醋酸生产技术发展动向

对国外现有主要醋酸生产技术和正在开发的醋酸新工艺和新技术作了比较和评述 ,为我国醋酸工业发展提供借鉴。     

Design and control of acetic acid dehydration system via heterogeneous azeotropic distillation

Acetic acid dehydration is an important operation in the production of aromatic acid, such as terephthalic acid or in the manufacture of cellulose acetate. Although acetic acid and water does not form azeotrope, but using simple distillation to separate these two components is not practical. The reason is because the system has tangent pinch on the pure water end, thus it is more customary in industry to use an entrainer via a heterogeneous azeotropic distillation column system for the separation. In this study, a suitable entrainer is selected from three candidate acetates through rigorous steady-state simulation of this system. Optimum process design and operating condition are determined to keep high-purity bottom acetic acid composition and also keep a small acetic acid loss through top aqueous draw. Furthermore, the overall control strategy of this column system is proposed to hold both bottom and top product specifications in spite of feed rate and feed composition load disturbances. The proposed overall control strategy is very simple requiring only one tray temperature control loop inside the heterogeneous azeotropic column.     

ACETIC ACID AS AN OXYGEN CARRIER BETWEEN TWO PHASES FOR EPOXIDATION OF OLEIC ACID

Acetic acid was found to be an effective oxygen carrier for epoxidation of oleic acid. The reaction model of oleic acid epoxidation in the two-phase reaction system was systematically analyzed and the rate determining step was experimentally identified.

The results indicated that the rate of oxidation of the unsaturated acid was independent of the concentration of oleic acid and depended on the mixing rate and the rate of formation peracetic acid which in turn depended on the concentration of acetic acid, strength of acid catalyst and the oxygen source, hydrogen peroxide. In the region of reaction control, the rate equation of epoxidation was found to be

$

where k = 2.98 × 10^-2 M^-2 min^-1 at temperature of 35^°C.     

RECOVERY OF ACETIC ACID OVER WATER BY PERVAPORATION WITH A COMBINATION OF HYDROPHOBIC IONIC LIQUIDS

The present work considers the application of an integrated pervaporation process to improve the pervaporation performance of acetic acid over water. This integrated pervaporation process was based on a plain PDMS membrane with a hydrophobic ionic liquid composed of a heterocyclic cation and [PF₆]^- anions. The hydrophobic ionic liquid was introduced as the third phase between the aqueous phase and the plain PDMS membrane for improving mass-transfer of acetic acid from its aqueous matrix to the PDMS membrane. The primary results indicated that the ionic liquid as an extractant prior to pervaporation was favorable for improving the permeate selectivity and the permeate flux of acetic acid compared with using only a plain PDMS membrane. This performance could be attributed to the acetic acid concentrated and the water molecules rejected by ionic liquid prior to pervaporation. Extraction of a real effluent containing acetic acid from an antibiotic pharmaceutical plant was carried out using the above integrated pervaporation, and the results imply that this integrated pervaporation process could be scaled up for recovering acetic acids over its water-rich effluents.     

RECOVERY OF ACETIC ACID OVER WATER BY PERVAPORATION WITH A COMBINATION OF HYDROPHOBIC IONIC LIQUIDS

The present work considers the application of an integrated pervaporation process to improve the pervaporation performance of acetic acid over water. This integrated pervaporation process was based on a plain PDMS membrane with a hydrophobic ionic liquid composed of a heterocyclic cation and [PF₆]^? anions. The hydrophobic ionic liquid was introduced as the third phase between the aqueous phase and the plain PDMS membrane for improving mass-transfer of acetic acid from its aqueous matrix to the PDMS membrane. The primary results indicated that the ionic liquid as an extractant prior to pervaporation was favorable for improving the permeate selectivity and the permeate flux of acetic acid compared with using only a plain PDMS membrane. This performance could be attributed to the acetic acid concentrated and the water molecules rejected by ionic liquid prior to pervaporation. Extraction of a real effluent containing acetic acid from an antibiotic pharmaceutical plant was carried out using the above integrated pervaporation, and the results imply that this integrated pervaporation process could be scaled up for recovering acetic acids over its water-rich effluents.     

