Efficient removal of aromatic sulfonates from wastewater by a recyclable polymer: 2-naphthalene sulfonate as a representative pollutant

As a family of hydrophobic ionizable organic compounds, aromatic sulfonates can be present at high levels in industrial wastewaters. They tend to exist as anions over a wide range of pH and cannot be effectively trapped by conventional adsorbents. In the current study, a recyclable acrylic ester polymer (NDA-801) was synthesized for effective removal of aromatic sulfonates from wastewater of high acidity (e.g., pH < 1) and inorganic salts (e.g., approximately 5-10% Na2SO4 in mass), for which sodium 2-naphthalene sulfonate (2-NS) was chosen as a representative target contaminant 2-NS uptake onto NDA-801 increased with the increasing acidity of the solution. The zeta potential of NDA-801 measured at different pH levels as well as batch 2-NS adsorption from methanol/water binary systems demonstrated the favorable roles of electrostatic and hydrophobic interaction in 2-NS adsorption. As compared to a granular activated carbon GAC-1, NDA-801 exhibited much higher removal efficiency and capacity of 2-NS in fixed-bed adsorption. Moreover, the exhausted NDA-801 beads by 2-NS can be completely regenerated by water wash for repeated use, which is more economically desirable than by other regenerants, such as NaOH solution. Continuous column adsorption-regeneration cycles indicated negligible capacity loss of NDA-801 during operation and further validated its feasibility for potential application in associated wastewater treatment.     

Characterization of hydrophobic hypercrosslinked polymer as an adsorbent for removal of chlorinated volatile organic compounds

A hydrophobic hypercrosslinked polymer with poly (4-tert-butylstyrene-styrene-divinylbenzene) matrix (LC-1) was prepared as adsorbent for the removal of volatile organic compounds from gas streams. The content of oxygen-containing functional groups of LC-1 was about one-fourth that of commercial hypercrosslinked polymeric adsorbent (NDA-201). The results of the water vapor adsorption experiment indicated that LC-1 had a more hydrophobic surface than NDA-201. Three chlorinated volatile organic compounds (trichloroethylene, trichloromethane, and 1, 2-dichloroethane) were used to investigate the adsorption characteristics of LC-1 under dry and humid conditions. Equilibrium adsorption data in dry streams showed that LC-1 had good adsorption abilities for three chlorinated VOCs due to its abundant micropore structure. Moreover, the presence of water vapor in the gas stream had negligible effect on breakthrough time of three chlorinated VOCs adsorption onto LC-1 when values of relative humidity were equal to or below 50%; the breakthrough time of three chlorinated VOCs decreased less than 11% even if the relative humidity was 90%. Taken together, it is expected that LC-1 would be a promising adsorbent for the removal of VOCs vapor from the humid gas streams.     

Sorption of Ethyl Butyrate and Octanal Constituents of Orange Essence by Polymeric Adsorbents

Sorption characteristics, rates and capacities of polymeric adsorbents (XAD-4, XAD-7, XAD-16, Duolite ES-865, Duolite S-761, Porapak-Q and XUS-43436) for ethyl butyrate and octanal were determined using model solutions. Sorption of these two principal components of aqueous orange essence, was evaluated utilizing the Freundlich isotherm model. Breakthrough curves were determined using XAD-16 as adsorbent. The capacity of XAD-16 for ethyl butyrate in the column system was 426±212 mg/g. There was no column breakthrough for octanal even after 130 bed volumes. Most (91.4%) of the adsorbed ethyl butyrate was eluted from XAD-16 resin by 95% ethanol elution. Recovery of adsorbed octanal from the resin was 66.4%.     

PA、H103及XAD-4树脂在茶多酚吸附工艺中的特性研究

本文主要研究了PA、H103及XAD-4树脂在茶多酚吸附分离体系中的吸附热力学特性及吸附动力学特性。热力学研究表明,三种吸附剂的吸附等温线都属于优惠型的吸附等温线,并可以用Langmiur 方程来描述,且与Langmiur方程高度相关;动力学特性研究表明,PA和H103树脂为中速吸附型的吸附剂,XAD-4为慢速吸附型的吸附剂。PA、H103及XAD-4树脂的吸附平衡速率常数依次为KPA=1.461h-1,KH103=1.198h-1,KXAD-4=0.498h-1。     

