Production of hydrogen-rich gas from plant biomass by catalytic pyrolysis at low temperature

The catalytic pyrolysis of plant biomass was investigated in a dual-particle powder fluidized-bed (PPFB), where the primary decompositions and secondary reactions occurred simultaneously under ambient pressure. The yields and distributions of the pyrolysis products were studied under various operating conditions. In the absence of catalyst, the amount of volatile released from woody biomass depended on the pyrolysis temperature, and only 13.8 g H₂/kg biomass (def: dry ash-free basis) was produced at 1173 K. NiMo/Al₂O₃ catalyst promoted the decomposition of tar and light aromatic hydrocarbon compounds from the primary decomposition reaction, and significantly reduced the temperature required for the secondary phase reaction. With NiMo/Al₂O₃ catalyst at 723 K, clean combustion gas accounted for 91.25 vol% of the total gas products, which was composed of 49.73 vol% of H₂, 34.50 vol% of CO, and 7.03 vol% of low molecular weight hydrocarbon gases. The contents of H₂ and CO were 33.6 g H₂/kg biomass (def) and 326.3 g CO/kg biomass (def), respectively. Therefore, it is critical to control the secondary phase reaction conditions during the catalytic pyrolysis in order to produce hydrogen-rich gas.     

Premium quality fuels and chemicals from the fluidised bed pyrolysis of biomass with zeolite catalyst upgrading

Biomass in the form of pine wood was pyrolysed in an externally heated fluidised bed pyrolysis reactor with nitrogen as the fluidising gas. A section of the freeboard of the reactor was packed with zeolite ZSM-5 catalyst. The pyrolysis oils before and after catalysis were collected in a series of condensers and cold traps. In addition, gases were analysed off-line by packed column gas chromatography. The composition of the oils and gases were determined before and after catalysis in relation to process conditions. The oils were analysed by liquid chromatography followed by gas chromatography/mass spectrometry. The results showed that the oils before catalysis were highly oxygenated, after catalysis the oils were markedly reduced in oxygenated species with an increase in aromatic species, producing a premium grade gasoline type fuel. The gases were CO₂, CO, H₂, CH₄, C₂H₄ and C₃H₆ and minor concentrations of other hydrocarbon gases. After catalysis the concentration of CO₂ and CO were increased. Detailed analysis of the upgraded oils showed that there were high concentrations of economically valuable chemicals. However, biologically active polycyclic aromatic species were also present in the catalysed oil, which increased with increasing catalyst temperature.     

Catalytic pyrolysis of microalgae to high-quality liquid bio-fuels

The pyrolytic conversion of chlorella algae to liquid fuel precursor in presence of a catalyst (Na₂CO₃) has been studied. Thermal decomposition studies of the algae samples were performed using TGA coupled with MS. Liquid oil samples were collected from pyrolysis experiments in a fixed-bed reactor and characterized for water content and heating value. The oil composition was analyzed by GC-MS. Pretreatment of chlorella with Na₂CO₃ influences the primary conversion of chlorella by shifting the decomposition temperature to a lower value. In the presence of Na₂CO₃, gas yield increased and liquid yield decreased when compared with non-catalytic pyrolysis at the same temperatures. However, pyrolysis oil from catalytic runs carries higher heating value and lower acidity. Lower content of acids in the bio-oil, higher aromatics, combined with higher heating value show promise for production of high-quality bio-oil from algae via catalytic pyrolysis, resulting in energy recovery in bio-oil of 40%.     

