Effects of CaO on nitrogen transformation during pyrolysis of soybean protein

To elucidate the effects of CaO on nitrogen transformation during sludge pyrolysis, transformation behavior from char N into NO_x precursors during pyrolysis of soybean protein (SP) with CaO at 600–700°C was investigated. Results showed that CaO inhibited the transformation of pyridine N and quaternary N into HCN and promoted HCN conversion into NH₃ at 600–700°C. CaO inhibited the conversion of protein N and tar N into NH₃ at 600°C but promoted it at 700°C. NO_x precursor yield was the lowest when SP was pyrolyzed with CaO/N of 5.5 at 600°C (reduced by 11.66% compared with raw SP pyrolysis).     

Comparison between hydrogen-rich biogas production from conventional pyrolysis and microwave pyrolysis of sewage sludge: is microwave pyrolysis always better in the whole temperature range?

To investigate the influence of the pyrolysis temperature on biogas production from sewage sludge, conventional pyrolysis and microwave pyrolysis were carried out in the temperature range from 600 °C to 900 °C and all products were analyzed. With the temperature increasing, the product yields for conventional pyrolysis varied significantly, while those for microwave pyrolysis changed quite slightly. In conventional pyrolysis, the yield of H₂ increased from 1.26 mmol/g at 600 °C to 9.07 mmol/g at 900 °C, while it was varied only from 1.84 mmol/g to 3.67 mmol/g in microwave pyrolysis. Under microwave pyrolysis, a high ratio of H/C indicated that more hydrogen atoms converted directly to tar instead of being released into biogas, which was caused by side reactions (such as the hydrogen transfer reaction). More aromatic compounds in the tar during microwave pyrolysis illustrated that the hydrogen transfer reaction was enhanced by microwave at the higher temperatures. It has been found that the sludge microwave pyrolysis had some drawbacks for the hydrogen-rich biogas production, because it could promote some side reactions to suppress the H₂ production, especially the hydrogen transfer reaction.     

Enhanced hydrogen production in catalytic pyrolysis of sewage sludge by red mud: Thermogravimetric kinetic analysis and pyrolysis characteristics

The catalytic mechanism of red mud (RM) on the pyrolysis of sewage sludge was investigated. The thermogravimetric data were used to study the kinetic characteristics by using a discrete distributed activation energy model (DAEM) to clarify the effects of three main components (Fe₂O₃, Al₂O₃, SiO₂) in the RM on the pyrolysis of organic matters in sewage sludge. The modeling results showed that the pyrolysis of organic matters, especially at the higher temperature stage, was promoted by Fe₂O₃ and Al₂O₃ in the RM. Adding Fe₂O₃ or the RM alone could reduce the mean activation energy of sewage sludge pyrolysis by 13.9 and 20.1 kJ mol^?1, respectively. The modeling results were validated by pyrolysis experiments of raw sludge with different additives at 600, 700, 800, and 900 °C. The experimental results showed that the addition of Al₂O₃, Fe₂O₃ or the RM could produce more gas than the addition of SiO₂, especially at high temperatures. Fe₂O₃ and Al₂O₃ acted as catalysts in the tar decomposition by in-situ catalyzing the cracking of CC and CH bonds to produce more gases. Especially, Fe₂O₃ and Al₂O₃ increased the H₂ yield from sewage sludge pyrolysis at 700, 800, and 900 °C by 268.5 and 50.7%, 111.1 and 56.0%, 10.9 and 10.3%, respectively. The char obtained from pyrolysis of sewage sludge with the RM possessed magnetic property, which has various potential applications. The research indicates that the RM is an efficient catalyst in the pyrolysis of sewage sludge.     

