Effect of iron impregnation ratio on the properties and adsorption of KOH activated biochar for removal of tetracycline and heavy metals.

The effect of iron impregnation ratio on magnetic biochars (MBCs) prepared by biomass pyrolysis accompanied by KOH activation has been less reported. In this study, MBCs were produced by one-step pyrolysis/KOH-activation of walnut shell, rice husk and cornstalk with different impregnation ratios (0.3-0.6). The properties, adsorption capacity and cycling performance for Pb(II), Cd(II) and tetracycline of MBCs were determined. MBCs prepared with low impregnation ratio (0.3) showed stronger adsorption capacity on tetracycline. The adsorption capacity of WS-0.3 toward tetracycline was up to 405.01 mg g-1, while that of WS-0.6 was only 213.81 mg g-1. It is noteworthy that rice husk and cornstalk biochar with an impregnation ratio of 0.6 were more effective in removing Pb(II) and Cd(II), and the content of Fe0 crystals on surface strengthened the ion exchange and chemical precipitation. This work highlights that the impregnation ratio should be changed according to the actual application scenarios of MBC.

Visual experimental study on the effect of heat exchange area on the evolution of biomass pyrolysis vapors in a vertical indirect condensing field.

The effect of heat exchange area on the componential evolutions of biomass pyrolysis vapors was visualized through an innovative combining method of bio-oil composition inversion and function fitting. As the maximal diameter of condenser at 340 K increased from 35 mm to 55 mm, the fitted heat maps showed that the recovery of organics increased in the top of condenser and remained steady in the bottom, whereas the water recovery only increased in the top but decreased in the bottom. The recovery proportion of furfural and phenolic compounds increased by 20-40% with unvaried water recovery, and the content enrichment of high value-added components increased by 30-45% at 37 wt% of bio-oil yield. Heat exchange area exhibited a finer regulation effect on the condensation of pyrolysis vapors than traditional condensing adjustment methods, which first provided a remarkable promotion for the recovery and enrichment of organic components without improving water recovery.

Alternating magnetic field initiated catalytic deconstruction of medical waste to produce hydrogen-rich gases and graphite.

During the coronavirus 2019 (COVID-19) pandemic, there has been a dramatic increase in the use of medical products and personal protective equipment, such as masks, gowns, and disposable syringes, to treat patients or administer vaccines. However, this may lead to generation of large quantities of biohazardous medical waste. Here, an alternating-magnetic-field-initiated catalytic strategy is proposed to convert disposable syringes into hydrogen-rich gases and high-value graphite. Specifically, in addition to selecting heavy fraction of bio-oil as initiator, disposable syringe needles are used as radio frequency electromagnetic wave receptors to initiate the deconstruction of disposable syringe plastic. The highest H2 yield of 39.9 mmol g-1 is achieved, and 30.1 mmol g-1 is maintained after 10 cycles. Moreover, a high carbon yield of 286 mg g-1 can be obtained. Beyond disposable syringes, this strategy could help to solve the emerging issue for other types of medical waste (e.g., mask and protective clothing) disposal.

Experimental study on the composition evolution and selective separation of biomass pyrolysis vapors in the four-staged indirect heat exchangers.

This study was devoted to proposing an effective experimental method based on bio-oil composition inversion for understanding biomass pyrolysis vapor evolution in four-staged condensers. The effective length of each condenser was 200 mm. The evolution curves and heat maps of condensable vapors in the whole multi-staged condensing field were provided by Logistics model fitting. With changing condition from "365-345-325-305" to "345-325-305-285", the condensing efficiency of the first condenser increased by 100% but that of the third condenser decreased by 80%. Under condition "365-345-325-305", the largest recovery rate of water was observed at 400 mm away from multi-staged condensing field entrance while that of eugenol was observed at 50 mm away from the entrance, which explained that water was primarily recovered by the second and third condensers whereas eugenol was recovered by the first condenser, and verified the remarkable effect of fractional condensation on the separation of water and high-boiling phenols.

