10℃条件下纳米C-S-H掺量对水泥早期水化的影响

目的探究10℃条件下不同掺量纳米C-S-H对水泥早期水化进程及强度发展的影响,并分析其早强剂作用机理。方法通过溶液共沉淀法制备纳米C-S-H悬浮液,将其掺入到普通硅酸盐水泥中,在10℃条件下进行养护,分析其对水泥凝结时间、抗折强度、抗压强度的影响;通过XRD、TG等检测手段分析水泥的水化进程及对水化产物的影响。结果掺入0.05%纳米C-S-H,可使水泥初凝时间缩短9.9%,终凝时间缩短10.4%;24 h时抗折强度和抗压强度分别提高了34%和33.5%。纳米C-S-H的掺入造成水泥3 d抗折强度略有降低。水化产物中Ca(OH)2质量分数在12 h、16 h和24 h时较参比样分别提高了17.6%、21.3%和29.6%。结论在10℃条件下,纳米C-S-H的加入能够有效促进C 3S和C 2S的水化过程,形成更多的水化产物,从而缩短水泥凝结时间,提高24 h内水泥砂浆强度,28 d强度没有显著降低。

Dehydration Characteristics of C-S-H with Ca/Si Ratio 1.0 Prepared Via Precipitation

Calcium silicate hydrate（C-S-H） with Ca/Si ratio 1.0 was prepared via precipitation in solution and heated at various temperatures to investigate its dehydration behavior. The dehydration, structural collapse and recrystallization characteristics of C-S-H and its microstructural change during heating process were investigated by XRD, SEM, Raman and TG-DSC techniques. C-S-H gradually lost non-evaporable water upon heating, about 50% and 80% non-evaporable water was removed below 200 and 400 ℃, respectively, and the rest was removed up to about 1 000 ℃. At 400 ℃, dehydrated C-S-H exhibited the increasing disordering of calcium/silicon environment and the decreasing symmetrical bending vibration of Si-O-Si of Q^2 silicate chains. At 650 ℃ non-bridging oxygen atoms（O（non）） attached to silicon were almost removed, and significant structural change occurred, and at 815 ℃ C-S-H dehydrated to wollastonite.

A thermodynamic-based model for modeling thermo-elastoplastic behaviors of saturated clayey soils considering bound water dehydration

The non-isothermal deformation of soft mudrocks or clay soils is one of the most critical issues in energy and environmental related geotechnics.Clay-related geomaterials hold complex microstructure and mineral composition,which brings difficulty in investigating their thermo-mechanical behaviors.Previous studies pay little attention to the difference between a thermal plastic strain and the strain from clay dehydration.In this study,a new constitutive model is proposed for describing the thermoelastoplastic behaviors of clayey soils under water-saturated condition.The effect of temperature variation and mechanical loading on elastoplastic strains and dehydration are investigated.The thermodynamics laws and the unconventional plasticity are applied to quantify the thermo-mechanical behavior.The irreversible strain is captured by using Cam-Clay plasticity and subloading yield surface concept.The dehydration strain is described by utilizing a novel method based on generalized thermodynamics approach and Helmholtz free energy function.The internal variables,and the first and second laws of thermodynamics are applied in the model.The hardening rule is established by implementing the laws of physical conservation,energy dissipation,and plastic flow.The proposed model is validated using specially designed thermal consolidation tests on laboratory prepared heavily consolidated clayey soils and some published data of clayey soils with different geological origins.

Role of Calcination Temperature on Isosorbide Production from Sorbitol Dehydration over the Catalyst Derived from Ce(IV)Sulfate

Isosorbide is a multi-purpose chemical that can be produced from renewable resources.Specifically,it has been investigated as a replacement for toxic bisphenol A(BPA)in the production of polycarbonate(PC).In this study,the synthesis of isosorbide by sorbitol dehydration using a cerium-based catalyst derived from calcined cerium(IV)sulfate(300°C,400°C,450°C,500°C,and 650°C)was investigated.The reaction occurred in a high-pressure reactor containing nitrogen gas.Advanced instrumental techniques were applied to analyze the characteristics of the calcined catalyst.The results showed that the calcined catalysts demonstrated different crystalline structures and sulfate species at different temperatures.However,the acidic properties(strength and amount)of the catalyst did not change with the calcination temperature.The cerium(IV)sulfate calcined at 400°C exhibited the best catalytic performance,achieving the highest isosorbide yield(55.7%)and complete conversion of sorbitol at 180°C,20 bar of N2,and 6 h using CeSO-400.The presence of a sulfate group on the catalyst was the most important factor in determining the catalytic performance of sorbitol dehydration to isosorbide.This work suggests that CeSO-400 catalysts may play an important role in reducing reaction conditions.

