Refining of rice bran oil by neutralization with calcium hydroxide

The applicability of calcium hydroxide (lime) in the neutralization of rice bran oil (RBO) was investigated. Crude RBO samples of three different free fatty acids (FFAs) (3.5–8.4 wt%) were degummed, dewaxed, bleached, and neutralized with lime and deodorized. The oils obtained thus were characterized by determining the color, peroxide value (PV), content of unsaponifiable matter (UM), and FFA. Conventionally practiced caustic soda neutralization (at 80–90°C) of FFA has in the present investigation been replaced by a high temperature (150–210°C) low pressure (2–4 mm Hg) reaction with lime. It was observed that neutralization with Ca(OH)₂ at high temperature (210°C) and under low pressure (2–4 mm Hg pressure) may substantially reduce the FFA content (0.8 wt%, after 2 h). The deodorized oil was found to be of acceptable color, PV, and content of UM and FFA. Neutralization of oil was also carried out by using NaHCO₃ and Na₂CO₃, nonconventional alkalies for neutralization, and the results were compared with NaOH and Ca(OH)₂. Overall recovery of oil in Ca(OH)₂ refining process (88.5 ± 0.6 wt%, for Sample 1 containing 8.4%‐wt FFA) was found to be more than other competitive processes studied.     

小型污水处理用氢氧化钙生产线的工艺设计

介绍了氢氧化钙消化机理、消化工艺及技术特点,并对氢氧化钙各项质量指标进行了分析。分析结果表明,采用干法生产的氢氧化钙,具有质量指标高、生产环境条件好和工艺简便等特点。     

The role of calcium hydroxide in the formation of thaumasite

It has recently been derived by thermodynamic calculation that the presence or absence of calcium hydroxide plays a vital role in the resistance of cement paste or concrete against the formation of thaumasite. To obtain experimental data on this matter, special binders have been mixed and used for the preparation of mortar bars. These specimens were exposed to moderate sulphate attack for a period of 18 months at a temperature of 8 °C. Mortar bars containing calcium hydroxide showed visual signs of attack a few months after exposure, leading to expansion, mass loss and complete failure. In contrast to this, no signs of attack were observed when no calcium hydroxide was present in the microstructure.These results confirm the conclusions of earlier thermodynamic calculations that the presence of calcium hydroxide has an important impact on the formation of thaumasite. Calcium-rich C-S-H formed in the presence of calcium hydroxide is vulnerable against sulphate attack and the formation of thaumasite. In the absence of calcium hydroxide, C-S-H has a much lower calcium/silicon ratio and a higher resistance against the formation of thaumasite.     

氢氧化钙脱除湿法磷酸中砷的研究

采用氢氧化钙作为沉淀剂,研究了搅拌速度、沉淀剂用量、反应时间、反应温度等因素对湿法磷酸中砷的脱除率及P2O5收率的影响,并通过正交实验,得出了适宜的工艺条件。在适宜的工艺条件下可得到较纯净的湿法磷酸。     

Effect of calcium hydroxide removal techniques on the bond strength of root canal sealers

To evaluate the influence of calcium-hydroxide(CH) with different vehicles on the push-out bond strength of different canal sealers to radicular dentin. 152 decrowned single-rooted human teeth were used. After preparation of root canals with nickel-titanium rotary files, 8 roots served as control groups. Then, the roots were divided as follows: (1) Calasept and (2) Surepaste (n = 72). Roots were further subgrouped according to the CH removal techniques: (1) %17 ethylenediaminetetraacetic acid (EDTA) + rotary file, (2) %17EDTA + hand file, and (3) %17EDTA (n = 24). Eight roots from each group sectioned longitudinally, divided into two pairs and photographed by stereomicroscope (n = 16). The remaining 16 roots in CH intracanal dressing groups were further divided into 2 subgroups according to the sealer used: (1) AH-Plus-jet and (2) Apexit-Plus (n = 8). Bond strengths of the root canal sealers to root canal dentin were measured using a push-out test setup. The data were statistically analyzed using multivariate analysis of variance p = 0.05. The push-out bond strength values were significantly affected by type of vehicle and the removal techniques (p < 0.05). The mean bond strength of AH-Plus-jet was significantly higher than Apexit-Plus, regardless of type of vehicle and the removal techniques (p < 0.05). There was no difference between vehicles on CH removal (p > 0.05). When examining the removal techniques, only irrigation with %17 EDTA left significantly larger amount of residue (p < 0.05). AH-Plus-jet showed better dislocation resistance than Apexit-Plus. Type of vehicle does not play a fundamental role in the degree of persistence of CH residues on the dentin walls. Instrumentation improves the removal efficiency of CH from root canal.     

