Activated biochars used as adsorbents for dyes removal

Adsorption represents one of the most interesting technique for the removal of pollutants from wastewaters. Activated carbons show the best performances on this kind of processes but their high production costs limit their applications. In this context a big challenge is to find new materials having characteristic similar to those of commercial activated carbons but being environmental friendly and cheaper. In this work the adsorption efficiency of activated biochars produced from pine wood was investigated on the removal of dyes from water. An innovative method for the activation of the biochar using deep eutectic solvents (DES) was tuned and the characteristics of the obtained adsorbent material were compared with those of biochar activated with traditional method and non-activated biochar. The best adsorption capacities were obtained with the DES activated biochar, reaching a value of 480 mg/g for the methylene blue adsorption. Adsorption isotherm and kinetic models were applied to experimental data in order to understand the adsorption mechanism of the process

CFD model of a spinning disk reactor for nanoparticle production

The use of a spinning disk reactor (SDR) was investigated for the continuous production of nanoparticles of hydroxyapatite. SDR is an effective apparatus for the production of nanoparticles by wet chemical synthesis. Rotation of the disc surface at high speed creates high centrifugal fields, which promote thin film flow with a thickness in the range 50-500 ?m. Films are highly sheared and have numerous unstable surface ripples, giving rise to intense mixing. SDR performances are strongly affected by the adopted operating conditions such as the influence of rotation speed that determines the attainment of micro-mixing and the feeding point location that has a great influence on the particle size distribution of the product. The experimental device consists of a cylindrical vessel with an inner disk, 8.5 cm in diameter, made by PVC coated by an acrylic layer. The rotational velocity of the disc is controlled and ranges from 0 to 147 rad/s. The reagent solutions are fed over the disk at a distance of 5 mm from the disc surface through tubes, 1 mm in diameter. A computational fluid dynamic model, validated in a previous work, was used to optimize the operative conditions of SDR. Through the CFD model it is possible to analyse the hydrodynamic of the thin liquid film formed on the disk at different speed rotations and to individuate the best mixing conditions between the reagents varying the feeding point positions. The production of hydroxyapatite was also investigated adding the reaction kinetic to model the product formation in the liquid phase and the population balance equation to predict particle size distribution. The simulation results were compared with available experimental data showing that the CFD model is fully capable to describe the process and qualifies as a suitable engineering tool to perform the SDR process design. Copyright © 2015, AIDIC Servizi S.r.l

Biomass gasification plant and syngas clean-up system

Gasification is recognized as one of the most promising technologies to convert low quality fuels into more valuable ones. The principal problem related with the use of biomass in gasification processes is the high amount of tar released during the pyrolysis step. It is thus necessary to recover tar and to transform it in lighter combustible gas species such as CH4, CO and H-2. In this work the experimental results of a medium industrial scale plant fed with olive husk and having a capacity of 250 kWt are presented. The gasifier is composed by a up-draft reactor which is followed by a secondary fixed bed reactor filled with alluminium oxide spheres having high porosity dedicated to the tar conversion reactions. The syngas is then used to feed an internal combustion engine with a production of 60 kWe

Methane dry reforming over nickel perovsikite catalysts

In recent years dry reforming of methane (DRM) has received considerable attention as a promising alternative to steam reforming for synthesis gas (H2 and CO) production. This process could be industrially advantageous, yielding a syngas with a H2/CO ratio close to 1, suitable for Fischer-Tropsch synthesis to liquid hydrocarbons and for production of valuable oxygenated chemicals. The major drawback of the process is the endothermicity of the reaction that implies the use of a suitable catalyst to work at relatively low temperatures (923-1,023 K). Higher temperatures would make the process unaffordable for an industrial development and would increase the risk of undesirable side reactions, such as coke formation, that are the main causes of catalyst deactivation. In this work the activity of nickel perovskite catalysts were studied and the results were compared with rhodium perovskite. It is well known that rhodium is very active and stable for dry reforming but its high cost makes its utilization limited. The Ni, due to its low cost, is a promising substitute even if it is more susceptible to coking. The perovskite structure allows a high dispersion of the metal into the catalyst increasing the catalytic activity. In this work the Ni perovskite was obtained with two methods (auto-combustion and modified citrate methods). The results pointed out that the Ni perovskite obtained with the auto-combustion method is a promising route for the use of Ni in this process. The experimental tests show that with Ni catalyst very good activity can be achieved from temperature of 973 K

