Cold Flow Properties Research Articles

Performance and emission characteristics of a diesel engine running on optimized ethyl levulinate–biodiesel–diesel blends

In this study, biomass-based EL (ethyl levulinate) was evaluated as an additional fuel to biodiesel and diesel. Physical and chemical properties, including intersolubility, cold flow properties, spray evaporation, oxidation stability, anti-corrosive property, cleanliness, fire reliability and heating value of twelve different EL–biodiesel–diesel blends were analyzed. The results show that the fuel blends that were in line with China's national standard for biodiesel blend fuel (B5) have similar physical and chemical properties to pure diesel with improved cold flow properties. Optimized fuel blends based on grey relational analysis and analytic hierarchy process were selected to evaluate engine performance and emissions using an unmodified diesel engine test bench. The results show that engine power and torque with the fuel blends were in general similar to those with diesel (less than 3% differences). Both brake specific fuel and energy consumption were lower with the fuel blends than with diesel, suggesting higher fuel conversion efficiencies for the fuel blends. HC (Hydrocarbon) and CO (carbon monoxide) emissions and smoke opacity reduced significantly with the fuel blends compared with diesel while NOx (nitrogen oxides) and CO2 (carbon dioxide) emissions increased. Our study suggests that EL produced from lignocellulosic biomass could be used as a blending component with biodiesel and diesel for use in unmodified diesel engines and could potentially be a promising environment-friendly fuel.

Microwave assisted synthesis of biodiesel from soybean oil: Effect of poly (lactic acid)-oligomer on cold flow properties, IC engine performance and emission characteristics

In this study, the effect of poly (lactic acid)-oligomer (OLLA) on cold flow properties, IC engine performance and subsequently, exhaust gas emission characteristics is evaluated using microwave synthesized biodiesel from soybean oil. Biodiesel was synthesized by achieving maximum 99% conversion using KOH as catalyst at 60°C under optimum reaction time of five minutes. Cloud point, pour point, flash point and fire point of synthesized biodiesel were analyzed as reference properties. OLLA is synthesized in absence of catalyst at 150°C with the targeted molecular weight Mn∼1000Da and density ∼1.21gm/cm3. Subsequently, by blending ethyl lactate stabilized OLLA with biodiesel, the cloud point, pour point, flash point and fire point were reduced significantly. Polarizing optical microscopic images during temperature scan relate the effect of OLLA on cloud point crystal morphology which delayed the crystal formation with reduction in crystal nucleation density and size of the crystals. Rheological analyses are conducted to understand the Newtonian flow regime at lower temperature and change in the viscosity and flow activation energy of biodiesel in the presence of neat as well as with ethyl lactate stabilized OLLA. The engine performance test reveals the comparative utilization of brake specific fuel consumption and break thermal efficiency with significant reduction in carbon monoxide and incombustible hydrocarbon in the exhaust gases. Hence, present research demonstrates the use of OLLA for improvement in the cold flow properties of biodiesel and the exhaust gas emission characteristics.

Enhancement of Biodiesel Oxidation Stability Using Additives Obtained from Sewage Sludge Fast-Pyrolysis Liquids

In the present work, bio-oil derived from the catalytic pyrolysis of sewage sludge has been blended in small amounts with sunflower biodiesel with the aim of evaluating its potential as a novel, low-cost, and renewable biodiesel additive that could replace costly commercial biodiesel antioxidants normally used to date. The effect of blending small amounts of bio-oil with sunflower biodiesel on the biodiesel properties (oxidation stability, cold flow properties, flash point, and viscosity) has been analyzed. Furthermore, apart from studying the effect of adding low bio-oil concentrations (0.1, 1.8, and 3.5 mass %), the effect of other operating conditions, specifically the temperature (278–333 K) and mixing time (5–60 min), during the bio-oil and biodiesel blend preparations has also been analyzed. With regard the oxidation stability, blends prepared adding 3.5% mass fraction of bio-oil complied with the limits imposed by the ASTM D6751 and EN 14214 standards. Blending sewage sludge bio-oil and sunflower b...

