HCl Cleaning Research Articles

Application of vacuum membrane distillation-Fenton oxidation process for deep purification of low-level radioactive organic wastewater

During the production of UO2 kernel for the high temperature gas-cooled nuclear reactor, a large amount of low-level radioactive organic wastewater (LLROW) containing ammonia, uranium and organic compounds are generated. The current treatment process is suffered from the production of radioactive solid wastes, low adsorption efficiency of organic matters and the frequent membrane fouling during RO process. In this study, vacuum membrane distillation (VMD)-Fenton oxidation process was developed for the deep purification of the LLROW. The process parameters were optimized and the system performance was evaluated. As a result, all major contaminates such as uranium, NH3-N, TN and COD could meet the GB8978-1996 (secondary standard) and GB/T31962-2015 (B standard) for direct discharge. The membrane fouling was also studied by membrane autopsy as well as the quantum calculation. It was found that weak hydrogen bonds were formed between PTFE membrane and contaminants while the membrane fouling could be recovered by 0.1 M HCl cleaning.

Enhancing minority carrier lifetime in Ge: Insights from HF and HCl cleaning procedures

Efficiently passivating germanium (Ge) surfaces is crucial to reduce the unwanted recombination current in high-performance devices. Chemical surface cleaning is critical to remove surface contaminants and Ge oxides, ensuring effective surface passivation after dielectric deposition. However, Ge oxides can rapidly regrow upon air exposure. To understand the surface evolution after wet cleaning, we present a comprehensive study comparing HF and HCl deoxidation steps on p-type Ge surfaces and monitor the surface as a function of air exposure time. Distinct oxide regrowth dynamics are observed: HF-treated samples exhibit swift regrowth of all Ge oxide states, whereas HCl-treated Ge surfaces exhibit a lower concentration of low degrees of oxidation and slower or no regrowth of high oxide states even after 110 min of air exposure. In addition, the presence of Ge–Cl bonds induces different oxidation dynamics compared to the Ge–OH bonds resulting from HF cleaning. This leads to varying surface electronic band structures, with HF-treated Ge exhibiting a strong positive band bending (+0.20 eV). Conversely, HCl-treated samples display a lower band curvature (+0.07 eV), mostly due to the presence of Ge–Cl bonds on the Ge surface. During air exposure, the increased GeOx coverage significantly reduces the band bending after HF, while a constant band bending is observed after HCl. Finally, these factors induce a reduction in the surface recombination velocity after wet etching. Combining both chemical and field-induced passivation, HF-treated Ge without rinsing exceeds 800 μs.

Effect of urea-based chemical cleaning on TrOCs rejection by nanofiltration membranes

Nanofiltration (NF) is an effective method for removing trace organic compounds (TrOCs) from drinking and reused water. However, chemical cleaning of NF membranes may impact their properties, leading to a decrease in TrOCs rejection. To better understand the mechanisms behind changes in membrane rejection after chemical cleaning, we investigated the changes in surface properties and TrOCs rejection of two commercial membranes (NF270 and NF90) after urea/ hydrochloric acid (HCl) cleaning, and compared them to conventional sodium hydroxide (NaOH)/HCl cleaning. The findings indicated that urea cleaning increased the membrane pore size and hydrophilicity while marginally affecting membrane crosslinking and zeta potential. Possibly due to the thicker and denser active layer of NF90, neither urea-based nor NaOH-based cleaning had a significant impact on its TrOCs rejection and permeability. In contrast, NF270 was more susceptible to chemical cleaning, and urea-based cleaning had less impact on its TrOCs rejection than NaOH-based cleaning. Although urea cleaning increased the pore size of the NF270 membrane, its pore size recovered well after HCl cleaning, resulting in good recovery of the rejection of hydrophilic neutral TrOCs. Moreover, urea cleaning had limited effects on the electrical properties of the NF270 and might enhance the hydrophilicity of the membrane, resulting in full recovery of the rejection of hydrophobic and negatively charged TrOCs after urea/HCl cleaning.

