The catalytic pyrolysis of food waste by microwave heating

Production of activated carbon from food wastes (chicken bones and rice waste) by microwave assisted ZnCl2 activation: an optimized process for crystal violet dye removal

A major worldwide challenge that presents significant economic, environmental, and social concerns is the rising generation of food waste. The current work used chicken bones (CB) and rice (R) food waste as alternate precursors for the production of activated carbon (CBRAC) by microwave radiation-assisted ZnCl2 activation. The adsorption characteristics of CBRAC were investigated in depth by removing an organic dye (crystal violet, CV) from an aquatic environment. To establish ideal conditions from the significant adsorption factors (A: CBRAC dosage (0.02-0.12 g/100 mL); B: pH (4-10); and C: duration (30-420), a numerical desirability function of Box-Behnken design (BBD) was utilized. The highest CV decolorization by CBRAC was reported to be 90.06% when the following conditions were met: dose = 0.118 g/100 mL, pH = 9.0, and time = 408 min. Adsorption kinetics revealed that the pseudo-first order (PFO) model best matches the data, whereas the Langmuir model was characterized by equilibrium adsorption, where the adsorption capacity of CBRAC for CV dye was calculated to be 57.9 mg/g. CV adsorption is accomplished by several processes, including electrostatic forces, pore diffusion, π-π stacking, and H-bonding. This study demonstrates the use of CB and R as biomass precursors for the efficient creation of CBRAC and their use in wastewater treatment, resulting in a greener environment.

State-of-the-art of the pyrolysis and co-pyrolysis of food waste: Progress and challenges

The continuous growth of population and the steady improvement of people's living standards have accelerated the generation of massive food waste. Untreated food waste has great potential to harm the environment and human health due to bad odor release, bacterial leaching, and virus transmission. However, the application of traditional disposal techniques like composting, landfilling, animal feeding, and anaerobic digestion are difficult to ease the environmental burdens because of problems such as large land occupation, virus transmission, hazardous gas emissions, and poor efficiency. Pyrolysis is a practical and promising route to reduce the environmental burden by converting food waste into bioenergy. This paper aims to analyze the characteristics of food waste, introduce the production of biofuels from conventional and advanced pyrolysis of food waste, and provide a basis for scientific disposal and sustainable management of food waste. The review shows that co-pyrolysis and catalytic pyrolysis significantly impact the pyrolysis process and product characteristics. The addition of tire waste promotes the synthesis of hydrocarbons and inhibits the formation of oxygenated compounds efficiently. The application of calcium oxide (CaO) exhibits good performance in the increment of bio-oil yield and hydrocarbon content. Based on this literature review, pyrolysis can be considered as the optimal technique for dealing with food waste and producing valuable products.

Comparative Investigation of the Physicochemical Properties of Chars Produced by Hydrothermal Carbonization, Pyrolysis, and Microwave-Induced Pyrolysis of Food Waste

This work presents a comparative study of the physicochemical properties of chars derived by three thermochemical pathways, namely: hydrothermal carbonization, HTC (at 180, 200 and 220 °C), pyrolysis, PY, (at 500, 600 and 700 °C) and microwave assisted pyrolysis, MW (at 300, 450 and 600 W). The mass yield of HTC samples showed a decrease (78.7 to 26.7%) as the HTC temperature increased from 180 to 220 °C. A similar decreasing trend in the mass yield was also observed after PY (28.45 to 26.67%) and MW (56.45 to 22.44%) of the food waste mixture from 500 to 700 °C and 300 to 600 W, respectively. The calorific value analysis shows that the best among the chars prepared by three different heating methods may be ranked according to the decreasing value of the heating value as: PY500, MW300, and HTC180. Similarly, a decreasing trend in H/C values was observed as: PY500 (0.887), MW300 (0.306), and HTC180 (0.013). The scanning electron microscope (SEM) analyses revealed that the structure of the three chars was distinct due to the different temperature gradients provided by the thermochemical processes. The results clearly show that the suitable temperature for the HTC and PY of food waste was 180 °C and 500 °C, respectively, while the suitable power for the MW of food waste was 300 W.

