Slurry Filtration Research Articles

Modeling of pharmaceutical filtration and continuous integrated crystallization-filtration processes

As continuous manufacturing is evolving in the pharmaceutical industry, continuous filtration has emerged as a bottleneck for connecting the crystallization of the active pharmaceutical ingredient with the formulation of the final drug product. This work aims the modeling of filtration to improve the understanding of the process, to support the development of continuous filtration methodologies, and to aid the integration of crystallization and filtration. The presented model utilizes the generalized form of Darcy’s law together with the calculation of the cake porosity and specific cake resistance based on the full crystal size distribution (CSD) of the slurry, without the need for experimental filtration data. The model is applied the first time for the dynamic simulation of an automated batch- type continuous filtration, which is also integrated with a population balance model of crystallization. The effect of the slurry properties (solid concentration, CSD) and the crystallization and filtration process parameters (crystallization temperature, flow rates, filter pressure difference, carousel rotation time) on the specific cake resistance, filtration time and residual moisture content are determined. It is concluded that continuous filtration facilitates the filtration of slurries with bad filterability through the modification of the rotation time and provides an opportunity to control the filtration when connected to a continuous crystallization. The simulation results show good agreement with real integrated continuous crystallization and filtration experiments of acetylsalicylic acid. The presented methodology could be used for both batch Nutsche filtration and continuous filtration to predict filterability and for optimization, risk analysis and control purposes.

Study on filtration process of geotextile with LBM-DEM-DLVO coupling method

The method of filtering and dewatering waste slurry using geotextiles has been widely used in recent years. It is important to adopt suitable geotextiles to get a high dewatering rate and a high retention performance. In view of the unclear influence of the geotextile properties on the cake and the unclear soil particle retention mechanism in geotextiles, this paper uses the Lattice Boltzmann method-Discrete Element method-DLVO (LBM-DEM-DLVO) coupling method to simulate the mesoscopic process of slurry filtration process using geotextiles. The numerical results show that the nature of the geotextile does not affect the hydraulic conductivity of the cake. And the retention mechanism for soil particles being trapped inside geotextile was proposed. The mechanism is related to the relative relationship between the interaction force between the geotextile fiber and the soil particle Finter and the drag force of the soil particle Fdy in the geotextile. The dimensionless ratio αsl=Finter/(Fdy+G) was proposed to quantify this retention mechanism; the smaller αsl is, the greater the probability that the geotextile will lose particles. When αsl ≥ 1.04, the geotextile does not lose particles. According to these results, some suggestions of geotextiles for dewatering slurry were proposed.

Development of mathematical models to control the technological properties of cement slurries

Oil and gas producing enterprises are making increasingly high demands on well casing quality, including the actual process of injection and displacement of cement slurry, taking into account requirements for the annular cement level, eliminating possible hydraulic fracturing, with developing a hydraulic cementing program. It is necessary to prevent deep invasion of cement slurry filtrate into the formation to exclude bridging of productive layers. It is impossible to fulfill all these requirements at the same time without application of modifying additives; complex cement compositions are being developed and applied more often. Furthermore, need to adjust cement slurries recipes appears for almost every particular well.
 In order to select and justify cement slurries recipes and their prompt adjustment, taking into account requirements of well construction project, as well as geological and technical conditions for cementing casing strings, mathematical models of the main technological properties of cement slurries for cementing production casing strings in the Perm Region were developed. Analysis of the effect of polycarboxylic plasticizer (Pl) and a filtration reducer (fluid loss additive) based on hydroxyethyl cellulose (FR) on plastic viscosity (V), spreadability (S) and filtration (F) of cement slurries is conducted. Development of mathematical models is performed according to more than 90 measurements.