The conversion of sewage sludge into biochar reduces polycyclic aromatic hydrocarbon content and ecotoxicity but increases trace metal content

The presence of contaminants considerably restricts the application of sewage sludge for the fertilisation and reclamation of soils. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment and vary widely in sewage sludge depending on the input of industrial effluents. The objective of the study was the investigation whether the pyrolysis affect (reduces or adds) the total quantity of PAHs in sewage sludge-derived biochars and whether the pyrolysis changes the PAHs spectrum in terms of relative contributions of more hazardous components. Additionally, the trace metal content was determined before and after pyrolysis as well as the ecotoxicological parameters test towards plant (Lepidium sativum), bacteria (Vibrio fischeri) and crustacean (Daphnia magna). Sewage sludges conversion to biochar significantly reduced the content of PAHs (from 8- to 25-fold depending on pyrolysis temperature and kind of sludge). The exception was the content of naphthalene. Naphthalene was predominant in sewage sludge-derived biochars. However the concentration of the most hazardous 5- and 6-rings PAHs in sewage sludge-derived biochars was much lower compared to sewage sludge. The pyrolysis of sewage sludges caused also a significant reduction of their toxicity towards the test organisms. Only in the case of crustacean it was observed that the extracts from some biochars, obtained at higher temperatures (600 °C and 700 °C) were more toxic to D. magna than extracts from sewage sludge. In turn, after pyrolysis an increase was noted for trace metals content (Pb, Cd, Zn, Cu, Ni and Cr).     

Hydrogen-rich gas production from pyrolysis of wet sludge in situ steam agent

A series of wet sludge samples with different moisture contents were pyrolyzed in situ steam in a bench-scale fixed bed reactor in order to examine the influence of moisture and temperature on product distribution and gas composition. The results demonstrated that inherent moisture in wet sludge had a great effect on the product yield. The pyrolysis of wet sludge (43.38% moisture content) at 800 °C exhibited maximum H₂ yield (7.76 mol kg^?1 dry basis wet sludge) and dry gas yield (0.61 Nm³ kg^?1) and H₂ content of 42.13 vol%. When the moisture exceeded 43.38%, H₂ yield and gas yield both tended to decline. It was also shown that the elevated temperature exhibited a significant influence on gas content increase and tar reduction; at the same time, H₂ yield and H₂ content were increased from 1.83 mol kg^?1 dry basis wet sludge and 16.67 vol% to 9.15 mol kg^?1 dry basis wet sludge and 45.67 vol%, respectively, as temperature increased from 600 °C to 850 °C. LHV of fuel gas varies from 15.49 MJ Nm^?3 to 11.65 MJ Nm^?3 because of decrease in CH₄ and C₂H₄ content as temperature increasing. In conclusion, hydrogen rich gas production by pyrolysis of wet sludge which avoided pre-drying process and utilized in situ steam agent from wet sludge is an economic method.     

Effect of pyrolysis temperature on the composition of the oils obtained from sewage sludge

Sewage sludge was pyrolysed in a quartz reactor at 350, 450, 550 and 950 °C. The pyrolysis oils from the sewage sludge were characterized in detail by means of gas chromatography–mass spectrometry (GC–MS). Changes in the composition of the oils related to the process conditions were assessed by normalizing the areas of the peaks. It was demonstrated that, as the temperature of pyrolysis increased from 350 to 950 °C, the concentration of mono-aromatic hydrocarbons in the oils also increased. Conversely, phenol and its alkyl derivatives showed a strong decrease in their concentration as temperature rose. Polycyclic aromatic hydrocarbons (PAHs) with two to three rings passed through a maximum at a pyrolysis temperature of 450 °C. PAHs with 4–5 rings also presented a major increase as temperature increased up to 450 °C, the concentration at 950 °C being slightly higher than that at 450 °C. Quantification of the main compounds showed that sewage sludge pyrolysis oils contain significant quantities of potentially high-value hydrocarbons such as mono-aromatic hydrocarbons and phenolic compounds. The oils also contain substantial concentrations of PAHs, even at the lowest temperature of 350 °C. The pathway to PAH formation is believed to be via the Diels–Alder reaction and also via secondary reactions of oxygenated compounds such as phenols.     