Interaction mechanisms of fouling and cleaning protocol for A/O-MBR treatment of coal⁃to⁃hydrogen wastewater

The anoxic/aerobic membrane bioreactor (A/O-MBR) was conducted to investigate pollutants removal in coal⁃to⁃hydrogen wastewater at the pilot experiment. Results showed that the system exhibited effective removal of chemical oxygen demand (∼90%), ammonia nitrogen (>95%), and total phenols (>95%). Moreover, the Extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) approach was used to predict the MBR system's membrane fouling and chemical cleaning mechanisms in the MBR system. The results indicated that the initial stage dominated membrane fouling by the acid-base (AB) interaction energy. With aggravated membrane fouling, the determinate role was the van der Waals (LW) interaction energy. Furthermore, the cleaning agent NaClO obtained the highest trans-membrane pressure recovery (104.7% of the virgin trans-membrane pressure) in CGW treatment, compared with HCl or NaOH cleaning. It was attributed to the higher LW interaction energy between foulants and the NaClO-cleaned membrane than those between foulants and the HCl-/NaOH-cleaned membrane. Meanwhile, it could effectively restrain AB interaction energy decline between them. The findings of this study confirmed successful development of A/O-MBR for bio-refractory CGW treatment with NaClO chemically enhanced backwash. It also provided an in-depth understanding on the fouling and cleaning mechanisms of the MBR system.

Interactions of high temperature H2S and HCl cleaning sorbents with biosyngas main components and testing in a pilot integrated biomass gasifier SOFC system

High temperature biosyngas cleaning is more efficient when the end user operates at elevated temperature, as in biomass gasifier solid oxide fuel cell systems. However, there is not much experience with this technology and low temperature gas cleaning is usually adopted. This paper advances current knowledge by presenting the results from the investigation of side reactions catalysed by commercially available sorbents involving biosyngas main components, and the results obtained with the pilot plant developed within the Horizon2020 project “Flexifuel-SOFC”. K2CO3, used for HCl removal, appeared catalytically active towards the water gas shift reaction. Under conditions representative of a real system, the residence time was not sufficient for the gas composition to reach thermodynamic equilibrium. ZnO–CuO, used for H2S removal, showed a catalytic activity significantly higher. Both sorbents seemed not active towards the methanation reaction. The pilot plant tests confirmed the occurrence of the WGS reaction in the HCl removal reactor. The sorbents decreased H2S and HCl below the target value of 1 ppmv for H2S and 5 ppmv for HCl. The catalytic activity of sorbents and the heat released by these reactions should be carefully considered in the design phase of high temperature gas cleaning units.

Highly sensitive and reusable ion-sensor based on functionalized graphene

Some sub-products from the industrial activity are rich in metals, very often being highly toxic to human health and to the environment. Thus, the development of real-time and ultrasensitive techniques for metals detection is relevant. Herein, we report an ion-sensitive field-effect transistor (ISFET) based on l-phenylalanine functionalized graphene that detects Na+, Co2+, and Al3+ at the nanomolar range and Cu2+ at the picomolar range. Our sensor is prepared using a simple functionalization method and is reusable after a standard HCl cleaning process. Altogether, the ISFET is a promising device for real-time detection of metal ions at low concentrations.

Production of silica gel from waste metal silica residue

Silica gel is a synthetic silica compound that can be extracted from metal silica residue by the sol–gel method. The aim of this research was the extraction of silica gel from silica metal residue presenting a methodology that optimizes the process of silica extraction and its future use in cement compounds. Extraction processes with and without HCl cleaning showed yields of 27 and 25% silica gel, respectively. This result was also confirmed in X-ray fluorescence and Fourier transform infrared spectroscopy analyzes. The thermogravimetric analysis and differential scanning calorimetry of the samples of silica gel with and without HCl cleaning in different atmospheres showed that in the oxygen atmosphere the process of mass loss occurred at lower temperatures.

