油茶壳活性炭对西番莲废水色素的吸附性能

研究以油茶壳水热炭为原料,KOH为活化剂制备油茶壳活性炭,研究了油茶壳活性炭添加量、吸附温度、吸附时间对西番莲废水色素吸附率的影响。通过研究活性炭对废水色素的吸附等温线、动力学与热力学性质,分析活性炭吸附特性。结果表明,油茶壳活性炭对废水色素的吸附率随活性炭的增加,先增大后趋于平衡;吸附时间和温度有助于色素的吸附。油茶壳活性炭添加量0.06 g/10 mL时,废水色素吸附360 min趋于饱和,30,40,50℃对应平衡吸附率分别为74.41%,83.11%,83.89%。油茶壳活性炭对废水色素的吸附符合准二级动力学模型(R²>0.99),吸附等温线采用Freundlich模型拟合较好(R2>0.99),吸附等温线采用Freundlich模型拟合较好(R²>0.82)。活性炭对废水色素吸附的焓变ΔH和熵变ΔS分别为6.566 2×102>0.82)。活性炭对废水色素吸附的焓变ΔH和熵变ΔS分别为6.566 2×10³ J/mol、17.725 J/(mol·K),吸附过程是自发、吸热、熵增过程。     

坡缕石-活性炭-壳聚糖负载环糊精对硝基苯酚的吸附性质

研究了坡缕石-活性炭-壳聚糖负载环糊精吸附剂对对硝基苯酚、邻硝基苯酚的吸附行为以及pH、温度等对吸附的影响。在pH=5.0-7.5时,自制吸附剂对对硝基苯酚,邻硝基苯酚具有较好的吸附作用。等温吸附曲线拟合结果显示,吸附剂对硝基苯酚的吸附更符合Langmu ir方程。热力学函数计算表明,吸附剂对硝基酚的吸附是自发的放热过程,对硝基苯酚的吸附热和熵变分别为-27.49 kJ/mol和-70.39 J/(mol.K),邻硝基苯酚的吸附热和熵变分别为-29.06 kJ/mol和-78.87 J/(mol.K),吸附自由能均随温度的升高而增加。     

凹凸棒石/CoFe_2O_4磁性复合材料制备及对亚甲基蓝吸附性能

通过低温回流法制备具有吸附和磁性能的凹凸棒石/CoFe2O4磁性复合材料(MAT),利用傅里叶红外光谱(FTIR)、振动样品磁强计(VSM)、扫描电镜(SEM)、X射线衍射(XRD)等对MAT进行表征,并研究了MAT对亚甲基蓝(MB)的吸附性能。结果表明,磁性粒子CoFe2O4以简单的物理沉积负载于凹凸棒石表面;MAT饱和比磁化强度14 emu/g,磁性较强,易于磁分离;比表面积175.85 m2/g,略大于凹凸棒石。对于25 m L浓度100 mg/L MB溶液,MAT最佳投加量为0.050 g;在pH 3⁹范围内,MAT吸附量随pH值的增大而增大;当温度在2939范围内,MAT吸附量随pH值的增大而增大;当温度在293³38 K,MAT的吸附等温线符合Langmuir方程,吸附焓变1.61 k J/mol,Gibbs自由能变-28.51338 K,MAT的吸附等温线符合Langmuir方程,吸附焓变1.61 k J/mol,Gibbs自由能变-28.51³3.16 k J/mol,吸附熵变102.4833.16 k J/mol,吸附熵变102.48¹02.87 k J/mol,表明该吸附是个吸热、自发且熵增过程;MAT对MB的吸附动力学符合准二级动力学方程,是外表面吸附。     

基于离子交换的乙二醇富液脱盐实验研究

为简化深水气田乙二醇回收系统,采用离子交换工艺替代常规乙二醇脱盐工艺,对乙二醇吸附脱盐进行实验研究。通过静态吸附脱盐实验,在含盐乙二醇富液体系中对4种离子交换树脂进行了筛选,并对筛选出的树脂进行了吸附热力学研究。根据吸附能力,筛选出D113阳离子交换树脂和D201阴离子交换树脂用于实验,阴阳树脂体积比例为2∶1时上清液呈中性,阴阳混合树脂用量为200 mL/L,脱盐率为73.89%。D201树脂吸附Cl^-过程中的熵变ΔS为-26.605 J/(mol·K)、焓变ΔH为-13.386 kJ/mol, D113树脂吸附Ca-过程中的熵变ΔS为-26.605 J/(mol·K)、焓变ΔH为-13.386 kJ/mol, D113树脂吸附Ca⁽²⁺⁾过程中的熵变ΔS为-95.794 J/(mol·K)、焓变ΔH为-32.220 kJ/mol,吸附过程符合Langmuir模型,吉布斯自由能变ΔG<0,表明树脂在乙二醇富液中的吸附是放热、自发的过程,D113和D201树脂可用于乙二醇富液脱盐。     