Comparison of linear and nonlinear function to describe and predict componential evolution of biomass pyrolysis vapors during condensation in a tubular indirect heat exchanger.

A novel experimental method based on the combination of bio-oil composition inversion and function fitting was purposed and verified for describing the componential evolution curves during the liquefaction of biomass pyrolysis vapors. The evolution curves of representative condensable components were fitted by linear and Slogistic function in the short, middle and long three condensing fields. Linear function exhibited a significant effectiveness for the description and prediction of low-boiling water and furfural and the relative deviations were no more than 5% between actual values in long condenser and predictive values from the elongation of curves in short and middle condensers. For high-boiling phenolic compounds, linear function failed to fit their evolutions in long condenser but Slogistic fitting remained effective despite the relative deviation increasing to about 10%. This investigation provided a unique and effective prediction method for the vapor evolution in industrial shell and tube heat exchanger according to laboratory-scale experiment.

Novel insights into the enrichment of phenols from walnut shell pyrolysis loop: Torrefaction coupled fractional condensation.

Enriching high-value chemicals from the pyrolysis of agricultural and forestry waste is an efficient way to achieve sustainable development and large-scale application of biomass pyrolysis. Phenols, as important chemical raw materials, spices and food additives, have attracted widespread attention. Herein, a novel technical route of torrefaction pretreatment combined with fractional condensation in pyrolysis loop was proposed to enrich the phenols in liquid products. In this study, the enrichment of phenols from the pyrolysis loop of walnut shell under the combination of torrefaction and fractional condensation was explored using a fixed-bed pyrolysis reactor equipped with a three-stage condensation system. Simultaneously, the effects of torrefaction on feedstocks were investigated through a thermogravimetric analyzer based on the characteristics of feedstocks. The results showed that the torrefaction and pyrolysis loop had a negative impact on the pyrolysis efficiency and the yield of liquid products, while the change in the condensation efficiency depended on the combined effects of torrefaction and pyrolysis loop. In addition, phenols tended to be enriched in the second condensation stage, especially phenol, o-cresol, 4-ethylphenol. Importantly, torrefaction could significantly enrich phenols in the liquid products, and the enrichment of phenols is relatively increased by 109.44% at least. Moreover, the pyrolysis loop was also beneficial to the enrichment of phenols, which was at least 90% higher than that of walnut shell. This study provided a potential route to enrich high value-added products from the pyrolysis loop of lignocellulosic biomass.

High-value utilization of mask and heavy fraction of bio-oil: From hazardous waste to biochar, bio-oil, and graphene films.

At present, it is very common to wear mask outdoors in order to avoid coronavirus disease 19 (COVID-19) infection. However, this leads to the formation of numerous plastic wastes that threaten humans and ecosystem. Against this major background, a novel co-pyrolysis coupled chemical vapor deposition (CVD) strategy is proposed to systematically convert mask and heavy fraction of bio-oil (HB) into biochar, bio-oil, and three-dimensional graphene films (3DGFs) is proposed. The biochar exhibits high higher heating value (HHV) (33.22-33.75 MJ/kg) and low ash content (2.34%), which is obviously superior to that of the walnut shell and anthracite coal. The bio-oil contains rich aromatic components, such as 1,2-dimethylbenzene and 2-methylnaphthalene, which can be used as chemical feedstock for insecticides. Furthermore, the 3DGF800 has a wide range of applications in the fields of oil spill cleanup and oil/water separation according to its fire resistance, high absorbability (40-89 g g-1) and long-term cycling stability. This research sheds new light on converting plastic wastes and industrial by-products into high added-value chemicals.

Experimental study on composition evolution of biomass pyrolysis vapors with condensing temperature in a vertical tubular condenser.

