Field of the Invention

The present invention relates to a process of producing synthetic hydrocarbon and oxygenated fuels of substantially the same functionality and purity as commercial diesel or petrol or other petroleum fractions from a variety of feedstock materials including solids, liquids, gases and combinations thereof.

Background of Invention

Finding alternative fuel sources and fuels is becoming important due to diminishing fossil fuel reserves and the environmental hazards associated with exhaust gases. Currently short chain alcohols such as methanol and ethanol can be used as an additive to conventional petroleum based fuel. Biodiesel is also known as an alternative diesel fuel or additive to currently used petroleum-based automotive or other vehicular fuel. The disadvantage of ethanol and ethanol as fuels is that whilst they are very clean burning they have lower energy by unit volume and therefore vehicles would require larger fuel tanks.

Biodiesel as an alternative diesel fuel from edible/non-edible oils and animal fats have shown promise as alternative diesel fuels. Though several methods are available for synthesis, transesterification is the preferred route for biodiesel synthesis. The current techniques for transesterification of the oils to biodiesel are based on acid/alkali catalysis. However, these methods are not cost effective for oils with high free fatty acid content and also require an additional downstream step for separation of glycerine and soap from the product. Much of the process complexity originates from contaminants in the feedstock, such as water and free fatty acids, or impurities in the final product, such as methanol, free glycerol, and soap.

Chemically, transesterified biodiesel comprises a mix of mono-alkyl esters of long chain fatty acids. The most common form uses methanol (commonly converted to sodium methoxide) to produce methyl esters as it is the cheapest alcohol available, though ethanol can be used to produce an ethyl ester biodiesel and higher alcohols such as isopropanol and butanol have also been used. Using alcohols of higher molecular weights reduces the cold flow properties of the resulting ester, at the cost of a less efficient transesterification reaction.

A by-product of the transesterification process is the production of glycerol. For every 1 tonne of biodiesel that is manufactured, from 100 kg to 300kg of glycerol are produced. Usually this crude glycerol has to be purified, typically by performing vacuum distillation. This is rather energy intensive. The refined glycerol (98%+ purity) can then be utilised directly, or converted into other products.

Originally, there was a valuable market for the glycerol, which assisted the economics of the process as a whole. However, with the increase in global biodiesel production, the market price for this crude glycerol (containing 20% water and catalyst residues) has declined significantly. Research is being conducted globally to use this glycerol as a chemical building block. However glycerol is now considered a waste by product with concomittant waste disposal problems.

Although the transesterification of vegetable oils or animal fats can be done in an unsophisticated process, the process conditions must be carefully controlled and or modified to achieve maximum yield at the lowest temperature and reaction time. The process of transesterification is affected by the mode of reaction condition, molar ratio of alcohol to oil, type of alcohol, type and amount of catalysts, reaction time and temperature and purity of reactants.

From the foregoing discussion, some of the drawbacks of conventional production of biodiesel arise from poor quality feedstock, dependence on reaction parameters and the need to separate undesired by-products from transesterification reaction. The production of biodiesel is also limited to use of liquid feedstock.

One approach to address the effect of poor quality feedstock has been to provide a feedstock low in fatty acid content to help minimise effect of saponification. Food crops such as corn and soy are known to have a relatively low fatty acid content and have been grown and harvested as a biodiesel feedstock material.

The ability to produce a sufficient quantity of biodiesel of a suitable quality and conversion however places a heavy burden on the supply of food crops such as soy and corn. It is concevable that there is not enough regrowth available or growable to accommodate the average fuel consumption in for example the US alone.

Consumption of diesel in the US amounts to about 220 million gallons per day. The rate at which food crops can be grown as a source of material in the synthesis of biodiesel is subject to seasonality, and requires access to watering, fertilizing, harvesting and transporting.

Large-scale biofuel production could well have serious environmental consequences as native ecosystems are replaced by the likes of soybeans, oil palm and sugarcane plantations. Hence global development of a biofuels industry can increase rather than decrease greenhouse gas emissions if production is poorly managed.

