RÉGIMEN MUNICIPAL
PUBLICACIÓN DE UNA VEZ COLEGIO PROFESIONAL DE PSICÓLOGOS
The techniques under this section are relevant for oil and gaseous products coming from both bench and pilot tests. Except that for pilot tests, Physico-chemical properties of condensable products (oil and wax) were performed in addition.
3.5.1 Gas Chromatography/Mass Spectrometry (GC/MS)
Simulated distillation (see Appendix C) was used to group the compounds present in oil/wax products into diesel and gasoline fractions. Simulated distillation is a chromatographic technique which correlates retention times with boiling points of compounds (Das & Tiwari, 2018). A standard of known composition was injected and used as a benchmark for grouping compounds into different fractions (Arabiourrutia et al., 2012). A C7 - C40 mixture of saturated
alkane standard (Supelco, USA) was used for grouping detected compounds into gasoline and diesel fractions. Peaks eluting with retention times between those of C6 and C10 alkanes were
grouped as gasoline while C11 and C23 alkanes were grouped as diesel. Chloroform (99% purity,
BDH Analytical Chemicals) was used as solvent for all samples. Samples containing mixtures of oil and wax were thoroughly stirred to mix up before analysis to ensure a uniform
59 representative sample was used. For all tests, peak area was assumed to be the mass of compound detected.
An Agilent Technologies 7890A gas chromatograph coupled with an Agilent Technologies 5975C mass spectrometer (mass-selective detector) was used for the analysis. A Zebron ZB- 1701:002 column (length – 60 m; internal diameter – 0.25 mm and film thickness – 0.25 μm) was used for separation. Helium was used as the carrier gas with a steady flowrate of 1.3 mL/min. The process was started by heating the oven at 45 ºC and held for 10 minutes, then increased to 100 ºC at a heating rate of 2 ᵒC/min. It was finally heated from 100 ᵒC to 260 ᵒC at a heating rate of 7 ᵒC/min and held there for 20 minutes. Injected volume of samples per run was 1 μL and a split ratio of 20:1 was employed.
3.5.2 Gas Analysis
Analysis of the permanent gases for both bench and pilot scale tests, followed the same method used in previous studies by Mundike et al., (2017) and Brown et al., (2019) where a CompactGC (Global Analyser Solutions) was calibrated to quantify concentrations of nitrogen, C1 - C5 linear hydrocarbon gases, hydrogen, carbon monoxide and carbon dioxide. Mixtures of
known concentrations of these gases (Afrox, South Africa) were used for the calibration. N2
was employed as an internal standard to determine the yield of each gas compound. The CompactGC was made up of three channels. The first channel consisted of a Molsieve 5A column heated at 65 °C and a TCD detector used for the analysis of N2, H2, CO and CH4. The
second channel comprised of a PP-Q-bond column at 50 °C and a TCD detector that was used for the analysis of CO2, C2H4 and C2H6. The third channel was equipped with a Rtx-1 column
at 45 °C coupled with an FID detector used for the analysis of C2 - C4 hydrocarbons.
For pilot and atmospheric experiments at bench scale, permanent gases were collected at the end of the 4th condenser in tedlar bags at regular time intervals and fed immediately into the
CompactGC 4.0 gas chromatograph. For vacuum conditions at bench-scale, gas sampling was done at the exit point of the vacuum pump. The maximum volume of the bag (5 L) and the time it takes to completely fill the bag (77 sec) were used to estimate the volume of gas that was sampled per minute (about 3.9 L). This volume coupled with volume fractions obtained from the CompactGC were used to calculate the total mass of gases produced and to complete the mass balance of the process.
