Patent Application
20240263089
The present application relates generally to a method of converting thermoplastics to short chain hydrocarbons, and more particularly relates to a method of converting thermoplastics to create a usable hydrocarbon fuel.
This section provides background information to facilitate a better understanding of the various aspects of the invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
The heating of thermoplastics in the absence of oxygen produces liquid hydrocarbon due to the presence of alpha and di-alpha olefins in the product. This liquid is not generally accepted as refinery feedstock. When plastic is heated to the point of decomposition, or cracking, the new molecules are generally deficient in hydrogen because the large molecular weight polyolefin precursors do not contain sufficient hydrogen to allow for saturation of the short chain hydrocarbons that are formed. This results in a plurality of molecules containing an elevated proportion of alpha and di-alpha olefins being formed. Alpha olefins contain a carbon-carbon double bond at one end of the molecules, while di-alpha olefins contain a carbon-carbon double bond at both ends of the molecules.
There is provided a method of converting thermoplastics to short chain hydrocarbons is provided. The method involves heating a thermoplastic such that the thermoplastic is decomposed into a plurality of molecules. The plurality of molecules includes at least one olefin having at least one carbon-carbon double bond. The carbon-carbon double bonds may be found on one terminal end or both terminal ends of the olefin. Simultaneously, water in the form of steam is provided during the heating of the thermoplastic such that the oxygen atoms in the steam react with the plurality of molecules as the thermoplastic is broken down. The reaction with the steam consumes the terminal carbon-carbon double bonds from the at least one olefin molecule to create a hydrocarbon fuel and at least one byproduct. Byproducts can include, but are not limited to, carbon oxides and hydrogen. The hydrocarbon fuel is collected for third party use. Byproducts may be disposed of or collected for other uses.
In one embodiment, the hydrocarbon fuel is olefin free.
In one embodiment, the at least one byproduct includes hydrogen and carbon monoxide. The hydrogen and carbon monoxide can be used as a process fuel.
In one embodiment, the at least one byproduct includes coke. The coke may be treated by steam reformation to break down the coke into carbon oxides, such as carbon monoxide and carbon dioxide, and hydrogen.
In one embodiment, the thermoplastic contains a biomass. The biomass is generally present due to the use of unwashed thermoplastics. The biomass may decompose to a char which may then be treated by steam reformation to create carbon oxides, such as carbon monoxide and carbon dioxide, and hydrogen.
In one embodiment, the thermoplastic contains at least one of polyethylene, polypropylene, or polystyrene.
In one embodiment, the thermoplastic is heated to a temperature of 575 degrees Kelvin to 1000 degrees Kelvin.
In another embodiment, the thermoplastic is heated to a temperature of 900 degrees Kelvin to 1000 degrees Kelvin.
In one embodiment, a further step of soaking at least one of the hydrocarbon fuel at a temperature of 575 degrees Kelvin to 725 degrees Kelvin is completed. Soaking may result in any of the at least one olefin present in the hydrocarbon fuel forming into cyclic structures instead of carbon-carbon double bonds. Soaking may occur for minutes to hours depending upon user preference.
In one embodiment, a further step of hydrogenating of the hydrocarbon fuel to increase hydrogenation is completed.
In one embodiment, a further step of removing excess hydrogen from at least one of the hydrocarbon fuel and the at least one byproduct is completed.
In one embodiment, the decomposition of the thermoplastics and providing water in the form of steam occurs in an air free container.
In one embodiment, the decomposition of the thermoplastics and providing water in the form of steam occurs at atmospheric pressure.
In one embodiment, at least one of the byproducts are passed through a scrubber to remove unwanted contaminants.
A method of recycling plastic is described in which the hydrocarbon fuel that is created can be sold meeting the specifications of a refinery feed stock in the form of crude oil. The main reason that creating a hydrocarbon fuel using thermoplastics does not meet the specifications for crude oil is that olefins are present in the fuel. Crude oil specifications require that there be essentially no olefins present.