Hydrogen production from cellulose using a reduced nickel catalyst

Cellulose, a major component of biomass, was gasified in hot-compressed water using a reduced nickel catalyst at different reaction temperatures from 200°C to 350°C. The reaction mixture was separated to gases, oil, char and water-soluble products to discuss reaction mechanism based on the product distribution. The water-soluble products were considered as intermediates, and the obtained hydrogen was consumed by methanation reaction. The following simplified reaction scheme was proposed:

The effect of supports was also examined. Supports showed the strong effect on the gas yield, and the catalytic activity depended on the overall catalyst size rather than the surface area.     

Hydrogen production from used lubricating oils

Used lubricating oils (lube oils) are generated throughout the year and collected in central locations in many communities. Disposing lube oil in an improper manner contaminates environment to a great degree. Used lube oil can be valuable as a re-refined lubricant or as an energy source. Lube oil is a complex mixture of aliphatic and polycyclic hydrocarbons formulated to withstand high service temperatures in internal combustion engines. Both synthetic and mineral oils contain a high concentration of hydrogen (about 13–14 wt%). At the Florida Solar Energy Center, we have developed a process that converts lube oils to hydrogen and other valuable low molecular weight hydrocarbons. The lube oil reformation experiments were carried out using several commercially available dehydrogenation catalysts at a range of reactor temperatures and pressures, residence times and steam to carbon ratios. In this paper, the data obtained to date and the results are presented and discussed.     

Crystallisation of calcium hydroxide in early age model and ordinary cementitious systems

The distribution and morphology of CH particles in various cementitious systems was investigated to determine which parameters influence their nucleation and growth. Morphological image analysis of SEM-BSE images of polished cross-sections was used to measure CH distribution, particle size and shape within the microstructure. It was observed that CH crystallises according to two main patterns, the first consisting of a few, large, convoluted and unevenly distributed clusters, while the second consists of numerous smaller particles, evenly and closely distributed in the matrix. The growth of CH in Portland cement type systems seems to be the result of a specific interaction between the availability of gypsum and alumina, with CH crystals nucleating in the vicinity of gypsum particles.     

Biopolymer-assisted green synthesis and characterization of calcium hydroxide nanoparticles

The use of biopolymers in the synthesis of different nanostructures can be a cost effective and eco-friendly approach. In the present study, a facile and “green” sol–gel method was employed for preparing calcium hydroxide nanoparticles (Ca(OH)₂-NPs) in gelatin matrix as a bio-template. Prepared nanoparticles were characterized by different instruments such as powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), and Fourier transform infrared spectroscopy (FTIR). The PXRD analysis revealed hexagonal Ca(OH)₂-NPs with preferential orientation in (101) reflection plane. They are hexagonal in shape with a mean particle size of approximately 42 nm in thickness. The synthesized Ca(OH)₂-NPs using gelatin were found to be comparable to those obtained from conventional methods using hazardous capping/stabilizing polymeric agents or surfactants and this route can be an excellent alternative for the synthesis of Ca(OH)₂-NPs using biomaterials.     

Hydrogen production from bioethanol reforming in supercritical water

Hydrogen production by reforming and oxidative reforming of ethanol in supercritical water (SCW) at the intermediate temperature range of 500-600 °C and pressure of 25 MPa were investigated at different ethanol concentrations or water to ethanol ratios (3, 20 and 30), with the absence and the presence of oxygen (oxygen to ethanol ratio between 0 and 0.156). Hydrogen was the main product accompanied with relatively low amounts of carbon dioxide, methane and carbon monoxide. Some liquid products, such as acetaldehyde and, occasionally, methanol were present. The ethanol conversion and hydrogen yield and selectivity increased substantially as the water to ethanol ratio and the reaction temperature increased. Ethanol was almost completely reformed and mainly converted to hydrogen giving a H₂/CO ratio of 2.6 at 550 °C and water to ethanol ratio of 30 without carbon formation. Coke deposition was favored at low water to ethanol ratio, especially at high temperatures (≥550 °C). The hydrogen yield improved as the ethanol was partially oxidized by the oxygen added into the feed at oxygen to ethanol ratios <0.071. It was evidenced that the metal components in Inconel 625 reactor wall reduced by a hydrogen stream acted as a catalyst promoting hydrocarbon reforming as well as water-gas-shift reactions while dehydrogenation of ethanol forming acetaldehyde can proceed homogeneously under the SCW condition. However, at high oxygen to ethanol ratio, the reactor wall was gradually deactivated after being exposed to the oxidant in the feed. The loss of the catalytic activity of the reactor surface was mainly due to the metal oxide formation resulting in reduction of catalytic activity of the reactor wall and reforming of carbon species was no longer promoted.     