The use of different adsorbents for selective removal of compounds from olive residue oil miscella

The selective removal of several impurities from a solution of crude olive residue oil in n-hexane (miscella) using batch adsorption by different materials, used separately or in sequence, was investigated. The following adsorbents were tested: activated diatomaceous earths, powdered activated carbon and synthetic neutral resins ("Amberlite XAD-4, XAD-7, XAD-16). The adsorption efficiency of every group of compounds depended on the adsorbent and the ratio (amount of adsorbent/amount of oil) used. The activated earths and carbon were very much more effective in the adsorption of the compounds from the miscella than the resins. Results were similar for every resin tested. An effective removal of green pigments (chlorophylls and pheophytins) and carotenoids was achieved with every adsorbent tested. With respect to the adsorption of conjugated hydroperoxides (HP), a removal of 50-60% was attained with activated carbon and earths, in contrast to a 20% removal by the resins. For the final oxidation products (FOP), a 60% removal was observed with powdered carbon, 20-30% with earths and 20% with resins. A removal of 20% of free fatty acids (FFA) by activated earths or powdered carbon and 40% by the resins was observed. When the adsorbents were used in sequence (carbon or earths followed by XAD-7 resin), the resin was able to adsorb the remaining FFA, HP and FOP.     

沙棘果汁树脂降酸工艺研究

研究阴离子交换树脂降低沙棘果汁含酸量的效果。结果显示,D941弱碱性阴离子交换树脂能降低沙棘果汁酸度,升高果汁色值及透光率,对Vc的吸附能力较弱,其可滴定酸表观交换吸附量为2.70g/100mL,吸附平衡时间为3h,适宜工作流量为4BV/h,再生剂NaOH适宜浓度为0.2%,再生周期为4次。D941弱碱性阴离子交换树脂可用于沙棘果汁的降酸。     

大孔吸附树脂对石榴皮多酚的分离纯化

石榴皮中多酚含量丰富,具有抗氧化、抗衰老、抗癌防癌、抗菌、润肤美容、降血压和预防心脑血管疾病等多种生理和药理活性。在食品、医药和日用化学品等领域显示出巨大的应用价值。从XAD-16、XAD-1180、XAD-7HP、D101、DM-11、DM130、SP-700、SP-850、X-5、AB-8和H-103大孔吸附树脂中通过静态实验筛选出SP-700树脂,详细研究了其对石榴皮总单宁的静态与动态吸附和解吸性能。结果表明,SP-700树脂对石榴皮多酚的饱和吸附量为70.52mg/g(干树脂),吸附等温线符合Freundlich方程,为多分子层吸附,饱和吸附时间为5h,适宜解吸剂为体积分数70%的乙醇溶液,测定20、25、30、35℃下吸附等温线,表明最适宜的吸附温度是25℃,此时最大吸附量达到96.71mg/g(干树脂);以5mg/mL质量浓度的石榴皮提取液上柱,流速为4～4.5BV/h时,树脂的多酚穿透吸附容量65.72mg/g(干树脂),3.5BV体积分数70%的乙醇溶液可将吸附于柱上的石榴皮多酚完全洗脱。以该条件纯化石榴皮多酚提取物时,纯化样的收率为26.5g/100g(干石榴皮),多酚质量分数从48%提高到...     

A modified Polanyi-based model for mechanistic understanding of adsorption of phenolic compounds onto polymeric adsorbents

To obtain mechanistic insight into adsorption of phenolic compounds by two representative polymeric adsorbents, XAD-4 (polystyrene) and XAD-7 (polymethacrylate), a modified Polanyi-based Dubinin-Ashtakhov (D-A) model was developed based on a unique combination of the Polanyi theory, polyparameter linear energy relationships and infinitely dilute solution in n-hexadecane as the reference state. The adsorption potential in the D-A model ε = -RTln(C(w)/C(w) (sat)) was redefined by replacing the term (C(w)/C(w) (sat)) with the normalized equivalent concentration in n-hexadecane (CHD), where Cw is the aqueous equilibrium concentration and C(w) (sat) is the aqueous solubility of the solute. Using the new reference state allows quantitative comparison among various solutes. By fitting adsorption isotherms to the modified model using εHD = -RTln(CHD/10 000), a new normalizing factor (E(m)) was obtained to quantify the contributions of specific interactions (i.e., H-bonding, dipolar/polarizability, etc.) to the overall adsorption energy. Significant linear correlations were established between "A", the hydrogen-bond acidity, and "E(m)" for the investigated compounds, suggesting that, in addition to hydrophobic interactions, hydrogen-bonding is predominantly responsible for the adsorption of phenols by XAD-4 and XAD-7. Additionally, adsorption capacity and affinity of phenolates were significantly less than those of phenols; another model was proposed to accurately predict the effect of pH on the adsorption behavior of phenols.     

