Triboelectrostatic Separation Research Articles

Importance of pressing temperature on protein enrichment by electrostatic separation of rapeseed press cakes

Electrostatic separation presents a promising method to concentrate protein from rapeseed. Previous research, with focus on meals neglected, the impact of de-oiling methods on the separation process and protein functionality. Therefore, this study describes the impact of processing history on the electrostatic protein enrichment from rapeseed press cakes pressed at varying temperatures on separation efficiency and hydration properties. A defatted meal was used as control. Pressing temperatures ranging from 60 to 130 °C resulted in varied oil removal, with most removal at 80 °C, yielding final oil and protein contents of 20 and 24 g/100 g dry matter, respectively. Subsequent milling and electrostatic separation produced protein fractions with protein enrichment levels of 17 %–30 % compared to the initial press cakes. Recovery of these fractions was influenced by residual oil content and heat-induced structural changes. The press cake with the least oil demonstrated protein yields comparable to rapeseed meal, recovering 0.4 g protein/g press cake protein. Hydration properties revealed that protein solubility was improved by protein enrichment. No significant effect on water holding capacity was noted due to protein enrichment. These findings demonstrate a promising approach for producing protein-rich ingredients from rapeseed press cakes using tribo-electrostatic separation.

Canola Seed Protein: Pretreatment, Extraction, Structure, Physicochemical and Functional Characteristics.

The rapid growth of the global population has led to an unprecedented demand for dietary protein. Canola seeds, being a widely utilized oil resource, generate substantial meal by-products following oil extraction. Fortunately, canola meals are rich in protein. In this present review, foremost attention is directed towards summarizing the characteristics of canola seed and canola seed protein. Afterwards, points of discussion related to pretreatment include an introduction to pulsed electric field treatment (PEF), microwave treatment (MC), and ultrasound treatment (UL). Then, the extraction method is illustrated, including alkaline extraction, isoelectric precipitation, acid precipitation, micellization (salt extraction), and dry fractionation and tribo-electrostatic separation. Finally, the structural complexity, physicochemical properties, and functional capabilities of rapeseed seeds, as well as the profound impact of various applications of rapeseed proteins, are elaborated. Through a narrative review of recent research findings, this paper aims to enhance a comprehensive understanding of the potential of canola seed protein as a valuable nutritional supplement, highlighting the pivotal role played by various extraction methods. Additionally, it sheds light on the broad spectrum of applications where canola protein demonstrates its versatility and indispensability as a resource.

Optimization of Parameters for Fluidized Bed-Type Tribo-Electrostatic Separation of End-of-Life Vehicle Waste Polymer Particles by Response Surface Methodology

End-of-life vehicles (ELVs) have resulted in huge quantities of waste vehicle polymers, the reuse of which could be effective in mitigating pollution and creating economic value. Based on the developed fluidized bed-type electrostatic separation equipment, this paper investigated the separation of two groups of commonly used mixed vehicle-use polymer particles, namely, acrylonitrile-butadiene-styrene (ABS)-polyamide (PA)-polypropylene (PP) (black) and polyethylene (PE)-PP (white)-polyvinyl chloride (PVC). First, the force of the particle in an electric field was analyzed, and the kinetic model of the particle in a high-voltage electrostatic field was established. Then, individual factor experiments were conducted on the fluidization time (T), the first-stage electrostatic separation chamber electrode voltage (U 1), the second-stage electrostatic separation chamber right field electrode voltage (U 3) and the second-stage electrostatic separation chamber left field electrode voltage (U 5) to investigate the pattern of separation results affected by each of these factors, individually. Finally, based on response surface methodology (RSM) experiments, the effects of the abovementioned three factors and their interactions on the purity of the separation of the three types of particles in each group were analyzed. The optimum separation parameters for ABS-PA-PP (black) particles in the experiments were determined as follows: T of 385 s, U 1(U 3) of −32 kV and U 5 of −37 kV. The optimum separation parameters for PE-PP (white)-PVC particles were found as follows: T of 398 s, U 1(U 3) of −40 kV and U 5 of −38 kV. The experimental validation of the abovementioned parameters obtained the purities of the three set of ABS-PA-PP (black) types of particles being 95.67%, 91.34% and 99.12%, respectively. The purities of the three set of PE-PP (white)-PVC types of particles being 96.21%, 93.20% and 86.74%.

