butanol leading to an enlarged two-phase region of the mixture. The effect was more pronounced at high salt concentration. In view of extraction, ternary mixture containing water, 1-butanol and lactic acid, (NH 4 ) 2 SO 4 effectively salted-out 1-butanol and lactic acid leading to a reduced concentration of these two components in the aqueous phase. Distribution coefficient and degree of lactic acid extraction were significantly improved with increasing concentration of the salt. Additionally, (NH 4 ) 2 SO 4 helped lessen the transfer of one solvent into the other, which is the problem normally encountered in extraction when partially miscible solvents are employed. It also advantageously allowed the extraction to be carried out at a high solvent-to-aqueous phase volume ratio, where large recovery of the acid was achieved. Extraction of lactic acid in this mixed solvent electrolyte system could be further improved by operating it in a stage-wise mode rather than a batch one.

Scrap tyres represent a severe environmental problem that must be solved by developing technologies allowing the processing of high quantities of this residue. This work presents the results of pyrolysis oil and pyrolytic char production by intermediate pyrolysis of rubber recovered from scrap tyres. The influence of process variables such as particle size, temperature and reaction time on the characteristics of the products obtained was analysed. Maximal yields of 52.56 and 39.50 wt% of pyrolysis oil and pyrolytic char, respectively, were obtained, under operational conditions that favoured the production of pyrolysis oil. The products obtained were a pyrolytic char with a maximal surface area of 85.16 m 2 /g and fixed carbon content of 78.55 wt%; and pyrolysis oil with a higher heating value of 42.94 MJ/kg, real density of 0.948 g/mL, viscosity 2.29×10 −3 Pa s and acidity between 0.39 and 1.57 mg KOH/g. The highest total aromatics (benzene, toluene, xylenes and ethylbenzene) yield in pyrolysis oil was obtained at a temperature of 466°C and volumetric gas flow of 155 NmL/min. In addition, at these conditions, the pyrolysis oil having the maximum aromatic yield showed the lowest acidity. Nevertheless, it was observed that the highest pyrolysis oil yield does not necessarily lead to a higher yield of aromatics.