H2 Yield Research Articles

Co-gasification behavior and products distribution of wet sewage sludge and corn stalks: Effect and mechanism analysis of self-moisture utilization

Wet sewage sludge (WSS) self-moisture gasification is a promising route for H2-rich syngas production. This research investigated the co-gasification of WSS and corn stalks (CS), focusing on the effects of self-moisture content. Thermogravimetric analysis of the pyrolysis of the mixture (WSS:CS = 40:60 wt%) revealed that the reactions followed a three-parallel-reaction model. The co-gasification process was performed to compare the effects of self-moisture and external steam used as gasification agents, respectively. The results showed that the self-moisture gasification led to higher H2 yields (0.057–0.11 L/g), gas yields (0.19–0.21 L/g), and specific gas energy (2.62–2.72 MJ/kg) than those in external steam gasification (0.055–0.090 L/g, 0.16–0.18 L/g and 2.32–2.52 MJ/kg, respectively). Additionally, self-moisture gasification also resulted in lighter tar with primarily light organic acids (28.0%), and char with weaker aromatic structure features, attributed to longer reaction time during diffusion of pyrolysis products. Overall, this study provided theoretical foundations for the high-value exploitation of WSS.

Feasibility of a Plasma Furnace for Methane Pyrolysis: Hydrogen and Carbon Production

The imperative to achieve a climate-neutral industry necessitates CO2-free alternatives for H2 production. Recent developments suggest that plasma technology holds promise in this regard. This study investigates H2 production by methane pyrolysis using a lab-scale plasma furnace, with the primary objective of achieving a high H2 yield through continuous production. The plasma furnace features a DC-transferred thermal plasma arc system. The plasma gas comprises Ar and CH4, introduced into the reaction zone through the graphite hollow cathode. The off-gas is channeled for further analysis, while the plasma arc is recorded by a camera installed on the top lid. Results showcase a high H2 yield in the range of up to 100%. A stable process is facilitated by a higher power and lower CH4 input, contributing to a higher H2 yield in the end. Conversely, an increased gas flow results in a shorter gas residence time, reducing H2 yield. The images of the plasma arc zone vividly depict the formation and growth of carbon, leading to disruptive interruptions in the arc, hence declining efficiency. The produced solid carbon exhibits high purity with a fluffy and fine structure. This paper concludes that further optimization and development of the process are essential to achieve stable continuous operation with a high utilization degree.

Evaluating the role of salinity in enhanced biogas production from two-stage anaerobic digestion of food waste by zero-valent iron

Salts including NaCl are the most common food flavoring agents so they are often accumulated in food waste (FW) and have potential impact on anaerobic digestion (AD) of FW. In this study, the enhanced biogas production from two-stage anaerobic digestion (TSAD) of FW by microscale zero-valent iron (ZVI) under different salinity (3, 6, 9, and 15 g NaCl/L) was evaluated. Under salinity stress, ZVI becomes a continue-release electron donor due to the enhanced corrosion and dissolution effect and the slow-down surface passivation, further improving the performance of TSAD. Experimental results revealed that the biogas production including H2 and CH4 from TSAD with 10 g/L ZVI addition was promoted under salinity stress. The maximum H2 and CH4 yield (303.38 mL H2/g-VS and 253.84 mL CH4/g-VS) were observed at the salinity 9 g NaCl/L. Compared with that of zero salinity, they increased by 40.94% and 318.46%, respectively. Additionally, Sedimentibacter, an exoelectrogen that can participate in the direct interspecies electron transfer, also exhibited the highest relative abundance (34.96%) at the salinity 9 g NaCl/L. These findings obtained in this study might be of great importance for understanding the influence of salinity on the enhanced AD by ZVI.

