Thermal decomposition and gasification of biomass pyrolysis gases using a hot bed of waste derived pyrolysis char

Catalytic performance of activated lignite chars on biomass tar cracking

The tar problems are the major obstacle to developing the biomass pyrolysis technology. The coal chars derived from in situ pyrolysis and/or partially gasification are a promising alternative tar cracking catalyst with great industrial application potential because of its cheap and easily available characteristics. This work investigated the application of lignite chars as catalysts for biomass tar decomposition. Raw lignite char was further gasified with CO₂ for 5 min (GC5) and 15 min (GC15) and used as tar cracking catalysts. Effects of pyrolysis temperature, char/biomass mass ratio, and pore structure of char on the pyrolysis tar removal were studied. The results showed that increasing pyrolysis temperature and char/biomass mass ratio would promote tar decomposition. When using GC15 as catalyst, tar yield was as low as 0.10 wt% at the temperature of 850 °C and the mass ratio of 2. Gasification treatment increased the specific surface area of raw char from 284.1 to 342.7 m²/g (GC5) and 435.6 m²/g (GC15). Comparing the catalytic activity of lignite chars with commercial activated carbon demonstrated that mesopores were more influential than micropores in tar removal. In addition, water produced during biomass pyrolysis could in situ contribute to tar reforming and char gasification reactions. The results obtained in this study suggested that a cheaper coal char-based catalyst with excellent performance for biomass tar cracking could be achieved by combining with a coal gasification process and optimizing gasification conditions.

Comparative study of carbon-deNOx process by different sewage sludge chars

Sewage sludge char (SC) reduces NO to N₂ at high temperatures thus acting as a potential reducing agent in flue gas cleaning systems. However, SC needs to be modified to enhance the carbon-deNO_x performance. In this study, coal char (CC) and different types of SCs, i.e., original (SC-R), pyrolytic volatiles activated (SC-V) and KOH activated (SC-K), were compared in terms of their carbon-deNO_x performance, including NO removal rate and secondary pollution discharged. The results showed that when the oxygen content in the flue gas was 5-6%, the carbon-deNO_x efficiency of the three types of SCs was greater than 70%, which was higher than that of the CC. SC-V has lower emissions of CO and gaseous nitrogen-containing compounds (NH₃, HNCO, HCN) among the three types of SCs. For the oxygen content of 8-11% in the flue gases, the NO conversion performance was found in the order of SC-K > SC-R > SC-V > CC. The physical and chemical characterization of activated carbon shows that pyrolytic-volatile activation increases the ratio of C-O and C=O functional groups on its surface of SC-V, which not only facilitates the chemisorption of NO but are also easily converted under high oxygen conditions. SC-V is found as a suitable reductant for carbon-deNO_x within the temperature range of 300-350 °C.

Pyrolysis of RDF and Catalytic Decomposition of the Produced Tar in a Char Bed Secondary Reactor as an Efficient Source of Syngas

One of the technical limitations of refuse-derived fuel (RDF) pyrolysis is the high content of tar in its gas products. In order to resolve this problem, a two-stage RDF pyrolysis with a catalyst based on char from RDF pyrolysis is proposed. This paper presents the results of municipal waste pyrolysis beginning in an oven heated to 480 °C and ending with catalytic tar cracking carried out in the temperature range from 800 to 1000 °C. Thermal and catalytic pyrolysis with a char catalyst containing a minimum of 6% Fe resulted in increases in the CO and H2 contents in gas products and decreases in CO2 and CH4. At 1000 °C, the mass ratio of gaseous products to liquids was greater than 6. The residence time of the gases in the catalytic zone was about 3–5 s. The reactor was a good source of hydrogen and carbon monoxide.

