WO2023111135A1

WO2023111135A1 - A method for the production of concrete

Info

Publication number: WO2023111135A1
Application number: PCT/EP2022/086066
Authority: WO
Inventors: John REDSHAW
Original assignee: Plastic Energy Ltd
Current assignee: Plastic Energy Ltd
Priority date: 2021-12-17
Filing date: 2022-12-15
Publication date: 2023-06-22
Anticipated expiration: 2024-06-17
Also published as: GB2613875A; GB2613875B

Abstract

There is provided a method for the production of concrete for use in applications requiring thermal insulation properties, the method comprising: providing an end-of-life-plastic feedstock; pyrolysing the feedstock to produce a pyrolysis char; and mixing the pyrolysis char into a concrete composition in an amount of from 0.1 to 15 wt%, based on the total dry weight of the mixture.

Description

A method for the production of concrete

The present invention relates to a method for the production of concrete for use in applications requiring thermal insulation properties. In particular, the method relates to the provision of concrete including char from the pyrolysis of end-of-life plastics as a filler. This material is particularly effective for improving the thermal properties, while at the same time providing a key reuse option for the by-products of a plastics reuse mechanism. In addition, substitution of virgin aggregates for end-of-life plastic pyrolysis char reduces the environmental damage caused by mineral extraction, in particular, but not limited to, destruction of aquatic environments caused by dredging of waterways and coastlines.

End-of-life plastic (ELP) chemical recycling is an emerging technology designed to recycle mixed waste-plastics into a variety of liquid hydrocarbon products. The waste plastics for use in such a process may, for example, include low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), and/or polypropylene (PP).

Pyrolysis treatments are known for converting these waste plastics into the liquid hydrocarbon products by heating and then pumping the plastic feed in molten form into reactor vessels. The reactor vessels are heated by combustion systems to a temperature in excess of 350°C. This produces rich saturated hydrocarbon vapour from the molten plastic. This flows out of the reactor vessels through contactor vessels and will condense the heavier vapour fractions to maintain a target outlet temperature set point which is determined by the end-product specification. This is then distilled at near-atmospheric pressures in a downstream condensing column. This process obtains a so-called pyrolysis oil. The pyrolysis oil can be used in the manufacture of virgin plastics or the production of a fuel.

At the same time, there is produced a solid char material. The char is formed primarily of some carbonised carbonaceous material and plastic polymer forming additives, pigmentation and ELP contamination. This material is typically disposed of in landfill and constitutes an undesirable by-product of the pyrolysis oil production process.

WO2021123822 discloses a method for pyrolysing plastic material. The method comprises the steps of: heating and densifying plastic material; transporting the plastic material to one or more reactors; and pyrolysing the plastic material in the one or more reactors. The plastic material is maintained in a heated state during the transporting step. WO2016030460 discloses a pyrolysis reactor system suitable for the treatment of end-of-life plastics.

WO2011077419 also discloses a process for treating waste plastics material to provide at least one on-specification fuel product. Plastics material is melted (4) and then pyrolysed in an oxygen-free atmosphere to provide pyrolysis gases. The pyrolysis gases are brought into contact with plates (13) in a contactor vessel (7) so that some long chain gas components condense and return to be further pyrolysed to achieve thermal degradation. Short chain gas components exit the contactor in gaseous form; and proceed to distillation to provide one or more on-specification fuel products. There is a pipe (12) directly linking the pyrolysis chamber (6) to the contactor (7), suitable for conveying upwardly-moving pyrolysis gases and downwardly-flowing long-chain liquid for thermal degradation. There is a vacuum distillation tower (26) for further processing of liquid feeds from the first (atmospheric) distillation column (20). It has been found that having thermal degradation in the contactor and pyrolysis chamber and by having a second, vacuum, distillation column helps to provide a particularly good quality on-specification liquid fuel.

Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second- most-used substance in the world after water, and is the most widely used building material by weight. Significant research and development is being done to try to reduce the emissions or make concrete a source of carbon sequestration, and increase recycled and secondary raw materials content into the mix to achieve a circular economy. Concrete is expected to be a key material for structures resilient to climate disasters, as well as a solution to mitigate the pollution of other industries, capturing wastes such as coal fly ash or bauxite tailings and residue.