Catalytic characteristics of innovative Ni/slag catalysts for syngas production and tar removal from biomass pyrolysis

In this study, innovative Ni-based catalysts supported by five typical slag carriers (magnesium slag (MS), steel slag (SS), blast furnace slag (BFS), pyrite cinder (PyC) and calcium silicate slag (CSS)) were prepared by wet impregnation. With the prepared catalysts and Ni/γ-Al₂O₃ catalyst, catalytic reforming of pyrolysis volatiles from pine sawdust for syngas production and tar removal was investigated. The catalysts were characterized by BET, XRD, SEM, TEM and Raman. The catalytic performances of the six catalysts were decreasing in the following order: Ni/MS > Ni/γ-Al₂O₃ > Ni/SS > Ni/BFS > Ni/CSS > Ni/PyC. Ni/MS catalyst exhibited excellent catalytic reactivity as well as thermal stability in terms of tar conversion (95.19%), gas yield (1.46 Nm³/kg) and CO₂ capture ability (CO₂ yield of 0.5%). Both amorphous carbon and graphite-type carbon were formed on the catalysts after catalytic reforming and the D/G ratio (the relative intensity ratio of the D-band to the G-band) was positively correlated to the catalytic activity.     

Catalytic fast pyrolysis of waste pepper stems over HZSM-5

Catalytic fast pyrolysis over HZSM-5 of red pepper stems, a representative agricultural residue material in the southern area of South Korea, was carried out. The SiO₂/Al₂O₃ ratio of the catalyst were 23 and 280. Pyrolysis-gas chromatography/mass spectrometry was used to pyrolyze the pepper stem samples at 550 °C and directly analyze the product distribution. The main product species of the non-catalytic pyrolysis of pepper stems were phenolics, followed by oxygenates and acids. The production of aliphatic and aromatic hydrocarbons was marginal. On the contrary, catalytic pyrolysis over HZSM-5 reduced the fractions of phenolics and acids significantly, while considerably increasing the fractions of aliphatic and aromatic hydrocarbons. The catalytic activity of the HZSM-5 with a SiO₂/Al₂O₃ ratio of 23 was much higher, owing to its much larger amount of strong Brønsted acid sites, than the one with a SiO₂/Al₂O₃ ratio of 280. Conversion of carbohydrate via furans to aromatics over strong acid sites was observed, which was in good agreement with previous studies. This study suggests that the catalytic pyrolysis of lignin-rich biomass over acidic zeolite catalysts can be a promising method to produce valuable chemicals such as aromatic compounds.     

Catalytic pyrolysis of mannose as a model compound of hemicellulose over zeolites

Mannose was selected as a model compound of hemicellulose and its thermal behavior over zeolites has been investigated using a TG-FTIR analyzer. There was an initial study of the chemical structure of mannose and a characterization of the catalysts. All three catalysts, HZSM-5, H-β and USY, had a significant influence on the dehydration, cracking and deoxygenation reactions during the pyrolysis of mannose. The dehydration reaction in the initial stage was enhanced, resulting in two separate water release processes, while the char formation was suppressed. USY had the best effect on dehydration, and HZSM-5 obtained the highest deoxygenation efficiency. The presence of HZSM-5 and H-β catalyzed the formation of water and CO₂, while suppressing the formation of oxygenated compounds and char residues.     

Catalytic fast pyrolysis of rice husk: Influence of commercial and synthesized microporous zeolites on deoxygenation of biomass pyrolysis vapors

Research on utilization of abundant rice residue for valuable bioenergy products is still not explored completely. A simple, robust, cheap, and one‐step fast pyrolysis reactor is still a key demand for production of bioenergy products, ie, high quality bio‐oil and biochar. Bio‐oil extracted from fast pyrolysis does not have adequate quality (eg, acidic and highly oxygenated). Catalytic fast pyrolysis using zeolites in the fast pyrolysis process effectively reduces the oxygen content (no H₂ required). In this paper, the zeolites with different pore sizes and shapes (small pore, SAPO‐34 (0.56) and ferrierite (30); medium pore, ZSM‐5 (30), MCM‐22 (30), and ITQ‐2 (30); and large pore zeolite, mordenite (30)) were tested in a drop‐type fixed‐bed pyrolyzer. Catalytic deoxygenation is conducted at 450°C at the catalyst/biomass ratio of 0.1. Zeolite catalysts, its pore size and shape, could influence largely on deoxygenation. It was found that the small pore zeolites did not produce aromatics as compared to higher amount of aromatics formed in case of medium pore zeolites. ZSM‐5 and ITQ‐2 zeolites were especially efficient for the higher deoxygenation of biomass pyrolysis vapors due to better pore dimension and higher acidity.     

