摘要
在火电厂和冶炼厂烟气脱硫的同时，如能将其低浓度SO_2转化成硫酸则可实现硫的资源化。但在传统的两转两吸接触氧化制硫酸工艺中，由SO_2转化为SO_3的过程要求在较高温度和催化剂存在的条件下完成，对SO_2气相氧化能量要求高，成本也高。如在液相氧化则可使SO_2转化难度大幅度降低，但在酸性溶液中SO_2又很难溶于液相，限制了液相氧化制硫酸工艺的实现。因此，探索快速溶解SO_2并能氧化制成硫酸的新方法具有重要意义。
本文探索了将臭氧作为氧化剂引入硫酸工艺中，利用其自身的强氧化性，将溶解于溶液中的二氧化硫迅速氧化为硫酸的新方法。并对新方法的氧化效果及氧化机理进行了研究。同时对双氧水协同氧气液相氧化SO_2产硫酸的过程也进行了初步的研究。
实验结果表明向酸性液体中加入臭氧能够显著地提高二氧化硫转变成硫酸的速度和气相二氧化硫的吸收率。通过对其机理的解析结果表明臭氧的存在提高了二氧化硫由气相转移到液相的能力，对其原因分析发现为加快了亚硫酸向硫酸的转化且提高了二氧化硫的氧化速率。进一步解析发现臭氧的存在显著提高了溶液的氧化还原电位，可能是由亚硫酸向硫酸转化能力提高的根本原因。
通过对SO_2氧化和溶液中氧元素的存在形式的解析研究表明，臭氧的存在促进了氧气参与到二氧化硫的氧化过程。在吸收液硫酸浓度为3%，二氧化硫气相浓度为1.33%，臭氧浓度为1.31%，反应时间为10.15min时，每摩尔臭氧在与SO_2反应过程中，臭氧除产生的1mol氧原子参与反应外，还促进0.602mol氧气参与二氧化硫的氧化反应中。
在气相二氧化硫浓度较低的情况下，即吸收液硫酸浓度为3%，二氧化硫气相浓度为0.67%（V/V），臭氧气相浓度为1.31%（V/V）时，硫酸根产率接近100%。随着气相中SO_2浓度的提高，使液相中亚硫酸根的累积量增加，造成SO_2的吸收效率降低。在高浓度气相SO_2的情况下，增加气相臭氧浓度可使二氧化硫的吸收和转化效果大幅提高。
另外，通过对双氧水协同氧气液相氧化制硫酸的实验研究，发现当用氧气取代部分双氧水协同氧化SO_2时，产生的硫酸根的量与单独双氧水液相氧化时产生的量相当，且SO_2的氧化速率也相近。因此双氧水协同氧气液相氧化也可作为脱除烟气中的SO_2并副产硫酸的一种途径。但添加双氧水中的水分会稀释所得到的硫酸溶液，降低硫酸的浓度。
In the process of flue gas desulfurization for power plant and smeltery, how couldconverse into sulphuric acid from low concentration SO_2will realize the resourceutilization of sulfur element. In the traditional double-absorption contact oxidationprocess of sulphuric acid production, energy input and operating cost for the oxidationof gas SO_2are higher because of the conversion from SO_2into SO_3requiring highertemperature and catalyst. Oxidating in liquid phase could greatly decrease thedifficulty in the conversion of SO_2, but in the acid solution SO_2is little dissolved inthe liquid phase, and it has hampered the application of sulphuric acid production byoxidating SO_2in the liquid phase. Therefore, it has important significance forexploring a new technique of sulphuric acid production by dissolving rapidly andoxidating SO_2.
In this study, a new method of sulphuric acid production in the liquid wasproposed, in which ozone as the oxidant was introduced and oxidated rapidly SO_2inthe liquid into sulphuric acid by its own strong oxidative ability. The oxidation effectand oxidation mechanism of this method was investigated. Moreover, SO_2oxidatedby hydrogen peroxide combining with oxygen in the liquid phase into sulphuric acidwas primary explored.
The results showed that ozone introduced in the acid solution could greatlyimprove the conversion rate of SO_2into sulphuric acid and absorptivity of gas SO_2.By analyzing the oxidation mechanism of SO_2, it was found out that the masstransmission of SO_2was improved from the gas phase to the liquid phase in thepresence of ozone, which results from the strengthen of transformation velocity ofsulfuric acid into sulphuric acid and the enhancement of oxidation rate of SO_2. Further,the oxidation-reduction potential of the solution significantly increased, it may be thekey reason of the improvement of conversion from sulfuric acid into sulphuric acid.
By analyzing the oxidation of SO_2and existing forms of oxygen element in thesolution, it implied that the existence of ozone could promote the oxygen from ozonegenerator involved in the oxidation process of SO_2. Besides1mol oxygen atomproduced by ozone involving the oxidation process,0.602mol oxygen was alsopromoted to react with per mole of ozone under the condition of10.15min, sulphuric acid concentration of3%(mass concentration), SO_2concentration of1.33%(V/V)and ozone concentration of1.31%.
For low concentration gas SO_2, sulfate ion yield was up to100%at sulphuric acidsolution of3%(mass concentration), SO_2gas concentration of0.67%(V/V), ozoneconcentration of1.31%(V/V). The increase of gas SO_2concentration and theaccumulation of sulfuric acid in the liquid led to the decrease of absorbing efficiencyof SO_2. For high concentration gas SO_2, the increase of gas ozone concentration couldgreatly enhance the absorptivity and conversion of SO_2in the gas phase.
In addition, the sulphuric acid production through SO_2oxidated by hydrogenperoxide combining with oxygen in the liquid phase was studied. The results showedthat the amount of sulfate ion produced from half of hydrogen peroxide substituted byoxygen was equivalent to that of hydrogen peroxide alone, and the oxidation rate ofSO_2between them was close, which implied hydrogen peroxide combining withoxygen is feasible for the oxidation of SO_2in the liquid phase into sulphuric acid toremove SO_2in flue gas. However, water in hydrogen peroxide will lead to the dilutionof sulphuric acid produced and decrease the concentration of sulphuric acid.
引文
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