Extraction of cellulose with subcritical and Supercritical ethanol

Cotton cellulose was extracted with ethanol in sub-and supercritical states dynamically. The degree of conversion was 95.4% and the extract yield was 55.2% when cotton cellulose was non-isothermally extracted with ethanol from 20°C to 400°C. From an engineering standpoint, in the temperature range from 200°C to 320°C, the rate of extract formation could adequately be described by a second-order reaction kinetics equation with the activation energy of 105.3 kJ/mol and the pre-exponential factor of 3.53×107 s?1. With the non-isothermal experimental technique, it was possible to determine the kinetic parameters; conversion degree and extract yield by one experiment.

High-pressure Phase Equilibria for Binary Ethanol System Containing Supercritical CO_2

High-pressure phase behavior of supercritical (SC) CO2+ethanol system was investigated at 333.2 K,348.2K, 353.2K, 368.2K, 413.2K and 453.2K and pressure from 2.0MPa to 14.3MPa. The measurement was carried out in a cylindrical autoclave with a moveable piston and a window for adjustment and observation of phase equilibria at given T and p. The samples were taken from two coexisting phases and were analyzed to obtain their compositions. It is shown that the solubility of SC CO2 in ethanol increases drastically with pressures at the given temperature, but the content of ethanol in CO2-rich phase increase faintly.

Pressure Effect on the Local Composition SurroundingEthyl Acetoacetate in Supercritical CO_2 - Ethanol Mixture

The keto-enol tautomerization of ethyl acetoacetate (EAA) in supercritical CO2-ethanol mixture has been investigated at 308.15 K and at different pressures using UV-Visspectroscopy. A method for calculating the local composition about EAA has been developed based on the relationship between the equilibrium constant and dielectric property of the mixing solvent. The results indicate that the local concentration of ethanol surrounding EAA is much higher than that in the bulk.

Supercritical fluid extraction of useful compounds from sage

A qualitative analysis of supercritical fluid extraction (SFE) of the medically useful compound, sage (Salvia officinalis) is presented in this study. Carbon dioxide was used as a supercritical solvent. Effects of operating conditions such as temperature, pressure, and extraction time were investigated. The effect of addition of cosolvents was also studied. The extracted useful compounds were identified and analyzed using GC-MS chromatography. The analysis of the extract obtained by SFE showed certain significant major compounds that are considered medically important. These major compounds are 1R-.alpha.-Pinene, D-Limonene, l-Camphene, and b-Pinene, and Eucalyptol. Although, there was no consistent trend with respect to the effect of the studied parameters on the composition of the extract, the selectivity of these major compounds are dependant on the operating conditions, manily the operating pressure. An increase in the pressure resulted in an increase in herb extraction yield;this is true for certain group of extracts, while the inverse is also true for other group of compounds. The effect of certain cosolvents on the extractability of sage showed a significant improvement of the yield of some particular constituents of sage.

Separation of Erucic Acid from Rape-Seed Oil Using Supercritical Carbon Dioxide with Entrainer

Separation of erucic acid from rape-seed oil using supercritical carbon dioxide with entrainer was carried on a pilot column with an inner diameter 14 mm and an effective total height 2.2 m. Experiments were focused on the effects of entrainers, i.e. acetone, ethanol and ethyl acetate, on the extraction. It is showed that entrainers made selectivity lower, but separation time shorter.

A catalyst-free novel synthesis of diethyl carbonate from ethyl carbamate in supercritical ethanol

Diethyl carbonate has been synthesized via the alcoholysis of ethyl carbamate in supercritical ethanol under catalyst-free conditions.The influences of various parameters such as reaction temperature,reaction time,reaction pressure,ethanol/ethyl molar ratios and reaction loading volume on the yield of DEC were studied systematically.The experimental results indicated that the alcoholysis of ethyl carbamate was greatly improved in supercritical ethanol.The optimal reaction conditions were as follows：a reaction temperature of 573 K,a reaction time of 30 min,a reaction pressure of 13.2 MPa,an ethanol/ethyl carbamate molar ratio of 10 and a reactor loading volume of 285 μL respectively.The optimal yield of DEC was 22.9%.