Hydrogen production via catalytic pyrolysis of biomass in a two-stage fixed bed reactor system

This study introduces an innovative process of generating hydrogen-rich gas from biomass through the catalytic pyrolysis of biomass in a two-stage fixed bed reactor system. Water hyacinth was used as the biomass feedstock. The effects of various factors such as pyrolysis temperature, catalytic bed temperature, residence time, catalyst, and the nickel content of the catalyst on the pyrolysis productivity were investigated and the yields of H₂, CO, CH₄, and CO₂ were obtained. Results showed that the high productivity of hydrogen can be obtained particularly by increasing the catalytic bed temperature, residence time, and catalysts. The favorable reaction conditions are as follows: a first-stage pyrolysis temperature of 650 °C–700 °C, a second-stage catalytic bed temperature of 800 °C, a catalytic pyrolysis reaction time of 17 min, and a nickel content of 9% (wt %).     

裂解温度对生物质热解焦油成分的影响

以锯末粉体为生物质热解焦油研究对象,研究了热解温度对焦油产量和焦油化学成分的影响规律,结果表明,热解温度为500℃时,生物质热解产生的焦油量最大,温度过高或过低都有利于焦油的减少。不同热解温度下,焦油中碳氢化合物的成分主要是芳香烃和少量的脂肪烃,含氧化合物主要是苯酚及其烷基衍生物,含氮化合物主要是吡啶、吡咯及其烷基衍生物等杂环化合物。     

生物质热解制炭与制气一体化研究

在自行设计的管式炉上进行生物质热解制炭与制气一体化研究,对生物质种类和热解终温两个因素进行了实验和分析,得到了生物质热解过程中气体析出的规律和固体炭的产率。当以制炭和制气一体化为目的,在4种生物质原料中选用麦秆,热解终温选择500℃时,可以得到较大的固体炭产率和气体析出浓度。     

One-step synthesis of biochar-supported potassium-iron catalyst for catalytic cracking of biomass pyrolysis tar

In this work, K–Fe bimetallic catalyst supported on porous biomass char was synthesized via a one-step synthesis method by pyrolysis of biomass (peanut shells) after impregnation of a small amount of potassium ferrate (PSC–K₂FeO₄), and was evaluated for the cracking of biomass pyrolysis tar. Control experiments using the pure char (PSC) and char-supported catalysts after impregnation of KOH (PSC–KOH) and FeCl₃ (PSC–FeCl₃) were also performed for comparison. The as-prepared PSC-K₂FeO₄ possessed a porous structure with the dispersion of particles/clusters of Fe metal, K₂CO₃ and KFeO₂ on the char support. Tar cracking experiments showed that the PSC-K₂FeO₄ exhibited excellent catalytic activity on the cracking of biomass pyrolysis tar in the temperature range of 600–800 °C, and the obtained tar conversion efficiencies were obviously higher than that in the control experiments, particularly at relatively lower temperatures (600 and 700 °C). The yields of combustible gas compounds including CO, H₂ and CH₄ increased significantly using PSC-K₂FeO₄ as the catalyst due to the enhanced tar cracking and reforming reactions. The porous structure and the active crystal structures of the spent catalyst were well retained, indicating the potential for efficient and long-term utilization of the catalyst in tar cracking. PSC-K₂FeO₄ exhibited excellent reusability during the five times reuse under the same conditions without regeneration, which showed almost no obvious decrease in the tar conversion efficiency and gas yields.     

