Optimization of froth flotation procedure for poly(ethylene terephthalate) recycling industry

This article addresses the separation of polyethylene terephthalate (PET) from ternary blends with polyvinyl chloride (PVC) and polystyrene (PS) by froth flotation. The experimental work was carried out with representative samples from post‐consumer waste packages collected at drop‐off‐points. Previous to froth flotation, PET selective wetting was achieved by alkaline treatment followed by surfactant adsorption. For this purpose, an aqueous solution of NaOH and an industrial detergent commonly used for waste plastic washing were tested as alkaline treatment, and calcium lignosulphonate and Hostaphat were tested as surfactants. An enriched product with 98.9% grade in PET and only 0.6% in PVC was recovered in the nonfloated product. The PET recovery in this product was 97% while ～96% of PVC and 91% of PS were recovered in the floated product. An analytical method was developed for the quantification of the waste plastic composition. The method was based on the selective dissolution of the plastics in the mixture. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

环境对改性塑料表面亲/疏水转变的作用机制

塑料制品因其质量轻、性质稳定等优点而得到广泛使用,但大部分废旧塑料未被合理回收而成为污染物,对环境造成了危害。因此,废旧塑料回收、再加工成为保护环境和资源利用的有效途径。而分离是废旧塑料能进行再加工的重要环节,目前已经发展了丰富的分离方法,其中塑料浮选法因具有工艺简单、污染少的特点而受到人们的青睐。但在塑料浮选中,其表面亲疏水性受环境的影响,该过程进一步恶化分离效果。为了避免分离过程的波动性,急需探究环境因素对亲疏水性的作用。基于此,本文选取了ABS、PC、PS三种废旧塑料,探究环境对浮选分离及表面亲疏水性基团重构的影响。结果表明：氧化改性后的ABS、PC、PS处于极性环境时,塑料可浮性基本未发生改变,接触角发生轻微浮动,表面仍保持亲水性。处于乙醇环境中,塑料可浮性上升,其接触角上升至75°左右,表面疏水性恢复速度大于极性环境。而在非极性环境中,塑料可浮性上升速度较快,表面完全恢复为未改性前的疏水性。在极性环境中,亲水基团更容易停留在表面,随着极性的减小,亲水基团逐渐迁移至本体,塑料表面恢复为疏水。因此,极性环境更有利于塑料表面保持亲水性。     

溶气浮选法分离废旧ABS / PS塑料

以分离废旧ABS/PS塑料为目标,在实验室特制的溶气浮选柱中考查了润湿剂、起泡剂、调整时间、浮选时间等因素对废旧塑料浮选行为的影响,获得了最佳浮选分离工艺条件。实验表明,采用溶气浮选技术,以单宁酸为润湿剂,在其浓度25mg/L,起泡剂松油醇浓度5mg/L、调整时间15min、浮选时间15min的条件下,可以成功地实现废旧ABS和PS塑料的浮选分离,上浮产物PS的纯度90.12%,回收率97.45%,下沉产物ABS的纯度97.24%,回收率89.38%。研究结果同时表明,要有效地克服混合塑料给浮选过程带来的不利影响,塑料颗粒间相互作用的系统研究将是该领域的重要课题。     

Selective froth flotation of PVC from PVC/PET mixtures for the plastics recycling industry

It was found that strongly alkaline solutions of sodium hydroxide are able to destroy the hydrophobicity of polyethylene terephthalate (PET) whereas the hydrophobicity of polyvinyl chloride (PVC) remains only slightly affected by these solutions. On this basis, a technology involving treatment of PET and PVC particles with alkaline solutions followed by froth flotation of PVC with nonionic surfactants has been developed and tested at a laboratory scale. In both steps of this technology, appropriate experimental conditions, such as concentration of reagents, temperature and residence time, have been optimized through a detailed examination of all these variables on the efficiency and selectivity of PVC separation from PVC/PET mixtures of varying composition. It is demonstrated that using this technology 95–100% recovery of PET and PVC can be achieved in separate products from a variety of PVC/PET mixtures.     

