Comparative study of stability and properties of alcohol-diesel blends

Transcription

1 Indian Journal of Chemical Technology Vol. 19, March 2012, pp Comparative study of stability and properties of alcohol-diesel blends Rakhi N Mehta 1, Mousumi Chakraborty 2* & Parimal A Parikh 2* 1 Department of Chemical Engineering, Sarvajanik College of Engineering & Technology, Surat , India 2 Department of Chemical Engineering, Sardar Vallabhbhai National Institute of Technology, Surat , India Received 2 May 2011; accepted 13 January 2012 Present study deals with the blending of petro-diesel with ethanol and butanol, where biodiesel is added as an amphiphile (surfactant) to stabilize the blends. It is observed from the experiments that butanol forms more stable blends as compared to ethanol which has been justified by the backscattering profiles and droplet size distributions of the emulsified blends. In order to ascertain the applicability of blends as fuel, physical properties such as density, kinematic viscosity, flash point, cold filter plugging point and surface tension of most stable blends (both ethanol and butanol) have been determined as per the ASTM standards. The quality of the blends is checked using copper strip corrosion and oxidation stability. Cetane index is calculated using four variable equation method. Results suggest that all the properties are in accordance with the stipulated standard values with the only exception of flash points. Keywords: Backscattering profiles, Droplet size distribution, Physical properties, Stabilized blends World today is swarming with people and their needs for the petroleum products is increasing in leaps and bounds. However, the increase in prices of diesel fuel, stringent emission regulations, and foreseeable future depletion of petroleum reserves make it necessary to ponder on to the issue of searching the new alternatives for fuel and to develop new technologies such as common-rail system, fuel injection control strategies, exhaust gas recirculation, fuel-related techniques, and so on to meet demands for environment and energy. Studies on alternative fuels, especially renewable fuels, become very important research areas among fuel-related studies. Nowadays considerable attention has been paid to the development of alternative fuel sources in various countries, with particular emphasis on biofuels. Over the past few decades, researchers have investigated the use of different alcohols such as ethanol and butanol as a blending agent in petrodiesel 1,2. Bioethanol is produced from bio-derived materials such as sugar cane molasses or cassava root, have lower production cost and is environment friendly 3. Ethanol can be used without much modification in the diesel engine, but it has some limitations of lower miscibility, which may cause * Corresponding authors. mch@ched.svnit.ac.in; pap@ched.svnit.ac.in phase separation as ethanol is immiscible in diesel over a wide range of temperatures 4. This instability of blends may also be attributed to the higher affinity of ethanol towards water, which promotes phase separation 5. As all the automotive fuels are required to be in a clear, single-liquid phase which does not undergo phase separation, surfactants or emulsifiers are added to improve the stability of such blends 6. A group of researchers have worked on injection, ignition and combustion of 10-20% ethanol-diesel blends and concluded that in presence of additives the blends remain stable and give almost same performance as petro-diesel with reduced emissions 7. Another work was carried out to study the phase behavior and miscibility of ethanol into diesel, which concluded that aromatic contents and intermediate distillate temperatures had a significant impact on miscibility limits of the blending fuels 8. Property studies and engine performance of ethanol blended fuels have given appreciable results when studied by the current group of researchers 9,10. Butanol has also been used effectively as a blending agent with diesel to clear blend bearing single phase 11. When such blends were fueled to a multicylinder CI engine, it showed improvement in exhaust gas temperature and brake thermal efficiency. Also the emissions of CO and HC were drastically reduced 12. In the current study, biodiesel is added as an amphiphile