Tunable Dewatering Behavior of Montmorillonite Suspension by Adjusting Solution pH and Electrolyte Concentration

Montmorillonite is always a troublemaker for the dewatering in coal processing since its existence can decrease the rates of sedimentation and filtration of coal slurry. To eliminate the adverse effect of montmorillonite, adjusting the slurry pH and adding electrolytes are always the key methods. However, the underlying mechanism still needs to be further studied. The dewatering of Na-montmorillonite (Na-Mt) suspensions has been studied as a function of NaCl concentration (10−3, 10−2, and 10−1 M) at different pH values (6.0, 7.7, 8.1, 9.2). The point of zero charge of edge surface of Na-Mt (pHPZC,edge) appeared at the pH value of 6.8. The sedimentation and rheology experiments described the coagulation and flow behaviors of Na-Mt suspensions, respectively. The Na-Mt suspension coagulated spontaneously at low salt concentration with the pH ~ 6.0. For the pH > pHPZC,edge, the height of the sediment bed reduced and apparent viscosity increased with the increase of the electrolyte concentration. The filtration properties were evaluated on the basis of Darcy’s law. The obtained result clearly demonstrated that the filtration rate was accelerated with the increase of pH and electrolyte concentration. The modes of particle association and its effect on filtration performance were discussed. Moreover, a comparison with related results from the literature was performed. At pH ~ 6 and low electrolyte concentration, the positively charged Edge surfaces and negatively charged Face surfaces coagulate rapidly to form a sealed structure by electrostatic attraction. Furthermore, inside this sealed structure, the water molecules cannot be removed in the filtration process easily. However, by increasing the electrolyte concentration at pH > pHPZC,edge, the gradually formed Face/Face structure increases the filtration rate sharply because of the inhibiting effect of the electric double layer (EDL) and the osmotic expansion. Therefore, adjusting solution conditions of the aqueous suspension to tune the particle coagulation behavior is one of the effective methods to solve the problem of montmorillonite dewatering.

Optimization of starch isolation process for sweet potato and characterization of the prepared starch

The study was conducted to standardize the parameters of centrifugation method of starch isolation for sweet potato to yield better quality starch. The effects of solid-to-solvent ratio in slurry-making, numbers of blending, slurry filtration and starch washings were studied for obtaining maximum yield and purity of starch with desired color and amylose content. The goal of the study was to develop a suitable process for small scale/on-farm processing of sweet potato for preparation of starch. A widely grown pink-skinned cream fleshed cultivar (Kanjangad) was used for the experiments. The studied parameters were slurry making solid-to-solvent ratio (1:2, 1:3 and 1:4), number of blendings (1 and 2 times), number of slurry filtration water washings (2, 3 and 4 times) and starch washings (2, 3 and 4 times). The study showed that the starch yield, purity, color and amylose were influenced by altering the starch isolation procedures. The solid-to-solvent ratio of 1:2 in the starch isolation process yielded the best results. Also, the increase in number of blendings degraded the purity, amylose and color of starch. The optimal process was slurry making at 1:2 solid-to-solvent ratio and once blending, slurry filtration washing for 2 times and starch washing for 2 times. Accordingly, the starch yield, purity, amylose, and L, a and b values were 13.967 ± 1.135%, 80.640 ± 1.139%, 29.220 ± 0.759%, and 57.88 ± 2.982, 0.386 ± 0.204, and 2.68 ± 0.127, respectively. The prepared starch was characterized for chemical composition, water activity, paste clarity, swelling power, water solubility index, pasting property and granule size and morphology. The study suggested that the prepared starch was suitable for food uses.

Adsorption interaction between cement hydrates minerals with fluid loss additive investigated by fluorescence technique

The mechanism of synthetic polymer fluid loss additive (FLA) was based on adsorption of FLA on the surface of hydrating cement particles and the formation of a complex network structure, resulting in decline of cement slurry filtrate. However, due to the complexity of early hydration environment of cement slurry, there was lack of effective and intuitive way to characterize the adsorption interaction between FLA and cement particles. In this study we described our quest in furthering understanding of the adsorption action of fluid loss additive on the cement minerals. By fluorescence staining technique (combined polymer additives with organic fluorescent dyes), we observed that the skin of the hydrated particles was coated with dyed polymer, which led to a successful fluid loss additive. More importantly, the analysis of the fluorescence intensity of luminous polymer in cement pore solution distinguished the respective adsorption capacity of various admixtures (dyed and undyed) on the surface of the cement particles, so as to solve the problem of the traditional method in characterizing the competitive adsorption between polymers, thus gave a convenient way to analyze the interaction mechanism between polymer admixture and cement particles from the theory and technology.