Phase equilibria of supercritical CO_2-ethanol-stearic acid ternary system and hydrogen bonding between ethanol and stearic acid

Solubility of stearic acid in supercritical CO 2 with ethanol cosolvent was determined at 308.15 K in the pressure range from 8 to 16 MPa, and the cosolvent concentration ranges from 0 mol% to 4 mol%. The corresponding densities of the fluid phases were also measured. It was observed that ethanol enhances the solubility significantly. The solubility increases with pressure noticeably at lower pressure, especially at lower cosolvent concentrations. The effect of pressure on the solubility is very limited at higher pressures or higher cosolvent concentrations. The hydrogen bonding between ethanol and stearic acid in supercritical CO 2 was also studied using FTIR in order to understand the mechanism of the solubility enhancement by ethanol.

Relationship between the density of supercritical CO_(2)^(+) ethanol binary system and its critical properties

The dependent relation between temperature and pressure of supercritical CO2+ ethanol binary system under the pressure range from 5 to 10 MPa with the variety of densities and mole fractions of ethanol that range from 0 to 2% was investigated by the static visual method in a constant volume. The critical temperature and pressure were experimentally determined simultaneously. The PTρ figures at different ethanol contents were described based on the determined pressure and temperature data, from which pressure of supercritical CO2 + ethanol binary system was found to increase linearly with the increasing temperature. P-T lines show certain convergent feature in a specific concentration of ethanol and the convergent points shift to the region of higher temperature and pressure with the increasing ethanol compositions. Furthermore, the effect of density and ethanol concentration on the critical point of CO2 + ethanol binary system was discussed in details. Critical points increase linearly with the increasing mole fraction of ethanol in specific density and critical points change at different densities. The critical compressibility factors Zc of supercritical CO2 + ethanol binary systems at different compositions of ethanol were calculated and Z c -ρ figure was obtained accordingly. It was found from Z c -ρ figure that critical compressibility factors of supercritical CO2 unitary or binary systems decline linearly with the increasing density, by which the critical point can be predicted precisely.

Catalytic depolymerization/degradation of alkali lignin by dual-component catalysts in supercritical ethanol

Depolymerization of lignin is an important step to obtain lignin monomer for the synthesis of functional bio-polymers.In this paper,catalytic degradation/depolymerization of an alkali lignin was investigated in a supercritical ethanol system.The process conditions were optimized in terms of lignin monomer yield,and the liquid products and solid residue were characterized.Results show that the conversion rate of the alkali lignin was improved in both the Ni7Au3 catalyzed and Nickel-catalyzed systems with supercritical ethanol as the solvent.The maximum lignin conversion rate was 69.57%and 68%respectively for the Ni7Au3 and Nickel-based catalysis systems.Gas chromatography/mass spectroscopy(GC/MS)analysis indicated that the catalytic depolymerization products of alkali lignin were mainly monomeric phenolic compounds such as 2-methoxyphenol.The highest yield of 2-methoxyphenol(84.72%)was achieved with Ni7Au3 as the catalyst.

乙醇废水的超临界水氧化处理工艺研究

研究了以超临界水氧化法 (SCWO)处理乙醇废水的工艺过程 .实验表明 ,一氧化碳和二氧化碳分别是反应中间产物和最终产物 .5 5 0℃、2 5MPa、停留时间大于 15s时 ,SCWO能将乙醇完全氧化为二氧化碳 ,达到彻底处理的目的 .随停留时间增大、温度升高 ,乙醇的去除率增大 。

