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The co-gasification of coal and dried sewage sludge (DSS) was conducted using a two-stage gasifier consisting of a fluidized bed gasifier and a tar-cracking reactor. In this study, the effect of the blending ratio of coal and DSS was investigated. Producer gases that were obtained from the tar-cracking reactor filled with active carbon contained high levels of hydrogen (maximum H2: 27.7 vol%) and low tar contents (minimum tar: 0 mg/Nm3). Upon gasification of the coal/DSS blends, the hydrogen content decreased and tar content increased with increasing DSS. Blends with coal/DSS ratios of 70/30 and 50/50 showed a synergetic effect on tar reduction, which could be attributed to the high ash content of the DSS. The gasification of the 70% DSS blend increased the condensed tar yield by only 0.1 wt%, compared to coal gasification. Lastly, a hot filter filled with Fe-impregnated active carbon was applied to completely remove tar from producer gas, which led to the production of a tar-free and hydrogen-rich gas (30 vol%). Furthermore, the Fe-impregnated active carbon reduced the H2S content to 229 ppmv. In summary, it was possible to produce a clean gas from coal and DSS blends in the UOS gasification process.

In this study, a separate two-step pyrolysis (using auger and fixed-bed reactors) and a continuous two-stage pyrolysis (using auger and fluidized bed reactors) were conducted. This two-step pyrolysis was conducted to understand the effect of a 300 °C thermal pretreatment with the auger reactor before main pyrolysis on the chlorine removal. The fixed-bed pyrolysis of a solid product obtained after the pretreatment produced an oil with 464 ppm chlorine. An oil with only 14 ppm of organic chlorine could be obtained when a solid containing CaO was pyrolyzed in the fixed-bed reactor. Thermal pretreatment also caused changes in the yield and product composition; pretreatment led to an increase in gas yield and aromatic content of the oil. In the continuous two-stage pyrolysis of a waste plastic mixture having 3 wt.% polyvinyl chloride at 730 °C, chlorine in the feed material was removed in parallel from the outlet of the auger reactor line and through a CaO hot filter; this produced an oil with 6.3 ppm organic chlorine. In the two-stage pyrolysis, an aromatic-rich oil (80 wt.%) was obtained. The two-stage pyrolysis successfully converted the waste plastic mixture into an oil which could be acceptable as a feedstock for petrochemical industries.

Waste polyethylene (PE) was pyrolyzed in a continuous two-stage pyrolysis process having auger and fluidized bed reactors. The main aim of the study was to produce a pyrolysis gas containing high contents of olefins along with a clean pyrolysis oil at moderate reaction conditions. In the experiment, the temperatures of the auger and fluidized bed reactors were varied from 30 to 300 °C and from 653 to 736 °C, and a CaO hot filter was used to capture HCl liberated during pyrolysis. At elevated auger reactor temperatures, the PE molecules in the reactor shifted to higher vibrational energy states, resulting in the weakening of the C C bond of PE molecule. The PE melt leaving the auger reactor could finally be decomposed into short chains in the fluidized bed reactor. The total yield of ethene, propene, and 1,3-butadiene was 30–53 wt.%. The olefin yield increased with increasing auger reactor temperature. The highest gas (74.6 wt.%) and ethene (34.5 wt.%) yields were obtained when N2 was used as the fluidizing medium. Pyrolysis oil, whose yield was 15–38 wt.%, was mostly composed of aromatic hydrocarbons. The CaO hot filter could reduce the chlorine content in the pyrolysis oil to 66.5 ppm.

Air gasification of waste polyethylene (PE) was conducted using active carbon as a tar removal agent in a new type of three-stage gasifier. The main focus was on the in-situ regeneration of active carbon, which was conducted simply with air treatment, which was mainly performed with variations of treatment time and air flow rate. In the experiments, active carbon was found to be very effective in hydrogen production and tar removal. The maximum hydrogen content of the producer gas obtained with active carbon was approximately 27 vol%, while the producer gas was free of tar. Active carbon, treated with air for 10 min, while stopping feeding, had a surface area of 937 m2/g (83% recovery rate). A 4 h of gasification performed with a dolomite guard bed and a mesh type distributor produced a gas having H2 and heavier tar than toluene contents of 28 and 0 vol%, respectively. The regeneration study suggested that a severe coke formation could be diminished, when methods such as frequent air regeneration with short treatment time, the use of other regeneration agents, such as CO2 or H2O and/or the selection of a proper distributor would be applied.

