Progress in the Study of Microwave Pyrolysis Technology and Its Influencing Factors

In recent years, the effective conversion of organic wastes into valuable products has been a focus and difficulty in sustainable energy and environmental management. Organic wastes come from a wide range of sources, and industrial and agricultural sources are the main sources of organic waste in China, which can be controlled by microwave pyrolysis technology. In microwave pyrolysis treatment, catalysts have been the key material, microwave absorber, and catalyst of the research hotspot in recent years. This paper summarises the typical influencing parameters of microwave pyrolysis (including microwave power, pyrolysis temperature and microwave absorber), and also summarises the various catalysts applied in microwave pyrolysis, and looks forward to the potential application prospect of pyrolysis products, and the future development direction.

Influence of carbon coating prepared by microwave pyrolysis on properties of LiNi_(1/3) Mn_(1/3) Co_(1/3) O_2

A novel synthesis method of carbon-coated LiNil/3Mnl/3COl/302 cathode material for lithium-ion battery was reported. The carbon coating was produced from a precursor, glucose, by microwave-pyrolysis method. The prepared powders were characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, X-ray fluorescence （XRF） and charge/discharge tests. XRD results indicate that the carbon coating does not change the phase structure of LiNil/3Mnl/3C01/302 material. SEM results show that the surface of spherical carbon-coated material becomes rough. Electrochemical performance results show that the carbon coating can improve the cycling performance of LiNii/3Mnl/3C01/302. The specific discharge capacity retention of the carbon-coated LiNi1/3Mnt/3Col/30z reached 85.0%-96.0% at the 50th cycle at 0.2C rate, and the specific discharge capacity retention is improved at a high rate.

Efficient recovery of valuable metals from waste printed circuit boards by microwave pyrolysis

The recycling of waste printed circuit board(WPCBs) is of great significance for saving resources and protecting the environment. In this study, the WPCBs were pyrolyzed by microwave and the contained valuable metals Cu, Sn and Pb were recovered from the pyrolyzed WPCBs. The effect of pyrolysis temperature and time on the recovery efficiency of valuable metals was investigated. Additionally, the characterization for morphology and surface elemental distribution of pyrolysis residues was carried out to investigate the pyrolysis mechanism. The plastic fiber boards turned into black carbides, and they can be easily separated from the metals by manual. The results indicate that 91.2%, 96.1% and 94.4% of Cu, Sn and Pb can be recovered after microwave pyrolysis at 700 °C for 60 minutes. After pyrolysis, about 79.8%(mass)solid products, 11.9%(mass) oil and 8.3%(mass) gas were produced. These gas and oil can be used as fuel and raw materials of organic chemicals, respectively. This process provides an efficient and energy-saving technology for recovering valuable metals from WPCBs.

Kinetic and thermodynamic investigations of CO2 gasification of coal chars prepared via conventional and microwave pyrolysis

This study examined an isothermal CO2 gasification of four chars prepared via two different methods,i.e.,conventional and microwave-assisted pyrolysis,by the approach of thermogravimetric analysis.Physical,chemical,and structural behaviours of chars were examined using ultimate analysis,X-ray diffraction,and scanning electronic microscopy.Kinetic parameters were calculated by applying the shrinking unreacted core(SCM)and random pore(RPM)models.Moreover,char-CO2 gasification was further simulated by using Aspen Plus to investigate thermodynamic performances in terms of syngas composition and cold gas efficiency(CGE).The microwave-induced char has the largest C/H mass ratio and most ordered carbon structure,but the smallest gasification reactivity.Kinetic analysis indicates that the RPM is better for describing both gasification conversion and reaction rates of the studied chars,and the activation energies and pre-exponential factors varied in the range of 78.45–194.72 kJ/mol and 3.15–102,231.99 s−1,respectively.In addition,a compensation effect was noted during gasification.Finally,the microwave-derived char exhibits better thermodynamic performances than the conventional chars,with the highest CGE and CO molar concentration of 1.30%and 86.18%,respectively.Increasing the pyrolysis temperature,gasification temperature,and CO2-to-carbon molar ratio improved the CGE.

Experimental study on microwave pyrolysis of eucalyptus camaldulensis leaves:a promising approach for bio-oil recovery

Eucalyptus species are extensively cultivated trees commonly used for timber production,firewood,paper manufacturing,and essential nutrient extraction,while lacking consumption of the leaves increases soil acidity.The objective of this study was to recover bio-oil through microwave pyrolysis of eucalyptus camaldulensis leaves.The effects of microwave power(450,550,650,750,and 850 W),pyrolysis temperature(500,550,600,650,and 700°C),and silicon carbide amount(10,25,40,55,and 70 g)on the products yields and bio-oil constituents were investigated.The yields of bio-oil,gas,and residue varied within the ranges of 19.8–39.25,33.75–46.7,and 26.0–33.5 wt%,respectively.The optimal bio-oil yield of 39.25 wt%was achieved at 650 W,600°C,and 40 g.The oxygenated derivatives,aromatic compounds,aliphatic hydrocarbons,and phenols constituted 40.24–74.25,3.25–23.19,0.3–9.77,and 1.58–7.75 area%of the bio-oils,respectively.Acetic acid(8.17–38.18 area%)was identified as a major bio-oil constituent,and hydrocarbons with carbon numbers C_(1) and C_(2) were found to be abundant.The experimental results demonstrate the potential of microwave pyrolysis as an eco-friendly and efficient way for converting eucalyptus waste into valuable bio-oil,contributing to the sustainable utilization of biomass resources.