Helichrysum arenarium-mediated facile green synthesis, antibacterial, catalytic activity and hydrogen evolution of metallic (Ag, Cu) and bimetallic (Ag/Cu) nanoparticles

Metallic Ag, Cu and bimetallic Ag/Cu nanoparticles (NPs) easily and economically synthesized by green synthesis method using Helichrysum arenarium plant extracts used as reducing agent were characterized with analysis of SEM (Scanning electron microscopy), TEM (Transmission electron microscopy) and BET (Brunauer-Emmett-Teller). The adsorption study of the synthesized nanoparticles for Congo Red (CR) azo dyestuff was carried out and dyestuff removal properties were investigated in detail. At 100 min, the CR removal percentages were found to be 90.2 %, 77.8 % and 66.1 % by Cu NPs, Ag/Cu NPs and Ag NPs, respectively and the adsorption was found to be in accordance with the second order kinetic model and Langmuir isotherm model. In reusability studies of Cu NPs adsorbent, CR removal was found to be 90.2 %, 88.9 % and 83.4 % in three experimental cycles, respectively. For antimicrobial activity of Helichrysum arenarium extract, Cu NPs, Ag/Cu NPs and Ag NPs were used to against 6 pathogenic microorganisms via disc diffusion assay. As a result of the antimicrobial assay, while Helichrysum arenarium extract did not show any effect against the tested pathogenic microorganisms, both Ag NPs and Ag/Cu NPs showed an inhibition zone diameter against the tested pathogenic microorganisms (p < 0.05). It is conceivable that it would be effective in controlling the growth of resistant microorganisms in aqueous media since it produces a similar level of inhibition in methicillin-resistant and non-resistant S. aureus. Finally, the catalytic activity of the synthesized nanoparticles was evaluated in hydrogen (H2) production by hydrolysis of NaBH4. Based on experimental results, the efficiency of hydrogen production was determined as Cu NPs > Ag/Cu NPs > Ag NPs. The optimum conditions for the highest yield of H2 were investigated and the catalysis results were compared with sonocatalysis. This research shows that NPs can be synthesized in a simple, economical and environmentally friendly way and has a wide range of uses.

Ca2Fe2O5-Based WGS Catalysts to Enhance the H2 Yield of Producer Gases

Ca2Fe2O5-based catalysts were synthesized from siderite and calcite precursors, which were processed in the form of pelletized samples and tested as water gas shift catalysts. Catalytic tests were performed in a tubular reactor, at temperatures in the range 400–500 °C and with different H2O:CO ratios, diluted with N2; this demonstrates the positive impact of Ca2Fe2O5 on conversion of CO and H2 yield, relative to corresponding tests without catalyst. The catalytic performance was also remarkably boosted in a microwave-heated reactor, relative to conventional electric heating. Post-mortem analysis of spent catalysts showed significant XRD reflections of spinel phases (Fe3O4 and CaFe2O4), and SiO2 from the siderite precursor. Traces of calcium carbonate were also identified, and FTIR analysis revealed relevant bands ascribed to calcium carbonate and adsorbed CO2. Thermodynamic modelling was performed to assess the redox tolerance of Ca2Fe2O5-based catalysts in conditions expected for gasification of biomass and thermochemical conditions at somewhat lower temperatures (≤500 °C), as a guideline for suitable conditions for water gas shift. This modelling, combined with the results of catalytic tests and post-mortem analysis of spent catalysts, indicated that the O2 and CO2 storage ability of Ca2Fe2O5 contributes to its catalytic activity, suggesting prospects to enhance the H2 content of producer gases by water gas shift.

Synergetic effects of conductive materials and bacterial population in inoculum on mixed-culture biohydrogen production

This study examined the effect of conductive materials (softwood pellet biochar pyrolyzed at 550 °C and 700 °C, powdered activated carbon and stainless-steel) on the two series of batch biohydrogen production inoculated with three types of heated-treated anaerobic digester sludge. Biochar pyrolyzed at 550 °C and stainless-steel exhibited the highest enhanced hydrogen yield up to 117 % in the first and second series of experiments, respectively. Importantly, the enhancement effect by the introduction of conductive materials was significantly affected by the microbial population in inoculum, particularly the relative abundance of electroactive H2-producing Clostridium sp. Metabolic flux analysis revealed that the enhanced H2 yield was concurrent with the decrease of lactate production and the increase of H2-producing acetogenesis. Conductive materials also improved electron transport system activity and NADH/NAD+ ratio, which are related with the metabolic activity. This study shows that introducing conductive material can control intracellular redox environment, thereby reinforcing the metabolic activity selectively.

