Desulfurization and upgrade of pyrolytic oil and gas during waste tires pyrolysis: The role of metal oxides.

Pyrolysis can effectively convert waste tires into high-value products. However, the sulfur-containing compounds in pyrolysis oil and gas would significantly reduce the environmental and economic feasibility of this technology. Here, the desulfurization and upgrade of waste tire pyrolysis oil and gas were performed by adding different metal oxides (Fe2O3, CuO, and CaO). Results showed that Fe2O3 exhibited the highest removal efficiency of 87.7 % for the sulfur-containing gas at 600 °C with an outstanding removal efficiency of 99.5 % for H2S. CuO and CaO were slightly inferior to Fe2O3, with desulfurization efficiencies of 75.9 % and 45.2 % in the gas when added at 5 %. Fe2O3 also demonstrated a notable efficacy in eliminating benzothiophene, the most abundant sulfur compound in pyrolysis oil, with a removal efficiency of 78.1 %. Molecular dynamics simulations and experiments showed that the desulfurization mechanism of Fe2O3 involved the bonding of Fe-S, the breakage of C-S, dehydrogenation and oxygen migration process, which promoted the conversion of Fe2O3 to FeO, FeS and Fe2(SO4)3. Meanwhile, Fe2O3 enhanced the cyclization and dehydrogenation reaction, facilitating the upgrade of oil and gas (monocyclic aromatics to 57.4 % and H2 to 22.3 %). This study may be helpful for the clean and high-value conversion of waste tires.

The reusing of waste bio-oil as additive on enhanced urea-based selective non-catalytic reduction denitrification.

Pyrolysis polygeneration has been proven to be effective in solid waste recycling, while cleaner production is hindered by nitrogen oxide emissions and waste oil utilization. In this study, waste bio-oil was proposed as additive for promoting urea-based selective non-catalytic reduction (SNCR) denitrification efficiency to establish bio-oil reusing process and the influence of waste bio-oil on promoting SNCR denitrification were investigated. Then the effects of temperature, bio-oil components and fly ash on SNCR denitrification characteristics were explored. The results illustrated that 5 wt% bio-oil additives would widen the optimum denitrification temperature window by 24.8 % (from 210.25 to 262.43 °C), reduce the reduction temperature by 62.11 °C (from 944.04 to 881.93 °C), and increase the denitrification efficiency by 21 %. Among the main components in waste bio-oil, acetic acid was more effective than phenol and furfural in promoting SNCR denitrification under 900 °C, a large amount of OH was produced to promote the reduction of NH3 and HNCO. In addition, the existence of fly ash could promote urea oxidation and reduce denitrification efficiency because of the catalytic effect of CaO and Fe2O3 on urea oxidation.

Production mechanism of high-quality carbon black from high-temperature pyrolysis of waste tire.

High-temperature pyrolysis of waste tires is a promising method to produce high-quality carbon black. In this study, carbon black formation characteristics were investigated during tire pyrolysis at 1000-1300 °C with residence times of < 1 s, 1-2 s, and 2-4 s. It is shown that with temperature increasing from 1000 °C to 1300 °C carbon black yield was increased from 10% to 27% with residence times of 2-4 s. Carbon black exhibited a core-shell nanostructure over 1100 °C and the graphitization degree was promoted with the temperature and residence time. While the mean particle diameter decreased with the temperature to 69 nm at 1300 °C and further increased by residence time. The molecular-level evolution from tire to initial carbon black was further revealed by reactive force field molecular dynamics simulations. Light oil, gas, and radicals were transformed to initial cyclic molecules and long carbon chains via carbon-addition-hydrogen-migration, H-abstraction-C2H2-addition, and radical-chain reactions, subsequently forming PAHs. The coupling of PAHs aliphatic side chains formed large graphene layers that gradually bent to fullerene-like cores and generated incipient carbon black. The process mechanism from volatiles evolution to carbon black was proposed, which may be helpful for obtaining high-quality carbon black from high-temperature pyrolysis of waste tires.

Biomass hydrothermal conversion under CO2 atmosphere: A way to improve the regulation of hydrothermal products.

In this study, batched hydrothermal experiments on corn stalk were conducted at 240-330 °C under CO2 or inert (N2) atmosphere. The distribution and characteristics of gaseous, solid, and liquid products were analyzed in detail to comprehensively investigate the effects of CO2 on the hydrothermal conversion of biomass, especially on the cellulose and lignin in biomass. The results demonstrate that compared with N2, CO2 slightly increased the liquid and gas yields and significantly improved the control effect of temperature on bio-oil components. Under CO2 atmosphere, bio-oil achieved effective enrichment of ketones and phenols at 240 °C and 300 °C, respectively, and their highest relative contents reached 44.8% and 62.0%, respectively. In addition, the hydrochar obtained under CO2 atmosphere showed higher crystallinity, which is conducive to its subsequent utilization. This study explored the feasibility of introducing CO2 into the biomass hydrothermal process to realize the high-value utilization of biomass waste and the reuse of CO2.