New Vibrating-Table-Type Tribo-Electrostatic Separator for Selective Sorting of Granular Plastic Wastes

New Vibrating-Table-Type Tribo-Electrostatic Separator for Selective Sorting of Granular Plastic Wastes

Effect of moisture content on the triboelectric charging of polymers

The triboelectrostatic separation allows the sorting of granular polymers according to their contact charging characteristics. It consists in the appropriate triboelectric charging of particles, followed by their selective sorting in an electrostatic field. Exposed to a humid atmosphere, the polymer granules adsorb water moisture onto their surfaces, which modifies their charging characteristics, by improving the contact between surfaces. The present work was aimed at studying the effect of storage environmental conditions on the triboelectric charging of granular polymers in vibratory-type devices. Four granular different plastic wastes were placed in a climatic chamber and kept for 96 hours under controlled humidity, RH = 82% ± 4%, at 19 °C ± 1 °C. The measurement of the water content of the polymer granules pointed out an increase of at least 10% after 96 h of exposure to high relative humidity ambient conditions. The granules were successively charged by triboelectric effect in a vibratory device equipped with recipients in two different materials, at ambient conditions. The tribocharging efficiency was analyzed by measuring the electric charge of the granules with a Faraday pail connected to an electrometer. The thin water layer formed at the surface of the particle can explain their modified triboelectric behavior. The difference between the triboelectric charging behavior of “humid” and “normal” polymer granules depended also on the nature of the recipient of the tribocharging device.

Effect of ambient humidity on the tribo-electrostatic separation of granular plastic wastes

The separation of plastic mixtures from waste electrical and electronic equipment is an increasingly active domain of research. Several electrostatic separation processes and devices have been developed to recover plastic waste. All these processes are based on the use of the triboelectric effect to charge the plastic granules to separate them in an intense electric field. The objective of this study is to investigate the effect of ambient humidity on the efficiency of the triboelectric charging and electrostatic separation process, especially in an industrial environment where granular plastic waste may contain residual moisture due to previous processing by flotation or inappropriate storage. The experiments were carried out using a rotating-multi-cylinder tribocharger and a roll-type electrostatic separator. The samples were composed in equal proportions of either: (1) acrylonitrile butadiene styrene (ABS) and polystyrene (PS) or (2) polypropylene (PP) and polyethylene (PE), the average particle diameter of which was between 2 and 6 mm. The efficiency of the tribo-electrostatic separation was evaluated by measuring the purity and recovery of the products. The results confirm that separating (ABS + PS) and (PP + PE) mixtures is feasible. The best separation results were obtained when the materials were stored and processed at an ambient relative humidity of around 50%.

Effect of moisture content on charging and triboelectrostatic separation of coal gasification fine ash

Resource utilization of coal gasification fine ash is restricted by moisture content. Drying and dewatering are indispensable in triboelectrostatic separation. The study aims to determine the minimum required moisture content for effective gasification fine ash separation. Thereinto, experiments reveal a profound influence of moisture content on the electrical properties of gasification fine ash, subsequently impacting the separation process. With higher moisture content, the resistivity and relative dielectric constant of gasification fine ash decrease and increase, respectively. The electrical conductivity of gasification fine ash is enhanced by moisture, but the ability to retain charge is reduced, resulting in a decline in the charge-to-mass ratio. Additionally, severely agglomerated particles and poor separation will be generated by a high moisture content. Comprehensive triboelectrostatic separation experiments demonstrate that gasification fine ash with an additional moisture content of 10% could still be effectively separated yielding carbon-enriched and ash-enriched products with a LOI of 37.17% and 12.47%, respectively. Remarkably, the carbon recovery rate reaches a high of 78.44%. To a certain extent, the drying energy consumption is reduced. This paper provides significant inspiration for resource utilization of coal gasification fine ash.

The influence of ball collision charging on carbon recovery of fly ash triboelectrostatic separation

ABSTRACT The recovery of unburned carbon particles from fly ash by triboelectrostatic separation can realize energy conservation and solid waste recycling. Collision charging by metal ball has been proposed to enhance the particle charging and improve the unburned carbon recovery efficiency. It can increase the particle contact area, shorten the contact time, and improve the charge–mass ratio of particles. The charging model of ball collision was established. The collision charging process between particles and ball was simulated by CFD-DEM coupling method. The influence of ball material and gas velocity on the charge–mass ratio was studied, and that of gas velocity and voltage on separation was evaluated by experiments. The results showed that the collision charge between particles and metal ball was greater than that between particles. With the gas velocity of 30 m/s, Cu ball collisions obtained a relative maximum charge–mass ratio of 0.393nC/g and 0.275nC/g for carbon and ash particles, respectively. The reasonable experimental conditions were gas velocity of 20 m/s and voltage of 15kV. The loss on ignition of 14.3% and carbon recovery of 90.36% were obtained. Compared with the no-ball system, the ball collision improved the carbon recovery rate by 55.20%.