Cellulose pyrolysis under NH3 atmosphere for levoglucosan and pyrrole: An experimental and theoretical study

Cellulose pyrolysis for valuable levoglucosan (LG) can improve the value of cellulose utilization. Here, NH3 was introduced into cellulose pyrolysis by a fixed-bed system to investigate the effect of NH3 on the formation of LG and pyrrole, and the reaction pathways of LG and pyrrole formation were explored by combining experimental results with DFT calculations. Results showed that the highest CO yield reached 147.66 mL/g at 800 °C. The yields of H2 and CH4 significantly increased, while CO2 yield decreased. NH3 increased the content of oxygen-containing substances while inhibiting the formation of aromatic and aliphatic hydrocarbons. In addition, some nitrogen-containing products were generated, and their content increased with increasing temperature, among which, the nitrogen-containing products were mainly pyrroles. The content of LG increased about two times, and its absolute yield reached 10.96 wt% at 600 °C, which was about 4.6 times that of direct pyrolysis. DFT calculations showed that NH3 had a promoting effect on cellulose pyrolysis to produce LG, and the reaction energy barrier of the optimal pathway is 194.05 kJ/mol. Cellobiose is transferred to the glycosidic bond O-site by hydrogen transfer from the C2-site to break the glycosidic bond to form the intermediate a4-i1 and glucose. The intermediate a4-i1 was combined with NH3 to form LG via hydrogen transfer, while the resulting glucose was dehydrated to form LG by combining with NH3. For the pathway of cellulose pyrolysis to form pyrrole, NH3 promoted the deoxidation of FF to form furan, and the combination of NH3 with furan promoted furan to undergo a ring-opening reaction more than that of H2O. After the ring opening, the C2 position amino group was linked to the C5 position to form a ring, and the O atom was removed by dehydration with the formation of a hydroxyl group to form pyrrole. The reaction energy barrier for cellulose pyrolysis to form pyrrole under an NH3 atmosphere was 280.08 kJ/mol. It provided a new approach for the preparation of LG and pyrrole from cellulose.

Nickel-decorated graphite phase carbon nitride photocatalysts coupled with carbazole-based calixarene dyes for high-efficiency visible light-driven hydrogen evolution

The development of artificial devices that mimic the highly efficient and sophisticated photosystems found in nature is a subject worthy of in-depth study. Two calixarene D-π-A dyes, C4-CZSTP and C4-CZBTP, containing an N-methylcarbazole group as a secondary auxiliary electron donor, are synthesized on the basis of our previously reported calixarene dye C4-BTP. These dyes are then cooperated with Ni-deposited g-C3N4 to prepare ternary photocatalysts, denoted as C4-CZSTP/Ni/g-C3N4, C4-CZBTP/Ni/g-C3N4 and C4-BTP/Ni/g-C3N4, and their photocatalytic performances are evaluated under visible light irradiation. The optimized 4.0 wt% C4-CZSTP/Ni/g-C3N4 sample gives a remarkable H2 evolution rate of 5552 μmol g−1 h−1, representing one of the highest records among the reported analogous systems based on g-C3N4. And after an extended test of 49 h, a total H2 yield of 63.57 mmol g−1 is obtained, corresponding to a turnover number (TON) based on C4-CZSTP moles (TONC4-CZSTP) of 3180. This performance can be attributed to the enhanced light-harvesting and photoelectron conversion of the as-prepared calixarene dyes, the adjusted energy levels and the effective cooperation of the three components. The optimal performance of C4-CZSTP/Ni/g-C3N4 among the three dye-sensitized systems is due to its higher lowest unoccupied molecular orbital (LUMO) value, i.e. stronger electronic driving force from the excited dye to g-C3N4. This study provides an interesting example for the design and preparation of a low-cost, high-efficiency and noble metal-free photocatalytic system for solar fuel production.

