Thermal Conversion of Polymer Wastes (LDPE) into Hydrocarbon Diesel Fuel without Cracking Catalysts

Headnote

Abstract: Thermal conversion process was applies with low density polyethylene (LDPE) waste plastic without using any kind of cracking catalyst, and two types of temperature was use for diesel grade fuel collection. Experimental purposed LDPE waste plastic was use 100% by weight and initial feed LDPE sample was 800 gm. In this experiment was perform laboratory small scale under Labconco fume hood without vacuum in presence of oxygen and fully closed system. LDPE waste plastic to diesel grade fuel fractional distillation collection temperature was 260-290 °C and LDPE waste plastic to direct liquefaction process temperature was 120-430 °C. Produced fuel was analysis by Perkin Elmer GC/MS, FT-IR and DSC. Fuel density is 0.80 g/ml. By using GC/MS analysis result showed hydrocarbon compounds range is C^sub 3^ to C^sub 28^, FT-IR analysis result indicate that produce fuel has functional group such as H Bonded NH, C-CH3, CH3, - CH=CH2, -CH=CH-(cis), C=CH2 etc. DSC analysis result indicates that fuel enthalpy delta H value 18116.1385 J/g. Produce fuel could be use as combustion engines or feed stock for refinery process.

Keywords: Thermal conversion, waste plastic, fuel, hydrocarbon, diesel, conversion, GC/MS.

1. Introduction:

The amount of plastic wastes is growing year after year, and the fraction of plastics in municipal solid wastes (MSW) and in refuse-derived fuels (RDF) is progressively increasing. Pyrolysis and gasification processes appear to be promising routes for the upgrading of solid wastes to more usable and energy dense materials such as gas fuel and/or fuel oil or to high value feed stocks for the chemical industry. Therefore the characterization of the pyrolysis behavior of plastic wastes is of interest in the optimization of pyrolysis processes for the recovery of energy rich or valuable product fractions. Furthermore, a pyrolysis step is always present in the initial stages of gasification and of combustion. Pyrolysis and gasification processes yield three different product fractions: a solid fraction (char), a condensable fraction (tar), and a gaseous fraction. The operating conditions (mainly heating rate and temperature) and the starting materials influence the composition and the relative amount of the three product fractions. Moreover the final product yields from pyrolysis and gasification processes are strongly influenced by secondary gas-phase reactions occurring to the primary products released during solid degradation [1].

The thermal pyrolysis of plastic wastes produces a broad distribution of hydrocarbons, from methane to waxy products. This process takes place at high temperatures. The gaseous compounds generated can be burned out to provide the process heat requirements, but the overall yield of valuable gasoline range hydrocarbons is poor, so that the pyrolysis process as a means for feedstock recycling of the plastic waste stream is rarely practiced on an industrial scale at present [2, 3]. In contrast, thermal cracking at low temperatures is usually aimed at the production of waxy oil fractions, which may be used in industrial units for steam cracking and in fluid catalytic cracking units [4]. An alternative to improve gasoline yield from plastics pyrolysis is to introduce suitable catalysts. High conversions and interesting product distributions are obtained when plastics are cracked over zeolites [5-7]. Moreover the catalytic cracking of polymers has proven itself to be a very versatile process, since a variety of products can be obtained depending on the catalyst, [8-11] the polymer, [12, 13] the reactor type, [14, 15] and the experimental conditions used, [16, 17, 18] among other variables. Most published studies concentrate on discussing the results obtained from the analysis of the global composition of the products generated. However, studies regarding the evaluation of the composition of the products generated in the degradation process at different conversion levels are scarcely available. This type of study can provide very interesting information regarding the reaction sequences during the course of the degradation process or the deactivation suffered by the catalysts.