In addition to the environmental impact, the rising reliance on biofuels over the next decade threatens to drive up food prices in poor countries, where they are already facing upward pressure from consumer demand.

In comparison, there is almost an unlimited supply of waste material such as plastics, biomass, household rubbish, cellulose, municipal solid waste (MSW), agricultural residues, farm waste and other biodegradable waste. To date Fisher-Tropsch has been the method conventionally used to utilise waste material to produce alternative fuels to reduce the use of fossil fuels, reduce greenhouse gas emissions and reduce pollution and waste management problems.

Refineries for converting natural gas, coal deposits, and biomass, which are in abundant supply, to synthetic fuels are known which use the Fisher-Tropsch synthesis. Such refineries start with a gasification pre-treatment in which methane, coal or biomass feedstock is subject to partial oxidation forming intermediate products carbon dioxide, carbon monoxide, hydrogen and water. The intermediates are catalytically reacted typically over a transition metal catalyst selected from iron, cobalt, ruthenium, platinum, palladium and nickel catalyst to produce liquid hydrocarbons and other byproducts.

A major drawback of the conventional process is that feedstock has to be scrupulously cleaned of sulphur, chlorine and various other poisons to avoid catalyst degradation. Once the catalyst is depleted, consumed or poisoned, it may not be able to be regenerated, and the catalyst itself then represents a toxic waste problem. A further drawback is that the feedstock requires gasification.

Further improvements are therefore still needed to combat the drawbacks associated with existing processes.

It is therefore an object of the present invention to address one or more of the disadvantages of the prior art conversion systems.

It is a further object to provide a process which can produce an alternative fuel from suitable solid, liquids and gaseous material, including waste material.

It is therefore an object of the present invention to address one or more of the disadvantages of the prior art systems.

Summary of the Invention

In accordance with the invention there is provided a method for producing hydrocarbons or oxygenates for use as a synthetic fuel source from suitable material, the method including: providing a feedstock stream comprising solid and/or liquid and/or gaseous material under pressure to a mixing vessel at a predetermined feed rate; injecting a stream of a reactant gas capable of dissolving in the feedstock into the feedstock stream for mixing; transferring a stream of feedstock and gas reactant mixture to a reaction vessel downstream therefrom; subjecting the feedstock and gas mixture in the reaction vessel to at or near supercritical conditions; wherein the solubilised material is broken down in the reaction vessel into a distribution of molecular weight fractions, and wherein the reactant gas selectively adds or subtracts from the molecular weight fractions to provide a hydrocarbon or oxygenateof predetermined chain length suitable as an alternative fuel.

The present invention represents a significant advance over the prior art since the instant process does not require conversion of solids, liquids or gaseous material as in the Fisher-Tropsch process.

The present invention is also not limited by requiring quality feedstock material. Indeed the process of the invention can be used to produce a synthetic fuel from any suitable material including coal, waste material including domestic waste, commercial municipal waste, agricultural waste, chemical waste, plastics and biomass such as cellulose.

The reactant gas can be selected from a range of gases including hydrocarbons, carbon dioxide, carbon monoxide, nitrogen or steam. Preferably the reactant gas stream comprises methane. As embodiments of the invention the source of methane can be derived from decomposition of the waste material, flare gas or town gas.

In the process of the present invention, the reaction occurring in the reaction vessel can be exothermic, and in which case the heat of reaction can be collected by a heat exchanger downstream from the reaction vessel and the heat redirected to the reaction vessel to help maintain reaction conditions.

In the process of the present invention, the reaction occurring in the reaction vessel can be endothermic, and in which case the heat for the reaction can be supplied by a heat exchanger upstream from the reaction vessel.

In a related aspect of the present invention there is provided a method of producing hydrocarbons for use as a synthetic fuel source including: providing a feedstock stream comprising solid, liquid or gaseous material; mixing a stream of a reactant gas with the feedstock stream; transferring the feedstock and gas mixture to a reaction vessel; subjecting the feedstock and gas mixture in the reaction vessel to sub- or supercritical temperature and pressure, wherein the gas is at least partially dissolved in the feedstock material; wherein the feedstock material is selectively changed into a predetermined quantifiable fraction and wherein the solubilised hydrocarbon gas selectively substitutes on the fraction to provide a hydrocarbon or oxygenate liquid fuel of predetermined chain length suitable as an alternative fuel.