A novel multi-objective optimization model of solar-driven methanol steam reforming system combining response surface methodology and three-dimensional numerical simulation

Solar-driven methanol steam reforming (MSR) to produce hydrogen is a pivotal thermochemical process for enhancing green energy utilization with low-carbon emissions. While this process has been explored in the thermochemical reforming literature, with valuable studies on fuel to hydrogen, this study marks the first comprehensive examination and multi-objective optimization of the MSR process within a solar-driven catalyst-filled reactor. The study begins by modeling and validating the MSR’s reaction kinetic. Subsequently, the effects of the reactor surface energy flux density and key operating characteristics, such as steam-to-methanol ratio (SMR) and space velocity, on the gas composition and conversion efficiency as well as H2 yield are comprehensively analyzed. In order to effectively optimize the operating parameters, the interactions between the various factors were elucidated and an optimization procedure was established to scrutinize the impact of these factors on hydrogen production. The model accuracy is assessed using Analysis of Variance (ANOVA), which also identifies optimal operating parameters under varying conditions. Predictions from the Response surface methodology (RSM) indicate optimal conditions with a SMR of 1.13, a gas hourly space velocity of 45.24, and an inlet temperature of 507.4 K. Numerical calculations confirm the practicality of these conditions, yielding an actual methanol conversion of 0.9998, deviating only by 0.17 % from the predicted value. This work underscores the feasibility and efficacy of studying MSR performance based on response surface method. The analysis of factor significance and interactions provides valuable guidance for practical operations.

Ultrathin NiV Layered Double Hydroxide for Methanol Electrooxidation: Understanding the Proton Detachment Kinetics and Methanol Dehydrogenation Oxidation.

Electrochemical methanol oxidation reaction (MOR) is regarded as a promising pathway to obtain value-added chemicals and drive cathodic H2 production, while the rational design of catalyst and in-depth understanding of the structure-activity relationship remains challenging. Herein, the ultrathin NiV-LDH (u-NiV-LDH) with abundant defects is successfully synthesized, and the defect-enriched structure is finely determined by X-ray adsorption fine structure etc. When applied for MOR, the as-prepared u-NiV-LDH presents a low potential of 1.41V versus RHE at 100mA cm-2, which is much lower than that of bulk NiV-LDH (1.75V vs RHE) at the same current density. The yield of H2 and formate is 98.2% and 88.1% as its initial over five cycles and the ultrathin structure of u-NiV-LDH can be well maintained. Various operando experiments and theoretical calculations prove that the few-layer stacking structure makes u-NiV-LDH free from the interlayer hydrogen diffusion process and the hydrogen can be directly detached from LDH laminate. Moreover, the abundant surface defects upshift the d-band center of u-NiV-LDH and endow a higher local methanol concentration, resulting in an accelerated dehydrogenation kinetics on u-NiV-LDH. The synergy of the proton detachment from the laminate and the methanol dehydrogenation oxidation contributes to the excellent MOR performance of u-NiV-LDH.

Steam Reforming of Isobutanol on Biochar-Supported Ni–Co Catalysts

The equilibrium parameters of steam isobutanol reforming were calculated. These include the H2 yield, selectivity with respect to carbon-containing gases, and feed conversion. The calculated data, on the whole, agree with the published data and experimental values of the isobutanol conversion and yield of isobutyraldehyde and higher alkanes on Ni–Co catalysts supported on biochars prepared by hydrothermal carbonization of cellulose. On the other hand, the calculated yields of H2, СО, and СН4 disagree with the experimental data, which suggests that the equilibrium in the experiments on the steam isobutanol reforming on this catalyst is not attained. Feeding a homogeneous mixture of water, isobutanol, and ethanol into the reactor at 700°С allows the Н2 yield to be increased from 58 to 66% and the water conversion, from 58 to 76% compared to the steam reforming of isobutanol without ethanol. The addition of ethanol allows the coking to be significantly reduced and the H2 and СО yield higher than 90% at 900°С to be reached.