微波辅助酸改性粉煤灰对镉的吸附性能研究

采用微波辅助酸改性粉煤灰,制备的改性粉煤灰用于处理含Cd~(2+)废水,进行静态吸附实验研究,测定了298~308 K范围内吸附等温线。结果表明,改性粉煤灰对Cd2+有良好的吸附性能,吸附符合Langmuir等温方程,最大饱和吸附量为12.5 mg/g。吸附焓变为38.87 k J/mol,吸附Gibbs自由能为-4.25~-2.85 k J/mol,吸附熵变为117 J/(mol·K),表明该吸附过程是自发吸热过程。     

碳酸锂在碳酸钠溶液中的溶解度与热力学

采用等温溶解平衡法开展碳酸锂在碳酸钠溶液中(278.15～358.15 K)的溶解平衡实验研究,测定平衡体系碳酸锂溶解度和平衡溶液密度,利用E-DH方程对碳酸锂溶解度实验数据进行关联,标准偏差小于0.01;利用Connaughton方程对液相密度数据进行关联,标准偏差小于2×10^-3。实验和计算研究结果表明：在同离子和盐效应协同影响下,碳酸锂在Na₂CO₃-H₂O体系中溶解度随碳酸钠浓度增加先降低后降低趋势变缓,在278.15～358.15 K温度范围内,溶解度转变折点为碳酸钠浓度约为0.1 mol·kg^-1;通过溶解热力学计算,得到碳酸锂在碳酸钠中的溶解焓变(ΔH_d)、熵变(ΔS_d)和Gibbs自由能变(ΔG_d),结果表明溶解过程为放热、熵减的非自发过程,溶解焓变和熵变随着碳酸钠浓度增加而增加,Gibbs自由能变在0.6 mol·kg^-1出现最大值,且溶解过程为熵控制过程。研究结果将为卤水提锂碳化沉锂过程设计提供基础数据。     

负载纳米TiO_2凹凸棒石黏土对Ni(Ⅱ)的吸附热力学研究

利用静态吸附实验的方法,研究了负载纳米二氧化钛的凹凸棒石黏土对溶液中Ni(Ⅱ)的吸附热力学特性。结果表明,吸附等温线符合Freundlich吸附模型。根据热力学函数关系计算出吸附过程的ΔH为-26.56 k J/mol,ΔG为-5.12^-0.73 k J/mol,ΔS为-73.18 J/(mol·K),表明负载纳米二氧化钛的凹凸棒石黏土对溶液中Ni(Ⅱ)的吸附是自发、放热、熵减的过程,为物理吸附。     

微波辅助酸改性粉煤灰对镉的吸附性能研究

采用微波辅助酸改性粉煤灰,制备的改性粉煤灰用于处理含Cd⁽²⁺⁾废水,进行静态吸附实验研究,测定了298(2+)废水,进行静态吸附实验研究,测定了298³08 K范围内吸附等温线。结果表明,改性粉煤灰对Cd2+有良好的吸附性能,吸附符合Langmuir等温方程,最大饱和吸附量为12.5 mg/g。吸附焓变为38.87 k J/mol,吸附Gibbs自由能为-4.25308 K范围内吸附等温线。结果表明,改性粉煤灰对Cd2+有良好的吸附性能,吸附符合Langmuir等温方程,最大饱和吸附量为12.5 mg/g。吸附焓变为38.87 k J/mol,吸附Gibbs自由能为-4.25^-2.85 k J/mol,吸附熵变为117 J/(mol·K),表明该吸附过程是自发吸热过程。     

邻苯二甲酸二辛酯合成热力学及动力学研究

邻苯二甲酸二辛酯(DOP)的合成过程分苯酐(PA)和异辛醇(2-EH)反应生成邻苯二甲酸单辛酯(MEHP)、MEHP和2-EH反应生成DOP两步进行,其中后一步是关键控制步骤。针对MEHP和2-EH之间的可逆反应,采用基团贡献法对反应焓变和熵变进行了理论计算;并采用间歇实验测定了无外加催化剂条件下的反应平衡和易挥发组分2-EH与水的汽液平衡,以及以钛酸四丁酯为催化剂的反应动力学。通过热力学实验确定了433.15~493.15 K时反应平衡常数为4.79~8.93,回归得到的反应焓为17.91 k J/mol、反应熵为54.64 J/(K·mol),与基团贡献法计算值基本相符;活度系数Redlich-Kister方程能较好地关联2-EH和水的汽液平衡数据。动力学研究结果表明高转化率下DOP水解反应影响不可忽略,MEHP和2-EH间的正、逆反应都符合二级反应规律,回归得到453.15~493.15 K时正反应活化能为83.49 k J/mol,指前因子为1.75×107 kg/(mol·min)。     

