FIELD OF INVENTION

The present disclosure relates to methods and systems having non-catalytic two stage continuous thermal cracking process using plug flow type, electrically heated, tubular coiled thermal cracking reactors for production of biofuels having maximum yields of < Cis molecular size hydrocarbons from a feedstock comprising all types of polypropylenes and polyethylenes segregated separately or collectively from waste plastics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This invention takes priority from an earlier filed patent application no. 202211024296 filed on April 25, 2022; which is incorporated herein as reference

BACKGROUND OF THE INVENTION

In today’s world, petroleum products in the form of liquid/gaseous fuels and different types of plastics made from the petroleum products hold an integral position in our lives. Petroleum being a non-renewable resource, has limited and finite resources. Being the non-renewable resource is a main cause of petroleum’s shortage and high prices across the world. Therefore, there is a huge demand for alternative sources of fuels that have cleaner-burning, are cheaper in cost and are preferably derived from renewable resources.

The rapid rate of urbanization and development has led to increase in consumption of plastic products vis-a-vis plastic waste generation. Petroleum derived plastics are non-biodegradable and remains on earth for thousands of years. The burning of plastic wastes under uncontrolled conditions lead to generation of different hazardous air pollutants (HAPs), depending upon the type of polymers and additives used. However, the waste plastics can be recycled and reused but after every thermal treatment/recy cling, there is a deterioration in quality of recycled plastic products. Thus, plastic waste can be recycled only 3-4 times.

Biofuels offers the answer for ever-worsening fuel problem (from non-renewable sources) and management/handling of waste plastics. Biofuels can be derived from natural renewable resources, exhibits similar fuel properties and results in substantially less environment damaging emissions. Similarly, biofuels can also be produced from some of the majorly used waste plastics such as polypropylenes and polyethylenes. The biofuels produced from waste plastics such as polypropylenes and polyethylenes exhibit excellent liquid fuel characteristics and can be replaced with conventional petroleum-based fuels. Although biofuels produced from renewable resources and waste plastics such as polypropylenes and polyethylenes fit in perfectly as the ideal substitutes for conventional petroleum products, and to reduce wastes and cost(s) associated thereof, there is still a need to devise effective methods and systems for production of biofuels wherein the processes are efficient, cost effective, facilitate easy plant setup.

The process description of the present disclosure overcomes the drawbacks of the prior art(s) and offers an improved and economical way of biofuel production from waste plastics producing higher yields of < Cis molecular size hydrocarbons as is desired for its usage as fuels, replacing petroleum fuels by providing non-catalytic two stage thermal cracking process using plug flow type, electrically heated, tubular coiled thermal cracking reactors. The present disclosure also provides a mechanism for the continuous removal of physically inseparable inorganic impurities present in the feedstock as filler (calcium salts) and some other left-over impurities present during the segregation process of waste plastics, which is the foremost challenge in the conversion of waste plastics into liquid hydrocarbons of desired molecular size. Further, the present disclosure also provides a mechanism for the saturation of olefins and removal of organic impurities present in the biofuels.

SUMMARY OF THE INVENTION

The present disclosure relates to methods and systems for converting polypropylenes and polyethylenes constituents of waste plastics into < Cis molecular size hydrocarbons as biofuels by non-catalytic two stage thermal cracking process using plug flow type, electrically heated, tubular coiled thermal cracking reactors and providing higher yields of <Cis molecular size hydrocarbons. The method provides solution for continuous removal of physically inseparable inorganic impurities present in the feedstock as filler and some other left-over impurities present during a segregation process of the waste plastics.

Desired feedstock of up to 5 millimeter (mm) size containing polypropylenes and polyethylenes components is segregated from mixed waste plastics. The feedstock is melted through single or double screw extruders to generate homogeneous molten liquid mass from the feedstock at a discharge header of the single or double screw extruders. The molten liquid mass from the discharge header of the single or double screw extruders is fed to a stage 1 thermal cracking reactor for partial thermal cracking reactions conducted at temperatures of up to 450 °C and pressure of up to 20 bar to receive thermally cracked products having hydrocarbon chain length of up to < C30. Inorganic impurities present in the feedstock are continuously removed from the stage 1 thermal cracking reactor as suspension along with vapors and liquid produced as product that includes thermally cracked products having hydrocarbon chain length of up to < C30. Stage 1 thermal cracking products are separated into non-condensable gases, olefinic liquid biofuels having carbon chain length of < Cis and long chain hydrocarbons having carbon chain length of up to < C30 along with inorganic impurities composed of calcium carbonate as major impurities. Inorganic impurities are separated from the long chain hydrocarbons having carbon chain length of up to < C30 before stage 2 thermal cracking reactions of the long chain hydrocarbons using filtration alone through a filter media having a pore size varying from 0.5 micrometer (pm) to 10 pm or filtration followed by hot water rinsing or only with hot water rinsing.