Coeffect of pyrolysis temperature and potassium phosphate impregnation on characteristics, stability, and adsorption mechanism of phosphorus-enriched biochar.

Potassium phosphate (K3PO4)-impregnated bamboo was pyrolyzed at temperatures ranging from 350 to 950 °C to explore the coeffect of pyrolysis temperature and K3PO4 impregnation on biochar's characteristics and adsorption behavior. The degree of aromatization and graphitization in phosphorus-enriched biochars (PRBCs) rose as temperature increased, whereas H/C and O/C ratios, pH value, and O-containing group content decreased. The pre-aging impact of K3PO4 impregnation results in increased stability and adsorption performance of PRBCs. Adsorption mechanism of PRBCs to heavy metal varies from pyrolysis temperature. Micropores dominate medium-temperature PRBCs (prepared at 550 âˆ¼ 750 °C), possessing the highest P-containing group content (116 % that of PRBC-350) and maximal adsorption capacity (greater than289 mg/g). The medium-temperature PRBCs adsorb Cd (II) via the role of O-containing groups, PO43-, and P2O74-, mainly by reactions of organic complexation, precipitation and inorganic complexation, respectively. 550 °C is the optimal pyrolysis temperature for both energy saving and heavy metal adsorption.

Effects of phosphorous precursors and speciation on reducing bioavailability of heavy metal in paddy soil by engineered biochars.

Ammonium phosphate (AP), phosphoric acid (PC), and potassium phosphate (TKP) were used for the modification of biochar for enhanced heavy metal passivation in soil. The effect of various phosphorus (P) precursors on adsorption-related properties, P speciation distribution pattern, and the passivation mechanism was investigated by BET, FTIR, XRD, XPS, and 31P NMR analysis. The mobility and bio-availability of cadmium (Cd) were studied by extraction experiments, and the P release kinetics was also determined. Results showed that the immobilization efficiency of Cd (II) by biochars followed the order: TKP-BC > PC-BC > AP-BC > BC, and TKP-BC reduced available Cd content by 81% treated with 2% addition. The P speciation shows a significant effect on the P-enriched biochars' passivation performance, especially orthophosphate, which is essential for the immobilization of Cd2+ by forming phosphate precipitation. Pyrophosphate and orthophosphate monoester in AP-BC and PC-BC can promote Cd2+ passivation via the formation of P-Cd complexes or organometallic chelates. It is also shown that PC-BC has the lowest P release rate while TKP-BC has the highest percentage of P (15.50%) remaining in the biochar. The results may contribute to the development of modified biochar for soil remediation based on P-related technologies.

Nano nickel embedded in N-doped CNTs-supported porous biochar for adsorption-reduction of hexavalent chromium.

Nitrogen-doped carbon coated transition metal hybrids for the removal of hazardous hexavalent chromium (Cr(VI)) has attracted increasing attention in wastewater treatment recently. In this study, three-dimensional nano-nickel particles embedded in N-doped carbon nanotubes supported on porous biochar (Ni@N-K-C) were synthesized by a two-stage strategy of KOH activation followed by annealing. The effect of KOH activation treatment on the doping process and Cr(VI) removal properties were investigated. The results indicate that KOH activation can improve the pore parameters and promote subsequent doping of Ni and N and the growth of carbon nanotubes (CNTs). After KOH pretreatment, the specific surface area of Ni@N-K-C increased significantly to 604.62 m2/g. The improved pore structure accelerates the mass diffusion of Cr(VI) ions and provides an available surface for the adsorption and reduction of Cr(VI). Therefore, the Ni@N-K-C obtained at 900 °C showed a high removal capacity for Cr(VI) (824.4 mg/g) and a stronger ability to reduce to Cr(III).

One-pot hydrothermal synthesis of dual metal incorporated CuCe-SAPO-34 zeolite for enhancing ammonia selective catalytic reduction.