Catalytic conversion of coal pyrolysis vapors to light aromatics over hierarchical Y-type zeolites

A series of hierarchical Y-type zeolites were prepared by a post-treatment method. All the samples were characterized using nitrogen adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and temperature-programmed desorption of ammonia (NH₃-TPD). The results show that hierarchical Y-type zeolites with different porosities can be obtained, and the mesopore size can be controlled by changing the treatment conditions. The acidity of catalysts was also adjusted in this process. The catalysts were evaluated with respect to catalytic conversion of coal pyrolysis vapors to light aromatics online by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Moreover, several model compounds were selected to evaluate the formation pathway of light aromatics during the upgrading of coal pyrolysis vapors over Y-type zeolite. It was found that pore-structure-modified Y-type zeolite has good catalytic performance for the upgrading of coal pyrolysis vapors. After catalytic cracking by EDY zeolites, the total amount of light aromatics such as benzene, toluene, ethyl-benzene, xylene, and naphthalene (BTEXN) in coal pyrolysis vapors increased from 5600 ng/mg (raw coal pyrolysis) to 18,800 ng/mg. The results of model compound catalytic pyrolysis show that Y-type zeolite is beneficial for the catalytic cracking of polycyclic aromatic hydrocarbons, the breaking of phenolic hydroxyl, and the decomposition of heterocyclic compounds, thus promoting the formation of BTEXN. Hierarchical catalysts with wide pore size and large mesopore volume contribute to the diffusion of bulky reactants and their contact with active sites in channels, further promoting the generation of light aromatics.     

生物质的热裂解与热解油的精制

生物质能属于可再生能源，其利用符合社会可持续发展的原则。生物质在中等温度下(约500℃)热裂解主要得到热解油。介绍了温度对热裂解过程的影响、热解油——水的二元相图、热裂解过程的机理和热解油的特性，综述了催化剂种类，溶剂等对热解油催化裂解的影响。结果表明，催化剂H-ZSM-5的脱氧效果最好，以四氢萘为溶剂时，精制油的收率大幅提高，达39．4％。     

Highly efficient catalytic pyrolysis of biomass vapors upgraded into jet fuel range hydrocarbon-rich bio-oil over a bimetallic Pt–Ni/γ-Al2O3 catalyst

Catalytic pyrolysis is an effective method for converting biomass to value-added chemicals. However, the development of cost-effective catalysts remains a major challenge. In this study, a highly efficient bimetallic Pt–Ni catalyst (Pt to Ni ratio = 0:1, 2:1, 1:1, 1:2, 1:0) was fabricated and used for catalytic biomass pyrolysis upgrading into hydrocarbon-rich bio-oil with pyrolysis-gaschromatography × gaschromatography/mass spectrometry (Py-GC1 GC/MS). The product yield and selectivity of upgraded bio-oil, thermal properties, kinetic and deactivation mechanisms were also determined to investigate the reaction mechanism. It was determined that Pt addition strengthened the NiO and alumina interaction and improved nickel dispersion, promoting CO hydrogenation. Bimetallic catalysts had a higher stability and activity owing to synergistic action of platinum and nickel on γ-Al₂O₃, and the surface oxygen vacancies were derived from the electron transfer of Pt to Ni and the higher number of super acid-base sites, which inhibited coke deposition. In addition, the higher valence Pt (Pt²⁺) in the catalyst was favorable for decarboxylation and hydrodecarbonylation reactions. Various metal ratios were employed, and the Pt–Ni/Al = 1:2 catalyst exhibited an excellent catalytic performance, achieving highest peak areas of desired hydrocarbons and aromatic hydrocarbons at 52.67% and 40.25%, respectively, and the lowest peak area of deposited coke at 7.26%, along with a 13.98% weightloss rate.     

