Effect of copper ions on transformation of organic sulfur in cationic exchange resins in Li2CO3-Na2CO3-K2CO3 molten-salt system.

Cationic exchange resins (CERs) were applied for purification and clarifying process of radioactive wastewater in nuclear industry, which was a kind of sulfur-containing organic material. Molten-salt oxidation (MSO) method can be applied for the treatment of spent CERs and the absorption of acid gas (such as SO2). The experiments about the molten salt destruction of the original resin and Cu ions doped resin were conducted. The transformation of organic sulfur in Cu ions doped resin was investigated. Compared with the original resin, the content of tail gas (such as CH4, C2H4, H2S and SO2) released from the decomposition of Cu ions doped resin was relatively high at 323-657 °C. Sulfur elements in the form of sulfates and copper sulfides were fixed in spent salt through XRD analysis. The XPS result revealed that the portion of functional sulfonic acid groups (-SO3H) in Cu ions doped resin was converted into sulfonyl bridges (-SO2-) at 325 °C. With the enhancement of temperature, sulfonyl bridges (-SO2-) were further decomposed to sulfoxides sulfur (-SO-) and organic sulfide sulfur. The destruction of thiophenic sulfur to H2S and CH4 was prompted by copper ions in copper sulfide. Sulfoxide were oxidized to the sulfone sulfur in molten salt. Sulfones sulfur consumed by reduction of Cu ions at 720 °C was more than it produced by oxidation of sulfoxide through XPS analysis, and the relative proportion of sulfone sulfur was 16.51%.

Single step carbonating and activating fir sawdust to activated carbon by recyclable molten carbonates and steam.

Molten carbonate pyrolysis with steam on fir sawdust was conducted to produce activated carbon, in which physical and recycling chemical activation was combined with carbonization as a single step process. The effects of temperature, molten carbonate pyrolysis and steam flow rate on the activated carbon were investigated. The BET results showed an excellent specific surface area of 822.02 m2/g and a pore diameter of 2.39 nm. The adsorption capacities of the activated carbon achieved ideal values on methylene blue and iodine and reached a removal capacity of 196.5 mg/g for the elimination of Cr(VI) in wastewater. There were four stages in developing the porous structure of activated carbon by the joint effects of molten carbonates and steam as the temperature rising. The activated carbon had abundant micropores inside the macropore structure at temperatures ranging from 700 °C to 750 °C. Molten carbonates promoted the formation of mesopores and macropores and reduced the reaction temperature as a catalyst and heat transfer medium, while steam promoted micropore generation by water-gas shift reactions. A recycling study indicated that the Cr(VI) adsorption capacity of the activated carbon generated after five recycling cycles of molten carbonates was still reached 195 mg/g.

Investigation and improvement of the desulfurization performance of molten carbonates under the influence of typical pyrolysis gases.

Co-pyrolysis with oxygen-lean waste tires could improve the quality of pyrolytic oil from the bio-wastes while H2S/COS generated during co-pyrolysis process has a negative impact on the utilization of oil/syngas as well as the flue gas pollution control. Compared to traditional wet desulfurization process, high-temperature desulfurization via molten carbonates could reduce heat loss and favor the recycling of captured sulfur. Notably, small-molecule pyrolytic gases might change the species of sulfur-containing gases and promote the re-emission of absorbed sulfur from the molten salts. To fully understand the effects of pyrolysis gases (H2/CO/H2O/CO2) on molten salts desulfurization efficiency as well as mutual conversion mechanism of H2S and COS, equilibrium compositions calculations and adsorption experiments were carried out in the present study. The results showed that H2/CO had few effects on molten salts desulfurization performance and mutual conversion of H2S/COS. In contrast, CO2 and H2O had obvious adverse effects on desulfurization efficiency through the transferring of free S2- into emitted sulfur-containing gases. More specifically, only a small amount of CO2 reacted with S2- to produce COS while more S2- was converted to H2S and released from the reactor outlet when H2O was introduced. Fortunately, the impact of H2O or CO2 on molten salts desulfurization could be weakened with the addition of CaCO3 by transferring the molten free S2- into precipitated CaS. Besides, multi-stage desulfurization units connected in series and parallel were proposed and estimated, which was confirmed to show good performance to maintain the high desulfurization efficiency from the complicated pyrolytic gases.