2. Materials and Process Description:

LDPE waste plastic was collected from local restaurant and LDPE waste plastic was transparent color food /soup container cover. Collected all LDPE waste plastic food container cover washed with liquid soap and dry into room atmosphere. LDPE waste plastic food container cover was hard shape and it was grinded by grinder machine for fit into reactor chamber. After grinder finished LDPE waste plastic put into reactor chamber and placed into reactor inside with LDPE waste plastic as initial feed. Reactor cover was covered with screw and screw tighten was properly prevent gas or any vapor loss. In this experimental process was setup small scale under laboratory Labconco fume hood without any vacuums system and set up was fully closed system but in presence of oxygen.

In this experiment performed without catalyst or any kind of chemicals. Experimental process setup explain in figure 1 from LDPE waste plastic to diesel grade fuel production such as 1 = LDPE waste plastic, 2= Steel reactor, 3 = Fractional distillation column, 4= 1st fractional temperature, 5= 2nd fractional temperature, 6=3rd fractional temperature, 7= 4th fractional temperature, 8= 5th fractional temperature, 9= light gas cleaning system with alkali solution, 10= 1st fractional fuel collection tank, 11=2nd fractional fuel collection tank, 12=3rd fractional fuel collection tank, 13=4th fractional fuel collection tank, 14 = 5th fractional fuel collection tank, 15 = Small pump for gas transfer into Teflon Bag, 16 = Teflon bag for light gas storage. For experimental purposes initial feed was use only 800 gm by weight. In this experiment main goal was LDPE waste plastic to liquefaction then fractionation process to diesel grade fuel collection. For LDPE waste plastic to diesel grade fuel production purposed two type temperature was used one for liquefaction temperature and another for fractionation temperature profile. LDPE waste plastic to liquefaction temperature range was 120-430 °C and fractional distillation column temperature was 260-290 °C for diesel grade fuel collection. In the experiment LDPE plastic melting point 120°C known temperature for that reason LDPE waste plastic to diesel grade fuel collection experiment starting temperature was 120 °C and finished temperature was 430 °C. Temperature was increased gradually from 120°C to up to 430 °C, then plastic start to melt, then melted plastic turn into liquid phase when temperature increased, then liquid phase plastic turn into vapor when temperature profile more than 300 °C and at the end vapor travel through fractional distillation column according to their boiling point range wise. Light fraction boiling point hydrocarbon which boiling point range negative that gas will come out faster and was not condense and its call light gas or natural gas. Low boiling to high boiling point range hydrocarbon was collected different by fractional column and diesel grade fractional fuel was collected in the diagram 13 number collection tank and fractional column number was 7 and temperature range for diesel grade fuel collection at 260-290 °C. This process was batch process and light gases were purified by using alkali solution wash then transferred into Teflon bag using small pump. Light gas is hydrocarbon mixture such as methane, ethane, propane and butane. Produced diesel grade fuel was purified after finished whole experiment and separated into container for further analysis. Produced fuel density was 0.80g/ml. in this experiment mass balance calculation indicate that initial feed 800 gm LDPE waste plastic to diesel grade liquid fuel was 152 gm, rest of other grade fuel was 584 gm, light gas was from 800 gm initial feed to 32 gm and leftover solid black residue is 32 gm from total initial feed. In percentage calculation for this experiment from 800 gm LDEP waste plastic to diesel grade fuel is 19%, other grade fuels is 73%, and light gas is 4% and solid black residue is 4%. Total experiment run time was 6 hours 45 minutes and input electricity was 7.52 kWh. In put electricity cost could be reduce by using produced light gas as a heat source when commercialization plant will be implement.

