Conversion of Waste Polystyrene to Fuel Oil using High Alumina Cement as Catalyst

Abstract

The global issue of plastic waste accumulation requires a scientific approach to transform it into valuable resources like fuel oil, thereby reducing environmental pollution. Waste polystyrene plastic was converted into fuel oil through catalytic pyrolysis, focusing specifically on the utilization of high alumina cement as a catalyst. A batch reactor of 549.77 cm3 capacity was fabricated for catalytic pyrolysis. The surface properties of high alumina cement were investigated using BET analysis and compared with those of natural zeolite. The resulting pyrolysis fuel oil was characterized using FTIR to identify functional groups, and GC-MS to determine its components. The findings contribute to the understanding of the efficacy of high alumina cement as a catalyst in waste plastic pyrolysis and its potential advantages over traditional catalysts.

Specification

Description:FIELD OF INVENTION
[001] The invention relates to waste to energy conversion. In particular, the invention pertains to utilizing high alumina cement as a catalyst for converting polystyrene waste to fuel oil through pyrolysis that can be further used for various applications upon fractionation.
BACKGROUND AND PRIOR ART
[002] The International Patent No. WO 2016/049782 A1 details the provision of recycled polystyrene polymers with a melt flow index of less than approximately 25 g/10 min. It also describes processes for recycling polystyrene waste. These processes may involve dissolving the polystyrene waste in p-cymene to create a polystyrene/p-cymene mixture, which is then introduced into a hydrocarbon polystyrene non-solvent to precipitate the polystyrene. The precipitated polystyrene is subsequently washed with additional amounts of the hydrocarbon polystyrene non-solvent, resulting in twice-washed polystyrene. This twice-washed polystyrene can be optionally dried and formed into polystyrene pellets. The patent also covers the recycled polystyrene produced through these recycling processes.
[003] The International Patent No. WO 2020/206498 A1 discloses a method for recycling expanded polystyrene. The method involves stacking used expanded polystyrene foam articles to occupy at least 20% of the internal volume in the vertical block machine and mixing it with virgin polystyrene beads to occupy remaining internal volume of block machine. It is then heated to a temperature of 75°C and pressurised steam is supplied into it to fuse the virgin polystyrene beads and the stacked expanded polystyrene foam articles to form expanded polystyrene foam article.
[004] The Canadian Patent No. CA 3153134 A1 discloses a method for recycling polystyrene thermoplastic polymer or copolymer waste involves dissolving the waste in a solvent like cymene, xylene, or ethylbenzene. The mixture is heated under acidic and optionally neutral conditions with a reducing agent, then cooled to obtain a supernatant containing the polymer or copolymer and a solid residue. The supernatant may be filtered and treated with a hydrocarbon non-solvent to precipitate the polymer or copolymer, which is then washed, dried, and formed into pellets.
[005] The International Publication Number: IN995/MUM/2008 discloses a process for converting waste plastic materials into useful fuel oils and other petroleum products. The process involves catalytic degradation of waste plastics using zeolite and bentonite catalysts, often ion- exchanged with transition metals. Key features include refluxing of volatile products during heating, allowing for extended catalyst contact and favourable molecular restructuring. The process uses sodium aluminosilicate catalysts (zeolites A, X, Y, and mordenite) and bentonite clays, optionally ion-exchanged with transition metals like Ni, Co, Fe, and Mn. The temperature range of 200-550°C is maintained for 1-20 hours. The process can handle various plastic wastes including polyolefins, polystyrene, PVC, PET, and waste wax, producing liquid fuel oils (up to 90-95% yield), gases, waxes, and minimal carbonaceous residue. There's an option to mix different plastic wastes to modify product properties (e.g., increasing octane value), and the catalysts can potentially be reused. The process aims to reduce plastic waste pollution while producing valuable hydrocarbon products with minimal environmental impact. The resulting fuel oils can be fractionated for various applications.
SUMMARY OF THE INVENTION
[006] The invention focuses on an approach to pyrolyze the waste polystyrene plastic. Pyrolysis offers a sustainable solution by breaking down plastics into valuable resources such as fuel oil.
[007] Waste polystyrene plastic dissolved in acetone, was pyrolyzed in a stainless-steel batch reactor at 350°C. High alumina cement and natural zeolite were used as catalyst for separate trials. The choice of high alumina cement as catalyst is the key parameter which makes this project innovative. High alumina cement is a solid phase, Lewis-acid type of catalyst having Si:Al ratio in the range of 0-1. It mainly constitutes of alumina, silica, calcium hydroxide, metal oxides and inorganics. It serves as a cost-effective alternative compared to the catalysts that are being used currently for pyrolysis.
[008] The use of high alumina cement yielded 62.06% higher fuel oil as compared to natural zeolite and reduced the time taken by 50%. This substantial enhancement in both yield and process efficiency clearly demonstrates the superior performance of high alumina cement in converting waste plastic into valuable fuel oil, making it a noteworthy invention in the field of waste to energy conversion and environmental sustainability.
BRIEF DESCRIPTIONS OF DRAWINGS
[009] FIG. 1: shows the sectional view of batch reactor (all dimensions are in mm).
[010] FIG. 2: shows the schematic diagram of experimental setup.
[011] FIG. 3: shows the comparison of yield of fuel oil derived with and without using catalysts.
