EP4061914A1

EP4061914A1 - High-energy solid fuel from plastic waste

Info

Publication number: EP4061914A1
Application number: EP20815929.3A
Authority: EP
Inventors: Pavel GULAS
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-11-19
Filing date: 2020-11-15
Publication date: 2022-09-28
Also published as: WO2021099907A1; SK1382019A3

Abstract

High-energy solid fuel from plastic waste consisting of the mixture of thermosets, thermoplastics, and catalysts, having heating value from 17 to 30 GJ/kg depending on volume and type of the thermoplastic used. Preferably, sorted plastic waste is to be used as thermoplastic, e.g. polyethylene sacks, foils, and bags having heating value over 40 GJ/kg, and the plant biomass as the source of thermoset. The catalysts may be added to the mixture of thermosets and thermoplastics in the form of finely pulverized minerals, or may be provided by any suitable combination of various types of the biomass. Combustion of the high-energy solid fuel achieves much higher heating value, higher flame temperature, and fewer toxic emissions are generated.

Description

HIGH-ENERGY SOLID FUEL FROM PLASTIC WASTE

The present disclosure relates to composition of high-energy solid fuel consisting of thermosets, thermoplastics, and catalysts, wherein plastic waste is used as thermosets, and the fuel complies with conditions for high heating value adjustable in the range from 17 to 30 MJ/kg. When burning the fuel, less emission is generated in contrast to burning of pure wood.

Current annual production of plastics is around 400 million tons, of which only 9% plastics is recycled, 12% is combusted in incineration plantsand cement plants, and 79% produces environmental burden on waste dumps and in nature. At present, there are estimated 150 million tons of accumulated plastic waste in oceans with 8 million tons added each year. High resistance of plastic to natural decomposition results in accumulation of plastic.

Current methods for plastic processing mainly include catalytic polymeric degradation such as cracking, pyrolysis, depolymerization that takes place at medium-high temperatures, without access of air, and under normal atmospheric pressure, wherein natural gas, propane-butane is used for heating of input feedstock, for example. Heating oil, lighter lacquer diluent, diesel oil, are produced therefrom; waxes as representatives of heavier fractions are produced as well.

Another method includes hydrothermal liquefaction of polyolefins at temperature of 400–500°C, reaction time from 0.5 to 6 hours, and approximate pressure of 23MPa. The resulting product is oil-like liquid consisting of paraffins, olefins, cyclic compounds such as cyclopentanes, cyclohexanes and more, aromatic compounds such as benzene, xylene, etc., higher fatty alcohols such as butynol, nonanol, etc.

A new method for processing of plastic waste is plasma liquefaction, product of which is flammable poisonous synthesis gas consisting of H ₂, CO, CO ₂, H ₂O, CH ₄, N ₂, a C ₂ ⁺, and ceramic and metal remains.

Use of these methods for production of energy is uneconomical and depends on subsidies. Depolymerization effects and output thereof are relatively low, poisonous toxic gases are produced that may escape to environment already during the phase of their production.

Technologies and apparatuses required are complex, which increases the risk of failures and production emergencies.

Most often used method is combustion of plastic waste in incineration plants and cement plants, while it being the most controversial method in which unsorted waste is combusted (the waste includes also chlorinated, fluoridated polymers, polymers with sulphur content, and the question is, what is really combusted, what is output thereof, and how variously emissions deviate).

The prior art does not provide a sufficient solution of environmentally friendly combustion of plastic waste, in particular with respect to forming of environmentally friendly fuels for use thereof in combustion process.

To a substantial extent, the drawbacks of the prior art are resolved by the high-energy solid fuel according to the present invention characterized in that it consists of the mixture of:

at least 35% by weight, preferably 50–60% by weight of cellulose, hemicellulose, and potentially contained synthetic thermosets, content of which does not exceed ¼ of weight of cellulose, hemicellulose, and synthetic thermosets,

0,1 to 16% by weight of water, preferably 0.1 to 8% by weight,
up to 60% by weight of lignin and synthetic thermoplastics, of which the synthetic thermoplastics preferably amount to 15–30% by weight of total sold fuel weight,
or as the case may be added acid-base and redox catalysts from the group including metal oxides, alkaline metal oxides, alkaline earth metal oxides, transient metal oxides, semimetal oxides, non-metal oxides, and mixtures thereof, wherein composition of the solid fuel is that the ash content after burning is 2 to 20% by weight of the solid fuel.