Fouling characterization and aeration performance recovery of fine-pore diffusers operated for 10 years in a full-scale wastewater treatment plant

Fouling characterization and aeration performance recovery of fine-pore diffusers operated for 10 years in a full-scale wastewater treatment plant were investigated to elucidate fouling mechanisms and develop cleaning strategy. The performance decline of diffusers was observed with dynamic wet pressure increased by 3.2 times and standard oxygen transfer efficiency dropped to 73%, which contributed to 15.0% increase in total energy consumption. Oxygen-affinity, filamentous and extracellular polymeric substances secreting bacteria tended to accumulate on the diffuser surface. External (mainly biofilm growth), internal (organic and inorganic matters) and irrecoverable (mainly material aging) foulants accounted for 34.1%, 45.4% and 20.1% of total fouling, respectively. HCl cleaning failed to restore aeration efficiency because it eliminated structural support formed by inorganics, leaving organic foulants broken into smaller fragments and distributed more dispersed. NaClO showed better cleaning efficiency by effectively removing organic foulants. Sequential cleaning by NaClO and HCl, which achieved the best recovery, was recommended.

Supramolecular-Based Regenerable Coating Layer of a Thin-Film Composite Nanofiltration Membrane for Simultaneously Enhanced Desalination and Antifouling Properties.

A high-performance nanofiltration (NF) membrane with simultaneously improved desalination and antifouling properties while maintaining regeneration ability is highly desirable in water treatment. Surface modification is an effective approach to enhance the performance of NF membranes. In the present study, a multifunctional thin-film composite NF membrane (Fe-TFC) was fabricated via coating a regenerable ferric ion-tannic acid (FeIII-TA) layer on the nascent polyamide membrane surface. The Fe-TFC membrane exhibited enhanced hydrophilicity, smaller pore size, and lower negative charge compared with the control membrane. The salt rejections and selectivity of divalent to monovalent ions were greatly improved with only a slight decrease in water permeability due to the presence of the coating layer. Meanwhile, dynamic fouling tests with humic acid demonstrated that the Fe-TFC membrane possessed an enhanced antifouling property and excellent flux recovery rate. After coating, the normalized water flux and flux recovery of the Fe-TFC membrane increased from 0.02 to 0.26 and 32.1 to 76.4% at the end of five cycles of fouling tests, respectively. In addition, the resultant membrane exhibited excellent durability and stability under harsh conditions for ∼10 days. Interestingly, the fouled coating layer can be easily removed by HCl cleaning and regenerated through an in situ strategy. Consequently, the regenerated membranes presented stable antifouling properties and desalination performance after several times of regeneration. It was demonstrated that the unique feature of FeIII-TA networks enables the coating layer to act as a protective layer for the underlying polyamide membrane, leading to the high performance of the composite membrane. This study provides a new insight for surface functionalization and easy regeneration of the TFC nanofiltration membrane in water treatment technology.

Nutrient recovery from pig manure digestate using electrodialysis reversal: Membrane fouling and feasibility of long-term operation

Membrane technologies are challenged by severe membrane fouling when treating animal manure digestate due to high turbidity and high concentrations of organic and inorganic matter. In this study, a bench-scale electrodialysis reversal (EDR) was carried out to assess its feasibility for nutrient recovery from pig manure digestate. Pretreatment consisted of acidification for releasing phosphorus to the liquid phase and low-speed centrifugation for removing large particles. Results showed complete removal of NH4+ and removal of phosphate up to 84% from the feed solution, with their concentrations in the product reaching 4.2 and 0.7 g/L at a volumetric ratio of 6/2, respectively. During the semi-continuous operation, particle and chemical deposition were significantly mitigated. Despite periodical HCl cleaning, tyrosine-like and humic-like substances fouled anion-exchange membranes (AM) gradually. Nevertheless, this fouling ceased after treating the digestate at a capacity of 330 L/m2 membrane when the conductivity and ion-exchange capacity of AM decreased by 18.5% and 13.3% compared with the virgin membrane, respectively. Based on infrared spectra, these organic foulants existed in the fouling area around the membrane surface, rather than migrating deeper into the interior of the membrane. This study reveals a potential of long-term operation of EDR for treating pig manure digestate.

