Enhancing the selectivity for light olefins through catalytic cracking of n-hexane by phosphorus doping on lanthanum-modified ZSM-5.

Naphtha, as the primary raw material in the production of light olefins, could well accommodate their increasing demand through the energy-efficient process of catalytic cracking with ZSM-5. In the current work, different amounts of lanthanum and phosphorous were loaded on ZSM-5 using the wet impregnation method to tune the acidic properties of ZSM-5 for selective catalytic cracking of n-hexane to produce light olefins. Various characterization techniques such as X-ray diffraction (XRD), Al nuclear magnetic resonance (NMR), temperature-programmed desorption of NH3 (NH3-TPD), Py-Fourier transform infra-red (Py-FTIR), inductively coupled plasma optical emission spectroscopy (ICP-OES), N2 adsorption-desorption, X-ray photoelectron spectra (XPS), and scanning electron microscopy were adopted to investigate the modified zeolites. It was found that adding La to ZSM-5 (0.25 wt% to 1 wt%) improved the catalytic life and increased the n-hexane conversion (to 99.7%), while the further addition had a negative impact, reducing the conversion rate and deviating the product selectivity towards a substantial, undesired benzene, toluene, and xylene (BTX) fraction (33%). On the other hand, a 64% selectivity for light olefins was achieved on phosphorous-doped ZSM-5 (at a loading amount of 1 wt%) while reducing the BTX fraction (2.3%) and converting 69% of the n-hexane. A dual metal-modified ZSM-5 with optimal loading amount, 1P0.25LaZ5 (phosphorus 1 wt% and La 0.25 wt%), helped boost the light olefin selectivity to 62% in the tuned Lewis acid sites at an n-hexane conversion of about 77% while decreasing the undesired BTX selectivity to 3% by reducing the number of Brønsted sites. Thus, the current study reveals that tuning the acidic sites of ZMS-5 by dual metal augmentation with P.La is an effective way of controlling the amount of undesirable BTX produced at a stable n-hexane conversion rate and substantial olefin selectivity.

Study on the Formation Mechanism of Cold-Rolled Sludge and the Biodiesel Production from Sludge.

Cold-rolled sludge (CRS) has become a challenge due to its large volumetric capacity and high toxicity and is difficult to be degraded under natural conditions. This article aims to explore the feasibility of the solvent extraction method for recovering oil and fat from CRS and utilizing it as a raw material to prepare biodiesel with the application of a homogeneous catalyst H2SO4 to mediate esterification and transesterification. The formation mechanism of CRS was proposed with its detailed analysis; hydroxylates were preferentially adsorbed on the metal surface by hydrogen bonds, and free fatty acids were hooked by carbon chains to form a second layer of adsorption. It revealed the reason for the residual oil content on the surface of the extracted solid phase. Experimental data represented an optimum biodiesel yield of 96.5% at a catalyst dosage of 25 wt %, a reaction time of 24 h, a methanol-to-oil molar ratio of 70:1, and a reaction temperature of 60 °C. The main properties of the biodiesel were tested and confirmed to meet ASTM D6751 standards.