临界区乙醇中聚碳酸酯解聚研究

在温度160～260℃、压力1.4～8.5MPa、反应时间15～60min条件下,研究聚碳酸酯(PC)在超、亚临界乙醇中的解聚反应,着重考察反应温度、反应时间等条件对聚碳酸酯解聚行为的影响。结果表明:随温度的升高、反应时间的延长,解聚率增加;随温度的升高,主产物双酚A(BPA)产率先升高,之后下降;随着反应时间的延长,双酚A产率下降。其中温度对双酚A产率的影响最大。当投料比为8.0,反应温度为220℃,反应时间为15min时,主产物双酚A产率可达到80.4%,此时解聚率为98.8%。根据聚碳酸酯在超亚临界乙醇中解聚产物的分析,并结合聚碳酸酯的链节特点,提出聚碳酸酯的解聚机理。通过实验数据关联,得出解聚反应级数为一级,解聚反应活化能为58.03kJ·mol-1。研究结果为选择解聚介质和工艺参数提供依据。

秸秆超(亚)临界水预处理与水解技术

秸秆的资源化特别是乙醇化技术由于其技术可行性和产物高值化受到了广泛关注。预处理与水解是乙醇化的关键过程。目前针对秸秆的转化已经开展了多种化学或生物技术的研究,其中超(亚)临界技术与传统技术相比显示了独特的优势,如更高的反应速率、不需催化剂、无产物抑制等。本文在总结秸秆传统预处理与水解技术的基础上,对秸秆超(亚)临界水预处理与水解的过程和机理,特别是超临界和亚临界组合技术的研究现状、工艺及其相关研究进展进行了综述和分析,并阐述了超临界亚临界组合技术首先在超临界水中打破纤维结构进行初级水解,再通过亚临界反应将初级水解产物低聚糖进一步水解为葡萄糖的基本原理。最后对超(亚)临界技术在秸秆资源化领域中的研究和应用前景进行了展望。

聚碳酸酯在超临界乙醇中的降解

利用高压间歇反应器研究了聚碳酸酯（PC）在215～286℃、3．1～8．2MPa条件下乙醇溶液中的降解行为。通过气相色谱／质谱（GC／MS）和气相色谱（GC）对液相产物进行了定性和定量分析，同时分别通过红外（IR）和气相色谱对固相产物和气相产物进行了定性分析，在此基础上，提出了PC在超临界乙醇中的降解机理和降解反应模型，并进行了动力学研究。结果表明：PC在乙醇溶液中的降解可分为3个区域：超临界区、非超临界区和中间过渡区。在超临界区中，PC可实现完全降解，其主要单体双酚A（BPA）和碳酸二乙酯（DEC）的收率分别为92．26％和88．929／6。在超临界区PC的降解活化能为89．73kJ／mol；在非超临界区，PC的降解活化能为21．02kJ／mol。

TiO_2-活性炭复合材料吸附及光催化净化甲醛的研究

超临界乙醇条件下制备的TiO2-活性炭(Sc-TiO2-AC)复合材料,表征了所制备样品的结构,且对样品的吸附及光催化净化甲醛的性能进行了分析。实验表明,在超临界乙醇条件下可快速有效地制备出具很好的光催化与吸附协同效应的Sc-TiO2-AC复合材料。而且协同效应优于活性炭与Sc-TiO2样品的简单混合样品。研究表明产生这一协同效应时,光催化甲醛降解速率加快,同时光催化作用促使被活性炭吸附的污染物向TiO2表面迁移,使活性炭的吸附能力得以恢复,实现原位再生。实验表明,在300℃制备的Sc-TiO2-AC复合材料的甲醛去除率最高。300、350和400℃时的甲醛去除率在实验进行240min后分别达到100%、96%和93%。

超临界CO_2+CH_3OH及C_2H_5OH二元系的气液平衡

在带有石英可视窗和内搅拌的可变体积高压釜内 ,测定了超临界 CO2 +CH3OH及 C2 H5OH两个系统的相平衡数据 ,温度为 5 0～ 2 0 0℃ ,压力 4.0～ 1 6.0 MPa.利用从硬球模型得出的适用于高压高温的状态方程 ,计算了这两个系统的临界曲线 ,并与实验值进行比较 .