Experimental and numerical studies of Ca(OH)_(2)/CaO dehydration process in a fixed-bed reactor for thermochemical energy storage

The Ca(OH)_(2)/CaO thermochemical energy storage(TCES)system based on calcium looping has received extensive attention owing to its high energy storage density,prolonged energy storage time,and environmental friendliness.The heat storage process of the Ca(OH)_(2)/CaO TCES system in a mixed heating reactor was evaluated in this study,by employing a combination of direct and indirect heating modes.The dehydration process was studied experimentally,and a numerical model was established and verified based on the experimental results.The dehydration behavior of 500 g of Ca(OH)_(2) powder was investigated in a fixed-bed reactor with mixed heating.The experimental and simulation results indicated that mixed heating causes combined centripetal and horizontal propulsion.Heat input is the main limiting factor in the heat storage process,because the radial advance of the reaction is hindered by the low thermal conductivity of the solid reactant particles.Heat transmission partitions were added to enhance the performance of the reactor.The performance of the modified reactor was compared with that of a conventional reactor.The radial heat transmission partitions in the modified reactor effectively enhance the energy storage rate and reduce the reaction time by 59.5%compared with the reactor without partitions.

纳米C-S-H晶核对水泥浆体流变性能的影响

纳米C-S-H晶核由于对水泥早期水化的显著加速效果逐渐被广泛用作早强剂,通过流变仪测试掺纳米C-S-H晶核水泥浆体的塑性黏度、动态屈服应力、静态屈服应力和触变性,以研究纳米C-S-H晶核对水泥浆体流变性能的影响。结果表明:纳米C-S-H晶核掺入水泥浆体后,水泥浆体塑性黏度、动态屈服应力、静态屈服应力和触变性均随之增加,掺量越大,增加越多。水灰比对水泥浆体的流变性能也具有显著影响,水灰比越小,浆体的塑性黏度、动态屈服应力、静态屈服应力和触变性越大。

纳米C-S-H掺量对再生砂浆力学性能的影响

为了提高再生砂浆的早期力学性能,采用纳米水化硅酸钙(C-S-H)对再生砂浆进行改性,并对其增强机理进行了探讨。同时,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、压汞法(MIP)等微观测试方法对纳米C-S-H改性再生砂浆的微观结构进行了测试。结果表明,纳米C-S-H的增强效果显著,再生砂浆的7d抗压和抗折强度分别达到33.5MPa和2.3MPa,相对于未添加C-S-H的试样分别提高了31.4%和27.8%。SEM照片显示,添加纳米C-S-H后,再生砂浆基体更加致密;XRD结果表明,随着纳米C-S-H的添加,再生砂浆的水化产物含量增加;MIP结果表明,纳米C-S-H细化了孔结构,再生砂浆的孔隙率明显降低。

Mass transfer model,preparation and applications of zeolite membranes for pervaporation dehydration:A review

Pervaporation(including vapor permeation) is a kind of new membrane separation technology, possessing the advantages of high efficiency, energy saving and convenient operation. It has promising application in the separation and purification of organic solvents. Dehydration is an important step in the production and recovery of organic solvents. Zeolite membranes have attracted wide attention for pervaporation dehydration due to their high separation performance and good thermal/chemical stability. So far, zeolite membranes have been preliminarily industrialized for dehydration of organic solvents. This paper reviews the recent development of zeolite membranes for pervaporation dehydration, including mass transfer models, preparation and applications of zeolite membranes. The review also discusses the current industrial applications of zeolite membranes and their future development in pervaporation.

Comparison of three methods for natural gas dehydration

This paper compares three methods for natural gas dehydration that are widely applied in industry：（1） absorption by triethylene glycol, （2） adsorption on solid desiccants and （3） condensation. A comparison is made according to their energy demand and suitability for use. The energy calculations are performed on a model where 105 Nm3/h water saturated natural gas is processed at 30 °C. The pressure of the gas varies from 7 to 20 MPa. The required outlet concentration of water in natural gas is equivalent to the dew point temperature of -10 °C at gas pressure of 4 MPa.