3. Result and Discussion:

Perkin Elmer GC/MS analysis of LDPE waste plastics to 4th fractional fuel/ diesel fuel (Figure 2 and Table 1) hydrocarbon compound list is analyzed based on their peak intensity. GC/MS chromatogram analysis is showing higher concentration level peak intensity. This fuel fractional temperature is 340- 365 °C. This fuel is similar to fuel oil category. Chromatogram analysis starting compound is Propane (C3H8) at retention time is 1.53 minutes. From data table we saw all hydrocarbon compounds are straight chain hydrocarbon compounds and some are branch chain hydrocarbon compounds are as well. From the fuel we found alkane group and alkene group compound. Long chain hydrocarbon compound showing at retention time 29.97 minutes and compound is Heptacosane (C27H56) and molecular weight is 380. In the fuel all hydrocarbon compounds contains heavy hydrocarbon and their derivatives as well as hydrocarbon range is C5-C28.In the detail analysis prospects maximum compounds are mention from the analysis result index. Such as in detail analysis according to the retention 1.65 and trace mass 43, compound is Butane (C4H10), retention time 1.91 and trace mass 42, compound is Cyclopropane, ethyl ( C5H10), retention time 2.60 and trace mass 41, compound is Hexane (C6H12), retention time 3.65 and trace mass 41,compound is 1-Heptene (C7H14), retention time 3.77 and trace mass 43, compound is Heptane (C7H16), retention time 5.19 and trace mass 41, compound is 1-Octene (C8H16), retention time 5.34 and trace mass 43, compound is Octane (C8H18), retention time 6.92 and trace mass 41,compound is 1-Nonene (C9H18), retention time 7.07 and trace mass 43,compound is Nonane (C9H20), retention time 8.64 and trace mass 41,compound is 1-Decene (C10H20), retention time 8.79 and trace mass 43, compound is compound is Decane (C10H22), retention time 10.30 and trace mass 41, compound is 1-Undecene (C11H22), retention time 10.43 and trace mass 43, compound is Undecane (C11H24) ,retention time 11.85 and trace mass 41, compound is 1-Decene (C10H24), retention time 11.98 and trace mass 57, compound is Dodecane (C12H26), retention time 13.32 and trace mass 41, compound is 3-Tridecene,(E)- (C13H28), retention time 13.45 and trace mass 43, compound is Tridecane (C13H28), retention time 14.60 and trace mass 70, compound is 3-Tetradecene,(E)- (C14H28) , retention time 14.82 and trace mass 71, compound is Tetradecane (C14H30), retention time 16.01 and trace mass 43, compound is 1-Pentadecene (C15H30), retention time 16.12 and trace mass 57, compound is Pentadecane (C15H32), retention time 17.24 and trace mass 41, compound is 1-Hexadecene (C16H32), retention time 17.35 and trace mass 43, compound is Hexadecane (C16H34), retention time 18.40 and trace mass 43, compound is E-14-Hexadecenal, (C16H30O), retention time 18.50 and trace mass 57, compound is Heptadecane (C17H36), retention time 19.51 and trace mass 43, compound is E-15-Heptadecenal (C17H32O), retention time 20.65 and trace mass 71, compound is Nonadecane (C19H40), retention time 21.65 and trace mass 57, compound is Eicosane (C20H42), retention time 22.61 and trace mass 85 , compound is Heneicosane (C21H44) etc. In the ultimate phase of the analysis index at retention time 23.51 and trace mass 71, compound is Heneicosane (C21H44), retention time 24.39 and trace mass 43, and compound is Heneicosane (C21H44) as well, retention time 25.24 and trace mass 57, compound is Tetracosane (C24H50), retention time 26.06 and trace mass 57, compound is Heneicosane (C21H44), retention time 26.86 and trace mass 57, compound is Octacosane (C28H58), retention time 26.86 and trace mass 57, compound is Octacosane (C28H58), retention time 29.20 and trace mass 57, compound is Octacosane (C28H58) and eventually retention time 29.97 and trace mass 57, compound is Heptacosane (C28H58) respectively.