Biocrude production by hydrothermal liquefaction of olive residue

Hydrothermal liquefaction (HTL) converts biomass into a crude bio-oil by thermally and hydrolytically decomposing the biomacromolecules into smaller compounds. The crude bio-oil, or biocrude, is an energy dense product that can potentially be used as a substitute for petroleum crudes. Liquefaction also produces gases, solids, and water-soluble compounds that can be converted to obtain valuable chemical species or can be used as energy vectors. The process is usually performed in water at 250°C-370°C and under pressures of 4-22 MPa: depending on the adopted pressure and temperature the process can be carried out in sub-critical or super-critical conditions. In the conditions reached in hydrothermal reactors, water changes its properties and acts as a catalyst for the biomass decomposition reactions. One of the main advantages of this process is that the energy expensive biomass-drying step, required in all the thermochemical processes, is not necessary, allowing the use of biomass with high moisture content such as microalgae or olive residue and grape mark. In this work, the feasibility of a hydrothermal process conducted under sub-critical conditions to obtain a bio-oil from the residue of olive oil production is investigated. The experimental tests were performed at 320°C and about 13 MPa, using a biomass to water weight ratio of 1:5. The influence of two different catalysts on the bio-oil yield and quality was investigated: CaO and a zeolite (faujasite-Na). CaO allows the increase of bio-oil yields, while the selected zeolite enhances the deoxygenation reactions, thus improving the bio-oil quality in terms of heating value

Use of low-cost materials for tar abatement process

In the present work char, olivine and mayenite were used as bed materials to study ability to remove tar produced in biomass thermal processing. The tar gases formed from the pyrolysis reactions of the olive pomace biomass were forced to pass through the bed material. Nitrogen was used as carrier gas. The temperature of the bed was set at 660 °C and no oxidizing agent was added during the tests. The char was produced from the pyrolysis of olive pomace biomass. Olivine was used without any pre-treatment. Mayenite was synthesized in laboratory using CaCO3 and Al2O3 as precursors. Among the tested materials, mayenite showed the best tar removal capacity and stability, with a total tar removal of about 60% after 60 min time on stream, while in the case of char and olivine the attained value was 15%. The measured average nitrogen-free gas flow value in the tests carried out with mayenite was 0.84 NL min-1, whereas in the case of char and olivine the obtained average gas flow values were 0.65 and 0.55 NL min-1, respectively. Accordingly, the higher average hydrogen amount was measured in the tests using mayenite as bed material (36%)

Hydroxyapatite Production by an Intensification Process

Hydroxyapatite (HAP) is a worthwhile compound for its biomedical applications. Nanoparticles (NPs) and nanostructured HAP scaffolds promote and intensify the interaction between artificial material and natural bone due to their high surface/volume ratio. In this chapter, first, the technique for the production of HPA nanoparticles smaller than 100 nm is addressed. It consists of the use of a rotating disk reactor to optimize the reaction-precipitation process. The centrifugal force dispersed into the liquid layer over the disk surface enables the attainment of micromixing conditions between the reagents and maximizes the reaction rate as a consequence. The reaction between calcium chloride and ammonium phosphate in the presence of ammonium hydroxide was adopted. NPs minimum size, equal to 78 μm, was obtained using a rotational velocity of 147 rad/s and feeding points of reagents 3 cm from the disk center. A computational fluid dynamics (CFD) model of the liquid layer was specifically developed for the interpretation of the obtained experimental results on the production of pure HAP. In the second part of the chapter, the feasibility of producing Mg2+ doped hydroxyapatite (Mg-HAP) by adding MgCl2 and using the same technique is reported. Satisfactory results were obtained: nanoparticles were between 50 and 70 μm in size and Mg2+/Ca2+ molar ratio was equal to 0.06, according to the composition target