Preparation of nanocrystalline γ-Al_2O_3 catalyst using different procedures for methanol dehydration to dimethyl ether

A series of nanocrystalline γ-alumina are synthesized by different procedures, namely, thermal decomposition method （sample A）, precipita-tion method （sample B） and sol-gel method using sucrose and hexadecyltrimethyl ammonium bromide （CTAB） as templates （samples C and D, respectively）. Textural and acidic properties of γ-alumina samples are characterized by XRD, N2 adsorption-desorption and NH3-TPD techniques. Vapor-phase dehydration of methanol into dimethyl ether is carried out over these samples. Among them, sample C shows the highest catalytic activity. NH3-TPD analysis reveals that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently higher catalytic activity. Thermal decomposition method leads to decrease in both surface area and moderate acidity, therefore it is the cause of lower catalytic activity.

Catalytic performance of hierarchical H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether

Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5zeolite as the source and characterized by scanning electron microscopy,transmission electron microscopy,energy dispersive spectroscopy,X-ray diffraction,N2 adsorption-desorption measurement and NH3 temperature-programmed desorption.The catalytic performances for the methanol dehydration to dimethyl ether over H-ZSM-5/MCM-41 were evaluated.Among these catalysts,H-ZSM-5/MCM-41 prepared with NaOH dosage (nNa/nSi) varying from 0.4 to 0.47 presented excellent catalytic activity with more than 80%methanol conversion and 100%dimethyl ether selectivity in a wide temperature range of 170—300℃,and H-ZSM-5/MCM-41 prepared with nNa/nSi=0.47 showed constant methanol conversion of about 88.7%,100% dimethyl ether selectivity and excellent lifetime at 220℃.The excellent catalytic performances were due to the highly active and uniform acidic sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves.The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether process was also discussed.

Recent advances in acid-resistant zeolite T membranes for dehydration of organics

Zeolite membranes offer outstanding potentials in separation of many molecular mixtures due to their molecular sieving selectivity and the high thermal and mechanical stability that allow them to operate at harsh conditions.Development of durable and high separation performance membranes with lower fabrication and operation cost are highly demanded for industrial applications. Zeolite T membrane possesses good acid-resistance with excellent hydrophilic properties as compared to NaA zeolite membrane and can be extended to industrial organic dehydrations under an acidic environment. In the present review the research advances in development of zeolite T membranes for the dehydration of organic mixtures in acidic conditions are summarized. Especially the low temperature synthesis, and epitaxial growth of the zeolite membrane with high performance are well addressed, besides emphasis is particularly placed on ensemble synthesis of hollow fiber zeolite T membrane module and its future prospects for industrial separations.

The effect of FER zeolite acid sites in methanol-to-dimethyl-ether catalytic dehydration

In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.

Dehydration of xylose to furfural over niobium phosphate catalyst in biphasic solvent system

Phosphoric acid treated niobic acid(NbP)was used for the dehydration of xylose to furfural in biphasic solvent system,which was found to exhibit the best performance among the tested catalysts.The excellent performance of NbP could be explained by the better synergistic cooperation between Bro¨nsted and Lewis acid sites.Moreover,NbP showed good stability and no obvious deactivation or leaching of Nb could be observed after six continuous recycles.

Effects of Ultrasonic on the Dehydration Function of Sludge and Discussion on Internal Mechanism

[Objective] The aim was to study the effects of ultrasonic on the dehydration function of sludge and internal mechanism.[Method] Taking the residual sludge from a municipal domestic sewage treatment plant as an object,the effects of ultrasonic time and sound energy density on the dehydration function of sludge were studied firstly,then the internal mechanism of improvement of sludge dehydration function by ultrasonic was discussed.[Result] As the increase of ultrasonic time,sludge particles became smaller,and COD of sludge filtrate went up obviously;meanwhile,the capillary suction time (CST) of sludge increased firstly and then decreased,and the minimum value (75.7 s) appeared when ultrasonic time was 8 s.With the raising of sound energy density,the size of sludge particles went down gradually.However,long ultrasonic time and high sound energy density could decrease the dehydration function of sludge.For the possible mechanism of improvement of sludge dehydration function by ultrasonic,ultrasonic adjusted and regrouped sludge,and hydration water in the sludge was released.[Conclusion] The study could provide certain theoretical foundation for the industrial application of ultrasonic.

Synthesis of nanocrystalline γ-Al_2O_3 by sol-gel and precipitation methods for methanol dehydration to dimethyl ether

The capability of sol-gel and conventional precipitation techniques for the synthesis of nanocrystalline γ-alumina was investigated. These catalysts were used for vapor-phase dehydration of methanol to dimethyl ether in a fixed-bed reactor under the same operating conditions （T = 300 ？C, P = 1 bar, LHSV = 2.8, 11.7, 26.1 h？1） and characterized by means of N2 adsorption-desorption, NH3-TPD, XRD, TGA and SEM techniques. According to the experimental results, the catalysts prepared using sol-gel method in non-aqueous medium showed better performance compared with those prepared by other methods.