Impact of ternary blends of biodiesel on diesel engine performance

The Pongamia and waste cooking oils are the main non edible oils for biodiesel production in India. The aim of the present work is to evaluate the fuel properties and investigate the impact on engine performance using Pongamia and waste cooking biodiesel and their ternary blend with diesel. The investigation of the fuel properties shows that Pongamia biodiesel and waste cooking biodiesel have poor cold flow property. This will lead to starting problem in the engine operation. To overcome this problem the ternary blends of diesel, waste cooking biodiesel and Pongamia biodiesel are prepared. The cloud and pour point for ternary blend, (WCB20:PB20:D60) were found to be 7°C and 6.5°C which are comparable to cloud and pour point of diesel 6°C and 5°C, respectively. The result of the test showed that brake specific fuel consumption for Pongamia biodiesel and waste cooking biodiesel is higher than ternary blend, (WCB20:PB20:D60) due to their lower energy content. The brake thermal efficiency of ternary blend and diesel is comparable while the Pongamia and waste cooking biodiesel have low efficiency. The result of investigation showed that ternary blend can be developed as alternate fuel.

Combustion Analysis of Polanga (<i>Calophyllum inophyllum</i>) Biodiesel

There is a mounting concern in many countries to explore fuels that are environment friendly. Although straight vegetable oils can be used in diesel engines, there are limitations in their usage due to their high viscosity, low volatility, and poor cold flow property. Biodiesel is a fatty acid alkyl ester, which can be derived from any vegetable oil by transesterification. Biodiesel is a renewable, biodegradable and non-toxic fuel. In the present study, polanga (Calophyllum inophyllum) oil was transesterified with methanol using sodium hydroxide as catalyst to obtain polanga biodiesel. To evaluate the combustion analysis, polanga biodiesel was tested in a single-cylinder, four-stroke, direct-injection, constant speed, diesel engine. The results were compared with combustion characteristics of diesel fuel. The result showed that polanga biodiesel exhibits similar combustion characteristics as that of diesel. The actual start of injection and start of combustion were found to be earlier for polanga biodiesel as compared to diesel. The ignition delay period was found to be shorter with polanga biodiesel. The magnitude of peak heat release rate and peak pressure was observed to be lower for polanga biodiesel. Though the location of peak heat release rate was earlier for polanga biodiesel, its peak pressure location was found be delayed when compared to diesel. Polanga biodiesel exhibits a shorter combustion duration than diesel. Since the measured parameters for biodiesel differs only by a smaller magnitude when compared with diesel, this investigation ensures the suitability of polanga biodiesel as a fuel for CI engines.

Effect of a glycerol-derived advanced biofuel –FAGE (fatty acid formal glycerol ester)– on the emissions of a diesel engine tested under the New European Driving Cycle

A new advanced biofuel –FAGE (fatty acid formal glycerol ester)– produced from crude glycerol has been blended with diesel fuel (20% FAGE content) and tested in an automotive engine following the New European Driving Cycle. Since cold flow properties, volatility and viscosity are the critical properties of this biofuel, the driving cycles were performed from both warm and cold starts. The FAGE blend showed significant benefits in hydrocarbon, carbon monoxide and particle emissions, particle number and opacity when the cycle was started from warm conditions. Such benefits were even more important during the extra-urban period, where also small engine efficiency benefits were found. Differently, the mentioned emissions increased substantially with respect to those of diesel during the first urban sub-cycle at cold start. Among the emitted hydrocarbons, the non-oxygenated ones were more sensible to the engine temperature. Also, the nucleation mode in the particle size distributions increased at cold conditions. NOx emissions were slightly increased with the FAGE blend during the extra-urban sub-cycle, and differences in the NO2/NO ratio were found during the initial urban sub-cycle from cold start. The results have been explained based mainly on the injection timings, the fuel–air ratio, the oxidation catalyst performance and the fuel properties.

Studying of the efficiency of a catalytic dewaxing process utilizing zeolite-based catalyst with an iron additive

The possibility of producing diesel fuel for cold climates from middle distillates of different origin in the process of the catalytic dewaxing over zeolite catalysts with additions of iron is investigated. Introducing iron into the zeolite ensures the high stability of the catalyst. To mitigate the known disadvantages of the above process, a flowsheet with the separation of hydrogenate into fractions depending on the characteristics of the feedstock, followed by the dewaxing of the separated heavy diesel fraction and combining the resulting product with a light fraction that has the desired cold flow properties and does not require dewaxing, is proposed. The technical result of using this flowsheet in combination with any catalytic dewaxing process is the production of diesel fuel for cold and arctic climates that meets the requirements of GOST R (Russian State Standard) 52368-2005 and/or GOST R (Russian State Standard) 55475-2013 with minimized production costs.