Development and experimental study on environmental slurry for slurry shield tunneling

Abstract Slurry shield is widely used in undersea and cross-river tunnels. The wide use of slurry shield leads to a lot of wasted excavated slurries. At present, most of the slurries are consisted of clay, bentonite, water and carboxymethyl cellulose (CMC), which makes slurries difficult to degrade and pollutes the environment. Biodegradable pregelatinized starch (PGS), harmless to the environment, was found to utilize its network structure in solutions to effectively decrease API filtration and increase Russian funnel viscosity of slurries. The effects of different PGS content on the variations in the properties of slurry were studied by experiments on mixing proportions in slurries. The filtration test of PGS slurries with a specific mixing proportion in medium-coarse sand strata was performed. By measuring the filter loss and the variation in excess static pore water pressure during the test process, whether the slurry effectively filled the strata pores and provided support pressure could be evaluated. The experimental results showed that adding 0.3% PGS by total weight to a slurry with a 0.0833 mass mixing proportion of bentonite to tap water performed good fluidity and control of water loss, and formed filter cake with a thickness of 3 mm. Based on the results from airtightness tests, the airtight pressure of the above filter cake is 0.12 MPa, and, correspondingly, the airtight time is approximately 6000 s. Thus, it is conceivable to use PGS for slurry preparation during normal tunneling.

Pore structure and permeability of filter cake in coal slurry filtration

ABSTRACT The dewatering performance is dependent on the understanding of the pore structure and permeability of the filter cake in coal slurry filtration. In this paper, filter cakes were prepared from three different coal samples under the filtration pressure of 0.6 MPa with different filtration times, and the pore distribution and pore complexity of filter cakes were investigated using image processing technology and fractal theory, and the calculation of permeability of filter cakes were carried out on the basis of Darcy’s law. With an increase in filtration time, the filter cake is characterized by smaller pore diameter and porosity, narrower pore diameter distribution, and greater fractal dimension. The relationship between the permeability of filter cake and its thickness in filtration process obeys first-order exponential decay, and it could be expressed by . The critical thickness of filter cake is proposed and calculated using the maximum curvature point of K(Lc) curve, which provides theoretical support for achieving high-efficiency filtration of coal slurry.

Slurry filtration process and filter cake formation during shield tunnelling: Insight from coupled CFD-DEM simulations of slurry filtration column test

The slurry infiltration process plays a crucial role in the slurry shield tunneling process, during which a filter cake is expected to form on the tunnel face to transmit the support pressure. This paper proposed a coupled computational fluid dynamics (CFD)-discrete element method (DEM) numerical approach to investigate the slurry infiltration and filter cake formation by modeling the slurry filtration column test, which incorporates the particles, fluid phase, and their interactions. The Simplified Johnson-Kendall-Roberts (SJKR) model was employed to consider the cohesion effect between slurry particles. The validity of the current approach was verified based on the Kozeny-Carman Equation modified by Ergun (1952). The slurry filtration process was divided into four stages with different characteristics of filter cake porosity and pressure drop. Influences of some key model parameters including externally-applied pressure, friction coefficient and cohesion energy density on filter cake formation were investigated and the underlying mechanisms were explored. The law of pressure variation within the filter cake was proposed. A linear relationship between pressure drop ratio and porosity of filter cake was established, which will be useful for predicting the effectiveness of support pressure transmission due to slurry filtration.

Self-healing cement composite: Amine- and ammonium-based pH-sensitive superabsorbent polymers

Poor zonal isolation due to microcracks in cement sheath is a common problem that affects oil and gas exploration and also impacts the environment. In this study, pH-sensitive superabsorbent polymers (SAPs) have been successfully synthesized through copolymerization of 2-(Dimethylamino)ethyl methacrylate (DMAEMA) and acryloyloxyethyltrimethyl ammonium chloride (DAC) to achieve self-healing of microcracks in cement sheath. The chemical structure of p(DMAEMA-co-DAC) SAP was characterized using Fourier transform infrared (FTIR) spectroscopy. Water absorption tests determined the effect of cross-linker dosage and DMAEMA/DAC molar ratio on their water absorption rate (WAR). pH-sensitive tests showed they absorbed considerable water in neutral and weak alkaline solutions but little water in strong alkaline solutions. In addition, the WARs were quite small in high concentration calcium chloride solutions. The WARs in distilled water reduced after they were processed in cement slurry filtrate (CSF) due to hydrolysis of ester groups and the crosslinking effect of Ca2+ ions. Additionally, the SAP showed good compatibility with the cement slurry. It had little impact on the thickening time, rheological property, fluid loss, and early compressive strength of cement slurry/stone. Eventually, sealing pressure test results indicated the self-healing properties of p(DMAEMA-co-DAC) SAP-modified oil well cement. Using a 2 wt.% SAP addition, microcracks up to 166 μm can be sealed.

