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.

Equimolar ternary breakthrough experiments of n-heptane (nHEP), methylcyclohexane (MCH), and 2,2,4-trimethylpentane (224TMP) were carried out at a high hydrocarbon pressure of 10 kPa and a low hydrocarbon pressure of 0.9 kPa with varying adsorption temperature (408–498 K). Binary breakthrough experiments of nHEP/MCH and nHEP/224TMP were performed at 408 K respectively, covering the nHEP partial pressure range from 0.5 to 10 kPa (total hydrocarbon pressure maintains perpetually at nearly 10.5 kPa). The adsorption performance of No. 120 solvent oil and chemical pure nHEP on UiO-66 packed bed were investigated at 408 K. In the ternary experiments (nHEP/MCH/224TMP), the maximum selectivity of MCH/nHEP and 224TMP/nHEP are 5 and 3 respectively. The binary experiments show that increasing the nHEP partial pressure could improve the selectivity of MCH/nHEP and 224TMP/nHEP greatly. High purity nHEP (mass content of more than 99 %) will not be obtained using No. 120 solvent oil (nHEP content of 32.47 %) as raw material directly, but successfully obtained by using chemical pure nHEP (nHEP content of 97.48 %).

•ZIF-8 shows a high potential for n-pentane/isopentane separation.•The equilibrium adsorption capacity and rate of n-pentane are higher than isopentane on ZIF-8.•ZIF-8 shows higher adsorption capacity and lower desorption temperature for n-pentane than 5A molecular sieve.Adsorption equilibrium and kinetic data is essential for the design of an adsorption process. In this work, the adsorption isotherms of n-pentane/isopentane on zeolitic imidazolate framework material (ZIF-8) were measured at 308, 343 and 373 K over the pressure range from 0 to 9.7 kPa by a gravimetric system. The equilibrium adsorption capacity at 303 K and 9.7 kPa is 0.2504 g g−1 for n-pentane and 0.1439 g g−1 for isopentane. Langmuir model was used to fit the adsorption isotherms. The adsorption kinetics of n-pentane/isopentane was studied at 308 K in the pressure range from 0 to 69.9 kPa. The data was well fitted with linear driving force model (LDF) model. The adsorption rate constant of n-pentane is from 0.0019 to 0.0326 s−1, which is higher than that of isopentane, represented 0.0007–0.0036 s−1. The adsorption selectivity of n-pentane/isopentane on ZIF-8 was contrast by the measurement of the binary breakthrough experiments at 343 K, 363 K and 393 K in the partial pressure of 7 kPa. When the adsorption temperature is 363 K, the adsorption selectivity of n-pentane/isopentane on ZIF-8 reaches the maximum 55. Compared with 5A molecular sieve, the desorption temperature of n-pentane on ZIF-8 was analyzed by temperature-programmed-desorption (TPD) method. The peak temperature of n-pentane desorption on ZIF-8 is 361 K. However are 392 K and 443 K on a 5A molecular sieve. Thus, ZIF-8 is more selective or preferential adsorption for n-pentane in comparison to isopentane molecules at low temperature.

Coconut-shell-based activated carbon (ACS-1) was used as a sorbent to simultaneously remove H2S and SO2 from simulated Claus tail gas. Adsorption and regeneration tests were performed to systematically investigate the desulfurization performance, regenerability, and stability of the ACS-1 sorbent. The physicochemical properties of ACS-1 before and after adsorption were characterized by nitrogen adsorption, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The experimental results revealed that the ACS-1 sorbent exhibited good desulfurization performance under a feed gas of H2S (20 000 ppmv), SO2 (10 000 ppmv), and N2 (balance), and the concentrations of H2S and SO2 in the simulated Claus tail gas could be reduced to less than 10 mg/m3 by ACS-1. The breakthrough sulfur capacity of ACS-1 is 64.27 mg of S/g of sorbent at an adsorption temperature of 30 °C and a gas hourly space velocity of 237.7 h–1. The micropores with sizes of around 0.5 nm in ACS-1 are the main active centers for adsorption of H2S and SO2, whereas mesopores have little desulfurization activity for deep removal of H2S and SO2. Both physical adsorption and chemical adsorption coexisted in the process of desulfurization. The majority of sulfides were removed by physical adsorption, and 11% of the sulfur compounds existing in the form of elemental sulfur (ca. 20 atom %) and sulfate (ca. 80 atom %) were derived from the chemical adsorption. The mechanism of H2S and SO2 adsorption on the ACS-1 sorbent is also discussed. H2S and SO2 are first adsorbed on ACS-1 by physical adsorption and then partially oxidized to elemental sulfur and sulfate, respectively, by the oxygen adsorbed on ACS-1. At the same time, the Claus reaction between H2S and SO2 occurs. In addition, the ACS-1 sorbent can be completely regenerated using water vapor at 450 °C with a stable breakthrough sulfur capacity during five adsorption–regeneration cycles.