Effects of oxygen vacancy defect on microwave pyrolysis of biomass to produce high-quality syngas and bio-oil: Microwave absorption and in-situ catalytic

This paper proposed to use ferric oxide (Fe₂O₃) and ferroferric oxide (Fe₃O₄) as catalysts with both microwave absorption and catalytic properties. Carbon dioxide (CO₂) was introduced as the reaction atmosphere to further improve the quality of biofuel produced by microwave pyrolysis of food waste (FW). The results showed the bio-gas yield and the syngas concentration (H₂ + CO) increased to 70.34 wt% and 61.50 mol%, respectively, using Fe₃O₄ as the catalyst. The content of aliphatic hydrocarbons in bio-oil produced with the catalyst Fe₂O₃ increased to 67.48% and the heating value reached 30.45 MJ/kg. Compared with Fe₂O₃ catalyst, Fe₃O₄ exhibited better microwave absorption properties and catalytic properties. Transmission electron microscopy (TEM) and Electron paramagnetic resonance (EPR) characterizations confirmed that the crystal surface of Fe₃O₄ formed more oxygen vacancy defects and unpaired electrons. Additionally, according to the X-ray photoelectron spectroscopy (XPS) analysis, the content of lattice oxygen in Fe₃O₄ was 14.11%, a value that was much lower than Fe₂O₃ (38.54%). The oxygen vacancy defects not only improved the efficient utilization of microwave energy but also provided the reactive sites for the reaction between the volatile organic compounds (VOCs) and CO₂ to generate CO. This paper provides a new perspective for selecting catalysts that have both microwave absorption and catalytic properties during the microwave pyrolysis of biomass.

Microwave-Assisted Catalytic Fast Pyrolysis of Biomass for Hydrocarbon Production with Physically Mixed MCM-41 and ZSM-5

To delve into the law of hydrocarbon production in microwave-assisted catalytic fast pyrolysis (MACFP) of corn straw, physical mixed Mesoporous Crystalline Material-41 (MCM-41) and Zeolite Socony Mobile-5 (ZSM-5) catalyst prototypes were exploited in this study. Besides, the effects exerted by temperature of reaction and MCM-41/ZSM-5 mass ratio were explored. As revealed from the results, carbon outputs of hydrocarbons rose initially as the temperature of MACFP rose and reached the maximal data at 550 °C; subsequently, it declined as reaction temperature rose. Moreover, the MCM-41/ZSM-5 mass ratio of 1:2 was second-to-none for hydrocarbon formation in the course of biomass MACFP. It was reported that adding MCM-41 can hinder coke formation on ZSM-5. Furthermore, MCM-41/ZSM-5 mixture exhibited more significant catalytic activity than ZSM-5/MCM-41 composite, demonstrating that hydrocarbon producing process can be stimulated by a simple physical MCM-41 and ZSM-5 catalysts mixture instead of synthesizing complex hierarchically-structured ZSM-5/MCM-41 composite.

Microwaves and Heterogeneous Catalysis: A Review on Selected Catalytic Processes

Since the late 1980s, the scientific community has been attracted to microwave energy as an alternative method of heating, due to the advantages that this technology offers over conventional heating technologies. In fact, differently from these, the microwave heating mechanism is a volumetric process in which heat is generated within the material itself, and, consequently, it can be very rapid and selective. In this way, the microwave-susceptible material can absorb the energy embodied in the microwaves. Application of the microwave heating technique to a chemical process can lead to both a reduction in processing time as well as an increase in the production rate, which is obtained by enhancing the chemical reactions and results in energy saving. The synthesis and sintering of materials by means of microwave radiation has been used for more than 20 years, while, future challenges will be, among others, the development of processes that achieve lower greenhouse gas (e.g., CO2) emissions and discover novel energy-saving catalyzed reactions. A natural choice in such efforts would be the combination of catalysis and microwave radiation. The main aim of this review is to give an overview of microwave applications in the heterogeneous catalysis, including the preparation of catalysts, as well as explore some selected microwave assisted catalytic reactions. The review is divided into three principal topics: (i) introduction to microwave chemistry and microwave materials processing; (ii) description of the loss mechanisms and microwave-specific effects in heterogeneous catalysis; and (iii) applications of microwaves in some selected chemical processes, including the preparation of heterogeneous catalysts.