Characteristics of tar,NOx precursors and their absorption performance with different scrubbing solvents during the pyrolysis of sewage sludge

Recently thermal utilizations of sewage sludge, especially pyrolysis and gasification, are regarded as promising technologies due to efficient utilization of fuel gas. In this study, characteristics of tar and NOx precursors were investigated during the pyrolysis of sewage sludge. Moreover, absorption performance for tar and NOx precursors were also studied by using four kinds of scrubbing mediums: cooking oil, diesel oil, BDF and water. The results showed that nitrogenous light PAHs were the major components of nitrogenous tar produced from the pyrolysis of sewage sludge. As for gravimetric tar and major nitrogenous tar compounds removal, cooking oil was the most suitable absorbent. With respect to NOx precursors, it was concluded that HCN, sharing of about 39.5% of total nitrogen of the sewage sludge, was the main NOx precursor gas whereas NH₃ content could be neglected. Absorption capacity of hydrophobic scrubbing mediums against NOx precursor gases could be arranged as followed: diesel oil > cooking oil > BDF.     

The effects of Fe2O3 catalyst on the conversion of organic matter and bio-fuel production during pyrolysis of sewage sludge

In this paper, the pyrolysis treatment of sewage sludge is studied in a fixed bed reactor at temperatures range of 400–600 °C. Meanwhile, the catalytic effect of Fe₂O₃ on the characteristics of the resulting gases, bio-oil and bio-char are also investigated. The experimental results indicate that the yields of gases and bio-oil respectively increase from 8.69 wt% and 32.54 wt% to 11.62 wt% and 38.74 wt%, and the char yield decreases from 58.77 wt% to 49.64 wt% during Fe-embedded sewage sludge pyrolysis when Fe₂O₃ is added equal to 5% in the dried sewage sludge. Meanwhile, Fe₂O₃ promotes the CO and H₂ formation and inhibits the CH₄ formation, while it exhibits no significantly effect on the composition of the bio-oil. Moreover, the bio-oil should be direct combustion for power generation due it contains higher oxygenated hydrocarbons. In addition, the bio-char exhibits good desulfurization activity.     

Effect of wastewater treatment processes on the pyrolysis properties of the pyrolysis tars from sewage sludges

The pyrolysis properties of five different pyrolysis tars, which the tars from 1# to 5# are obtained by pyrolyzing the sewage sludges of anaerobic digestion and indigestion from the A2/O wastewater treatment process, those from the activated sludge process and the indigested sludge from the continuous SBR process respectively, were studied by thermal gravimetric analysis at a heating rate of 10 ℃/min in the nitrogen atmosphere. The results show that the pyrolysis processes of the pyrolysis tars of 1#, 2#, 3# and 5# all can be divided into four stages: the stages of light organic compounds releasing, heavy polar organic compounds decomposition, heavy organic compounds decomposition and the residual organic compounds decomposition. However, the process of 4# pyrolysis tar is only divided into three stages: the stages of light organic compounds releasing, decomposition of heavy polar organic compounds and the residual heavy organic compounds respectively. Both the sludge anaerobic digestion and the "anaerobic" process in wastewater treatment processes make the content of light organic compounds in tars decrease, but make that of heavy organic compounds with complex structure increase. Besides, both make the pyrolysis properties of the tars become worse. The pyrolysis reaction mechanisms of the five pyrolysis tars have been studied with Coats-Redfern equation. It shows that there are the same mechanism functions in the first stage for the five tars and in the second and third stage for the tars of 1#, 2#, 3# and 5#, which is different with the function in the second stage for 4# tar. The five tars are easy to volatile.     