Influence of the catalyst support on the steam reforming performance of toluene as tar model compound

The large amount of tar produced along with the syngas during biomass gasification is one of the major obstacle for the diffusion of gasifiers at industrial scale. Catalytic cracking and reforming are the most suitable processes for the transformation of tar into lighter gases. The selection of suitable catalysts is a critical step. The catalysts must own high activity and high resistance to deactivation for coke deposition. In this work the effect of two different supports, mayenite and aluminium oxide, on the activity of the nickel was investigated in the steam reforming of toluene that was used as tar model compound. In particular, the performed experimentations aimed to test the mayenite in terms of improvement of resistance to carbon deposition in conditions similar to those of gasification reactors. The obtained results indicate that Ni /mayenite catalyst needs higher temperature to activate and leads to lower value of toluene conversion with respect to Ni / alumina. However, mayenite, which is known from literature to have higher resistance to coke deposition due to the presence of free oxygens in the lattice which oxidize the coke deposited on the catalyst surface showed higher resistance to deactivation especially for low steam to carbon ratios

The boundary flux. New perspectives for membrane process design

In the last decades much effort was put in understanding fouling phenomena on membranes. Many new concepts have been introduced in time, and parallel to this many parameters capable to quantify fouling issues and fouling evolution. One successful approach was the introduction of the critical flux theory. At first validated for microfiltration, the theory applied to ultrafiltration and nanofiltration, too. The possibility to measure a maximum value of the permeate flux for a given system without incurring in fouling issues was a breakthrough in membrane process design. Nevertheless, the application to the concept remains very limited: in many cases, in particular on systems where fouling is a main issue, critical fluxes were found to be very low, lower than economical feasibility permits to make membrane technology advantageous. Despite these arguments, the knowledge of the critical flux value still remains and must be considered as a good starting point for process design concerning productivity and longevity. In 2011, a new concept was introduced, that is the threshold flux. In this case, the concept evaluates the maximum permeate flow rate characterized by a low constant rate fouling regime, due to formation of a secondary, selective layer of foulant on the membrane surface. This concept, more than the critical flux, may be a new practical tool for membrane process designers. In this paper a brief review on critical and threshold flux will be reported and analyzed. In fact, critical and threshold flux concepts share many common aspects which merge perfectly into a new concept that is the boundary flux. The validation will occur mainly by the analysis of previous collected data by the authors, during the treatment of olive mill wastewater. A novel membrane process design method based on the boundary flux will then be presented

Improved photocatalytic properties of doped titanium-based nanometric oxides

Photocatalysis is considered one of the most promising technologies for applications in the environmental field especially in the abatement of water-soluble organic pollutants. In this field, titanium dioxide nanoparticles have drawn much attention recently; however, the use of this oxide presents some limitation since it allows to obtain high photoresponse and degradation efficiency only under UV light irradiation, that represents the 3 to 4% of the solar radiation, so preventing its environmental large-scale applications under diffuse daylight. In this work the photocatalytic efficiencyoftitanium-based oxides systems containing alkaline earth metals such as barium and strontium, prepared by a simple sol-gel method was investigated, evaluating the degradation of methylene blue as model compound under UV and visible light irradiation. The results were compared with those obtained with Degussa P25 titanium dioxide. The achieved degradation percentage of methylene blue are very promising showing that under visible light irradiation it is possible to obtain a maximum dye removal percentage ~ 50 % higher than that obtained with the Degussa P25