SO_2抑制二噁英从头合成的实验及其过程模拟

Experiments and reaction simulation for SO_2 inhibition on de novo formation of PCDD/Fs

实验研究了不同温度下SO2对二噁英(PCDD/Fs)从头合成的抑制特点,运用HSC Chemistry 6.1软件对主要无机化学反应过程进行模拟,探究了SO2的抑制机理。结果表明,SO2对PCDD/Fs总浓度和I-TEQ浓度的抑制效果随温度的升高而增强。PCDD/Fs总浓度和I-TEQ浓度抑制率从200℃不足20%分别提高到300℃时的75.6%和77.3%及400℃时的89.2%和80.5%;SO2的添加促进了PCDD/Fs尤其是PCDDs同系物分布的低氯代化。在从头合成的高温段和低温段,SO2分别侧重抑制PCDFs和PCDDs。相平衡计算和Gibbs自由能计算表明,SO2优先与催化剂CuCl2反应生成无催化活性的CuSO4,其次与氯源Cl2反应,最终实现PCDD/Fs的生成抑制。模拟结果对现有硫基抑制机理进行了验证和补充,对高效、廉价抑制剂的开发及工程使用具有重要意义。

The objective of this article is to study the inhibition characteristics of SO2 on de novo formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans （PCDD/Fs） at various temperatures and to explore its inhibition mechanism by simulation of reaction process utilizing HSC Chemistry 6.1 software. Model fly ash and flue gas （10%O2/5%H20/85%N2） were used as materials of the de novo formation of PCDD/Fs in a temperature range of 200-400℃. SO2 of concentration 200 mg. m-3 was added as inhibitor in inhibiting experiments. The suppression rate and homologue distribution of PCDD/Fs were analyzed to find SO2 inhibiting characteristics. The results showed that the control ability of SO2 was obvious and became stronger along with increase of temperature. Both total suppression rates and toxic equivalent concentration of PCDD/Fs increased with temperature, at 200℃ both below 20%, at 300℃ 75.6% and 77.3%, and at 400℃ up to 89.2% and 80.5% respectively. SO2 caused a lower-chlorinated distribution of PCDD/Fs, especially for PCDDs. At higher temperature, SO2 restrained chiefly PCDFs while at lower temperature PCDDs was mainly inhibited. Besides, SO2 showed selective inhibition for dioxin isomer. At 300℃ de-chlorination of high-chlorinated PCDFs, like HpCDFand OCDF, made 2,3,7,8-TCDF increase. Based on the computation for Gibbs free energy of pivotal reactions and their equilibrium composition, SO2 preferentially reacted with CuCl2, and CuSO4 formed had no catalytic activity. Then, reaction of SO2 with C12 made decrease of chlorine source. So, formation of PCDD/Fs was brought down. The results of reaction simulation could not only verify and replenished the sulfur inhibition mechanism existed but also could be an effective and creative method for exploring inhibition mechanism of different kinds of inhibitors like nitrogen-compounds. This could help develop high-effective inhibitors and apply in municipal solid waste incinerator practically.