The use of bio-char as a filler in concrete is well documented in academic literature. Some companies market a thermally insulating concrete which enables construction of buildings without other insulation layers being added. It is believed that these compositions utilise hollow glass beads and power-station fly ash. Power station fly ash is a by-product of coal combustion. As coal-fired power stations are shuttered owing to global carbon emission targets, power station fly ash will become increasingly scarce. Thus, an alternative means to producing highly insulating concrete will be required. Chen et aL, “Lightweight Brick by Carbon Ash from The Mixed Plastic Waste Treatment Plant” MATEC Web of Conferences, 67, 2016, 07025, relates to use of waste mixed plastic carbon ash in the production of lightweight concrete.

DE3218778C1 discloses use of a carbonaceous pyrolyzate as a replacement of carbon black for the purpose of providing inexpensive pigment for colouring cementitious objects.

Wijesekara et aL, “Prospects of using chars derives from mixed post waste plastic pyrolysis in civil engineering applications” Journal of Cleaner Production, 317, 2021 , 128212, provides a review of plastic pyrolysis and applications of char.

CN113387648 relates to the use of a municipal solid waste pyrolyzate in concrete for the purpose of improving strength. The garbage pyrolyzate may be considered a biochar since it is taught that inorganic substances such as metals, plastic products and construction wastes are removed from the waste before pyrolysis of the remaining organic matter.

Cuthbertson et aL, “Biochar from residual biomass as a concrete filler for improved thermal and acoustic properties” Biomass and Bioenergy, 120, 2019, 77-83, relates to the use of chars from biomass pyrolysis as an inert filler to concrete in the place of either sand or coarse aggregate.

Martin-Lara et aL, “Characterization and Use of Char Produced from Pyrolysis of Post- Consumer Mixed Plastic Waste” Water, 13, 2021 , 1188, relates to the use of the solid product of pyrolysis of post-consumer mixed plastic waste (PP, PS and PE) as adsorbent of lead present in aqueous media.

WO2011145080 relates to a process for the production of hydrogen and the contemporaneous sequestration of carbon dioxide starting from slags and/or industrial ashes.

WO2018203829 relates to use of biochar for preparation of construction material.

Accordingly, it is an object of the present invention to provide an improved method of producing thermal concrete, in particular one which provides an optimal use for the char byproduct of the pyrolysis treatment, to solve future anticipated supply issues for power station fly ash or at least to tackle problems associated therewith in the prior art, or provide a commercially viable alternative thereto. According to a first aspect there is provided a method for the production of concrete for use in applications requiring thermal insulation properties, the method comprising: providing an end-of-life-plastic feedstock; pyrolysing the feedstock to produce a pyrolysis char; and mixing the pyrolysis char into a concrete composition in an amount of from 0.1 to 15 wt%, based on the total dry weight of the mixture.

The present disclosure will now be described further. In the following passages different aspects/embodiments of the disclosure are defined in more detail. Each aspect/embodiment so defined may be combined with any other aspect/embodiment or aspects/embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. It is intended that the features disclosed in relation to the product may be combined with those disclosed in relation to the method and vice versa.

The present invention relates to a method for the production of concrete for use in applications requiring thermal insulation properties. That is, the method is suitable for providing a concrete product, preferably without compromising its structural properties, which has a reduced thermal conductance property.

In particular, the present invention is preferably a method for the production of concrete having a density of at least 1 ,400 kg/m³. That is, the present invention is particularly suited for use heavier concretes without compromising their structural properties. For heavier concretes, the inclusion of ELP char has been found to provide unexpectedly high reductions in thermal conductivity. Lightweight concretes may be categorised as having a broad range of densities, for example from 800 kg/m³ to 2,000 kg/m³, but more generally in the range of 1 ,200 kg/m³ to 1 ,800 kg/m³. Preferably, the concrete produced by the present method has a density of 1 ,800 kg/m³ or more, preferably 1 ,900 kg/m³ or more and more preferably 2,000 kg/m³ or more.

The present invention provides a method reliant on char obtained, specifically, from the pyrolysis of end-of-life plastics, rather than biochar, for example. The use of ELP char as a filler in concrete has a number of benefits. Firstly, there is a reduction in density of the concrete which reduces the loads and stresses on buildings, enabling a reduction in thickness of supports, thereby providing an environmental benefit. Secondly, there is a reduction in thermal conductivity of the concrete which enables a decrease in heating and cooling costs of buildings, thereby leading to an energy and environmental saving for buildings manufactured using concrete using the pyrolysis char filler.

It is considered that the combination of a density reduction and increase in thermal insulation is especially useful for concrete tiles, concrete cladding, and concrete blocks, though not exclusively to these uses. In addition, use of char in concrete may enable buildings to be manufactured solely using concrete walls and not needing additional insulation layers. This will therefore save resources, labour time and construction time, enabling more rapid construction of units and potentially decreasing costs. In addition to thermal insulation, the char will provide acoustic insulation and use of the char as a filler in concrete will also reduce noise pollution of buildings.

