Hydrogen production from polystyrene pyrolysis and gasification: Characteristics and kinetics

Polystyrene (PS) pyrolysis and gasification have been examined in a semi-batch reactor at temperatures of 700, 800 and 900 °C. Characteristic differences between pyrolysis and gasification of polystyrene (PS) have been evaluated with specific performance focus on the evolution of syngas flow rate, evolution of hydrogen flow rate, evolution of output power, syngas yield, hydrogen yield, energy yield, apparent thermal efficiency and syngas quality. Behavior of PS under either pyrolysis or gasification processes is compared to that of char based sample, such as paper and cardboard. In contrast to char based materials, PS gasification yielded less syngas, hydrogen and energy than pyrolysis at 700 °C. However, the gasification of PS yielded more syngas, hydrogen and energy than pyrolysis at 900 °C temperature. Gasification of PS is affected by reactor temperature more than PS pyrolysis. Syngas, hydrogen and energy yield increased exponentially with temperature in case of gasification. However, syngas and energy yield increased linearly with temperature having rather a mild slope in the case of pyrolysis. Pyrolysis resulted in higher syngas quality at all temperatures. Kinetics of hydrogen evolution from the PS pyrolysis is introduced. The Coats and Redfern method was used to determine the kinetic parameters, activation energy (E_act), pre-exponential factor (A) and reaction order (n). The model used is the nth order chemical reaction model. Kinetic parameters have been determined for three slow heating rates, namely 8, 10 and 12 °C/min. The average values obtained from the three heating rate experiments were used to compare the model with the experimental data.     

Oily Products from Mosses and Algae via Pyrolysis

In this study, the fuel properties of mosses and algae, and the effect of pyrolysis temperature on the yield of bio-oil from moss and alga samples, were investigated. The yield of bio-oil from pyrolysis of the samples increased with temperature. The yields were increased up to 750 K in order to reach the plateau values at 775 K. The maximum yields were 39.1, 34.3, 33.6, 37.0, 35.4, 48.2 and 55.3% of the sample for Polytrichum commune, Dicranum scoparium, Thuidium tamarascinum, Sphagnum palustre, Drepanocladus revolvens, Cladophora fracta and Chlorella protothecoides, respectively. The bio-oil yield for Chlorella protothecoides (a microalga sample) rose from 5.7 to 55.3% as the temperature rose from 525 to 775 K, and then gradually decreased to 51.8% and was obtained at 875 K with a heating rate of 10 K/s. Formulas can be developed to calculate higher heating value (HHV) of different moss and alga samples. The calculated HHV using these new correlations showed mean differences ranging from ?2.3% to +0.06%. The equation developed in this study showed good agreement with experimental results on moss and algae samples. The HHVs for bio-oils from mosses 21.5–24.8 MJ/kg and the HHVs for bio-oils from algae and microalga 32.5 and 39.7 MJ/kg, respectively, were obtained at temperature ranging from 775 to 825 K. In general, algae bio-oils are of higher quality than bio-oils from mosses. In general, microalgae bio-oils are higher quality than bio-oil from wood.     

Experimental investigation on the influence of the pyrolysis operating parameters upon the char reaction activity in supercritical water gasification

Supercritical water gasification of coal is a clean and efficient method for coal utilization which can convert coal into H₂ and CO₂. In order to further reduce costs, a novel two-step cascade utilization method was proposed in this study: conducting traditional pyrolysis first and then gasifying the pyrolysis char in supercritical water. The influences of different pyrolysis operating parameters on gaseous products and char gasification in supercritical water were investigated. Quartz tube reactors were used to ensure the complete collection of gaseous products in pyrolysis process. The experimental results showed that both carbon and hydrogen conversion efficiency increased with temperature, and the increasing trend became not obvious after reaction for 5 min. The thermo-gravimetric curves showed that volatilization removal process was completed at the pyrolysis time of 5 min and higher pyrolysis temperatures were beneficial to the subsequent gasification process. The result also showed that residual weight was 15%–20% of the initial weight. Hydroxyl radicals kept stable during pyrolysis process with the absorption peak intensity increasing first and then decreasing, and mineral substance disintegrated gradually as time increased. As pyrolysis temperature increased, the peak of CC double bonds decreased, turning into stable functional groups and carbonyl group increased. Dispersive pores occurred at the surface of coal as residence time increased with particle size decreasing, specific surface area and reactivity increasing. The results might be used for the design of a cascade utilization system based on coal gasification in supercritical water.     