Hydroisomerization of Biomass Derived n-Hexadecane Towards Diesel Pool: Effect of Selective Removal External Surface Sites from Pt/ZSM-22

Abstract Influence of dealumination of zeolite ZSM-22 (Si/Al ratio of 45) by treating it with oxalic acid on its catalytic performance in n-hexadecane hydroisomerization reaction was studied. This reaction is an attempt in the direction of green and sustainable source of diesel via improving the cold-flow properties of deoxygenated vegetable oils. Pt (0.5 wt%) on ZSM-22 treated with 1 M oxalic acid afforded highest yields of the mono-branched paraffins. This improved is attributed to selective removal of active sites on external surface of zeolite crystals (responsible for undesired cracking reactions) using the bulkier dealuminating agent, oxalic acid. Thus, pore-mouth key-lock mechanism was brought to play the role to cause high selectivity to mono-branched isomers. Preferential external site deactivation was inferred from mesitylene cracking results. Effects of operating parameters such as temperature, and space velocity on product distribution also were studied. Also, kinetics of the reactions involved too has been in brief reported.

Cold flow and fuel properties of methyl oleate and palm-oil methyl ester blends

Biodiesel is a renewable, alternative diesel fuel derived from various oils or fats through transesterification. Biodiesel usually consists of alkyl esters of the parent oil. Palm-oil methyl ester (PME) is a prominent biodiesel in Southeast Asian countries such as Malaysia and Indonesia, which have a surplus production of palm oil. However, given the substantial amount of saturated fatty acids in palm oil, its methyl ester has poor cold-flow characteristics. In the present study, the physicochemical properties of specified blends of technical-grade methyl oleate (MO) and PME, namely, PME80/MO20, PME70/MO30, PME60/MO40, and PME50/MO50 (vol/vol%) were studied. The aim was to determine the optimum blend and achieve better cold-flow properties than neat PME. Differential scanning calorimetry analysis showed that increasing the MO proportion until 50% (vol%, vol%) led to maximum improvements in cloud point and cold filter plugging point, which were reduced to 70.38% and 91.69%, respectively. Important fuel properties (i.e., cetane number (CN), kinematic viscosity, density, gross heating value, net heating value, flash point, oxidation stability, and acid value) were also examined. All fuel properties of PME–MO blends were observed within the specified permissible limits of biodiesel standard (ASTM D 6751).

Formulation of microemulsion based hybrid biofuel from waste cooking oil – A comparative study with biodiesel

This investigation highlights the feasibility of microemulsion based hybrid biofuel from waste cooking oil (WCO) as an alternative to petro diesel. In this study, microemulsification to produce biofuel has been demonstrated as energy intensive and economically viable alternative route of liquid biofuel production. The microemulsion based hybrid biofuel systems formulated using ethanol as dispersed phase exhibited fuel properties which satisfied ASTM D6751 standards for biodiesel. This study also emphasizes the preparation of simple biofuel system by microemulsification without using any externally added surfactant. These simple fuel systems formulated only by using butan-2-ol as cosurfactant showed excellent physical stability with the formation of transparent Winsor IV systems. The presence of nano-sized droplets in the formulations confirmed the formation of reverse micellar microemulsion system. Moreover, cold flow properties of the systems were much superior to that of biodiesel. The present investigation suggests that the microemulsion based biofuel systems formulated from WCO can be an attractive candidate for biofuel industry in near future.

Fuel property enhancement of biodiesel fuels from common and alternative feedstocks via complementary blending

Fatty acid methyl esters (biodiesel) prepared from field pennycress and meadowfoam seed oils were blended with methyl esters from camelina, cottonseed, palm, and soybean oils in an effort to ameliorate technical deficiencies inherent to these biodiesel fuels. For instance, camelina, cottonseed, and soybean oil-derived biodiesels exhibited poor oxidative stabilities but satisfactory kinematic viscosities. Field pennycress and meadowfoam seed oil methyl esters yielded excellent cold flow properties but high kinematic viscosities. Thus, field pennycress and meadowfoam-derived biodiesel fuels were blended with the other biodiesels to simultaneously ameliorate cold flow, oxidative stability, and viscosity deficiencies inherent to the individual fuels. Highly linear correlations were noted between blend ratio and cold flow as well as viscosity after least squares statistical regression whereas a non-linear relationship was observed for oxidative stability. Equations generated from statistical regression were highly accurate at predicting KV, reasonably accurate for prediction of cold flow properties, and less accurate at predicting oxidative stability. In summary, complementary blending enhanced fuel properties such as cold flow, kinematic viscosity, and oxidative stability of biodiesel.