Furthermore, the use of the char as a filler in concrete enables a reduction in the concentration of construction sand in the concrete. This therefore reduces the damage to aquatic ecosystems and reduces the environmental impact of concrete.

The method comprises providing an end-of-life-plastic feedstock. End-of-life or contaminated plastic waste feedstock, for plastic chemical recycling, may be received from, for example, municipal recovery facilities, recycling factories, or other plastic collection sources. During a pre-treatment process, the feedstock may be refined such that it only contains plastics suitable for the chemical recycling process, preferably hydrocarbon plastics. Such plastics are those that are formed of hydrocarbons (and therefore consist essential of carbon and hydrogen). Preferably, the hydrocarbon plastic is polyethylene (PE), such as low density polyethylene (LDPE) and/or high density polyethylene (HDPE), polystyrene (PS), and/or polypropylene (PP). Unsuitable materials, such as metals, paper and card, and glass, as well as humidity from the plastic waste, may be removed. For the avoidance of doubt, ELPs do not include rubbers or tyres.

As will be appreciated, the recycling of end-of-life plastics introduces various impurities that are preferably removed from the feedstock before recycling during the pre-treatment, for example by washing. Preferably, the ELP feedstock comprises at least 80 wt% plastic, more preferably at least 90 wt% plastic, preferably essentially 100% plastic. Moreover, it is preferred that the feedstock is substantially free of non-hydrocarbon plastic such as polyethylene terephthalate (PET) and polyvinylchloride (PVC). In a preferred embodiment, the ELP feedstock comprises non-aromatic hydrocarbon plastics, for example PE and/or PP. The method comprises pyrolysing the feedstock to produce a pyrolysis char. Pyrolysis is the heating of a material in a substantially oxygen-free environment. The preferred method is described in more detail below.

Preferably the step of pyrolysing the feedstock to produce a pyrolysis char further comprises a char drying step to adjust the wax content of the char material. This step is performed before the char leaves the pyrolysis reactor. Adjusting the wax content of the material can help to optimise the compatibility of the material with the concrete composition. Preferably the char has a wax content of less than 5 wt% (based on the weight of the char), more preferably less than 1 wt% and most preferably substantially no wax. In some embodiments, the inclusion of from 0.5 to 5 wt% wax may impart some additional water resistance to the concrete.

Preferably, after pyrolysing the feedstock to produce a pyrolysis char, and before mixing the pyrolysis char into a concrete composition, the char is quenched in water. This helps to provide a product having a suitable moisture content compatible with the concrete mixture. The char will generally be dewatered but not further dried before use.

If necessary there may be a further milling or grinding step performed on the char to reach a desired particle size. However, advantageously, the method described herein can be performed without any such step since the particle sizes directly obtained from the process are already suitable. Preferably the pyrolysis char has a mean primary particle size (D50) of less than 50 microns. Particle sizes can be measured using dry laser diffraction techniques which are well known in the art. Primary particles are the smallest constituent particles. That is, any agglomerate particle is comprised of primary particles adhered together. Primary particles cannot be made smaller, except with the application of high energy techniques such as high shear.

Preferably the char is used in the concrete composition without any chemical modification or treatment which would produce a functionalised char (for example, reaction with sulfuric acid to sulfonate the char).

The method comprises mixing the pyrolysis char into a concrete composition. The mixing step may be performed by hand or by use of a mixing machine, such as a concrete mixer. All such steps are well known in the art since concrete production has a long history and development. According to one alternative, the concrete composition is a dry power. That is, the filler is mixed with the cementitious ingredients to provide a concrete powder. This is then suitable for use on the addition of water to form a shapeable slurry. By providing the mixture as a dry powder it is suitable for storing before use. When it is desired to use the dry powder the method further comprises: adding water to form a ready-to-use concrete slurry, shaping the concrete slurry; and allowing the concrete slurry to dry/cure to form concrete.

According to an alternative method, the pyrolysis char is added to a concrete slurry. That is, the char is mixed through a pre-prepared concrete slurry and is thus immediately ready for use. The slurry can be shaped and used in place of a conventional concrete slurry. Thus, preferably the method further comprises: shaping the concrete slurry; and allowing the concrete slurry to dry/cure to form concrete.