Experimental Study on the Effect of Cation Exchange Capacity on Slurry Properties

The slurry was prepared by pre-hydration method in this study. The relationship between the content of bentonite in slurry and its cation exchange capacity was studied by changing the content of bentonite. After the density, funnel viscosity, filtrate volume and rheological properties of slurry were tested, the influence of cation exchange capacity on slurry performance and filter-cake quality was analyzed. The results showed that: When the cation exchange capacity of slurry is small, with the increase of cation exchange capacity, the funnel viscosity, apparent viscosity and plastic viscosity of slurry increase significantly, the filtrate volume decreases gradually, and the overall performance improves significantly, which can effectively form filter cake and maintain the stability of excavation surface; while when the cation exchange capacity exceeds a certain value, the funnel viscosity, apparent viscosity and plastic viscosity of slurry increase significantly. With the increase of cation exchange capacity, the filtrate volume and viscosity of the slurry still increase, and the filter cake performance tends to be stable, but its overall performance does not rise but fall. Considering the influence of cation exchange capacity on the slurry performance parameters, when the cation exchange capacity of the slurry is controlled around 7.58 i.e. the solid phase content is between 6% and 7%, the slurry filtrate volume is relatively small, and it is easy to form thin and compact filter cake with its best comprehensive performance.

The effect of pH adjustment on the properties and pressure filtration characteristics of bauxite residue slurries

The influence of the slurry pH on the characteristics of a topical unit operation, pressure filtration of bauxite residue slurries, was investigated in this experimental study. The primary aim of pH adjustment is to precipitate aluminate off from the liquid phase and to facilitate safe disposal of the residue. In the investigated cases, pH adjustment was performed with hydrochloric acid. The experiments were carried out by using two types of pressure filters, a Nutsche filter unit used for the acquisition of average filtration data, and a piston press used for measuring local cake characteristics. The Nutsche filter was used to separate the bauxite residue slurry with a pH of 13.3 and 11.0 at three different filtration pressures (300, 450 and 600 kPa), while the piston press was operated under a constant filtration pressure of 1200 kPa and with a wider pH range (13.3, 11.0 and 7.0). The average particle/agglomerate size increased as the pH was reduced, however, the width of particle size distribution increased somewhat as well when the pH was adjusted to 7.0. Based on the average cake properties, it could be concluded that the specific cake resistance and cake compressibility index increased, while cake solidosity decreased as the slurry pH was reduced from 13.3 to 11.0. The final average solidosity (at 300 kPa) decreased from 0.43 to 0.31 when the pH was adjusted from 13.3 to 11.0. The local filtration properties also showed that the cake became more compressible and the structure of the cake more porous as a consequence of pH reduction. The local hydrostatic pressure measurements indicated that the expression rate of the cakes was decreased for filter cakes formed from a slurry with a lower pH level (pH 11 and 7 compared to a pH of 13.3).

The use of zeolite-based additives for immobilising iron during pressure filtration of coal refuse slurry

Pressure filtration of coal refuse slurry has the potential to provide a concentrated solids stream that can be stacked, thereby offering multiple environmental benefits. However, potential leachates from the solids stream can impact the environment. In that context, this study performed preliminary investigations of the application of zeolite-based additives to adsorb metals leaching from coal refuse slurry at low pH. Additives were added to the coal refuse slurry, which was filtered using bench- and lab-scale pressure filtration units. Results indicated that the overall filtrate flux and cake moisture characteristics were not significantly affected by the addition of additives up to 20% (by weight of solids). It was shown that adsorption as high as 80% was achieved by using the additives to capture iron. It was concluded that the finer additive with less silicon content was more effective in capturing iron. The results showed that the thickener feed stream leached out less iron than the thickener underflow stream. The adsorption process was not significantly affected by slight variations in initial iron concentration in the solution. The use of lower pH water on the filter cakes treated with the additive showed minimal release of iron and manganese into the aqueous phase.

