Hydrothermal Carbonization of Waste Stream for Bio-coal Production

在英国，每年大约有93000吨服装垃圾被送往垃圾填埋场，其中通常含有55%的棉花和23%的聚酯。根据欧洲绿色协议，聚酯对苯二甲酸乙二醇酯（PET）制造商面临着到2030年将回收率提高到30%的压力。因此，本研究的重点是使用水热碳化（HTC）从彩色PET和含有染料的衣服废料中生产对苯二甲酸。对苯二甲酸的纯度对回收利用很重要，通常需要超过99%，不能测量颜色，才能制造再生塑料。因此，本研究的具体目的是从有色PET瓶和含聚酯的衣服废料中纯化对苯二甲酸，对于后者，生产一种可作为固体碳氢化合物的碳氢副产物。在研究含棉和聚酯织物的HTC之前，了解纯棉织物的行为是很重要的。以前有一些关于纤维素的HTC的研究，但没有关于棉布的研究。在HTC中，纤维素和棉布的主要区别在于碳氢化合物中产生芳香碳的温度。纤维素和棉布的温度分别为200℃和240℃。这是因为在棉布生产过程中添加了阻燃剂。研究了回用棉织物水溶液的影响，发现回用棉织物有利于提高棉织物的烃类产率，说明水溶性有机物通过组合反应参与了棉织物烃类的形成。然而，由于氧含量的增加，烃类产量的增加伴随着热值的降低。虽然PET的水解已被广泛研究，但如何有效地去除染料以从彩色PET瓶中生产无色高纯度对苯二甲酸尚无报道。对涤纶布的水解研究表明，随着回用水溶液的增加，由于反应物（水）的减少，未反应的聚酯增加。回收的对苯二甲酸收率也随着水溶液的循环而增加，这可能与水溶性有机物和乙二醇的存在有关。对于彩色PET瓶，用纯去离子水进行水解。过滤后的固体产物与氢氧化钠溶液混合，得到对苯二甲酸二钠溶液。成功地应用活性炭吸附法处理对苯二甲酸二钠溶液。与商业标准样品相比，去除染料产生的对苯二甲酸样品更白、更亮，纯度达到99%以上。对于混合布的水热碳化，回收含有未沉淀的对苯二甲酸和乙二醇的水溶液，可提高水焦收率。很可能酸作为催化剂提高了烃类的产率。这也降低了碳氢化合物的氧含量，导致更高的热值。利用混合布生产高纯度对苯二甲酸的研究，需要在有色聚乙烯对苯二甲酸瓶的脱色过程中增加一个步骤。过滤后的HTC固体产品在与氢氧化钠溶液混合前需无氧加热。之后，其他杂质，特别是染料，可以通过活性炭吸收从对苯二甲酸二钠溶液中去除，就像彩色PET瓶一样

In the UK around 93,000 tonnes of clothing waste, which typically contain 55% cotton and 23% polyester, are sent to landfill every year. Under the European Green Deal, polyester terephthalate (PET) manufacturers are under pressure to increase recycling rates to 30% by 2030. Therefore, this study focusses on using hydrothermal carbonisation (HTC) to produce terephthalic acid from both coloured PET and clothing waste containing dyes. The purity of terephthalic acid is important for recycling and typically needs to be over 99% without measurable colour for manufacturing recycled plastic. Therefore, the specific aim for this study is to purify terephthalic acid from coloured PET bottles and polyester-containing clothing waste and, for the latter, to produce a hydrochar co-product that can be used as a solid hydrochar.Prior to studying HTC of cloth containing cotton and polyester, it is important to understand the behaviours of pure cotton cloth. There are several previous studies on the HTC of cellulose, but none on cotton cloth. It was established that the main difference between cellulose and cotton cloth in HTC is the temperature at which aromatic carbon is produced in the hydrochar. These are 200 C and 240 C for cellulose and cotton cloth respectively. This is because of the flame retardants chemicals added during the cotton cloth manufacturing process. The impact of recycling the aqueous liquor was also investigated and it was found that this was beneficial for increasing the hydrochar yield for cotton cloth, implying that the water-soluble organics contribute to hydrochar formation through combination reactions. However, the increase in hydrochar yield was accompanied by a decrease in calorific value due to the oxygen content increasing.Although the hydrolysis of PET has been widely investigated, there are no previous reports on how dye can be removed effectively to produce colourless high purity terephthalic acid from coloured PET bottles. The study of hydrolysis of polyester cloth showed that unreacted polyester increased with the Run of recycling aqueous liquor, due to the reactant (water) reduction. The yield of recovered terephthalic acid also increased with recycling the aqueous liquor, due to less dissolving which could be related to the water-soluble organics and ethylene glycol presence. For the coloured PET bottles, hydrolysis took place with pure deionized water. After that, the filtered solid product was mixed with sodium hydroxide solution to produce disodium terephthalate solution. The activated carbon adsorption was successfully applied to treat the disodium terephthalate solution. The removal of dyes produced a whiter and brighter sample of terephthalic acid compared to a commercial standard sample and reached over 99 % purity.For the hydrothermal carbonisation of mixed cloth, the hydrochar yield increased on recycling the aqueous liquor containing any unprecipitated terephthalic acid and ethylene glycol. It is likely that the acid served as a catalyst to increase the hydrochar yield. This also reduced the oxygen content of the hydrochar leading to a higher calorific value. The study about producing high purity terephthalic acid from mixed cloth, needed one extra step to the process of removing dye from coloured polyethylene terephthalate bottles. The filtered HTC solid product needed heating without oxygen before being mixed with sodium hydroxide solution. After that, the other impurities, notably dyes, could be removed from the disodium terephthalate solution by activated carbon absorption as for the coloured PET bottles