Co-gasification of waste shiitake substrate and waste polyethylene in a fluidized bed reactor under CO2/steam atmospheres

This study investigated the co-gasification of agricultural and plastic wastes, which is a potential method for waste disposal. Waste shiitake substrate (WSS) and polyethylene (PE) were selected and their properties were investigated. The thermal degradation behavior and gases produced were explored using thermogravimetric analysis coupled with Fourier-transform infrared spectrometry (TG-FTIR). In addition, the activation energy was determined by the FWO method, and the synergistic effect and gas yield were estimated. The co-gasification of WSS and PE assisted by CO2 and steam was conducted using a bubbling fluidized bed gasifier. Results indicate that BR60 % had the maximum C–O band, C–C bond, C–H band, and CO yields. Blending WSS and PE resulted in an evident synergistic effect. The activation energies of BR20 % had the lowest value. The Taguchi method was used to determine the optimal parameters, maximum normalized H2 concentration, H2/CO ratio, CGE, and exergy efficiency. The H2 yield and H2/CO ratio were predominantly affected by the CO2/(CO2+H2O) ratio, and the best concentration and ratio were 28.6 % and 1.34. The CGE and exergy efficiencies were predominantly affected by gasification temperature, and the best results were 71.6 % and 72.4 %, respectively. Finally, the collected tars were analyzed using gas chromatography-mass spectrometry (GC/MS).

Enhanced photoelectrochemistry water splitting based on the bi-piezoelectric Z-scheme pn heterojunction of an n-CdTe/p-ZnO nanorods array

An n-type Cd-excess CdTe (n-CdTeCd)/p-type Sb-doped ZnO nanorods (p-ZnONR,Sb)/indium tin oxide photocathode with a bi-piezoelectric Z-scheme pn heterojunction is prepared by hydrothermal method and electrodeposition for photoelectrochemistry (PEC) water splitting. At 0 V vs RHE under 100 mW cm−2 Xe lamp illumination in 0.5 M aqueous Na2SO4 stirred at 1500 rpm, the photocurrent density, H2 (O2 evolved at a Pt anode) yield, and the apparent Faradaic efficiency for this photocathode are −3.86 mA cm−2, 58.5 (28.6) μmol cm−2 h−1 and 84.7%, respectively. After examining the other similar semiconductor combinations of n-CdTeCd or p-type Te-excess CdTe (p-CdTeTe) with n-type ZnO nanorods (n-ZnONR) or p-ZnOSb,NR, the co-effects of bi-piezoelectric and pn-junction electric fields on the separation and transfer of photogenerated charges for PEC water splitting are discussed in detail. This work may help to better understand various heterojunctions and the electric-field-modulated photogenerated charges’ separation and transfer for the development of relevant fields.

Process mechanisms of nanobubble technology enhanced hydrolytic acidification of anaerobic digestion of lignocellulosic biomass

This study explored the efficiency of CO2-, N2-, and H2- nanobubble treatment in anaerobic digestion (AD) of rice straw, with a focus on the processes and metabolic pathways of hydrolytic acidification, and revealed the underlying mechanisms. Mechanistic investigations revealed that nanobubbles, particularly CO2 nanobubbles, significantly increased the degradation of amorphous cellulose, resulting in higher levels of soluble carbohydrates (6.27 % – 11.13 %), VFAs (4.39 % – 24.50 %), and a remarkable cumulative H2 yield (74 – 94 times) Microbial community analysis indicated that the CO2 nanobubble promoted the growth of acidifying bacterial communities, such as Mobilitalea, unclassified_f_Lachnospiraceae, and Bacteroides. This indicates that the introduction of CO2 nanobubbles improved the total abundance of predicted functional enzymes were increased by 14 %, resulting in the production of more easily degradable intermediates. Based on the analysis of total methane production and kinetic analysis, it can be concluded that nanobubble addition enhanced methane production levels of 4.22 %−7.79 % with lower lag time (λ) (0.88–1.06 day) compared to the control group (1.09 day). The results also elucidated changes in relative enzymatic activities involved in the bioconversion of cellulose and hemicellulose during the hydrolysis stage with nanobubble treatment. This work is more beneficial for understanding the promoting effect and mechanism of nanobubbles on AD, facilitating the more precise application of nanobubble technology in the field of renewable energy.