Catalytic pyrolysis of distillers dried grain with solubles: An attempt towards obtaining value-added products

Catalytic pyrolysis of distillers dried grain with solubles by nickel-based catalysts was performed. The effects of pyrolysis temperature, catalytic carrier and components on the products were investigated. The catalysts were characterized with NH₃-TPD, XPS, H₂-TPR. The average higher heating value (HHV) of the bio-oil was about 61% of the HHV of gasoline. GC/MS analysis indicated that the bio-oil contained some value-added compounds such as 2-furaldehyde, 2-furanmethanol, 3-pyridinol, dodecane, etc. The pyrolysis gas rich in hydrogen was obtained under the direct catalysis of nickel-based catalysts. For Ni–Pd-γ-Al₂O₃, the volume percentage of hydrogen in gas reached 55.6 vol.% at 500 °C, revealing that there was a strong synergistic effect between Ni and Pd. According to the experimental results the possible mechanism was proposed. It was considered that the metal species over catalyst was the most important factor for its performance, and the influence from its Lewis acidity could not be ignored.     

Catalytic reforming of biomass primary tar from pyrolysis over waste steel slag based catalysts

Steel slag (SS) contains high amounts of metal oxides and could be applied as the catalyst or support material for the reforming of biomass derived tar. In this research, steel slag supported nickel catalysts were prepared by impregnation of a small amount of nickel (0–10 wt%) and calcination at 900 °C, and then tested for the catalytic reforming of biomass primary tar from pine sawdust pyrolysis. The steel slag after calcination was mainly composed of Fe₂O₃ and MgFe₂O₄, and granular NiO particles was formed and highly dispersed on the surface of nickel loaded steel slag which lead to a porous structure of the catalysts. The steel slag showed good activity on converting biomass primary tar into syngas, and its performance can be further enhanced by the loading of nickel. The yield of H₂ increased significantly with the increase of nickel loading amount, while excessive nickel loading resulted in the decrease in CO and CH₄ yields and significant increase in CO₂ yield. The presence of steam contributed to enhancing the tar steam reforming as well as reactions between steam and produced gases, while decrease the contact probability between the reactants and the active sites of catalysts, leading to a little decrease in tar conversion efficiency but significant increase in syngas yield. The iron and nickel oxides were reduced by the syngas (CO and H₂) from the biomass pyrolysis, and stable and porous structure was formed on the surface of the nickel loaded catalysts during tar reforming.     

Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the formation of phenolic compounds

The present study is aimed to investigate the upgrading of beech sawdust pyrolysis bio-oil through catalytic cracking of its vapors over Fe-modified ZSM-5 zeolite in a fixed bed tubular reactor. The zeolite supported iron catalyst was successfully prepared with varying metal loading ratios (1, 5, 10 wt%) via dry impregnation method and further characterized by BET, XRD, and SEM-EDX techniques. TG/FT-IR/MS analysis was used for the detection of biomass thermal degradation. Product yields of non-catalytic and catalytic pyrolysis experiments were determined and the obtained results show that bio-oil yields decreased in the presence of catalysts. Besides, the bio-oil composition is characterized by GC/MS. It was indicated that the entity of the ZSM-5 and Fe/ZSM-5 catalyst reveal a significant enhancement quality of the pyrolysis products in comparison with non-catalytic experiment. The catalyst increased oxygen removal from the organic phase of bio-oil and further developed the production of desirable products such as phenolics and aromatic compounds.     

Tar removal from biomass pyrolysis gas in two-step function of decomposition and adsorption