Preferably the feedstock stream is pumped under pressure of about 6 bar by a pumping means prior to entering a mixing station upstream from the pumping means. The mixing station can include a feed tank with a stirring means or static mixer.

The gas can be introduced into the feedstock stream at the mixing station by means of gas injection. Preferably the mixing station includes a static mixer.

Preferably the process includes a gas separating means. The process can be continuous.

Preferably the feedstock and gas mixture is subjected to compression at sub- or supercritical pressures and temperatures.

The feedstock and gas mixture is preferably preheated following compression before being transferred to the reaction vessel.

In one embodiment of the present invention the process includes a heat exchanger which is adapted to transfer heat from the reaction vessel and redirected upstream of the reaction vessel so as to preheat the reactants before input to the reaction vessel. In this way heat generated by reaction of the feedstock and gas mixture can be recovered and redirected to use for preheating combined gas and feedstock mixture before entering the reaction vessel. This represents a clear energy savings. The process can also include providing a catalyst. The catalyst can be present in varying quantities and are selected from either of two categories being:

(i) fixed catalyst; or

(ii) autogenous catalyst included within the feed stream.

In one embodiment of the present invention the reactant can be water. At or above the supercritical conditions of water (374 degrees C and 22.1 Mpa), water as with other supercritical fluids can readily solubilise the waste material and exposes relatively high molecular weight hydrocarbons in the waste material to cleavage to form a majority of low molecular weight short chain hydrocarbons.

Without wishing to be bound by any theory, it is believed that exposure of waste material feedstock to a gas at elevated pressure and temperature causes the waste feedstock to solubilise and break down into lower chain molecules and in some instances their constituent atoms. The lower chain molecules then combine with methane or its alkyl derivative to form hydrocarbon liquids suitable for use as alternative fuels.

In a related aspect of the present invention there is provided a process for producing synthetic fuel from a feedstock material selected from fats, oils, greases, cellulose, organic waste, plastics and the like including: cleaning and preheating the feedstock material; providing a source of a short chain hydrocarbon including an alcohol; providing a source of methane gas at a pressure and temperature effective to dissolve the feedstock and the hydrocarbon; combining the preheated feedstock material into a mixing chamber with a stream of methane from the source of methane at a predetermined rate to dissolve the feedstock material; and reacting the feedstock material with the gas or alcohol wherein the gas or the alcohol is provided at a predetermined rate into the mixing chamber.

The above process represents a departure from prior art processes. The process of the invention allows production of synthetic diesel fuel from a range of waste material including solids, liquids, gases and combinations thereof.

In one embodiment of the present invention the methane gas is provided at supercritical temperature and pressure. The use of methane in the process at supercritical conditions surprisingly becomes an excellent solvent and dissolves into the feedstock so that the reactants are in close proximity of each other and therefore react readily. This represents an advance over conventional, base-catalysed transesterification which does not work efficiently on the high free fatty acid (FFA) content typical of cheaper, lower-quality feedstocks.

Because methane has low solubility in the products at ambient temperature separation can easily be achieved by reduction of pressure.

A specific embodiment of a controller device in accordance with this invention will now be described with the aid of the accompanying drawings which are given by way of example only and should not be considered to be limiting.

Brief Description of the Drawings

Figure 1 : shows a schematic flow diagram of a process for producing hydrocarbon as a synthetic fuel source in accordance with the present invention

Figure 2: shows a flow diagram of an industrial process for producing a hydrocarbon as a synthetic fuel in accordance with the present invention.

Detailed description of the Preferred Embodiments with reference to the Accompanying drawings

Referring to figures 1 and 2 there is shown a schematic representation of a process for producing a synthetic fuel from a suitable material wherein the material can be selected from commercial, domestic and other waste materials typically solids waste including domestic waste such as paper, plastic, cellulosic matter, food wastes otherwise sent to landfill.