Co-crystalline zeolite FAU/LTA-0 was synthesized by hydrothermal method from lithium slag. To make the most of excess silicon and alkali sources in mother liquid derived from FAU/LTA-0, zeolite FAU/LTA-1b was synthesized in the same method with the use of mother liquid by adding a certain amount of aluminum source. Influences of different adding ways of aluminum source and recycling dosages of mother liquid on synthesis of zeolites FAU/LTA with mother liquid were investigated. The phase, microstructure and thermostability of FAU/LTA-0 and FAU/LTA-1b were characterized by XRD, SEM and TG-DTA. The calcium and magnesium cation exchange capacities (CECs) of the zeolites were determined. The results have shown that co-crystalline zeolite can be synthesized with the use of mother liquid by adding aluminum source after 2 h of reaction. Compared with FAU/LTA-0, the crystal twinning structure of FAU/LTA-1b became weaker, the grain size was smaller, and the thermostability was better. With a lower dosage of mother liquid, the content of P-type impurity in product decreased significantly, and the content of LTA phase increased. The reuse rate of mother liquid can reach 48%. The CECs of FAU/LTA-1b-150 can reach 343 mg CaCO3·g− 1 and 180 mg MgCO3·g− 1, showing more excellent adsorption capacities than FAU/LTA-0 and commercial zeolite 4A. The full recycling use of mother liquid to synthesize zeolite FAU/LTA which can be applied for detergent not only improves resource utilization but also reduces production cost.Mother liquid was used in the synthesis of Co-crystalline zeolite by hydrothermal method with lithium slag and NaOH as start materials. Adding ways of aluminum source and dosages of mother liquid have a great influence on structure and performance of co-crystalline zeolite. Zeolite FAU/LTA-1b-150 synthesized with utilization of mother liquid show excellent adsorption capacities for calcium and magnesium which can reach 343 mg CaCO3/g and 180 mg MgCO3/g. The utilization rate of mother liquid can reach 48% which can both save raw materials and reduce pollution of environment. So zeolite FAU/LTA synthesized from lithium slag with utilization of mother liquid has an excellent application prospect for replacing 4A as a detergent builder.Download full-size image

A new metal-organic framework of MIL-101 was synthesized by hydrothermal method and the powder prepared was pressed into a desired shape. The effects of molding on specific surface area and pore structure were investigated using a nitrogen adsorption method. The water adsorption isotherms were obtained by high vacuum gravimetric method, the desorption temperature of water on shaped MIL-101 was measured by thermo gravimetric analyzer, and the adsorption refrigeration performance of shaped MIL-101-water working pair was studied on the simulation device of adsorption refrigeration cycle system. The results indicate that an apparent hysteresis loop appears in the nitrogen adsorption/desorption isotherms when the forming pressure is 10 MPa. The equilibrium adsorption capacity of water is up to 0.95 kg·kg−1 at the forming pressure of 3 MPa (MIL-101-3). The desorption peak temperature of water on MIL-101-3 is 82 °C, which is 7 °C lower than that of silica gel, and the desorption temperature is no more than 100 °C. At the evaporation temperature of 10 °C, the refrigeration capacity of MIL-101-3-water is 1059 kJ·kg−1, which is 2.24 times higher than that of silica gel-water working pair. Thus MIL-101-water working pair presents an excellent adsorption refrigeration performance.