It should be first and foremost mentioned that the preferred solution includes the biomass as the source of cellulose and hemicellulose in the first step.

The most used synthetic thermosets in the second step are polyolefin, in particular PE and PP, and the biomass is the source of lignin.

In the third step, sufficient volume of catalysts in the mixture needs to be provided, function of which is acceleration of depolymerization of polymers followed by activation of oxidation of generated fragments in combustion.

Hence, presence of the catalysts is needed for proper combustion of fuel and for reduction of toxic emissions being produced.

The high-energy solid fuel may be processed in the form of pellets, briquettes, and similar.

The term “polymers” refers in general theory of the present industry to macromolecular substances consisting of monomers.

They may be natural or synthetic polymers depending on their origin. The synthetic polymers are then divided into plastics and elastomers. The plastics are divided into thermosets and thermoplastics.

Polymers containing chlorine, fluorine and sulphur and silicones are not suitable for the present invention.

The term “thermoset” refers to synthetic thermosets such as phenoplasts, epoxy resins, polyester resins, spatially cross-linked PET. Cellulose and hemicellulose polysaccharides, of which source is the biomass, have properties similar to thermosets and therefore, for the purpose of the present utility model, they will be referred to as “natural thermosets”. Synthetic thermosets may be added to the natural thermosets in the ratio of ¾ of natural thermosets and ¼ of synthetic thermosets. Under increasing temperature, thermosets do not become softer, do not melt, do not cross over the molten phase but gasify right from the solid phase. They maintain their construction structure and large surface until the end of the gasification.

The term “thermoplastic” refers to synthetic thermoplastic such as polyolefins, in particular PE, PP, PB, vinyl polymers, polyesters, polyethers, polyamides, styrene and acrylic polymers, and bioplastics such as polylactic acid PLA. Included in them is lignin, the most complex natural polymer. Lignin is the organic polymer of polyphenolic structure having thermoplastic properties and therefore, for the purpose of the present utility model, we will refer lignin to “natural thermoplastic”. Lignin is sourced from the biomass.

Under increasing temperature, thermoplastic becomes softer, become pliable, and the melt, which solidifies again after cooling, occurs.

Table No. 1 shows chemical composition of cellulose, hemicellulose, and lignin in each type of plant the biomass

Source	Cellulose content [%] Natural thermoset	Hemicellulose Content [%] Natural thermoset	Lignin content [%] Natural thermoplast
Deciduous trees	40-48	26-38	17-25
Coniferous trees	40-50	22-32	24-34
Wheat straw	30-45	20-30	10-20
Barley straw	30-35	20-29	13-25
Rape straw	35-45	16-30	14-20
Rice straw	28-41	20-30	9-24
Miscanthus Giganteus	37-45	19-26	17-24
Shells of apricot stone	33-39	15-34	23-51
Shells of walnuts	25-34	20-30	33-52

[Table 1]

The term “catalysts” refer to a small amount of a substance, which when added to a chemical process, reduces required activation reaction energy, and makes it accelerated. The catalysts are not consumed in this process. Common catalysts are, for example: metal oxides Al ₂O ₃, alkaline metal oxides – K ₂O, Na ₂O, alkaline earth metal oxides CaO, MgO, transient metal oxides Fe ₂O ₃, TiO ₂, semimetal oxides SiO ₂, and non-metal oxides P ₂O ₅, and mixtures thereof. They may be added to the mixture of plastics and thermosets in the form of finely pulverized particles such as zeolite: SiO ₂ + Al ₂O ₃, aluminium oxides, iron oxides (FeO, Fe ₂O ₃) and similar; catalysts surface area is important. Or, it may be beneficial that some types of the biomass contain salts of such elements: carbonates, phosphates, silicates in various ratios, which on heating convert into oxides defined as ash content after combustion. In this case the catalysts are ideally distributed within the biomass and has as the largest surface as possible. Also, fillers being added to some plastic products for adjustment of their properties, or making the final product cheaper, are the source of catalysts. The polymer products may contain mineral fillers such as talc (hydrated magnesium silicate Mg ₃Si ₄O ₁₀(OH) ₂), carbonates, mica, a wide group of aluminium silicate minerals with content of Al, Si, K, Na, Ca, Mg, Fe, Ti, and more. These minerals are in particular sources of SiO ₂, Al ₂O ₃, K ₂O, Fe ₂O ₃,CaO, MgO, TiO ₂.