醋酸生产精馏装置改造的研究

吉化电石厂的醋酸生产目前仍采用乙醛氧化法制取醋酸的工艺技术,精馏工艺采用的流程为高低高的双塔精馏方式。鉴于此,本研究采用的工艺为单塔精馏,减小物料在精馏过程中的停留时间,以达到节能,省时,减少费用的目的,避免双塔精馏所造成的设备与能源的浪费。     

乙烯装置丙烯精馏系统设计方案优化

介绍了丙烯精馏系统传统设计流程及改进设计流程,并对其流程特点进行了分析,明确指出了各自的优缺点。针对改进设计双塔流程,利用流程模拟计算PRO-Ⅱ软件平台,分别研究了无中间再沸器和设置中间再沸器两个流程方案,在能耗相同的条件下,计算出不同塔盘数时的丙烯损失,并对其增加塔盘数后的可实施性、投资增加与多回收丙烯的经济性进行了初步分析。无中间再沸器流程在投资及年收益方面均优于设置中间再沸器流程,在装置急冷水热量充足的情况下,应首先推荐应用。     

对铬酸渣回收利用的两次改造

介绍该厂铬盐车间利用磷酸法对铬酸渣回收利用的两次技术改造及主要设备的结构,以供同行业厂家参考。     

乙酸液相催化氧化动力学的研究

以乙酸钴、乙酸锰为催化剂，四溴乙烷为促进剂，在半间歇搅拌釜式钛材反应器中对乙酸的液相催化氧化动力学进行了研究，弄清了乙酸氧化损失的规律，提出了降低乙酸氧化速率的可行措施，得到了二氧化碳及乙酸甲酯的生成速率方程。     

Energy saving in acetic acid process using an azeotropic distillation column with a side stripper

Dilute acetic acid is obtained primarily from fermentation and synthesis processes and cannot be produced by simple distillation due to relatively low volatility of acetic acid compared to water. Instead, an azeotropic distillation is applied to increase the concentration of dilute acetic acid. When acetic acid is extracted from a dilute aqueous solution using a solvent mixture of ester and alcohol, its recovery requires an energy-intensive azeotropic distillation. In the water stripping process that follows azeotropic distillation, two distillation columns handle the acetic acid and water mixture in similar composition. Therefore, the two columns can be combined as a side stripper connected to the azeotropic distillation column. The energy-saving effect is examined with the HYSYS (Aspentech Corporation) evaluation of the process. Compared to the conventional process, the modified process suggests 39% reduction in heating duty and 24% coolant savings. The economic analysis shows 32% decrease in investment and 36% utility savings. Based on heat utilization analysis, the thermodynamic efficiency is enhanced by 11%.     

导向浮阀塔板在醋酸生产中的应用

导向浮阀塔板是在F1型浮阀塔板的基础上开发成功的，较早应用于炼油装置的常减压蒸馏塔，在提高轻油的收率上获得了较大的经济效益，在化工产品的分离中应用较少。该项目在醋酸装置的精馏工序中，采用先进的导向浮阀塔板改造原有的F1型浮阀塔板，达到节能降耗，提高醋酸收率，增加醋酸产量，提高经济效益的目的。     

稀醋酸催化精馏过程的反应动力学

研究了常压下温度308-328 K范围内用阳离子交换树脂作催化剂的稀醋酸合成醋酸甲酯本征反应动力学,得到基于Langmuir-Hinshelwood吸附理论用活度表示的通用动力学方程,在此基础上建立了数学模型并通过模拟计算证明了催化精馏过程是回收水溶液中醋酸的有效方案,为工业设计放大提供了理论依据.     

Investigating the need of a pre-concentrator column for acetic acid dehydration system via heterogeneous azeotropic distillation

In our previous study [Chien, I.L., Zeng, K.L., Chao, H.Y., Liu, J.H. (2004). Design and control of acetic acid dehydration system via heterogeneous azeotropic distillation. Chemical Engineering Science 59(21), 4547-4567.], an acetic acid dehydration system has been designed. The suitable entrainer selected for that system is iso-butyl acetate. Design and control of the system has been studied in detail to maintain high-purity bottom acetic acid concentration and also keep a small acetic acid loss through top aqueous draw. In that previous study, the feed composition is assumed to contain equal molar of acetic acid and water. However, in a typical waste acid recovery application, the above assumption may be too rich in acetic acid. In this paper, a feed stream containing 80 mol% water and 20 mol% of acetic acid is investigated. Several design alternatives can be deduced including one commonly used in industry by adding a pre-concentrator column in the upstream of a heterogeneous azeotropic distillation column. The necessity of this pre-concentrator column from design and control view points will be thoroughly investigated in this paper. The final recommended process design is a tradeoff between total annual cost (TAC) and operability of the system. The recommended design is a single heterogeneous azeotropic distillation column with aqueous reflux stream. Very wide feed composition and flow rate changes can be handled by this design with proper choice of the overall control strategy.     