Adsorption of fluoride on zirconium(IV)-impregnated collagen fiber

A novel adsorbent, zirconium(IV)-impregnated collagen fiber, was prepared. Zr(IV) was uniformly dispersed in collagen fiber, mainly through chemical bonds, and was able to withstand the extraction of water. This adsorbent is effective for the removal of fluoride from aqueous solutions. The adsorption capacity was 2.29 mmol/g at pH = 5.5 when 5.00 mmol/L fluoride solution was adsorbed by use of 0.100 g of adsorbent, and the extent of removal was 97.4% when the adsorbent dose was 0.300 g. The adsorption isotherms were well fitted by the Langmuir equation, and the maximum adsorption capacities calculated by the Langmuir equation were close to those determined by experiment. The adsorption capacity increased with rising temperature. These facts imply that the mechanism of chemical adsorption might be involved in the adsorption process of fluoride on the absorbent and that fluorides are adsorbed in the form of monolayer coverage on the surface of the adsorbent. The adsorption kinetics of fluoride onto Zr(IV)-impregnated collagen fiber could be described by Lagergren's pseudo-first-order rate mode. The investigation on desorption indicated that this adsorbent is easily regenerated by use of dilute NaOH solution.     

Synthesis of octadecyl acrylate-co-ethylene glycol dimethacrylate resin for removal of dark-colored compound from apple juice and comparison with polyvinylpolypirrolidone (PVPP)

Adsorption process has an importance for improving the color of juice and also stabilizing the final product during the shelf life. In this study, polyvinylpolypirrolidone (PVPP) and octadecyl acrylate-co-ethylene glycol dimethacrylate (ODA-EGDMA) polymeric resins were used as adsorbents for improving the color properties of apple juice. The ODA-EGDMA resin was prepared by classical suspension polymerization technique and characterized by electron microscopy. The obtained spherical particles diameters were between 20 and 140 μm. PVPP was selected as reference polymeric material for its importance in the juice industry. The adsorption kinetics of dark-colored compounds on adsorbent polymeric resins were studied at different adsorbent resins concentrations (1, 2, 4, and 8 g adsorbent resin per liter of apple juice) at the constant temperature (20 °C) in batch reactor. Langmuir adsorption model was applied for both PVPP and ODA-EGDMA polymeric adsorbents. The Langmuir isotherms were plotted for both polymeric adsorbents by evaluation of the absorbance data of apple juice at 420 nm. Langmuir isotherm's empirical constants known as K _ad and Q ₀ were calculated from the equilibrium data. Numerical value of K _ad and Q ₀ were determined as 5.0578 and 0.3089 for the ODA-EGDMA polymeric resin, 2.4824 and 0.5268 for the PVPP adsorbent, respectively. The scope of this study included comparison of reusability and regeneration properties of the each polymeric adsorbent. For this purpose, series of experiment were done in pack bed column application. Pressure drop measured throughout the PVPP pack bed column was 4.8 times higher than ODA-EGDMA pack bed column at same flow rate (2.5 mL/min) during the this group experiment. ODA-EGDMA resin and PVPP were regenerated with NaOH (4% w/v, 50 °C) after each run. After regeneration, average removal of dark color (relative absorbance change at 420 nm) of apple juice was determined as 76.47±0.90% for ODA-EGDMA and 91.51±0.86% for PVPP adsorbent resin.     