Phaeodactylum tricornutum derived biosilica purification for energy applications

The use of biosilica, obtained from living diatoms, for energy applications has recently shown a great promise, mainly due to the high production cost of such materials to the use of non-environmentally friendly processes. This study aims to analyze the frustule composition of Phaeodactylum tricornutum dried biomass particularly concerning the silicon percentage. To remove the organic and inorganic impurities, frustules were purified by acid cleaning, with different results dependent on the conditions applied. SEM/EDS analysis was used to observe frustules morphology and obtain the Si concentration. The treatment, consisting of HCl cleaning followed by baking process, revealed to damage the frustule structure, while the Si content reached 41.01 ± 8.80 wt% (dry weight). The selection of the most adequate method depends on the final use of the frustules and their applications.

Acid mine drainage treatment by nanofiltration: A study of membrane fouling, chemical cleaning, and membrane ageing

Abstract This study aimed to investigate the nanofiltration membrane fouling on the NF270 membrane formed during acid mine drainage (AMD) treatment, and the best chemical cleaning procedure to remove this fouling. Moreover, membrane ageing by AMD retentate alone and AMD retentate combined with periodic chemical cleaning solution was assessed. The AMD is a mining effluent with low pH, high concentrations of sulfate, and is mainly composed of dissolved inorganic compounds; its treatment by nanofiltration produces a permeate suitable for industrial reuse. AMD treatment resulted in an inorganic fouling layer, rich in aluminum, arsenic, calcium, chromium, nickel, potassium, and sodium. Among the evaluated cleaning solutions, the best cleaning agent was hydrochloric acid (HCl) at a concentration of 0.20% w/w; this concentration also provided the lowest membrane exposure to the acid. Membrane ageing reduced the NF270 membrane water permeability by 49% after 270 days of exposure to AMD, and by 45% after 270 days of exposure to AMD plus periodic HCl cleaning solution. However, the membrane selectivity to magnesium sulfate and glucose decreased less than 10% in both conditions. These results suggest that the NF270 membrane is stable during AMD treatment.

The Impact of Dummy Gate Processing on Si-Cap-Free SiGe Passivation: A Physical Characterization Study on Strained SiGe 25% and 45%

