Sorption equilibrium moisture and isosteric heat of Chinese wheat bran products added to rice to increase its dietary fibre content

More and more people concern about supplementing dietary food with wheat bran to increase fibre content,but there has been little study of the sorption isotherms and isosteric heats of wheat bran fibre products,which are important to the quality and storage durability of such commodities.This study collected equilibrium moisture content(EMC)and equilibrium relative humidity(ERH)data on six Chinese wheat bran products via the static gravimetric method and analysed their sorption isosteric heats.Results showed that all six wheat bran products had sigmoidal isotherms.The data were best fitted by polynomial,modified GAB,modified Oswin,and modified Halsey models.The relative safe moisture contents of the six wheat bran products were 12.20%–13.86%wet basis(w.b.).The heat of vaporization of wheat bran products approached the latent heat of pure water at around a moisture content(MC)of 22.5%and approximately 2450 kJ/kg.A process of extrusion and ultrafine grinding reduced the solid surface area and sorption isosteric heats of the monolayer,multilayer and condensed water regions in the wheat bran products.In the temperature range of 10–37℃,the EMC of sorption in monolayer,multilayer and condensed water regions decreased with increasing temperature.The milled rice to which 1%–3%200-mesh wheat bran product was added maintained its texture when made into cooked rice and its thermomechanical properties when made into rice dough.After processing by extrusion and ultrafine grinding,wheat bran products have a lower solid surface area and lower monolayer water content(Mm)and sorption isosteric heat values.Some 3%200-mesh wheat bran product can be added to cooked rice for increasing its fibre content and making it more nutritious.

Desorption isotherms and isosteric heat of anaerobic fermentation residues

This paper presents the equilibrium desorption isotherms and the isosteric heat of sorption of a mixture containing mechanically dewatered fermentation residue(obtained from a blend of chicken,swine and cattle manure)used in biogas plants and corn spoiled silage in a ratio of 2:1.The moisture desorption isotherms of the fermentation residue were determined at 32°C,40°C and 80°C and in the relative humidity range of 0.057/1 using static gravimetric method.Mathematical equations were used to analyze the desorption data of Modified Henderson,Modified Halsey,Modified Oswin,Modified Chung–Pfost and Modified GAB models.The constants of the model equations were calculated by non-linear regression analysis.The Modified Henderson model fitted to the desorption isotherm data well.Using the proposed function,the final moisture content of the material can be determined as long as it can be dried in infinite time with the drying gas in the given conditions.The isosteric heat of desorption was calculated by using the Modified Henderson model in the studied temperature range based on the Clausius–Clapeyron equation.The isosteric heat varied between 46 k J·mol-1 and 67 k J·mol-1 at moisture levels 1.91 b Xe<4.05 kgH2O·kgdP-1 for the material.

A developed dual-site Langmuir model to represent the high-pressure methane adsorption and thermodynamic parameters in shale

Comprehending the mechanism of methane adsorption in shales is a crucial step towards optimizing the development of deep-buried shale gas. This is because the methane adsorbed in shale represents a significant proportion of the subsurface shale gas resource. To properly characterize the methane adsorption on shale, which exhibits diverse mineral compositions and multi-scale pore sizes, it is crucial to capture the energy heterogeneity of the adsorption sites. In this paper, a dual-site Langmuir model is proposed, which accounts for the temperature and pressure dependence of the density of the adsorbed phase. The model is applied to the isothermals of methane adsorption on shale, at pressures of up to 30 MPa and temperatures ranging from 40 to 100 ℃. The results show that the proposed model can describe the adsorption behavior of methane on shale more accurately than conventional models, which assume a constant value for the density of adsorbed phase. Furthermore, the proposed model can be extrapolated to higher temperatures and pressures. Thermodynamic parameters were analyzed using correctly derived equations. The results indicate that the widely used, but incorrect, equation would underestimate the isosteric heat of adsorption. Neglecting the real gas behavior, volume of the adsorbed phase, and energy heterogeneity of the adsorption sites can lead to overestimation of the isosteric heat of adsorption. Furthermore, the isosteric heat evaluated from excess adsorption data can only be used to make a rough estimate of the real isosteric heat at very low pressure.

Water sorption on coal:effects of oxygen-containing function groups and pore structure

Coal-water interactions have profound influences on gas extraction from coal and coal utilization.Experimental measurements on three coals using X-ray photoelectron spectroscopy(XPS),low-temperature nitrogen adsorption and dynamic water vapor sorption(DVS)were conducted.A mechanism-based isotherm model was proposed to estimate the water vapor uptake at various relative humidities,which is well validated with the DVS data.The validated isotherm model of sorption was further used to derive the isosteric heat of water vapor sorption.The specific surface area of coal pores is not the determining parameter that controls water vapor sorption at least during the primary adsorption stage.Oxidation degree dominates the primary adsorption,and which togethering with the cumulative pore volume determine the secondary adsorption.Higher temperature has limited effects on primary adsorption process.The isosteric heat of water adsorption decreases as water vapor uptake increases,which is found to be close to the latent heat of bulk water condensation at higher relative humidity.The results confirmed that the primary adsorption is controlled by the stronger bonding energy while the interaction energy between water molecules during secondary adsorption stage is relatively weak.However,the thermodynamics of coal-water interactions are complicated since the internal bonding interactions within the coal are disrupted at the same time as new bonding interactions take place within water molecules.Coal has a shrinkage/swelling colloidal structure with moisture loss/gain and it may exhibit collapse behavior with some collapses irreversible as a function of relative humidity,which further plays a significant role in determining moisture retention.