Concrete is an artificial composite material, comprising a matrix of cementitious binder (typically a hydraulic cement such as Portland cement of which calcium hydroxide (often converted from limestone) is a key material) and a dispersed phase or "filler" of aggregate (typically a rocky material, loose stones, and sand). The binder "glues" the filler together to form a synthetic conglomerate. Many types of concrete are available, determined by the formulations of binders and the types of aggregate used to suit the application of the engineered material. These variables determine strength and density, as well as chemical and thermal resistance of the finished product.

The ingredients which form concrete are similarly well known. Preferably the concrete composition comprises a cementitious binder. Cement paste, most commonly made of Portland cement, is the most prevalent kind of concrete binder. For cementitious binders, water is mixed with the dry cement powder and aggregate, which produces a semi-liquid slurry (paste) that can be shaped, typically by pouring it into a form. The concrete solidifies and hardens through a chemical process called hydration where the binder is hydraulic. The water reacts with the cement, which bonds the other components together, creating a robust, stone-like material. Where the binder is non-hydraulic, the concrete solidifies and hardens through a chemical process called carbonation by reaction with carbon dioxide from the atmosphere. Other cementitious materials, such as fly ash and slag cement, are sometimes added — either pre-blended with the cement or directly as a concrete component — and become a part of the binder. Portland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar, and many plasters. It consists of a mixture of calcium silicates (alite, belite), aluminates and ferrites — compounds which combine calcium, silicon, aluminium and iron in forms which will react with water. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay or shale (a source of silicon, aluminium and iron) and grinding this product (called clinker) with a source of sulfate (most commonly gypsum). Preferably the cementitious binder comprises calcium silicates, aluminates and ferrites.

Fine and coarse aggregates make up the bulk of a concrete mixture. Sand, natural gravel, and crushed stone are used mainly for this purpose. Recycled aggregates (from construction, demolition, and excavation waste) are increasingly used as partial replacements for natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted. Preferably the concrete composition comprises an aggregate material. Aggregates consist of large chunks of material in a concrete mix, generally a coarse gravel or crushed rocks such as limestone, or granite, along with finer materials such as sand. Preferably the aggregate in the concrete composition comprises one or more of crushed stone and sand.

The size distribution of the aggregate determines how much binder is required. Aggregate with a very even size distribution has the biggest gaps whereas adding aggregate with smaller particles tends to fill these gaps. The binder must fill the gaps between the aggregate as well as paste the surfaces of the aggregate together, and is typically the most expensive component. Thus, variation in sizes of the aggregate reduces the cost of concrete. The aggregate is nearly always stronger than the binder, so its use does not negatively affect the strength of the concrete.

Additives may be added to modify the cure rate or properties of the material. The common types of admixtures, which are all well-known in the art, are as follows:

• Accelerators speed up the hydration (hardening) of the concrete. Typical materials used are calcium chloride, calcium nitrate and sodium nitrate. Accelerating admixtures are especially useful for modifying the properties of concrete in cold weather.

• Air entraining agents add and entrain tiny air bubbles in the concrete, which reduces damage during freeze-thaw cycles, increasing durability. • Bonding agents are used to create a bond between old and new concrete (typically a type of polymer) with wide temperature tolerance and corrosion resistance.

• Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete.

• Crystalline admixtures are typically added during batching of the concrete to lower permeability. Concrete with crystalline admixture can expect to self-seal as constant exposure to water will continuously initiate crystallization to ensure permanent waterproof protection.

• Pigments can be used to change the color of concrete, for aesthetics.

• Plasticizers increase the workability of plastic, or "fresh", concrete, allowing it to be placed more easily, with less consolidating effort. A typical plasticizer is lignosulfonate. Plasticizers can be used to reduce the water content of a concrete while maintaining workability and are sometimes called water-reducers due to this use. Such treatment improves its strength and durability characteristics.

• Pumping aids improve pumpability, thicken the paste and reduce separation and bleeding.

• Retarders slow the hydration of concrete and are used in large or difficult pours where partial setting is undesirable before completion of the pour. Typical polyol retarders are sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid.

Optionally, the concrete further comprises one or more additives, preferably selected from accelerators, air entraining agents, corrosion inhibitors, pigments, plasticisers, retarders and pumping agents.

The char is mixed into the concrete composition in an amount of from 0.1 to 15 wt%, based on the total dry weight of the mixture. Preferably the pyrolysis char is mixed into the concrete composition in an amount of from 1 to 12 wt%, preferably 2 to 10 wt%. More preferably, the char is mixed in an amount of at least 3 wt%, for example from 3 wt% to 8 wt%. These levels of addition are suitable for providing meaningful improvements in the thermal conductance properties without compromising the material properties of the concrete such as compressive strength. It has also been found that the setting times for the concrete can be improved when using the ELP char, compared to other filler materials.