A series of dual metal incorporated CuCex-SAPO-34(x = 0-0.04) samples were synthesized using one-pot hydrothermal method with diethylamine as organic structure-directing agent for selective catalytic reduction of NOx by NH3. The catalytic properties were elucidated in detail with physicochemical properties being analyzed using various instruments. All the catalysts exhibited typical SAPO-34 crystal structures with high specific surface areas. With the dual-metal incorporation, the surface acidity and amount of isolated Cu2+, which may be active sites for NH3-SCR, were significantly enhanced. However, excessive Ce restrained the formation of isolated Cu2+ due to its occupation of cationic sites. Therefore, the 0.05CuCe0.02-SAPO-34 exhibited high NO conversion (≥80%) at 168°C-500°C. Furthermore, the NH3-SCR mechanism over different catalysts was investigated in-situ DRIFTS experiments. For the 0.05Cu-SAPO-34, the adsorbed NH3 species react with gaseous NO and following the E-R mechanism throughout the reaction temperature range. Meanwhile, adsorbed NO2 was detected and reacted with the adsorbed NH3 species according to the L-H mechanism in low-temperature region. In contrast, the NH3-SCR reaction over the 0.05CuCe0.02-SAPO-34 primarily followed the E-R mechanism throughout the temperature range. The L-H mechanism was cut off due to the loss of the adsorption ability of nitrous species at high temperatures., resulting in NO conversion decreasing.

Reactive transport modeling of pollutants in heterogeneous layered paddy soils: a) Cadmium migration and vertical distributions.

Cadmium (Cd) pollution in soil has attracted more attention recently for its high toxicity and easy accumulation in crops. This study aims to investigate the mechanisms governing the transport behavior of Cd, and to simulate and predict the long-term migration of Cd in different paddy soil layers. Therefore, a layer-by-layer (LBL) model based on the geochemical model PHREEQC was developed. A dual-porosity finite difference method was applied to model the two-region diffusion process. The solute transport parameters were obtained by field measurement, literature review, or inversely estimation using PHREEQC based on the experimental results. Modeling and experimental results both indicate that different mechanisms (cation exchange reaction, preferential flow, etc.) control the transport and vertical distribution of Cd. The prediction results show that only the surface soil (< 0.3 m) would pose the risk of Cd2+ pollution. The coupled LBL model could correctly simulate the migration of Cd under near-field conditions.

Effect of deashing on activation process and lead adsorption capacities of sludge-based biochar.

To explore the effect of inorganic minerals on activation process and lead adsorption of sludge-based biochar, sludge-based biochar was pre-deashed using hydrochloric acid or hydrofluoric acid followed by potassium acetate activation. The results indicate that hydrochloric or hydrofluoric acid deashing can improve the pore parameters of sludge-based biochars and promote subsequent activation effect of potassium acetate. The specific surface area of biochar activated by potassium acetate after hydrochloric acid and hydrofluoric acid pretreatment increased from 583.36 m2/g to 718.70 m2/g and 991.55 m2/g, respectively. The enhancement of pore structure is conducive to enhancing the physical adsorption of lead on sludge-based biochar, while the chemical adsorption is not significantly affected at the same time. Thereby, the biochar and activated biochar pretreated with hydrofluoric acid showed better lead adsorption capacities (16.70 and 49.47 mg/g) than untreated biochar (7.56 and 38.49 mg/g).

Effect of phosphorus-modified biochars on immobilization of Cu (II), Cd (II), and As (V) in paddy soil.

Novel phosphorus-modified biochars were produced by pyrolyzing biomass feedstocks (wood, bamboo, cornstalk and rice husk) pre-impregnated with potassium phosphate (K3PO4). The soil heavy metal immobilization performance and mechanisms of modified biochars were investigated. Incubation experiments showed that impregnation with phosphorous can decrease the extraction of Cu (II) and Cd (II) by 2 to 3 times. Phosphorus-modified biochars enhanced the transformation of Cu (II) and Cd (II) ions from acid soluble to more stable forms. Characterization results showed that phosphorus (P) compounds in modified biochar played a vital role to immobilize Cu (II) and Cd (II) by forming precipitates or complexes with them. Additionally, the modified rice husk and cornstalk biochars have in the average 14-24% and 19-33% higher immobilization efficiency for Cd (II) and Cu (II) than the other two P-assisted biochars. However, regardless of the feedstock, both the extraction and mobility of As (V) were increased by phosphorous. This study indicates that the P-modified biochar can serve as a novel remediation agent for heavy metal polluted soils.

[Preparation of MgO Modified Lotus Shell Biochar and Its Phosphorus Adsorption Characteristics].