In this study, a continuous two-stage pyrolyzer consisting of an auger reactor and a fluidized bed reactor was applied to produce an oil with a low level of chlorine from a mixture of low density polyethylene and polyvinyl chloride waste. In the experiment, the auger reactor operated at 300–400 °C, thus releasing HCl prior to the main pyrolysis in the fluidized bed reactor. The auger reactor also played a role in elevating vibrational modes of molecules to promote the production of ethene, propene, and 1,3-butadiene. The yields of those monomers totaled 29 wt.%. Pyrolysis oils obtained from the fluidized bed reactor were enriched with aromatics up to 95 wt.%. Together with the two-stage pyrolyzer and a lime hot filter, a pyrolysis oil having only 9.25 ppm chlorine could be obtained. This value is the lowest ever reported. This study showed that a two-stage pyrolyzer together with a lime hot filter could produce a pyrolysis oil with a very low chlorine content. Further, this work implies that the production of valuable monomers from the pyrolysis of polyolefins can be enhanced when a two-stage pyrolyzer is applied.

Air gasification of dried sewage sludge was performed in a new-type three-stage gasifier consisting of an auger, a fluidized bed, and a tar-cracking reactors. The study aimed to evaluate the possibility of gasification using only condensers for the secondary tar removal method. The effects of Ni- and Fe-impregnated active carbons on the quality of producer gas were also investigated. Finally, to investigate the deactivation behavior of active carbon, a spent active carbon obtained after about 4.3 h of gasification, was used again for approximately 3.7 h of gasification. The active carbons used effectively reduced the contents of condensed and gaseous tars. Ni-impregnated active carbon produced a gas with a high H2 content (26 vol%) and a low NH3 content (198 ppmv), while Fe-impregnated active carbon produced a gas with a low H2S content (96 ppmv). The compositions of the producer gases obtained solely using condensers were similar to those obtained using electrostatic precipitator. During the total ∼8 h of gasification, active carbon could efficiently remove tar; however, its surface area and total pore volume slowly decreased with time.

Pyrolysis of municipal waste plastic was conducted using a two-stage pyrolysis process with auger and fluidized bed reactors. The current study comprises two parts: a kinetic study and pyrolysis experiments using activator-assisted pyrolysis. The kinetic study was performed using the distributed activation energy model, and it revealed that the average activation energy for activated molecules was 7 kJ/mol lower than that for unactivated molecules. The pyrolysis experiment confirmed that the activation of molecules resulted in an enhanced gas production. In particular, the methane and ethene yields increased by 11 and 8 wt%, respectively, when molecules were activated. A higher flow rate of the product gas used as the fluidizing gas resulted in a decrease in the gas yield. CaO and Na2CO3 were used as absorbents for chlorinated compounds produced during pyrolysis to reduce the level of Cl in the oil. The absorbents, at first, changed the product distribution, enhancing the production of mono-aromatics. In particular, the benzene yield with Na2CO3 amounted to 10 wt%. The two absorbents were excellent in reducing the Cl content in oil. Between the two absorbents, Na2CO3 proved to be the better, reducing the Cl content to 65 ppm.

Two-stage pyrolysis of corncob was performed to simultaneously produce acetic acid-rich and phenolic-rich bio-oils. The two-stage pyrolyzer consisted of an auger reactor and a fluidized bed reactor...

Scrap tire pyrolysis was conducted to produce low sulfur oil (below 0.45 wt%), which is strongly demanded for reduction of SOx emissions. In the experiments, a continuous two-stage pyrolyzer consisting of an auger reactor and fluidized bed reactor and various additives (CaO, Fe, FeO, calcined olivine) and fluidizing media (product gas and N2) were tested for the in-situ desulfurization. The auger reactor operated at ∼340 °C yielded a liquid with 3–5 wt.% of pyrolysis oil. The content of DL-limonene in this liquid product was ∼51 wt% and increased further to ∼76 wt% through subsequent ethanol extraction. The fluidized bed reactor (∼510 °C) produced pyrolysis oils with yields around 30–37 wt%. N2 reduced the sulfur content in pyrolysis oil more effective than product gas, due to its dilution effect. The majority of tested desulfurizing additives reduced the sulfur content in pyrolysis oil, and the application of FeO powder and N2 in particular produced pyrolysis oil with the lowest sulfur content (0.39 wt%). Two ex-situ desulfurization methods (ethanol extraction and oxidation/ethanol extraction) were tested to further reduce the sulfur content. The oxidation/ethanol extraction method decreased the content of sulfur in pyrolysis oil to 0.17 wt%.