Mechanism of wet sewage sludge pyrolysis in a tubular furnace

The main objective of this work was to develop a preliminary mechanistic understanding of wet sewage sludge decomposition from starting constituents to final products, including intermediates formed during the pyrolysis process. Sewage sludge with a moisture content of 84.2 wt% was pyrolyzed at different temperatures in a tubular furnace, the pyrolysis products (hydrogen-rich fuel gas, tar and solid char) were detected by micro-GC, GC-MS, and FTIR, respectively. The high moisture content of wet sewage sludge generated a steam-rich atmosphere at high temperatures, leading to an in situ steam reforming of the volatile compounds and a partial gasification of the solid char, which contributed to the production of hydrogen-rich fuel gas. The pyrolysis process can be divided into two steps: at a relatively low temperature (<600 °C), the breaking of the C-H bonds of alkyl gave rise to the release of CH₄ and C₂ hydrocarbons, and a large amount of CO and CO₂ evolved as the result of CO decreasing, both processes indicated the decomposition of volatile compounds. The increasing absorbance amount of C-O and C-H_aromatic demonstrated the formation of tar. As temperature increased further, the diminishing IR absorbance of C-O and C-H_aromatic was accompanied by a significant reduction of tar yield and an increase of H₂. H₂ was considered as an indicator for the occurrence of tar cracking. The Diels-Alder reaction mechanism followed by dehydrogenation was employed to explain the PAHs formation.     

Phosphorus recovery from sewage sludge char ash

Phosphorus was recovered from the ash obtained after combustion at different temperatures (600 °C, 750 °C and 900 °C) and after gasification (at 820 °C using a mixture of air and steam as fluidising agent) of char from sewage sludge fast pyrolysis carried out at 530 °C. Depending on the leaching conditions (extraction time, acid load and acid concentration, and type of acid) 90% mass of the original P was recovered. Regarding char combustion ash, higher phosphorus yields are obtained from ash obtained at 900 °C than at 600 °C and 750 °C when using sulphuric acid. Combustion temperature does not affect phosphorus leaching with oxalic acid. A contact time of 2 h and an oxalic acid load of 10 kg kg⁻¹ of P seem sufficient for phosphorus extraction. Almost all phosphorus present in gasification ash is leached after 2 h with both sulphuric and oxalic acid using an acid load of 14 kg kg⁻¹ of P. Char ash is a possible renewable source of phosphorus and it can be an alternative to rock phosphate in fertilizer production. The combination of sewage sludge pyrolysis, combustion or gasification of the char and phosphorus extraction from the final solid residue contributes to the integral exploitation of sewage sludge.     

Influence of pyrolysis conditions on nitrogen speciation in a biochar ‘preparation-application’ process

To investigate biochar nitrogen conversion in a ‘preparation-application’ system and the response of its transportation in plants, biochar samples were produced from rice straw at different pyrolysis temperatures (400 °C and 800 °C) and atmospheres (N₂ and CO₂). Subsequently, biochar was synthesized under CO₂ atmosphere to explore its nitrogen nutrient characteristics and further improve the chemical and physical properties of soil. Nitrogen speciation of the biochar and plant root samples were evaluated by X-ray photoelectron spectroscopy. Research has shown that organic nitrogen such as protein-N, free amino acid-N, and alkaloid-N in rice straw is converted into organic (nitrile-N, pyridine-N, amino-N, and pyrrole-N) and inorganic (NH₄⁺-N, NO₂^?-N, and NO₃^?-N) species in biochar during the biomass pyrolysis process. In turn, biochar nitrogen is transported to plants as protein-N, free amino acid-N, alkaloid-N, NH₄⁺-N, NO₂^?-N, and NO₃^?-N. Comprehensive consideration of the biochar quality and preparation cost indicated the lower pyrolysis temperature (400 °C) under CO₂ atmosphere as the best conditions for biochar preparation.     

