Lithium slag is an industrial waste residue of the extraction of lithium carbonate industry, which has the issue of high output and low utilization rate. In order to improve the utilization rate and value of lithium slag, it was directly used as a raw material to synthesize NaX zeolite using a hydrothermal and microwave-assisted method in this paper. The process of synthesizing NaX zeolite from lithium slag was analyzed and characterized by X-ray diffractometry, Fourier transform infrared spectroscopy and solid state nuclear magnetic resonance. The reaction mechanism of NaX zeolite from lithium slag was also proposed. The structure of NaX zeolite synthesized from lithium slag was characterized. The results indicate that during the synthesis, aluminum species in the lithium slag transform from Al^VI to Al^IV, and the silicon species undergo a transition from Q⁴ (0Al) and Q⁴ (1Al) structures to Q⁴ (1Al) and Q⁴ (2Al) structures. The synthesis time of NaX zeolite with the microwave-assisted method is only about 1/3 that of hydrothermal synthesis. Microwave irradiation accelerates the dissolution of lithium slag, the generation of aluminosilicate gels, and the crystallization of the NaX zeolite, but does not change the process of synthesis of NaX from lithium slag. The NaX zeolite synthesized from lithium slag has smaller grains (0.5–0.8 μm) and good stability, and the adsorption capacity of water reaches 32 wt% when the relative humidity is 90%. This study provides technical support for the large-scale production of NaX zeolite from lithium slag.

The adsorption desulfurization process of diesel fuel is suffering from adsorbent regeneration limitation. Adsorption performance of activated carbon (AC) for S-compounds and hydrocarbons in low-sulfur real diesel was investigated by an adsorption fixed bed. The exhausted AC was regenerated by different solvents, including n-octane, ethanol and cyclohexane. AC samples were characterized using N₂ adsorption–desorption isotherm at 77 K, TG and FT-IR. S-species and hydrocarbons-species in real diesel and the regeneration solutions were analyzed by gas chromatography-sulfur chemiluminescence detection (GC-SCD), gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC). The effects of hydrocarbons on desorption performance of S-compounds and extraction capability of n-octane were investigated. The effect of n-octane as a recycled regeneration solvent on the regeneration stability of AC in this work was also considered. The S-content in diesel was reduced to less than 10 ppm from an initial S-content of 34.83 ppm. The competitive adsorption between polycyclic aromatic hydrocarbons (PAHs) and S-compounds was the largest in hydrocarbons. The regeneration performance of different solvents for AC decreased as follows: n-octane > ethanol > cyclohexane. The regeneration efficiency of AC was 100% after a first adsorption–desorption cycle, and was held near 73% after 50 cycles using fresh n-octane as a regenerating solvent. The regeneration efficiency of AC can be maintained at 45% after 20 cycles using n-octane as a recycled regeneration solvent. According to the results of characterizations and tests, we found that multilayer adsorption of S-compounds and PAHs occurred in the mesopores of AC, while the aggregation phenomenon of small alkane molecules mainly existed in the micropores.

MIL-101 is a promising metal-organic frameworks (MOFs) material in adsorption chiller application due to its high adsorption capacity for water and excellent adsorption/desorption cyclic stability. Few layer graphene (FLG) as the thermal conductive additive was added into MIL-101 to improve inferior heat transfer of MIL-101 in the adsorption cooling process. The heat transfer characteristic of MIL-101/FLG adsorber and the adsorption cooling performance of the MIL-101/FLG-water working pair were studied. Results show that thermal conductivity of MIL-101/20%FLG composite is 5.79-6.54 times that of MIL-101. Adding FLG is conducive to the formation of heat transfer channels in MIL-101/FLG adsorber and the rapid removal of adsorption heat. The heating and cooling rate of MIL-101/FLG adsorber is ~2.2 times that of MIL-101 adsorber. Under typical adsorption water chiller conditions, the specific cooling power (SCP) and coefficient of performance (COP) of the MIL-101/FLG-water working pair is 72.2–81.0 W kg⁻¹ and 0.187–0.202, respectively, at desorption temperatures of 70 °C and 90 °C, which is 1.43–1.56 times higher than the MIL-101-water working pair. The excellent structural and adsorption/desorption cyclic stability of MIL-101/FLG composite is verified after 50 consecutive cycles. It can provide a promising adsorbent candidate (MIL-101/FLG composite) in adsorption water chiller process.

Aiming at the difficulty in qualitative and quantitative analysis of trace compositions in food preservative propionic acid, the trace compositions and the key components influencing the total aldehyde content in propionic acid were analyzed by gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC) and gas chromatography (GC) in this paper. The results show that the food preservative propionic acid contains 18 trace compositions. The main compositions affecting the total aldehyde content in propionic acid are acetaldehyde, propionaldehyde, 1-cyclopropyl-1-propanone and 2-methyl-2-pentenal, which account for ∼90% of the total aldehyde content in propionic acid. The total aldehyde content in propionic acid can be quickly determined by iodometric titration. However, the impurity compositions, solution oxygen content and pH value of propionic acid may affect the stability of NaHSO₃, which lead to a higher titration value of the aldehyde content. The total aldehyde contents in propionic acid determined by GC (148.535–337.890 mg L⁻¹) and HPLC (157.730–335.780 mg L⁻¹) are close and reliable with a relative deviation of 0.31–3.00%. The volatile low-carbon aldehydes and ketones including formaldehyde, acetaldehyde and acetone have a weak response and a high detection limit in GC. The derivation conditions of all aldehydes and ketones in propionic acid should affect the determination results of HPLC. It provides the basic data for quality improvement and ultra-deep purification of food-grade propionic acid.