High mobility channel materials like SiGe, Ge and IIIV receive lots of interest in order to enable the continuation of Moore’s path during the upcoming technology nodes. Recently Si-cap-free SiGe passivation with the number of interface states (NIT) down to 2 1011 cm-2 have been demonstrated. [1-3] A clear correlation was established between Ge-content in the SiGe-oxide and NIT. Unfortunately no process information has been provided on how the Ge-oxide-free interlayers were obtained. In a separate study the impact of HF, HCl and SC1 cleaning solution on the SiGe surface and oxide composition was reported. [4] A comparison of SiGe Gate-All-Around (GAA) and FinFET devices using a Si-cap-free SiGe 25% passivation scheme in a replacement metal gate (RMG) integration indicate the device performance is improved by a TMAH (aq) treatment prior to SiGe interlayer formation and high-k deposition. [5] Here the formation of a SiGe wet chemical oxide will be presented. The impact of dummy gate processing on the interlayer composition is reported. Also the impact of a TMAH (aq) treatment prior to chemical oxide formation has been analyzed and will be reported. Blanket strained SiGe 25% and 45% were grown by epitaxy. The SiGe-substrate and -oxide composition were measured by angle-resolved XPS using the Si2p and Ge3d peaks. The Ge3d peak is fitted with three different compounds: elemental Ge, GeO2 and Ge-suboxide. The angle dependence lets us estimate the distribution of the different components with respect to the sample top surface. An concentration increase with increasing angle (relative to the surface normal) indicates the compound is located closer to the sample surface. And reversely a concentration increase with increasing angle indicates the compound is located deeper into the sample. A native oxide was grown on SiGe 25 and 45% by exposing the wafers to the cleanroom air for approx. 1 week. The native oxide was found to be stoichiometric or nearly stoichiometric with a uniform Ge content throughout the oxide for SiGe 25 and 45% respectively. A wet chemical oxide was grown using an ‘imec clean’ [6] having a final O3/HCl (aq) rinse. The wet chemical oxide is Ge-poor compared to the SiGe substrate. No or only a small variation in Ge content of the SiGe-oxide is seen with ARXPS. However the fraction Ge-suboxide decreases with increasing angle, indicating the Ge-suboxide are located deeper within the sample, so closer to the SiGe-oxide/SiGe-substrate interface. The Ge-content of the SiGe-substrate after wet chemical oxidation shows a weak incident-angle-dependence, indicative a limited Ge enrichment of the SiGe substrate towards the SiGe-oxide/-substrate interface. The low Ge content of the SiGe-oxide is attributed to the water solubility of GeO2. The increase in Ge-content towards the SiGe-oxide/-substrate can be (at least partially) attributed to the poor water solubility of Ge-suboxide. The small increase in Ge content of the SiGe substrate can be attributed to the thermodynamically preferred oxidation of Si over Ge. The combined impact of dummy gate deposition, spike anneal and dummy gate removal prior to SiGe interlayer formation was investigated by AR-XPS and SIMS. The temperature used during spike anneal was found to have a significant impact on the Ge-content of the SiGe-oxide formed during an O3-last imec clean. The results will be reported in detail at the conference. The impact of TMAH (aq) on the chemical oxide composition and surface roughness will also be reported. TMAH (aq) was found to improve SiGe device performance. [5] Also the interaction with the subsequent HfO2 deposition will be reported. In summary SiGe is found to behave as a non-linear combination of Si and Ge. In HF-free aqueous solutions, the SiGe oxide composition is a combination of (1) thermodynamically preferred oxidation of Si versus Ge; (2) poor water-solubility of SiO2 and/or its low solubilization rate; and (3) fast dissolution of GeO2 but slow dissolution of Ge-suboxides. [1] CH Lee et al. VLSI 2016. [2] S. Siddiqui et al. presented MRS Spring Meeting 2016. [3] CH Lee et al. IEDM 2016. [4] S.L. Heslop et al. ECS Trans 69 (2015) 287. [5] H. Mertens et al VLSI 2015. [6] M. Meuris et al. Solid State Phenom, July 1995, p. 109. Figure 1

Experimental band alignment of Ta2O5/GaN for MIS-HEMT applications

The band alignment of Ta2O5/GaN has been measured experimentally. The HCl cleaning has been found to be effective in removing oxygen from the GaN surface and was used prior to deposition of the Ta2O5 films by radio frequency magnetron sputtering. Variable angle spectroscopic ellipsometry was performed to measure the thickness, optical constants and band gap of GaN and Ta2O5/GaN samples. The valence band offset of Ta2O5/GaN was measured by X-ray photoelectron spectroscopy using Kraut's method, and found to be 0.70±0.25eV. The results provide experimental evidence of an earlier theoretical study of higher effective barrier for holes than for electrons in the Ta2O5/GaN material system.

Effect of plasma surface treatment on embedded n-contact for GaN-based blue light-emitting diodes grown on Si substrate

