Gasoline Specifications Difference between Straight run gasoline & cracked gasoline Volatility 1-ASTM 2- Reid vapor pressure Gum Content 1-Existing gum 2-Poteintal gum 3-Oxidation Stability 4-Amount of Unsaturations 1
Gasoline Specifications Sulfur Content 1-Doctor test 2-Copper strip test 3-Sulfur bomb test 4-Sulfur lamp test 2
Difference between straight run gasoline & cracked gasoline Straight run gasoline Comes directly from distillation column (distillation of crude oil) Less amounts of unsaturated hydrocarbons (expected to have less gum) Cracked gasoline Comes from cracking of large compounds More amounts of unsaturated hydrocarbons (expected to have more gum) 3
Volatility/ASTM Method In this test, we calculate T c from the following rule where: T c (F) = 100 + (atmospheric temperature (F)/2) All the previous temperatures are in Fahrenheit (F) Then we see the location of T c on the ASTM curve of gasoline at 10% distilled volume and then start to compare where: IF T c > T, then this means that the gasoline sample will vaporize at lower temperature, it means that it is more volatile than required. 4
Volatility/ASTM Method Solution: Decrease its volatility by removing some of the butane contained with it IF T c < T, then this means that the gasoline sample will vaporize at higher temperature, it means that it is less volatile than required. Solution: Increase its volatility by adding some butane. 5
Volatility/Reid Vapor Pressure In this test, gasoline sample is put in certain equipment with certain design where above the sample, there is air chamber saturated with water vapor and at the top of this equipment a gauge pressure exist The whole previous equipment is put in a water bath kept at 100 F A mixer exist to ensure homogeneity in temperature every where around the equipment A thermometer exist to make sure that temperature is 100 F 6
Volatility/Reid Vapor Pressure As the temperature is 100 F, gasoline sample will vaporize and enters in the chamber with the water vapor that already exists The reading of the gauge pressure will be a measure for both the amounts of vapors that exist in the chamber which are the gasoline vapor and the water vapor Reading vapor pressure of water = Reid vapor pressure (RVP) The limit for the RVP is 6-12 PSI In Egypt, the limit is from 7 8 PSI, where it is 7 in summer and 8 in winter 7
Gum Content When unsaturated hydrocarbons are oxidized, the form resinous compounds called gum. Problem of gum is that it clog pipes, so it would be very dangerous if it exists in appreciable amounts and cause clogging of some parts of the engine Two types of gum exists which are: 1-Existing gum : already existing in gasoline 2-Potential gum: Could be formed upon storage 8
Amount of existing gum 100 CC of gasoline is heated in a standard apparatus with standard conditions where gasoline is put in a container and the container is put in water bath kept at 100 F. The gasoline sample will vaporize and only the gum will remain in the container Then the amount of gum is weighted and the gum content is reported as mgm gum/100 cc gasoline 9
Amount of potential gum In this test, standard volume of gasoline sample is put in a copper dish which is heated by steam and an oxygen stream is passed above the sample, the gasoline sample will vaporize also and the amount of gum remaining could be measured. In this test, the gum is formed during the experiment as unsaturated hydrocarbons are oxidized by oxygen at the presence of high temperature. Cu dish acts as a catalyst 10
Oxidation Stability In this test, we measure the resistance of the sample towards oxidation As gum is formed as result of oxidation of unsaturated hydrocarbons so if the sample resists oxidation this will result in lower gum content. Gasoline is put in standard apparatus where gauge pressure exists in it and there is an opening in it where oxygen can enter from it The whole apparatus is kept in water bath at standard temperature 11
Oxidation Stability 1. Pressure decreases as oxygen dissolute other components 2. The pressure remains constant for some time as the sample resists oxidation (stability region) 3. Pressure starts to decrease as chemical reaction occurs and oxygen is consumed 4. We measure the time taken by the sample to drop the pressure by 2 PSI 5. IF time is > 7 hours, then the sample can resists oxidation 12
Amount of Unsaturations In this test, we titrate our sample with a standard solution where: 100 grams of the gasoline sample is put in the conical flask In the burette, mixture of bromine and carbon tetra chloride is used We start titration, as bromine goes down with the sample it reacts with the unsaturated hydrocarbons and its color changes from red to colorless 13
Amount of Unsaturations When red color appears in the flask, it means that bromine did not find any unsaturated hydrocarbons to react with it is the end point We do not need any indicator as it is self indicating as bromine changes its color when it reacts and though we can determine the end point easily The amount of unsaturations is reported as number of grams of bromine required to saturate 100 grams of gasoline 14
Sulfur Content/Doctor Test In this test, the sample is put in beaker with a mixer and doctor solution is used where it is a mixture of sodium plombite & sulfur powder If mercaptans exist, they will react with sodium plombite and the sulfur powder to give PbS (black precipitate) according to the following reactions: 2 RSH + Na 2 PbO 2 2NaOH + RS-Pb-SR RS-Pb-SR + S PbS + RSSR 15
Sulfur Content/Cu-Strip Test In this test, Gasoline sample is put in a standard apparatus where: Cu strip is put with the sample The apparatus is put in a water bath The water bath is kept at standard temperature Heating is applied at standard rate Thermometer exist in the apparatus (in the flask itself) The sample is heated for certain standard time 16
Sulfur Content/Cu-Strip Test After the standard time pass, the copper strip is taken out and its color is determined A standard table was already done for this experiment at these standard conditions Correlating the sulfur content and color of strip Each color stands for certain amount of sulfur so by knowing the color of your strip, you can use the table to find the amount of sulfur compounds 17
Sulfur bomb Test In this test, air is allowed to react with the sulfur compounds to produce sulfur dioxide where the latter is absorbed in sodium carbonate and from calculations of strength of the solution used, they can determine the amount of sulfur. Gasoline sample is put in a metallic flask Molten sodium is placed around the flask where it takes heat produced from the reaction and heats the sample to accelerate the oxidation rate 18
Sulfur Bomb Test There are two tubes connected with the flask, one for air or oxygen to enter and the other for produced gases to get out SO 2 and CO 2 and H 2 O are produced SO 2 is absorbed in Na 2 CO 3 Strength of Na 2 SO 3 is calculated before and after the reaction and from these calculations, amount of sulfur can be determined 19
Sulfur Lamp Test Same idea as before but with some differences in the apparatus where: Glass flask is used instead of metallic flask An empty trap is used to trap any particles with the gases Water tap is used to assure that the SO 2 will move in the right direction where it is then absorbed in Na 2 CO 3 20