Cold flow properties improvement of Jatropha curcas biodiesel and waste cooking oil biodiesel using winterization and blending

The objective of this study was to study the cold flow properties of JCB (Jatropha curcas biodiesel) and WCB (Waste cooking oil biodiesel). For the purpose two methods were examined experimentally viz. winterization and blending of biodiesel samples with petro diesel and kerosene. Winterization was found to be effective as it improved the cold flow properties of biodiesel samples but at the same time decreased the yield and stability due to partially removal of saturated fatty acids. Blending was found to be more favorable for improvement in cold flow properties of biodiesel without any effect on yield, however, the biodiesel become more stable after blending. The CP and PP (pour point) for JCB for B20 blends with petro diesel were reported as 14.9 °C and 14 °C respectively, however, for WCB it was 12 °C and 11.5 °C respectively. Kerosene K20 samples was showing best result as the reported CP and PP were −1 °C and −2.2 °C respectively for JCB. However in case of WCB blends with kerosene, the reported CP and PP for K20 blends are −10.5 °C and −12 °C respectively.

Effect of pH on biodiesel production and the microbial structure of glucose-fed activated sludge

With the goal of reutilizing excess sludge, and decreasing the cost of lipid feedstocks, the effect of pH on enhancing biodiesel production via culturing special microbial communities from municipal activated sludge was investigated. The results indicated that controlling pH around 7.5 made biomass production and lipid accumulation more quickly under high initial glucose loading (40 g COD L−1) and COD:N ratio (90:1). Compared with the seed sludge (biodiesel yield of 5.2 ± 0.3 mg g−1 dry sludge), the cultivated sludge achieved higher biodiesel yields both with pH control and without. However, the biodiesel yield of the cultured sludge with pH control (69.3 ± 1.2 mg g−1 dry sludge) was higher than that of the sludge without (63.3 ± 0.4 mg g−1). More unsaturated fatty acid esters (64%, w/w total FAMEs) were obtained from the cultured sludge without pH control, which could improve the cold flow properties of biodiesel. The pH control did not make an essential difference in the microbial community at the end of cultivation. However, it improved the accumulation of Enterobacteriaceae and Shewanella in the cultured sludge. The dominant bacteria of Shewanella, Raoultella, Enterobacter, Kluyvera and two unclassified genera clustered with γ-proteobacteria within the cultured sludge possibly contributed to enhancing biodiesel production.

Co-processing of FCC light cycle oil and waste animal fats with straight run gas oil fraction

In the European Union the demand for middle distillates is growing, while decrease in the gasoline demand can be observed. Even the most complex refineries are not able to produce the economic yield distribution from the processed crude oil which constantly meets the changing market demand. The growing need of diesel fuel can only be satisfied by using unconventional feedstocks, such as bio-originated resources and less valuable refinery streams (e.g. light cycle oil with high aromatic content, >80%, from Fluid Catalytic Cracker).The aim of our experiments was the investigation (co-processing) of differently prepared mixtures from straight run gas oil (70–100%), light cycle oil (LCO: 0–10%) and waste animal fat (0–20%). There are no publicly available articles which present the use of these feedstock components. We investigated the effects of the process parameters (temperature: 300–380 °C, pressure: 40–70 bar, liquid hourly space velocity (LHSV): 0.75–2.0 h−1, H2/feedstock ratio: 600 Nm3/m3) on the quality and quantity of products obtained from different composition feedstocks. We found that with the usage of favourable parameter combination the total conversion of triglycerides and free fatty acids (FFA) into n-paraffins as well as the saturation of a significant part of the aromatic compounds and the desulphurisation of the LCO and straight run gas oil can be reached. Notable quality improvement was observed in case of all feedstock components at co-processing. High cetane number of alkanes formed from the conversion of triglycerides and FFAs, compensating the low cetane number of products (e.g. monoaromatics and diaromatics) from the saturation of polyaromatic components. Products obtained at advantageous process parameters can be excellent diesel fuel blending components, because they have low sulphur and aromatic content as well as adequate cetane number, density and cold flow properties. Besides these, they contain components from renewable sources, too.