Fast microwave-assisted pyrolysis of wastes for biofuels production - A review

Microwave-assisted pyrolysis of waste suffers from the problem that the waste generally has low microwave absorptivity thereby resulting in low heating rate and low pyrolysis temperature. In this case, fast microwave-assisted pyrolysis is proposed and developed to help the pyrolysis of waste. This study describes two methods that can be used to realize fast microwave-assisted pyrolysis of waste: (1) premixed method (wastes are mixed with microwave absorbent) and (2) non-premixed method (wastes are poured onto the heated microwave absorbent bed). Then, biofuels (bio-oil, bio-gas, and bio-char) produced from fast microwave-assisted pyrolysis of wastes are reviewed. The review results show that the yields of bio-oil, bio-gas, and bio-char obtained from fast microwave-assisted pyrolysis of wastes varied significantly in the ranges of 2-96 wt%, 2.4-86.8 wt%, and 0.3-83.2 wt%, respectively. Although the present research focused mainly on the premixed method, non-premixed/continuous fast microwave-assisted pyrolysis is still promising and challenging.

Food and Market Waste-A Pathway to Sustainable Fuels and Waste Valorization

Food and market waste (FMW) is one of the most abundant unrecycled products which poses waste management issues and negative environmental impacts. Thermo-catalytic reforming (TCR) is a pyrolysis based technology which can convert a wide range of biomass wastes into energy vectors bio-oil, syngas, and char. This paper investigates the conversion potential of FMW into sustainable biofuels. The FMW was processed using a laboratory scale 2 kg/h TCR reactor. The process produced 7 wt % organic bio-oil, 53 wt % permanent gas, and 22 wt % char. The bio-oil higher heating value (HHV) was found to be 36.72 MJ/kg, comparable to biodiesel, and contained a low oxygen content (<5%) due to cracking of higher molecular weight organics. Naphthalene was detected to be the most abundant aromatic compound within the oil, with relative abundance of 12.95% measured by GC-MS. The total acid number of the oil (TAN) and viscosity were 11.7 mg KOH/g and 6.3 cSt, respectively. The gross calorific value of the produced biochar was 23.64 MJ/kg, while the permanent gas showed a higher heating value of approximately 17 MJ/Nm³. Methane (CH₄) was found to be the largest fraction in the permanent gases reaching over 23%. This resulted either due to the partial methanation of biosyngas over the catalytically active FMW biochar or the hydrogenation of coke deposited on the biochar in the post reforming stage.

A review of catalysts used in microwave assisted pyrolysis and gasification

The review describes different catalysts and reactor-types used in microwave-assisted thermochemical biomass conversion. We present comparative review of various catalytic experiments and experimental conditions using catalysts in both in situ and ex situ processes. In situ catalytic processes are more frequently used due to simpler experimental set up. However, the process leads to higher catalytic deactivation rate and catalyst recovery is difficult. Catalysts used in ex situ processes require a more complex experimental set-up, the advantage being the fact that optimum temperature can be obtained to achieve best results catalyst recovery is facile, and its deactivation occurs at a lower rate. The catalysts described herein represent just a small part of the catalyst types/family that can be theoretically used. Commonly used catalysts are zeolites, metal oxides, various salts or carbon type materials but other materials or improvements of those mentioned need to be tested in the future.

Slow Pyrolysis Temperature and Duration Effects on Fuel Properties of Food Rice Waste Bio-Char

In this study, to convert high moisture content waste into bio-char, slow pyrolysis of cooked rice waste was proposed. The effects of temperature and duration of slow pyrolysis of cooked rice waste on the fuel properties of the biochar produced were investigated, namely the carbon content and energy density. The cooked rice waste was dried overnight at 80°C prior to pyrolysis to reduce moisture content. The carbon content was measured by using Thermo Finnigan Flash EA 1112 Series Elemental Analyser CHNS-O. Energy density was measured by using IKA Works C—5000 Control bomb calorimeter. Results demonstrated that pyrolysed rice waste at 250°C and 4 hour duration had the highest carbon content (60.30%). Moreover, the calorific values for pyrolysed cooked rice wastes demonstrated that biochar derived from cooked rice waste could be a promising alternative renewable energy source.