Comparison of thermochemical conversion processes of biomass to hydrogen-rich gas mixtures

Hydrogen can be produced from biomass materials via thermochemical conversion processes such as pyrolysis, gasification, steam gasification, steam-reforming, and supercritical water gasification (SCWG) of biomass. In general, the total hydrogen-rich gaseous products increased with increasing pyrolysis temperature for the biomass sample. The aim of gasification is to obtain a synthesis gas (bio-syngas) including mainly H₂ and CO. Steam reforming is a method of producing hydrogen-rich gas from biomass. Hydrothermal gasification in supercritical water medium has become a promising technique to produce hydrogen from biomass with high efficiency. Hydrogen production by biomass gasification in the supercritical water (SCW) is a promising technology for utilizing wet biomass. The effect of initial moisture content of biomass on the yields of hydrogen is good.     

Syngas yield during pyrolysis and steam gasification of paper

Main characteristics of gaseous yield from steam gasification have been investigated experimentally. Results of steam gasification have been compared to that of pyrolysis. The temperature range investigated were 600–1000 °C in steps of 100 °C. Results have been obtained under pyrolysis conditions at same temperatures. For steam gasification runs, steam flow rate was kept constant at 8.0 g/min. Investigated characteristics were evolution of syngas flow rate with time, hydrogen flow rate and chemical composition of syngas, energy yield and apparent thermal efficiency. Residuals from both processes were quantified and compared as well. Material destruction, hydrogen yield and energy yield is better with gasification as compared to pyrolysis. This advantage of the gasification process is attributed mainly to char gasification process. Char gasification is found to be more sensitive to the reactor temperature than pyrolysis. Pyrolysis can start at low temperatures of 400 °C; however char gasification starts at 700 °C. A partial overlap between gasification and pyrolysis exists and is presented here. This partial overlap increases with increase in temperature. As an example, at reactor temperature 800 °C this overlap represents around 27% of the char gasification process and almost 95% at reactor temperature 1000 °C.     

Supercritical water gasification and partial oxidation of municipal sewage sludge: An experimental and thermodynamic study

Supercritical gasification (SCWG) and supercritical partial oxidation (SCWPO) technologies have emerged as preferred means of converting wet biomass to hydrogen-rich gases. We experimentally investigated the effects of moisture content, pressure and oxidation coefficient (n) on mole fraction, yield, gasification efficiency and energy recovery of gaseous products from SCWG or SCWPO of municipal sewage sludge, as well as on the carbon and nitrogen contents in liquid products. Potential of sludge for producing gaseous products was thermodynamically analyzed by an Aspen Plus model. The results show that 87 wt%, 25 MPa and n = 0 were optimum conditions for sludge gasification. Sludge with 87 wt% moisture content was pumpable at 75 °C, and further increasing the moisture content decreased the heating value and energy recovery of gaseous products. Pressure played little role in both the experimental and equilibrium gas yields. Highest mole fractions and yields of H₂ and CH₄ were achieved at n = 0.     