Comparison of biofuel quality of waste derived oils as a function of oil extraction methods

Abstract Fish derived bio-oils have similar properties to petroleum-derived fuel oils and therefore the potential to be an alternative energy source. The quality of bio-oil as a fuel is determined by the quality of the feedstock and processing conditions. Fish oil may have poor cold flow properties due to the heterogeneity of the lipid composition. Different oil extraction methods produce different levels of homogeneity with respect to lipids. In this study, oil was extracted from fish waste via three different processes; modified fishmeal (MFM), supercritical extraction using carbon dioxide (SC-CO 2 ), and soxhlet extraction. The quality of oil extracted (composition, thermal degradation, physicochemical, and flow properties) were compared. The SC-CO 2 extracted 91% and the MFM extracted 71% of the total oil contained in the fish waste. The SC-CO 2 oil is more than 86 wt% triglycerides, representing a more homogeneous oil than the MFM at 70 wt% and soxhlet at 66 wt%. The free fatty acid (FFA) of SC-CO 2 oil is lower than MFM and soxhlet oil, making it a better feedstock for biodiesel production. Polar lipids were most abundant in the soxhlet oil at 22.98 wt%, followed by the MFM oil at 18.35 wt% and SC-CO 2 oil at 7.39 wt%. The MFM oil exhibited a shear-thinning non-Newtonian behavior, while the SC-CO 2 oil was Newtonian. Overall, the oil from SC-CO 2 showed better fuel properties, particularly as a blend and/or replacement for heating oil, than the MFM and soxhlet oil and the process has the potential for a lower environmental footprint.

Biodiesel production from waste salmon oil: kinetic modeling, properties of methyl esters, and economic feasibility of a low capacity plant

AbstractSalmon oil directly obtained from salmon silage in a tricanter centrifuge was subjected to homogeneous acid‐catalyzed esterification. Alcohol‐to‐oil molar ratio, catalyst amount, and reaction temperature were varied in order to obtain the kinetic parameters that fit the data satisfactory. A reaction mechanism with four consecutive reactions was considered and the attack of the nucleophile alcohol to the protonated carbonyl substrate was corroborated to be the rate‐determining step, in accordance with previous studies in free fatty acids esterification. A kinetic model with 8 independent parameters described with high accuracy the experimental data of 27 reactions with a regression coefficient of 90.94%. Pre‐esterified oil was submitted to transesterification and properties of resulting methyl esters were measured. Acidity, peroxide value, viscosity and flash point were acceptable to use as diesel‐grade fuel. However, cold flow properties and especially oxidative stability can limit its use as automotive fuel. Finally, a techno‐economic analysis was performed and the influence of salmon oil price on the viability of a low capacity fuel production plant was analyzed. Copyright © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Enhanced production of branched-chain fatty acids by replacing β-ketoacyl-(acyl-carrier-protein) synthase III (FabH).

Branched-chain fatty acids (BCFAs) are important precursors for the production of advanced biofuels with improved cold-flow properties. Previous efforts in engineering type II fatty acid synthase (FAS) for BCFA production suffered from low titers and/or the co-production of a large amount of straight-chain fatty acids (SCFAs), making it nearly impossible for further conversion of BCFAs to branched biofuels. Synthesis of both SCFAs and BCFAs requires FabH, the only β-ketoacyl-(acyl-carrier-protein) synthase in Escherichia coli that catalyzes the initial condensation reaction between malonyl-ACP and a short-chain acyl-CoA. In this study, we demonstrated that replacement of the acetyl-CoA-specific E. coli FabH with a branched-chain-acyl-CoA-specific FabH directed the flux to the synthesis of BCFAs, resulting in a significant enhancement in BCFA titer compared to a strain containing both acetyl-CoA- and branched-chain-acyl-CoA-specific FabHs. We further demonstrated that the composition of BCFAs can be tuned by engineering the upstream pathway to control the supply of different branched-chain acyl-CoAs, leading to the production either even-chain-iso-, odd-chain-iso-, or odd-chain-anteiso-BCFAs separately. Overall, the top-performing strain from this study produced BCFAs at 126 mg/L, comprising 52% of the total free fatty acids.