Acid-base catalysts are degradative (e.g., MgO, CaO, SiO ₂...), and they catalyse disintegration of hydrocarbons. Na ⁺ and K ⁺ cations have significant impact on disintegration of hardly degradable benzene compounds.

The catalysts having redox properties (e.g., oxides of iron, zinc, titanium, ...) boost oxidation (combustion).

In combustion, the acid-base catalysts improve efficiency of disintegration of polymer degradation into fractions in the first step, followed by effective oxidation and combustion under presence of redox catalysts. Mixture of such catalysts restricts production of polycyclic-aromatic hydrocarbons (PAH).

The term “ash content after combustion” refers to net ash not contaminated by non-combusted organic residues, of which composition is inorganic, expressed as % by weight, and content of which in the biomass is used as a catalyst. Table No. 3 illustrates generally known values of ash content after combustion of individual types of the biomass.

The term “plastic waste” refers to sorted out thermoplastics in the form of PE bags, foils, sacks, packets, containers and other PE products, as well as PP foil and other PP products, or polyesters and polyamides from automotive industry waste processing, and other.

Plastics with chlorine, fluorine, sulphur, and silicone content are not suitable for the present invention. The term “high-energy fuel” refers to solid fuel of which heating value is higher than heating value of wood, i.e., over 17 MJ/kg, ideally over 20 MJ/kg, and which consists of organic portion of hydrocarbons (natural and synthetic) and inorganic portion of catalyst.

Average heating values of types of the biomass and plastics are illustrated in Table 2.

		Heating value [MJ/kg]	Moisture content
Deciduous trees	Beech	15.5	10%
	Oak	16.0	10%
	Birch	16.5	10%
	Locust	15.5	10%
Coniferous trees	Spruce	16.0	10%
	Pine	16.5	10%
	Fir	17.0	10%
Straw	Wheat	15.8	8%
	Rice	14	10%
MiscanthusGigantheus		17.1	10%
Fruit stones	Plums	18.5	15%
	Apricot shells	20.2

Plastics	PE	46.5
	PP	45.5
	PS	42.0
	PMMA	26.5
	PET	24.0
	PES	26,0
	PVOH	23
	PVC	20
	PUR	25
	Phenol formaldehyde bitumen	32

The term “combustion (burning)” refers to redox exothermic reaction in which hydrocarbons (fuel) are oxidized by oxygen.

Hydrocarbons without benzene nuclei (e.g., pure cellulose) are easily gasified and therefore, their combustion flame is intensive and long, and no residue remains after combustion.

In combustion of wood (main components consist of organic portion: cellulose, hemicellulose and lignin, which is a mixture of mainly aromatic alcohols, and inorganic portion: carbonate salts, silicate salts, phosphate salts, ...), hemicellulose and cellulose burn out first. Easily degradable methoxyl groups from lignin are then added and finally, lignin remains and non-combusted residue thereof contains a high proportion of resistant and hardly degradable benzene compounds. They burn out successively as last by shorter flame, and mainly represent a source of toxic emissions, and the grounds for occurrence of tar residues. Ash in the form of oxides remains from the inorganic portion, and the ash may be contaminated by toxic tar residues from organic portion of the wood, in particular lignin.

In combustion of thermoplastics, melting occurs that results in reduction of their surface. The consequence of this is that the reduced surface absorbs less thermal energy from burning gases over their surface. However, production of flammable gases generated by degradation of polymers depends exactly on thermal energy being absorbed by surface. It should be also taken into account that the generated gas vaporizing from melt surface cools down the surface and therefore, no sufficient volume of flammable gases is produced.

In other words, thermal energy is needed for depolymerization, destruction of macromolecule so that sufficient volume of flammable gases is generated. In expansion from melt to atmosphere, these flammable gases again require energy, which is taken from the melt, which makes it cooler and deceleration of the process occurs. This takes the process up to the limit of ability of uninterrupted combustion as activation energy must be supplied for oxidation of produced gases itself. Droplets, melt blocks are the worst design for absorption of heat and gasification, and no sufficiently large surface and contact with oxygen is provided. Into this process a thermoplastic, e.g., PE enters as inert material but, in this combustion, whole portions of incompletely combusted polymer are ripped off, and the polymer cools down if located outside the combustion zone. The chemical compounds produced from this thermal disintegration start to re-link each other, but fail to produce back the inert linear chains; they group into most energetically favourable positions when they produce the most stable compounds, which are aromatic compounds with benzene nucleus. These are rather toxic and carcinogenic.

