Process Development of Recovered Terephthalic Acid from Poly(ethylene terephthalate) Recycling

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Title:	Process Development of Recovered Terephthalic Acid from Poly(ethylene terephthalate) Recycling
Authors:	邱琪雯;Chiu, Chi-Wen
Contributors:	化學工程與材料工程學系
Keywords:	寶特瓶回收;對苯二甲酸;顆粒大小;poly(ethylene terephthalate) recycling;terephthalic acid;particle size
Date:	2020-07-29
Issue Date:	2020-09-02 15:08:30 (UTC+8)
Publisher:	國立中央大學
Abstract:	由於寶特瓶(poly(ethylene terephthalate) bottles)的廣泛使用以及它不可生物降解的特性，寶特瓶的回收已經成為重要的議題。根據文獻，可以透過鹼水解來回收寶特瓶，反應所得的對苯二甲酸二鈉鹽(disodium terephthalate)可以經由加入硫酸(sulfuric acid)進而產生對苯二甲酸(terephthalic acid)，由於對苯二甲酸幾乎不溶於水的性質，因此在酸化過程中，對苯二甲酸會快速析出並產生非常小的顆粒，這些顆粒聚集並集結成硬塊，這將會增加後續過濾及乾燥上的困難。因此，本研究的主要為增加對苯二甲酸的顆粒大小以利於後續過濾及乾燥程序。首先，將寶特瓶碎片及氫氧化鈉水溶液加入附有200mL鐵氟龍杯的高壓反應器中並放入200oC烘箱，反應結束後，烘箱及高壓反應器自然降溫至室溫，過濾掉高壓反應器中殘留的固體或不純物並乾燥。所有的實驗皆在0.5L夾套玻璃攪拌槽中進行，攪拌器轉速為300rpm，使用硫酸將由鹼水解反應獲得的反應溶液酸化以得到對苯二甲酸。在本論文中進行了許多實驗以提升對苯二甲酸的特性，探討不同濃度的氫氧化鈉水溶液、反應溫度、二甲基亞碸(DMSO)體積以及硫酸的濃度和體積所造成的影響。並應用了立方添加法(cubic addition)、冷卻操作和溫度循環以降低對苯二甲酸的成核速率以及產生更大的對苯二甲酸顆粒。可藉由實驗中進行採樣觀察和評估顆粒大小及型態的演變，對苯二甲酸析出後將溶液過濾並乾燥，進而計算出濾餅阻力和乾燥時間。另外，二甲基亞碸的添加也能降低成核速率進而產生更大的對苯二甲酸。操作溫度是影響對苯二甲酸顆粒大小最主要的參數，當操作溫度越高，對苯二甲酸在二甲基亞碸中的溶解度越高，提供更寬的操作範圍以產生更大的對苯二甲酸，濾餅阻力越小。最後，從光學顯微鏡(OM)、傅立葉轉換紅外線光譜儀(FT-IR)、粉末X射線繞射儀(PXRD)和核磁共振儀(NMR)的檢測結果分別確認對苯二甲酸的化學特性與結構。;Recycling Poly(ethylene terephthalate) (PET) bottles has been discussed widely since its omnipresence and not biodegradable characteristic. It has been reported that PET can be recycled by alkaline hydrolysis. The recycled terephthalate disodium salt can be further converted to terephthalic acid (TPA) by treating with sulfuric acid (H2SO4). Since TPA is almost insoluble in aqueous media, its fast precipitation after the recovery via acidification causes very small TPA particles. They get lumped together to form a hard cake, and as a result, make filtration and drying difficult. Therefore, the aim of my research is to enhance the particle size to improve the downstream processing such as filtration and drying. First, a certain amount of PET flakes and aqueous solution of NaOH were added into an autoclave containing a Teflon cup of 200 mL size. The autoclave was then placed in a preheated oven at 200oC, then the autoclave was cooled to room temperature overnight along with the oven by turning it off. The solids and/or other impurities remaining in the autoclave were then filtered, dried at 40oC, weighed and characterized by FTIR. All experiments were carried out in a 0.5 L sized jacketed glass stirred tank, equipped with a four-bladed impeller, and a water jacket at different temperatures. The agitator was set to 300 rpm. The reaction mixture from PET recycling was acidified by aqueous H2SO4 solution to obtain TPA. To improve the properties of recovered TPA, many experiments were performed to engineer TPA precipitates. Experiments with the variables, such as different concentrations of aqueous NaOH solutions, reaction temperatures, DMSO volumes, and H2SO4 concentrations/volumes were carried out in this thesis. Cubic addition method was employed here to reduce the nucleation rate of TPA precipitation. Furthermore, to avoid the occurrence of fast precipitation of TPA by acidification or feeding, a ‘‘cooling’’ operation and a temperature cycle were applied to produce larger crystals of TPA. By means of sampling during the course of TPA recovery, the evolution of particle size and morphology could be observed and evaluated. After precipitation of TPA, the slurry was filtered and dried so that the specific cake resistance and drying time could be calculated. The addition of the reaction solution into the pre-charged DMSO could be used to slow down the nucleation rate so as to produce a larger size of TPA particles. Operating temperature was the dominant parameter for enhancement crystal size of TPA. The higher operating temperature was, the higher solubility of TPA in DMSO was. The higher solubility provided a wider operating window to achieve larger particle size of TPA and the smaller specific cake resistance. The results of the specific cake resistance approximately agreed with the trend in the particle size distribution of TPA. The solid-state characterizations for all sample solids by optical microscopy (OM), Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), and nuclear magnetic resonance (NMR) were carried out for ensuring the chemical and structural identity of the recovered TPA.
Appears in Collections:	[National Central University Department of Chemical & Materials Engineering] Electronic Thesis & Dissertation

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