氢在多壁碳纳米管上的等量吸附热

为说明氢在多壁碳纳米管(MWCNTs)上所受吸附作用的强弱,文中基于氢和77 K氮的吸附数据,比较了由非局域密度泛函理论(NDFT)、等量吸附线和归一化等温线线性化确定的等量吸附热。结果表明,氢在MWCNTs上等量吸附热随温度变化且表现出在弱的能量不均匀表面吸附的特点,平均值约为3—4 kJ/mol;由77 K氮吸附等温线确定的孔大小分布(PSD)和比表面积影响NDFT计算初始吸附时的精度;在吸附量和吸附温度都较低时,等量吸附线标绘结果与归一化等温线线性化方程确定的等量吸附热之间的偏差较小,在200—290 K温度区间则与ND-FT计算结果更为接近。然而,当温度大于310 K时,3种方法计算结果间的偏差较大。     

Moisture adsorption isotherms and thermodynamics properties of sucuk (Turkish dry-fermented sausage)

Moisture adsorption isotherms of sucuk were determined using the isopiestic method at 10 °C, 20 °C and 30 °C and within the range of 0.2-0.9 water activity. The isotherms of sucuk exhibited Type II behavior according to BET classification. The adsorption data were analyzed using mathematical equations of Halsey, Caurie, Peleg, Smith, Oswin, Henderson, Modified-BET, GAB, Ferro-Fontan and Harkins-Jura. The best fit of experimental data was obtained with Peleg equation in the range of temperatures and water activities investigated. Thermodynamic properties such as differential enthalpy and entropy, enthalpy-entropy compensation, spreading pressure, net integral enthalpy and entropy were determined from moisture adsorption isotherm data of sucuk. The net isosteric heat of sorption and differential entropy decreased with increasing moisture contents in an exponential function. The spreading pressure increased with increasing water activity, and decreased with increasing temperature. The net integral enthalpy decreased with increased moisture content. The integral entropy increased with moisture content, but it was negative in value. The enthalpy-entropy compensation theory was applied to water adsorption of sucuk.     

Moisture Adsorption Isotherms and Glass Transition Temperature of Xanthan Gum

The moisture adsorption isotherms of the xanthan gum were determined at 30–70°C over water activity ranging from 0.11 to 0.94. The moisture adsorption isotherms revealed that the equilibrium moisture content increased with water activity. Increased temperature, in general, resulted in decreased equilibrium moisture content. However, in some cases equilibrium moisture content values increased with temperature. Selected sorption models were tested to describe the adsorption isotherms. Parameters of each sorption model were determined by nonlinear regression analysis. The modified Oswin model gave the best fit for xanthan gum. The isosteric heat of sorption decreased with increase in moisture content and varied between 1.66 and 7.61 kJ/mol. The glass transition temperature decreased with increase in moisture content for xanthan gum.     

Moisture Adsorption Isotherms and Glass Transition Temperature of Xanthan Gum

The moisture adsorption isotherms of the xanthan gum were determined at 30-70°C over water activity ranging from 0.11 to 0.94. The moisture adsorption isotherms revealed that the equilibrium moisture content increased with water activity. Increased temperature, in general, resulted in decreased equilibrium moisture content. However, in some cases equilibrium moisture content values increased with temperature. Selected sorption models were tested to describe the adsorption isotherms. Parameters of each sorption model were determined by nonlinear regression analysis. The modified Oswin model gave the best fit for xanthan gum. The isosteric heat of sorption decreased with increase in moisture content and varied between 1.66 and 7.61 kJ/mol. The glass transition temperature decreased with increase in moisture content for xanthan gum.     

Modeling Moisture Desorption Isotherms and Thermodynamic Properties of Fermented Tea Dhool (Camellia sinensis var. assamica)

The desorption isotherms of fermented tea dhool were determined at 50, 55, 60, and 70°C by using static gravimetric method of saturated salt solutions within the water activity range of 0.05–0.81. Results indicated that the equilibrium moisture contents were decreased with the increase in temperature. A modified Oswin model was well fitted with the experimental data. Desorption isotherm curves obtained were type II sygmoidal. Thermodynamic properties like net isosteric heat of sorption and differential entropy were found to decrease exponentially with the increase in moisture content. Monolayer moisture content was also decreased linearly with the increase in temperature. The enthalpy-entropy compensation theory could be successfully applied for the moisture desorption behavior of fermented tea dhool samples and it was an enthalpy-driven spontaneous process.     

