|Alternative Title||Methods of oxygen recycling from spaceflight solid waste by hydrothermal process and mechanisms of contaminants control|
|Place of Conferral||北京|
|Keyword||航天废弃物,环控生保系统,氧循环利用,废弃药物,水热处理 Spaceflight Solid Waste, Environmental Control And Life Support System, Oxygen Recycling, Waste Medicine, Hydrothermal Treatment|
我国载人航天事业近年来得到了突飞猛进的发展，在中长期航天任务中会产生大量的废弃物，这些废弃物占用航天器内的宝贵空间、滋生有害病菌并危害航天员健康。另一方面，航天废弃物中含有大量的氧，这些氧资源的回收，可以供航天器内部使用，有效提高环境控制与生命保障系统（Environmental control and life support system，简称ECLSS）内部氧循环闭合程度。航天废弃物与地面生活垃圾存在着较大的差异，航天员携带的药物会随着报废和人体代谢迁移到废弃物中，需要采取相应的措施实现其无害化处理。本研究参考美国NASA的研究成果，以模拟航天废弃物（Low fidelity waste surrogate，简称LFWS）为研究对象，围绕氧资源回收和无害化处理开展研究，比较分析了水热和热解处理技术在回收航天废弃物中氧过程中的差异，并采用水热氧化技术（Hydrothermal oxidation，简称HTO）共处理废弃双氯芬酸钠（Diclofenac sodium，简称DS）药物和模拟航天废弃物，实现无害化处理和资源化利用。得到的主要研究结论如下：
（1）基于水热处理回收航天废弃物中氧的方法研究中，采用水热技术处理模拟航天废弃物，以氧回收效率作为指标，评价了水热技术回收航天废弃物中氧的潜力。分析了不同水热产物中的含氧组分以及氧在不同水热产物中的分布特点。研究发现，航天废弃物中的氧含量高于地面城市生活垃圾中的氧含量。氧在气体产物中占比和氧回收效率随着反应温度升高而显著增加，停留时间对氧在气体产物中占比和氧回收效率产生较大影响。在400 °C反应30 min时获得最大的氧回收效率为22.92%，理论回收氧气产量达到83.54 mg/g-LFWS。从航天废弃物中回收氧是一条提高ECLSS内部氧循环闭合程度的有效途径，水热处理可以有效地实现从航天废弃物中回收氧的目标。
（2）研究了热解处理回收航天废弃物中氧的方法，分析了不同热解产物中的含氧组分和氧在不同热解产物中的分布特点，并比较分析了水热处理和热解处理航天废弃物过程中的差异。研究发现，通过调控反应温度可以使航天废弃物中的氧向气体产物中转移，接近50%的氧以气体产物的形式存在，在700 °C时得到最优的氧回收效率为29.54%，理论回收氧气产量达到107.69 mg/g-LFWS。与热解处理相比，水热处理航天废弃物过程中氧在液体产物中所占比例更高，气体产物中CO的产量更低。在污染物控制方面，水热技术优于热解技术，因此，水热技术更适宜于航天废弃物处理过程中污染物控制和资源化利用。
（3）开发了HTO无害化处理长期航天任务中产生的废弃DS药物的工艺方法，以脱氯效率作为无害化程度的评价指标，研究了不同参数对脱氯效率的影响，并采用响应面分析方法优化了多因素交互影响作用下的反应条件。在最佳工艺条件下（H2O2：DS为0.3 mL/mg，反应时间为98 min，反应温度为196 °C），最高脱氯效率为98.9%。此外，通过对不同反应时间所得降解产物的分析和测定，探究并推断了降解机理，发现DS在HTO体系中的反应路径主要包括两个过程：（1）首先发生苯环之间C-N键的断裂，然后生成含苯环结构的中间产物；（2）在苯环上发生羟基化反应，然后经过脱羧和脱氯反应生成含苯环结构的产物，含苯环结构的产物进一步通过氧化开环反应转化为小分子有机酸和醇类，最终完全矿化为CO2和HCl。
（4）研究了HTO共处理航天废弃物和废弃DS药物的方法，以脱氯效率、硝酸根浓度、总有机碳（Total organic carbon，简称TOC）、总化学需氧量（Chemical oxygen demand，简称COD）和碳转化效率作为指标，评价了HTO共处理过程中的氧化降解程度（降解效果评价指标）。研究了不同反应参数（H2O2/废弃物比简称H/S、反应温度和时间）对不同氧化程度评价指标的影响，并确立了最优的反应参数：H/S为30 mL/g，反应温度为300 °C，停留时间为30 min。SEM-EDX和GC-MS分析表明共处理后混合废弃物中的有机氯完全转化为无机氯，脱氯效率接近100%，表明HTO共处理过程中的无害化程度效果明显。混合废弃物中的碳大部分转化为CO2，表明HTO共处理过程中的氧化降解效果明显。液体产物中含有适宜浓度的硝酸盐，同时TOC和COD的浓度范围适宜植物培养的需要，可以提高生保系统内部的物质循环闭合程度。与美国和俄罗斯研发的航天废弃物氧化处理技术相比，本研究所采用的HTO技术在处理对象的复杂程度和氧化剂消耗量等方面均具有优势。该研究开发的新方法和工艺可为航天废弃物中混入废弃药物时的无害化处理与资源化再利用提供新的技术手段和回收方法。
With the rapid development of manned space undertakings, a large amount of wastes will be generated during long-term space missions. Solid waste without treatment will occupy precious space inside manned spacecraft, and will also release unpleasant or toxic odors due to the pathogenic bacteria, which is harmful to astronauts' health. Moreover, spaceflight solid waste (SSW) contains large amounts of oxygen, and recycling oxygen from SSW could supplement the oxygen circulation in the environmental control and life support system (ECLSS). Medicine would migrate into the SSW after utilization and with human metabolites, increasing the risk of pollution in the ECLSS during long-term space mission. Corresponding treatment technique needed to achieve the harmless treatment of the mixed waste. In the present study, based on NASA’s research results, SSW surrogate was taken as the research object. This research focused on the oxygen recycling from SSW. The major differences between pyrolysis and hydrothermal process for recycling oxygen from SSW were analyzed. Hydrothermal oxidation (HTO) process was used to harmlessly co-dispose waste medicine and SSW during long-term space mission, aiming to achieve the pollution control and resource utilization of the entire treatment process. The main research outcomes are as follows:
(1) During the the hydrothermal process for recycling oxygen from SSW, oxygen recovery efficiency was used an indicator to evaluate the potential of recycling oxygen from SSW. Compared with terrestrial municipal solid waste, SSW contained higher content of oxygen. The amount of oxygen in the gaseous product (gas-O) and oxygen recovery efficiency increased with the increment of temperature, and gas-O and oxygen recovery efficiency changed significantly along with the residence time. The optimal oxygen recovery efficiency was 22.92% at 400 °C for 30 min, and the theoretical yield of oxygen was 83.54 mg/g-LFWS under this condition. Recycling oxygen from SSW was an effective way to enhance the closure level of oxygen loop in the ECLSS during long-term space missions.