The experiments on bio-oil recovery in a vertical tubular condenser with two flumes were conducted for speculating the componential distribution of walnut shell pyrolysis vapors during condensation. Bio-oil elements and functional groups from different locations of condenser were compared with each other. Aromatic H and H in phenolic OH were concentrated in the top and middle bio-oil and their percentage were improved with increasing water bath temperature. Ten representative compounds in bio-oil were chosen for quantitative analysis. As water bath temperature increased from 273 K to 353 K, the recovered water decreased by 85% whereas the guaiacol and its derivatives (guaiacols) merely decreased by 40%. Vapor distributions of water, acetic acid, furfural and guaiacols were simulated by the back analysis of bio-oil components. According to the simulated results, tubular condenser can be properly lengthened for promoting the recovery of specific components at high water bath temperatures.

Thermogravimetric investigation on the effect of reaction temperature and blend ratio on co-gasification characteristics of pyrolytic oil distillation residue with biochar.

In this study, the CO2 co-gasification characteristics of pyrolytic oil distillation residue and biochar under different reaction temperatures were investigated by thermogravimetric analyzer (TGA). The influence of blend ratio on co-gasification synergy was adequately characterized by correlating the evolution of chemical structure and active AAEMs. The results indicated that increasing proportion of pyrolytic oil distillation residue could effectively improve gasification reactivity of biochar and enhance synergistic behaviors during co-gasification process, whereas the raising reaction temperature dwindled the enhancement of co-gasification reactivity and mutual promotion between individual samples. Moreover, three gasification kinetic models suggested that the lowest apparent activation energy (181.49~182.72 kJ/mol) among blends was obtained by 70 wt% additions of pyrolytic oil distillation residue. Furthermore, the results of Raman and ICP-AES analysis well related to the co-gasification synergy. The migration of active AAEMs and evolution of carbon structure had a pronounced influence on synergistic effect as co-gasification reaction progressed.

Two-step pyrolysis of corncob for value-added chemicals and high-quality bio-oil: Effects of alkali and alkaline earth metals.

Two-step pyrolysis (TSP) of corncob(CC) coupled with water and acid washing pretreatment was conducted to investigate the effects of alkali and alkaline earth metals (AAEMs) on TSP by Py-GC/MS. TG-FTIR was used to analyze the pyrolysis characteristics of the samples. The results showed that the removal of AAEMs postponed the pyrolysis process and significantly influenced the distribution of the pyrolysis products. As the content of AAEMs decreased, the bio-oil yield increased and the biochar yield decreased. TSP of CC achieved high selectivities for phenols and ketones in the first step and for hydrocarbons in the second step. TSP of acid-washed corncob (ACC) achieved high selectivities for furans in the first step and for sugars in the second step. Additionally, some value-added chemicals such as furfural (11.54%, ACC), 4-vinylphenol (23.57%, CC) and levoglucosan (43.05%, ACC) were also enriched in TSP. Therefore, a promising polygeneration scheme of TSP for the efficient utilization of biomass was proposed.

Study on the effect of condensing temperature of walnut shells pyrolysis vapors on the composition and properties of bio-oil.

The effect of condensing temperature on composition of bio-oil obtained via fractional condensation was investigated by pyrolysis-condensation experiments of walnut shells at condensing temperatures from 290 K to 370 K. The condensing efficiency of the first stage condenser decreased from 0.59 to 0.12 with increasing temperature. Moisture of bio-oil decreased from 40% to 5%, but the C/O ratio increased from 0.50 to 1.50. Compared with contents observed at the lowest condensation temperature, the maximum content of each component increased by 50%-500%. Combined with variations in condensing efficiency and composition content, the optimum condensing temperature range for declining water in bio-oil was 340-350 K. The condensing temperature associated with the enrichment of acetic acid and furfural was 345 K. The 355 K optimum condensing temperature could be selected to achieve the maximum enrichment of guaiacol and its derivatives.

Experimental study on fluidization behaviors of walnut shell in a fluidized bed assisted by sand particles.