Microwave pyrolysis of moso bamboo for syngas production and bio-oil upgrading over bamboo-based biochar catalyst

Microwave pyrolysis of moso bamboo over bamboo-based biochar catalyst was conducted to achieve the bio-oil upgrading and high quality syngas production. The influence of the biochar on bamboo pyrolysis involving the temperature rise, product yield, and bio-oil and gas compositions was studied. The gas production was facilitated by the biochar mainly at the cost of the bio-oil, indicating the biochar had an excellent activity for the bio-oil cracking. The main compositions in bio-oil were acetic acid and phenol with the total contents ranging from 73.145% to 82.84% over the biochar catalysts, suggesting the upgrading of the bio-oil were achieved. The biochar exerted a positive effect on the syngas (CO + H₂) production with the maximum content reaching up to 65.13 vol% at the 20 wt% addition amount of biochar under microwave condition. The biochar became more effective on the bio-oil upgrading and syngas production under microwave heating than conventional heating.

The volatilization of heavy metals during co-combustion of food waste and polyvinyl chloride in air and carbon dioxide/oxygen atmosphere

The volatilization of three heavy metals (Cd, Cr and Zn) during food waste and PVC and their blending combustion in N₂/O₂ or CO₂/O₂ atmosphere in a lab-scale tubular furnace was investigated. The concentration of heavy metals in combustion ash was decreased with the increment of furnace temperature in most cases. The replacement of 80N₂/20O₂ by 80CO₂/20O₂ decreased the volatilization rate of Cd and Cr, but increased Zn. The increased amount of PVC added into food waste led to less content of Zn in combustion ash, 5% PVC added into food waste decreased the volatilization rate of Cr but 15% PVC added led to the higher volatilization. The volatilization rate of Zn in 70CO₂/30O₂ was significantly lower than in 85CO₂/15O₂ or 80CO₂/20O₂. The result contributes to the understanding of heavy metal volatilization during incineration and emission control of MSW oxy-fuel combustion.

Autocatalytic Pyrolysis of Wastewater Biosolids for Product Upgrading

The main goals for sustainable water resource recovery include maximizing energy generation, minimizing adverse environmental impacts, and recovering beneficial resources. Wastewater biosolids pyrolysis is a promising technology that could help facilities reach these goals because it produces biochar that is a valuable soil amendment as well as bio-oil and pyrolysis gas (py-gas) that can be used for energy. The raw bio-oil, however, is corrosive; therefore, employing it as fuel is challenging using standard equipment. A novel pyrolysis process using wastewater biosolids-derived biochar (WB-biochar) as a catalyst was investigated to decrease bio-oil and increase py-gas yield for easier energy recovery. WB-biochar catalyst increased the py-gas yield nearly 2-fold, while decreasing bio-oil production. The catalyzed bio-oil also contained fewer constituents based on GC-MS and GC-FID analyses. The energy shifted from bio-oil to py-gas, indicating the potential for easier on-site energy recovery using the relatively clean py-gas. The metals contained in wastewater biosolids played an important role in upgrading pyrolysis products. The Ca and Fe in WB-biochar reduced bio-oil yield and increased py-gas yield. The py-gas energy increase may be especially useful at water resource recovery facilities that already combust anaerobic digester biogas for energy since it may be possible to blend biogas and py-gas for combined use.

Effects of feedstock characteristics on microwave-assisted pyrolysis - A review

Microwave-assisted pyrolysis is an important approach to obtain bio-oil from biomass. Similar to conventional electrical heating pyrolysis, microwave-assisted pyrolysis is significantly affected by feedstock characteristics. However, microwave heating has its unique features which strongly depend on the physical and chemical properties of biomass feedstock. In this review, the relationships among heating, bio-oil yield, and feedstock particle size, moisture content, inorganics, and organics in microwave-assisted pyrolysis are discussed and compared with those in conventional electrical heating pyrolysis. The quantitative analysis of data reported in the literature showed a strong contrast between the conventional processes and microwave based processes. Microwave-assisted pyrolysis is a relatively new process with limited research compared with conventional electrical heating pyrolysis. The lack of understanding of some observed results warrant more and in-depth fundamental research.