Microwave pretreatment on microalgae: Evolution of gas and char in chemical looping gasification

Chemical looping gasification (CLG) of Chlorella vulgaris was investigated by TGA and FTIR technology. The release characteristic and evolution behavior of gaseous products and bio‐char in different conditions were analyzed to evaluate the effects of CLG and microwave pretreatment. The results indicated that the gas production of CLG was higher than that of SiO₂:Chlorella, and it would be higher after microwave pretreatment. CO, CO₂, and CH₄ were mainly produced in the pyrolysis and gasification stages. After adding Fe₂O₃, C―O, C═O, and C═C compounds decreased by 3.75%, 20.86%, and 24.72%, respectively. But more CO, CO₂, and CH₄ were produced. Microwave pretreatment was helpful for reducing the degrees of hydrogen‐rich, aliphatic structure, aromatization, and oxygen‐rich in char. Moreover, microwave pretreatment promoted the reduction of C―O, C═O, and C═C compounds. However, CO increased by 55.63%, and CO₂ decreased by 2.31% in this condition. Therefore, microwave pretreatment was beneficial to CLG reaction.     

Characterization of the physicochemical and structural evolution of biomass particles during combined pyrolysis and CO2 gasification

The combination of pyrolysis and CO₂ gasification was studied to synergistically improve the syngas yield and biochar quality. The subsequent 60-min CO₂ gasification at 800 °C after pyrolysis increased the syngas yield from 23.4% to 40.7% while decreasing the yields of biochar and bio-oil from 27.3% to 17.1% and from 49.3% to 42.2%, respectively. The BET area of the biochar obtained by the subsequent 60-min CO₂ gasification at 800 °C was 384.5 m²/g, compared to 6.8 m²/g for the biochar obtained by the 60-min pyrolysis at 800 °C, and 1.4 m²/g for the raw biomass. The biochar obtained above 500 °C was virtually amorphous.     

Distribution of Nitrogen Species During Vitrinite Pyrolysis and Gasification

The formation of HCN and NH₃ during pyrolysis in Ar and gasification in CO₂ and steam/Ar was investigated. Vitrinites were separated and purified from different rank coal from lignite to anthracite. Pyrolysis and gasification were carried out in the drop-tube/fixed-bed reactor at temperatures of 600–900°C. Results showed that with increase of reaction temperature the yield of HCN increased significantly during pyrolysis and gasification. Decrease of coal rank also increased the yield of HCN. Vitrinite from lower rank of coal with high volatile content released more HCN. The yield of NH₃ was the highest at 800°C during pyrolysis and gasification. And the yield of NH₃ from gasification in steam/Ar was far higher than that from gasification in CO₂, where the hydrogen radicals play a key role. Nitrogen retained in char was also investigated. The yield of char-N decreased with an increase of pyrolysis temperature. Vitrinite from lower rank coal had lower yield of char-N than that from the high rank coal.     

Numerical simulation of hydrogen production by gasification of large biomass particles in high temperature fluidized bed reactor

Biomass as a renewable fuel compared to fossil fuels usually contains high moisture content and volatile release. Hydrogen production by large particle biomass gasification is a promising technology for utilizing high moisture content biomass particle in the high temperature fluidized bed reactor. In the present work, simulation of large particles biomass gasification investigated at high temperature by using the discrete phase model (DPM). Combustible gases with homogeneous gas phase reactions, drying process with a heterogeneous reaction, primary and secondary pyrolysis with independent parallel-reaction by using two-competing-rate model to control a high and low temperature were used. During the thermochemical process of biomass, gaseous products containing of H₂, H₂O, CH₄, CO and CO₂ was obtained. The effects of concentration, mole and mass fraction and hydrodynamics effects on gaseous production during gasification were studied. The results showed that hydrodynamic effect of hot bed is different from cold bed. Concentration and molar fraction of CO and H₂ production by continually and stably state and small amount of CO₂, H₂O, and CH₄ was obtained. The hydrodynamic of bed plays the significant role on the rate of gaseous products.     