Alteration of Wax Ester Content and Composition in Euglena gracilis with Gene Silencing of 3-ketoacyl-CoA Thiolase Isozymes.

Euglena gracilis produces wax ester under hypoxic and anaerobic culture conditions with a net synthesis of ATP. In wax ester fermentation, fatty acids are synthesized by reversing beta-oxidation in mitochondria. A major species of wax ester produced by E. gracilis is myristyl myristate (14:0-14:0Alc). Because of its shorter carbon chain length with saturated compounds, biodiesel produced from E. gracilis wax ester may have good cold flow properties with high oxidative stability. We reasoned that a slight metabolic modification would enable E. gracilis to produce a biofuel of ideal composition. In order to produce wax ester with shorter acyl chain length, we focused on isozymes of the enzyme 3-ketoacyl-CoA thiolase (KAT), a condensing enzyme of the mitochondrial fatty acid synthesis pathway in E. gracilis. We performed a gene silencing study of KAT isozymes in E. gracilis. Six KAT isozymes were identified in the E. gracilis EST database, and silencing any three of them (EgKAT1-3) altered the wax ester amount and composition. In particular, silencing EgKAT1 induced a significant compositional shift to shorter carbon chain lengths in wax ester. A model fuel mixture inferred from the composition of wax ester in EgKAT1-silenced cells showed a significant decrease in melting point compared to that of the control cells.

Branched‐Chain Fatty Acid Methyl Esters as Cold Flow Improvers for Biodiesel

AbstractBiodiesel is an alternative diesel fuel derived mainly from the transesterification of plant oils with methanol or ethanol. This fuel is generally made from commodity oils such as canola, palm or soybean and has a number of properties that make it compatible in compression‐ignition engines. Despite its many advantages, biodiesel has poor cold flow properties that may impact its deployment during cooler months in moderate temperature climates. This work is a study on the use of skeletally branched‐chain‐fatty acid methyl esters (BC‐FAME) as additives and diluents to decrease the cloud point (CP) and pour point (PP) of biodiesel. Two BC‐FAME, methyl iso‐oleate and methyl iso‐stearate isomers (Me iso‐C18:1 and Me iso‐C18:0), were tested in mixtures with fatty acid methyl esters (FAME) of canola, palm and soybean oil (CaME, PME and SME). Results showed that mixing linear FAME with up to 2 mass% BC‐FAME did not greatly affect CP, PP or kinematic viscosity (ν) relative to the unmixed biodiesel fuels. In contrast, higher concentrations of BC‐FAME, namely between 17 and 39 mass%, significantly improved CP and PP without raising ν in excess of limits in the biodiesel fuel standard specification ASTM D 6751. Furthermore, it is shown that biodiesel/Me iso‐C18:0 mixtures matched or exceeded the performance of biodiesel/Me iso‐C18:1 mixtures in terms of decreasing CP and PP under certain conditions. This was taken as evidence that additives or diluents with chemical structures based on long‐chain saturated chains may be more effective at reducing the cold flow properties of mixtures with biodiesel than structures based on long‐chain unsaturated chains.

Optimal design and plantwide control of novel processes for di‐n‐pentyl ether production

AbstractBACKGROUNDDi‐n‐pentyl ether (DNPE) is a good candidate for diesel fuel formulations due to its blending cetane number, good cold flow properties and effectiveness in reducing diesel exhaust emissions, particulates and smokes. However, novel processes are required in order to drive the production costs down and to increase the efficiency at industrial scale.RESULTSThe dehydration of 1‐pentanol to yield DNPE is catalyzed by thermally stable resins, such as Amberlyst 70 which has high activity and selectivity at temperatures up to 190 °C. Two process options are proposed for a plant capacity of 26.5 ktpy: a reaction–separation–recycle (R–S–R) system based on an adiabatic tubular reactor and a catalytic distillation process. Both processes were optimized in terms of total annual costs (481 and 523 k$ year−1), leading to specific energy requirements of 225 and 256 kWh ton−1 DNPE, respectively. The controllability was assessed by dynamic simulation performed in Aspen Dynamics.CONCLUSIONCompared with the membrane reactor reported earlier, the new DNPE process alternatives (i.e. conventional reaction–separation–recycle system and catalytic distillation) are better process candidates, requiring simpler units leading to much smaller investment costs, while also having good controllability. © 2015 Society of Chemical Industry