Organic compounds, generated from different industries, produce a range of the problematic pollutants in wastewater. TiO2 based photocatalysts are novel materials that exhibit excellent absorption ...behavior toward organic compounds in wastewater due to their outstanding properties including nontoxicity, high photocatalytic degradation ability, and excellent thermal and chemical stabilities. However, several challenges exist regarding TiO2 applications for organic effluents such as particle aggregation, mass transfer limitation, poor affinity, high band energy, scattering conditions, and difficulty of recovery. Therefore, more design and optimization testing need to be conducted on the treatment conditions in order to reach higher removal efficiencies with lower costs. A variety of parameters of TiO2 based photocatalysts need to be studied: substrate, light intensity, dopant, particle size, structure. These parameters, which affect TiO2 photocatalytic activity on organic pollutants, are discussed in the current review. Thus, making the photocatalyst more anticipated and conducive to further research and development.
•Six unique challenges inhibit the application of TiO2 in organic effluents.•Various parameters such as TiO2 forms and substrates were discussed.•High band energy and transfer limitation are the primary limitations.•The key processing parameters are selection of TiO2 substrate and dopant.
•Lignin structural components and extraction techniques were reivewed.•Lignin conversion technologies were classified into pyrolysis and solvolysis.•Microwave assisted pyrolysis and solvolysis ...processes of lignin were summarized.•Advantages of microwave-assisted lignin conversion technology were reviewed.
Energy insecurity and resource shortage are driving societies to look for sustainable and renewable energy and resource supplies. Thus, converting biomass into useful energy and chemical products has attracted considerable attention in the past decades. As a carbon-rich renewable biomass source, lignin has been extensively studied as a raw material to produce bioenergy and value-added chemicals. Fuel gas and phenolic products can be obtained by converting lignin. This study strives to extensively review recent developments in the microwave-assisted pyrolysis and solvolysis of lignin. Lignin structural components and extraction techniques are described under different conditions. In addition, the fundamentals and advantages of microwave heating technology and the background of lignin pyrolysis and solvolysis are presented. The effectual parameters of the microwave-assisted pyrolysis and solvolysis of lignin and their advantages are also summarized. This review concludes that microwave-assisted technology is an effective method for significantly reducing reaction time and improving the yields and selectivity of target products. In the future, low-cost catalysts and microwave-assisted conversion units need to be developed to achieve large-scale production of renewable fuels and value-added chemicals from lignin.
The recovery of ammonia–nitrogen during wastewater treatment and water purification is increasingly critical in energy and economic development. The concentration of ammonia–nitrogen in wastewater is ...different depending on the type of wastewater, making it challenging to select ammonia–nitrogen recovery technology. Meanwhile, the conventional nitrogen removal method wastes ammonia–nitrogen resources. Based on the circular economy, this review comprehensively introduces the characteristics of several main ammonia–nitrogen source wastewater plants and their respective challenges in treatment, including municipal wastewater, industrial wastewater, livestock and poultry wastewater and landfill leachate. Furthermore, we introduce the main methods currently adopted in the ammonia–nitrogen removal process of wastewater from physical (air stripping, ion exchange and adsorption, membrane and capacitive deionization), chemical (chlorination, struvite precipitation, electrochemical oxidation and photocatalysis) and biological (classical and typical activated sludge, novel methods based on activated sludge, microalgae and photosynthetic bacteria) classification based on the ammonia recovery concept. We discuss the applicable methods of recovering ammonia nitrogen in several main wastewater plants. Finally, we prospect the research direction of ammonia removal and recovery in wastewater based on sustainable development.
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•Catalytic pyrolysis of LDPE was performed in a microwave reactor.•NiO and HY zeolite were used as in-situ and ex-situ catalysts, respectively.•56.5 wt% of oil and 93.8% of gasoline ...fraction were obtained over HY catalysis.•Adding NiO improved the octane number of the oil with minor effects on its yield.•The pyrolysis mechanism of LDPE over NiO and HY was proposed.
Recovering fuels or chemicals from plastic waste via pyrolysis is an innovative and promising route for both energy saving and refuse elimination. In this study, catalytic microwave-assisted pyrolysis of low-density polyethylene (LDPE) was performed to simultaneously improve yield and quality of gasoline-range products. NiO and HY zeolite were respectively used as in-situ and ex-situ catalysts in a two-stage pyrolysis-catalysis system. The results showed that the optimum pyrolysis and catalysis temperatures were 500 °C and 450 °C, respectively, with 56.53 wt% oil product and 93.80% gasoline-range fraction achieved. The content of high-octane-number compounds, primarily aromatics and isomerized aliphatics, increased from 23.5% to 80.4% as HY to LDPE ratio rose from 0 to 1:5. The optimized balance between oil yield and oil quality was obtained at the HY to LDPE ratio of 1:10. The presence of NiO during co-catalysis slightly decreased the oil yield by 5.3–8.5 wt%. Meanwhile, the production of aromatics was promoted obviously while the yield of normal aliphatics was inhibited, which were both favorable to improve the octane number of the oil product. The improved performance of co-catalysis could be related to the suitable hydrogen abstraction ability of NiO, which produced enormous alkenes. Subsequently, cycloalkenes and aromatics were synthesized through Diels-Alder reactions over the catalysis of HY. This co-catalysis approach in the microwave reactor provides a potentially profitable way to convert plastic waste into high-quality and high-yield gasoline fuels.