DETAILED DESCRIPTION OF THE INVENTION
[012] The waste polystyrene used in the process was sourced from roadside dumps and underwent thorough cleaning before being utilized for pyrolysis. The catalysts used for pyrolysis were natural zeolite and high alumina cement. A stainless-steel batch reactor was designed ensuring optimal conditions for pyrolysis of waste plastic material (FIG. 1).
[013] The feed was a slurry of polystyrene and acetone in 3:5 (weight-to-volume) ratio which was exposed to sunlight for 10 minutes to partially evaporate the acetone and thicken the slurry. Thermal activation of catalysts was done by heating natural zeolite at 250°C and high alumina cement at 600°C. The electrical connections were established for the batch reactor along with the condensing setup (FIG. 2).
[014] The feed of polystyrene-acetone slurry was introduced from top head of reactor along with the thermally activated catalyst. Specifically, 120 grams of polystyrene waste plastic was dissolved in 200 ml of acetone for each feed slurry preparation. Each catalyst was added in a 10 wt.% ratio of feed plastic, amounting to 12 grams. The reaction temperature was maintained at 350°C. The vapors produced moved through the gas tube from the reactor outlet and condensed upon contact with the condenser surface, which was maintained at 19°C. The resulting oil, characterized by its pale orange color and lighter density, accumulated on top of the water- acetone mixture. Trials were conducted for thermal pyrolysis (no catalyst), high alumina cement as catalyst and natural zeolite as catalyst separately. Upon completing the pyrolysis process, the oil was easily separated from the acetone-water mixture using a separating funnel due to its lower density.
[015] Upon completion of process, thermal pyrolysis yielded 17.41% oil in 3.3 hours, pyrolysis using natural zeolite yielded 30.21% in 2.5 hours whereas high alumina cement yielded 48.96% oil in just 1.25 hours (FIG. 3). High alumina cement yielded 62.06% higher fuel oil as compared to natural zeolite and reduced the time taken for pyrolysis by 50%. The obtained fuel oil showed the presence of alkenes and aromatic compounds upon characterization using FTIR and GC- MS analysis. To assess the surface properties of high alumina cement, it underwent BET analysis, revealing a surface area of 17.802 m²/g which exceeds the surface area of natural zeolites, which is 13.69 m²/g. , C , Claims:[016] 1. A process for catalytic pyrolysis of waste polystyrene plastic using high alumina cement as the catalyst to obtain fuel oil; comprises of.
a) fabricating a lab-scale batch reactor suitable for catalytic pyrolysis and easy handling post-reaction;
b) dissolving the waste polystyrene plastic in acetone to convert it into a feed slurry for convenient introduction into the reactor;
c) establishing the electrical connections, including a band heater, thermocouple, contactor, digital temperature controller (DTC), and variac;
d) preparing the setup with a condenser, beaker, and batch reactor;
e) adding the catalyst and feed to the reactor, initiating the process, and maintaining the temperature at 350°C;
f) conducting the catalytic pyrolysis batch-wise using two catalysts: natural zeolite and high alumina cement, to compare their results; and
g) separating the obtained fuel oil from acetone-water mixture and storing it appropriately.
[017] 2. The process of catalytic pyrolysis according to claim 1, wherein the process specifically targets polystyrene (PS) plastic sourced from roadside dumps, can be applicable to other types of waste plastics.
[018] 3. The process of catalytic pyrolysis according to claim 1, wherein the process involves the use of a batch reactor with the following specifications: the reactor has an internal volume of 549.77 cm³, a height of 280 mm, and an internal diameter of 50 mm. The material of construction is stainless-steel and features a removable head and bottom for easy handling. A vapor outlet is provided by welding a stainless-steel pipe bend onto the head of the reactor.
[019] 4. The process of catalytic pyrolysis according to claim 1, wherein the process uses high alumina cement as catalyst, which has a Si:Al ratio in the range of 0-1, functioning as a Lewis acid-type catalyst.
[020] 5. The process of catalytic pyrolysis according to claim 1, wherein the process involves preheating the high alumina cement catalyst to 520°C to convert calcium hydroxide to calcium oxide and disintegrate minor inorganic components, thereby making it suitable for the catalytic process.
[021] 6. The process of catalytic pyrolysis according to claim 1, wherein the process involves mixing polystyrene with acetone in a 3:5 (weight-to-volume) ratio to form a slurry. This slurry is exposed to sunlight for 10 minutes to allow the evaporation of acetone. The resulting thick slurry is then introduced into the reactor as the feed.
[022] 7. The process of catalytic pyrolysis according to claim 1, wherein the process includes subjecting the high alumina cement to thermal activation at 600°C following which it is added in 10 wt.% ratio of the feed plastic introduced to the reactor.
[023] 8. The process of catalytic pyrolysis according to claim 1, wherein the process involves conducting the pyrolysis batch-wise using natural zeolite and high alumina cement as catalysts. The process with high alumina cement as catalyst results in a higher quantity of oil compared to natural zeolite and completes in a shorter duration. Additionally, high alumina cement is more cost-effective as compared to natural zeolite.
[024] 9. The process of catalytic pyrolysis according to claim 1, wherein the process yields a flammable fuel oil that can be used in various applications. This fuel oil is suitable for blending with conventional fuels, serving as a fuel for boilers, and other energy-related uses.

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