Occurrence Mode of Sodium in Zhundong Coal, China: Relationship to Maceral Groups

The occurrence and separation relationships of Na and maceral groups in Zhundong coals were investigated in this study. The sequential extraction results indicate that the total Na content of all samples decreased with increasing sampling depth, and the level in inertinite-enriched samples (inertinite content 81.0%–84.0%) was significantly higher than that in corresponding raw coals and vitrinite-enriched samples (vitrinite content 90%). Additionally, H2O-Na (soluble salt species) and insoluble Na (acid-insoluble residues) were found to be concentrated in the inertinite-enriched samples. In combined SEM–EDS and microscope observations, local Na enrichments were detected in all raw coal and inertinite-enriched samples except for the vitrinite-enriched samples, but only inertinite-enriched samples were found to generally have over 10 wt% of Na enrichments, all of which occurred as NaCl. Moreover, Na is mostly filled or associated with cell-filling minerals in cells of fusinite. The maceral separation and Na removal of Zhundong coal were simultaneously achieved using triboelectrostatic separation. The vitrinite content in concentrates increased up to 60%, along with a reduced Na level, while the inertinite and sodium levels were both evidently raised in tailings. The obvious positive occurrence and separation correlation between sodium and inertinite offers new insight into, and a technical reference for, the sodium removal and maceral processing of Zhundong coal.

Tribo-charging and electrostatic separation of vehicle polymer particles using a new type of fluidized bed

High value-added reuse of waste vehicle polymers can effectively alleviate the global resource shortage and environmental degradation. How to separate mixed polymers cleanly and efficiently is an important prerequisite for their reuse. In the paper, polyamide (PA)/ polypropylene (PP)/acrylonitrile-butadiene-styrene (ABS) and polyethylene (PE)/PP/polyvinylchloride (PVC) of vehicle polymer mixed particles are taken as the research objects, and the tribo-electrostatic separation of three-component mixed particles is studied using the designed double-stage device for tribo-aero-electrostatic separation. First, the optimal installation angle of the fluidized bed reflow plate is determined to be 45° by using the coupling method of computational fluid dynamics and discrete element. Second, the gas velocity for forming a fast bed and the optimal charging time for two sets of mixed particles are identified by tribo-charging experiments. The separation voltage for the two sets of mixed particles is also determined using COMSOL software. Furthermore, based on the determined parameters, two sets of tribo-electrostatic separation experiments are carried out. Results showed that the purities of PA and ABS particles are more than 91%, the purities of the PE, PP (white), and PVC particles are more than 85%. The research provides a reference for the two-stage tribo-electrostatic separation of vehicle polymer mixed particles.

Triboelectrostatic separation of coal gasification fine ash based on different mineralogical characteristics

Unburned carbon particles in coal gasification fine ash can be recycled as fuel for further combustion and ash particles are highly valuable for utilization, which can only be of secondary utilization if the two are separated. Due to the small size of gasification fine ash particles, triboelectrostatic separation has more technological advantages than traditional flotation. In this study, a first attempt has been made to separate carbon and ash particles from coal gasification fine ash by triboelectrostatic separation. It aims to investigate the feasibility of the method and to study how different mineralogical characteristics affect triboelectrostatic separation. Herein, proximate analysis, X-ray fluorescence spectroscopy analysis and X-ray diffraction analysis were adopted to investigate the fundamental nature of raw ash. The triboelectrostatic separation experiments under single conditions were conducted. Carbon enriched products with loss on ignition of 37.45% and ash enriched products with that of 10.32% were obtained whose yield was 29.81% and 32.98%, respectively. Results demonstrated the feasibility of the dry technology to separate residual carbon and ash particles in coal gasification fine ash. Furthermore, triboelectrostatic separation of coal gasification fine ash was significantly affected by differences in particle size and microtopography. Particles of small size were firstly adsorbed by plates in the high voltage electric field. The charge capacity of flake and blocky carbon particles was stronger than that of bonded and flocculated carbon particles allowing them easier to be separated.

