Removal of tar derived from biomass gasification via synergy of non-thermal plasma and catalysis

Improving the Quality of Bio-oil Using the Interaction of Plastics and Biomass through Copyrolysis Coupled with Nonthermal Plasma Processing

Bio-oil produced from the pyrolysis of biomass is chemically complex, viscous, highly acidic, and highly oxygenated. Copyrolysis of biomass and plastics can enhance oil quality by raising the H/C ratio, leading to improved biofuel properties. In this work, copyrolysis of polystyrene and biomass was passed to a second-stage dielectric barrier discharge nonthermal plasma reactor with the aim to further improve the product bio-oil. Pyrolysis of the polystyrene and biomass produces volatiles that pass to the second stage to undergo cracking and autohydrogenation reactions under nonthermal plasma conditions. There was a synergistic interaction between biomass and polystyrene in terms of overall oil and gas yield and composition even in the absence of the nonthermal plasma. However, the introduction of the nonthermal plasma produced a marked increase in monocyclic aromatic hydrocarbons (e.g., ethylbenzene), whereas polycyclic aromatic compounds decreased in concentration. Most notably, the influence of the plasma markedly reduced the quantity of oxygenated compounds in the product oil. It is suggested that the unique reactive environment produced by the plasma involving high-energy electrons, excited radicals, ions, and intermediates increases the interaction of the polystyrene and biomass pyrolysis volatiles. Increasing input plasma power from 50 to 70 W further enhanced the effects of the nonthermal plasma.

Tar Formation in Gasification Systems: A Holistic Review of Remediation Approaches and Removal Methods

Gasification is an advanced thermochemical process that converts carbonaceous feedstock into syngas, a mixture of hydrogen, carbon monoxide, and other gases. However, the presence of tar in syngas, which is composed of higher molecular weight aromatic hydrocarbons, poses significant challenges for the downstream utilization of syngas. This Review offers a comprehensive overview of tar from gasification, encompassing gasifier chemistry and configuration that notably impact tar formation during gasification. It explores the concentration and composition of tar in the syngas and the purity of syngas required for the applications. Various tar removal methods are discussed, including mechanical, chemical/catalytic, and plasma technologies. The Review provides insights into the strengths, limitations, and challenges associated with each tar removal method. It also highlights the importance of integrating multiple techniques to enhance the tar removal efficiency and syngas quality. The selection of an appropriate tar removal strategy depends on factors such as tar composition, gasifier operating and design factors, economic considerations, and the extent of purity required at the downstream application. Future research should focus on developing cleaning strategies that consume less energy and cause a smaller environmental impact.

Recent progress of low-temperature plasma technology in biorefining process

In recent years, low-temperature plasma-assisted processes, featuring high reaction efficiency and wide application scope, have emerged as a promising alternative to conventional methods for biomass valorization. It is well established that charged species, chemically energetic molecules and radicals, and highly active photons playing key roles during processing. This review presents the major applications of low-temperature plasma for biomass conversion in terms of (i) pretreatment of biomass, (ii) chemo fractionation of biomass into value-added chemicals, and (iii) synthesis of heterogeneous catalyst for further chemo-catalytic conversion. The pretreatment of biomass is the first and foremost step for biomass upgrading to facilitate raw biomass transformation, which reduces the crystallinity, purification, and delignification. The chemo-catalytic conversion of biomass involves primary reactions to various kinds of target products, such as hydrolysis, hydrogenation, retro-aldol condensation and so on. Finally, recent researches on plasma-assisted chemo-catalysis as well as heterogeneous catalysts fabricated via low-temperature plasma at relatively mild condition were introduced. These catalysts were reported with comparable performance for biomass conversion to other state-of-the-art catalysts prepared using conventional methods.

Insights into direct reduction iron using bamboo biomass as a green and renewable reducer: Reduction behavior study and kinetics analysis

Biochar is a renewable, carbon-neutral energy source that can replace traditional fossil fuels for iron and steel production, so it is of great significance to reduce carbon emissions and reduce pollution. In this paper, the reaction characteristics and kinetics between biomass (bamboo powder) pyrolysis gas, biochar, and iron ore powder are studied by a thermogravimetric analyzer (TG). Comparing the samples with four different C/O ratios (C/O = 0.375, 0.5, 1, 3), it is found that the sample with C/O = 1 can completely reduce hematite. The mass loss process is divided into the following four stages: de-crystal water, hematite to magnetite, magnetite to wustite, and wustite to metallic iron. Among them, the latter three stages are following the kinetic model of random nucleation (n = 1, 2) and three-dimensional diffusion, and the activation energy of the three stages increases and then decreases. Through scanning electron microscopy (SEM), the surface of hematite particles changed from relatively flat to porous and finally the reduced metal iron aggregated, and connected into large pieces. By using online Thermogravimetry-Fourier Transform Infrared Reflection (TG-FTIR), when the reduction temperature is lower than 700 °C, biochar plays a leading role. On the contrary, the CO produced by biochar gasification plays a leading role.

Exploring Simultaneous Upgrading and Purification of Biomass−Gasified Gases Using Plasma Catalysis

Tar and substantial CH4 and CO2 are contained in gasified fuels, which pose an obstacle to direct chemical synthesis, and this is a predominant challenge for biomass gasification technology. Herein, a packed−bed dielectric barrier discharge (DBD) reactor was built for simultaneous CH4 dry reforming and tar removal with a La−Ni/γ−Al2O3 catalyst. The interaction between CH4 dry reforming and tar removal in plasma catalysis was investigated. The results indicated that plasma catalysis can achieve high−efficiency simultaneous tar removal and CH4 dry reforming, as indicated by the reactants’ conversion (14% increase for CCH4 and CCO2 at 450 °C in the presence of tar and a 37% increase for the tar removal rate at 360 °C when CH4 and CO2 were introduced), and the mechanism for mutual promotion of CH4 dry reforming and tar removal was elucidated through catalyst characterization results. In addition, a possible reaction mechanism for tar removal via plasma catalysis was proposed. These findings provide valuable insights for simultaneous upgrading and purification of gases generated by biomass gasification.