The pyrolysis char obtained from end-of-life plastics has the following composition (by dry weight):

Preferably the concrete is substantially devoid of any further filler materials. Indeed, it is further preferred that the char serves to substitute at least a portion of the sand which would otherwise be present in the composition.

Preferably, the pyrolysis char has a carbon content of from 35 wt% to 60 wt%, more preferably from 35 wt% to 50 wt%, Preferably, the pyrolysis char has an ash content of from 30 wt% to 60 wt%, more preferably from 40 wt% to 50 wt%. Bio-char can have a carbon content of about 40 wt% to 70 wt% and an ash content of less than 20 wt%. Similarly, impurities in ELP plastics can give rise to relatively high calcium contents, for example from 5 wt% to 20 wt%. On the other hand, bio-char may be substantially devoid of calcium and typically has much greater amounts of nitrogen, such as from 5 wt% to 10 wt%. As will be appreciated by those skilled in the art, ash is sum of inorganic (non-carbonaceous) components remaining in the char after pyrolysis. As such, the char consists of carbon, ash and optionally wax. Preferably the pyrolysis char has a surface area of 20 m²/g or less, preferably 2 m²/g or less. Preferably, the pyrolysis char has a density of 1 .25 g/cm³ or less, preferably from 0.9 to 1 .2 g/cm³.

The char characterised by any or all of these parameters is particularly suitable for the present invention. Most particularly, the inventors believe that the surface area being less than 20 m²/g is significantly lower than that of other chars known in the art which are often described as porous, and used for their porosity. The surface area of the char can be measured using conventional techniques, for example by nitrogen surface area (NSA) measurements. The surface area may be measured in accordance with ASTM D6556. Where the char is used having such a low porosity, the interaction with the concrete composition is significantly altered giving rise to advantageous physical properties, including reduced thermal conductivity when compared to bio-chars, for example. Bio-chars often have a surface area of more than 200 m²/g and a density of about 0.65 g/cm³.

According to a further aspect there is provided a concrete composition for use in applications requiring thermal and/or acoustic insulation properties obtainable by the method described herein.

According to a further aspect there is provided a concrete composition comprising from 0.5 to 60 wt% of a char material, wherein the char material is a pyrolysis char having a carbon content of from 35 wt% to 60 wt%, a surface area of 20 m²/g or less, and a density of 1 .25 g/cm³ or less. The concrete composition and the char additive are preferably as described herein.

The concrete composition is suitable for use in applications requiring recycled aggregates, and/or for uses where it is required to provide a less environmentally damaging owing to the reduction in virgin mined aggregates, and/or for reducing building energy usage associated with heating and cooling climate controls.

According to a further aspect there is provided the use of a pyrolysis char obtained from the pyrolysis of end-of-life plastics as a filler in concrete compositions.

All aspects of the method of making the concrete composition described herein may be applied equally to this further aspect relating to the use of the char.

Methods for pyrolysis of end-of-life plastics are well known in the art, including, for example, in WO2021123822, WO2016030460 and WO2011077419 which are each incorporated herein by reference. The preferred method of pyrolysis will now be described further in more detail.

Preferably the method for pyrolysis of end-of-life plastics involves the steps of: melting a waste plastics material, pyrolysing the molten material in an oxygen-free atmosphere to provide pyrolysis gases and a pyrolysis char; bringing the pyrolysis gases into a contactor having a bank of condenser elements so that some long chain gas components condense on said elements, returning said condensed long-chain material to be further pyrolysed to achieve thermal degradation, and allowing short chain gas components to exit from the contactor in gaseous form; and distilling said pyrolysis gases from the contactor in a distillation column to provide one or more fuel products.

The method described herein can be performed on a batch or continuous basis. Continuous treatment is preferred when there is a continuous large supply of end-of-life plastic available for treatment. Batch processes are more desirable where there are smaller volumes of oil being produced, or where it is being produced on an intermittent basis. In a batch process there may be a plurality of holding vessels used in parallel, giving a quasi-continuous effect on the treatment performed.

Preferably the contactor elements comprises a plurality of plates forming an arduous path for the pyrolysis gases in the contactor. Moreover, preferably the plates are sloped downwardly for runoff of the condensed long-chain hydrocarbon, and include apertures to allow upward progression of pyrolysis gases. In one embodiment, the contactor elements comprise arrays of plates on both sides of a gas path. Preferably the contactor element plates are of stainless steel. The contactor may be actively cooled such as by a heat exchanger for at least one contactor element.