Fast pyrolysis of corncob, palm kernel shell, and radiata pine was conducted at ∼430 °C to produce acetic acid-rich bio-oils. The bio-oil derived from corncob contained a high concentration of acetic acid (∼8 wt.%). Atmospheric and vacuum distillation of the bio-oil from corncob was performed to obtain bio-oil fractions enriched with acetic acid. The resultant atmospheric and vacuum distilled fractions were enriched with acetic acid containing ∼10 and 15 wt.% acetic acid. In particular, the vacuum distilled fraction contained very low contents of lignin degradation products. Calcium magnesium acetate (CMA), a biodegradable deicing agent, was then synthesized using corncob-derived bio-oils (a whole bio-oil, atmospheric and vacuum distilled fractions) and natural and calcined dolomite. Analytical results revealed that the CMAs synthesized by the reaction between atmospheric and vacuum distilled fractions and calcined dolomite were chemically identical to the commercial CMA. In particular, the vacuum distilled fraction and calcined dolomite proved to be the best reactants for the CMA production.

Phenols are a class of aromatic compounds that have at least one benzene ring joined with a hydroxyl group. Phenols are widely used in the manufacture of chemicals, resins, synthetic fibers, pesticides, and dyes and products made from phenols have become an indispensable part of modern life. The simplest form of phenols is phenol, which is industrially prepared on a very large scale from petroleum. Fossil-based chemicals like fossil phenol, however, face depletion in the near future. Hence, the demand for renewable chemicals is increasing, and this will also enhance opportunities of sustainable products. Biomass pyrolysis is an attractive route to produce valuable bio-chemicals. Representative bio-chemicals made via pyrolysis of lignocellulosic biomass are phenols, acetic acid, levoglucosan, and furfural. This chapter deals with the production of renewable phenols, especially phenol, from lignocellulosic biomass pyrolysis. Types of lignocellulosic biomass used in pyrolysis processes, and effect of reaction conditions on the production of phenols are discussed along with applications of phenolic-rich bio-oils.

Polyethylene terephthalate was gasified using a two-stage gasifier composed of a fluidized bed gasifier and tar-cracking reactor and air as the gasifying agent. The main challenge was to overcome problems such as equipment clogging caused by the condensable compounds (tars) generated during polyethylene terephthalate gasification. Active carbon was applied to the two-stage gasifier to reduce tar. As a result of gasification, we did not experience any problems caused by tar, thereby obtaining a clean producer gas. Active carbon played a crucial role in increasing H2 production and reducing the tar content. The tar-cracking reactor temperature and equivalence ratio turned out to have a significant influence on the gas quality. The gas produced from the gasification of polyethylene terephthalate had high contents of H2 and CO. At the tar-cracking reactor temperature of 844 °C and an equivalence ratio of 0.27, a producer gas containing 22 vol% H2, 25 vol% CO, and 7 mg/Nm3 of tar was obtained. Considering the high amount of O in polyethylene terephthalate compared with that in polyolefin, CO production from the two-stage air gasification of polyethylene terephthalate appeared to be very attractive when the process was implemented on a commercial scale.

Air gasification of polystyrene was conducted using a two-stage gasifier consisting of a fluidized bed and a tar-cracking reactor filled with active carbon. The aim was to obtain a hydrogen-rich producer gas with a low level of tar. In addition to the possibility of tar removal, the effects of the reaction temperature and equivalence ratio on the producer gas quality were investigated. In this study, it was found that the gasification of polystyrene had different characteristics to the gasification of other plastic, resulting in a high production of char. Active carbon played a crucial role, significantly decreasing the tar content in gas to 11 mg/Nm3. Furthermore, gasification with active carbon produced a gas having a high content of hydrogen (26 vol%). The change in fluidized bed gasifier temperature within the range of 700–900 °C exerted no significant effects on the gas quality. In contrast, a high tar-cracking reactor temperature clearly increased hydrogen and carbon monoxide contents. With an increasing equivalence ratio, oxidation of char was promoted, resulting in a significant increase in gas production and carbon oxides. The current study showed a good possibility for the recycling of polystyrene via gasification, producing a clean and hydrogen-rich gas.

A new three-stage gasifier consisting of an auger gasifier, a fluidized bed gasifier, and a tar-cracking zone was applied for the gasification of dried sewage sludge to obtain a high-quality producer gas with low levels of impurities (tar, NH3, and H2S). In the experiments, the effects of activated carbon (AC), equivalence ratio, the weight ratio of AC to fuel, and feed rate were investigated. In particular, approximately 5 h of gasification was conducted to see the deactivation behavior of AC and changes in gas compositions. The experiments showed that the equivalence ratio had a strong influence on impurity contents in producer gas, lowering them at a high equivalence ratio of 0.5. The increase in the ratio of AC to fuel not only led to an increase in the production of H2, but also to a decrease in impurity contents. The approximately 5 h of gasification proved the activity of AC for tar cracking. The maximum H2 content in producer gas (29 vol%) was obtained at the AC/fuel ratio of 3:1 and at an equivalence ratio of 0.35. The minimum tar, NH3, and H2S contents in producer gas were 27 mg/Nm3, 443, and 470 ppmv, respectively.