Synergistic effect of plasma power and temperature on the cracking of toluene in the N2 based product gas

In this research, a dielectric barrier discharge (DBD) reactor is used to study the cracking of the toluene into C₁-C₆ hydrocarbons. The combined effect of parameters such as temperature (20-400 °C) and plasma power (10-40 W) was investigated to evaluate the DBD reactor performance. The main gaseous products from the decomposition of toluene include lower hydrocarbon (C₁-C₆). The cracking of toluene increases with power at all temperatures (20-400 °C). On the otherhand, it decreases from 92.8 to 73.1% at 10 W, 97.2 to 80.5% at 20, 97.5 to 86.5% at 30 W, and 98.4 to 93.7% at 40 W with raising the temperature from 20 to 400 °C. Nonetheless, as the temperature and plasma input power increase, the methane yield increases. At 40 W, the maximum methane yield was 5.1%. At 10 and 20 W, the selectivity to C₂ increases as the temperature rises up to 400 °C. At 30 and 40 W, it began to drop after 300 °C due to the formation of methane and the yield of methane increases significantly beyond this temperature.

Degradation of toluene by tube-tube coaxial dielectric barrier discharge: power characteristics and power factor optimization

In this paper, the power characteristics and power factor optimization were investigated in a coaxial tube-tube dielectric barrier discharge (DBD) reactor. The effects of several parameters, including discharge voltage, discharge length, discharge frequency and gas flow rate on discharge power and power factor have been evaluated. The experiment results showed that higher discharge power can be obtained by increasing the discharge voltage, discharge frequency and electrode length. But for the power factor, with the increase of discharge frequency, the power factor increased firstly and then decreased. Moreover, with the discharge length increased, the discharge frequency when the power factor reached the maximum value reduced. The response surface method (RSM) and artificial neural network (ANN) were used to optimize the power factor, and their results were relatively consistent. The result of the ANN showed that when discharge voltage was 9.58 kV, discharge frequency was 8.69 kHz, discharge length was 15.8 cm, and gas flow rate was 1.5 L/min, the power factor reached the maximum value of 0.362. The degradation experiment of toluene was carried out in the reactor and its degradation effect was analyzed. The toluene degradation rate is positively correlated with the power factor, and the discharge voltage, gas flow rate and initial concentration are also the key parameters to determine the degradation of toluene. When the discharge voltage, gas flow rate, and initial concentration are 10 kV, 70 mL/min, and 50 ppm, respectively, the power factor and toluene degradation rate reach 0.34 and 74.3%.

Nickel catalyst in coupled plasma-catalytic system for tar removal

Tar formation is a significant issue during biomass gasification. Catalytic removal of tars with the use of nickel catalyst allows to obtain high conversion rate but coke formation on catalysts surface lead to its deactivation. Toluene decomposition as a tar imitator was studied in gliding discharge plasma-catalytic system with the use of 5%, 10% and 15% by weight Ni and NiO catalyst on Al2O3 (α-Al2O3) and Peshiney (γ-Al2O3) carrier in gas composition similar to the gas after biomass pyrolysis. The optimal concentration of nickel was identified to be 10% by weight on Al2O3. It was stable in all studied initial toluene concentrations, discharge power while C7H8 conversion rate remained high – up to 82%. During the process, nickel catalysts were deactivated by sooth formation on the surface. On catalysts surface, toluene decomposition products were identified including benzyl alcohol and 3-hexen-2-one.

Tar steam reforming for synthesis gas production over Ni-based on ceria/zirconia and La0.3Sr0.7Co0.7Fe0.3O3 in a packed-bed reactor

In this work, NiO level was varied from 5 to 40% whereas Ce_xZr_1-xO₂ (x = 0.5, 0.7 and 0.9) (CZO) and La_0.3Sr_0.7Co_0.7Fe_0.3O₃ (LSCF) were chosen as two different kinds of support. Regardless the type of support, the surface NiO (at 40%) was completely reduced at 600 °C, giving the amount of activated Ni at 8950 μmol/g_cat. The reducibility of the updoped LSCF was found to be much better than that of the undoped CZO, evidenced by the H₂-TPR of the both materials at 600 °C where the oxygen storage capacity (OSC) of LSCF and CZO was determined at 4273 and 307 μmol/g_cat, respectively. In contrast, the OSC of 40%Ni-CZO (where x = 0.7, 0.9) was found to be higher than that of the LSCF, implying that the addition of Ni more enhanced both electronic defect and oxygen mobility in CZO than in LSCF, according to the H₂-TPR results. Coke resistant of CZO is presumable more satisfying than that of LSCF, thus, the longer lifespan of the CZO catalyst system is expected. The catalytic performance of 40%Ni-CZO (x = 0.9) was however comparable with 40%Ni-LSCF as they accommodate the same number of active sites. The slightly better catalytic performance of the 40%Ni-CZO (x = 0.9) could be due to its smaller crystallite size (CZO = 26.83, LSCF = 35.73), rendering more access for the relative gaseous reactants. The best catalyst amongst all was 5%Ni-CZO (x = 0.9), giving 89% toluene conversion, 46% H₂ yield, 71% CO selectivity, and 25% CO₂ selectivity at optimum reaction temperature of 700 °C.