2 MEHTA et al.: COMPARATIVE STUDY OF STABILITY & PROPERTIES OF ALCOHOL-DIESEL BLENDS 135 (emulsifier) forming micelles that have non-polar tail oriented towards diesel and polar head towards ethanol or butanol 13. Thus, the motivation of blending bioderived ethanol and butanol to diesel along with biodiesel could be justified from the fact that its addition improves the values of kinematic viscosity, reduces environmental pollution, strengthens agricultural economy, creates job opportunities, reduces diesel requirements, and thus contributes in conserving a major commercial energy source. These blends were tested for their physical stability and properties in order to ascertain its aptness for using it as a fuel substitute. Experimental Procedure Certified diesel, 99.9% pure standard anhydrous ethanol (Merck make), n- butanol (99.9% pure, Merck India) and ethyl ester of Jatropha Curcas oil based biodiesel (local make) have been used for the study. As per the procedure provided by the biodiesel supplier, the transesterification of Jatropha oil was conducted using ethanol with optimum molar ratio (8:1) using the catalyst concentration of 1% KOH, reaction temperature 70 C and reaction time 210 min. At the end of the reaction, the mixture was allowed to settle overnight and crude glycerine (bottom) and biodiesel (top) were separated and washed with water, which was supplied after sand filtration. Initially in 100% diesel, ethanol was added in small increments of 1% with simultaneous increase in biodiesel. The quantity of biodiesel was decided on the basis of its effectiveness in the blends. Biodiesel less than 5% did not provide a stable emulsion, whereas its concentration of > 25% did not made any further improvement in the stability of the blends. It was observed that butanol showed clear single phase on splash blending therefore butanol upto 25% was blended easily in diesel. Ethanol also showed formation of microemulsions, hence the blends containing 5% (vol) ethanol were identified for checking the effect of change in biodiesel. Blend stability was analyzed on the basis of transmission and back scattering profiles obtained by scanning the samples using light rays of 880 nm wavelength in a Turbiscan classic MA 2000 (Formulaction, France) apparatus. The ethanol and butanol blends checked for stability criteria are enlisted in Table 1. Dispersed microemulsion droplet size measurements were carried out within few minutes after splash mixing of ethanol blends. The sample to be analyzed was contained in a cylindrical glass cuvette and examined throughout its length for about 20 min. The data of the percentage transmission and backscattering were obtained. The profile of backscattering (BS) was obtained as a function of the sample height (mm). These profiles constituted the macroscopic fingerprint of the sample at a given time. Microphotographs of surfactant-stabilized blends (1 ml) were taken using Coslab (India) microscopic camera. Droplets sizes and size distribution of the microemulsions were measured by Coslab software package. Physical properties of most stable blends were determined and compared. Density, kinematic viscosity and flash- and fire-points of the blends were determined using Anton Parr Densitometer [model DMA 4500(Austria)], Herzog kinematic viscosity meter [model HCP 852 (Germany)] and closed-cup Pensky Martens apparatus [Herzog (Germany)] respectively. Cold filter Plugging point was determined using Scavini CFPP apparatus (Italy). Surface tensions of blends were determined using ring method with the help of Kluss T9 Tensiometer (Germany). In the ring method the liquid is raised until contact with the surface is registered. The sample is then lowered again so that the liquid film produced beneath the ring is stretched. The maximum force is only determined exactly on this return movement and used to calculate the tension. These tests were performed in accordance with American Standard of Testing Methods (ASTM) standards. All the tests were performed thrice in order to ascertain the reproducibility of results. The quality of the blends was checked using copper strip corrosion and oxidation stability. Cetane index was calculated using four-variable equation method. Table 1 Selected ethanol and butanol blends (vol %) for stability check Blend Biodiesel, % Ethanol/Butanol a, % Diesel, % Ethanol blends B1 e B2 e B3 e B4 e Butanol blends B1 b B2 b B3 b B4 b a For butanol blends.

3 136 INDIAN J. CHEM. TECHNOL, MARCH 2012 Results and Discussion The blends were scanned from bottom (0 mm) to top of the cuvette (60 mm) for a period of 20 min. The back scattering (BS) profiles suggest that all the butanol blends show superimposing curves justifying its stability even at maximum substitution. Figure 1 shows the enlarged section of back scattering profile of butanol and ethanol, which signifies that butanol forms more stable blends as compared to ethanol blend. In this profile left hand ordinate shows percentage back-scattering, right hand ordinate shows time in minutes and abscissa shows the length (mm). Figure 2 shows that initially low biodiesel concentration in the ethanol blends shows non-superimposing curves, which signifies varied emulsion droplet size and distribution. But increasing the concentration of biodiesel (20% and 25%) provides superimposed curves and better back scattering profiles. These results suggest that at higher amphiphile (biodiesel) concentration stable blends with smaller droplet sizes are obtained. In order to find out exact emulsion droplet size distribution in blends, microphotographs of emulsions were analyzed as shown in Fig. 3. Emulsion size distribution From microphotographs and microemulsion droplet size distributions (Fig. 3), it is observed that the dispersed emulsion is in the range 2-10 μm. The variation in the droplet size denotes that with the gradual addition of surfactant into the blends, they become stabled with small sized droplet and almost clear single phase. Smaller emulsions droplets result into lower %BS, which supports the back scattering data. Depending on the physical stability criteria fulfillment two of the blends containing 5% ethanol and butanol (B1 e, B1 b ) were selected for testing fuel properties. Fuel blend properties Properties of selected blends were determined as per the ASTM/BIS standards. Densities of blends show resemblance with that of pure diesel, depending on the individual densities of pure components. Viscosity affects the atomization of a fuel upon injection into the combustion chamber, thereby ultimately the formation of engine deposits. The higher the viscosity, the greater is the tendency of the fuel to cause such problems 14. The kinematic viscosities (KV) of ethanol and butanol blends show minor increase in the values due to the presence of biodiesel which is comparatively viscous. The desirable range according to BIS standard is 2-5 cst, and the values of KV of blends justify the same. Flash points of both the blends are low as compared to virgin diesel due to the presence of low temperature flashing ethanol and butanol which has flash points 13 C and 29 C respectively. During the use of blended fuels in colder climates there is a possibility of formation of solids and crystals which rapidly grow and agglomerate due to the presence of saturated and unsaturated fatty compounds, thereby clogging fuel lines and filters causing major operatibility problems. Hence, it is inevitable to determine the cold filter plugging point (CFPP) of the blends for smooth cold operation of engines. The CFPP of ethanol and butanol blends are found to be -2 C and -3 C respectively, which is much lower than the stipulated values as per ASTM standards. Net heat of Fig. 1 Comparative view of backscattering profile of (a) butanol and (b) ethanol blends