Gasification of dried sewage sludge was performed in a newly developed three-stage gasifier consisting of an auger as well as fluidized and fixed bed reactors to produce a producer gas with low-levels of contaminants. The auger reactor was designed to generate tar in advance, thereby enhancing the tar destruction in the fluidized bed gasifier and fixed-bed reactor. In the study, the effects of each reactor temperature and activated carbon as an impurity absorbent were mainly investigated. The reaction temperatures of the auger and fixed bed reactors were shown to have a strong influence on the tar removal, while that of the fluidized bed reactor mainly affected the producer gas composition. The three-stage gasifier clearly decreased the tar content in producer gas and condensed tar and increased the H 2 production. In an experiment performed with activated carbon at the auger reactor temperature of ∼710 °C and the fluidized bed and fixed bed reactor temperatures of ∼830 °C, the tar and H 2 contents in producer gas were only 22 mg/Nm 3 and ∼29 vol%, respectively. Activated carbon clearly reduced the NH 3 and H 2 S contents in producer gas. The minimum NH 3 and H 2 S contents were 324 and 346 ppmv, respectively.

Scrap tire pyrolysis was performed using a two-stage pyrolyzer consisting of an auger reactor and a fluidized bed reactor to produce a low-sulfur pyrolysis oil. In the experiments, the effect of the residence time of the feed material in the auger reactor was investigated at ∼300 (auger reactor) and 500 °C (fluidized bed reactor). In addition, natural dolomite and olivine and calcined dolomite and olivine were used as the fluidized bed materials to examine their effects on reducing the sulfur content of pyrolysis oil. In the experiments, the yields of the oil from the auger reactor were 1.4–3.7 wt%, and it was enriched with dl -limonene whose content in the oil was 40–50 wt%. The yields of the oil from the fluidized bed reactor were 42–46 wt%. The optimum residence time of the feed material in the auger reactor turned out to be 3.5 min. Calcined dolomite and olivine significantly decreased the sulfur content of pyrolysis oil. Metal oxides of the additives appeared to react with H2S to form metal sulfides. The sulfur content of pyrolysis oil obtained with calcined olivine was 0.45 wt%.

Pyrolysis of palm kernel shell was performed using a two-stage pyrolyzer consisting of an auger reactor and a fluidized bed reactor within the auger reactor temperature range of ∼290–380 °C at the fluidized bed reactor temperature of ∼520 °C, and with a variable residence time of the feed material in the auger reactor. The highest bio-oil yield of the two-stage pyrolysis was ∼56 wt%. The bio-oil derived from the auger reactor contained degradation products of the hemicelluloses of PKS, such as acetic acid, and furfural, whereas the fluidized bed reactor produced a bio-oil with high concentrations of acetic acid and phenol. The auger reactor temperature and the residence time of PKS in the auger reactor had an influence on the acetic acid concentration in the bio-oil, while their changes did not induce an observable trend on the phenol concentration in the bio-oil derived from the fluidized bed reactor. The maximum concentrations of acetic acid and phenol in bio-oil were ∼78 and 12 wt% dry basis, respectively. As a result, it was possible for the two-stage pyrolyzer to separately produce two different bio-oils in one operation without any costly fractionation process of bio-oils.

The aim of this work was to reduce the sulfur content of pyrolysis oil derived from the scrap tire pyrolysis. In this respect, a series of pyrolysis experiments was conducted in both a fluidized bed reactor (one-stage pyrolysis) and a newly developed two-stage pyrolyzer consisting of an auger reactor and a fluidized bed reactor in series (two-stage pyrolysis). The one-stage pyrolysis was carried out at ∼500 and 600 °C with different fluidizing gases (N2 and product gas). In the experiments, the pyrolysis oil obtained at ∼500 °C had a lower sulfur content than that produced at ∼600 °C. N2 was better at producing a low-sulfur pyrolysis oil than product gas. The sulfur contents of the oils obtained from the one-stage pyrolysis ranged from 0.75 to 0.92 wt.%. The two-stage pyrolysis was conducted using product gas as the fluidizing medium at different auger reactor temperatures (∼230–450 °C) and at a constant fluidized bed reactor temperature (∼510 °C). A pyrolysis oil containing only 0.55 wt.% of sulfur could be produced at the temperatures of the auger reactor of ∼330 °C and fluidized bed reactor of ∼510 °C. Moreover, the two-stage pyrolysis could produce an oil with a low nitrogen content (0.28 wt.%). A pyrolysis oil obtained from the auger reactor contained d l -limonene up to 50 wt.%.

