Reducing Energy Consumption and CO2 Emissions in Thermally Coupled Azeotropic Distillation

The design and optimization procedures of a heterogeneous thermally coupled azeotropic distillation sequence with a side stripper (TCADS‐SS) for the purification of isopropanol has been investigated. The proposed procedures can detect the optimal values of the design variables and thereby guarantee the minimum energy consumption, which is related to the minimum CO₂ emissions and the lowest total annual cost (TAC). The procedures are applied to the study of the separation of azeotropic mixtures using the two distillation sequences. In the TCADS‐SS, the top end of the side stripper has both liquid and vapor exchange with the main column, which eliminates a condenser in contrast with the conventional heterogeneous azeotropic distillation sequence (CHADS). The results show that not only reductions in energy consumption and CO₂ emissions but also higher thermodynamic efficiency can be obtained for the TCADS‐SS.     

Economic model predictive control with time‐varying objective function for nonlinear process systems

Economic model predictive control (EMPC) is a control scheme that combines real‐time dynamic economic process optimization with the feedback properties of model predictive control (MPC) by replacing the quadratic cost function with a general economic cost function. Almost all the recent work on EMPC involves cost functions that are time invariant (do not explicitly account for time‐varying process economics). In the present work, we focus on the development of a Lyapunov‐based EMPC (LEMPC) scheme that is formulated with an explicitly time‐varying economic cost function. First, the formulation of the proposed two‐mode LEMPC is given. Second, closed‐loop stability is proven through a theoretical treatment. Last, we demonstrate through extensive closed‐loop simulations of a chemical process that the proposed LEMPC can achieve stability with time‐varying economic cost as well as improve economic performance of the process over a conventional MPC scheme. © 2013 American Institute of Chemical Engineers AIChE J 60: 507–519, 2014     

Design and control of fraction cutting for the separation of mixed alcohols from the Fischer-Tropsch aqueous by-products

Since the minimum-boiling azeotropes of C2-C8 alcohols with water and high-water content (up to 95% (mass)) in the Fischer-Tropsch aqueous by-products, the separation is energy-intensive and challenging. The energy-saving strategy for the complete separation of the Fischer-Tropsch aqueous by-products has received massive attention in recent decades. In this study, a stripper-sidestream decanter process is proposed by exploiting homogeneous azeotropes (C2-C3 alcohols-water) and heterogeneous azeotropes (C4-C8 alcohols-water). The introduction of the stripping column for pre-dehydration avoids the re-vaporization of the mixture, and energy carried by the overhead vapor is conserved instead of being removed in a condenser. The precise fraction cutting of C1-C3 alcohol-water mixture, C4-C8 alcohols, and water is realized by the sidestream distillation column. The C4-C8 alcohols rich mixture withdrawn from the sidestream flows into the decanter to break the distillation boundary, where the organic phase returns to the sidestream distillation column to obtain the dehydrated C4-C8 alcohols, and the aqueous phase enters the stripping column. Steady-state optimization based on total annual cost (TAC) minimization shows that the stripper-sidestream decanter process reduces TAC by 17.00% and saves energy by 21.27% compared with the conventional three-column distillation process. Further, a control structure of the process is established, and dynamic simulations show that the control structure combining a differential controller with a low-selector exhibits robust control. This study provides a novel design scheme and deepens the insights into the efficient separation of aqueous by-products of the Fischer-Tropsch synthesis.     

Implementation of Ethanol Dehydration Using Dividing-Wall Heterogeneous Azeotropic Distillation Column

In this article, the design and optimization procedures of a dividing-wall column for heterogeneous azeotropic distillation (DWC-A) using cyclohexane as an entrainer for ethanol dehydration are investigated. The proposed procedures can detect the optimal values of the design variables and thereby guarantee the minimum energy requirements, which is related to the minimum CO₂ emissions and the lowest total annual cost (TAC). Since ethanol and water form an azeotrope under atmosphere pressure, a conventional heterogeneous azeotropic distillation sequence (CHADS), including an azeotropic column and a recovery column, is usually used to perform the ethanol dehydration process. However, due to high energy requirements and equipment investments of CHADS, the TAC is at a relatively high level. DWC-A can be used to eliminate the condenser of the second column and decrease the degree of back-mixing. Both CHADS and DWC-A are simulated with Aspen Plus®, and the results show that DWC-A has an energy saving of 42.17% and the TAC reduction of 35.18% along with higher thermodynamic efficiency and reduction in greenhouse gas emissions.     