•Two pretreatments affect differently the hydrochar properties and its pyrolysis behaviors.•Hydrochar by conventional hydrothermal pretreatment shows higher thermal stability.•Microwave hydrothermal ...pretreatment removes more acetyl.•Hydrochar by microwave hydrothermal pretreatment produces more glucopyranose and less acids.
Comparative study on microwave and conventional hydrothermal pretreatment of bamboo sawdust was carried out in this study. Microwave and conventional hydrothermal pretreatment both improved the hydrochar properties and its pyrolysis behaviors. Proximate and elemental analyses show that the properties of hydrochar from microwave hydrothermal pretreatment are better than conventional hydrothermal pretreatment in terms of calorific value and oxygen content except for 150°C. Microwave hydrothermal pretreatment removes more acetyl groups in hemicellulose compared to conventional hydrothermal pretreatment, which may be attributed to the hot spot effect of microwave irradiation. The peaks of thermogravimetric and derivative thermogravimetric curves of pretreated samples always shifted to higher temperature region. Also, the conventional hydrothermal pretreated samples are more thermally stable than those by microwave heating. In addition, the glucopyranose content in pyrolysis vapors of microwave hydrothermal pretreated bamboo sawdust (190°C) was 9.82% higher than that from conventional hydrothermal pretreated bamboo sawdust. However, the acids content from microwave hydrothermal pretreated bamboo sawdust (150°C) was 4.12% lower. In this regard, microwave hydrothermal pretreatment is more suitable for upgrading the pyrolysis oil quality than conventional hydrothermal pretreatment.
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•Superb and reusable adsorbent WSH was successfully synthesized from shrimp shells.•Maximum adsorption capacity of WSH was 755.08 mg/g at optimal pH of 4.0.•Exothermic adsorption was ...spontaneous and followed monolayer adsorption pattern.•Electrostatic interaction was mainly responsible for the prominent adsorption.
Shrimp processing and consumption generate large amounts of waste shrimp shell (WSS) rich in chitin and protein. Herein, we successfully synthesized WSS-based hydrochar (WSH) adsorbent through deproteinization and deacetylation followed by hydrothermal carbonization (HTC) and acid washing. For comparison, another hydrochar (CCH) adsorbent was synthesized from HTC of commercial chitosan under identical conditions. Specifically, WSH contained rich nitrogen-containing functional groups with a long aliphatic chains structure. Acid etching of calcium carbonate in WSS led to a higher specific surface area of WSH (12.65 m2/g) which was nearly 6 times higher than that of CCH (2.13 m2/g). The lower deacetylation degree of WSH was responsible for higher amide I and amino groups retained therein. Under an optimal initial solution pH of 4.0, WSH could rapidly achieve a superb adsorption capacity of 755.08 mg/g for methyl orange molecule. Moreover, the adsorption process followed a pseudo-second-order kinetics model and was well described by a monolayer adsorption pattern based on the Langmuir isotherm model with correlation coefficients higher than 0.9989. Prominent adsorption performance of WSH for methyl orange was mainly attributed to electrostatic interactions, while steric hindrance effect had a detrimental impact on the adsorption capacity of CCH. Superb adsorption capacity and excellent regeneration performance suggest WSH could be a promising and affordable adsorbent candidate for anionic dye removal.
•Microwave-assisted ex-situ catalytic fast co-pyrolysis technology was developed.•The optimal catalyst parameters and lignin/polypropylene ratio were determined.•Ex-suit catalytic co-pyrolysis ...significantly reduced oxygenates yield in bio-oil.•The main products were cycloalkanes and aromatics in bio-oil.
Microwave-assisted fast co-pyrolysis of lignin and polypropylene for bio-oil production was conducted using the ex-situ catalysis technology. Effects of catalytic temperature, feedstock/catalyst ratio, and lignin/polypropylene ratio on product distribution and chemical components of bio-oil were investigated. The catalytic temperature of 250°C was the most conducive to bio-oil production in terms of the yield. The bio-oil yield decreased with the addition of catalyst during ex-situ catalytic co-pyrolysis. When the feedstock/catalyst ratio was 2:1, the minimum char and coke values were 21.22% and 1.54%, respectively. The proportion of cycloalkanes decreased and the aromatics increased with the increasing catalyst loading. A positive synergistic effect was observed between lignin and polypropylene. The char yield dramatically deceased and the bio-oil yield improved during co-pyrolysis compared with those during lignin pyrolysis alone. The proportion of oxygenates dramatically and the minimum value of 6.74% was obtained when the lignin/polypropylene ratio was 1:1.