The fluidization behaviors and their differences for walnut shell (WS) assisted by different-sized sands at various blending proportions were investigated experimentally in a cold visual fluidized bed at ambient temperature and pressure. Through analyzing the fluidization characteristic curves, it was found that the WS/sand mixtures were clearly characterized by stratified fluidization during the fluidization process, presenting a velocity interval rather than a threshold for transition from fixed to fluidized bed. Sand-3, as the fluidizing medium, showed better performance for WS fluidization in terms of the relative difference between initial (U mf,i) and final fluidization velocity (U mf,f) as well as the average fluidization rate (R f). Furthermore, the regularity and mechanism of mixing and segregation of WS/sand mixtures in two fluidized regions (semi and completed) are discussed in detail based on the flow pattern diagram, the axial and radial distribution of the components, as well as the mixing index.

Comparative study on pyrolysis of lignocellulosic and algal biomass using pyrolysis-gas chromatography/mass spectrometry.

The cornstalk and chlorella were selected as the representative of lignocelulosic and algal biomass, and the pyrolysis experiments of them were carried out using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The physicochemical properties of samples and the pyrolytic product distribution were presented. And then the compositional differences between the two kinds of pyrolytic products were studied, the relevant pyrolysis mechanisms were analyzed systematically. Pyrolytic vapor from lignocellulosic biomass contained more phenolic and carbonyl compounds while that from algal biomass contained more long-chain fatty acids, nitrogen-containing compounds and fewer carbonyl compounds. Maillard reaction is conducive to the conversion of carbonyl compounds to nitrogenous heterocyclic compounds with better thermal stability.

Ex-situ catalytic pyrolysis of wastewater sewage sludge - A micro-pyrolysis study.

Concerns over increasing amounts of sewage sludge and unsustainability of current disposal methods have led to development of alternative routes for sludge management. The large amount of organics in sewage sludge makes it potential feedstock for energy or fuel production via thermochemical pathways. In this study, ex-situ catalytic pyrolysis using HZSM-5 catalyst was explored for the production of olefinic and aromatic hydrocarbons and nutrient-rich char from sewage sludge. The optimal pyrolysis and catalysis temperatures were found to be 500°C and 600°C, respectively. Carbon yields of hydrocarbons from sewage sludge were higher than for lignocellulose; yield differences were attributed to the high extractives content in the sludge. Full recovery of most inorganic elements were found in the char, which suggests that catalyst deactivation maybe alleviated through ex-situ catalytic pyrolysis. Most of the nitrogen was retained in the char while 31.80% was released as ammonia, which suggests a potential for nitrogen recycling.

Reduction features of NO over a potassium-doped C12A7-O- catalyst.

The NO reduction features over a noble-metal-free NO(x) storage/reduction catalyst ([Ca24Al28O64](4+*)4O-/K, defined as C12A7-O-/K), including the NO conversion, the N2 selectivity, and sulfur tolerance, were investigated with hydrogen and C3H6 as the reducing agents in a fixed-bed continuous flow reactor. The NO conversion and the N2 selectivity on the C12A7-O-/K catalyst mainly depends on the sample temperature, the percentage of potassium, the reducing agents, and the composition of the mixture of gases. The C12A7-O-/10%K catalyst possessed the highest selective reduction ability (to N2) among the catalysts C12A7-O-/x%K. Over 50% of NO can be reduced to N2 with H2 as the reduction agent at 550-700 degrees C. The C12A7-O-/K catalyst also shows higher NO(x) storage capacity (183.9 micromol/g at about 550 degrees C) as well as sulfur tolerance for both the NO(x) storage and the reduction processes. The catalyst characteristics and the intermediate species formed in the NO storage and reduction processes were investigated by the X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and time-of-flight mass spectrometry. The mechanism of NO(x) reduction was addressed according to the above investigations.

Thermal conversion of rice husks and sawdust to liquid fuel.

The paper focuses on studying the conversion of rice husks and sawdust into liquid fuel. Rice husks, sawdust and their mixture are pyrolyzed at temperatures between 420 and 540 degrees C, and the main product of liquid fuel is obtained. The experimental result shows that the yield of liquid fuel depends on various factors such as feedstock and temperature. The maximum yields for rice husks, sawdust and their mixture are 56%, 61% and 60% at 465, 490 and 475 degrees C, respectively. Analyses with GC-MS and other apparatus show that the liquid fuel is a complicated compound with low caloric value and can be directly used as a fuel oil for combustion in a boiler or a furnace without any upgrading. Alternatively, the fuel can be refined to be used by vehicles.