A two-stage pyrolysis of wood was conducted to produce a phenol-rich bio-oil. The two-stage pyrolysis process included auger and fluidized bed reactors connected in series. In this study, the effects of temperatures of the auger and fluidized bed reactors and the type of fluidizing medium were mainly investigated. The auger reactor temperature was varied from room temperature to about 290 °C, whereas the fluidized bed reactor temperature ranged from about 500 to 700 °C. As the auger reactor temperature rose from about 20 to 290 °C, the gas yield increased from 27 to 31 wt%. At about 290 °C, the production of phenol was greatly enhanced. A high fluidized bed reactor temperature favored the formation of phenol, efficiently exploiting the weakened bond strength between C (benzene) and methoxy group of lignin molecules caused by heat treatment in the auger reactor. The use of nitrogen as the fluidizing medium drastically increased phenol production, which was achieved by reducing reactions of phenol produced inside the fluidized bed reactor with other components. In the current study, the maximum phenol content in bio-oil reached about 16 wt%. Bio-oil with a high phenol content has good potential as a reactant in the phenol resin synthesis.

Steam gasification of polyethylene was conducted using a two-stage gasifier consisting of a fluidized bed gasifier and a tar-cracking reactor filled with active carbon. The main aim of the work was to produce H2-rich syngas and simultaneously reduce tar. The main reaction variable was the steam-to-fuel ratio. The possibility of gasification without using an electrostatic precipitator was also examined in the study. In addition, the effect of the type of distributor (hook-type and mesh-type distributor) located between the fluidized bed gasifier and tar-cracking reactor on coke formation was investigated. Finally, the possibility of in situ regeneration of active carbon with steam was explored. As a result, the syngas from the two-stage gasifier contained a maximum 66 vol% hydrogen and a minimum 0 mg/Nm3 tar. The syngas produced without using an electrostatic precipitator had similar quality to that obtained with an electrostatic precipitator, providing a positive indication for the implementation of the two-stage gasifier in commercial applications. Additionally, the mesh-type distributor was found to be excellent against coke formation. The in situ regeneration of active carbon with steam significantly recovered the textural properties of the original active carbon, yielding a surface area recovery rate of approximately 63%. A long-term gasification for 4 h with repetitive in situ regeneration of active carbon with steam produced a syngas having 55 vol% H2 on average and toluene as a tar component.

The gasification of dried sewage sludge was performed using various additives (activated carbon, Ni-impregnated activated carbon, dolomite, and CaO) in a two-stage gasifier to produce a tar-free gas with a low NH3 content. This research also examined the effect of feed rate on the tar removal efficiency and the stability of the two-stage gasification system conducting a ∼3.7 h gasification. In all experiments, natural olivine was used as a fluidized bed material, and air as a gasifying agent. The equivalence ratio was kept almost constant at ∼0.36. When Ni (8.9 wt%)/activated carbon was applied, a tar-free gas with 31.3 vol% H2 and 114 ppm NH3 was obtained, with a tar removal efficiency of 97%. A higher feed rate turned out to have a negative effect on the tar removal. The gasification performed using multiple additives for ∼3.7 h produced a tar-free gas with 146 ppm NH3.

Steam/oxygen gasification of dried sewage sludge was performed in a two-stage gasifier to produce an H 2 -rich and tar-free syngas. The experiment mainly investigated the effects of activated carbon, ash of activated carbon, steam to fuel ratio and the combination of additives on syngas quality. In the results, all the syngases obtained with activated carbon did not contain any tar. Activated carbon increased the H 2 production and decreased the NH 3 content in syngas. Acid-treated activated carbon, which has less ash content than the original activated carbon, was less active in tar cracking and H 2 production. The steam to fuel ratio had a strong influence on syngas quality, causing a significant rise in the H 2 and NH 3 contents in syngas at a high steam to fuel ratio. The extra addition of CaO and activated carbon to the base additive (activated carbon) led to increased H 2 production and active tar cracking. The maximum H 2 content in syngas (52.2 vol%) was obtained with 2.5 kg of activated carbon at a steam to fuel ratio of 0.52. The minimum NH 3 content in syngas was 20 ppm.