Attapulgite-based titanosilicate zeolite-supported Ni catalyst for hydrogen production from catalytic steam reforming of toluene

Catalytic steam reforming for hydrogen production was a viable tar removal technology. The key issue of catalytic steam reforming of toluene (tar model) for hydrogen production (CSRT) was the devise and development of advantageous catalysts. In this work, attapulgite-based titanosilicate zeolite (ATS) supported Ni-based catalysts was prepared and applied into CSRT. In addition, compared with the attapulgite (ATP), attapulgite-derived silicon source (HTP) and commercial TiO2, the effects of four different supports over the catalytic performance of Ni-based catalysts for CSRT were further investigated. The structural characteristics of the prepared catalysts were revealed by various characterization methods. Amongst, N/ATS appeared the highest toluene conversion (90.71%) and H2 yield (63.57%) during 4 h of CSRT reaction, which mainly attributed to its highest surface Ni0 molar ratio. Additionally, N/ATS revealed unique resistance to carbon deposition under harsh reaction conditions. This was mainly due to the synthesized ATS had larger BET and the highest hierarchical factor (HF) of pore structure which better promoted mass and heat transfer and its unique nanocluster assembled lamellar structure better anchoring the Ni metal and inhibited sintering, while its superior dispersion of weak acidic sites resulted in less carbon deposits. This work provided a probability for the preparation of economical attapulgite-based heteroatom zeolite to support Ni for hydrogen production via steam reforming of biomass-based oxygenates.

Performance assessment of an energetically self-sufficient system for hydrogen production from oilfield wastewater treated by supercritical water gasification

Oilfield wastewater with high moisture content can be efficiently treated by supercritical water gasification (SCWG) technology to produce hydrogen. This paper conducted a thermodynamic and environmental analysis of the oilfield wastewater SCWG system to provide optimization strategies. The waste heat utilization technology can enhance the heat integration of the system to reduce the exergy destruction and increase the H2 yield. Sensitivity analysis showed that a ratio of preheating water to emulsion 3 can promote water-sensitive reactions to produce H2 and save the H2 needed to maintain the energetically self-sufficient system. Low system pressures, high feedstock preheating temperatures, and low oxidation reactor temperatures can reduce system energy destruction to obtain high H2 yield and system efficiency. Meantime, the developed SCWG system has the potential to achieve natural enrichment of greenhouse gases after the H2 separation has been completed. The use of waste heat utilization technology and carbon capture and storage (CCS) technology is expected to increase system efficiency to 53.43 % and reduce global warming potential (GWP) of 5.52 kg CO2-eq/kg H2. This work would be of great value to the process design and optimization for the SCWG system of oilfield wastewater.

Hydrogen-rich gas production via supercritical water gasification (SCWG) of oily sludge over waste tire-derived activated carbon impregnated with Ni: Characterization and optimization of activated carbon production

In this study, the production of activated carbon (AC) through the chemical activation of waste tire (WT) using H3PO4 and KOH for H2 production by SCWG of oily sludge (OS) donated by Persian Gulf Star Oil Company was investigated. H3PO4 was the best activating agent based on some pretests results, and then the synthesis of AC was optimized using Response Surface Methodology. Based on BET surface area of synthesized ACs, thirty combinations of the four variables namely; activation temperature (350–550 °C); activation time (1–4 h); H3PO4 to WT ratio (1–3 w.w−1); and H3PO4 concentration (20–40 wt%) were optimized. CHNS, TGA, FE-SEM, and EDS-mapping analyses were used to characterize the AC and catalyst synthesized in optimum condition (activation temperature: 450 °C; activation time: 2.5 h; H3PO4 to WT ratio: 2 w.w−1; and H3PO4 concentration: 40 wt%), which presented a surface area of 170 m2 g−1. Finally, Ni was impregnated on the optimized AC with different loadings (5–15 wt%) to evaluate its performance in H2 production by SCWG of OS. Although H2 yield in catalytic experiments was higher than that observed in non-catalytic experiment, results showed that the maximum H2 selectivity was 66% in SCWG of OS using AC impregnated with 10 wt% Ni.