This incomplete combustion may be avoided by providing a large surface area of thermoplastic. Mixing of thermoplastic with thermoset avoids casting of thermoplastic melt because thermoset does not cross over the melting phase when heated, and breaks down formation of compact melt blocks from thermoplastic. A suitable thermoset is cellulose contained in the biomass. Its structure is varied, has a large surface, contains various unevenness, micro, and macro capillaries. Large surface provides absorption of more energy, which results in production of high volume of flammable gases and good contact with oxygen.

Since the process poses high energy demands where thermal energy is required for destruction of polymers, vaporization of generated gases, and activation of combustion alone, the energy demand may be reduced, and entire chemical process streamlined by addition of destructive acid-base and redox catalysts.

Presence of thermoplastics and catalysts in fuel increases flame temperature during combustion by 100°C up to 200°C depending on quantity and type of synthetic thermoplastics used (in relation to flame temperature in combustion of the biomass alone). Higher temperature and presence of catalysts provides higher combustion process efficiency, and highly resistant aromatic compounds disintegrate and oxidize as well. Content of toxic substances in produced gases is lower in relation to combustion of the pure biomass, and the combustion process of high-energy fuel is relatively environment-friendly, when in particular CO ₂, water, and mineral ash are generated. Measured CO content in combustion products in combustion of samples of high-energy pellets was 30% up to 50% lower in relation to wooden pellets.

The high-energy solid fuel consists of the mixture of:

1. at least 35% by weight, preferably 50–60% by weight of cellulose, hemicellulose, and potentially contained synthetic thermosets, content of which does not exceed ¼ of weight of cellulose, hemicellulose, and synthetic thermosets. Cellulose and hemicellulose are polysaccharides. They can be found in the biomass: wood, straw, hay, energy plants such as Miscanthus Giganteus, hemp, sorrel, Jerusalem artichoke and similar, fruit stones, products from cellulose: paper, cardboard.

The source of synthetic thermosets may be waste from cabinetmaker workshops that may include phenol formaldehyde, epoxy, or other bitumen. Melamine formaldehyde bitumen is not suitable for the present purposes.

We use the biomass and thermosets pulverized to small particles up to sawdust size.

2. 0.1 to 16% by weight of water, preferably 0.1 to 8% by weight.

Water content in the high-energy solid fuel is water naturally occurring in the biomass. Water content in the biomass depends on partial pressure of water steams in air and therefore, water content in the biomass normally ranges from 10% to 15%. In fuel production process, water vaporizes and the synthetic thermoplastics used are mainly hydrophobic. Therefore, final water content in the fuel does not normally exceed 8% by weight.

3. Up to 60% by weight of lignin and synthetic thermoplastics, of which the synthetic thermoplastics preferably amount to 15–30% by weight of total sold fuel weight.

We use synthetic thermoplastics from plastic waste pulverized to small particles of sawdust size.

4. Or as the case may be added catalysts from the group of metal oxides, alkaline metal oxides, alkaline earth metal oxides, transient metal oxides, semimetal oxides, non-metal oxides, and mixtures thereof, wherein composition of the solid fuel is that the ash content after burning out is 2 to 20% by weight of the solid fuel. Presence of acid-base and redox catalysts is required for complete combustion (oxidation) of thermoplastics. They may be added to the mixture of finely pulverized particles such as Zeolite: SiO ₂ + Al ₂O ₃, aluminium oxides, iron oxides (FeO, Fe ₂O ₃), and more; surface size of catalyst is important. It is appropriate to prepare the mixture by adding the biomass that already contains significant volume of elements being used as catalysts in our case. These elements are essential and non-essential substances in plants in the form of salts, as a component of enzymes, proteins, chlorophyl. They are: Si, K, Ca, Mg, P, Al, Fe, Na, Ti, Cr, B, Cu, S, Cl, Mn, Zn, Mo, Ni, W, Sr, V, Se. In combustion process, they convert into oxides and their volume is defined as ash content after combustion.

Ash content after combustion for each type of the biomass is generally known, and refer to Table 3 for some type of the biomass.

Source	Ash content [%]
Woody plant without bark	0.2-0.6
Woody plant with bark	1-1.5
Tree bark	5-10
Straw	6-8
Miscanthus Giganheus	3-5
Fruit stones	1-2
Rice straw	14-18
Cardboard	14-18

Considering various content of acid-base and redox catalysts in the biomass, an appropriate composition of a recipe for production of the high-energy fuel is selected based on content and composition of ash of individual components used so that resulting 2–20 % by weight, ideally 3–8 % by weight of catalysts is provided.