To produce a bio-oil having a high concentration of furfural, corn stover was fast-pyrolyzed using ZnCl 2 in a fluidized bed reactor at 330–430 °C. The effects of various parameters such as reaction temperature, water- and acid-washing prior to pyrolysis, and ZnCl 2 content on the product and furfural yields were investigated. Moreover, solvent extraction was conducted using toluene at different mass ratios of bio-oil/toluene to recover furfural from the obtained bio-oil. The maximum yield of bio-oil was 59 wt%. The bio-oil mainly comprised acetic acid, α-hydroxyketones, and furfural. The maximum furfural yield was 11.5 wt% when the feed material was water-washed, impregnated with 18.5 wt% ZnCl 2 , and pyrolyzed. Although acid-washing removed alkali and alkaline earth metals much more efficiently than water-washing, water-washing was better than acid-washing for the furfural production. Toluene extraction was very effective to recover furfural from bio-oil. The maximum recovery rate (82%) was achieved at a bio-oil/toluene ratio of 1:4.

A plastic waste containing polyvinyl chloride was gasified in a two-stage gasifier consisting of a fluidized bed reactor and tar-cracking zone to produce a hydrogen-rich producer gas with low tar and HCl contents. In particular, this study investigated the effects of calcined Ca-based additives, especially oyster shells, and a Ni-loaded activated carbon on the chlorine and tar removal. Additionally, a ∼3 h gasification of the plastic waste was performed using a distributor with a large hole size to confirm the gasification stability. In the experiments, where 900 g activated carbon was applied, all the producer gases were free of tar. The maximum H 2 content (30 vol.%) in the producer gas was obtained with 900 g of Ni-loaded activated carbon. Chlorine in the feed material was mainly distributed in char and condensate liquid. The HCl contents in the producer gases obtained with the calcined Ca-based additives including oyster shells were under 1 ppm. The ∼3 h gasification revealed that the gasification was stable in terms of tar content in producer gas and producer gas composition.

Biomass pyrolysis is considered as a promising technology of producing valuable biochemicals. Representative chemicals that can be obtained from the pyrolysis of lignocellulosic biomass include acetic acid, furfural, and phenolic compounds. Acetic acid is primarily generated from the degradation of hemicellulose and partly from the degradation of cellulose and lignin. Furfural is a typical degradation product of hemicellulose, whereas phenolic compounds are the degradation products of lignin. This chapter covers the mechanism of formation of the above-stated chemicals during pyrolysis of lignocellulosic biomass and presents experimental data for the production of these chemicals via pyrolysis of different lignocellulosic feedstocks under various conditions.

A fraction of palm kernel shells (PKS) was pyrolyzed in a fluidized bed reactor. The experiments were performed in a temperature range of 479-555 °C to produce bio-oil, biochar, and gas. All the bio-oils were analyzed quantitatively and qualitatively by GC-FID and GC-MS. The maximum content of phenolic compounds in the bio-oil was 24.8 wt.% at ∼500 °C. The maximum phenol content in the bio-oil, as determined by the external standard method, was 8.1 wt.%. A bio-oil derived from the pyrolysis of PKS was used in the synthesis of phenolic resin, showing that the bio-oil could substitute for fossil phenol up to 25 wt.%. The biochar was activated using CO2 at a final activation temperature of 900 °C with different activation time (1-3 h) to produce activated carbon. Activated carbons produced were microporous, and the maximum surface area of the activated carbons produced was 807 m(2)/g.

This paper provides an overview of current research trends in the production and separation of phenolic-rich bio-oils, as well as their applications. The first part of this paper highlights the strong dependency of the phenolic content of bio-oil on the kinds of biomass feedstock, reaction system, reaction conditions, and the type of catalysts used in their production. More recent separation technologies are also discussed in the second part of the paper. The final part of the paper deals with recent experimental results from applications of phenolic-rich bio-oils in the synthesis of phenolic resins. The paper suggests that the microwave-assisted pyrolysis of palm residues is a promising route for phenolic-rich bio-oil production, and that the use of supercritical CO2 and switchable hydrophilicity solvents during extraction, as well as molecular distillation techniques, can be applied to increase the recovery of phenolic compounds from bio-oils.

Laboratory- and pilot-scale two-stage air gasification of various types of biomass was performed to produce hydrogen-rich and low-tar gas. Typical tar removal apparatuses, such as scrubbers and electrostatic precipitators, were not employed and the only tar removal agent used was coal-based active carbon. The hydrogen content of all producer gases was remarkably high, whereas the tar content was low (maximum H2: 29 vol%; minimum tar: 0 mg/Nm3). The producer gases from the pilot-scale experiment also exhibited an exceedingly high hydrogen content and low tar content (maximum H2: 27 vol%; minimum tar: 3.3 mg/Nm3). The pilot-scale operation continued without any external heat supply via autothermal operation. A gas engine was connected to the pilot-scale gasification plant to generate electricity. The generated power ranged from 20 to 35 kWe depending on the type of biomass used. This indicated that the two-stage gasification process could be applied to decentralized power generation. To summarize, the present study provided positive experimental results of the two-stage gasification process in terms of tar reduction, hydrogen production, and power generation. Furthermore, studies on long-term operation are needed to obtain more reliable results.