Catalytic conversion of gaseous tars using land, coastal and marine biomass-derived char catalysts in a bench-scale downstream combined fixed bed system

The catalytic activity of biochar for tar removal was evaluated in a bench-scale combined fixed bed reactor by comparison of gaseous tar catalytic cracking behaviors over land (Corn stalks, Cs), coastal (Reed, Re) and marine (Sargassum horneri, Sh) char catalyst. The experiments demonstrated that the tar yield after addition of the biochar was reduced significantly; the tar conversion efficiency reached to 94.6% for catalytic at 850 °C with 50 mm char bed length using Re char. And the yield and composition of gas also changed markedly. The percentage of H₂ and CO in the product gas were obviously increased. Sh has a higher H₂ content (49.3% of the total gas content), whereas, CO dominated in the gas products for Cs (45.4%) and Re (48.1%). The results from GC-MS analysis illustrated that the increase in temperature promoted the tar cracking and also promotes the polymerization of some tar components.

Orange peel valorization by pyrolysis under the carbon dioxide environment

To valorize biomass waste, pyrolysis of orange peel was mainly investigated as a case study. In an effort to establish a more sustainable thermolytic platform for orange peel, this study particularly employed CO₂ as reactive gas medium. Accordingly, this study laid great emphasis on elucidating the mechanistic role of CO₂ in pyrolysis of orange peel. The thermo-gravimetric analysis (TGA) confirmed that no occurrence of the heterogeneous reactions between the solid sample and CO₂. However, the gaseous effluents from pyrolysis of orange peel experimentally proved that CO₂ effectively suppressed dehydrogenation of volatile matters (VMs) evolved from the thermolysis of orange peel by random bond scissions. Moreover, CO₂ reacted VMs, thereby resulting in the formation of CO. Note that the formation of CO was being initiated at temperatures ≥550 °C. The two identified roles of CO₂ led to the compositional modification of pyrolytic oil by means of lowering aromaticity.

Microwave-assisted in-situ elimination of primary tars over biochar: Low temperature behaviours and mechanistic insights

An efficient method for microwave-assisted low temperature catalytic elimination of primary tars using cheap biochar as catalyst has been developed along with H₂ rich syngas production. Tar removal efficiency reached 94.03% after 8 min reaction at 600 °C, while the concentration of H₂ and syngas was up to 50.5 vol% and 94.5 vol% respectively, which were significantly comparable to conventional technologies at 700-900 °C. The FT-IR, ICP and EDX results indicated that the biochar surface contained O-containing functional groups and 12.6 wt% uniformly dispersed alkali and alkaline earth metals (AAEMs) in the carbon skeleton. The low temperature behaviours were attributed to the hot spots, which were induced by the increased dielectric properties of biochar and decentralized AAEMs under microwave heating. Possible reaction mechanism for the elimination of primary tars over biochar catalysts were discussed based on this experimental study.

Reforming sewage sludge pyrolysis volatile with Fe-embedded char: Minimization of liquid product yield

Obtaining high quality syngas from sewage sludge (SS) means transferring a low-grade SS into a high-grade fuel or raw materials for chemical products. In this study, Fe is added to SS in form of Fe₂(SO₄)₃ to produce an effective and self-sufficient catalyst in order to obtain more syngas and minimize liquid products from SS pyrolysis. The Fe-embedded sewage sludge chars (SSCs) were used as catalysts for volatile reforming at 600°C. It has been found that the gas yield increases from 15.9 to 35.8wt% of the SS and that of liquids decreases from 31.9 to 10.2wt% after volatile reforming with Fe-embedded SSC when Fe was added equal to 7 % in the dried SS. In addition, the content of nitrogen-containing compounds in the oily products decreased. After reforming with Fe-embedded SSC, the molar fractions of syngas combustible components, including H₂, CH₄ and CO, increase, and the higher heating value of the syngas increased to 17.0MJ/Nm³ from the original 12.5MJ/Nm³ obtained from SS pyrolysis at 550°C. Moreover, the volatile reforming seems to reduce the level of some important syngas pollutants, like H₂S, HCl and HCN, even though it was also observed an increase of the contents of SO₂, NH₃, NO_2, HCNO and N₂O.