Cleaned long chain hydrocarbons are pumped to a stage 2 thermal cracking reactor for optimum thermal cracking reactions of the long chain hydrocarbons at temperatures of up to 650°C and pressure of up to 50 bar to receive a maximum output of < Cis hydrocarbons. Stage 2 thermal cracking products are separated into non-condensable gases, olefinic liquid biofuels having carbon chain length of < Cis and pitch. Olefinic liquid biofuels received from stage 1 and stage 2 thermal cracking reactions are saturated and organic impurities that includes at least one of organic chlorides, nitrogen, sulphur, or oxygen are removed by hydrogenation reactions of the olefinic liquid biofuels. Hydrogenation reactions are conducted in the presence of Ni catalyst or any other metal catalyst of Group VIII metals of the periodic table to obtain paraffinic biofuels as a final product. After hydrogenation, the paraffinic biofuels are separated as per a specific use having a desired molecular size and a boiling point using a separate fractional distillation column.

BRIEF DESCRIPTION OF DRAWINGS

The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, and accompanying drawings where:

Figure 1 illustrates an exemplary process plant for segregating and pre-treating waste plastics according to the present disclosure.

Figure 2 illustrates an exemplary process plant for partial thermal cracking of a feedstock according to the present disclosure.

Figure 3 illustrates an exemplary process plant for thermal cracking of cleaned long chain hydrocarbons and hydrogenation of the thermally cracked biofuels according to the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Aspects of the present disclosure are best understood by reference to the description set forth herein. All the embodiments described herein will be better appreciated and understood when considered in conjunction with the following description. It should be understood, however, that the following descriptions, while indicating preferred, different embodiments, examples, and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope herein without departing from the spirit and scope thereof, and the present disclosure herein include all such modifications. It is to be understood that the embodiments may or may not overlap with each other. Thus, part of one embodiment, or specific embodiments thereof, may or may not fall within the ambit of another, or specific embodiments thereof, and vice versa.

A broad framework of the principles will be presented by describing various embodiments of this invention using specific examples. For clarity and ease of description, each aspect includes only a few embodiments. Different embodiments from different aspects may be combined or practiced separately, to design a customized process depending upon application requirements. Many different combinations and sub-combinations of a few representative processes shown within the broad framework of this invention, that may be apparent to those skilled in the art but not explicitly shown or described, should not be construed as precluded.

The present disclosure relates to methods and systems having non-catalytic two stage continuous thermal cracking process using plug flow type, electrically heated, tubular coiled thermal cracking reactors for production of biofuels having higher yields of < Cis molecular size hydrocarbons from a feedstock comprising all types of polypropylenes and polyethylenes segregated separately or collectively from waste plastics.

In the context of the present disclosure, the term “biofuels” refers to a liquid substance that is used as a fuel or an intermediate for production of plastic polymers, which is produced from polypropylenes and polyethylenes constituents of waste plastics. In particular, the word “biofuels” produced from waste plastics may be traced backwards for its nomenclature as - polypropylenes and polyethylenes segregated from waste plastics used as a feedstock for the production of biofuels are produced by the polymerisation of propylene orethylene gas, which is produced from thermal cracking of a desired quality of hydrocarbons such as Naphtha, which is produced from the crude petroleum oils and the crude petroleum oils are produced from the decomposition of plants and animals which are biological in nature. The term “maximum yield” refers to a maximum amount of product that could be formed from given amounts of reactants. The term “required flow” refers to a flow that is optimum for a reaction in a reactor. The term “desired size” refers to a size of the hydrocarbon according to an application or use.