Effect of biomass leaching on H2 production,ash and tar behavior during high temperature steam gasification (HTSG) process

The effect of biomass water leaching on H₂ production, as well as, prediction of ash thermal behavior and formation of biomass tar during high temperature steam gasification (HTSG) of olive kernel is the main aim of the present work. Within this study raw olive kernel samples (OK₁, OK₂) and a pre-treated one by water leaching (LOK₂) were examined with regard to their ash fouling propensity and tar concentration in the gaseous phase. Two temperatures (T = 850 and 950 °C) and a constant steam to biomass ratio (S/B = 1.28) were chosen in order to perform the steam gasification experiments. Results indicated that considering the samples' ash thermal behavior, it seemed that water leaching improved the fusibility behavior of olive kernel; however, it proved that water leaching does not favour tar steam reforming, while at the same time decreases the H₂ yield in gas product under air gasification conditions, due to possible loss of the catalytic effect of ash with water leaching.     

Catalytic gasification of glycine and glycerol in supercritical water

Glycine and glycerol were used as the model compounds of protein and fattiness, respectively. A continuous tubular-flow reactor was used for the gasification experiments operated at 380–500 °C and 25 MPa with or without Na₂CO₃ catalyst. Compared with a negative effect on glycerol gasification, Na₂CO₃ could increase hydrogen yield and Chemical Oxygen Demand (COD) destruction efficiency, and the catalytic performance of 0.1 wt% Na₂CO₃ was better than that of 0.2 wt% for glycine gasification. When 1 wt% glycine solution with 0.1 wt% Na₂CO₃, or 1 wt% glycerol solution without Na₂CO₃ was gasified at 500 °C with the residence time of 0.98 min, their corresponding gasification efficiencies were up to 95.8% and 98%, and hydrogen yields could reach 4.14 and 5.08 mol/mol, respectively. Hydrogen molar fraction in gaseous product was about 60% and liquid effluents could be reutilized. Correspondingly, the ideal overall reaction equations for glycine and glycerol gasification were proposed.     

Emission analysis of Botryococcus braunii algal biofuel using Ni-Doped ZnO nano additives for IC engines

Microalgae biodiesel has been considered ?as a clean renewable fuel for diesel marine engines. This is due to its optimistic characterizations such as ?rapid growth rate, high productivity, and its ability to convert CO₂ into fuel. In this study, the use of microalgae biodiesel, obtained from Botryococcus braunii, as an alternative fuel for diesel marine engines has been investigated. The diesel engine is verified experimentally using Ni-Doped ZnO nano additive blends with algae biodiesel and neat diesel fuel. The results showed that doped nano additive blends? produce less emission compared to B20.     

The effect of oxygen carrier content and temperature on chemical looping gasification of microalgae for syngas production

The study of the effect of oxygen carrier content and temperature on chemical looping gasification (CLG) of Chlorella vulgaris was carried out in a fixed bed reactor. In order to obtain the characterization and optimal conditions of CLG for syngas production, this paper analyzed the product fractional yields, gaseous yields, conversion efficiency, SEM, XRD and composition analysis of oxygen carriers. The results indicated that CLG had a greater performance on gasification characteristics. When O/C increased from 0.5 to 3.0, gas yield, CO₂ yield and carbon conversion efficiency increased gradually, but LHV, H₂ and CH₄ yields decreased. Meanwhile, CO yield and gasification efficiency increased firstly and then decreased. Oxygen carrier Fe₂O₃ exhibited the characteristics of step-wise reduction (Fe₂O₃ → Fe₃O₄ → FeO) in CLG process. More FeO were generated at O/C of 0.5 and then caused serious sintering and agglomeration. High temperature was helpful to improve gas yield, carbon conversion efficiency and gasification efficiency. However, higher temperature would cause sintering and then weaken the activity of oxygen carrier. Moreover, under the experimental condition, O/C of 1.0 and 800 °C were the optimal parameters to obtain a high conversion efficiency of biomass, high products yield, good LHV and great reducibility of oxygen carrier.     