Ozone applications for after‐clearing of disperse‐dyed poly(lactic acid) fibres

In this study, the effectiveness of the ozonation process, in neutral distilled water at room temperature, as a clearing process for disperse‐dyed poly(lactic acid) fibre fabrics is investigated. The efficiency of simultaneous decolorisation of dyebath effluent and clearing of dyed poly(lactic acid) in the cooled dyebath after completion of the poly(lactic acid) dyeing cycle is also explored. Conventional alkaline reduction clearing with sodium dithionite was chosen as a control clearing process for comparison. Wash fastness, colour difference, colour removal (in Hazen) and chemical oxygen demand values were determined and compared. Long ozone treatment times at high ozone dose resulted in unacceptable colour differences. The colour difference problem was solved by use of lower ozone dose; however, a warm soaping step had to be added to the after‐clearing sequence in order to achieve the desired fastness properties. A 33% reduction on the chemical oxygen demand load of the total process (dyeing + after‐clearing) could be achieved by ozone after‐clearing instead of using a conventional reduction clearing treatment. The addition of the warm soaping step to improve the fastness properties of the ozonated samples increased the total chemical oxygen demand of the process (dyeing + ozonation in water + warm soaping), but a 12–18% reduction on the chemical oxygen demand load of the total process was observed when compared with the conventional treatment sequence (dyeing + reduction clearing).     

Sorption enhanced steam reforming (SESR): a direct route towards efficient hydrogen production from biomass‐derived compounds

OVERVIEW: Efficient conversion of biomass to hydrogen is imperative in order to realize sustainable hydrogen production. Sorption enhanced steam reforming (SESR) is an emerging technology to produce high purity hydrogen directly from biomass‐derived oxygenates, by integrating steam reforming, water‐gas shift and CO₂ separation in one‐stage. Factors such as simplicity of the hydrogen production process, flexibility in feedstock, high hydrogen yield and low cost, make the SESR process attractive for biomass conversion to fuels. IMPACT: Recent work has demonstrated that SESR of biomass‐derived oxygenates has greater potential than conventional steam reforming for hydrogen production. The flexibility of SESR processes resides in the diversity of feedstocks, which can be gases (e.g. biogas, syngas from biomass gasification), liquids (e.g. bioethanol, glycerol, sugars or liquid wastes from biomass processing) and solids (e.g. lignocellulosic biomass). SESR can be developed to realize a simple biomass conversion process but with high energy efficiency. APPLICATIONS: Hydrogen production by SESR of biomass‐derived compounds can be integrated into existing oil refineries and bio‐refineries for hydrotreating processing, making the production of gasoline and diesel greener. Moreover, hydrogen from SESR can be directly fed to fuel cells for power generation. Copyright © 2012 Society of Chemical Industry     

Preparation of novel heterogeneous cation‐permeable membranes from blends of sulfonated poly(phenylene sulfide) and poly(ether sulfone)

Novel heterogeneous cation‐exchange membranes using poly (ether sulfone)(PES) as binder and sulfonated poly(phenylene sulfide) (SPPS) powder as polyelectrolyte were prepared by the solution casting‐immersion method. Compared with a conventional route for heterogeneous membrane, the steps of milling resin into fine powders and the pressing at high temperature are avoided, and thus permits a simple technique for the preparation of such membrane. The effect of the particle size and loading of SPPS resin on the properties of the membranes such as ion‐exchange capacity, water content, electrical resistance, transport number, diffusion coefficient of electrolytes, etc., have been studied. It is shown that the membrane fundamental properties are largely dependent on both the resin loading and the particle size of SPPS resin. By adjusting these two important parameters, one can obtain heterogeneous membrane with both good conductivity, selectivity, and proper water content for different industrial purposes such as electrodialysis, diffusional dialysis, etc. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 167–174, 2004     