The process of the present disclosure facilitates the use of polypropylenes and polyethylenes constituents segregated from waste plastics for biofuel production. The polypropylenes and polyethylenes may be used separately as an independent feedstock or may be used in combinations of each other. The polyethylenes include all their sub categories such as ultra-high-molecular- weight polyethylene (UHMWPE), ultralow molecular weight polyethylene (ULMWPE), high molecular weight polyethylene (HMWPE), high density poly ethylene (HDPE), cross-linked polyethylene (XLPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE), low density polyethylene (LDPE), and very low density polyethylene (VLDPE). The term “feedstock” includes all types of polypropylenes and polyethylenes segregated from the waste plastics. During segregation, the feedstock may contain some of non-desirable components of the waste plastics such as polyvinyl chloride, polyethylene terephthalate (PET) etc. but a concentration of the non-desirable components in the feedstock is required to be minimal and it may be limited to up to 5 % or up to 1% or up to 0.1%.

The embodiments related to methods and systems for the conversion of polypropylenes and polyethylenes constituents of the waste plastics into biofuels comprises as under: i. One of the biggest challenges for production of biofuels from the waste plastics is to have an economically self-sustainable mechanism for the waste plastics collection and their segregation to obtain the desired feedstock. Domestic and commercial waste plastics, especially packaging plastic wastes generation and its quantum is directly linked with the human population inhabitation, and a type of human population etc. Industrial waste plastics generation such as laminations plastic wastes from waste paper-based paper industries is concentrated at a point but a same type of industries generating the wastes are never located nearby. Further, a density of the waste plastics is very low even in baled form. Accordingly, to make an economically self-sustainable mechanism for waste plastics collection and segregation, the waste plastics needs to be collected and segregated at a short radial distance from the waste plastics to biofuels facility. To overcome the challenge, one of the most feasible solutions for the production of biofuels from the waste plastics is have small to medium sized plants ranging from 20 tons per day (TPD) to up to 100 TPD at any one location located nearby a source of waste plastics generation.

Presently, numerous thermal cracking reactors or thermal cracking furnaces or pyrolysis furnaces are operational using oil or gas fired heaters in petroleum refineries for the processing of crude oils and its by-products and in petrochemical industries for the production of hydrocarbon gases such as propylene and ethylene gas from various feedstocks ranging from crude oil to naphtha. Most of existing thermal cracking reactors are based on oil or gas fired heaters which are mounted on floors or walls of reactor furnaces and have tubular heat exchanging coils varying in diameter range from 25 millimeter (mm) to 150 mm, placed in a horizontal or vertical geometry. Most of the existing oil/ or gas fired heaters based thermal cracking reactors have been designed for turbulent flows in the coils and operates at higher liquid feed rate with an approximate range varying from 25 metric tons/hour (MT/hour) to up to 4000 MT/hour. The large-scale thermal cracking reactors based on oil/gas fired heaters have practical limitations for their use in the production of biofuels from the waste plastics due to their size and operating conditions required to be maintained for their use.

Hence, to overcome the challenge, an electrically heated, plug flow type, non-catalytic and non-fluidized tubular thermal cracking reactor for stage 1 and stage 2 thermal cracking reactions has been designed. Mineral insulated heat trace type electrical heaters will be installed at an outer surface of tubular coils of the tubular thermal cracking reactors with tube diameter ranging from 25 mm to 100 mm. Mineral insulated heat trace type electrical heaters will be installed in a spiral or any other form providing heat flux in a range from 4.0 to 10.0 kilowattXmeter ² to the tubular thermal cracking reactors. The tubes or tubular coils in the stage 1 and stage 2 thermal cracking reactors may be installed in a vertical or horizontal or inclined direction. Steam may be inserted at any intermediate location in the stage 1 and stage 2 thermal cracking reactors to achieve desired flow conditions as designed or required in the process. The stage 1 and stage 2 thermal cracking reactors may comprise a provision for intermediate steam insertion for maintaining the desired flow conditions. The term “provision” is to be understood for performing a particular process step and to be understood as including all physical articles (example pipelines, pumps, compressors, valves etc) that would be considered by a person skilled in the art in order to be able to perform this process step. The term “desired flow conditions” is to be understood as reaction conditions that are optimum for performing a reaction.