60 3.5.3 Fuel Tests
Oil products derived from pilot experiments were subjected to the following fuel tests to verify how they compare with commercial diesel and gasoline fuels.
i. Density @ 20 ᵒC, in accordance with ASTM D4052. For the procedure, a small volume of about 1 - 2 mL of condensable product (sample) was introduced into an oscillating sample tube and the changes in oscillating frequency (caused by the change in the mass of the tube) in conjunction with calibrated data were used to determine the density.
ii. Kinematic Viscosity @ 40 ᵒC, in accordance with ASTM D445. This employed the reverse or straight flow viscosity tubes that were immersed in a water bath. About 10 mL of condensable product (sample) was introduced into the viscosity tubes which was clean, dried and already calibrated. The viscosity tube was then immersed in a water bath at a stable temperature of 40 ± 0.02 ᵒC after which a vacuum pump was used to draw samples until it reached the upper meniscus of the viscosity tube. A stopwatch was then used to count the flow time between the upper and lower meniscus. This was repeated for each test sample and Equation 3.1 was used to estimate the kinematic viscosity for each sample.
Where,
𝑣 - kinematic viscosity (mm2/s)
C - viscosity calibration constant (mm2/s)/s
t - flow time (s)
iii. Distillation to determine boiling point range, in accordance with ASTM D86. This was performed using atmospheric distillation at ambient pressure. For the process, 100 mL of condensable product was transferred into a flat bottom flask equipped with a thermocouple used for the distillation. The flask was heated to keep a distillation ratio of 4 mL/min and 5 mL/min. The distilled sample was condensed and collected in a measuring cylinder at room temperature. The distillation volume recovered at 250, 350 and 365 ᵒC together with the initial and final boiling point temperatures were recorded. The temperature at which the first
61 drop of distillate was recovered was identified as the initial boiling point (IBP) whereas the temperature at which all samples in the distillation flask evaporated was recorded as the final boiling (FBP). The temperatures at which the following volumes of condensates were recovered were also recorded. Volumes include 10%, 50%, 90% and 95%.
iv. Pour point, in accordance with ASTM D97. This test employed cooling samples in a specified glass tube in a bath containing Isopropyl alcohol and Dry ice. The sample was cooled at specific rates and examined at intervals of 3 ᵒC for flow characteristics. The lowest temperature at which sample stops flowing was then recorded to be the pour point.
v. Aniline point, in accordance with ASTM D611. This was performed by mixing equal proportions of aniline with condensable products after the which the resultant mixture was heated till a complete mixage was obtained. Thereafter, a thermometer was used to check the temperature at which the mixture separated or got hazy and was recorded as the aniline point.
vi. Cetane Index was estimated by calculation using parameters from density of samples at 15 °C and temperatures at which 10%, 50% and 90% distillation condensates were obtained. Equation 3.2 was used for the estimation and is known as the four variable equation in accordance with ASTM D4737 (Drews, 1998; Owusu et al., 2018).
𝐶1 = 45.2 + 0.0892𝑇10𝑁+ (0.131 + 0.901𝐵)𝑇50𝑁+ (0.0523 − 0.420𝐵)𝑇90𝑁 + 0.00049(𝑇10𝑁2 − 𝑇
90𝑁2 ) + 107𝐵 + 60𝐵2 3.2
Where,
CI- Calculated Cetane Index 𝑇10𝑁 = 𝑇10− 215
𝑇50𝑁 = 𝑇50− 260
𝑇90𝑁 = 𝑇90− 310
𝐵 = [𝑒𝑥𝑝−3.5(𝜌−0.85)] − 1 ρ- Density of sample
62 A set of tests required about 250 ml of oil sample hence only oils from condensers 1 and 2 have been characterised for fuel. Oils from condensers 3 and 4 were not enough for fuel tests. Also, waxy oils obtained at higher pyrolysis temperatures (488 - 525 ᵒC) could not be characterised for distillation, flash point, cetane index and aniline point due to their high viscosity. All fuel test experiments were performed by Intertek, Cape Town except aniline point, which was performed by Intertek, Durban, all in South Africa.
63
Results and discussion
4.1 Introduction
This chapter tackles the effects of temperature and heating rate on condensable products (oil and wax) yield and quality under atmospheric and vacuum pyrolysis of polypropylene (PP) at bench scale. Furthermore, experiments performed at atmospheric conditions at bench level were scaled up to a pilot plant and results obtained were compared. The pilot plant was designed and commissioned as part of the study. Moreover, condensable products recovered from the pilot experiment were subjected to fuel tests that include density, viscosity, flash point and pour point to ascertain how these properties vary with the process parameters examined and also, how they compare with commercial diesel and gasoline fuels.