Treatment of perchlorate-contaminated groundwater using highly selective, regenerable ion-exchange technologies

Treatment of perchlorate-contaminated water using highly selective, regenerable ion-exchange and perchlorate-destruction technologies was demonstrated at a field site in California. Four treatment and four regeneration cycles were carried out, and no significant deterioration of resin performance was noted in 2 years. The bifunctional resin (Purolite A-530E) treated about 37,000 empty bed volumes (BVs) of groundwater before a significant breakthrough of perchlorate occurred at an average flow rate of 150 gpm (or 1 BV/min) and a feed perchlorate concentration of about 860 microg/L. Sorbed perchlorate (approximately 20 kg) was quantitatively recovered by eluting with as little as 1 BV of the FeCl3-HCl regenerant solution. The eluted ClO4- was highly concentrated in the third quarter of the first BV of the regenerant solution with a concentration up to 100,000 mg/L. This concentrated effluent greatly facilitated subsequent perchlorate destruction or recovery by precipitation as KClO4 salts. High perchlorate destruction efficiency (92-97%) was observed by reduction with FeCl2 in a thermoreactor, which enabled recycling of the FeCl3-HCl regenerant solution, thereby minimizing the need to dispose of secondary wastes containing ClO4-. This study demonstrates that a combination of novel selective, regenerable ion-exchange and perchlorate-destruction and/or recovery technologies could potentially lead to enhanced treatment efficiency and minimized secondary waste production.     

Regeneration of a Strong Acid Cation Exchange Resin for Deionizing Corn Syrup Solutions

The influence of regenerant flowrate and concentration on regeneration capacity of cation exchange resins used in refining corn syrups was investigated. A strong acid exchange resin (Duolite C-26®) was examined over a range of resin compositions. Co-current regeneration was modeled using hydrochloric acid at dosages ranging from 64 to 256 g/I (4 – 16 lb/cu. ft.). Resin beds exhausted with large amounts of calcium (and other divalent ions) are best regenerated at high acid concentrations and low regenerant flowrates. Resin beds with large amounts of sodium and/or other monovalent ions are most efficently regenerated at low acid concentrations. Flowrate has little influence on regeneration with large amounts of sodium. Syrup deionized prior to isomerization typically has a lower divalent ion content than syrup deionized after isomerization. This suggests that two separate procedures may be necessary in order to most effectively use the regenerant.     

乙胺基团增强聚吡咯材料对印染废水中Cr(Ⅵ)的吸附

印染废水中的Cr(Ⅵ)是一种毒性较大的污染物,而功能化聚吡咯材料对重金属离子具有优良的吸附性。通过共聚改性法成功合成了一种新型复合吸附剂聚[1-(2-氨乙基)吡咯](PPy-NH2),并将其用作吸附水溶液中Cr(Ⅵ)的吸附剂,重点研究了该吸附材料去除Cr(Ⅵ)的影响因素和吸附机理。结果表明:PPy-NH2的吸附能力随溶液pH的降低而增强,当pH=1.6时,吸附量为164.3mg/g;吸附量随着PPy-NH2用量的增加而增大,当PPy-NH2用量为4 g时基本达到吸附平衡,去除率为97.11%;任一共存离子浓度增加均会降低PPy-NH2对Cr(Ⅵ)的去除率。PPy-NH2复合材料是一种高效的Cr(Ⅵ)吸附剂。     

Efficient approach for Cd2+ and Ni2+ removal and recovery using mesoporous adsorbent with tunable selectivity

Cadmium pollution from the manufacture and disposal of NiCd batteries remains an important problem in developing countries. Among the available remedial technologies, adsorption is popular because of its low cost and simplicity. The mesoporous NH2-MCM-41 displays good adsorption capacities for cadmium and nickel ions. This work demonstrated for the first time the use of the competition between complexant and sorbentto create high adsorption selectivity. The selectivity was manipulated by the judicious use of a chelating agent, thus achieving on-demand 100% selectivity for either Cd2+ or Ni2+ adsorption. Single and binary components adsorption studies, carried out with different metals and EDTA concentrations, solution compositions and pH, showed that NH2-MCM-41 adsorbs only cadmium with a capacity of 0.56 mmol g(-1) from binary mixtures at [EDTA]/[M2+] = 0.5 and pH 5. The NH2-MCM-41 displays 100% selectivityfor nickel adsorption at [EDTA]/[M2+] = 0.5 and pH 2 with a measured adsorption capacity of 0.50 mmol g(-1). Pure Cd2+ and Ni2+ solutions were recovered by a simple acid wash, and the regenerated adsorbent could be reused without lost of performance (i.e., adsorption capacity and selectivity).     