An experimental study of triboelectrostatic particle charging behavior and its associated fundamentals

Triboelectrostatic separation is a unique dry particle separation process that has been applied to many industrial applications. However, little attention has been directed to the process of charge transfer during the particle collision and friction which is critical for the success of triboelectrostatic separation. The present study has been conducted to quantify the effects of particle size, collision speed, contact mode (collision or friction), etc. on the charge density, surface potential, morphology, etc. of quartz particles based on macroscopic triboelectrostatic charge measurements and microscopic atomic force microscopy (AFM) characterization. The macroscopic charging performance results showed that the charge to mass ratio of quartz particles depended on process parameters such as feed rate and charger rotation speed and the highest charge to mass ratio reached −56.21 μC/g. The microscopic AFM characterization data reveals that the increase in particle size and collision velocity fundamentally enhanced the triboelectrostatic charging process. The surface potential of quartz increased from −60.60 mV to −477.15 mV with increasing PVC particle size from 280 μm to 1250 μm and similar behavior was observed with increasing the collision velocity from 0.99 m/s to 2.62 m/s. The change in contact mode only changed the magnitude of charge transfer but did not change the polarity of charged particle. The process of charge transfer was accompanied with the change of surface morphology and the degree of change in surface morphology was not directly related to the amount of charge transfer.

Towards dry fractionation of soybean meal into protein and dietary fiber concentrates

Tribo-electrostatic separation of hexane-defatted soybean flour was studied to produce protein- and fiber-rich fractions. The separation was carried out under laminar and turbulent airflow rates and plate voltages ranging from ±1 to ±6.5 kV. The combination of laminar airflow rate and high plate voltage resulted in the highest yield of protein and fiber particles with modest enrichment levels. Accordingly, the soybean flour was enriched in protein from 55.3 to 58.4% and fiber from 15.4 to 19.6%, accounting for 44.4 and 16.8% protein and fiber separation efficiencies, respectively. The distribution of protein and fiber along the negatively charged electrode showed no significant difference in terms of enrichment level. Still, more protein and fiber particles accumulated at the bottom of the electrode, according to the yield results. At 7 LPM and ±6.5 kV, a direct relationship was found between protein content and the average particle size of the fractions. In contrast, a reverse relationship was found for the fiber content. • Soybean meal flour was fractionated via dry tribo-electrostatic separation. • The impact of voltage and flow rate on protein and fiber enrichment was investigated. • Laminar airflow and high voltage resulted in modest protein and fiber enrichments. • Protein and particle size of the fractions were directly correlated at laminar flow. • The protein and fiber were uniformly enriched along the negative electrode.

Tribo-electrostatic separation of yellow pea and its optimization based on milling types and screen sizes

Tribo-electrostatic separation of yellow pea and its optimization based on milling types and screen sizes

Occurrence Relationship between Sodium and Maceral Groups in Subbituminous Coal: A Case Study on Zhundong Coal and Shenfu Coal

The occurrence characteristics of sodium and its potential relationship with macerals in Zhundong coal, as well as in Shenfu coal with average sodium levels, are investigated in this study. A new five-step sequential extraction method was first conducted for determination. The occurrence status of sodium and its related macerals in samples was determined by microscope and SEM–EDS (scanning electron microscope–energy dispersive X-ray spectroscopy). Soluble sodium salts (H2O-Na) make up the primary proportion of sodium in Zhundong coal, at approximately 50%, while various sodium species are distributed in Shenfu coal with nonobvious differences. Inertinite contains more sodium than vitrinite does in both coals, and the highest enrichment degree of sodium was discovered in inertinite from Zhundong coal, which presented primarily as NaCl crystals (H2O-Na) in fusinite cells, with a local weight percentage of over 15%. More specifically, H2O-Na and insoluble Na both tend to enrich in fusinite. Additionally, it is found that maceral-rich products can be gathered using triboelectrostatic separation, and a portion of sodium can thus be removed from the coal by removing inertinite. This study may provide new insights and references regarding sodium removal from Zhundong coal.

Effect of storage at different levels of relative humidity of ambient air on the tribo-electrostatic separation of granular plastics containing brominated flame retardants

The aim of the present work is to investigate the impact of storage conditions, and more specifically of the relative humidity ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RH</i> ) of ambient air, on the triboelectric charging and electrostatic separation of granular insulating mixtures containing brominated flame retardants (BFR). The study was carried out on two model granular mixtures consisting in equal quantities of Polypropylene (PP) / Polyethylene (PE) particles either BFR-free or containing 4.7% of BFR, in mass (i.e., 40000 ppm of bromine). After being stored for 24 hours either in a climatic chamber ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RH</i> = 30 %, 50 %, 70 %, 20°C) or in ambient air ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RH</i> = 56.5% ± 1.5%; 20°C ± 2°C), the plastic particles were tribocharged in a fluidized bed device the walls of which were made of polystyrene (PS). Then they were introduced in roll type electrostatic separator to be selectively sorted. The results showed a slight difference between the different cases studied, best separation results were obtained for mixtures stored at controlled humidity of 50% or under ambient conditions <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RH</i> 55 % to 58%, at temperatures ranging between 18°C and 22°C.