Unlike the finger-like n-contact that is prepared after the wafer bonding and the N-polar GaN surface roughening for GaN-based vertical structure light-emitting diodes (LEDs) grown on Si substrates, the embedded via-like n-contact is formed prior to the wafer bonding. The high temperature process of the wafer bonding often causes the electrical characteristics of the via-like embedded n-contact to degrade. In this paper, we study in detail the effect of plasma treatment of the n-GaN surface on the forward voltage of GaN-based LED grown on Si substrate. It is shown that with no plasma treatment on the n-GaN surface, the forward voltage (at 350 mA) of the 1.1 mm1.1 mm chip with a highly reflective electrode of Cr (1.1 nm)/Al is 3.43 V, which is 0.28 V higher than that of the chip with a pure Cr-based electrode. The LED forward voltages for both kinds of n-contacts can be reduced by an O2 plasma treatment on the n-GaN surface. But the LED forward voltage with a Cr/Al-based electrode is still 0.14 V higher than that of the chips with a pure Cr-based electrode. However, after an Ar plasma treatment on the n-GaN surface, the LED forward voltage with a Cr/Al-based electrode is reduced to 2.92 V, which is equal to that of the chip with a pure Cr-based electrode. The process window of the n-GaN surface after the Ar plasma treatment is broader. X-ray photoelectron spectroscopy is used to help elucidate the mechanism. It is found that Ar plasma treatment can increase the concentration of N-vacancies (VN) at the n-GaN surface. VN acts as donors, and higher VN helps improve the thermal stability of n-contact because it alleviates the degradation of the n-contact characteristics caused by the high temperature wafer bonding process. It is also found that the O content increases slightly after the Ar plasma treatment and HCl cleaning. The O atoms are mainly present in the dielectric GaOx film before the Ar plasma treatment and the HCl cleaning, and they exist almost equivalently in the conductive GaOxN1-x film and the dielectric GaOx film after Ar treatment and HCl cleaning. The conductive GaOxN1-x film and the VN donors formed during the plasma treatment can reduce the contact resistance and the LED forward voltage.

Stability of Chlorine Termination on Ge(100) and Ge(111) Surfaces

The different cleaning solution; HCl and HF solution are used to remove the suboxide and oxide component on Ge surface. The HCl cleaning results chlorine (Cl) termination on Ge surface whereas no Fluorine (F) termination was observed just after HF cleaning. The growth of Ge oxide is studied after treated with HCl cleaning on two surface orientations; (100) and (111), respectively in dry oxygen ambient and cleanroom air by spectroscopic ellipsometry (SE) and x-ray photoelectron spectroscopy (XPS). A clear step and terrace trend was observed for the oxidation growth of Ge (100) and Ge (111) in dry oxygen ambient compared to in clean room air. This trend shows the difference in surface reaction of Ge oxidation as humidity varies. The stability of chlorine termination of Ge (111) than Ge (100) explains the slower growth of oxidation in dry oxygen ambient.

Sacrificial Self-Assembled Monolayers for the Passivation of GaAs (100) Surfaces and Interfaces

The use of sacrificial self-assembled monolayers (SAMs) to prepare clean n-type GaAs (100) surfaces without band bending in vacuo is demonstrated. GaAs surface passivation using octadecanethiol SAMs after HCl cleaning is shown to lead to an enhancement of the room-temperature photoluminescence intensity. Synchrotron-radiation photoelectron spectroscopy (SRPES) finds that the interfacial oxide between GaAs and the SAM remains below the detection limit. Evidence for both Ga–S and As–S bonds at the GaAs–thiolate interface is found. The limited thermal stability of the SAM allows the desorption of the alkyl chains by in situ thermal annealing at temperatures above 180 °C, leaving S bonded to Ga behind. The resulting surface contains only a very small amount of O (0.05 ML coverage) and C (about 3% of the SAM remaining) and shows no band bending with the surface Fermi level close to the conduction band. Atomic layer deposition of Al2O3 on this surface occurs via the formation of Al–S bonds without introducing any additional band bending. This indicates that the surface preparation of n-type GaAs (100) using sacrificial octadecanethiol SAMs followed by in situ thermal removal provides a route toward GaAs/oxide interfaces without interfacial oxides and without band bending.