南极磷虾脂质提取方法的比较

实验分别比较了氯仿甲醇、正己烷和95%乙醇三种不同溶剂以及超临界CO2提取的南极磷虾脂质成分差异,为南极磷虾脂质的研究提供一定基础。结果表明,氯仿甲醇提取的脂质得率最高,为19.21%±0.59%。正己烷提取的得率最低,仅为14.24%±0.38%,甘油三酯和胆固醇含量最高,分别为46.98%±1.00%和3.68%±0.30%,但对极性脂的提取效果不理想,磷脂含量仅为19.20%±3.45%。95%乙醇提取的脂质磷脂含量35.59%±2.69%,不饱和脂肪酸中EPA和DHA含量是最高的,占总脂肪酸含量的41.13%,且95%乙醇安全性高,价格低廉,适合大规模工业化生产,可以作进一步的探讨。超临界CO2萃取技术作为脂质的一种温和提取手段,得到的脂质基本成分与氯仿甲醇近似,虽然安全性更高,但是超临界设备成本较高,不适于中小型企业工业化生产。

含乙醇废水的超临界水氧化反应动力学及反应机理

研究了等温平推流反应器中乙醇的超临界水氧化反应 (SCWO) ,反应温度 475～ 5 5 0℃、压力 2 2～ 3 0MPa、停留时间 0 6～ 63 7s、氧气与乙醇摩尔浓度比 4 5 6～ 9 0 9.一氧化碳和二氧化碳分别是反应中间产物和最终产物 .随停留时间增大、温度升高 ,乙醇去除率增大 ,压力和氧气浓度变化对过程无显著影响 .以幂指数方程描述乙醇SCWO动力学 ,乙醇和氧气的反应级数分别为 1和 0 ,计算值和实验值相差基本在 10 %以内 .超临界条件下分别以过氧化氢和氧气为氧化剂时乙醇的氧化反应无明显差别 ,亚临界条件下过氧化氢氧化速率大于氧气 .基于对此现象的分析 ,作者推测 :无论以过氧化氢或氧气作为氧化剂 ,在超临界水中 ,它们之间可以通过一系列自由基反应迅速达到平衡 ,且各物种的平衡分布与初始分布无关 。

玉米秆超临界乙醇解聚产物分析

[目的]研究玉米秆在超临界乙醇条件下的解聚产物。[方法]采用FTIR和GC/MS分析解聚产物。[结果]超临界乙醇解聚产物成分十分复杂,GC/MS分析鉴定出89种有机化合物,其中72种为含氧化合物,主要有酯、酚、醚、酮和醇等,还检测出少量烷烃、烯烃、芳烃、苯硫酚和含氮化合物,反映了解聚产物的高含氧量和低含氮硫量的特性。其中42.7%乙酯类可能是C12-C30的饱和脂肪酸、部分不饱和脂肪酸、邻苯二甲酸或苯丙酸等与乙醇酯化的结果;而22.9%的苯酚和苯二酚类物质、芳烃类及甲氧基苯类物质可能来源于木质素在超临界乙醇中的解聚作用。[结论]玉米秆的超临界乙醇解聚产物成分十分复杂,乙醇参与了玉米秆的超临界解聚反应。

甘油三乙酸酯超临界酯交换反应及其动力学研究

研究了在超临界条件下甘油三乙酸酯与甲醇或乙醇的酯交换反应,分别考察了超临界状态下醇油摩尔比和温度对反应的影响。实验结果表明,甲醇或乙醇与甘油三乙酸酯的摩尔比为14、反应温度为350℃、反应时间为20m in时,乙酸甲酯或乙酸乙酯的收率分别达100%和60%。对超临界状态下动力学的研究结果表明,甘油三乙酸酯与甲醇或乙醇的酯交换反应为拟一级反应,在相同的反应条件下,采用甲醇时酯交换反应速率比用乙醇时快,相应的甘油三乙酸酯的转化率也高;甘油三乙酸酯在超临界甲醇或乙醇中酯交换反应的表观活化能分别为58.7 kJ/mol和75.1 kJ/mol,甘油三乙酸酯与甲醇酯交换反应的活化能低于与乙醇酯交换反应的活化能,表明碳链短的醇更易进行酯交换反应。