分隔壁萃取精馏塔分离醋酸水溶液的模拟

提出了一种新的单塔萃取精馏精制醋酸水溶液的新工艺,该工艺采用分隔壁萃取精馏塔(DWC-E)替代常规萃取精馏流程的萃取精馏塔及溶剂回收塔,不仅节省了设备投资,而且降低了总能耗。利用Aspen Plus模拟软件,对DWC-E塔及常规萃取流程进行了模拟。DWC-E塔的操作条件:塔板数40块,侧线精馏段的板数10块,回流比2,溶剂摩尔比2.5,在此条件下,比较了常规萃取精馏流程与分隔壁精馏塔内温度、液相组成及汽液相流量的变化。结果表明,DWC-E塔比常规的2塔萃取精馏流程节能23.91%。     

Control analysis of an extractive dividing-wall column used for ethanol dehydration

This paper deals with design and control of an extractive dividing-wall distillation column (EDWC) for ethanol dehydration using ethylene glycol as entrainer. An initial design, based on a section analogy procedure for a conventional extractive distillation sequence, was obtained and then used in an optimization process to minimize the total annual cost. It was shown that the EDWC can result in significant savings over the conventional process. As these savings sometimes go along with a decrease in the control properties, an investigation of two control structures for the EDWC and one for the conventional column configuration was performed next.It was observed in closed-loop simulations that the EDWC with an appropriate structure exhibited good control properties and that its closed-loop responses were similar to those obtained for the operation of a conventional extractive distillation system.     

Rapid mass production of novel 3D Cu@CuI core‐shell mesh as highly flexible and efficient photocatalyst

We report a relatively simple and economical approach for mass production of Cu@CuI mesh. This novel core‐shell structure is CuI‐coated Cu mesh, fabricated by one‐step in situ iodination of commercial copper mesh at an ambient temperature. Such a Cu@CuI mesh is low‐cost and can be successfully used for the degradation of soluble organic pollutants in water under UV light. The novel 3D Cu@CuI core‐shell structure allows for high electron/hole separation and thus leads to high catalytic efficiency. Rhodamine B (RhB) is fully degraded in even just 6 minutes using a Cu@CuI mesh as the photocatalyst. Unlike the currently reported photocatalysts mostly in the form of powders, nanoparticles, and/or nanowires, the 3D Cu@CuI mesh is freestanding and flexible, and therefore is easily separated from water after photocatalysis without causing secondary pollution. This is a significant advance toward tackling the expansive separation issue of the conventional catalysts, because the ultra‐simple separation process of 3D Cu@CuI mesh can facilitate its industry application. With a fantastic combination of low cost, facile and green fabrication, high catalytic efficiency and easy separation 3D architecture, the Cu@CuI mesh may serve as a promising candidate for water purification.     

基于VPLS的TE过程统计产品质量与费用控制

Product quality and operation cost control obtain increasing emphases in modern chemical system engineering. To improve the fault detection power of the partial least square (PLS) method for quality control, a new QRPV statistic is proposed in terms of the VP (variable importance in projection) indices of monitored process variables, which is significantly advanced over and different from the conventional Q statistic. QRPV is calculated only by the residuals of the remarkable process variables (RPVs). Therefore, it is the dominant relation between quality and RPV not all process variables (as in the case of the conventional PLS) that is monitored by this new VP-PLS (VPLS) method. The combination of QRPV and T2 statistics is applied to the quality and cost control of the Tennessee Eastman (TE) process, and weak faults can be detected as quickly as possible. Consequently, the product quality of TE process is guaranteed and operation costs are reduced.     

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.     

Effect of sludge retention time in sludge holding tank on excess sludge production in the oxic‐settling‐anoxic (OSA) activated sludge process

The activated sludge process is a core technology in wastewater treatment plants. Excess sludge produced in the process must be treated and disposed of properly and may account for up to 60% of total plant operating cost. Therefore, it is necessary to develop new biological concepts to minimize excess sludge production. The oxic‐settling‐anoxic process (OSA process), a modified activated sludge process, may produce less excess sludge than the conventional activated sludge process. The effect of sludge retention time in the sludge holding tank of the OSA process on excess sludge yield has been studied. Four pilot‐scale activated sludge systems were employed, one of which was a conventional activated sludge process, and was used as the control system. The other three were OSA systems operated with different sludge retention times (5.5 h, 7.6 h, and 11.5 h) in the sludge holding tank. All systems were operated with synthetic wastewater for 7 months. Results showed that the three OSA processes with 5.5 h, 7.6 h, and 11.5 h sludge retention time reduced the excess sludge by 33%, 23% and 14%, respectively. Compared to the control process, chemical oxygen demand (COD) removal efficiency and effluent NH₃–N concentration were not significantly influenced, but total nitrogen (TN) removal efficiency decreased by 0–9%. Total phosphorus (TP) removal efficiency of OSA processes with 7.6 h and 11.5 h sludge retention time increased by 19%. Sludge settleability was excellent in the three OSA processes. No distinct shift in the diversity of the predominant species was found in microbial populations. We conclude that the OSA system could reduce excess sludge production. Results suggest 6–7 h sludge retention time would be optimal. Copyright © 2007 Society of Chemical Industry     