Alternative cooling means may comprise a contactor jacket and cooling fluid directed into the jacket. There may be a valve linking the jacket with a flue, whereby opening of the valve causing cooling by down-draught and closing of the valve causing heating. The valve may provide access to a flue for exhaust gases of a combustion unit of the pyrolysis chamber.

Preferably there is a pipe directly linking the pyrolysis chamber to the contactor, the pipe being arranged for conveying upwardly-moving pyrolysis gases and downwardly-flowing long-chain liquid for thermal degradation.

Preferably infeed to the pyrolysis chamber is controlled according to monitoring of level of molten plastics in the chamber, as detected by a gamma radiation detector arranged to emit gamma radiation through the chamber and detect the radiation on an opposed side, intensity of received radiation indicating the density of contents of the chamber.

Preferably the pyrolysis chamber is agitated by rotation of at least two helical blades arranged to rotate close to an internal surface of the pyrolysis chamber. Optionally, the pyrolysis chamber is further agitated by a central auger. Advantageously, the auger can be located so that reverse operation of it causes output of char via a char outlet.

Preferably the temperature of pyrolysis gases at an outlet of the contactor is maintained in the range of 240°C to 280°C. The contactor outlet temperature can be maintained by a heat exchanger at a contactor outlet.

A bottom section of the distillation column is preferably maintained at a temperature in the range of 150°C to 200°C, preferably 160°C to 190°C. The top of the distillation column is preferably maintained at a temperature in the range of 90°C to 130°C, preferably approximately 100°C.

Optionally there is further distillation of some material in a vacuum distillation column. Heavy or waxy oil fractions are drawn from the bottom of the vacuum distillation column and can be recycled back to the pyrolysis chamber. Desired grade on-specification pyrolysis oil can be drawn from a middle section of the vacuum distillation column. Light fractions are drawn from a top section of the vacuum distillation column and are condensed.

The method of producing the char from end-of-life plastics will now be discussed in more detail.

The end-of-life plastic (ELP) from the walking floor silo is discharged into the extruder hopper, which is designed to deliver heated ELP to the reactors. The extruder is supplied with variable speed drives that permit lower flow rates to be fed to the reactors, if required, during start-up and shutdown of an extruder. The extruder heats up the plastic from ambient conditions to the target set temperature using shear force generated by the rotation of the extruder screw. The high temperatures on the outlet of the extruder is required to ensure that the plastic temperature, which is lower than the reactor operating temperature, does not adversely affect the thermal performance of the reactor when loaded in.

The extruder barrel can be electrically heated, especially during start-up. During normal operation, the electric heating function is not used because the shear force from the auger screw will provide sufficient heat to melt the plastic.

Plasticised ELP is expelled from the extruder under high pressure into a melt feed line that connects the extruder to three Reactors via a header pipe. Multiple instruments monitor pressure and temperature along the melt feed line during feeding to assure flow. The plant has multiple jacketed reactors that form the core of the process. Each conical based reactor is enclosed by a reactor jacket which provides the heat required to decompose the ELP and generate the desired hydrocarbon vapour. Each reactor is physically located above a char receiver and below a contactor.

Each individual reactor is provided with an agitator designed to maintain thermal efficiency of the process by minimising char build up on the walls of the reactor by maintaining close steel to steel clearance with the vessel walls; suspend any char produced during pyrolysis in the plastic mass to prevent build-up on the internal surfaces of the reactor; and homogenise the molten ELP in the reactor during processing; and remove char once pyrolysis is complete and the char is dry.

The agitator homogenises the vessel mass by pushing ELP down the walls of the reactor, to the centre of the vessel and up the agitator shaft when running in forward. When operating in reverse, it pushes medium down the agitator shaft and from the centre of the vessel to vessel walls. This promotes char removal through a bottom outlet nozzle located at the lowest point of the vessel conical dished end.

An individual reactor is designed to process 5 tonnes of ELP every day. Future generations may have a higher capacity. Reactors are grouped in threes and each trio of reactors is fed sequentially such that only one of each trio of vessels is being fed with fresh ELP at any one time whilst the other two are either completing pyrolysis or processing char.

ELP is fed into a reactor vessel by its respective Extruder. The reactor is operated at a temperature of 350°C or more, preferably 380 to 450°C and up to 0.5 barg in an inerted oxygen free environment. At these temperatures the ELP polymer chains decompose into shorter hydrocarbon chains and are vaporised to form a rich saturated hydrocarbon vapour. This vapour exits the vessel via an outlet located on the top of the vessel which leads to the reactor’s respective contactor.