纤维素/壳聚糖磁性气凝胶的冻融法制备及其对染料吸附性能

为开发一种高效可再生的磁性生物质基吸附剂,以微晶纤维素(MCC)和壳聚糖(CS)为凝胶网络框架、纳米Fe3 O4为掺杂剂,通过悬浮液滴和冻融结合法制备MCC/CS磁性气凝胶.借助扫描电子显微镜、傅里叶红外光谱、X射线衍射等表征其微观形貌及化学结构,并探讨了对染料刚果红的去除效果.结果 表明:在加入1.0 g纳米Fe3 ...     

Synthesis and Application of Starch 3, 5‐Dinitrobenzoate

A novel starch ester was prepared by the reaction of starch and 3, 5‐dinitrobenzoyl chloride (DNBZ‐Cl). The product (starch 3, 5‐dinitrobenzoate, DNBZ‐ST) was characterized by means of elemental analysis, Fourier Transform Infrared (FTIR) and ¹³C NMR spectroscopy. The influences of molar ratio of DNBZ‐Cl to anhydroglucose (AGU), reaction temperature and time, and amount of pyridine on the degree of substitution (DS) were studied. The esterification reaction is essentially complete after 2 h. Increase in the molar ratio of DNBZ‐Cl to AGU leads to an increase in DS when the former varies from 2:1 to 5:1. DS increases with the reaction temperature when the latter is varied from 70 to 100 °C. DS first increases and then decreases with amount of pyridine, the highest DS was obtained when V(pyridine)/m(starch) was 53 mL/g. The thermal stability of DNBZ‐ST increases when the DS increases, and the degradation starts at 353 °C for the sample of DS 2.14. Creatinine is a toxin accumulated in the blood of chronic renal failure (CRF) patients and a special adsorbent for creatinine is not reported in literature. DNBZ‐ST displayed specific adsorption ability for creatinine, the adsorption equilibrium is reached after 4 h. The adsorption capacity increases with the DS of adsorbent and creatinine concentration. When the creatinine concentration is higher than 300 mg/L, concentration has no apparent effect on the adsorption capacity. As the temperature of the solution is varied from 19 to 49 °C, adsorption capacity first decreases and then increases, being lowest at 37 °C. The adsorption capacity first increases and then decreases as the pH value increases, and is highest at pH 8.The highest adsorption capacity obtained was 25 mg of creatinine per gram of adsorbent at 37 °C, pH 7 and a creatinine concentration of 100 mg/L. The study on the FTIR and UV‐VIS spectra suggested that some chemical reaction took place between the DNBZ‐ST and creatinine in buffer solution.     

ONION FLAVOR RECOVERY IN THE PROCESS OF ADSORPTION AND SUPERCRITICAL CARBON DIOXIDE DESORPTION

Recovery of onion oil from onion juice was accomplished by adsorption of onion oil onto a polymeric adsorbent prior to supercritical carbon dioxide desorption. At 20.7 MPa, 37C, with a carbon dioxide flow rate of 1 L standard temperature and pressure (STP) per minute, an increase in the amount of onion juice used to load the adsorbent from 1 to 6 L resulted in an increase in the gravimetric yield of onion oil desorbed by weight. Additionally, the weight of onion oil desorbed per volume of carbon dioxide used increased. However, the gravimetric yield of onion oil by percentage with respect to the amount of onion juice fed through the adsorbent decreased.     

Arsenate adsorption on an Fe-Ce bimetal oxide adsorbent: role of surface properties