(2) This work studied the the pyrolysis process for recycling oxygen from SSW. The oxygen distributions and oxygen-containing species in various products at different pyrolysis conditions were investigated. More oxygen in SSW could be easily converted into the gaseous phase for oxygen recovery by adjusting treatment temperature. Nearly 50% of oxygen in SSW was converted in the form of the gaseous product, and the optimal oxygen recovery efficiency was 29.54% at 700 °C. The theoretical oxygen yield was 107.69 mg/g-LFWS under this condition. Compared with pyrolysis process, the liquid-O was much higher and the proportion of CO was extremely lower in the hydrothermal process. Hydrothermal process is much better than pyrolysis process in the field of pollutants control. Therefore, hydrothermal process is more suitable for the pollutants control and resource utilization of SSW disposal.
(3) The present study established the operation methods of the harmless treatment of waste diclofenac sodium (DS) medicine by HTO. Dechloridation efficiency was used to assess the detoxification level during the treatment process. The effects of different parameters on dechlorination efficiency were studied, and response surface methodology (RSM) was carried out to establish the optimum conditions under multi-factor interaction. The optimal conditions were determined as follow, H2O2: DS, reaction time, and reaction temperature were 0.3 mL/mg, 98 min, and 196 °C, respectively. Under the optimal conditions, the dechlorination efficiency was 98.9%. Analysis of the intermediate products showed that there were two different reaction pathways for the degradation of DS by HTO process: (1) the C-N bond between the two benzene rings was cleaved, followed by benzene rings opened and dechlorinated through oxidation reaction; (2) the benzene rings of DS were firstly hydroxylated, followed by benzene rings opened and dechlorinated through oxidation reaction. The oxidative ring-opening products were converted to small molecule organics, e.g. acids and alcohols, which were eventually mineralized to CO2 and HCl.
(4) The present study developed the HTO co-treatment of waste DS and SSW during long-term space missions. Dechloridation efficiency was used to evaluate the detoxification level during the co-treatment process. COD and TOC of the liquid products, concentrations of nitrate ion in the liquid products, and carbon conversion efficiency were also measured as indicators to comprehensively evaluate the oxidation level of the whole co-treatment process. The effects of different parameters (H/S，temperature and residence time) on the different indicators were systematically investigated. The optimal conditions containing temperature, residence time and H/S were 300 °C, 30 min and 30 mL/g, respectively. Characterizations of SEM-EDX and GC-MS showed the organic chlorine in the mixed waste was converted to inorganic chlorine after the HTO process. Dechlorination efficiency of the whole process was nearly 100%, indicating the high harmless treatment level was obtained. Carbon in the mixed waste were mainly converted to CO2, indicating the high oxidation level was achieved. The liquid products with a suitable concentration of nitrate, TOC and COD showed the enormous potential to cultivate plants during long-term space missions, which could improve the closure level of material circulation in the ECLSS. Compared with other oxidation techniques for waste disposal in space, HTO process exhibited various significant technical advantages for the co-treatment of waste medicine and SSW. The proposed HTO co-treatment process provides a new recycling method for harmless and resourceful treatment for SSW containing discarded medicines during long-term space missions.
|史瑞. 航天废弃物中氧的水热回收方法与污染物控制机制研究[D]. 北京. 中国科学院生态环境研究中心,2018.|
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