Promotion of hydrogen-rich gas and phenolic-rich bio-oil production from green macroalgae Cladophora glomerata via pyrolysis over its bio-char

Conversion of Cladophora glomerata (C. glomerata) as a Caspian Sea's green macroalgae into gaseous, liquid and solid products was carried out via pyrolysis at different temperatures to determine its potential for bio-oil and hydrogen-rich gas production for further industrial utilization. Non-catalytic tests were performed to determine the optimum condition for bio-oil production. The highest portion of bio-oil was retrieved at 500°C. The catalytic test was performed using the bio-char derived at 500°C as a catalyst. Effect of the addition of the algal bio-char on the composition of the bio-oil and also gaseous products was investigated. Pyrolysis derived bio-char was characterized by BET, FESEM and ICP method to show its surface area, porosity, and presence of inorganic metals on its surface, respectively. Phenols were increased from 8.5 to 20.76area% by the addition of bio-char. Moreover, the hydrogen concentration and hydrogen selectivity were also enhanced by the factors of 1.37, 1.59 respectively.

Effects of volatile-char interactions on char during pyrolysis of rice husk at mild temperatures

In order to understand the sensitivity of volatile-char interactions to mild temperatures (600-800°C), in-situ rice husk char was prepared from fast pyrolysis (>10(3)Ks(-1)) on a fixed-bed reactor. Retention of K in char, changes in char structure and char reactivity were determined. The results showed that volatile-char interactions did not cause obvious effect on the char yield but showed an inhibitory effect on char reactivity. The inhibition began only above 650°C and intensified with temperature rise, but kept almost unchanged at 700-800°C. Char structure and retention of K have a combined effect on char reactivity. The decreased reactivity was caused by additional volatilization of K from char matrix and transformation of relatively smaller aromatic ring systems to large ring systems (>6 benzene rings) above 650°C.

Catalytic ethanolysis and gasification of kraft lignin into aromatic alcohols and H2-rich gas over Rh supported on La2O3/CeO2-ZrO2

Efficient catalytic ethanolysis and gasification of kraft lignin were conducted over a versatile supported catalyst Rh/La2O3/CeO2-ZrO2 to give high-value aromatic alcohols and H2-rich gas. The removal of phenolic hydroxyl group was the most prevalent reaction, and importantly, almost no phenols, undesired char and saturating the aromatic ring were detected. Meanwhile, the feedstock and solvent both played key roles in H2 generation that contributed to the hydrodeoxygenation of liquid components and made the whole catalytic process out of H2 supply. Reusability tests of catalyst indicated that the crystalline phase transition and agglomeration of support, the loss of noble metal Rh and carbon deposition were the possible reasons for its deactivation in supercritical ethanol. Comparing with water, methanol and isopropanol system, ethanol was the only effective solvent for the depolymerization process.

Production of activated carbons from waste tyres for low temperature NOx control

Waste tyres were pyrolysed in a bench scale reactor and the product chars were chemically activated with alkali chemical agents, KOH, K2CO3, NaOH and Na2CO3 to produce waste tyre derived activated carbons. The activated carbon products were then examined in terms of their ability to adsorb NOx (NO) at low temperature (25°C) from a simulated industrial process flue gas. This study investigates the influence of surface area and porosity of the carbons produced with the different alkali chemical activating agents on NO capture from the simulated flue gas. The influence of varying the chemical activation conditions on the porous texture and corresponding NO removal from the flue gas was studied. The activated carbon sorbents were characterized in relation to BET surface area, micropore and mesopore volumes and chemical composition. The highest NO removal efficiency for the waste tyre derived activated carbons was ∼75% which was obtained with the adsorbent treated with KOH which correlated with both the highest BET surface area and largest micropore volume. In contrast, the waste tyre derived activated carbons prepared using K2CO3, NaOH and Na2CO3 alkali activating agents appeared to have little influence on NO removal from the flue gases. The results suggest problematic waste tyres, have the potential to be converted to activated carbons with NOx removal efficiency comparable with conventionally produced carbons.