Effects of reaction temperature,time and particle size on switchgrass microwave pyrolysis and reaction kinetics

This study investigated microwave pyrolysis of switchgrass with particle sizes from 0.5 mm to 4 mm and determined the effects of reaction temperature and time on the yields of bio-oil,syngas,and bio-char.A prediction model was satisfactorily developed to describe the bio-oil conversion yield as a function of reaction temperature and time.Second-order reaction kinetics was also developed to model the switchgrass pyrolysis.Switchgrass with different particle sizes was found to be similarly pyrolyzed by microwave heating.The research results indicated that thermochemical conversion reactions can take place rapidly in large-sized switchgrass by using microwave pyrolysis.GC-MS analysis indicates that the bio-oil contained a series of important and useful chemical compounds:phenols,aliphatic hydrocarbons,aromatic hydrocarbons,and furan derivatives.These chemical compounds evolved were related to the pyrolysis conditions.

Conversion of Biomass to Hydrocarbon-rich Bio-oil via Microwave-assisted Catalytic Pyrolysis： A Review

The method for pyrolysis of biomass to manufacture hydrocarbon-rich fuel remains challenging in terms of conversion of multifunctional biomass with high oxygen content and low thermal stability into a high-quality compound, featuring high content of hydrocarbons, low oxygen content, few functional groups, and high thermal stability. This study offers a promising prospect to derive hydrocarbon-rich oil through microwave-assisted fast catalytic pyrolysis by improving the effective hydrogen to carbon ratio(H/Ceff) of the raw materials. The proposed technique can promote the production of high-quality bio-oil through the molecular sieve catalyzed reduction of oxygenated compounds and mutagenic polyaromatic hydrocarbons. This work aims to review and summarize the research progress on microwave copyrolysis and microwave catalytic copyrolysis to demonstrate their benefits on enhancement of bio-oils derived from the biomass. This review focuses on the potential of optimizing the H/Ceff ratio, the microwave absorbent, and the HZSM-5 catalyst during the microwave copyrolysis to produce the valuable liquid fuel. This paper also proposes future directions for the use of this technique to obtain high yields of bio-oils.

Catalytic microwave assisted pyrolysis of aspen

The effect of catalysts on the microwave pyrolysis of aspen pellets was studied.A range of chlorides,nitrates and metal-oxides were added at 2%of the aspen mass(air dry aspen pellet weight basis).Chlorides in particular were found to favor liquid yield,especially the yield of water phase residue.Average liquid yield with added chlorides was 41%mass of the total biomass input,compared to 35%mass without catalyst.Metal-oxides were found to favor pyrolysis heavy oil,and thus total oil yield,since the yield of light oils seemed to be fairly constant.Nitrates were found to favor pyrolysis gas production.Pure light oils and light oils blended with diesel were found to be a potential diesel fuel substitute.

Microwave-assisted pyrolysis of vegetable oil soapstock:Comparative study of rapeseed,sunflower,corn,soybean,rice,and peanut oil soapstock

In this study,the effects of catalytic temperature and the type of soapstock on products from microwave-assisted pyrolysis were investigated.HZSM-5 was used as the catalyst to study the pyrolysis of six different soapstocks at 200℃,300℃,and 400℃ catalytic temperature.Results showed that the bio-oil yields initially increased and then decreased with the increase in catalytic temperature.When the catalytic temperature was 300℃,the bio-oil reached up to the maximum value(65.8 wt.%).Findings indicated that the composition of bio-oil was related to the degree of unsaturation of fatty acids sodium in the soapstocks.In the case of saturated fatty acid sodium,a series of alkanes was formed,whereas the pyrolysis of monounsaturated fatty acid sodium resulted mainly in cycloalkanes,the cycloalkenes obtained from bio-oil was produced by polyunsaturated fatty acid sodium.

Two-step fast microwave-assisted pyrolysis of biomass for bio-oil production using microwave absorbent and HZSM-5 catalyst

A novel technology of two-step fast microwave-assisted pyrolysis（f MAP） of corn stover for bio-oil production was investigated in the presence of microwave absorbent（Si C） and HZSM-5catalyst. Effects of f MAP temperature and catalyst-to-biomass ratio on bio-oil yield and chemical components were examined. The results showed that this technology, employing microwave, microwave absorbent and HZSM-5 catalyst, was effective and promising for biomass fast pyrolysis. The f MAP temperature of 500°C was considered the optimum condition for maximum yield and best quality of bio-oil. Besides, the bio-oil yield decreased linearly and the chemical components in bio-oil were improved sequentially with the increase of catalyst-to-biomass ratio from 1：100 to 1：20. The elemental compositions of bio-char were also determined. Additionally, compared to one-step f MAP process, two-step f MAP could promote the bio-oil quality with a smaller catalyst-to-biomass ratio.

Processing and properties of rigid polyurethane foams based on bio-oils from microwave-assisted pyrolysis of corn stover

A new kind of rigid polyurethane(PU)foam was synthesized from the oil phase of bio-oils from microwave-assisted pyrolysis of corn stover.The recipes for the PU foams consisted of polyol-rich bio-oils,water as blowing agent,polyethylene glycol(PEG)as both polyol donor and plasticizer,diphenylmethane-4,4’-diisocyanate(polymeric MDI)as cross-linking agent,silicon-based surfactant,and tin-based catalyst.The mechanical properties of rigid foams were measured with universal testing machine(Instron4206).The effects of individual ingredients on the physical and mechanical properties of the foams were studied.It was found that water content,bio-oil content,and isocyanate dosage were important variables in making PU foams in terms of mechanical strength,density,and cellular structure Under optimal conditions,the compression strength of the prepared PU foams reached 1130 kPa with a density of 152.9 g/L.The results show that bio-oils are potential renewable polyol sources for making rigid PU foams.