Synergetic effect on methylene blue adsorption to biochar with gentian violet in dyeing and printing wastewater under competitive adsorption mechanism

Decolorization of dyeing/printing wastewater by carbon-based materials has been carried out to study the adsorption of dye molecules onto adsorbent. Biomass-derived activated carbon (SAC) was sampled from cornstalk pyrolysis in the presence of K2CO3 as an activator. Adsorption of methylene blue (MB) and gentian violet (GV) onto SAC was examined to probe the mechanisms, isotherms, and kinetics of dye removal in single- or two-component systems. According to the adsorption rate in a single-component system, three stages were identified. The equilibrium adsorption capacity for MB onto SAC in the single-component system is 274.84 mg g−1 which is higher than that for GV of 266.57, meanwhile the pseudo-second-order (PSO) model would describe the adsorption kinetics with the correlation coefficient higher than 0.99. In the binary GV-MB system, presence of GV promoted MB adsorption to 325.15 mg g−1 and 287.73 mg g−1 at different GV concentrations while the PSO model was also applicable. Furthermore, differences between experimental and calculated values by the Freundlich and Langmuir isotherms indicated the occurrence of competitive adsorption in the two-component system. The gained insights are beneficial for removing the multiple dyes from industrial wastewater, economically and effectively and thus paving the way to the establishment of a greener society

CFD modelling of the thermal degradation of biomass in fluidized beds

Pyrolysis is considered as a promising technology of recovering bioenergy from biomass into gas, liquid and solid fuels. A series of works have been carried out previously on the fundamentals and the decomposition mechanism of pyrolysis empirically. Based on these experimental works, numerical approaches are employed to achieve a better understanding of the pyrolysis mechanism or aid the applications in experimental and industrial area.In order to construct a systematic model of the thermochemical processes in biomass pyrolysis in a fluidized bed, the mass and heat transfer processes are investigated by two sub-subjects: modelling of the heat exchange between an immersed tube and a fluidized bed; modelling of mixing-segregation phenomena of binary mixture loaded in a fluidized bed as bed materials. Based on the finished studies, two reacting beds are represented by Eulerian approaches. The fast pyrolysis and catalytic pyrolysis of biomass is modelled by incorporating the corresponding kinetic schemes into the mass and heat transfer processes. The relevant models, coefficients and functions are tested and discussed for the sensitivity and the simulation results show qualitative consistence with the existing experimental works. The general model for thermochemical processes of biomass in the fluidised beds is built up in the present work successfully. The entire structure and methods can be introduced into other applications but not limited to biomass pyrolysis. The further optimization based on this model can be a useful tool on design of a large-scale pyrolyzor.<br/

Numerical Analysis of Heat Transfer Enhancement Due to Nanoparticles under the Magnetic Field in a Solar-Driven Hydrothermal Pretreatment System

Solar-driven hydrothermal pretreatment is an efficient approach for the pretreatment of microalgae biomass for biofuel production. In order to enhance the heat transfer, the magnetic fields effects on flow and heat transfer of nanofluids were investigated in a three-dimensional circular pipe. The magnetic fields were applied in different directions and magnetic field intensities to the flow. In this paper, Finite Volume Method was used to simulate flow and heat transfer of nanofluids under a magnetic field, and the Discrete Phase Model was selected to calculate two-phase flow, which was water mixed with metal nanoparticles. The research was also carried out with the various physical properties of nanoparticles, including the volume share of nanoparticles, particle diameter, and particle types. When the magnetic fields were applied along the X, Y, and Z directions and the intensity of magnetic fields was 0.5 T, the heat transfer coefficients of Cu-H2O nanofluids flow were increased evenly by 9.17%, 10.28%, and 10.32%, respectively. When the magnetic field was applied, the heat transfer coefficients and the Nusselt numbers were both increased with the increment of intensities of the magnetic field

Effects of feeding rate on catalytic pyrolysis of sawdust in bubbling fluidized beds

Catalytic cracking of sawdust has been studied numerically in bubbling fluidized beds with in situ catalyst. The upgrading of bio-oil is one of the critical issues in applications of biomass pyrolysis products. Due to the interactions of multiphase flow dynamics coupled with chemical reaction, computational modelling of thermo-chemical processing of biomass can be quite complex. In current work, the online catalytic upgrading of bio-oil derived by sawdust pyrolysis is investigated. The Eulerian-Eulerian models coupled with the Kinetic Theory of Granular Flows are employed to model the multiphase flow in fluidized beds. The user defined functions (UDF) is developed based on the chemical kinetics to represent the decomposition of biomass and upgrading of bio-oil. The simulation results show that the heterogeneous reactions can perform significant effects on hydrodynamics of fluidized beds while different space time, the ratio of catalyst mass to tar flow rate, will vary the yield distribution of products

In Situ Removal of Benzene as a Biomass Tar Model Compound Employing Hematite Oxygen Carrier