To study the potential application characteristics of biochar as a phosphate adsorbent, nano-MgO-biochar was prepared by rapid pyrolysis of a mixture of MgO and lotus shells. The physicochemical properties were characterized by XRD, BET, SEM, and TEM, and adsorption experiments were conducted. The results showed that MgO was mainly supported on the surface of carbon in the form of flakes and granules, which increased the adsorption active site, and the adsorption amount of MgO-biochar MBC3 was 14 times higher than that of biochar MBC1 without MgO. The adsorption capacity of MBC9, which was prepared by rapid pyrolysis under 10% CO2 atmosphere, was further increased 16 times higher than that of MBC1. The adsorption kinetics followed a pseudo-second-order model, which indicated the adsorption of phosphate on MgO-biochar was dominated by chemical adsorption. According to the Langmuir equation, the maximum adsorption capacity of MBC3 and MBC9 could reach 283.26 mg·g-1 and 297.96 mg·g-1, respectively. MgO-biochar is a high-efficiency phosphate adsorbent, which can be used to control the eutrophication of water.

Effects of biomass pyrolysis derived wood vinegar on microbial activity and communities of activated sludge.

The effects of wood vinegar (WVG) on microbial activity and communities of activated sludge were investigated in a sequencing batch reactor (SBR) process. Results showed that the optimal WVG concentration was 4 µL/L when the pollutants removal efficiency and microbial activity were promoted by a WVG dilution factor of 1000. WVG could reduce the increase in microbial species richness, which led to a more notable variety of microbial species diversity. The enhanced microbial activity and communities were addressed to the promotion of 7 main classes of microbes in Proteobacteria, Bacteroidetes, Acidobacteria, and Nitrospirae phyla. The growth of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and main genera of denitrifying bacteria (DNB), phosphorus-accumulating organisms (PAOs), and glycogen-accumulating organisms (GAOs) could be promoted by WVG, which improved the sewage treatment effectiveness in a SBR.

Effects of biomass pyrolysis derived wood vinegar (WVG) on extracellular polymeric substances and performances of activated sludge.

The effects of wood vinegar (WVG) on extracellular polymeric substances (EPS), and flocculation, sedimentation and dewatering performances of activated sludge were investigated in sequencing batch reactor (SBR) process. Results showed that polysaccharide (PS) and DNA were accounted for the largest and smallest proportion of EPS, respectively. With WVG injection, productions of soluble EPS (S-EPS), loosely bound EPS (LB-EPS), tightly bound EPS (TB-EPS), protein (PN), PS, and DNA were significantly increased. The optimal WVG concentration was found as 4 µl/l. The effects of WVG on different types of EPS followed an order of LB-EPS > TB-EPS > S-EPS. According to batch and long-term SBR operations, WVG could increase the biomass amount of activated sludge, which was beneficial to improve sewage treatment efficiencies. However, WVG showed negative impact on flocculation, sedimentation, and dewatering performance of activated sludge.

Enhancing the production of light olefins and aromatics from catalytic fast pyrolysis of cellulose in a dual-catalyst fixed bed reactor.

In this study, the effects of a macroporous catalyst (CaO), mesoporous catalyst (MCM-41), and microporous catalysts (ZSM-5 and SAPO-34) on the production of light olefins and aromatics from cellulose catalytic fast pyrolysis were investigated in a dual-catalyst fixed bed reactor. Further the fractional catalytic pyrolysis of MCM-41 or CaO with ZSM-5 or SAPO-34 was explored. The results showed that ZSM-5 was the most efficient catalyst for the formation of light olefins and aromatics followed by MCM-41, CaO and SAPO-34, and no aromatics were found with SAPO-34 only. Moreover, 15% CaO combined 85% ZSM-5 produced the highest yield of light olefins (5.59%) and aromatic (13.42%). The addition of CaO and MCM-41 promoted the selectivity of C2H4 and decreased the production of naphthalene.

Influence of torrefaction with Mg-based additives on the pyrolysis of cotton stalk.

The study presented an approach to introduce Mg-based additives into cotton stalk for strengthening deoxygenation effect during torrefaction. Then catalytic pyrolysis of torrefied feedstock with Mg-based additives residue as catalyst was performed at 550 °C for 10 min in a fixed-bed reactor. The effects of torrefaction temperature (200, 230, 260, 290, 320, 350 °C), type of Mg-based additive (MgO and MgO-K2CO3), mass ratio of additive to biomass (0.5, 1 and 2) on pyrolysis were investigated. The results indicated that yields of bio-char and bio-oil significantly increased and decreased with torrefaction temperature rising to 350 °C. MgO inhibited pyrolysis bio-char yield increase with torrefaction severity. MgO-K2CO3 increased H2 yield a lot from 1.39 to 3.67 mmol/g. It also effectively improved the aromatic hydrocarbons in bio-oil and the reduction of acids. A maximum aromatic hydrocarbons yield of 16.05% was obtained with MgO-K2CO3 (the mass ratio of 0.5:1) at torrefaction temperature of 320 °C.