Co-production of upgraded bio-oils and H2-rich gas from microalgae via chemical looping pyrolysis

In order to produce high-quality bio-oils and syngas from biomass, a novel pyrolysis approach based on the chemical looping concept, namely chemical looping pyrolysis (CLPy), was proposed. In the current work, thermodynamic feasibility study and experimental investigations of the proposed CLPy with calcium-ferrite oxygen carriers and Nannochloropsis sp. microalgal biomass were conducted. The results suggested that the reduced calcium-ferrite oxygen carrier facilitated the denitrification, ketonization, and hydrodeoxygenation (HDO) of bio-oils during the pyrolysis stage. Since large amounts of oxygen in bio-oils were transferred to the reduced oxygen carrier, the heating value of bio-oils was remarkably increased up to 34.2 MJ/kg and 36.0 MJ/kg by employing the reduced CaFe₂O₄ and Ca₂Fe₂O₅ oxygen carrier, respectively. In addition, a high H₂ content of 50% in the pyrolysis gas was observed at the optimal pyrolysis temperature. In the gasification stage, the production of high-quality syngas was achieved. The content of H₂ accounted for up to 70% of the gasification products when taking steam as gasifying agent, while that of CO was composed of 66% without the use of a gasifying agent. Moreover, the oxygen carrier was reduced to its reduction state, available for the next loop. In summary, CLPy proposed in this work involves the continuous transference of the oxygen from bio-oils to syngas by an oxygen carrier and provides a brand-new approach for the comprehensive utilization of biomass.     

Microbial oil production from thermophile cyanobacteria for biodiesel production

Compared to lipid extraction from algae, little work has been performed for cyanobacteria. In this article it is aimed to show high lipid accumulation potential of Synechococcus sp., Cyanobacterium aponinum and Phormidium sp. cells in BG-11 medium. Four different pH values (6–9) and NaNO₃ (0.25, 0.5, 1.0, 1.5 g/L) concentrations were examined at different incubation days to discover the highest lipid accumulation. The maximum lipid content could be achieved in the medium containing 0.25 g/L NaNO₃ at pH 7 for Synechococcus sp., pH 8 for C. aponinum and pH 9 for Phormidium sp. after 15 days. The maximum lipid contents and C16 and C18 methyl ester yields were measured as 42.8% and 46.9% for Synechococcus sp., 45.0% and 67.7% for C. aponinum, 38.2% and 90.6% for Phormidium sp. The saturated compounds were 74.5%, 77.9%, 84.7% for Synechococcus sp., C. aponinum and Phormidium sp., respectively. These crude lipids could be promising feedstock for biodiesel production.     

Gaseous products evolution during microwave pyrolysis of tire powders

Microwave pyrolysis of tire powders were run in a laboratory scale microwave oven (2.45 GHz). A special attention was dedicated to the yields of gaseous products during the microwave pyrolysis at different powers (300, 500, and 700 W). Triple-channel refinery gas chromatograph was used to quickly detect the gas composition of tire pyrolysis and its evolution during the process. H₂, CO, and CH₄, up to 90% of the total volume of pyrolytic gases, were the most predominant gaseous products. As the pyrolysis proceeded, the composition exhibited a significantly changes, e.g., more H₂ was produced and less CH₄ was generated. As the power increased, the content of CH₄ + CO₂ decreased, while the fractions of H₂ + CO rapidly increased at the intense stage of the microwave pyrolysis. The maximum yields of gaseous and liquid products and the maximum conversion of tires were obtained at 500 W.     