High quality syngas produced from the co-pyrolysis of wet sewage sludge with sawdust

A method for wet sewage sludge (WS) direct pyrolysis with sawdust (SD) at high temperature for syngas production in a screw moving bed reactor was proposed to solve the issue of direct WS utilization. Meanwhile, the co-pyrolysis characteristics of WS with SD at 900 °C was investigated by TG, Py-GC/MS analysis. The TG analysis showed that significant interactive effects, including inhibition and acceleration occurred when the ratio of SD increased from 20 to 80 wt%. According to Py-GC/MS and co-pyrolysis experiment results, lowest yields of O-containing compounds, aromatic hydrocarbons and the liquid were found under 40 wt% SD addition ratio. Meanwhile, synergetic effects — effects of acceleration as well as moisture on syngas, became more distinct in the same addition ratio. The catalytic in-situ steam, which performed as an oxidizer, promoted steam reforming reaction and secondary cracking of macromolecular. Under the optimum SD addition ratio (40 wt%), the quality of syngas was improved, e.g. H₂+CO content increased about 10.19%, H₂/CO increased about 0.14, syngas heat produced from 1 kg raw material increased about 4.04 MJ/kg and carbon conversion increased about 12.75%, respectively.     

Effects of Fe2O3 on pyrolysis characteristics of soybean protein and release of NOx precursors

The effects of ferric oxide (Fe₂O₃) on the pyrolysis characteristics of soybean protein and the release of precursors to nitrogen oxides (NOx) were studied using thermogravimetry and mass spectrometry. The results show that, as the content of Fe₂O₃ increases, there is no major difference between initial and peak temperatures of protein pyrolysis samples. Moreover, between the temperature range of 204 and 550°C where weight loss mainly occurs, total weight-loss rate decreases before increasing, with obvious weight loss occurring around the temperature of 650°C. Fe₂O₃ displays both inhibiting and promoting effects on the precipitation of nitrogen-containing gases such as ammonia (NH₃), hydrogen cyanide (HCN), isocyanic acid (HNCO), and acetonitrile (CH₃CN), with the inhibition effect prevailing over promotion effect on the whole.     

Pyrolysis of biomass in a semi-industrial scale reactor: Study of the fuel-nitrogen oxidation during combustion of volatiles

In this work, an experimental study of the NOx-fuel formation, carried out on a semi-industrial scale reactor during combustion of volatiles of the pyrolysis, is performed. Two different biomasses with different nitrogen contents such as a mixture of organic sludge and wood were tested. Results show that the temperature of pyrolysis does not obviously affect the production of NOx-fuel because of the most active precursors (NH₃ and HCN) are already released at low temperatures (400 °C). In the case of sludge mixture, the combustion conditions play the discriminating role in the production of NOx-fuel: the higher the excess air ratio the larger the production of nitrogen oxides from N-fuel.     

Investigation on the decomposition of chemical compositions during hydrothermal conversion of dewatered sewage sludge

Hydrothermal conversion (HC) can be used to convert sewage sludge into fuel-like products. The investigation of biomass compositions conversion can facilitate the understanding of reaction pathways. HC of dewatered sewage sludge (DSS) is conducted in sub-/supercritical water with batch reactors. Hemicellulose has the highest conversion efficiency of 99.1 wt %, followed by crude protein, cellulose, lignin, and lipid/oil. The total gas and H₂ yields increase slowly from 200 to 300 °C, then sharply rise up from 350 to 450 °C. At 450 °C, the H₂ yield reaches to the maximum of 0.70 mol/kg organic matter. HC of DSS includes reactants degradation to intermediates and final products formation from intermediates. The water-soluble products (WSPs) are formed throughout the HC process, the oil-phase products (OPs) are mostly produced at low temperatures (250–350 °C), and char and gases are mainly generated at higher temperatures (above 350 °C).     