Tar is an unavoidable biomass gasification byproduct. Tar formation reduces gasification efficiency and limits the further application of biomass gasification technology. Hence, efficient tar removal is a major problem to be solved in the formation and application of biomass gasification technology. Chemical looping gasification (CLG), a novel and promising gasification technology has attracted extensive attention owing to its low tar generation. Active oxygen carriers (OCs), the reduced OC in CLG, are considered to be excellent catalysts for tar cracking. In this study, the use of benzene as a typical tar model compound for tar removal using the iron ore OC is investigated. In the blank experiment, where an inert material (SiO2) is used as the carrier, the benzene cracking is relatively low, and the benzene conversion, H2 yield, and carbon conversion are 53.65%, 6.33%, and 1.24%, respectively. The addition of hematite promotes benzene cracking. A large amount of oxygen-containing gases (CO and CO2) are generated. Additionally, the conversion degrees for benzene, H2 and carbon are about 67.75%, 21.55%, and 38.39%, respectively. These results indicate that hematite performs both oxidation and catalysis during benzene cracking. The extension of the residence time facilitates benzene removal, owing to the good interaction between the gas phase and solid phase. The addition of water vapor inhibits the benzene conversion and promotes the conversion of carbon deposition. The lattice oxygen reactivity of hematite OC shows an uptrend as the cycle number is increased during the benzene conversion cycle. The experimental results confirm that CLG has a low-tar advantage and that hematite is an effective OC for benzene removal

Chemical looping gasification of sewage sludge using copper slag modified by NiO as an oxygen carrier

Chemical looping gasification (CLG) provides a novel approach to dispose the sewage sludge. In order to improve the reactivity of the calcined copper slag, NiO modification is considered as one of the good solutions. The copper slag calcined at 1100 degrees C doped with 20 wt% NiO (Ni20-CS) was used as an oxygen carrier (OC) in sludge CLG in the work. The modification of NiO can evidently enhance the reactivity of copper slag to promote the sludge conversion, especially for sludge char conversion. The carbon conversion and valid gas yield (V-g) increase from 67.02% and 0.23 m(3).kg(-1) using the original OC to 78.34% and 0.29 m(3).kg(-1) using the Ni20-CS OC, respectively. The increase of equivalent coefficient (Omega) facilitates the sludge conversion and a suitable Omega value is determined at 0.47 to obtain the highest valid gas yield (0.29m(3).kg(-1)). A suitable steam content is assigned at 27.22% to obtain the maximum carbon conversion of 87.09%, where an acceptable LHV of 12.63 MJ.m(-3) and V-g of 0.39 m(3).kg(-1) are obtained. Although the reactivity of Ni20-CS OC gradually decreases with the increase in cycle numbers because of the generation of NiFe2O4- (delta) species, the deposition of sludge ash containing many metallic elements is beneficial to the sludge conversion. As a result, the carbon conversion shows a slight uptrend with the increase of cycle numbers in sludge CLG. It indicates that the Ni20-CS sample is a good OC for sludge CLG. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved

Chemical looping gasification of high nitrogen wood waste using a copper slag oxygen carrier modified by alkali and alkaline earth metals

Chemical looping gasification (CLG) can achieve clean and highly efficient use of high nitrogen wood waste (HNWW). In this work, the feasibility of CLG of HNWW is explored using a modified copper slag (CS1100) as an oxygen carrier (OC). The CS1100 sample modified by alkali and alkaline earth metals (AAEMs) was first prepared, and then the reactivity of different OCs was evaluated. The K-modified CS1100 (K-CS) sample showed the highest reactivity due to the formation of KFe2O4. Lattice oxygen was beneficial to char conversion, evidently promoting HNWW conversion. The K-CS sample showed the highest carbon conversion (74.65%) and valid gas yield (641 mL/g), followed by the Ca-CS and Na-CS samples, which exhibited a much higher carbon conversion than the inert SiO2 sample (40.45% and 327 mL/g). The K-CS sample can evidently promote the release of N and the subsequent oxidation of nitrogen-containing pollutants (i.e., NH3 and HCN), thus lowering the emissions of nitrogen pollutants. Char-N accounts for 22.54% of N during pyrolysis; however, char-N only accounts for 2.27% of N during CLG. Additionally, compared to pyrolysis, the emissions of nitrogen-containing pollutants decreased by approximately 20% in CLG. The Protein-N (N-P) and Urea-N (N-U) were decomposed to form Pyrrole-N (N-5) and Pyridine-N (N-6); and then formed Protonated pyridine N (N-Q) and Pyridine N-oxide (N-X) during thermal conversion of HNWW. Additionally, more N-X and N-6 remained in the residual char during CLG than during pyrolysis because of the presence of active OC. KFe2O4 acted as a catalyst rather than an oxidizer during CLG, and the K-CS sample can act as an OC for recycling