Efficient production of tunable syngas through multistage sorption-enhanced steam gasification of corncob

As “carbon neutrality” becomes one of the most critical topics in the world, interest in capturing carbon dioxide from industrial processes is growing. In this study, we proposed an efficient process for recycling biomass resources. Firstly, a bifunctional Ni/CaO catalyst based on Ce modification was developed by conducting corncob steam gasification experiments at 600 °C in a tube furnace. At Ce doping of 0.75 and Steam/Carbon = 7, the H2 concentration reached 87.65 ± 1.46 vol% and the H2 yield reached 40.04 ± 0.74 mmol/gbiomass. The cycle test verified that Ce0.75-Ni1/Ca7 had good cycle stability. Secondly, we designed multi-stage variable temperature steam gasification experiments. The experimental results showed that the CO yield in the second stage was 15 times higher than before the introduction of gasification carbon, and the total syngas yield was increased by 2.32 times. Furthermore, the H2/CO molar ratio could be controlled by modifying the addition of gasification carbon, which was advantageous for downstream product synthesis. Implement the synergistic capture and conversion of CO2 in an integrated process, while simultaneously producing high-value synthesis gas, fully utilizing the biomass.

Enhancing hydrogen-rich fuel gas production from dewatered sludge pyrolysis: The effect of hybrid conditioning with peroxyacetic acid, polyaluminium chloride, and KOH-modified activated carbon

Pyrolysis is a promising technology for the disposal of sewage sludge, because it not only greatly reduces the volume of sludge but also converts it into high calorific and pollution-free clean energy, H2. Direct pyrolysis of raw sludge (with moisture content of about 98%) consumes a lot of energy, thus it is necessary to dewater the raw sludge before pyrolysis. However, sludge is a heterogeneous colloidal system, making it difficult to reduce water content with traditional pressurization. Conditioning agents often are needed to improve the dewatering efficiency. In this work, we applied peroxyacetic acid (PA) and polyaluminium chloride (PAC) combined with KOH-modified activated carbon (KAC) to condition the raw sludge (denoted as PA/PAC/KAC) before conducting dewatering and pyrolysis. We found that changes of organic matter composition of the dewatered sludge exerted by the conditioning significantly influenced pyrolysis gas production. The pyrolysis H2 yield from the conditioned sludge can be 4–5-fold higher than the unconditioned. The PA oxidation mediated by KAC led to more olefin substances appearing in the dewatered sludge, which further promoted the production of low aromatic hydrocarbons through the Diels-Alder reaction in pyrolysis and enhanced tar cracking rate. Potassium loaded on KAC catalyzed tar cracking. KAC remained in the dewatered sludge promoted water–gas-shift (WGS) and steam reforming reactions to produce more H2. This study provides a new path to enhance the resource utilization of dewatered sludge and facilitate the resource utilization of the dewatered sludge in potential applications.

Three-stage pyrolysis–steam reforming–water gas shift processing of household, commercial and industrial waste plastics for hydrogen production

Five common single plastics and nine different household, commercial and industrial waste plastics were processed using a three-stage (i) pyrolysis, (ii) catalytic steam reforming and (iii) water gas shift reaction system to produce hydrogen. Pyrolysis of plastics produces a range of different hydrocarbon species which are subsequently catalytically steam reformed to produce H2 and CO and then undergo water gas shift reaction to produce further H2. The process mimics the commercial process for hydrogen production from natural gas. Processing of the single polyalkene plastics (high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP)) produced similar H2 yields between 115 mmol and 120 mmol per gram plastic. Even though PS produced an aromatic product slate from the pyrolysis stage, further stages of reforming and water gas shift reaction produced a gas yield and composition similar to that of the polyalkene plastics (115 mmol H2 per gram plastic). PET gave significantly lower H2 yield (41 mmol per gram plastic) due to the formation of mainly CO, CO2 and organic acids from the pyrolysis stage which were not conducive to further reforming and water gas shift reaction. A mixture of the single plastics typical of that found in municipal solid waste produced a H2 yield of 102 mmol per gram plastic. Knowing the gas yields and composition from the single plastics enabled an estimation of the yields from a simulated waste plastic mixture and a ‘real-world’ waste plastic mixture to be determined. The different household, commercial and industrial waste plastic mixtures produced H2 yields between 70 mmol and 107 mmol per gram plastic. The H2 yield and gas composition from the single waste plastics gave an indication of the type of plastics in the mixed waste plastic samples.Graphical abstract