Hydrothermal Carbonization of Waste Stream for Bio-coal Production

在英国，每年约有93,000吨服装废料被送往垃圾填埋场，其中通常含有55%的棉花和23%的聚酯。根据欧洲绿色协议，聚酯对苯二甲酸酯(PET)制造商面临压力，要求他们在2030年之前将回收利用率提高到30%。因此，这项研究集中在利用水热碳化(HTC)法从有色聚酯和含染料的服装废料中生产对苯二甲酸。对苯二甲酸的纯度对回收很重要，通常需要大于99%的纯度才能生产再生塑料，而且没有可测量的颜色。因此，本研究的具体目的是从有色PET瓶和含涤纶的服装废料中提纯对苯二甲酸，并为后者生产可用作固体氢化物的加氢焦联产品。在研究含棉和涤纶的织物的HTC之前，了解纯棉织物的行为是很重要的。以前有几项关于纤维素的HTC的研究，但还没有关于棉布的研究。结果表明，在高温下，纤维和棉布的主要区别在于加氢焦生成芳香碳的温度不同。纤维素和棉布的温度分别为200摄氏度和240摄氏度。这是因为在棉布生产过程中添加了阻燃化学品。研究了水溶液循环使用对棉织物加氢焦得率的影响，发现这有利于提高棉织物的加氢焦得率，这表明水溶性有机物通过组合反应促进了加氢炭产率的形成。然而，加氢焦产率的增加伴随着氧气含量的增加而导致热值的下降。尽管人们对PET的水解进行了广泛的研究，但如何有效地从有色的PET瓶中去除染料来生产无色的高纯度对苯二甲酸还没有报道。对涤纶织物的水解研究表明，由于反应物(水)的减少，未反应的聚酯纤维随着循环水溶液的运行而增加。回收对苯二甲酸的产率也随着水溶液的循环使用而增加，这可能与水溶性有机物和乙二醇的存在有关。对于有色的PET瓶，用纯去离子水进行水解。然后将过滤后的固体产物与氢氧化钠溶液混合，制得对苯二甲酸二钠溶液。将活性炭吸附技术成功地应用于对苯二甲酸二钠溶液的处理。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，循环使用含有任何未沉淀的对苯二甲酸和乙二醇水溶液，可提高氢焦产率。酸可能起到了催化剂的作用，提高了加氢焦产率。这也降低了加氢焦中的氧含量，从而导致更高的热值。利用混纺布料生产高纯度对苯二甲酸的研究，需要对有色聚对苯二甲酸乙二醇酯瓶中的染料去除过程增加一个步骤。过滤后的HTC固体产品需要在无氧条件下加热，然后与氢氧化钠溶液混合。在此之后，其他杂质，特别是染料，可以通过活性碳吸附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