Mineral insulated heat trace type electrical heated thermal cracking reactors will have the distinctive advantage for (i) precise temperature control in different sections of the tubular thermal cracking reactors, (ii) maintenance of desired vapor liquid ratio in the tubular thermal cracking reactors with varied temperature pressure combinations to keep the inorganic impurities suspended in the fluid, (iii) flexibility in a design of a size of a process plant for production of biofuels from the waste plastics, (iv) flexibility of operating the process under desired flow conditions, (v) no requirements of any external catalyst or media for heat transfer or conducting thermal cracking reactions in the process. ii. Preparation of desired feedstock constituting polypropylenes and polyethylenes for the thermal cracking of the waste plastics is a very important step as the quality and cost of treatment of liquid hydrocarbons is directly related with the feedstock quality used in the process. Segregation steps involved in the preparation of the desired feedstock constituting all types of polypropylenes and polyethylenes includes - shredding of the waste plastics, density separation of desired raw materials using a sink float method with water as a medium (density of water may be altered by adding salts such as sodium chloride to achieve the desired density separation), dewatering of segregated plastics by compaction, second stage shredding and density separation of desired raw materials using the sink float method with water as the medium, second stage dewatering of segregated plastics by compaction, hot air drying of the dewatered material and finally further shredding of segregated raw material to generate a homogeneous density feedstock having a desired size of up to 5 mm. The feedstock preparation can be made as a part of the overall thermal cracking process or it may be split, outsourced and got done by developing ancillary waste plastics segregators by providing them the desired specifications/requirements of the feedstock. iii. Melting of feedstock will be done in screw extruders having single or double screw, commonly used for melting of plastics. Depending upon a size of the plant for the production of biofuels from the waste plastics, there may be a single or multiple number of extruders joined together through a common discharge header of the extruder(s). Desired back pressure of up to 50 bars to the molten liquid mass at an outlet of discharge header may be attained by the extruders or by putting up a positive displacement metering pump at the outlet of the discharge header connected with the stage 1 thermal cracking reactor. Temperature at the outlet of the discharge header may be maintained between 200 °C to 300 °C or between 220 °C to 250 °C. iv. The molten mass in the liquid form produced at the discharge header of the extruder(s) will be conveyed to the stage 1 thermal cracking reactor for conducting the stage 1 thermal cracking reactions of the molten liquid mass. As described earlier in embodiment i, stage 1 thermal cracking reactor will be a plug flow type, electrically heated tubular reactor with tube diameter ranging from 25 mm to 100 mm.

Partial thermal cracking reactions will be carried out in the stage 1 thermal cracking reactor within a pressure range of up to 20 bars and a temperature range of up to 450 °C. Stage 1 thermal cracking reactions may be conducted under the pressure range of 1.5 to 5 bars or from 3 to 20 bars and temperature range of 380 °C to 410 °C or from 400 °C to 450 °C so as to receive thermally cracked products having hydrocarbon chain length of up to < C30 or up to < C24 or may be up to < C21. Two phase flow will be maintained during the stage 1 thermal cracking reactions with a composition of fluid having liquid contents in a range of 10 to 90 % or between 40 to 70 %. Two phase flow is to be understood as a flow with two distinct phases. v. The mixed phase fluid at an outlet of stage 1 thermal cracking reactor will be having liquid hydrocarbons, vapors and solid particles as inorganic impurities, generated during the stage 1 thermal cracking reactions of the molten liquid mass. The mixed phase fluid from the outlet of the stage 1 thermal cracking reactor may be discharged into a heat and mass transfer equipment such as a fractional distillation column, shell and tube heat exchangers etc. for the separation of mixed phase fluid components into non-condensable gases, olefinic liquid biofuels having hydrocarbon chain length of < Cis or < C15 or may be < C12 and long chain liquid hydrocarbons having carbon chain length of > Cis and < C30 or > C15 and < C24 or may be > C12 and < C21 or any other desired chain length along with inorganic impurities. Long chain hydrocarbons containing inorganic impurities as stated will be collected in a receiver vessel for further treatment for the separation of hydrocarbons from inorganic impurities. Some quantity of hydrocarbons ranging from < Cis and > C12 may be added in the long chain hydrocarbons containing inorganic impurities for its dilution. The quantity of hydrocarbons ranging from < Cis and > C12 that may be added to long chain hydrocarbons containing inorganic impurities may range from 1 % to 50 % of the long chain hydrocarbons.

During the production of different plastic products from virgin polypropylenes and polyethylenes polymers, calcium salts such as calcium carbonate as filler is added along with the virgin polymers varying in proportion from 1 % to 30 % or any other percentage, decided by the manufacturers at the time of production. Calcium carbonate used as filler during the production of various plastic products from virgin polypropylenes and polyethylenes polymers is added to improve their physical properties, for providing colour to polymers and for the cost reduction of products.