The reactor is designed to operate on a cycle. Each cycle consists of three periods. The first is a ELP feed period known as “charging” in which ELP is loaded to the reactor and pyrolysed. In the second period, pyrolysis is completed and the non-pyrolysable material (char) in the reactor is dried to allow for easy handling after removal from the reactor in anticipation of the next charge of ELP. This stage is called “cooking”. The third stage is called “removal” and involves removing char from the reactor by opening the reactor bottom outlet valve and then reversing the reactor’s agitator which in turn forces char out of the reactor into the char receiver below it. Once all the char is removed the bottom outlet valve is closed and plastic feeding can recommence.

Char is formed primarily of carbonaceous material, plastic polymer-forming additives, pigmentation and ELP contamination. Char continually forms in the reactor throughout pyrolysis and must be removed prior to commencement of another charge else the effective volume of the reactor reduces.

Char is removed through the bottom outlet nozzle and valve (BOV). When char removal is required the bottom outlet valve is opened to the char receiver below. The agitator is then set to reverse to assist char removal. Char should fall out of the chamber under gravity because of the conical shape of the reactor however if it does not, the agitator has been designed to assist it by breaking up char lumps which may have formed in the nozzle.

Each reactor has its own reactor jacket. The reactor jacket is an internally insulated cylindrical non-pressure vessel with a bespoke internal arrangement for efficient distribution of combustion gases. Heat is provided to the reactor jacket by a burner attached to a separate combustion chamber. The heat is generally provided by combusting syngas or natural gas.

When char in a reactor is cooked, dried and ready for removal, any remaining hydrocarbon vapours in the reactor atmosphere must be flushed with nitrogen from the reactor prior to discharging the char into a char receiver. This is to reduce the volume of atmospheric condensable hydrocarbons in the reactor and ensure the atmosphere in the char receiver remains inert.

Char is a fine and light material with the consistency of carbon black and is easy to disturb. To complete Reactor Flush without disturbing the char bed in the reactor, nitrogen must be slowly purged through the chamber (<30m³/hr).

Char is removed from the reactor through the bottom outlet nozzle when the bottom outlet ball valve is open. Char is removed by gravity with the assistance of the reactor agitator operating in reverse. The char receiver, which is located directly underneath the reactor and reactor jacket, can receive char at any temperature between ambient and 450°C.

Completion of char removal is determined when the agitator load decreases to its empty reverse load at the same speed value. Once the char is confirmed removed, the agitator will stop and return to running in the forward direction. The reactor bottom outlet valve will then be flushed clean and closed at which point the reactor is ready to accept another charge of ELP.

A nitrogen blanket is kept on the char receiver at 30mbarg whilst char is held in the receiver. The vessel has a nitrogen control valve to ensure the atmosphere inside the vessel is constantly inert and mitigating against fire risk.

Char is discharged from the vessel through a bottom outlet nozzle, which is connected directly to the inlet of a char auger with cooling jacket. The char auger is designed to process and cool the char to below 60°C at a rate of up to 250kg/hr. The char auger jacket uses cooling water at about 25°C to provide the cooling required to reduce the char’s temperature. The auger is kept full of char and a positive nitrogen blanket pressure to minimise risk of air backflow.

Cooled char from the char receivers is discharged from their respective char auger onto a common enclosed conveyor system where the char will be dropped to a char hopper. The char will be stored in a char storage container and weighed by the char scale prior to offtake to char storage area.

The contactor is a jacketed pressure vessel. It contains an internal baffle arrangement that is designed to selectively knock back heavy or long-chain hydrocarbons that have not been sufficiently thermally degraded in the reactor with the application of cooling air through the vessel’s jacket. Condensed heavier material drains back into the reactor under gravity where it can be decomposed further to increase desired product volumes. Lighter fractions constitute a pyrolysis oil which is recovered as a desirable product of the process.

Cooled char from the char augers is discharged onto the Char Discharge Belted Conveyor that runs the length of all the core modules, this carries the char to the Char Transfer Belted Conveyor that transfers the char into a Char Storage Container. Once the container is full it will be moved to the Char Storage Area and the container will be replaced with an empty one.

The invention will now be described further in relation to the following non-limiting examples. Pyrolysis char obtained from the pyrolysis of end-of-life plastics in accordance with the method described herein was added to concrete at 2% and 5% by weight to concrete and tested for thermal conductivity, density and compressive strength. This was compared with concrete without pyrolysis char added as a baseline.

