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Coal-to-liquid technology is a key technology to ensuring national energy security, with the Fischer–Tropsch synthesis process at its core. However, in actual production, Fischer–Tropsch wax residue exhibits the characteristics of spontaneous combustion due to heat accumulation, posing a fire hazard when exposed to air for extended periods. This significantly threatens the safe production operations of coal-to-liquid chemical enterprises. This study primarily focuses on the experimental investigation of the oxidative spontaneous combustion process of three typical types of wax residues produced during Fischer–Tropsch synthesis. Differential Scanning Calorimetry (DSC) was used to test the thermal flow curves of the three wax residue samples. Kinetic analysis was performed using the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods to calculate their apparent activation energy. This study analyzed the thermal behavior characteristics, exothermic properties, and kinetic parameters of three typical wax residue samples, exploring the ease of reaction between wax residues and oxygen and their tendency for spontaneous combustion. The results indicate that Wax Residue 1 is rich in low-carbon chain alkanes and olefins, Wax Residue 2 contains relatively fewer low-carbon chain alkanes and olefins, while Wax Residue 3 primarily consists of high-carbon chain alkanes and olefins. This leads to different thermal behavior characteristics among the three typical wax residue samples, with Wax Residue 1 having the lowest heat release and average apparent activation energy and Wax Residue 3 having the highest heat release and average apparent activation energy. These findings suggest that Wax Residue 1 has a higher tendency for spontaneous combustion. This research provides a scientific basis for the safety management of the coal chemical industry, and further exploration into the storage and handling methods of wax residues could reduce fire risks in the future.

Here, the efficient synthesis of propylene from methanol was achieved using a series of HZSM-5 catalysts. The effect of the structure and morphology of ZSM-5 on the conversion of methanol to propylene was studied. The structure and physicochemical properties of the synthesized catalysts were analyzed by multiple characterization techniques. The characterization results revealed that the alumina content rationally modified the acid properties of ZSM-5. When using a ZSM-5 catalyst with a hexagonal single crystal and a Si/Al ratio of 177, the selectivity of propylene reached 39.7% at 480 °C. Furthermore, the formation of methane was reduced. This provides a clue for catalyst design to enable the selective transformation of methanol into propylene.

Abstract Spent methanol-to-propylene (MTP) catalysts have a large specific surface area and high porosity but are usually disposed of in landfills directly, and recycling has rarely been reported. In this study, the spent MTP catalyst was moderately dealuminized with organic acids and etched with alkali solvent to increase its specific surface area, further silanized by octyl triethoxy silane (OTS). A novel superhydrophobic adsorbent covered with –Si(CH2)7CH3 groups was obtained. The characterization of XRD, SEM, FTIR and XPS shows that the adsorbent maintains a typical ZSM-5 zeolite structure, and the –Si(CH2)7CH3 group is successfully grafted into the sample, not only on the surface but also in some pore space. Taking high chemical oxygen demand (COD) wastewater as the object, the influence of contract time, pH and temperature on COD removal was investigated. The removal process could be better depicted by the Langmuir isotherm model and the pseudo second-order dynamic model. Furthermore, the results of the thermodynamic study (∆G is − 79.35 kJ/mol, ∆S is 423.68 J/mol K, and ∆H is 46.91 kJ/mol) show that the adsorption was a spontaneous and endothermic process. These findings indicate that the modified spent MTP catalyst has potential application for the removal of COD from wastewater.

Reduction process is a key step to fabricate metal zeolite catalysts, but existing reduction technologies are always energy intensive and inevitably cause the agglomeration of metallic particles or destroy zeolite structure. Here the authors find that zeolites after ion exchange of ammonium display an interesting and unexpected self-reducing feature.

Spent methanol-to-propylene (MTP) catalysts have a large specific surface area and high porosity but are usually directly disposed of in landfills, and recycling is rare. In this study, spent MTP catalyst was moderately dealuminized with acids and etched with an alkali solvent to increase its specific surface area. A novel adsorbent was obtained. XRD, SEM, FT-IR, XRD, XRF, and MAS-NMR characterization shows that the adsorbent maintains a typical ZSM-5 zeolite structure, and the dealumination effect of H2C2O4 is better than that of HCl. HCl mainly removes the framework aluminum of the molecular sieve; H2C2O4 not only removes the framework aluminum but also dissolves some of the nonframework aluminum, which increases the BET-specific surface area and pore diameter. The spent catalyst maintains an irregular ellipsoidal shape. After alkali treatment, the surface of the spherical particles becomes rough. With increasing alkali concentration, the damage degree increases. After treatment with 4 mol/L H2C2O4 and 0.1 mol/L NaOH, the p-xylene and n-hexane adsorption capacities reach the maximum, with values of 141.04 mg/g and 106.87 mg/g, respectively, 20.7% and 16.2% greater than those before treatment. These findings indicate that modified spent MTP catalyst has the potential for application in the removal of VOCs from the air.

Deposition of carbonaceous compounds was used to improve the propylene selectivity of ZSM-5 by deactivating some acid sites meanwhile maintaining the high activity for methanol conversion. The carbonaceous species of pre-coked samples before and after MTP reactions were investigated by elementary analysis and thermogravimetric analysis (TGA). The results showed that pre-coke formed at low temperature (250°C) was unstable and easy to transform into polyaromatics species at the high reacting temperature, while combining 5% pre-coking process with 95% steam treatment at high temperature (480°C) was effective in inhibiting the formation of coke deposits and presented a significant improvement in the propylene selectivity.

Typical hydroxyl polyaluminum solutions (purified Keggin-Al13 and OH/Al = 0.5~2.3) were employed to study the influence of different developer dosage (Ferron, 7-iodo-8-hydroxyquinoline-5-sulfonicacid, [Ferron]) on the variation trend of absorbance-time (A-t) curves determined by Ferron timed spectrophotometry (Ferron assay) and exact determination of Alb content ([Alb]). On this basis, the difference existed between [Alb] and Keggin-Al13 (K-Al13) content ([Al13, NMR], determined by 27Al NMR) in the same solution was further inspected in the hydroxyl polyaluminum solutions (HPAs) with different OH/Al molar ratios. Results indicated that: (1) in chromogenic system, the optimal [Ferron] achieving accurate determination of [Alb] is 2.0×10-3~3.0×10-3 mol/L, where the total Al concentration ([AlT]) is within 2.0×10-5~8.0×10-5 mol/L. Insufficient [Ferron] will result in unreasonably low measuring results. (2) Significant difference exists between [Alb] and [Al13, NMR] in the same HPAs, and ΔAlb = [Al13, NMR]-[Alb]>0. This study lays a scientific foundation for right denotation of the content of effective Al species in HPAs, and clarifies the confusion existed in the speciation correlation between Alb and K-Al13. [ABSTRACT FROM AUTHOR]