Continuous removal of inorganic impurities such as calcium carbonate and other inorganic impurities present in the polypropylenes and polyethylenes components of segregated from waste plastics is essential during the stage 1 thermal cracking reactions for the continuous and long run operations of the process. The major problem associated with the continuous non-removal of the inorganic impurities as stated before leads to their precipitation on the surface of thermal cracking tubular coils especially at elevated temperatures of more than 400 °C. The precipitation of calcium carbonate and inorganic impurities on the surface of the thermal cracking tubular coils leads to (i) clogging of the thermal cracking tubular coils due to the reduction in surface area of the thermal cracking tubular coils and (ii) absorption of oil contents on the surface of the precipitation and thereby creating coking in the thermal cracking tubular coils. The precipitation and coking in the thermal cracking tubular coils create undesired differential pressures and hence shutdown of the plant at very short intervals of time. To overcome clogging and coking problems and to sustain continuous long run of the thermal cracking reactor, calcium carbonate and other inorganic impurities must be removed continuously from the stage 1 thermal cracking reactor along with the cracked hydrocarbons. vi. The fluid containing long chain hydrocarbons, inorganic impurities and a desired quantity of hydrocarbons ranging from < Cis and > C12 will be separately treated for the separation of the inorganic impurities from the hydrocarbons. Depending upon the characteristics of the mixed fluid, the separation of the inorganic impurities from the hydrocarbons may be carried out by filtration alone or filtration followed by hot water rinsing or only with hot water rinsing. Filtration may be carried out using any of a liquid filtration mechanism such as a pressure leaf filter or a hydraulic filter press or any other suitable equipment capable of filtration of liquid hydrocarbons through a filter media having a pore size varying from 0.5 micrometer (pm) to 10 pm. The filtration may be carried out under hot conditions with a temperature of mixed fluid being maintained up to 200 °C or between 80 °C to 150 °C. Hot water rinsing may be carried out by agitating the mixed fluid in hot water having water contents of up to 1 to 50 % and the temperature of the mixture being maintained in the range of 50 °C to 90 °C. Hot water rinsing may be carried out once or multiple times depending upon the presence of impurities in the hydrocarbons. Density separation or layer separation of the cleaned hydrocarbons may be carried out from water component containing impurities. Cleaned hydrocarbons separated from the inorganic impurities may be dried and collected as a feedstock for stage - 2 thermal cracking reactions. vii. The cleaned hydrocarbons obtained after the separation of inorganic impurities will be subjected to the stage 2 thermal cracking reactions in a separate thermal cracking reactor. As described earlier in embodiment i, stage 2 thermal cracking reactor will be a plug flow type tubular reactor having electrically heated tubular coils with a tube diameter ranging from 25 mm to 100 mm. The cleaned hydrocarbons may be partially heated in shell and tube heat exchangers with hot thermic oil before entering the stage 2 thermal cracking reactor. Optimum thermal cracking reactions under controlled conditions will be carried out in the stage 2 thermal cracking reactor within a pressure range of up to 50 bars and a temperature range of up to 650 °C to achieve a maximum yield of < Cis hydrocarbons. Stage 2 thermal cracking reactions may be conducted under the pressure range of 1.2 to 15 bars or from 2 to 25 bars and temperature range of 420 °C to 520 °C or from 440 °C to 480 °C so as to receive maximum of thermally cracked products having hydrocarbon chain length of up to < Cis. Two phase flow will be maintained during the stage 2 thermal cracking reactions with the composition of fluid having liquid contents between 5 to 30 % or between 2 to 20 %. viii. The thermally cracked products from an outlet of the stage 2 thermal cracking reactor will be discharged into a fractional distillation column for the separation of hydrocarbons components into non-condensable gases, olefinic liquid biofuels having hydrocarbon chain length of up to < Cis and residual pitch.

The non-condensable gases generated from the stage 1 and stage 2 thermal cracking reactor may be utilised for the provision of energy required in the process in a thermic fluid heater or a steam generator or production of electrical energy. The residual pitch generated from the stage 2 thermal cracking reactions may be used as source of energy in the downstream industry. ix. The olefinic liquid biofuels produced during stage 1 and stage 2 thermal cracking reactions may contain some unwanted impurities such as organic chlorides, nitrogen, sulphur, and oxygen etc. The source of organic impurities in the olefinic liquid biofuels may be presence of some constituents of polyvinyl chloride (PVC), polyethylene terephthalate (PET) or any other type of plastics which may be present as unwanted impurities in the feedstock during the stage 1 thermal cracking reactions. To make the olefinic liquid biofuels compatible for its use as transportation fuel or in the petrochemical industry for further processing, the organic impurities need to be removed and the olefins needs to be saturated to convert them into paraffinic biofuels.