Tribo-electrostatic separation of binary mixtures from polymeric and food materials

Tribo-electrostatic separation in a free-fall separator with a set of prepared mixtures from seven powder materials was investigated, five of them being polymers, whilst the other two are commonly used powders of food origin (cellulose, PTFE, barley starch, whey protein, high-density polyethylene, polyethylene and polyamide). Quantification of material content on the separated fractions attached to the electrodes led to deduce a triboelectric series, where materials are ranked in a sequential mode according to their charging behavior. The obtained material proportion in the separated fractions partially reproduces the idea that, the farther apart two materials are located in the triboelectric series, the larger the difference between their relative proportions on each electrode. The experimental work is supplemented with an estimation of the relative strength of forces acting on the charged particles as they move to the electrodes.

Study on Tribo-Electrostatic Separation for Protein Concentration of Soybean Powder

Study on Tribo-Electrostatic Separation for Protein Concentration of Soybean Powder

Separation behavior of sieved endosperm-enriched oat fractions via tribo-electrostatic approach

Endosperm-enriched oat fraction passed through 106-μm aperture size sieving of oat groats was further processed by dry and chemical-free tribo-electrostatic separation approach for protein enrichment. The sieved oat flour consisting of both bran and endosperm particles was fluidized in dry air to be tribo-charged in a polytetrafluoroethylene (PTFE) tube before being separated under an external electric field into protein-rich and protein-depleted fractions. The effects of airflow rate and electric field strength were assessed by conducting fifteen tribo-electrostatic separations at five different plate voltages of ±1, ±3, ±7, ±12, and ± 15 kV, as well as three different airflow rates of 7, 10, and 14 l per minute (LPM), providing laminar, transient, and turbulent conditions in the tribo-charger tube, respectively. All fractions attracted to the negatively charged plate (i.e., NCP fraction) were enriched in protein. However, the fractions absorbed on the positively charged plate (PCP fraction) or collected by gravity at the bottom of the separation chamber (i.e., CB fraction) were all depleted of proteins. Higher protein enrichments were observed for NCP fractions at laminar airflow rate, where the lowest yields and protein separation efficiencies were obtained. Increasing plate voltages slightly reduced the NCP fractions' protein content but significantly improved their yields and protein separation efficiencies. Therefore, a laminar airflow rate of 7 LPM and a high plate voltage of ±12 kV was selected as the best separation conditions for sieved oat flour. The SEM images of the NCP fraction obtained at 7 LPM and ± 12 kV showed the presence of bran and endosperm particles, while the PCP and CB fractions were depleted of bran particles. The full compositional analysis of the fractions produced at 7 LPM and ± 12 kV conditions showed the highest percentage of dietary fiber content in the PCP fraction. A negative correlation was observed between the protein content and mean particle size (D50) of the electrostatically separated fractions at the laminar and transient airflow rates. However, the protein-rich NCP fractions had the largest particle sizes at the turbulent airflow rate due to particle agglomeration and intense particle-particle interactions. An indirect offline approach was adapted to assess the charging behavior of all electrostatically separated fractions as functions of their protein content and particle sizes. All NCP fractions acquired higher charge density values than other fractions, which could be attributed to their higher protein contents. An online tribo-charge analysis method should be developed to assess the particle-particle interactions in the tribo-charger tube during electrostatic separation.

Triboelectrostatic charging behavior of pulse particles in a vortex flow tribocharger

Triboelectrostatic separation (TES) has shown its great potential in dry fractionation of food ingredients. The principle of the TES technique is straightforward, i.e., charging particles through interactions of particle–particle and/or particle–wall of the contact material, followed by the effect of an electric field. However, optimization of TES efficiency is complex due to obscure understandings, unknowns, and inconsistencies in the charging mechanism between the tribocharger and the agro-food materials. To broaden the design and applications of the TES technique and shed some light on the charging mechanism, experiments were conducted in a vortex flow tribocharger made of three different materials (Copper, Stainless Steel, and PTFE) to investigate the chargeability of five type of selected pulses particles. A Faraday cup measurement system was applied to measure the electric charge of the particles collected at the core and wall regions of the tribocharger. The charges of the pulse particles induced by the vibratory feeder were also measured to verify the chargeability of the particles. Ideal charging material was suggested by comparing the specific charge of particles using the three vessels. A simple “wave propagation” mode based on the vortex flow dynamics has been proposed with an attempt to explore the role of particle–particle and particle–wall interactions on the triboelectrostatic charging.