Investigation of calcium zirconate formation by sintering zirconium dioxide with calcium hydroxide

The present paper analysed the formation of calcium zirconate from zirconium dioxide and calcium hydroxide through solid state reaction. Different mole ratios and sintering temperatures are investigated. The sintering temperature was reduced to 1200?°C. Due to the decomposition process of the calcia source during firing the volume expansion in the sintered samples was remarkable. A good homogenisation of the raw mixture is necessary to obtain a complete reaction of the material. The microstructure of the calcium zirconate gained from calcium hydroxide and from calcium carbonate did not differ. Moreover, a difference in reactivity due to varying microstructure and temperature of decomposition between the different calcia sources could not be determined. Thus calcium carbonate is less hazardous and resulted in a higher yield of calcium zirconate compared to calcium hydroxide as calcia source.     

Hydrogen production from catalytic gasification of cellulose in supercritical water

Interests in large-scale use of biomass for energy and in hydrogen are motivated largely by global environmental issues. Cellulose and sawdust were gasified in supercritical water to produce hydrogen-rich gas in this paper, and Ru/C, Pd/C, CeO₂ paticles, nano-CeO₂ and nano-(CeZr)_xO₂ were selected as catalysts. The experimental results showed that the catalytic activities were Ru/C > Pd/C > nano-(CeZr)_xO₂ > nano-CeO₂ > CeO₂ particle in turn. Low-concentration sodium carboxymethylcellulose (CMC) (2–3 wt.%) was mixed with particulate biomass and water to form a uniform and stable viscous paste which can be efficiently gasified. The 10 wt.% cellulose or sawdust with CMC can be gasified near completely with Ru/C catalyst to produce 2–4 g hydrogen yield and 11–15 g potential hydrogen yield per 100 g feedstock at the condition of 500 °C, 27 MPa, 20 min residence time in supercritical water.     

Gas absorption into aqueous reactive slurries of calcium and magnesium hydroxide in a multiphase reactor

Investigation of absorption of SO₂ into aqueous slurries of fine and reactive hydroxide particle of calcium and magnesium was carried out in a stirred vessel at 298 K at realistically high mass transfer coefficients. Enhancement in the rate of gas absorption was measured at different solid loadings and speed of agitation. The absorption process is theoretically analyzed using two different models. For the SO₂–Ca(OH)₂ system, a single reaction plane model was used and for the SO₂–Mg(OH)₂ system, a two reaction plane model incorporating the solids dissolution promoted by the reactions with the absorbed SO₂ in the liquid film was employed. A correct procedure was adopted to estimate the contribution of the suspended particles in the enhancement of gas absorption. Theoretical enhancement factors thus obtained compared well with the experimental data. The extra enhancement observed for the SO₂–Mg(OH)₂ system could be explained from the reaction between SO₂ and the dissolved [SO₃]²⁻.     

聚丙烯酰胺原位合成氢氧化钙颗粒的研究

利用超声波技术,以氯化钙和氢氧化钠为原料,在聚丙烯酰胺(PAAM)水溶液中原位合成氢氧化钙,考察了超声波作用时间和PAAM浓度对Ca(OH)2粒径的影响。结果表明:超声波在反应前期起到分散作用,但到反应后期反而起到促进颗粒团聚的作用;当PAAM质量百分数为0.24%时合成产物的粒径最小。     

Improving the high-temperature performances of a layered double hydroxide, [Ni4Al(OH)10]NO3, through calcium hydroxide coatings

In order to improve high-temperature performances, calcium hydroxide was coated onto [Ni₄Al(OH)₁₀]NO₃ through surface modification or mechanical blending. The existence of Ca(OH)₂ was revealed by XRD, and SEM which showed that there are Ca(OH)₂-rich blocks in the sample containing 13.0 wt% calcium prepared by surface modification. The addition of Ca(OH)₂ can retard the structural transformation from the layered double hydroxide [Ni₄Al(OH)₁₀]NO₃ to β-Ni(OH)₂. In addition, it improves charge/discharge performances and electrochemical reversibility by elevating the oxygen evolution potential, increasing the double layer capacity C_dl and decreasing the charge transfer resistance R_ct.     