Tar content in syngas pyrolysis is a serious problem for fuel gas utilization in downstream applications. This paper investigated tar removal, by the two-step function of decomposition and adsorption, from the pyrolysis gas. The temperature of the tar decomposition process was fixed at 800 °C both with and without steam, with air as the reforming agent. Both steam and air had a strong influence on the tar decomposition reaction. The reduction of the gravimetric tar mass was 78% in the case of the thermal cracking, whereas, it was in the range of 77–92% in the case of the steam and air forming. Under conditions of tar decomposition, the gravimetric tar mass reduced, while the yield of the combustible gaseous components in the syngas increased. Synchronously, the amount of light tars increased. This should be eliminated later by fixed-bed adsorption. Three adsorbents (activated carbon, wood chip, and synthetic porous cordierite) were selected to evaluate the adsorption performance of light tars, especially of condensable tar. Activated carbon showed the best adsorption performance among all light tars, in view of the adsorption capacity and breakthrough time. On the other hand, activated carbon decreased the efficiency of the system due to its high adsorption performance with non-condensable tar, which is a combustible substance in syngas. Synthetic porous cordierite showed very low adsorption performance with almost all light tars, whereas, wood chip showed a high adsorption performance with condensable tar and low adsorption performance with non-condensable tar. When compared with other adsorbents, wood chip showed a prominent adsorption selectivity that was suitable for practical use, by minimizing the condensable tar without decreasing the efficiency of the system.     

Catalytic performance of modified kaolinite in pyrolysis of benzyl phenyl ether: A model compound of low rank coal

A serials of modified kaolinites were prepared by calcination and further acid treatment and characterized by in-situ XRD, N₂ adsorption, NH₃-TPD, Py-IR and ²⁷Al MAS-NMR. And their catalytic performance in pyrolysis of methanol/benzyl phenyl ether (MeOH-BPE), a model compound of low-rank coal, were investigated at 400 °C in a fixed-bed reactor to explore the correlation between the structure of modified samples and their catalytic performances. The results show that calcination temperature above 500 °C causes the collapse of kaolinite structure. Further acid leaching facilitates the formation of micropores and mesopores. The calcination of kaolinite leads to the transformation of six-coordinate Al atoms (Al^VI) into four and five coordinate species (Al^IV and Al^V), while the subsequent acid treatment increases the contents of Al^IV and Al^VI and removes Al^V. Total acid sites exhibit a first increase and then decrease tendency with the raising calcination temperature. In the presence of the modified kaolinites, BPE conversion significantly enhances and reaches the highest value of 91.41% over K-A-700 prepared by calcination at 700 °C of kaolinite and further acid leaching. Besides, the maximum content of phenol and toluene is also achieved due to the highest acid sites and Al^IV content of K-A-700, which favors the generation of ·H, thus resulting in an obvious inhibition of bibenzyl formation but a significant increase of 2-benzylphenol. In-situ pyrolysis by time-of-flight mass spectrometry suggests that the cleavage of C_al-O bond of BPE to form phenol radicals and benzyl radicals is the primary way, while insufficient ·H results in the formation of dominant product of 2-benzylphenol.     

Evolution of PM2.5 from biomass high-temperature pyrolysis in an entrained flow reactor

In this study, wheat straw pyrolysis was conducted in an entrained flow reactor at 900–1300 °C, and PM_2.5 were sampled from the flue gas through a heated sampling system. Multi-phase PM_2.5 including carbonaceous matter, potassium-containing particles, and ash particles, was separated and quantified using a thermogravimetric analyzer (TGA). The micro-morphologies and chemical compositions of these three phases were characterized by scanning electron microscopy (SEM), scanning transmission electron microscope (STEM), energy dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD). Results show that PM_2.5 yields during biomass pyrolysis are in the range of 7–34 g/kg (dry-basis biomass) and increase with the increase of pyrolysis temperature. At low pyrolysis temperatures (900–1000 °C), the carbonaceous matter is dominated by char-carbon. When the pyrolysis temperature increase from 1000 °C to 1100 °C, the production of soot is greatly enhanced and soot becomes dominant in PM_2.5, and the amorphous morphologies of soot are replaced by the concentric graphitic layers. With the further increasing in pyrolysis temperature, soot particles become more spherical and onion-like. Above 1100 °C, the KCl content in PM_2.5 declines, which is because of the capture of KCl and the formation of low-melting potassium aluminosilicates in large char particles. At 1300 °C, the fragmentation of char particles is significantly strengthened, resulting in more ash in PM_2.5.