To produce activated carbon and bio-coke, palm kernel shells (PKS), walnut shells (WNS) and cashew nut shells (CNS) were carbonized and (or) activated. The activation was conducted using CO 2 in a fixed bed reactor. In the activation of PKS, the influence of CO 2 flow rate on the surface area development was also examined. Meanwhile, to evaluate the suitability of chars obtained from CNS as metallurgical bio-coke, carbonization was carried out in N 2 at temperatures of 700–800 °C. The maximum surface areas of the resultant activated carbons derived from each biomass were about 700–810 m 2 /g, and all the activated carbons had a microporous nature. At a CO 2 flow rate of 1 NL/min, the activated carbon obtained from PKS showed the highest surface area of 912 m 2 /g. The char produced from CNS, with its low ash and volatile matter contents and its sufficient compressive strength, demonstrated promising potential as metallurgical bio-coke.

Waste tire rubber (WTR) was pyrolyzed in a fixed bed reactor in the final temperature range of 500–800 °C. Pyrolysis oils were analyzed both quantitatively and qualitatively. Pyrolysis chars obtained were activated using CO 2 at a final temperature of 950 °C with a final activation time of 1–3 h. In addition, the influence of the acid treatment of pyrolysis char on the physicochemical properties was investigated. In the experiments, the yields of pyrolysis oil and pyrolysis char were 30–38 and about 37 wt.%, respectively. The pyrolysis oils consisted mainly of limonene, aromatic hydrocarbons such as xylene, and some heteroatom-containing compounds, such as benzothiazole and 2,4-dimethylquinoline. The sulfur contents of the pyrolysis oils were 0.85–0.96 wt.%. Most of the sulfur remained in the pyrolysis char. The maximum surface area of the activated char obtained by CO 2 activation was 437 m 2 /g. The acid treatment of the pyrolysis char decreased the ash and sulfur contents, which supported the strong potential of the acid-treated char for use in commercial applications.

Air gasification of mixed plastic waste was conducted in a two-stage gasifier. The effects of the combination of olivine as the fluidized bed material and activated carbon with or without other additives for tar cracking, as well as a Ni-plated distributor, the use of steam as a gasifying agent, and the calcination of olivine on the producer gas compositions and tar production, were also investigated. The maximum H 2 concentration (27.3 vol%) was obtained with 900 g of activated carbon in the tar-cracking zone, and through the use of calcined olivine as the bed material. In the experiments, the maximum tar removal efficiency calculated using a base case reached 98.2%. The LHVs of the producer gases were in the range of 6.1–9.0 MJ/Nm 3 . The increase in the activated carbon amount led to an enhanced H 2 production, as well as a decrease in tar production. The Ni-plated distributor was found to be effective for tar removal. In the application of dolomite in the tar-cracking zone and the use of steam as a fluidizing medium resulted in a high rate of HCl removal. The minimum HCl concentration in the producer gases was under 1 ppm.

Biochars were produced by intermediate pyrolysis in a fixed-bed reactor, and their physicochemical properties were investigated. In addition, activated carbons were prepared by three different methods (N2/CO2 without cooling, N2/CO2 with cooling and direct CO2), and their properties were compared to evaluate the efficiency of the three methods. Surface areas of biochars obtained by intermediate pyrolysis at 500 and 800 °C were 107 and 249 m2/g. The maximum surface area of activated carbon (1126 m2/g) was obtained by the N2/CO2 without cooling method at a final activation temperature of 900 °C and with a 1-h final activation time. Comparison between the N2/CO2 methods with and without cooling showed no significant difference in terms of the surface area of activated carbon. The activated carbons produced by the direct CO2 method had a specific surface area of approximately 800 m2/g which appeared to be sufficiently high for commercial uses. The activated carbons produced had predominantly microporous structures (≤ 1 nm).

Air gasification of dried sewage sludge (DSS) was performed with olivine as the bed material and coal-based activated carbon as the tar-cracking additive in a two-stage gasifier to produce a hydrogen-rich producer gas with low tar content. Additionally, to investigate the possible regeneration of coal-based activated carbon, two different activating agents (carbon dioxide and steam) were applied. Finally, to reduce ammonia and tar contents, the performance of a Ni-coated distributor was examined. In the experiments, gasification at a steam to fuel ratio (STF) of 1.11 achieved a tar removal efficiency of 98% and a maximum hydrogen content of 34 vol.%. Furthermore, the activated carbon used for the gasification was less deactivated, compared to those used in the experiments without any reforming agent. When a Ni-coated distributor was applied, the ammonia content in the producer gas was significantly reduced to 11 ppm.