Synthesis of pH-sensitive water and oil dual-absorption material using microemulsion polymerization process

ABSTRACTpH-sensitive water and oil dual-absorption material (WODAM) has been successfully synthesized through microemulsion polymerization. Firstly, microemulsions prepared with monomers were analyzed by pseudo-ternary phase diagram. In addition, conductivities of microemulsions were tested to identify microemulsion types. Meanwhile, the factors that affected microemulsion types were analyzed. Then WODAMs were prepared, and the chemical structure was characterized using Fourier transform infrared (FTIR) spectroscopy. Liquid absorption tests indicated that both monomer ratio and microstructure of WODAMs had influences on their water absorption rate (WAR) and oil absorption rate (OAR). In addition, pH sensitivity tests showed that WODAM absorbed much water in neutral and weak alkaline solutions, but little water in strong alkaline solutions. What’s more, liquid absorption tests in cement slurry filtrate (CSF) showed that WODAM was applied to oil well cement. This paper prepared a new self-healing agent, and is of great significance to realize self-healing cement in complex downhole condition.

Reusable Floating Beads with Immobilized Xylose-Fermenting Yeast Cells for Simultaneous Saccharification and Fermentation of Lime-Pretreated Rice Straw.

Novel bioreactor beads for simultaneous saccharification and fermentation (SSF) of lime-pretreated rice straw (RS) into ethanol were prepared. Genetically modified Saccharomyces cerevisiae cells expressing genes encoding xylose reductase, xylitol dehydrogenase, and xylulokinase were immobilized in calcium alginate beads containing inorganic lightweight filler particles to reduce specific gravity. For SSF experiments, the beads were floated in slurry composed of lime-pretreated RS and enzymes and incubated under CO2 atmosphere to reduce the pH for saccharification and fermentation. Following this reaction, beads were readily picked up from the upper part of the slurry and were directly transferred to the next vessel with slurry. After 240 h of incubation, ethanol production by the beads was equivalent to that by free cells, a trend that was repeated in nine additional runs, with slightly improved ethanol yields. Slurry with pre-saccharified lime-pretreated RS was subjected to SSF with floating beads for 168 h. Although higher cell concentrations in beads resulted in more rapid initial ethanol production rates, with negligible diauxic behavior for glucose and xylose utilization, no improvement in the ethanol yield was observed. A fermentor-scale SSF experiment with floating beads was successfully performed twice, with repeated use of the beads, resulting in the production of 40.0 and 39.7 g/L ethanol. There was no decomposition of the beads during agitation at 60 rpm. Thus, this bioreactor enables reuse of yeast cells for efficient ethanol production by SSF of lignocellulosic feedstock, without the need for instruments for centrifugation or filtration of whole slurry.

Organic amendment-driven removal and speciation of metals using wormwood in two contrasting soils near an abandoned copper mine

To test the hypothesis that humic acid (HA), anaerobically digested pig slurry filtrate (APS), and their combination would differently affect the chemical speciation and extractability of metals (cadmium, copper, and zinc) and their uptake by plants, we conducted a pot experiment using wormwood in two texturally contrasting soils (sandy loam and clay loam) collected from a field near an abandoned Cu mine. Four treatments were laid out: HA at 23.5 g kg−1 (HA), APS at 330 mL kg−1 (APS), HA at 23.5 g kg−1 and APS at 330 mL kg−1 (HA + APS), and a control. Each treatment affected the chemical speciation and mobility of the metals, and thereby resulting in variable patterns of plant biomass yield and metal uptake. The APS supported plant growth by increasing nutrient availability. HA supported or hindered plant growth by impacting the soil’s water and nutrient retention capacity and aeration, in a soil texture-dependent manner, while consistently enhancing the immobilization of heavy metals. Temporal increases in whole-plant dry matter yield and metal accumulation suggested that the plants were capable of metal hyperaccumulation. The results were discussed in terms of the mobility of metals and plant growth and corroborated by the 15N recovery of soil- and plant-N pools under H and HS treatments. Therefore, for effective phytoremediation of polluted soils, an appropriate combination of plant growth promoters (APS) and chelating agents (HA) should be predetermined at the site where chemical stabilization of pollutants is desired.