Effect of osmosis and ultrasound pretreatment on the moisture adsorption isotherms of quince

The effect of pretreatment osmotic–ultrasonic dehydration on the sorption isotherms of quince was determined by static gravimetric method at temperatures of 30 °C, 45 °C, and 60 °C. The curves obtained can be considered as type II according to the Brunauer–Emmett–Teller (BET) classification. Adsorption data were fitted into seven isotherm models. The best fit of the experimental data was obtained with Peleg for both fresh- and pretreated dried quince slices.Thermodynamic properties such as net isosteric heat, differential entropy, enthalpy–entropy compensation, and spreading pressure were determined from moisture adsorption isotherm data of quince. The net isosteric heat of sorption and differential entropy decreased with increasing moisture contents in an exponential function. A plot of differential heat versus entropy satisfied the enthalpy–entropy compensation theory. The spreading pressure increased with increasing water activity, and decreased with increasing temperature. The value of net isosteric heat, differential entropy and spreading pressure of untreated samples is higher than that of pretreated samples of quince.     

THERMODYNAMIC BEHAVIOR OF FISH MEAL DURING ADSORPTION

Anchovy fish meal with an approximate uniform moisture content of 10% was used for this study. Vapor adsorption isotherms were determined at 25 ° C, 35 ° C and 45 ° C. The differential and integral thermodynamic properties were estimated using the Othmer method. The isosteric heat or differential enthalpy, as a function of moisture content, showed a maximum value around 4.5 g of water/100 g d. s. The heat of sorption increased gradually with an increase in sorbed water until reaching its maximum value near the monolayer, and at a given moisture content, decreasing with temperature. The molar entropy values obtained were high at low water contents and fell to a minimum near the monolayer value.     

Heats and Entropies of Sorption of Cereal Grains : A Comparison Between Integral and Differential Quantities

Several thermodynamic properties for maize, rough rice and wheat has been calculated using desorption isotherms available in the literature. It was obtained an analytical expression to predict the differential heat (isosteric) as function of moisture content using a three parameters equilibrium model, based on enthalpy-entropy compensation effect, which takes into account the effet of temperature. Two integral heats of sorption were calculated, the first from the slopes of the iso-spreading pressure lines and the second from integration of the differential heat. This last one was used to estimate the energy requirement to remove water from initial moisture content to different final moisture levels, which is useful in drying area. Finally it was calculated the differential and integral entropies of sorption as function of moisture content.     

THERMODYNAMIC BEHAVIOR OF FISH MEAL DURING ADSORPTION

ABSTRACT

Anchovy fish meal with an approximate uniform moisture content of 10% was used for this study. Vapor adsorption isotherms were determined at 25 ° C, 35 ° C and 45 ° C. The differential and integral thermodynamic properties were estimated using the Othmer method. The isosteric heat or differential enthalpy, as a function of moisture content, showed a maximum value around 4.5 g of water/100 g d. s. The heat of sorption increased gradually with an increase in sorbed water until reaching its maximum value near the monolayer, and at a given moisture content, decreasing with temperature. The molar entropy values obtained were high at low water contents and fell to a minimum near the monolayer value.     

THERMODYNAMIC MODELS FOR WATER SORPTION BY GRAPE SKIN AND PULP

ABSTRACT

The enthalpy-entropy compensation theory was applied to water sorption for grapes of Italy variety. The moisture sorption isotherms were analyzed using the static gravimetric method at 35, 40, 50, 60, 70 and 75° C. For isotherms construction, the skin and pulp of the grape were used separately and it was possible to observe significant differences. The GAB equation was fitted to the experimental data, using direct nonlinear regression analysis; the agreement between experimental and calculated values was satisfactory. The net isosteric heat or enthalpy of water sorption, determined from the equilibrium sorption data, showed a different behavior when compared with other works, as it was obtained for skin and pulp separately. Plots of Ah vs AS for skin and pulp provided the isokinetic temperatures T_BS = 423.2 ± 27.6 K and T_BP = 424.5 ± 25.3 K, respectively, indicating an enthalpy-controlled desorption process over the whole range of moisture content considered.     

Experimental Determination and Modeling of Sorption Isotherms of Erythrina Fusca Lour Bark

The water sorption isotherms of the Erythrina fusca Lour bark at 30 and 40°C were determined over relative humidity ranging from 55 to 85%. The equilibrium moisture content was determined gravimetrically. The moisture sorption isotherms showed that the equilibrium moisture decreases with increase of temperature. Six models were used for to fit the experimental curves of equilibrium humidity. Parameters of each equation were determined by nonlinear regression analysis. The isosteric heat of moisture sorption was calculated using the Claussius-Clapeyron equation.