Adsorption of benzene, cyclohexane and hexane on ordered mesoporous carbon

Ordered mesoporous carbon（OMC） with high specific surface area and large pore volume was synthesized and tested for use as an adsorbent for volatile organic compound（VOC）disposal. Benzene, cyclohexane and hexane were selected as typical adsorbates due to their different molecular sizes and extensive utilization in industrial processes. In spite of their structural differences, high adsorption amounts were achieved for all three adsorbates, as the pore size of OMC is large enough for the access of these VOCs. In addition, the unusual bimodal-like pore size distribution gives the adsorbates a higher diffusion rate compared with conventional adsorbents such as activated carbon and carbon molecular sieve. Kinetic analysis suggests that the adsorption barriers mainly originated from the difficulty of VOC vapor molecules entering the pore channels of adsorbents. Therefore, its superior adsorption ability toward VOCs, together with a high diffusion rate, makes the ordered mesoporous carbon a promising potential adsorbent for VOC disposal.

Energy Aspects of CO_2 Sorption in the Context of Sequestration in Coal Deposits

This paper summarises the results of experimental testing of carbon dioxide sorption on five coal samples. Sorption tests were done at the temperature 288, 298, 313 and 323 K, in the pressure range 0-5 MPa. The analysis of sorption isotherms and the effects of temperature on sorption capacity reveal that in the case of samples NR1, Pn, Tu, Be the temperature increase from 298 to 323 K led to 1.3-fold decrease of the sorption value. In the ease of coal Th the decrease of sorption capacity was 3-fold. It appears that the analysis of maceral content plays a major role. In the case of coals, porosity is associated with the petrographic composition. The values of the isosteric heat of sorption and the work of expansion and desorption were derived for the investigated sorption systems. Test data reveal that for hard coals the isosteric heat is inversely proportional to the ＂reserve＂ of volumetric work-a major parameter triggering the sudden release of gas from the coalbed, thus enabling us to assess the potential risk involved in rapid unsealing of the coalbed.

Two comparable Ba-MOFs with similar linkers for enhanced CO_(2)capture and separation by introducing N-rich groups

Two new different metal-organic frameworks(MOFs)[Ba(L1)(H_(2)O)_(2)]_(n)·nH_(2)O(MOF 1)and[Ba(L2)(-n2 O)_(2)]_(n)·0.5 nDMF·0.5 nH_(2)O(MOF 2)were yielded by the assembly of oxygen-friendly Ba(Ⅱ)ions and two similar linkers,namely 2-(imidazol-1-yl)terephthalic acid(H_(2)L1)and 2-(1 H-1,2,4-triazol-1-yl)terephthalic acid(H_(2)L2).Single-crystal X-ray diffractions(XRD)indicate that MOF1 is a new three-dimensional(3 D)stacking dense network formed by the one-dimensional(1 D)rod-shaped chains and L1 linkers,whereas MOF 2 presents a 3 D nanotube porous framework with cylindrical tunnels based on the 1 D loop chains as the secondary building units(SBUs)by replacing the imidazole group in H_(2)L1 with the triazole group in H_(2)L2.As a result,MOF 2 has a higher density of active sites and Lewis acid sites in the porous surface of nanotube than MOF 1.Thereby,the CO_(2)capture and separation capacity of MOF 2 is great higher than that of CH_(4)at298 K.

Moisture sorption characteristics of full fat and defatted pistachio kernel flour

The sorption isotherms of full-fat(FPKF),partially defatted(PDPKF),and totally defatted(TDPKF)pistachio kernel flour were performed in the range of water activity(aw)from 0.113 to 0.859 at 15℃,25℃and 35℃,and the applicability of six mathematical models(Smith,Oswin,Henderson,GAB,Halsey and BET)in data prediction was evaluated.Sorption isotherms were typeⅡ,according to Brunauer’s classification.Equilibrium moisture content(EMC)increased with an increase in aw at constant temperatures.The sorption isotherms of all three flour samples exhibited hysteresis.Significant differences were found among equilibrium data of FPKF,PDPKF and TDPKF samples.TDPKF showed higher hygroscopic characteristics than PDPKF,and PDPKF showed higher hygroscopic characteristics than FPKF at any temperature and aw studied.It was found that the Smith model was the most satisfactory one for representation of the sorption data of full fat sample,but for defatted samples,Halsey was the best model.The average monolayer moisture content(MMC)calculated by GAB model were 2.443-3.781 g/100 g(d.b.),3.585-4.886 g/100 g(d.b.)and 5.093-6.918 g/100 g(d.b.)for FPKF,PDPKF and TDPKF,respectively.The isosteric sorption heat(Qst)calculated by means of Clausius-Clapeyron equation decreased with increasing moisture content.The Qst values were 44.76-74.67 kJ/mol,44.75-99.44 kJ/mol and 44.80-133.28 kJ/mol for FPKF,PDPKF and TDPKF,respectively,in the range of moisture content of 2%to 41%(d.b.)at 25℃.