Study on pyrolysis characteristics of lignocellulosic biomass impregnated with ammonia source.

The current study presents the pyrolysis characteristics of rice husk impregnated with different kinds of ammonia source (ammonium acetate, urea, ammonium sulfate and ammonium dihydrogen phosphate) in a fixed bed reactor. The introduction of ammonia source in pyrolysis process achieved the conversation from carbonyl compounds to nitrogenous heterocyclic compounds. The liquid product of urea-impregnated biomass has higher content of nitrogenous heterocyclic compounds (8.35%) and phenols (30.4%). For ammonium sulfate and ammonium dihydrogen phosphate-impregnated biomass, the quantity of compounds in liquid products reduces remarkably, and the gas products are rich in CO and H2. All the solid products of pyrolysis have great potential application in biochar-based fertilizer and activated carbon for their high N content.

Biodiesel production from waste cooking oil using a heterogeneous catalyst from pyrolyzed rice husk.

A solid acid catalyst was prepared by sulfonating pyrolyzed rice husk with concentrated sulfuric acid, and the physical and chemical properties of the catalyst were characterized in detail. The catalyst was then used to simultaneously catalyze esterification and transesterification to produce biodiesel from waste cooking oil (WCO). In the presence of the as-prepared catalyst, the free fatty acid (FFA) conversion reached 98.17% after 3h, and the fatty acid methyl ester (FAME) yield reached 87.57% after 15 h. By contrast, the typical solid acid catalyst Amberlyst-15 obtained only 95.25% and 45.17% FFA conversion and FAME yield, respectively. Thus, the prepared catalyst had a high catalytic activity for simultaneous esterification and transesterification. In addition, the catalyst had excellent stability, thereby having potential use as a heterogeneous catalyst for biodiesel production from WCO with a high FFA content.

In-depth investigation on the pyrolysis kinetics of raw biomass. Part I: kinetic analysis for the drying and devolatilization stages.

An in-depth investigation was conducted on the kinetic analysis of raw biomass using thermogravimetric analysis (TGA), from which the activation energy distribution of the whole pyrolysis process was obtained. Two different stages, namely, drying stage (Stage I) and devolatilization stage (Stage II), were shown in the pyrolysis process in which the activation energy values changed with conversion. The activation energy at low conversions (below 0.15) in the drying stage ranged from 10 to 30 kJ/mol. Such energy was calculated using the nonisothermal Page model, known as the best model to describe the drying kinetics. Kinetic analysis was performed using the distributed activation energy model in a wide range of conversions (0.15-0.95) in the devolatilization stage. The activation energy first ranged from 178.23 to 245.58 kJ/mol and from 159.66 to 210.76 kJ/mol for corn straw and wheat straw, respectively, then increasing remarkably with an irregular trend.

Determination of effective moisture diffusivity and drying kinetics for poplar sawdust by thermogravimetric analysis under isothermal condition.

The current study presents a thermogravimetric method to determine the effective moisture diffusivity and drying kinetics of biomass. Drying experiments on poplar sawdust were performed at four temperatures (60, 70, 80, and 90°C) by a thermogravimetric analyzer (TGA). The major assumption in experimentally determining effective diffusivity by Fick's diffusion equation is that drying is mass transfer limited and temperature remains isothermal during drying. The results indicated that TGA could well achieve these determining conditions. The drying process of sawdust mostly took place in the falling rate period. Midilli-Kucuk model showed the best fit for all experimental data. The effective diffusivity values changed from 9.38 × 10(-10)m(2)/s to 1.38 × 10(-9)m(2)/s within the given temperature range, and the activation energy was calculated to be 12.3 kJ/mol.