The production of polyvinyl chloride (PVC) via the calcium carbide process utilizes a catalyst containing large amounts of mercury (Hg) and is therefore one of the most important sources of anthropogenic Hg in China. To measure the emission of Hg from PVC production, we established a flowchart for the calcium carbide process, for which we quantified the Hg content of the material/product at each step. Results indicated that 71.5% of the total Hg (Hg(T)) was lost from the catalyst, most of which was recovered by the Hg remover, accounting for 46.0% of the total Hg (Hg(T)). We determined that 3.7% of the Hg(T) was released into the environment, mostly in solid wastes and byproducts such as hydrochloric acid. Furthermore, no Hg has been detected in the PVC end product. However, we were only able to account for 78.1% of the Hg across the whole system, leaving 21.7% unaccounted for in the mass balance. A rough estimation indicates that most of the "missing" Hg had accumulated in deposits on the inner surface of converters and downstream pipelines; however, the emission to the atmosphere was ≤ 1% of the Hg(T). For a PVC production line equipped with a Hg remover, emissions of Hg to the atmosphere have been estimated to be 4.9 g per tonne PVC. Currently, almost all calcium carbide facilities have been equipped with a Hg remover, which may reduce the release of Hg in China by ∼ 500 t/year.
The activity and hydrothermal stability of Cu/SAPO and xMn-2Cu/SAPO for low-temperature selective catalytic reduction of NO x with ammonia were investigated. An ion-exchanged method was employed to synthesize xMn-2Cu/SAPO, which was characterized by N 2 adsorption, ICP-AES, X-ray diffraction (XRD), NH 3 -temperature programmed desorption (NH 3 -TPD), NO oxidation, X-ray photoelectron spectrum (XPS), UV-vis, H 2 -temperature programmed reduction (H 2 -TPR) and diffuse reflectance infrared Fourier transform spectra (DRIFTS). 2Mn-2Cu/SAPO and 4Mn-2Cu/SAPO showed the best SCR activity, in that at 150 C NO conversion reached 76% and N 2 selectivity was above 95% for the samples.NO oxidation results showed that the 2Mn-2Cu/SAPO had the best NO oxidation activity and the BET surface area decreased as manganese loading increased. XRD results showed that the metal species was well dispersed. NH 3 -TPD showed that the acid sites have no significant influence on the SCR activity of xMn-2Cu/SAPO. H 2 -TPR patterns showed good redox capacity for xMn-2Cu/SAPO. UV-vis and H 2 -TPR showed that the ratio of Mn 4+ to Mn 3+ increased as manganese loading increased. XPS spectra showed a significant amount of Mn 3+ and Mn 4+ species on the surface and addition of manganese increased the ratio of Cu 2+ . The promotion effect of manganese to 2Cu/SAPO comes from the generation of Mn 3+ and Mn 4+ species. Deduced from the DRIFTS spectra, the Elay-Rideal mechanism was effective on 4Mn-2Cu/SAPO.
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