Techno‐Economic Comparison of a 7‐MWth Biomass Chemical Looping Gasification Unit with Conventional Systems

The chemical looping process is an alternative method to provide conventional gasification (CG) systems with the required oxygen. The syngas produced via chemical looping has a higher calorific value than that generated by a conventional process with air. For comparison, a conventional gasification unit with pure oxygen (CGPO) and a chemical looping gasification (CLG) system were simulated with Aspen Plus. The CGPO reactor consisted of a bubbling fluidized bed and sand as bed material with oxygen supplied via a pressure swing adsorption unit. The CLG comprised a bubbling fluidized‐bed gasifier working in parallel with a fast fluidized‐bed oxidizer. The total capital investment (TCI) of the CLG unit was higher than that of the CGPO unit but the annual operating cost of the former was less which repays the difference in TCI in less than six years.     

Design of entrainer-enhanced reactive distillation for the synthesis of butyl cellosolve acetate

An innovative entrainer-enhanced reactive distillation (RD) process is presented, which aims to the production of high-purity butyl cellosolve acetate from butyl cellosolve and acetic acid via an esterification reaction. This entrainer-enhanced RD process can procure technical advantages from both heterogeneous azeotropic distillation and RD. Solvents such as cyclohexane, ethylene dichloride, toluene, and octane are considered as candidates in this esterification RD process. The function of entrainers is to simplify the separation between water and acetic acid. For this purpose, the proper entrainer to use is thus evaluated based on its mutual solubility with water in two liquid phases. Simulation results reveal that total annual cost can be substantially reduced when cyclohexane, toluene, and octane are used as entrainers in the RD column. The octane-enhanced RD provides the most economical design in this studied case.     

Conceptual design of energy-saving stripping process for industrial sour water

Sour water contains ammonia, carbon dioxide, and hydrogen sulfides, producing from oil refining, coking, and coal gasification. To reduce the energy consumption in sour water stripping, a novel process is proposed which integrates with the bottom flashing mechanical vapor recompression heat pump (MVRHP) for treating such wastewater. Here, Aspen Plus^TM as a powerful set of chemical process simulation software is utilized to investigate the economy and feasibility of the novel process. Comparison of the results of two process simulations, it can be seen that it is possible to reduce the total annual cost by nearly 45% to adopt the novel process, despite the capital investment increase 45% more than the conventional process. Thus, the provided conceptual design will play a guiding role in the industrialization of the process.     

费托合成水相副产物混合醇分离： 馏分切割工艺设计及控制

费托合成水相副产物主要为C₁~C₈醇（甲醇、乙醇、丙醇、丁醇、戊醇、己醇、庚醇和辛醇）与水的混合物,其中水的质量分数高达95%,且C₂~C₈醇与水均形成最低共沸物。此类醇水混合物的完全分离虽具重要价值,但难度大、能耗高,一直是学界和工业界的关注热点。本研究充分利用C₂~C₃醇水混合物的均相共沸物特性和C₄~C₈醇水混合物的高度非均相共沸物特性,提出两塔-侧线分相器工艺：通过侧线精馏塔实现C₁~C₃醇水、富C₄~C₈醇水和水的精准馏分切割;富C₄~C₈醇水混合物通入分相器以打破精馏边界,其中富水相返回侧线精馏塔,富醇相进入汽提塔,得到无水C₄~C₈醇混合物。基于年度总成本（total annual cost,TAC）的稳态优化表明,与常规三塔粗分流程相比,两塔-侧线分相器工艺能够降低TAC 14.79%,节约能耗15.96%。进一步,建立了两塔-侧线分相器工艺的控制结构,动态模拟表明,结合浓度控制器与前馈比例的控制结构表现出良好的控制性能。     