NH3BH3 as an internal hydrogen source for high pressure experiments

Aminoborane NH₃BH₃ is proposed as an appropriate material to produce hydrogen in the high-pressure cells designed for the synthesis of hydrides in sizeable amounts at pressures of a few GPa and elevated temperatures. Aminoborane is a non-hydroscopic material and it does not noticeably react with air that permits assembling the high-pressure cells under ambient conditions without any precautions. If heated to 300 °C at any pressure from 0.6 to 9 GPa, aminoborane decomposes to H₂ gas and chemically inert amorphous BN and does not further absorb the liberated hydrogen. Experiments using NH₃BH₃ and AlH₃ alternatively as the internal hydrogen source gave coinciding isotherms of hydrogen solubility in rhodium at 600 °C and pressures up to 9 GPa therefore demonstrating that the partial pressure of impurities (if any) in the H₂ gas generated by NH₃BH₃ is well below the accuracy ±0.3 GPa of determination of the total gas pressure.     

Behaviour of nitrogen during liquefaction of dewatered sewage sludge

The behaviour of nitrogen compounds during the liquefaction of dewatered sewage sludge was examined. After liquefaction (at 150–350°C), the product mixture was separated into oil A (water-soluble), oil B (water-insoluble), aqueous phase and solid residue. Partition of nitrogen to oil occurred at > 150°C. Above 150°C, 60% of the nitrogen in the sewage sludge was transferred to the aqueous phase. Solubilization and decomposition of the nitrogen compounds were promoted at 150°C. The distribution of nitrogen to oil B obtained by liquefaction at 300°C was 9%, whereas that to oil A was 11%.     

Aromatic fuel oils produced from the pyrolysis-catalysis of polyethylene plastic with metal-impregnated zeolite catalysts

Pyrolysis-catalysis of high density polyethylene (HPDE) was carried out in a fixed bed, two stage reactor for the production of upgraded aromatic pyrolysis oils. The catalysts investigated were Y-zeolite impregnated with transition metal promoters with 1 wt% and 5 wt% metal loading of Ni, Fe, Mo, Ga, Ru and Co to determine the influence on aromatic fuel composition. Pyrolysis of the HDPE took place at 600 °C in the first stage of the reactor system and the evolved pyrolysis gases were passed to the second stage catalytic reactor, which had been pre-heated to 600 °C. Loading of metals on the Y-zeolite catalyst led to a higher production of aromatic hydrocarbons in the product oil with greater concentration of single ring aromatic hydrocarbons produced. The single ring aromatic compounds consisted of mainly toluene, ethylbenzene and xylenes, while the 2-ring hydrocarbons were mainly naphthalene and their alkylated derivatives. There was a reduction in the production of multiple ring aromatic compounds such as, phenanthrene and pyrene. The addition of the promoter metals appeared to have only a small influence on aromatic oil content, but increased the hydrogen yield from the HDPE. However, there was significant carbon deposition on the catalysts in the range 14–22 wt% for the 1% metal-Y-zeolite catalysts and increased to 18–26 wt% for the 5 wt% metal-Y-zeolite catalysts.     

Enhanced dehydrogenation of LiBH4·NH3–LiAlH4 composites

Constructing reactive composite is a feasible approach to promote the dehydrogenation of high-capacity B-/Al-based complex hydrides, such as LiBH₄ and LiAlH₄. In this work, LiBH₄·NH₃ was firstly synthesized by exposing LiBH₄ to liquefied NH₃. In the heating process, the NH₃ was released from LiBH₄·NH₃ instead of reacting with LiBH₄. The LiBH₄·NH₃ was further manually mixed with LiAlH₄ at different ratio, and the resultant composites started releasing hydrogen in the range of 90–110 °C, which is due to the reaction between LiAlH₄ and NH₃. The residual LiBH₄ decomposed at ～400 °C, which is lower than that of pure LiBH₄. The total hydrogen desorption amount of the composite reaches up to maximum ～6.53 wt.%, without NH₃ release. The present work shows a new compositing way of complex hydrides for high-capacity hydrogen storage.