Effects of humidity on calcite block fabrication using calcium hydroxide compact

Calcite has attracted attention as an artificial bone replacement material and as a precursor for the fabrication of carbonate apatite, which is also an artificial bone replacement material. In this study, the effect of humidity on calcite block fabrication was investigated using calcium hydroxide (Ca(OH)₂) compact. Ca(OH)₂ compact and Ca(OH)₂ paste compact were exposed to CO₂ at room temperature under 0%, 50%, and 100% humidity for two weeks. No carbonation was observed when Ca(OH)₂ compact was exposed to CO₂ under 0% humidity. In contrast, Ca(OH)₂ compact transformed into pure calcite under 100% humidity. Forty percent of the Ca(OH)₂ compact transformed into calcite under 50% humidity, while 30% of the Ca(OH)₂ paste compact transformed into calcite. Interestingly, the diametral tensile strength of the Ca(OH)₂ paste compact was four times higher than that of the Ca(OH)₂ compact when both were exposed to CO₂ under 100% humidity, despite the paste compact׳s lower conversion into apatite. After exposure to CO₂, SEM observations revealed that in the case of the paste compact, the Ca(OH)₂ powder was bridged with a precipitate, whereas in the case of Ca(OH)₂ compact, no precipitate was found. Results obtained in this study demonstrated that carbonation of the Ca(OH)₂ compact at room temperature was the result of a dissolution–precipitation reaction. Ca(OH)₂ powder was dissolved into water to supply the Ca²⁺, and CO₃²⁻ was supplied for the calcite precipitation from the interaction of CO₂ and water. Excess humidity from the paste compact was the key to the precipitation of the calcite bridge. The presence of the calcite bridge resulted in a higher mechanical strength for the calcite block.     

Assessment of a synchrotron X-ray method for quantitative analysis of calcium hydroxide

Thermogravimetric analysis (TGA) and quantitative X-ray diffraction (QXRD) are widely used to determine the calcium hydroxide (CH) content in cementitious systems containing blends of Portland cement, fly ash, blast furnace slag, silica fume and other pozzolanic and hydraulic materials. These techniques, however, are destructive to cement samples and subject to various forms of error. While precise weight losses can be measured by TGA, extracting information from samples with multiple overlapping thermal events is difficult. And, however, while QXRD can offer easier deconvolution, the accuracy for components below about 5 wt.% is typically poor when a laboratory X-ray source is used. Furthermore, the destructive nature of both techniques prevents using them to study the in situ hydration of a single contiguous sample for kinetic analysis. In an attempt to overcome these problems, the present research evaluated the use of synchrotron X-rays for quantitative analysis of CH.A synchrotron X-ray source was used to develop calibration data for quantification of the amount of CH in mixtures with fly ash. These data were compared to conventional laboratory XRD data for like samples. While both methods were found to offer good quantification, synchrotron XRD (SXRD) provided a broader range of detectability and higher accuracy than laboratory diffraction and removed the subjectivity as compared to TGA analysis. Further, the sealed glass capillaries used with the synchrotron source provided a nondestructive closed, in situ environment for tracking hydrating specimens from zero to any desired age.     

Biodiesel production from soybean oil using calcined Li–Al layered double hydroxide catalysts

The transesterification of soybean oil to fatty acid methyl esters was studied using a calcined Li–Al layered double hydroxide catalyst. The catalyst exhibited high activity, with near quantitative oil conversion being obtained under mild conditions (reflux temperature of methanol) and short reaction times (≤ 4 h). The influence of relevant parameters (catalyst calcination temperature, methanol to oil mole ratio, catalyst charge and reaction duration) was examined.     

Hydrogen production by the partial oxidation and steam reforming of tar from hot coke oven gas

Hot coke oven gas (COG) with a temperature of about 1050 K was produced from a test unit for coke production, the capacity of which was 80 kg of coal. The COG was introduced into an experimental unit with a tar converter where oxygen and steam were injected. Over 98% of the total carbon in the hot COG was partially oxidized, reformed with steam and converted to hydrogen and CO. About 1 Nm³/h of hydrogen was continuously produced for 5 h in this experiment. The experimental results suggest that three to five times the amount of hydrogen and CO that were present in the original COG could be recovered by this technology, utilizing the heat of the hot COG for the reaction. The feasibility study showed that hydrogen can be produced by this technology at a lower cost and higher efficiency than by the separation of cold COG.     

非离子表面活性剂存在下纳米氢氧化镁的水热处理

本文研究了在非离子表面活性剂PEG6000存在下纳米氢氧化镁的水热处理规律。产品采用X射线衍射、热重-差热分析、透射电子显微镜等进行了表征。结果表明:由于PEG6000的空间位阻作用以及与晶面的吸附作用,在PEG6000存在下进行氢氧化镁的水热处理,不仅可以改善氢氧化镁的结晶性和分散性,而且可有效地防止粒径的快速增长。当PEG6000的用量为氢氧化镁质量的4.4%,水热温度为180℃,水热时间为5h时,可制得结晶完整、分散性好、平均粒径61nm的六方片状纳米级氢氧化镁。