It is promising to convert waste oil and plastics to renewable fuels and chemicals by microwave catalytic co-pyrolysis, enabling pollution reduction and resource recovery. The purpose of this study ...was to evaluate the effect of catalysts on the product selectivity of microwave-assisted co-pyrolysis of waste cooking oil and low-density polyethylene and optimize the pyrolysis process, including pyrolysis temperature, catalytic temperature, waste cooking oil to low-density polyethylene ratio, and catalyst to feedstocks ratio. The results indicated that catalysts had a great influence on the product distribution, and the yield of BTX (benzene, toluene, and xylenes), which increased in the following order: SAPO-34 < Hβ < HY < HZSM-5. HZSM-5 was more active for the formation of light aromatic hydrocarbons as compared to others, where the concentrations of toluene, benzene and xylenes reached 252.59 mg/mL, 114.7 mg/mL and 132.91 mg/mL, respectively. The optimum pyrolysis temperature, catalytic temperature, waste cooking oil to low-density polyethylene ratio and catalyst to feedstocks ratio could be 550 °C, 450 °C, 1:1 and 1:2, respectively, to maximize the formation of BTX and inhibit the formation of polycyclic aromatic hydrocarbons.
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•Microwave co-pyrolysis of waste cooking oil and LDPE comprehensively investigated.•HZSM-5 was the most effective aromatization catalyst for light aromatics.•This co-pyrolysis increased the content of monocyclic aromatic hydrocarbons.•Benzene, toluene, xylenes, ethylbenzene, and styrene were quantified.
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•Iron nanoparticles-based biochar catalyst was used to produce phenols firstly.•High yields and selectivities of phenols were achieved in the process.•Deactivation mechanism of ...catalyst was illustrated in detail.
Selective production of phenols via ex-situ catalytic pyrolysis of lignocellulosic biomass is a promising route in biomass conversion. Therefore, developing a low-cost and effective catalyst for this process has emerged as an important topic. Here, the iron nanoparticles-based carbonaceous catalysts were prepared via combining hydrothermal carbonization and pyrolysis approach and first used in the catalytic microwave-assisted pyrolysis of torrefied corn cob for phenols production. The effects of catalyst types, catalytic temperature, and catalyst to feedstock ratio on the production of phenolic compounds were studied. The total selectivity of phenols can reach 91.07 area% with the total yield of 18706.6 µg/ml bio-oil using the FeHC@ hydrochar catalyst (prepared by hydrothermal carbonization in the Fe(NO3)3 solution and pyrolysis) at the catalytic temperature of 450 °C and catalyst to feedstock ratio of 5:10. After using seven times, partial loss of catalytic activity of FeHC@hydrochar was found. This study also presented unique insights into the deactivation of carbonaceous catalysts, showing that sintering, oxidation of α-Fe and Fe3C phases, active site coverage, and pore blockage were the causes of the reduction of catalytic performance. Regeneration experiments showed that it is impracticable to calcine deactivated catalyst at an inert atmosphere and more advanced techniques needed to be developed to solve this problem. Overall, this study can provide a reference for realistic scale-up production of renewable phenols.
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•A tandem catalytic bed (TCB) was developed in an analytical pyrolyzer.•CeO2 was effective in deoxygenating from acids, aldehydes and methoxy phenols.•The TCB of CeO2 and HZSM-5 ...enhanced hydrocarbon yield to utmost 85%.•An effective H/C ratio of 0.7 was optimum for producing hydrocarbons in the TCB.•Mechanisms on co-pyrolysis of corn stover and LDPE in the TCB were discussed.
The excessive oxygen content in biomass obstructs the production of high-quality bio-oils. In this work, we developed a tandem catalytic bed (TCB) of CeO2 and HZSM-5 in an analytical pyrolyzer to enhance the hydrocarbon production from co-pyrolysis of corn stover (CS) and LDPE. Results indicated that CeO2 could remove oxygen from acids, aldehydes and methoxy phenols, producing a maximum yield of hydrocarbons of 85% and highest selectivity of monocyclic aromatics of 73% in the TCB. The addition of LDPE exhibited a near-complete elimination of oxygenates, leaving hydrocarbons as the overwhelming products. With increasing LDPE proportion, the yield of aliphatics and the selectivity of BTX kept increasing. An optimum H/Ceff of 0.7 was superior to that reported in literature. Mechanisms consisting of deoxygenation, Diels-Alder reactions, hydrocarbon pool and hydrogen transfer reactions were discussed extensively. Our findings provide an efficient method to produce high-quality biofuels from renewable biomass resources.
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