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•Continuous microwave assisted pyrolysis for chemical recycling of plastic wastes.•Talc as a plastic filler showed high cracking activity in pyrolysis of PP.•ZSM-5 improved pyrolysis ...product quality but suffered from rapid deactivation.•5 MJ electrical energy consumption/kg of HDPE, giving an 89.6% energy efficiency.•CMAP system has advantages over fluidized bed reactors for industrial application.
The soaring use of plastics has resulted in alarming issues such as environmental pollution and unsustainable production of plastics. Pyrolysis of plastic wastes has emerged as a promising chemical recycling method, to recover energy and materials from this resource. In this study, the pyrolysis of plastic wastes was conducted in a novel, continuous, microwave-assisted pyrolysis (CMAP) system for fuel production; the effects of temperature, plastic composition, and catalysis on the product yields and composition were investigated. Higher pyrolysis temperatures promoted the cracking of wax and production of lighter and more stable hydrocarbons. Talc as a plastic filler in polypropylene showed a high cracking activity. Incorporating ZSM-5 catalysts at a weight hourly space velocity of 10 h−1 and a pyrolysis temperature of 620 °C resulted in a liquid yield of 48.9%, and this product consisted of 73.5% gasoline-range hydrocarbons rich in aromatic (45.0%) and isomerized aliphatic (24.6%) contents. The catalyst rapidly lost its activity at a feedstock/catalyst ratio of 5. Energy balance analysis showed that 5 MJ of electrical energy was required to process 1 kg of HDPE with the CMAP system, giving an energy efficiency as high as 89.6% 6.1 MJ electrical energy could be generated from the gas products alone, making the process energy self-sufficient. Overall, the CMAP system, featuring a combination of microwave heating with a SiC mixing-ball-bed, is a promising design for industrial application of energy recovery from plastic wastes due to its advantages, including: 1) higher energy efficiency, and 2) lower processing temperature than conventional fluidized-bed reactors.
•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.
•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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•Composite catalysts (ZSM-5/MCM-41) were synthesized and its optimum catalytic conditions were studied.•Microwave-assisted catalytic fast co-pyrolysis (co-MACFP) was adopted in this ...experiment.•The synergistic effect of lignin and catalyst promotes the formation of aromatic compounds.
Microwave-assisted catalytic fast co-pyrolysis (MACFP) of lignin and waste oil with SiC as microwave absorbent and hierarchical ZSM-5/MCM-41 as catalyst were implemented in a microwave-induced reactor. ZSM-5/MCM-41 is a kind of composite catalyst with MCM-41 as shell and ZSM as core. The effects of catalyst temperature, the ratio of feedstock-to-catalyst and the ratio of two reactants (lignin and waste oil) on product distribution and yield were studied. The study shows that catalytic co-pyrolysis is a complex reaction process, and many reaction conditions could affect the final reaction results. The optimum reaction conditions are as follows: catalytic temperature 400 °C, the feedstock-to-catalyst ratio of 10:1 and the ratio of lignin to waste oil of 2:1. Under this reaction condition, the conversion of feedstocks reached 76.00%, the proportion of aromatics was 50.31% and the selectivity of monocyclic aromatic hydrocarbons (MAHs) was 42.83%.
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•Catalytic conversion of soapstock over HZSM-5 was conducted to produce aromatics.•Effect of unsaturation degree on product distribution and composition was studied.•The pyrolysis ...mechanism of soapstock and fatty acid salt over HZSM-5 was proposed.
Hydrocarbon-rich fuel from vegetable oil soapstock is potentially a good alternative to conventional fossil-derived fuels. This paper reported on pyrolysis experiments with compounds including vegetable oil soapstock, sodium stearate(C18), sodium palmitate(C16), sodium oleate(C18:1), and sodium linoleate(C18:2). The effects of pyrolysis temperature, HZSM-5 catalyst, unsaturation degree and carbon chain length on the formation of aromatic hydrocarbons were explored. Experimental results indicated that the relative content of oxygenated compounds significantly decreased in the condensable organic compounds of soapstock pyrolysis, and aromatic hydrocarbons increased when the HZSM-5 catalyst was used, in which toluene and xylene had the highest relative selectivity. High catalytic pyrolysis temperature was beneficial to the relative selectivity of benzene and toluene, but inhibited the relative selectivity of xylene and ethylbenzene. The increase in saturation of fatty acid salts promoted the reaction toward the production of polycyclic aromatic hydrocarbons, which were a kind of typical precursor of catalyst coking deactivation and carcinogenic pollutants.
Considering the potential environmental issues caused by the Haber–Bosch nitrogen fixation process, developing green technology for nitrogen fixation has become a heated topic. In this work, a ...modified “concentrated high-intensity electric field” (CHIEF) non-thermal plasma system was developed, by combining photocatalysis and electrodialysis for the continuous production of high-concentration nitrated water using air and water. The main system design factors, including: voltage, duty cycle, gas flow rate, N
2
/O
2
ratio, and reactor parameters, show significant impacts on the nitrogen fixation, and the composition in the resulting nitrated water. Under high voltage in the CHIEF system, N
2
and O
2
were excited, and generated various reactive nitrogen and oxygen species, resulting in the
in-situ
reaction with water. These reactions led to the formation of NH
4
+
, NO
2
−
and NO
3
−
(ammonium, nitrite, and nitrate ions) in the solution via a series of reactions in the gas phase, gas–liquid interface, and liquid phase. Due to the rapid in situ reaction, the highest nitrogen species yield rate reached 48.28 μmol/min, which was much higher than other reports. The best (least) energy consumption was 23.5 MJ/mol of Nitrogen. In addition, photocatalysis mediated by TiO
2
under UV exposure, greatly promoted the conversion of nitrite to nitrate, because of the generation of ·OH and ·O
2
−
species. Furthermore, the electrodialysis concentration was able to efficiently decrease the conductivity in the CHIEF system, and enriched the nitrate concentration over dozens of times. This enabled the CHIEF system to continuously achieve high-level nitrogen fixation in an efficient manner.
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