Ultrahigh-strength silicone aerogels reinforced by an armor-like epoxy framework via a temperature-controlled sequential reaction strategy.

Aerogels with low density and high porosity are extremely attractive for high-performance insulation, but their brittleness, complicated fabrication, and poor mechanical properties greatly limit their practical applications. Herein, we report an ultrahigh-strength silicone aerogel with an armor-like epoxy framework via a temperature-controlled sequential reaction strategy. The key to this synthesis is forming a Si-O-Si framework via the polycondensation of silanes at 100 °C, followed by in-situ armoring an epoxy framework via an intermolecular cyclization at an elevated temperature of 150 °C. Owing to the enhanced framework, the resulting aerogel could withstand capillary tension in the drying process, enabling it to be dried at ambient pressure without shrinkage. The obtained aerogel possesses a tunable density of 0.17-0.45 g/cm3 and ultrahigh-strength with compressive modulus up to 37.8-244.3 MPa, which surpasses other polymer-reinforced silicone aerogels by a factor of five in mechanical properties. It also demonstrates outstanding thermal insulation, with an extremely low thermal conductivity from 0.025 to 0.051 W m-1 K-1 at room temperature, and maintains thermal characteristics across a temperature range of -20 to 300 °C. Furthermore, the aerogel composites prepared by the reinforcement of low-density fiber mats have tunable densities of 0.36-0.87 g/cm3, much enhanced tensile strengths of 15.9-72.3 MPa, and low thermal conductivities at room temperature of 0.042-0.078 W m-1 K-1. This study presents a cost-effective method for enhancing the production of silicone aerogel materials, offering considerable opportunities for their application in insulation, energy transport, and the aerospace sector.

Study on emission factors of FCC flue gas pollutants in petroleum refineries.

Fluid catalytic cracking (FCC) unit is one of the means to lighten heavy oil in refineries, and its regenerated flue gas is also the main source of air pollutants from refinery. However, it is not clear about the type and amount of pollutants discharged from FCC units in China. The emissions of regenerated pollutants in the stack flue gases of three typical FCC units in China were investigated in this study, including a partial regeneration unit without a CO boiler (U1), a partial regeneration unit with a CO boiler (U2), and a full regeneration unit (U3). Different monitoring methods were used to analyze the concentration of sulfur dioxide (SO2) and nitrogen oxides (NOx), and the results showed that Fourier transform infrared spectroscopy (FTIR) monitoring results of SO2 and NOx are approximately 10 times and 5 times larger than those of the continuous emission monitoring system (CEMS) data, respectively. Also, the contents of characteristic pollutants such as NH3, C6H6, HCN, C8H8, C2H4, CH4, and CO were also monitored by FTIR, and the emission factors based on coke burn-off rate and throughput were investigated. The pollutants in U1 exhibited relatively higher contents with the NH3, HCN, and C6H6 of 116.99, 71.94, and 56.41 mg/Nm3 in flue gas, respectively. The emission of regenerated pollutants in U2 and U3 are significantly different from U1. Regeneration processes (including coke properties, operating modes, and presence or absence of CO boilers) affected pollutants' emission factors in varying degrees. At last, reasonable emission factors based on the different FCC regeneration processes contribute to the prediction, assessment, and control for the pollutant emission.

Influence of wet flue gas desulfurization on the pollutants monitoring in FCC flue gas.

Fluid catalytic cracking (FCC) unit emits a large amount of flue gas, which is a major concern of environmental protection supervision. Wet flue gas desulfurization (WFGD) technologies have been widely used to control the emissions of SO2 in refineries. In this study, stack tests for pollutants emission of a typical FCC unit were conducted. The emission characteristics of the FCC unit indicated that WFGD would cause a large amount of water vapor in the flue gas, which indirectly leads to large quantities of salt pollutants entrained in the flue gas including ammonium sulfite ((NH4)2SO3) and ammonium sulfate ((NH4)2SO4). A strong correlation among the concentrations of SO2, NH3, and H2O was observed, and factor analysis shows that these concentrations are dominated by a common factor. It was also found that a mass quantity of NH4+ and SO32- existed in the condensate water of the flue gas. The TG-MS analysis shows that (NH4)2SO3 could be decomposed at 94.1 °C, and NH3, SO2, and H2O are released as reaction products in the form of gas. Therefore, a part of the NH3 and SO2 obtained by Fourier transform infrared spectroscopy (FTIR) monitoring may be derived from the decomposition of (NH4)2SO3 in the flue gas due to the high temperature during the sampling process, which was also confirmed in a lab experiment. The hot and wet sampling process will lead to overestimation of NH3 and SO2 emissions rather than FTIR method itself when monitoring the high-humidity FCC flue gas. Thus, the concentration of H2O in the flue gas and the type of sampling process need to be taken into consideration during the monitoring process.