木塑复合材料改性研究进展

针对PE、PP、PVC以及废旧塑料和其他树脂基的木塑复合材料体系,介绍了国内外在性能改进方面取得的一些进展;展望了木塑复合材料的应用领域及市场前景。     

硫酸钡表面改性及其在PVC中的性能研究

使用γ-氨丙基三乙氧基硅烷(KH-550)、γ-缩水甘油醚氧丙基三甲氧基硅烷(KH-560)、γ-(甲基丙烯酰氧)丙基三甲氧基硅烷(KH-570)以及硬脂酸(SA)对沉淀硫酸钡(BaSO4)粉末进行表面处理,并使用接触角测试仪、管式炉和红外光谱仪对改性BaSO4进行表征。进一步将改性BaSO4添加到聚氯乙烯(PVC)中,研究了它们对PVC/BaSO4复合材料基本力学性能的影响,并分析了复合材料冲击截面的断裂面形貌。结果表明,改性BaSO4的表面接触角显著增大,红外光谱显示有基团峰出现,质量损失率明显变大,其中SA的改性效果最佳,接触角为134.5°,质量损失率为4.65%。和添加未改性BaSO4的PVC复合材料相比较而言,添加改性BaSO4的PVC复合材料的拉伸性能和撕裂性能均有所增强,硬度变化不大,其中,总体上SA的表面改性效果最佳,PVC/BaSO4复合材料的拉伸强度、撕裂强度和邵氏D硬度分别达到28.68 MPa、151.03 N/mm、70.2。复合材料断裂表面的扫描电子显微镜分析表明,经过改性的BaSO4粉末在复合材料中的分散性变得更好。     

Modeling the Relationship between Froth Bubble Size and Flotation Performance Using Image Analysis and Neural Networks

Machine vision technology now offers a viable means of monitoring and control of froth flotation systems. In this study the relationship between process conditions and the surface bubble size as well as the process performance in the batch flotation of a copper sulfide ore is discussed and modeled by neural networks. Flotation experiments are conducted at a wide range of process conditions (i.e., gas flow rate, slurry solids %, frother/collector dosage, and pH) and the froth mean bubble size along with the metallurgical parameters are determined for each run. An adaptive marker based watershed algorithm is successfully developed for segmentation of the froth images and measurement of the bubble size at different conditions. The results show that there is a strong correlation between process conditions and the froth mean bubble size, which is of great importance for control purposes. Even though the metallurgical parameters can be estimated from the froth mean bubble size alone, other froth features (i.e., froth velocity, color, and stability) are required to be measured in order to achieve more accurate predictions of the process performance.     

Application of Image Processing and Adaptive Neuro-fuzzy System for Estimation of the Metallurgical Parameters of a Flotation Process

It is a well-known fact in the literature and practice that flotation froth features are closely related to process conditions and performance. The authors have already developed some reliable algorithms for measurement of the froth surface visual parameters such as bubble size distribution, froth color, velocity and stability. Furthermore, the metallurgical parameters of a laboratory flotation cell were successfully predicted from the extracted froth features.

In this research study, the fuzzy c-mean clustering technique is utilized to classify the froth images (collected under different process conditions) based on the extracted visual characteristics. The classification of the images is actually necessary to determine the ideal froth structure and the target set-points for a machine vision control system. The results show that the captured froth images are well-classified into five categorizes on the basis of the extracted features. The correlation between the visual properties of froth (in different classes) and the metallurgical parameters is discussed and modeled by the adaptive neuro-fuzzy inference system (ANFIS). The promising results illustrate that the performance of the existing batch flotation system can be satisfactorily estimated from the measured froth characteristics. Therefore, the outputs from the current machine vision system can be inputted to a process control system.     

Froth flotation as primary treatment of flowback water: Removal of total organic carbon and prediction of kinetics

Petroleum and exploration industries employ a hydrofracking process where a large volume of water (fracturing fluid) is injected and a fraction (known as flowback water) is returned to the surface. Froth flotation is a typical process employed for the primary treatment of water. In the present work, froth flotation has been used as a pretreatment method for real flowback water sourced from the petroleum and shale gas exploration industry. In the present work, a first-principle based convective mass transfer model has been developed to describe the froth flotation performance. The resultant equation was solved analytically and compared with the numerical solution, and a parametric sensitivity analysis of the process performance was also undertaken. In addition, a correlation to estimate the flotation rate constant was proposed, thereby circumventing the need to obtain a large number of cumbersome parameters experimentally. Overall, this study proposes froth flotation as an efficient primary treatment method towards the separation of dispersed oil droplets from the flowback water and the corresponding prediction of kinetics using a first-principle based transport model.     

悬浮法聚氯乙烯生产废水处理技术应用与研究进展

近10年来,悬浮法聚氯乙烯(SPVC)生产量不断增加,但生产过程中需要大量的淡水资源,同时释放出相当数量的生产废水,对环境造成了严重威胁。因此很有必要采取有效措施进行水污染控制和水循环利用。作者首先简要介绍了悬浮法聚氯乙烯生产废水的来源及特点,并从工程应用及研究探索两个方面综述了国内外该类废水的治理现状和进展。对一些成功的技术工艺进行了较为详细的介绍,并在此基础上提出接触氧化一臭氧工艺有望成为该类废水处理及回用的主导工艺。     

Triboelectrostatic separation of pvc materials from mixed plastics for waste plastic recycling