Economics of small solar-assisted multiple-effect stack distillation plants

The objective of this paper is to compare the economics of using solar energy to operate small, multiple-effect seawater distillation systems in remote areas with the conventional method of using fossil fuels. The particular multiple-effect system used is an advanced horizontal-tube, falling-film system called “multiple-effect stack” (MES) in which the pumping energy requirement is relatively low compared with the horizontal in-line system. Three system configurations were investigated: (1) a conventional system using a steam generator to provide steam for the MES evaporator and a diesel generator to provide pumping power, (2) a solar-assisted system which uses solar thermal collectors to provide hot water (instead of steam) for the evaporator and a diesel generator for pumping power, and (3) a solar stand-alone system which uses solar thermal collectors for the evaporator heat requirement and a solar PV array to provide electrical energy for pumping. At the present time, solar energy cannot compete favorably with fossil energy, particularly under the present international market prices of crude oil. However, in many remote sunny areas of the world where the real cost of fossil energy can be very high, the use of solar energy can be an attractive alternative. Two important cost parameters affect the relative economics of solar energy vis-à-vis conventional (fossil) energy: the collector cost in dollars per square meter and the cost of diesel oil in dollars per giga Joule. Solar energy becomes more competitive as the local cost of procuring conventional fuel increases and as the collector cost decreases. The water cost from a solar thermal-diesel-MES system (configuration #2) can be seen to approach the water cost from a steam generator-diesel-MES system (configuration #1) when the collector cost drops to $200/m² and diesel oil cost at the remote site reaches $50/GJ. Using a 100% solar system (configuration #3) with solar thermal and solar PV collectors, the economics was seen to improve in favor of the solar system. Even when diesel fuel can be procured at $10/GJ at the remote site, the cost of water from the solar system can be seen to approach that from a conventional plant when thermal collectors costing $200/m² are used. The cost of water from the solar system was shown to be always less than that from a conventional system which uses diesel oil procured at the high price of $50/GJ, but always higher than water produced from a conventional system using diesel oil at the low price of $10/GJ.     

Toward a Continuous‐Flow Synthesis of Boscalid®

A two‐step continuous‐flow protocol for the synthesis of 2‐amino‐4′‐chlorobiphenyl, a key intermediate for the industrial preparation of the fungicide Boscalid^® is described. Initial tetrakis(triphenylphosphine)palladium‐catalyzed high‐temperature Suzuki–Miyaura cross‐coupling of 1‐chloro‐2‐nitrobenzene with 4‐chlorophenylboronic acid in a microtubular flow reactor at 160 °C using the tert‐butanol/water/potassium tert‐butoxide solvent/base system provides 4′‐chloro‐2‐nitrobiphenyl in high yield. After in‐line scavenging of palladium metal with the aid of a thiourea‐based resin, subsequent heterogeneous catalytic hydrogenation is performed over platinum‐on‐charcoal in a dedicated continuous‐flow hydrogenation device. The overall two‐step homogeneous/heterogeneous catalytic process can be performed in a single operation providing the desired 2‐amino‐4′‐chlorobiphenyl in good overall yield and high selectivity.     

An eco‐efficient rationalized leather process

BACKGROUND: The leather industry is under pressure to develop environmentally efficient leather‐making processes to comply with modern pollution and discharge legislation. Conventional leather‐processing methods are known to contribute significant pollution loads in tannery wastewaters. The rationalized process described here involves a salt‐free curing, lime and sulfide‐free beamhouse process and post‐tanning followed by tanning employing a reverse leather‐processing technique. RESULTS: Scanning electron microscopy (SEM) analysis substantiated that the grain surface, fibre separation and tight packing of fibres are similar for leathers from conventional and rationalized processes. The functional performance of the leathers is found to be on par with that of conventionally processed leathers. The rationalized leather process reduces the usage and discharge of chemicals by 68% and 82%, respectively. It also enjoys the reduction in biochemical oxygen demand (BOD), chemical oxygen demand, Cl^?, SO₄^2? and total solids loads by 58%, 62%, 95%, 66% and 85%, respectively. The rationalized process also results in reduction of water consumption and discharge and energy by 37%, 37% and 38%, respectively. CONCLUSION: The rationalized process utilizes resources efficiently with reduced environmental impact without compromising leather qualities and can be seen as being eco‐efficient compared to the conventional leather process. Copyright © 2007 Society of Chemical Industry