An Fe-Ce bimetal adsorbent was investigated with X-ray powder diffraction (XRD), transmission electron micrograph (TEM), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS) methods for a better understanding of the effect of surface properties on arsenate (As(V)) adsorption. In the adsorption test, the bimetal oxide adsorbent showed a significantly higher As(V) adsorption capacity than the referenced Ce and Fe oxides (CeO2 and Fe3O4) prepared by the same procedure and some other arsenate adsorbents reported recently. XRD measurement of the adsorbent demonstrated that the phase of magnetite (Fe3O4) disappears gradually with the increasing dosage of Ce4+ ions until reaching a molar ratio of Ce4+ to Fe3+ and Fe2+ of 0.08:0.2:0.1 (Fe-CeO8 refers to the adsorbent prepared at this ratio), and the phase of CeO2 begins to appear following a further increase of the Ce dose. Combined with the results of TEM observation, it was assumed that a solid solution of Fe-Ce is formed following the disappearance of the magnetite phase. Occurrence of a characteristic surface hydroxyl group (MOH, metal surface hydroxyl, 1126 cm(-1)), which showed the highest band intensity in the solid solution state, was confirmed on the bimetal oxide adsorbent by FTIR. Quantificational calculation from the XPS narrow scan results of O(1s) spectra also indicated that the formation of the bimetal Fe-CeO8 was composed of more hydroxyl (30.8%) than was the formation of CeO2 and Fe3O4 (12.6% and 19.6%). The results of adsorption tests on Fe-CeO8 at differentAs(V) concentrations indicated that both the integral area of the As-O band at 836 cm(-1) and the As(V) adsorption capacity increased almost linearly with the decrease of the integral area of M-OH bands at 1126 cm(-1), proving that the adsorption of As(V) by Fe-CeO8 is mainly realized through the mechanism of quantitative ligand exchange. The atomic ratio of Fe on Fe-CeOB decreased from 20.1% to 7.7% with the increase of the As atom ratio from 0 to 16% after As(V) adsorption, suggesting that As(V) adsorption might be realized through the replacement of the M-OH group of Fe (Fe-OH) with arsenate. The well splitting of three v3 bands at As-O band (836 cm(-1)) of FTIR and the hydroxyl ratio (1.7) of Fe-CeO8 calculated from the XPS results suggested that the diprotonated monodentate complex (SOAsO(OH)2) is possibly dominant on the surface of Fe-CeO8.     

Adsorption of Cu2+ by Crosslinked Graft Copolymers of Starch

With the use of acrylic acid(AA)as a monomer,humic acid(HA)and starch as raw materials,potassium persulfate(KPS)as initiator,and N,Ndimethylacrylamide(MBA)as a cross-linking agent,AA/HA/Starch graft copolymer was prepared and characterized by SEM and FT-IR.The effects of temperature,adsorption time,adsorbent dosage,pH value and Cu²⁺initial concentration of the solution on the adsorption performance of the crosslinked graft copolymer were also investigated.The results showed that the Cu²⁺adsorption capacity of the AA/HA/Starch graft copolymer increased firstly and then decreased with increasing adsorbent dosage and the initial pH value of Cu²⁺solution.With the increase of Cu²⁺initial concentration and the extension of adsorption time,the adsorption amount of Cu²⁺increased rapidly and then stabilized.And it decreased slightly with the increase of temperature.At pH value of 5.5,temperature of 298 K,adsorbent dosage of 50 mg,adsorption time of 125 min,and 100 mL Cu²⁺solution with Cu²⁺initial concentration of 100 mg/L,the Cu²⁺adsorption capacity of the crosslinked graft copolymer was 238 mg/g.The adsorption of Cu²⁺by the adsorbent followed the pseudo-second-order kinetic equation and Langmuir isothermal adsorption model,and the adsorption was attached to monolayer chemical adsorption.This study proved that AA/HA/Starch graft copolymer could be used as an efficient adsorbent for the removal of harmful and toxic metal cations such as Cu²⁺from industrial wastewater.     

Microwave-swing adsorption to capture and recover vapors from air streams with activated carbon fiber cloth

Adsorption with regeneration is a desirable means to control the emissions of organic vapors such as hazardous air pollutants (HAPs) and volatile organic compounds (VOCs) from air streams as it allows for capture, recovery, and reuse of those VOCs/HAPS. Integration of activated-carbon fiber-cloth (ACFC) adsorbent with microwave regeneration provides promise as a new adsorption/ regeneration technology. This research investigates the feasibility of using microwaves to regenerate ACFC as part of a process for capture and recovery of organic vapors from gas streams. A bench-scale fixed-bed microwave-swing adsorption (MSA) system was built and tested for adsorption of water vapor, methyl ethyl ketone (MEK), and tetrachloroethylene (PERC) from an airstream and then recovery of those vapors with microwave regeneration. The electromagnetic heating behavior of dry and vapor-saturated ACFC was also characterized. The MSA system successfully adsorbed organic vapors from the airstreams, allowed for rapid regeneration of the ACFC cartridge, and recovered the water and organic vapors as liquids.