Saturation of olefins liquid biofuels and removal of organic impurities such as organic chlorides, nitrogen, sulphur, and oxygen may be done simultaneously with the hydrogenation of olefinic liquid biofuels. The olefinic liquid biofuels in the liquid phase will be reacted with hydrogen gas in the presence of Ni catalyst or any other metal catalyst of Group VIII metals of a periodic table in a hydrogenation reactor. The hydrogenation reactions will be carried out under hydrogen pressure with a gas pressure range varying from 2 to 50 bar (0.2MPa to 5MPa) and temperature of the fluid in the hydrogenation reactor varying from 120 °C to 250 °C. x. The hydrogenated biofuels may be passed through another fractional distillation column operated under vacuum for the separation of products as per specific use, based on their carbon chain length and boiling points.

The present disclosure will now be illustrated in greater detail with reference to an example, but the present disclosure should not be interpreted as being restricted thereto. The following is the example that is described in detail about the method of production of biofuels from waste plastics. The source of waste plastics may be industrial, commercial or residential waste plastics.

Segregation and pretreatment of Waste Plastics (In accordance with Figure 1)

The primary objective of this process operation is to convert the waste plastics constituting polypropylene (PP) and polyethylene (PE) into the desired feedstock by (i) removing physically separable impurities from the waste plastics and (ii) reduction of the waste plastic size as per the desired requirements for the efficient operation of the extruder for melting of the waste plastics. Figure 1 illustrates an exemplary pretreatment plant (10) for segregating and pretreating of the waste plastics The pretreatment plant (10) includes a shredder (115), a first sink float tank (120), a first screw press (135), a granulator (140), a second sink float tank (145), a second screw press (155), and a hot air dryer (160). Segregation and pretreatment of the waste plastics was conducted as under; a) 2 MT of waste plastics consisting of mixed polypropylene and polyethylene (packaging material) (110) was procured. The waste plastics contained physically separable impurities like sand particles, paper, some quantity of PVC, PET etc. b) The waste plastics was shredded in a coarse shredder (115) and the size of the waste plastic was reduced to around 25 mm. The coarse shredded material was washed in the first sink float tank (120) using water. Density of water was maintained at 1050 kilogram/metre ³ (kgs/m ³ ) by adding sodium chloride (125) in the first sink float tank (120). Impurities being heavier than the water settled at a bottom of the first sink float tank (120) along with water whereas the washed shredded plastic material floated at the surface of the first sink float tank (120). The floating plastic material (130) was collected and dewatered by using a first screw press (135). c) The washed and dewater plastic material was again shredded in a granulator (140) to further reduce its size to up to 5 mm. The granulated material was again washed in the second sink float tank (145) using alkaline hot water (150). Residual impurities settled at the bottom of the second sink float tank (145) whereas a final washed and cleaned granulated material floated at the surface of the second sink float tank (145). d) The floating material was collected, dewatered by using the second screw press (155) and dried using hot air-dryer (160). 1700 kgs. of dried, cleaned feedstock (165) containing mixed polypropylene and polyethylene having granular size of around 5 mm was recovered and stored for further processing. e) Analytical testing of the dried, cleaned feedstock (165) indicated that it contains 8 % of CaCOs as an inorganic filler material along with polypropylenes (PP) and polyethylenes (PE) which remained with the feedstock and was not physically separable in pretreatment process operations.