Tree bark, straw, hay, energy plants, white cardboard are suitable sources of the catalysts.

Examples of Embodiment of Invention

It should be appreciated that each embodiment according to the present invention is illustrative only and in no way limiting the present disclosure. Persons skilled in the art may find or will be capable of finding with the use of not more than routine experimentation the equivalents to specific embodiments of the invention. These equivalents will fall into the scope of the following patent claims. Persons skilled in the art may easily find an optimum design of the composition of the subject of the invention from feedstock available to them.

Example 1

The high-energy fuel according to claim 1 consists of the mixture of

60% by weight of biomass – wheat straw with 63.5% of natural thermoset, 23.5% of natural thermoplastic, and 13 % of water. Catalyst content in the biomass 8%.
40 % by weight of synthetic thermoplastic being low-density polyethylene (LDPE). Catalyst content in LDPE 0.5%.

Ash content in the prepared mixture defined by laboratory: 5.08%.
Heating value of the fuel formed in this way defined by laboratory: 26.94 MJ/kg.

Example 2

The high-energy fuel according to claim 1 consists of the mixture of

34.3% by weight of biomass – wood sawdust with 66% by natural thermoset, 24% of natural thermoplastic, and 10 % of water. Catalyst content in the biomass 0.5%.
34.3% by weight of natural thermoset of fruit stones, 65% content of natural thermoset, 25% natural thermoplastic, and 10% of water. Catalyst content in the stones 1.5%.
15.5% of synthetic thermoplastic which is polypropylene from plastic waste. Catalyst content in waste polypropylene 4%.
11,6 % by weight of synthetic thermoplastic being low-density polyethylene (LDPE). Catalyst content in LDPE 0.5%.
4.4% by weight of synthetic thermoplastic, which is the mixture of polyesters (PES)

Catalyst content in PES 34.1%.
Ash content in the prepared mixture defined by laboratory: 2.95%.
Heating value of the fuel formed in this way defined by laboratory: 25.21 MJ/kg.

Example 3

The high-energy fuel according to claim 1 consists of the mixture of

60% by weight of biomass – wood sawdust with 66% by natural thermoset, 24% of natural thermoplastic, and 10 % of water. Catalyst content in the biomass 0.5%.
10% by weight of thermoset, which is cardboard waste. Catalyst content in cardboard 14%.
20 % by weight of synthetic thermoplastic being low-density polyethylene (LDPE). Catalyst content in LDPE 0.5%.
10% by weight of synthetic thermoplastic, which is the mixture of polyesters (PES)

Catalyst content in PES 34.1%.
Ash content in the prepared mixture defined by laboratory: 5.25%.
Heating value of the fuel formed in this way defined by laboratory: 23.12 MJ/kg.

Example 4

The high-energy fuel according to claim 1 consists of the mixture of:

80% by weight of biomass – Miscanthus Giganteus with 68% by natural thermoset, 20% of natural thermoplastic, and 12 % of water. Catalyst content in Miscanthus 4%.
20 % by weight of synthetic thermoplastic being low-density polyethylene (LDPE). Catalyst content in LDPE 0.5%.

Ash content in the prepared mixture defined by laboratory: 3.48%.
Heating value of the fuel formed in this way defined by laboratory: 22.68 MJ/kg.

Claims

High-energy solid fuel from plastic waste based on plant biomass and plastic waste characterized in that it consists of the following mixture:
at least 35% by weight, preferably 50–60% by weight of cellulose, hemicellulose, and potentially contained synthetic thermosets, content of which does not exceed ¼ of weight of cellulose, hemicellulose, and synthetic thermosets,

0,1 to 16% by weight of water, preferably 0.1 to 8% by weight,

up to 60% by weight of lignin and synthetic thermoplastics, of which the synthetic thermoplastics preferably amount to 15–30% by weight of total sold fuel weight,

or as the case may be added acid-base and reduction oxidation catalysts from the group of metal oxides, alkaline metal oxides, alkaline earth metal oxides, transient metal oxides, semimetal oxides, non-metal oxides, and mixtures thereof, wherein composition of the solid fuel is that the ash content after burning is 2 to 20% by weight of the solid fuel.
High-energy solid fuel according to claim 1 characterized in that the synthetic thermoplastics are polyolefins, in particular PE, PP, PB, vinyl polymers, polyesters, polyethers, polyamides, styrene and acrylic polymers, and bio plastics such as polylactic acid PLA, or mixtures thereof.