This study covers the triboelectrostatic separation of Polyvinylchloride (PVC) materials from mixed plastics such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polystyrene (PS). The PVC material generates hazardous hydrogen chloride gas resulting from the combustion in the incinerators. The laboratory scale triboelectrostatic separation system consists of a fluidized-bed tribocharger, a separation chamber, a collection chamber and a controller. Negative and positive surface charges can be imparted to the PVC and PET particles, respectively, due to the difference of triboelectric charging series between the particles in the fluidized-bed tribocharger. They can be separated by passing through an external electric field. A highly concentrated PVC (91.9%) can be recovered with a yield of about 96.1% from the mixture of PVC and PET materials in a single stage of processing. For the removal of PVC from the two-component mixed plastics such as PVC/PET, PVC/PP, PVC/PE or PVC/PS, separation results show the recovery of 96–99% with the pure extract content in excess of 90%. The triboelectrostatic separation system using the fluidized-bed tribocharger shows the potential to be an effective method for removing PVC from mixed plastics for waste plastic recycling.     

十二烷基吗啉选择性浮选氯化钠颗粒的作用机理

通过研究十二烷基吗啉（DMP）在饱和卤水中对氯化钠颗粒的浮选行为,揭示了氯化钠颗粒通过增强体系泡沫的稳定性而提高了十二烷基吗啉的浮选性能;运用红外光谱法研究证明,DMP分子以物理作用力吸附于氯化钠颗粒表面;同时,研究了十二烷基吗啉分子在氯化钠颗粒表面的吸附行为及精光卤石颗粒与各种条件下氯化钠颗粒表面的接触角.研究结果表明,十二烷基吗啉选择性浮选分离氯化钠颗粒的作用原理是：十二烷基吗啉分子在饱和卤水介质中由于受到很强的疏水力,选择性吸附于氯化钠颗粒表面;且因精光卤石（KCl•MgCl₂•6H₂O）颗粒表面有很强的水合斥力,十二烷基吗啉分子不能吸附于精光卤石颗粒表面;因此,在浮选过程中,吸附在气泡界面的DMP分子因受到疏水作用力,使气泡吸附在氯化钠颗粒表面,氯化钠颗粒被浮选分离.     

Tween 20‐modified poly(vinyl chloride) exhibits enhanced blood‐compatibility

Poly(vinyl chloride) (PVC) resin was modified by grafting the non‐ionic surfactant poly(oxyethylene 20 sorbitan) monolaurate (Tween^® 20) using isocyanate chemistry. PVC was aminated using ethylenediamine and coupled with hexamethylene diisocyanate. Tween 20 was then reacted with the polymer, resulting in the grafting of the surfactant. The polymer modification was confirmed using infrared and X‐ray photo‐electron spectroscopy. Films of modified polymer were cast from a solution of tetrahydrofuran. The surface of films prepared from the modified polymer showed increased hydrophilicity as evidenced by contact‐angle measurements. The solid/water free energy of the modified polymer surface was nearly a quarter of the energy of the bare PVC surface. Static platelet adhesion studies using platelet‐rich plasma demonstrated significantly reduced adhesion onto a modified PVC surface compared with unmodified PVC. Data obtained demonstrate that modification of polymers with Tween 20 may be an interesting way of imparting protein‐ and cell‐repelling characteristics to them, thereby improving their blood‐compatibility. Copyright © 2005 Society of Chemical Industry     

PVC — origin,growth, and future

Application of poly(vinyl chloride) (PVC) was first described in a patent in 1913, but only after 1930 did a sustained interest in PVC arise in a number of industrial laboratories. Nowadays PVC is the second thermoplastic resin behind polyolefins with a worldwide capacity of ca. 31 million tons. In its nearly 70 year history, PVC has contributed to much progress in polymer science and technology, e. g., to emulsion and suspension polymerization, detailed analysis of polymer structure, chemistry of stabilization, plasticization, chemical modification, and plastics processing. But PVC also plays an important role in many environmental discussions on polymers, e. g. chlorine chemistry, toxicity of vinyl chloride, or waste and recycling problems. Within the time frame of 70 years, some recent developments in controlled polymerization of vinyl chloride, stabilization, modification of bulk properties and chemical and material recycling of PVC are discussed.     