Partial Thermal Cracking of Feedstock (In accordance with Figure - 2)

The main objective of the partial thermal cracking of feedstock in the electrically heated, plug flow type stage 1 thermal cracking tubular reactor was to convert the waste plastics into (i) a desired product comprising olefinic liquid biofuels having carbon chain length of < Cis, and (ii) long chain hydrocarbons having carbon chain length of up to < C30 along with continuous and complete removal of CaCOs from the stage 1 thermal cracking reactor without any significant coke formation so as to run the stage 1 thermal cracking process continuously for long run lengths without any shutdown. Figure 2 illustrates an exemplary process plant (20) for partial thermal cracking of feedstock. The process plant (20) includes an extruder (170), a stage 1 thermal cracking reactor (175), a first distillation column (180), a first filter press (195), and an agitated vessel (210). Stage 1 thermal cracking process operations were conducted as under; a) The prepared feedstock (165) was continuously fed into a screw type melt extruder (170) @ 10 kgs/hour. Temperature at the discharge header of the screw type melt extruder (170) was maintained @ 250 °C. Molten liquid mass from a discharge header outlet was pumped into stage - 1 thermal cracking reactor (175). b) Stage 1 thermal cracking reactor (175) used in the process was a plug flow type, electrically heated with mineral insulated heat trace type electrical heaters, having vertical coils of 50 mm NB (nominal bore). Two phase flow was maintained at the outlet of the stage 1 thermal cracking reactor (175) with the fluid having around 70 % liquid in it for carrying out the continuous and complete removal of CaCCh as suspension in the liquid. c) The outlet parameters of the stage 1 thermal cracking reactor (175) were maintained as under;

(i) Temperature - 390 °C

(ii) Pressure - 5 Bar (Gauge Pressure)

(iii) Retention Period - 60 Minutes d) The outlet of the stage 1 thermal cracking reactor (175) was connected to the firstdistillation column (180) operated at 0.5 bar pressure (gauge pressure). The top-level temperature of the first distillation column (180) was maintained at 330 °C to recover only up to <Cis hydrocarbons. The vapors from a top of the first distillation column (180) were condensed in a condenser (not shown) and the olefinic liquid hydrocarbons/ olefinic liquid biofuel (185) having molecular size of <Cis were collected as an intermediate product. 680 kgs. or 850 liters of intermediate olefinic liquid hydrocarbons as biofuels was recovered from distillation process. e) Long chain hydrocarbons (190) is cleaned in a long chain hydrocarbons cleaning unit. The long chain hydrocarbons cleaning unit includes, but not limited to, the first filter press (195), and the agitated vessel (210). Long chain hydrocarbons (190) having molecular size > Cis and < C30 were collected from a bottom of the first distillation column (180), passed through a condenser to maintain temperature of up to 200 °C and sent to the first filter press (195) for the removal of CaCCh from the long chain hydrocarbons (190). CaCCL with some oil constituents was recovered as cake (200) whereas clear hydrocarbons were recovered as filtrate (205). 150 kgs. of filter cake (200) containing CaCCL, coke particles and some oil constituents was recovered from the filtration operations. 850 kgs. of long chain hydrocarbons having molecular size > Cis and < C30 was recovered as the filtrate (205). Balance material of 20 kgs. retained in the pipelines and screw type melt extruder (170) which was recovered as unprocessed material, after the completion of process operations. f) The filtrate (205) was sent to an agitated vessel (210) having heating coils. Hot water (215) was purged into the agitated vessel (210) for rinsing operations. Water rinsing with water to hydrocarbon ratio of 1:1 was done for 30 minutes and thereafter the slurry was sent to a decanter (not shown) for the separation of hydrocarbons and water containing residual impurities. 15 kgs. of mixed impurities containing CaCOi and some coke particles were recovered along with water from water rinsing operations. g) Finally, 835 kgs. of cleaned long chain hydrocarbons (220) having molecular size > Cis and < C30 was produced which was stored separately for stage 2 thermal cracking reactions to achieve the maximum yield of <C18 hydrocarbons. h) The stage - 1 partial thermal cracking process was operated continuously for more than 7 days i.e., 170 hours @ 10 kgs/hour of feed and there was no shutdown of the process due to either retention of CaCCT or due to coke formation within the stage 1 thermal cracking reactor (175). After the process completion, the stage 1 thermal cracking reactor (175) was inspected and a surface of the stage 1 thermal cracking reactor (175) was found clean without any significant attached impurities.