4 MEHTA et al.: COMPARATIVE STUDY OF STABILITY & PROPERTIES OF ALCOHOL-DIESEL BLENDS 137 Fig 2 Backscattering profile of ethanol blends with increase in biodiesel % Fig. 3 (a) Microphotograph of emulsions and (b) dispersed microemulsion droplet size distribution of B4 e blend

5 138 INDIAN J. CHEM. TECHNOL, MARCH 2012 Table 2 Fuel properties Parameter Density At 15 o C g/ml Kinematic viscosity at 40 o C, cst Flash point o C Cold filter plugging point, o C Net heat of combustion MJ/kg Cetane index Copper strip corrosion Oxidation stability mg/10 ml Surface tension mn/m Diesel Not worse than (a) Butanol < Ethanol Biodiesel Not worse than (a) B1 e < Not worse than (a) B1 b Not worse than 1(a) ASTM/BIS standards BIS:1448 [P: 32] D-445 D-93 BIS: 1448 [P: 110] D-240 D a D-130 D Ring method combustion was estimated using D ASTM method. Since water, ash and sulfur contents of the blends are found to be negligible, they are not included in the estimation of heats of combustion (Table 2). As both butanol and ethanol have lower heating values, it marginally affects the net heat of combustion of blends. Cetane indices (CI) which determine the fuel burning properties are determined using standard calculation method (Table 2). The blends show decrease in their cetane index due to the lower CI of virgin alcohols. Nonetheless B1 b blend shows better CI value as compared to B1 e blend, thereby suggesting better combustion property and hence clean burning. Corrosion is one of the biggest threats for any compression engine, hence in order to determine the corrosive nature of the blend, copper strip corrosion test was performed. The blends were subjected to the test for 3 h at 100 C and the results are given in Table 2. Oxidation stability is an important property for determining the sediment content of the fuel when subjected to oxygenated ambience at higher temperatures for longer period of time. Because the blends studied contain biodiesel, which is susceptible to slow oxidation this test became inevitable 15. According to the ASTM the sediments produced during oxidation stability test should be less than 2.5 mg/100 ml. Both the blends fulfill the stipulated standards. Fuel atomization is the first process encountered during the combustion of fuels to increase the surface area and hence the evaporation rate in a compression ignition engine and is largely determined by the fuel's viscosity and surface tension 16. The observations suggest that surface tension marginally increases due to the presence of biodiesel. Conclusion (i) The turbiscan plots (back scattering profiles) show that butanol blend is more stable than ethanol blend. (ii) The blends show appreciable resemblance in physical properties, such as density, viscosity, cold filter plugging point, net-calorific values, cetane index, copper strip corrosion, oxidation stability and surface tension with that of the petro-diesel. Only the flash points are reduced due to the presence of alcohols in the blends. (iii) On comparison, the butanol blend shows better properties such as density, flash point and cetane index as compared to ethanol blend. (iv) Hence, if the cost of producing butanol could be reduced or some more economical method of production could be established, it could prove to be most viable fuel blend for the future. References 1 Ribeiro N M, Pinto A C & Quintella C M, Energy Fuels, 21 (2007) Wu M, Wu Y & Wang M, Biotechnol Prog, 22 (2006) Kwanchareon P, Luengnaruemitchai A & Jai-In S, Fuel, 86 (2007) Hansen A L, Zhang Q & Lyne P, Bioresour Technol, 96 (2005) French R & Malone P, Fluid Phase Equilib, 228 (2005) Chotwichien A, Luengnaruemitchai A, & Jai-In S, Fuel, 88 (2009)

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