Different photodegradation processes of PVC with different average degrees of polymerization

The influence of ultraviolet (UV)‐irradiation on the photodegradation mechanism of different average degrees of polymerization (DP ) of poly(vinyl) chloride (PVC) with UV‐irradiation time was investigated by viscosity‐average molecular weight determination, UV‐vis spectroscopy, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), contact angle measurement, and scanning electron microscopy (SEM). PVC films with different DP (800, 1000, 1300, 3000) were prepared by solution casting. It was carried out exposing specimens to a xenon‐arc light source with a spectral irradiance of 0.68 W/(m² ·nm) at 63°C. It was found that the photodegradation mechanism of the lower DP of PVC (DP = 1000) was different from the higher DP of PVC (DP = 3000). This was because the lower DP of PVC was a homopolymer, while the higher DP of PVC was often produced by copolymerizing with a certain quantity of crosslinking agent (e.g., DAP and DAM). UV‐vis and FTIR spectroscopy studies provided some results concerning the structure of the irradiated PVC, and the carbonyl index and C? Cl index were induced to study the process of PVC photodegradation with different DP . TGA showed that the degradation temperatures of different weight loss increased with the irradiation time. The surface morphology of the irradiated polymer films with different DP was observed by contact angle measurement and SEM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

废旧塑料分选技术

废旧塑料的回收包括 3个阶段 :收集、分选、加工或再生等步骤。只有清洁的废旧塑料才能生产高质量的产品 ,这需要有效的塑料分选方法。评述了光选、电选、风力分选、密度分选、浮选等废旧塑料分选技术 ,指出浮选在废旧塑料分选方面具备独特优势     

DTCWT-based zinc fast roughing working condition identification

The surface texture of mineral flotation froth is well acknowledged as an important index of the flotation process. The surface texture feature closely relates to the flotation working conditions and hence can be used as a visual indicator for the zinc fast roughing working condition. A novel working condition identification method based on the dual-tree complex wavelet transform (DTCWT) is proposed for process monitoring of zinc fast roughing. Three-level DTCWT is implemented to decompose the froth image into different directions and resolutions in advance, and then the energy parameter of each sub-image is extracted as the froth texture feature. Then, an improved random forest integrated classification (iRFIC) with 10-fold cross-validation model is introduced as the classifier to identify the roughing working condition, which effectively improves the shortcomings of the single model and overcomes the characteristic redundancy but achieves higher generalization performance. Extensive experiments have verified the effectiveness of the proposed method.     

汽车破碎残余物中PVC处理技术进展

汽车破碎残余物(Automobile Shredder Residues,ASR)通常定义为报废汽车(End-of-Life Vehicles,ELVs)经去污、拆解、破碎,除去金属后产生的残渣。包含塑料、橡胶、涂料、泡沫、纤维、金属等几十种物质的碎片和粉末,其中塑料最具有回收价值。ASR中含量最多的四种塑料是聚乙烯(PE)、聚丙烯(PP)、聚氯乙稀(PVC)、聚氨酯(PU)。在ASR的回收过程中,特别是热解和汽化,PVC中Cl的存在将严重影响ASR的回收。文章简要概述了ASR的特性以及国内外PVC的分离及脱氯技术研究进展。     

废旧塑料浮选分离研究进展

介绍了塑料浮选的发展历史与研究进展。根据润湿机理,塑料的选择性润湿方法主要分为吸附润湿、表面氧化、吸收润湿和Gamma浮选4类。目前发展出的浮选分离方法主要有控制液气界面张力的Gamma浮选、物理方式对塑料表面改性的物理调控浮选和润湿剂吸附的化学调控浮选3类。物理调控方法包括等离子体处理、火焰处理、臭氧氧化、颗粒调控、湿式氧化和电晕放电等技术,化学调控浮选常用润湿剂包括甲基纤维素、木质素磺酸钙、单宁酸等。最后对近10年来塑料浮选的研究进展进行综述。     

Macro-pore structure characteristics of a low-rank coal and its froth flotation fractions

A high pressure Mercury Porosimeter (M.P.) (max. oper. press: 2000 atm) and an optical microscope interfaced with a Quantimct image analyser were employed to investigate the internal macro-pore structure of froth flotation concentrates of low-rank coal. The objective of the froth flotation process is to produce a demineralized product from a pulverized low-rank feed coal suitable for use in industrial combustors as the solid component of a coal-oil mixture (COM). The effectiveness of the coal for this use is associated with a rapid rate of combustion for which a knowledge of macro-pore distribution is useful. It is also of interest to know whether the pore-size distribution of the treated coal influences in any way the froth flotation process, possibly leading to selective separation based on internal pore structure. The experimental distributions showed a bimodal configuration with maxima located at pore sizes of ≈ 10 and ≈ 5500 nm. Overall specific surface areas ranging between 3.50 and 11.80 m²/g_c are substantially higher in comparison with results from literature obtained by M.P. and N₂ adsorption at ?196 °C. M.P. hysteresis results are discussed and a low mercury entrapment of ≈ 5% of the ultimate detected porosity was observed on froth flotation tailings with an ash content approaching ≈ 77%.