Stage - 2 thermal cracking of cleaned long chain hydrocarbons (In accordance with Figure - 3) The main objective of the stage 2 thermal cracking of cleaned long chain hydrocarbons was to achieve maximum yield of <C18 hydrocarbons. Figure 3 illustrates an exemplary process plant (30) for thermal cracking of cleaned long chain hydrocarbons and hydrogenation of the thermally cracked biofuels. The process plant (30) includes a stage 2 thermal cracking reactor (225), a second distillation column (230), a hydrogenator reactor (245), hydrogen cylinders (250), a second filter press (255), and a third distillation column (260). Stage 2 thermal cracking process operations were conducted as under; a) Cleaned long chain hydrocarbons (220) having molecular size > Cis and < C30 was pumped into a stage 2 thermal cracking reactor (225) @ 10 kgs/hour. Plug flow type, electrically operated stage 2 thermal cracking reactor (225) having vertical coils of 50 mm NB was used for the optimum thermal cracking of the long chain hydrocarbons (220) having molecular size > Cis and < C30. Two phase flow was maintained at an outlet of the stage 2 thermal cracking reactor (225) with fluid having ~ 20 % liquid contents. b) The outlet parameters of the stage 2 thermal cracking reactor (225) were maintained as under;

(i) Temperature - 450 °C

(ii) Pressure - 1.5 Bar (Gauge Pressure)

(iii) Retention Period - 40 Minutes c) The outlet of the stage 2 thermal cracking reactor (225) was connected to the second distillation column (230) operated at 0.5 bar pressure (gauge pressure). The top-level temperature of the second distillation column (230) was maintained at 330 °C to recover only up to <Ci8 hydrocarbons. The vapors from a top of the second distillation column (230) were condensed in a condenser (not shown) and the olefinic liquid hydrocarbons/ olefinic liquid biofuels (235) having molecular size of <Cis were collected as an intermediate product. 750 kgs. or 940 liters of intermediate olefinic liquid hydrocarbons (235) as biofuels was recovered from distillation process. d) Residue as pitch (240) was collected from a bottom of the second distillation column (230), passed through a condenser and collected in a separate vessel (not shown). 85 kgs. of pitch (240) was recovered from the bottom of the second distillation column (230). e) The stage 2 thermal cracking process was operated continuously for more than 3 days i.e., 83 hours @ 10 kgs/hour of feed and there was no shutdown of the process due to coke formation in the stage 2 thermal cracking reactor (225).

Hydrogenation of the olefinic intermediate biofuels a) 1430 kgs. of intermediate biofuels (235 & 185) as received from stage 1 and stage 2 thermal cracking process was transferred to a 3000 liters capacity hydrogenation reactor (245). The temperature of the feed was raised to 150 °C and air present in the hydrogenation reactor (245) was evacuated using a vacuum pump. b) Raney’s nickel @ 0.01 % of the feed was added in the feed and the feed was continuously agitated @ 60 RPM. Hydrogen was added using hydrogen cylinders (250) grouped together using a manifold and pressure inside the hydrogenation reactor (245) was maintained @ 15 Bar. c) Temperature of the feed was maintained @ 150 °C during the reaction and the extra heat generated was evacuated using water. The hydrogenation reaction was conducted for 3 hours and after the reaction, the hydrogenated product was cooled and filtered using the second filter press (255).

The filtrate was distilled in the third distillation column (260) operated at 0.5 Bar pressure (Gauge Pressure). The top-level temperature of the third distillation column (260) was maintained at 330 °C to recover only up to <Cis hydrocarbons. The vapors from a top of the third distillation column (260) were condensed in a condenser and the final distilled paraffinic biofuels (265) having molecular size of <Cis were collected as final product. 1400 kgs. or 1750 liters of paraffinic biofuels (265) was received as final product.

Although the invention has been described with regard to its embodiments, specific embodiments and various examples, which constitute the best mode presently known to the inventors, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention as set forth in the claims appended hereto.

LIST OF REFERENCE NUMERALS

10 - pre-treatment plant

20, 30 - process plant

110 - waste plastics containing polypropylene and polyethylene

115 - shredder

120 - first sink float tank

125 - sodium chloride

130 - floating material

135 - first screw press

140 - granulator

145 - second sink float tank

150 - alkaline water

155 - second screw press

160 - hot air dryer

165 - feedstock

170 - extruder

175 - stage 1 thermal cracking reactor

180 - first distillation column

185 - olefinic liquid biofuels

190 - long chain hydrocarbons with inorganic impurities

195 - first filter press

200 - inorganic impurities including CaCOs

205 - filtrate

210 - agitated vessel

215 - hot water

220 - cleaned long chain hydrocarbons

225 - stage 2 thermal cracking reactor 230 - second distillation column

235 - olefinic liquid biofuels

240 - pitch

245 - hydrogenator reactor 250 - hydrogen cylinders

255 - second filter press

260 - third distillation column

265 - paraffinic biofuels