Improvement of the filtration characteristics of calcite slurry by hydrocyclone classification

Hydrocyclones are used in the classification of solids for instance in the mining and minerals processing industries for modifying the particle size distribution of solids, as well as for ore concentration purposes. Improvement in the filtration properties of the slurry is usually achieved as a result of the classification process when only the underflow is evaluated, owing to the coarse and narrow particle size distribution. However, overall comparisons of the filtration properties incorporating filtration of both the underflow and overflow streams have not been discussed a lot in the literature. The objective of this study is to investigate hydrocyclone classification of a calcite slurry, to evaluate the resulting pressure filtration properties of the underflow and overflow streams, and to compare the required total filtration areas for a constant solids production capacity. The results show that the average specific cake resistance depended primarily on the fine particle content of the slurry, and therefore the Kozeny-Carman equation was not suitable for the prediction of the specific cake resistance. The specific resistances of feed and underflow filter cakes were underestimated consistently. Wide particle size distribution was one of the most apparent factors reducing cake porosity. The main outcome of the comparison of the required filtration areas was that a low specific cake resistance and high solids concentration of the underflow caused the total area requirement to decrease almost in all cases, compared to the area required for the filtration of the feed slurry. Moreover, as high as 99% reduction in the total filtration area, compared to the feed slurry, could be achieved by filtering only the underflow streams, omitting the dewatering of the overflow streams. In the light of the promising results of the study, the incorporation of a classification step prior to filtration should be investigated further, e.g. in tailings treatment applications.

Effects of cake thickness and pressure on the filtration of coal refuse slurry

The effects of pressure and cake thickness were studied using a split-plot design for pressure filtration of a fine refuse slurry obtained from a bituminous coal preparation facility. Pressure filtration offers the potential to significantly reduce the moisture content of the fine refuse stream with the addition of little to no flocculants, thereby minimizing the volume of refuse stored in impoundments and providing a recycle water stream for use within the plant. Experimental results showed that the final cake moisture decreased with increase in pressure and decrease in cake thickness. In addition, specific cake resistances calculated for the various tests indicated an increasing trend with increasing pressure and decreasing cake thickness. With increase in cake thickness, an increase in cake moisture and the weight of solids deposited in the cake was observed. An ANOVA analysis indicated that both cake thickness and pressure significantly affected the cake moisture, while only cake thickness statistically influenced the weight of solids in the cake. A regression model was developed with an R2 value of about 0.99 to relate cake thickness, the single largest statistically significant factor, with the weight of solids in the cake. Filter capacities were calculated in terms of the solids deposited per unit time based on a product specification of 25 percent cake moisture, and it was observed that the thinnest cake had the highest filter capacity.

Influence of clays on fine particle filtration

Abstract Filtration of fine particle slurries is known to be inefficient in most plant operations and the problem is exacerbated by the presence of even small quantities of clay minerals. This paper discusses the influence of the commonly encountered clay types, bentonite and kaolin, in the filtration of a pyritic gold ore and how the adverse effects can be mitigated by the addition of Ca2 + ions and a hydrophobic reagent respectively, depending on the clay type. The presence of both kaolin and bentonite clays resulted in increasing specific cake resistance, filter medium resistance and final cake moisture content while effects of bentonite clay being more detrimental. The addition of hydrophobic reagent DAH (dodecylamine hydrochloride) improved the filtration rate of kaolin-containing ore. The moisture content of the filter cake was also reduced. By contrast, in the case of the bentonite-containing ore, the presence of DAH did not affect the filtration rate and the moisture content. Filtration of the bentonite-containing ore was significantly improved with the addition of Ca2 + ions.

Cement slurry resistance to chemical aggressiveness of carbon capture and storage (CCS) method

Nowadays, scientists from all over the world are focused on environmental issues connected with the greenhouse gases. The carbon dioxide is one of those gases. Therefore, researches are carried out to limit the emission or utilization the already ones. The aim of laboratory research was to find additives and admixtures resistant to CO2 presence and at the same time, able to modify rheological parameters of fresh cement slurry, as it is desirable during cementing of the wellbore. Moreover, research included the effect of newly synthesized polymers on the cement parameters. Laboratory research included filtration of the cement slurry, rheological parameters – Yield point, mechanical properties of hardened cement slurry obtained from hydraulic press and photographs of changes in mineralogical structure of cement from the electron microscope. The research was divided into two parts. The first one was based on the cement mixtures with commonly used superplastifier (SPL). In the second one, the SPL was replaced with newly synthesized polymer.