FT-IR analysis of LDPE waste plastic to diesel grade fuel or 4th fractional fuel (Figure 3 and Table 2) shows the following types of functional groups at wave number 3618.53 cm-1, derived functional group is Free OH, wave number 3077.01 cm-1, functional group is H bonded NH, wave number 2932.59 cm-1,2730.56 cm-1 and 2672.73 cm-1 functional group is C-CH3, wave number 1821.23 cm-1, 1716.17 cm-1, and 1641.60 cm-1 functional group is Non-Conjugated, wave number 1606.78 cm-1 functional group is Conjugated. As well as wave number 1465.79 cm-1 and 1378.50 cm-1 functional group is CH3,wave number 991.78 cm-1 and 909.32 cm-1,functional group is -CH=CH2 and ultimately wave number 887.81 cm-1 functional group is C=CH2 and wave number 721.33 cm-1 functional group is -CH=CH-(cis). Energy values are calculated for all functional group and using formula is E=hυ, Where h=Planks Constant, h =6.626x10-34 J, υ= Frequency in Hertz (sec-1), Where υ=c/λ, c=Speed of light, where, c=3x1010 m/s, W=1/λ, where λ is wave length and W is wave number in cm-1. Therefore the equation E=hυ, can substitute by the following equation, E=hcW. According to their wave number such as for 3618.53 (cm-1) calculated energy value is 7.18x10-20 J, wave number such as for 3077.01 (cm-1) calculated energy value is 6.11x10-20 J , 2932.59 (cm-1) calculated energy, E=5.82x10- 20 J, wave number such as for 2730.56 (cm-1) calculated energy value is 5.42x10-20 J, wave number such as for 2672 (cm-1) calculated energy value is 5.30x10-20 J. Similarly, wave number 1821.23 (cm- 1) energy, E =3.61x10-20 J, wave number 1716.17 (cm-1), energy, E =3.40x10-20 J, wave number 1606.78 (cm-1), energy, E =3.19x10-20 J , wave number 1465.79 (cm-1), energy, E =2.91x10-20 J, wave number 1378.50 (cm-1) energy, E = 2.73x10-20 J, wave number 991.78 (cm-1), energy, E =1.97x10-20 J, wave number 965.08 (cm-1), energy, E =1.91x10-20 J, wave number 909.32 (cm-1), energy, E =1.80x10-20 J, wave number 887.81 (cm-1), energy, E =1.76x10-20 J and eventually wave number 721.33 (cm-1) functional group is 1.43x10-20 J respectively.

Diesel grade fuel collected from LDPE waste plastic and diesel grade fuel (Figure 4) was analyzed by using DSC equipment for messaging boiling point temperature and enthalpy value. The fractional temperature range was for diesel grade fuel collection during production period at 260-285 °C. This temperature is giving longer hydrocarbon compounds based on their boiling point range wise. Perkin Elmer DSC analysis graph showed in this fuel onset temperature is 14.74 °C, peak temperature is 205.50 °C, peak height is 36.3382 mW, area is 18116.139 mJ and enthalpy delta H value is 18116.1385 J/g. Peak height is representing heat Endo up 50% from total 100%. This fuel hydrocarbon compounds are heavier and fuel hydrocarbon compounds mixtures of alkane and alkene groups. This fuel is giving us high boiling point because this fuel has heavier long chain hydrocarbon compounds as usual. Fuel analysis temperature profile indicates that 17.53% fuel was boiled at 100 °C and 100% fuel boiled was 396 °C.

4. Conclusion:

Most of the LDPE plastic is using as shopping bag and LDPE waste plastic percentage is 23 % from total waste plastics. LDPE waste plastic problem is biggest environmental concern because LDPE waste plastic thin and light for that reason every sector are using LDPE plastic. For saving the environmental problems from LDPE waste plastic can convert into diesel grade fuel by using thermal degradation with fractional distillation process without adding any kind of catalyst or chemicals in this process. Produce fuel density is 0.80 g/ml which is similar density like commercial diesel fuel. Produced diesel fuel was analysis by GC/MS and found hydrocarbon compounds range showed GC/MS chromatogram Propane (C3H8) to Octacosane (C28H58). Because initial raw material has straight chain hydrocarbon which was break down into short chain hydrocarbon as well as long chain hydrocarbon by using thermal and fractional distillation process. Produce fuel could be use in internal combustion engine and feed for feed stock refinery or using diesel grade fuel could be generated electricity as well.

Acknowledgement:

The authors acknowledge the support of Dr. Karin Kaufman, the founder and sole owner of Natural State Research, Inc. The authors also acknowledge the valuable contributions NSR laboratory team members during the preparation of this manuscript.

References

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