Mechanisms of chemical cleaning of ion exchange membranes: A case study of plant-scale electrodialysis for oily wastewater treatment

Chemical cleaning of ion exchange membranes (IEMs) in plant-scale electrodialysis (ED) for treating oily wastewater was investigated. Bench-scale ED experiments were conducted to elucidate the effects of chemical cleaning on the desalination performance of the IEMs and results showed that HCl was a more efficient cleaning agent for both cation exchange membrane (CEM) and anion exchange membrane (AEM) than NaOH. By analyzing the composition of the cleaning solutions, we suggested that NaOH could effectively remove anionic polyacrylamide (APAM) fouling on CEMs while HCl was better in removing APAM on AEMs, which can be reasonably explained by the deprotonation/protonation effects of NaOH/HCl on the electrostatic interactions between APAM molecules and IEMs. Results also demonstrated that NaOH was more effective in removing oil on IEMs; inorganic precipitations could be eliminated by HCl cleaning through double decomposition and neutralization reactions. Moreover, morphologies analysis of the cleaned IEMs along with the fouled ones were conducted, and results confirmed that the inorganic scales were mostly removed by HCl cleaning. Furthermore, X-ray diffraction (XRD) analysis of the scales revealed that the inorganic fouling on the IEMs was mainly caused by the deposition of calcite.

Role of various physical and chemical techniques for hollow fibre forward osmosis membrane cleaning

Fouling is an inevitable phenomenon with most of the water treatment systems. Similar to RO, NF and other membrane-based systems, fouling also seriously affects the performance of low-cost forward-osmosis (FO) systems and disturbs the overall efficiency of these systems, and various cleaning practices have been evaluated to restore their designed performances. This study evaluates the performance of various physical and chemical cleaning techniques for hollow fibre forward-osmosis (HFFO) membrane. HFFO membrane was subjected to various fouling conditions using different brackish groundwater qualities and model organic foulants such as alginate, humic acid and bovine serum albumin. Results indicated that physical cleaning affects differently the flux restoration according to the type of foulants (i.e. inorganic or organic) and the crossflow rates play an important role in membrane cleaning in both membrane orientation. The higher cross flow Re values at any particular area seem important for the cleaning. With hydraulic flushing, the flux performances of HFFO were recovered fully when operated in AL-FS orientation, as high shear force helps to detach all scaling layers from the surface; however, the lower shear force did not fully restore the flux for the FS membrane in AL-DS orientation. Chemical cleaning was planned for the fouled HFFO membrane, and HCl and NaOH were used in various combination sequences. It was found that HCl did not clean the membrane used for AL-DS orientation for combined fouling. HCl cleaning (at pH 2) was found to be more effective for removing inorganic scale, whereas NaOH cleaning (at pH 11) for a similar period successfully restored the flux for all the membranes used for FS with inorganic and/or organic foulants. ethylenediamine tetra acetic acid (EDTA) was also evaluated for its cleaning performances and it was found that compared to NaOH, EDTA cleaning (1mM concentration at pH 11) showed superior results in terms of membrane cleaning, as it helped to successfully restore the membrane flux in a very short time.

Cleaning of gaseous hydrogen chloride in a syngas by spray-dried potassium-based solid sorbents

There are corrosive gases such as H2S and HCl in a coal- or biomass-derived syngas. HCl can be removed by Na2CO3 or K2CO3 at hot temperatures. Hot syngas cleaning has the advantage of improving thermal efficiency. We investigated HCl removal by spray-dried potassium-based solid sorbents which were originally developed for post-combustion CO2 capture. Both fresh and spent CO2 sorbents were tested to confirm the applicability as a sorbent for HCl cleaning. Saturation chlorine sorption capacity was measured using a fixed-bed reactor at a temperatures of 300–500 °C under an ambient pressure. Both fresh and spent CO2 sorbents showed saturation chlorine sorption capacity above 15 wt%. HCl removal performance of the sorbents was investigated in a micro fluidized-bed reactor and a bench-scale bubbling fluidized-bed reactor. HCl concentration was lowered from 150–900 ppmv to less than 5 ppmv and from 130–390 ppmv to less than 1 ppmv in a micro fluidized-bed reactor and in a bench-scale bubbling fluidized-bed reactor, respectively, at 300–540 °C and 20 bar. It could be concluded that both fresh and spent spray-dried potassium-based CO2 sorbents could be utilized as a disposable HCl sorbent for hot syngas cleaning.