Pyrolysis process for the treatment of food waste

Different waste materials were pyrolysed in the laboratory pyrolysis unit to the final temperature of 800°C with a 10min delay at the final temperature. After the pyrolysis process a mass balance of the resulting products, off-line analysis of the pyrolysis gas and evaluation of solid and liquid products were carried out. The gas from the pyrolysis experiments was captured discontinuously into Tedlar gas sampling bags and the selected components were analyzed by gas chromatography (methane, ethene, ethane, propane, propene, hydrogen, carbon monoxide and carbon dioxide). The highest concentration of measured hydrogen (WaCe 61%vol.; WaPC 66%vol.) was analyzed at the temperature from 750 to 800°C. The heating values of the solid and liquid residues indicate the possibility of its further use for energy recovery.

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 (fMAP) of corn stover for bio-oil production was investigated in the presence of microwave absorbent (SiC) and HZSM-5 catalyst. Effects of fMAP 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 fMAP 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 fMAP process, two-step fMAP could promote the bio-oil quality with a smaller catalyst-to-biomass ratio.

Effects of additives on the co-pyrolysis of municipal solid waste and paper sludge by using thermogravimetric analysis

By using thermogravimetric analysis (TGA), the effects of different additives (MgO, Al2O3 and ZnO) on the pyrolysis characteristics and activation energy of municipal solid waste (MSW), paper sludge (PS) and their blends in N2 atmosphere had been investigated in this study. The experiments resulted that these additives were effective in reducing the initial temperature and activation energy. However, not all the additives were beneficial to reduce the residue mass and enhance the index D. For the different ratios of MSW and PS, the same additive even had the different influences. The catalytic effects of additives were not obvious and the pyrolysis became difficult with the increase of the proportion of PS. Based on all the contrast of the pyrolysis characteristics, MgO was the best additive and 70M30P was the best ratio, respectively.

Food waste generation and industrial uses: A review

Food waste is made up of materials intended for human consumption that are subsequently discharged, lost, degraded or contaminated. The problem of food waste is currently on an increase, involving all sectors of waste management from collection to disposal; the identifying of sustainable solutions extends to all contributors to the food supply chains, agricultural and industrial sectors, as well as retailers and final consumers. A series of solutions may be implemented in the appropriate management of food waste, and prioritised in a similar way to waste management hierarchy. The most sought-after solutions are represented by avoidance and donation of edible fractions to social services. Food waste is also employed in industrial processes for the production of biofuels or biopolymers. Further steps foresee the recovery of nutrients and fixation of carbon by composting. Final and less desirable options are incineration and landfilling. A considerable amount of research has been carried out on food waste with a view to the recovery of energy or related products. The present review aims to provide an overview of current debate on food waste definitions, generation and reduction strategies, and conversion technologies emerging from the biorefinery concept.

Catalytic fast co-pyrolysis of biomass and food waste to produce aromatics: Analytical Py-GC/MS study

In this study, catalytic fast co-pyrolysis (co-CFP) of corn stalk and food waste (FW) was carried out to produce aromatics using quantitative pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and ZSM-5 zeolite in the hydrogen form was employed as the catalyst. Co-CFP temperature and a parameter called hydrogen to carbon effective ratio (H/C(eff) ratio) were examined for their effects on the relative content of aromatics. Experimental results showed that co-CFP temperature of 600 °C was optimal for the formation of aromatics and other organic pyrolysis products. Besides, H/C(eff) ratio had an important influence on product distribution. The yield of total organic pyrolysis products and relative content of aromatics increased non-linearly with increasing H/C(eff) ratio. There was an apparent synergistic effect between corn stalk and FW during co-CFP process, which promoted the production of aromatics significantly. Co-CFP of biomass and FW was an effective method to produce aromatics and other petrochemicals.