Thermal conductivity of the concrete reduced by over 40% at 5% char loading, in addition to the density of the concrete reducing by 2%. This result is particularly surprising such a large reduction in thermal conductivity would not have been expected based on the results in the prior art with the use of bio-chars.

The term “comprising” as used herein can be exchanged for the definitions “consisting essentially of” or “consisting of”. The term “comprising” is intended to mean that the named elements are essential, but other elements may be added and still form a construct within the scope of the claim. The term “consisting essentially of” limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claimed invention. The term “consisting of” closes the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

For the avoidance of doubt, the entire contents of all documents acknowledged herein are incorporated herein by reference.

Claims

Claims:

1 . A method for the production of concrete for use in applications requiring thermal insulation properties, the method comprising: providing an end-of-life-plastic feedstock; pyrolysing the feedstock to produce a pyrolysis char; and mixing the pyrolysis char into a concrete composition in an amount of from 0.1 to

15 wt%, based on the total dry weight of the mixture.

2. The method according to claim 1 , wherein the end-of-life-plastic feedstock comprises hydrocarbon plastic, preferably in an amount of at least 80 wt%, more preferably at least

90 wt%.

3. The method according to claim 2, wherein the hydrocarbon plastic is selected from the group consisting of polyethylene (PE), polystyrene (PS), polypropylene (PP), and mixtures thereof.

4. The method according to any preceding claim, wherein the concrete has a density of 1 ,400 kg/m³ or more, preferably 1 ,800 kg/m³ or more, more preferably 1 ,900 kg/m³ or more.

5. The method according to any preceding claim, wherein the pyrolysis char is mixed into the concrete composition in an amount of from 2 to 10 wt%, preferably from 3 to 8 wt%.

6. The method according to any preceding claim, wherein the pyrolysis char has a mean primary particle size (D50) of less than 50 microns, preferably less than 10 microns, more preferably less than 5 microns.

7. The method according to any preceding claim, wherein the pyrolysis char has a carbon content of from 35 wt% to 60 wt%, preferably from 35 wt% to 50 wt%, and/or an ash content of from 30 wt% to 60 wt%, preferably from 40 wt% to 50 wt%.

8. The method according to any preceding claim, wherein the pyrolysis char has a surface area of 20 m²/g or less, preferably 2 m²/g or less.

9. The method according to any preceding claim, wherein the pyrolysis char has a density of 1 .25 g/cm³ or less, preferably from 0.9 to 1 .2 g/cm³.

10. The method according to any preceding claim, wherein the concrete composition is a dry power.

11 . The method according to claim 10, wherein the method further comprises: adding water to form a ready-to-use concrete slurry, shaping the concrete slurry; and allowing the concrete slurry to dry to form concrete.

12. The method according to any of claims 1 to 9, wherein the pyrolysis char is added to a concrete slurry.

13. The method according to claim 12, wherein the method further comprises: shaping the concrete slurry; and allowing the concrete slurry to dry to form concrete.

14. The method according to any preceding claim, wherein the concrete composition comprises:

(i) a cementitious binder, preferably comprising calcium silicates, aluminates and ferrites;

(ii) aggregate material, preferably one or more of crushed stone and sand; and

(iii) optionally, one or more additives, preferably selected from accelerators, air entraining agents, corrosion inhibitors, pigments, plasticisers and pumping agents.

15. The method according to any preceding claim, wherein the concrete is substantially devoid of any further filler materials.

16. The method according to any preceding claim, wherein, after pyrolysing the feedstock to produce a pyrolysis char, and before mixing the pyrolysis char into a concrete composition, the char is quenched in water.

17. The method according to any preceding claim, wherein the step of pyrolysing the feedstock to produce a pyrolysis char further comprises a char drying step to adjust the wax content of the char material.

18. A concrete composition for use in applications requiring thermal and/or acoustic insulation properties obtainable by the method according to any preceding claim.

19. A concrete composition comprising from 0.5 to 60 wt% of a char material, wherein the char material is a pyrolysis char having a carbon content of from 35 wt% to 60 wt%, a surface area of 20 m²/g or less, and a density of 1 .25 g/cm³ or less.

20. Use of a pyrolysis char obtained from the pyrolysis of end-of-life plastics as a filler in concrete compositions.

21 . Use of a pyrolysis char obtained from the pyrolysis of end-of-life plastics to improve the thermal and/or acoustic properties of a concrete composition.

22. Use of a pyrolysis char obtained from the pyrolysis of end-of-life plastics to reduce the carbon footprint and/or use of virgin mined aggregates of a concrete composition.