Thermoplastics are heated to cause the thermoplastic to decompose, or “crack”, into a plurality of molecules. Many thermoplastics commonly contain at least one of polyethylene, polypropylene, or polystyrene, however any type of thermoplastic may be used. A person of skill will understand at what temperatures a thermoplastic will break down into a plurality of molecules. It is preferred that the thermoplastics be heated to a temperature between 575 degrees Kelvin to 1000 degrees Kelvin, and more specifically between 900 degrees Kelvin to 1000 degrees Kelvin. While this process is generally done in the absence of air or with very little air and at atmospheric pressures, it will be understood by a person skilled in the art that air may be present and atmospheric pressures may be changed to allow for higher or lower temperatures to be used. Different pressures may also have an effect on the types of byproducts that form. These molecules include hydrocarbons, olefins having terminal carbon-carbon double bonds at one or both terminal ends, and/or other byproducts such as coke, carbon monoxide, carbon dioxide, hydrogen, and non-condensable hydrocarbons. It will be understood by a person skilled in the art that decomposition of olefins having terminal carbon-carbon double bonds may also occur when thermoplastics undergo decomposition. Simultaneously with heating, water in the form of steam is provided to provide oxygen atoms, with hydrogen molecule byproducts. The oxygen atoms in the steam react with the unsaturated molecules (the carbon-carbon double bonds) that are created as the thermoplastics are decomposed. When a carbon-carbon double bond forms, the reactive oxygen atoms contained in the steam may react with the carbon-carbon double bonded olefin to oxidize the double bond and create a saturated terminal carbon with no terminal carbon-carbon double bond. The hydrocarbons that are created during break down of the thermoplastics using the steam can be collected as a hydrocarbon fuel. It is preferred that the hydrocarbon fuel that is collected be olefin free such that it meets the specification of refinery stock crude oil. While each midstream pipeline or trucking company can have their own specifications for acceptable refinery stock crude oil, a person of skill will understand the common requirements. All other molecules, compounds, and waste can be collected as byproducts. Some of the byproducts may be treated further or reused as process fuels or fuels for other purposes as needed.
These reactions can be shown in relation to the chemical formulas below:
It will be understood by a person skilled in the art that the main target of the oxygen provided through water in the form of steam are alpha-olefins having a single terminal carbon-carbon double bond but that di-alpha olefins are also decomposed.
Some types of thermoplastics can be found, such as those commonly found in plastics drinking bottles and clam shell style packaging, that contain polyethylene terephthalate. When heated to decomposition, polyethylene terephthalate does not make oil but does produce the same byproducts of carbon oxides and hydrogen, along with non-condensable hydrocarbon gases. The hydrocarbon gases can be used as fuel. Other types of plastic may or may not make oil but will also produce the same byproducts of carbon oxides and hydrogen, along with non-condensable hydrocarbon gases. Some plastics may produce acidic gases when they decompose. Known scrubbing technologies could be utilizes as needed to remove the acidic gases and allow for the decomposition of these types of plastics.
Hydrogen and carbon monoxide are at least some of the byproducts that are created when heating and simultaneously treating thermoplastics with steam as described in this method. The hydrogen and carbon monoxide can be collected and separated as needed and later used as process fuels. Both the hydrogen and carbon monoxide can be used to help heat the steam to the temperatures required for use in this method.
It is possible that coke can form as a byproduct during the heating and steam treatment of the thermoplastics. The coke may be collected and used for other purposes, disposed of, or may be treated in-situ by steam reformation to produce hydrogen and carbon oxides. The process of steam reformation is known to a person of skill in the art. The steam reformation reaction can be shown as follows:
Thermoplastics are commonly found in bottles and plastic food containers. It is common for these items to not be completely clean before being used in the method described above. As a result, biomass may be found in and on the thermoplastics. During decomposition of the thermoplastics, the biomass is turned into a char and this char may be treated by steam reformation to produce hydrogen and carbon oxides.
The hydrocarbon fuel and/or the byproducts can be soaked at a temperature of 575 degrees Kelvin to 725 degrees Kelvin. Soaking is a process by which the hydrocarbon fuel and/or the byproducts are held at an elevated temperature below the cracking temperature to allow olefins still remaining to form into cyclic structures to accommodate the hydrogen deficiency in cracked products. Cyclic structures are preferable to terminal carbon-carbon double bonds. The hydrocarbon fuel and/or byproducts may be held at soaking temperatures for minutes to hours depending upon user preference. Costs associated with soaking can increase as the length of time soaking increases. For that reason, different users may choose to soak for different lengths of time based on their own cost to benefit analyses.
After decomposing in the presence of steam and collecting the hydrocarbon fuel, the hydrocarbon fuel may be hydrogenated using the catalytic addition of hydrogen atoms at unsaturated sites. The process of hydrogenation is known to a person of skill in the art. Excess hydrogen may be removed as needed.
After cracking in the presence of steam, excess hydrogen may be removed from the hydrocarbon fuel and/or the byproducts as needed. The process of hydrogen separation is known to a person of skill in the art.
Any use herein of any terms describing an interaction between elements is not meant to limit the interaction to direct interaction between the subject elements, and may also include indirect interaction between the elements such as through secondary or intermediary structure unless specifically stated otherwise.
In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.
It will be apparent that changes may be made to the illustrative embodiments, while falling within the scope of the invention. As such, the scope of the following claims should not be limited by the preferred embodiments set forth in the examples and drawings described above, but should be given the broadest interpretation consistent with the description as a whole.
| Number | Date | Country | Kind |
|---|---|---|---|
| 3187692 | Jan 2023 | CA | national |