PEG-SO_3H as catalyst for the Beckmann rearrangement and dehydration of oximes

Under mild conditions, conversion of a variety of ketoximes and aldoximes to their corresponding amides and nitriles proceeded in the presence of PEG-SO3H with high yields.

Chemical dehydration coupling multi-effect evaporation to treat waste sulfuric acid in titanium dioxide production process

In order to concentrate the diluted sulfuric acid from the titanium dioxide(TiO2)production of sulphate process,a new concentration process was proposed by coupling chemical dehydration and multi-effect evaporation.The ferrous sulfate monohydrate(FeSO4·H2O),as the dehydrant,was added to the diluted sulfuric acid to form ferrous sulfate heptahydrate(FeSO4·7H2O)according to the H2SO4-FeSO4-H2O phase diagrams,which partially removes the water.This process was named as Chemical Dehydration Process.The residual water was further removed by two-effect evaporation and finally 70 wt%sulfuric acid was obtained.The FeSO4·H2O can be regenerated through drying and dehydration of FeSO4·7H2O.The results show that FeSO4·H2O is the most suitable dehydrant,the optimal reaction time of chemical dehydration process is 30 min,and low temperature is favorable for the dehydration reaction.45.17%of the entire removed water can be removed by chemical dehydration from the diluted sulfuric acid.This chemical dehydration process is also energy efficient with 24.76%saving compared with the direct evaporation process.Furthermore,51.21%of the FeSO4 dissolved originally in the diluted sulfuric acid are precipitated out during the chemical dehydration,which greatly reduces the solid precipitation and effectively alleviates the scaling in the subsequent multi-effect evaporation process.

Phosphorylated mesoporous carbon as effective catalyst for the selective fructose dehydration to HMF

Phosphorylated mesoporous carbons （PMCs） were investigated as catalysts in the dehydration of fructose to hydroxymethylfurfural （HMF）. The acidic PMCs show better selectivity to HMF compared to sulfonated carbon catalyst （SC） despite lower activity. The concentration of P-O groups on the PMC was correlated with the activity/selectivity of the catalysts; the higher the P-O concentration, the higher the activity. However, the higher the P-O content, the lower the selectivity to HME Indeed, a lower concentration of the P-O groups minimized the degradation of HMF to levulinic acid and the formation of by-products, such as humines. Stability tests showed that these systems deactivate due to the formation of humines and water insoluble by-products derived from the dehydration of fructose which blocked the catalytically active sites.

Predictors of dehydration and acute renal failure in patients with diverting loop ileostomy creation after colorectal surgery

BACKGROUND Despite the potential benefits of fecal diversion after low pelvic anastomosis in colorectal surgery, diverting loop ileostomy construction is related to significant rates of complications. AIM To determine potential predictors of high output related complications in patients with diverting loop ileostomy creation after colorectal surgery. METHODS Patients who underwent open and laparoscopic colorectal surgery requiring a diverting loop ileostomy from January 2010 to March 2018 were retrospectively analyzed. We included patients older than 18 years, who underwent colorectal surgery with primary low pelvic anastomosis, and with the creation of a diverting loop ileostomy, at elective or emergency settings for the treatment of benign or malignant conditions. Univariate and multivariate logistic regression analysis was used to determine the effect of the potential predictors on the rate of high output related complications. The high output related complications were dehydration and acute renal failure that required visits to the emergency department and hospitalizations. RESULTS Of the 102 patients included in the study, 23.5%(n = 24) suffered high output related complications. In this group of patients at least one visit to the emergency department (mean 1.6), and at least one readmission to the hospital was needed. The factors associated with high-output ileostomy, in the univariate analysis, were: urgent surgical intervention (OR = 2.6;P = 0.047), the development of postoperative complications (OR = 3;P = 0.024), have ulcerative colitis (OR = 4.8;P = 0.017), use of steroids (OR = 4.3;P = 0.010), mean output at discharge greater than 1000 mL/24 h (OR = 3.2;P = 0.016), and use of loperamide at discharge (OR = 2.8;P = 0.032). Multivariate logistic regression analysis identified two independent risk factors for high output related complications: ulcerative colitis [OR = 7.6 (95%CI: 1.81-31.95);P = 0.006], and ileostomy output at discharge ≥ 1000 mL/24 h [OR = 3.3 (1.18-9.37);P = 0.023]. CONCLUSION In our study, patients with ulcerative colitis and those with an ileostomy output above 1000 mL/24 h at discharge, were at increased risk of high output related complications.