The enhancement mechanism of hydrogen photoproduction in Chlorella protothecoides under nitrogen limitation and sulfur deprivation

The aim of this study was to understand the enhancement mechanism of H₂ photoproduction in Chlorella protothecoides under simultaneous nitrogen limitation and sulfur deprivation (LNS). Nitrogen limitation (LN) rather than sulfur deprivation significantly inhibited relative variable fluorescence at K-step (W_K) and J-step (V_J), photochemical efficiency of PSII (photosystem II), F_v/F_m, during the process of incubation in the light. Under such conditions, photosynthetic O₂ evolution decreased and the anaerobiosis was established after 12 h of incubation. The algae generated large amounts of H₂ under nitrogen limitation but generated only trace amounts under sulfur deprivation. Obviously, nitrogen limitation rather than sulfur deprivation was the decisive factor that induced H₂ photoproduction in C. protothecoides under LNS. The LNS culture generated much more H₂ than the LN culture in the presence of DCMU during incubation, suggesting that a PSII-independent electron source contributed many more electrons for transfer to hydrogenase in the LNS culture. PSII electron transport includes linear electron flow (LEF) and cyclic electron flow (CEF) of PSII in C. protothecoides. In the PSII-dependent electron source for H₂ photoproduction, PSII supplies electrons to hydrogenase through the LEF. The LNS culture showed much higher LEF and lower CEF than the LN culture during the H₂ photoproduction phase, as indicated by the large lower quantum yield of PSII electron transport (Φ_PSII) in the LNS culture in the presence of DCMU. Therefore, compared with nitrogen limitation, simultaneous nitrogen limitation and sulfur deprivation enhanced H₂ photoproduction in C. protothecoides mainly due to enhanced PSII-dependent and -independent electron sources.     

Hydrogen production from coal gasification in supercritical water with a continuous flowing system

The technology of supercritical water gasification can convert coal to hydrogen-rich gaseous product efficiently and cleanly. A novel continuous-flow system for coal gasification in supercritical water was developed successfully in State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF). The experimental device was designed for the temperature up to 800 °C and the pressure up to 30 MPa. The gasification characteristics of coal were investigated within the experimental condition range of temperature at 650–800 °C, pressure at 23–27 MPa and flow rate from 3 kg h⁻¹ to 7 kg h⁻¹. K₂CO₃ and Raney-Ni were used as catalyst and H₂O₂ as oxidant. The effects of main operation parameters (temperature, pressure, flow rate, catalyst, oxidant, concentration of coal slurry) upon gasification were carried out. The slurry of 16 wt% coal + 1.5 wt% CMC was successfully transported into the reactor and continuously gasified in supercritical water in the system. The hydrogen fraction reached up to 72.85%. The experimental results demonstrate the bright future of efficient and clean conversion of coal.     

Mobilisation of trace elements during thermal conversion of algae cultivated in ash dam water

The work presented here assesses the potential for the mobilisation of 11 trace elements (As, Be, Co, Cu, Mn, Ni, Pb, Sb, Se, V, Zn) during the thermal conversion of micro- and macroalgae that were cultivated in ash dam water. The volatility of the trace elements was quantified by mass balances based on elemental analyses of char and ash residues. The residues were prepared in a laboratory-scale fixed-bed reactor at a range of different temperatures (500–1100 °C) and gas atmospheres (N₂, 2% O₂ and CO₂) to simulate pyrolysis, combustion and gasification processes. The results showed high volatilities for Se (∼79–97%) and As (∼51–79%) below 500 °C. Zn, Pb and Sb were mainly volatilised above 700 °C. The different gas atmospheres had little influence on the volatility of these elements, which increased sharply to more than 90% with increasing temperature from 700 to 1100 °C. Volatilities for V, Mn, Cu, Co, Ni and Be were relatively minor over the full range of investigated operating conditions. Samples of each alga and their thermal conversion residues were subject to batch leaching in water. All of the tested trace elements, except for Pb and Be, were partially leached from the algae. Vanadium was up to 4–5 times more leachable in the combustion residues than in the algae. The other trace elements were generally less leachable following thermal conversion. The trace elements were more stable in residues prepared under pyrolysis and gasification conditions than in residues prepared under combustion conditions at the same temperature.