萃取-蒸馏法处理与回收糠醛废水中醋酸的研究

本文研究了溶剂萃取法去除糠醛废水中醋酸的工艺过程。通过实验得出，用含磷溶剂和烷烃化合物组成的混合溶剂处理糠醛废水中，醋酸的回收率较高。含醋酸的溶剂可以通过蒸馏回收醋酸，回收的溶剂可以循环使用，经处理过的废水可以利用，从而达到不排放或少排放的闭路循环。     

Process optimization of an industrial acetic acid dehydration progress via heterogeneous azeotropic distillation

The simulated process model of the HAc dehydration process under actual overloaded condition was conducted by amending the model of standard condition in our previous work using the process data collected from actual production. Based on the actual process model, the operation optimization analysis of each plant(HAc dehydration column, decanter and NPA recycle column) was conducted using Residue Curve Maps(RCMs),sensitivity analysis and software optimization module. Based on the optimized parameters, the influence of feed impurity MA and the temperature of decanter on the separating effect and energy consumption of the whole process were analyzed. Then the whole process operation optimizing strategy was proposed with the objective that the total reboiler duty Q Total of C-1 and C-3 reaches the minimum value, keeping C-1 and C-3 at their optimized separation parameters obtained above, connecting all the broken recycle and connection streams, and using the temperature of D-1 as operation variable. The optimization result shows that the total reboiler duty Q Total of the whole process can reach the minimum value of 128.32 × 10~6 k J·h~(-1) when the temperature of decanter is 352.35 K, and it can save 5.94 × 10~6 k J·h~(-1), about 2.56 t·h~(-1) low-pressure saturated vapor.     

EFFECT OF ACETIC ACID ON CO2 CORROSION OF CARBON STEEL IN VAPOR-WATER TWO-PHASE HORIZONTAL FLOW

The effect of acetic acid on the corrosion behavior of X 65 and C 1018 carbon steel in vapor-water two-phase stratified flow (Vsg: 2 m/s; Vsl: 0.1 m/s) at 2 bars total pressure, 1.54 bars CO₂ partial pressure, pH 5.5, and 80°C was studied in a low pressure-high temperature multiphase flow horizontal loop using electrochemical and mass loss techniques. The liquid phase is composed of 1% NaCl aqueous solution containing different concentrations of acetic acid (500 to 5000 ppm total acetic acid), and the gas phase is composed of CO₂-acetic acid-water vapor mixture. The corrosion rates, on both the top and bottom of the line, increase with increase in acetic acid concentration, which was attributed to the contribution of hydrogen ions by the free acetic acid to the cathodic reaction. Partial coverage of the metal surface by FeCO₃ on both the top and bottom of the line is reported to be responsible for the observed localized corrosion. Surface analysis investigated with SEM and XRD is reported.

A vapor-liquid equilibrium model was developed for the system studied.     

醋酸水溶液络合萃取过程优化与分析

用正交试验设计络合萃取醋酸过程研究方案,通过极差分析法和统计软件分析试验结果,得出过程在所选因素水平范围内的最优条件为：0．2331mol/L的醋酸、体积百分比为30％的三烷基胺、50％的正辛醇、温度25℃;在影响醋酸络合萃取过程的因素中,正辛醇的体积百分比最显著,其次为三烷基胺的体积百分比。研究结果对各种因素相互制约与交叉且会同时变化的实际络合萃取过程具有指导意义。     

Choice of suitable entrainer in heteroazeotropic batch distillation system for acetic acid dehydration

Mixture containing acetic acid and water does not form azeotrope. However, because of tangent pinch on the pure water end, it is customary in industry to add an entrainer into this mixture to aid the separation via heterogeneous azeotropic distillation. When the production scale is relatively small, it is more beneficial to run the acetic acid dehydration in batch mode. In Chien et al. [Chien, I. L., K. L. Zeng, H. Y. Chao, and J. H. Liu, “Design and Control of Acetic Acid Dehydration System via Heterogeneous Azeotropic Distillation,” Chemical Engineering Science, 59, 4547 (2004)], a suitable entrainer for acetic acid dehydration operating in continuous mode was found to be iso-butyl acetate. This paper demonstrates that although iso-butyl acetate is a good entrainer for continuous heterogeneous azeotropic distillation system, it is not suitable in heteroazeotropic batch system for acetic acid dehydration. Instead, the performances of two other acetates are compared for the suggestion of better entrainer in batch operation. An extremely simple batch operating sequence for acetic acid dehydration will be demonstrated via dynamic simulation. The proposed batch operation is very robust in terms of the particular values chosen for the operating variables. This proposed batch operation gives very similar separation performance comparing to a multivessel operation and requires less process, instrumentation, and control equipments.     

MATHEMATICAL AND EXPERIMENTAL INVESTIGATION ON NOX RECOVERY IN FLUIDIZED BED ADSORBERS FOR EXHAUST GASES OF NITRIC ACID PLANTS

A mathematical model for sorption of NOx from exhaust gas of nitric acid plants by activated carbon (AC) in a fluidized bed is proposed based on two-phase flow theory of fluidization. To solve the proposed model a computer program has been developed. The output of this program reveals the effects of various parameters such as temperature, inlet gas velocity, particle diameter, and inlet gas concentration on the rate of adsorption. To evaluate the proposed model, a pilot-scale plant was erected and the obtained experimental data were compared with the values predicted by the model. A good agreement is observed between these values. Once the validity of the proposed model is checked, it could be used for obtaining the optimum operating condition for this type of bed.