Fast pyrolysis of ACQ (alkaline copper quaternary)-treated wood was carried out in a bench-scale pyrolysis plant equipped with a fluidized bed reactor and char separation system. This study focused on the production of a bio-oil with low copper and chlorine contents, especially by adopting the fractional condensation of bio-oil using water condensers, an impact separator and an electrostatic precipitator. In addition, various analytical tools were applied to investigate the physicochemical properties of the pyrolysis products and the behavior of the preservative during pyrolysis. The bio-oil yield was maximized at 63.7 wt% at a pyrolysis temperature of 411 °C. Highly water-soluble holocellulose-derived components such as acetic acid and hydroxyacetone were mainly collected by the condensers, while lignin-derived components and levoglucosan were mainly observed in the oils collected by the impact separator and electrostatic precipitator. All the bio-oils produced in the experiments were almost free of copper and chlorine. Most copper in ACQ was transferred into the char.

One of the most promising ways to recycle plastic is pyrolysis. Valuable fuels and chemicals can be obtained by pyrolysis of waste plastic. In this study, pyrolysis of polypropylene was conducted using a novel continuous two-stage process equipped with auger and fluidized bed reactors connected in series. The auger reactor played an important role as an activator to elevate the vibrational states of molecules fed into the fluidized bed reactor. Hence, the two-stage pyrolysis conducted herein was called activator-assisted pyrolysis. In this study, the effects of the temperatures of the auger reactor (or activator) and bubbling and freeboard zones of the fluidized bed reactor, the type of the fluidizing medium (product gas and N 2 ), and the residence time of pyrolysis vapor on the product distribution and composition were investigated. In the experiments, the activator facilitated decomposition of polypropylene molecules, resulting in a high yield of the product gases (81 wt%) consisting mainly of H 2 and CH 4 . The maximum olefin (ethene, propene, 1,3-butadiene, and butenes) yield was 52 wt%. The pyrolysis oil mainly consisted of aromatics (up to 92 wt%), particularly mono-aromatics. The activation energies of the activated and unactivated molecules were calculated using the Friedman and Flynn–Ozawa–Wall methods. The activation energy of the activated molecules was approximately 17 kJ/mol lower than that of unactivated molecules. Hence, it was clear that the degradation mechanism of polypropylene was different when activator-assisted pyrolysis was applied. The new activator-assisted pyrolysis proposed in the current work could be helpful to produce valuable chemicals from the pyrolysis of polyolefin waste.

The aim of this study was to produce pyrolysis oils from waste high impact polystyrene (HIPS) and acrylonitrile–butadiene–styrene (ABS) in a pyrolysis plant equipped with a fluidized bed reactor. The influence of various reaction parameters, such as temperature, feed rate and the kind of fluidizing medium, was investigated. The maximum oil yields were about 87 wt.% (474 °C) for the HIPS and 84 wt.% (525 °C) for the ABS. A higher feed rate and the use of product gas as a fluidizing medium were favorable for the oil production. The oils produced from the HIPS pyrolysis consisted chiefly of toluene, ethylbenzene, styrene, cumene, α-methylstyrene and styrene dimers and they appeared to be usable directly as a fuel or chemical source. Main compounds of the ABS pyrolysis oils were similar to those obtained from the HIPS, except for nitrogen-containing compounds. In the nitrogen mass balance of the ABS pyrolysis products, most of the nitrogen was concentrated in the oil with a content of 6.5–7.1 wt.%. The pyrolysis oil from the ABS seemed to require further treatment for its use as a fuel source.

A fraction of mixed plastic waste was gasified using olivine as a bed material and activated carbon as a tar-cracking additive in a two-stage gasifier. The effects of the amount of activated carbon, the use of an activated carbon filter, and the removal of an EP (electrostatic precipitator) from the process on the gas composition and tar amount generated were investigated. The effects of the ER (equivalence ratio), the type of distributor, the use of steam and the use of a wire mesh basket for activated carbon on the coke removal were also examined. As a result, H 2 concentrations of around 30 vol% were obtained with 1500 g of activated carbon. The tar removal efficiency was maximized at about 98% with the application of 1500 g of activated carbon and steam. The LHVs (lower heating values) of the producer gases obtained with the two additives at ERs of about 0.31 were in the range of 5.3–6.2 MJ/Nm 3 .