The process of figure 1 shows a feedstock stream 3 indicating directional flow of a feedstock such as cellulose from a waste feed station towards a mixing chamber 1. The mixing station is fitted with a stirring mechanism 40 such as a static mixer 2. The feedstock stream 3 is supplied to the mixing chamber at a first predetermined temperature and feed rate and subjected to stirring.

A reactant gas stream 4, which is shown as methane in this example, is injected into the mixer and mixed with the waste material. The reactant gas stream is delivered to the mixing chamber at a predetermined pressure and rate to suit the feedstock characteristic and feed rate.

The process further includes a high pressure pump 5 located downstream from the mixing chamber, which receives the combined feedstock and reactant gas from the mixing chamber. The pump 5 increases the pressure of the combined feedstock and gas reactant mixture to a desired level at sub- or supercritical temperatures and pressure of the reactant gas. Referring to Table 1, the supercritical conditions for a range of reactant gases is shown.

At or near such pressures the methane gas the reactant gas methane becomes soluble in the feedstock material. As seen in figure 2 a pressure control valve 6 is located proximal to the pump 5 and regulates the back-pressure.

As shown in figure 1, the feedstock and gas reactant, having been subjected to high pressure, are transferred to a supercritical reaction vessel 20 downstream from the pump 5. In the reaction vessel the feedstock and gas reactant are subjected to the sub- or supercritical temperatures of the gas reactant (46 bar and 190.6 K).

In figure 1, the schematic representation shows an exothermic process. Depending on the nature of the feedstock material, such as its capability to transfer oxygen, will influence the selection of reactant gas. The process can be endothermic or exothermic depending on the oxidation/reduction capabilities of the feedstock and reactant gas. For example, if the feedstock material is a hydrocarbon then the reactant gas can be steam.

As shown in figure 1, heat of reaction 21 in the case of an exothermic reaction, is recovered and used to preheat the reactant stream before entering the reaction vessel. After completion of the reaction, a final product stream 22 exits the reactor. In one embodiment (not shown), the final product stream is passed through a separating means such as a chromatograph 23, which provides a qualitative analysis of end product.

In figure 1 the feedstock material is primarily a cellulose material, which apart from being a cheap and abundant source of waste feedstock, provides a source of oxygen. In the presence of cellulosic feedstock material the reactant gas is methane but can be a hydrocarbon such as methane, ethane, propane or the like. The process is shown using methane gas as this can be readily and cost effectively obtained from the waste feedstock or derived from flare gas or even domestic gas supply.

Without being bound by any theory, it is postulated that when the combined feedstock material (being cellulosic material in this example) and gas reactant (methane in this example) is subject to at or near supercritical reaction conditions for methane (see Table 1) in the reaction vessel, the cellulosic material undergoes a chemical reduction to a short chain hydrocarbon, and the available oxygen in the cellulosic feedstock partially oxidises the reactant gas to produce methanol and other alcohols.

Because methane has relatively low solubility in the products at ambient temperature separation can easily be achieved by reduction of pressure.

In an alternative process, the process produces levulinic acid and or methyl or ethyl levulinate having a cetane rating of about 52, which provides a direct replacement for high quality diesel. In addition, the formation of levulinic acid and its derivitives provides a useful precursor for PET plastics as well as many other feedstock chemicals. As can be seen in the industrial process of figure 2, there is provided a combined reaction vessel and heat exchanger 20 . At least part of the heat provided for reaction is provided by a furnace chamber 8, which uses heating oil or molten salt to transfer heat to the reaction vessel.

In the examples shown, the reaction process is exothermic, and the heat produced can be received and redirected back to the input stream 9 prior to entry to the reaction vessel by the heat exchanger. A clear advantage is achieved in minimising heating costs by using the heat of reaction.

The process as shown in figure 2 further includes a fire-safe valve 10, which acts as a safety means to allow escape of material to a water-filled dump tank 15 in the event of a reactor leakage. Additional safety is provided by a pressurised water tank 16, which deluges the process space in the event of a fire. Downstream from the reactor there is provided a gas separator 11 , which serves to remove water vapour and any residual gas from the end product 22.

Table 1 : Supercritical Temperature and Pressure of gases