The conversion of biomass to light olefins on Fe-modified ZSM-5 catalyst: Effect of pyrolysis parameters.

Light olefins are the key building blocks for the petrochemical industry. In this study, the effects of in-situ and ex-situ process, temperature, Fe loading, catalyst to feed ratio and gas flow rate on the olefins carbon yield and selectivity were explored. The results showed that Fe-modified ZSM-5 catalyst increased the olefins yield significantly, and the ex-situ process was much better than in-situ. With the increasing of temperature, Fe-loading amount, catalyst to feed ratio, and gas flow rate, the carbon yields of light olefins were firstly increased and further decreased. The maximum carbon yield of light olefins (6.98% C-mol) was obtained at the pyrolysis temperature of 600°C, catalyst to feed ratio of 2, gas flow rate of 100ml/min, and 3wt% Fe/ZSM-5 for cellulose. The selectivity of C2H4 was more than 60% for all feedstock, and the total light olefins followed the decreasing order of cellulose, corn stalk, hemicelluloses and lignin.

Co-gasification of coal and biomass: Synergy, characterization and reactivity of the residual char.

The synergy effect between coal and biomass in their co-gasification was studied in a vertical fixed bed reactor, and the physic-chemical structural characteristics and gasification reactivity of the residual char obtained from co-gasification were also investigated. The results shows that, conversion of the residual char and tar into gas is enhanced due to the synergy effect between coal and biomass. The physical structure of residual char shows more pore on coal char when more biomass is added in the co-gasification. The migration of inorganic elements between coal and biomass was found, the formation and competitive role of K2SiO3, KAlSiO4, and Ca3Al2(SiO4)3 is a mechanism behind the synergy. The graphization degree is enhanced but size of graphite crystallite in the residual char decreases with biomass blending ratio increasing. TGA results strongly suggest the big difference in the reactivity of chars derived from coal and biomass in spite of influence from co-gasification.

The densification of bio-char: Effect of pyrolysis temperature on the qualities of pellets.

The densification of bio-chars pyrolyzed at different temperatures were investigated to elucidate the effect of temperature on the properties of bio-char pellets and determine the bonding mechanism of pellets. Optimized process conditions were obtained with 128MPa compressive pressure and 35% water addition content. Results showed that both the volume density and compressive strength of bio-char pellets initially decreased and subsequently increased, while the energy consumption increased first and then decreased, with the increase of pyrolysis temperature. The moisture adsorption of bio-char pellets was noticeably lower than raw woody shavings but had elevated than the corresponding char particles. Hydrophilic functional groups, particle size and binder were the main factors that contributed to the cementation of bio-char particles at different temperatures. The result indicated that pyrolysis of woody shavings at 550-650°C and followed by densification was suitable to form bio-char pellets for application as renewable biofuels.

MSW oxy-enriched incineration technology applied in China: combustion temperature, flue gas loss and economic considerations.

To investigate the application prospect of MSW oxy-enriched incineration technology in China, the technical and economical analyses of a municipal solid waste (MSW) grate furnace with oxy-fuel incineration technology in comparison to co-incineration with coal are performed. The rated capacity of the grate furnace is 350 tonnes MSW per day. When raw MSW is burned, the amount of pure oxygen injected should be about 14.5 wt.% under 25% O2 oxy-fuel combustion conditions with the mode of oxygen supply determined by the actual situation. According to the isothermal combustion temperature (Ta), the combustion effect of 25% O2 oxy-enriched incineration (α = 1.43) is identical with that of MSW co-incineration with 20% mass ratio of coal (α = 1.91). However, the former is better than the latter in terms of plant cost, flue gas loss, and environmental impact. Despite the lower costs of MSW co-incineration with mass ratio of 5% and 10% coal (α = 1.91), 25% O2 oxy-enriched incineration (α = 1.43) is far more advantageous in combustion and pollutant control. Conventional combustion flue gas loss (q2) for co-incineration with 0% coal, 20% coal, 10% coal, 5% coal are around 17%, 13%, 14% and 15%, respectively, while that under the condition of 25% O2 oxy-enriched combustion is approximately 12% (α = 1.43). Clearly, q2 of oxy-enriched incineration is less than other methods under the same combustion conditions. High moisture content presents challenges for MSW incineration, therefore it is necessary to dry MSW prior to incineration, and making oxy-enriched incineration technology achieves higher combustion temperature and lower flue gas loss. In conclusion, based on technical and economical analysis, MSW oxy-enriched incineration retains obvious advantages and demonstrates great future prospects for MSW incineration in China.