Autothermal liquefaction of waste materials.

Abstract

Waste streams of organic matter, such as sewage, plant matter, and plastic materials, are accepted for recycling and treated at elevated temperatures and pressures to produce useful organic products, such as bio-oil and gas. By-products, such as an aqueous phase containing char and water, can be selectively recycled or disposed of as is. An oxidant added to a reactor containing waste from the waste stream promotes an autothermal reaction under the temperature and pressure applied to the reactor, slightly boosting the temperature from the reaction therein. The reactor produces useful hydrocarbons, such as bio-oil, resulting from the breaking of organic bonds. The combination of oxidation and radical initiation resulting from the oxidant provides an increased yield of bio-oil while reducing char compared to temperature and pressure alone. A stoichiometric amount of oxidant limits the complete conversion of carbon to carbon dioxide by limiting available oxygen and thus promoting hydrocarbon formation.

Description

[Technical Field]

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was developed, at least in part, with U.S. government support under Contract No. DE-EE0009507 awarded by the Department of Energy and the National Science Foundation Graduate Research Fellowship Program, Award No. 2038257. The government has certain rights in this invention. [Background technology]

[0002] Waste disproportionately contributes to many of the environmental problems of the 21st century, from waste fertilizer runoff resulting in harmful algae blooms, to plastics clogging waterways, to landfill gas changing the global climate. Converting waste into useful products gives it a place to trade and makes it less of a burden on the environment. Conventional approaches to the recycling of organic waste often involve extreme temperature and pressure conditions, which result in high upfront capital costs and the simultaneous production of low-value solid by-products. Furthermore, different feedstreams react at distinctly different temperatures, meaning that not all feedstreams can be processed simultaneously. Summary of the Invention [Means for solving the problem]

[0003] Waste streams of organic matter, such as sewage, plant matter, and plastic materials, are accepted for reuse and treated at elevated temperatures and pressures to produce useful organic products, such as bio-oil and gas. By-products, such as char and an aqueous phase containing water, can be selectively recycled or disposed of as is. An oxidant added to a reactor containing waste from the waste stream promotes autothermal reactions under the applied temperature and pressure of the reactor, slightly boosting the temperature from the reactions therein, providing a source of highly reactive radicals, and partially oxidizing the feed stream, making it more reactive. The reactor produces useful hydrocarbons, such as oil (so-called "biocrede" or "bio-oil"), resulting from the breaking of carbon-carbon and carbon-hydrogen bonds present in macromolecules that are reassembled into smaller molecules. The combination of exothermic reactions, partial oxidation, and radical initiation from the oxidant provides an increased yield of bio-oil while reducing char when compared to liquefaction based on temperature and pressure alone. Substoichiometric amounts of oxidant limit the complete conversion of carbon to carbon dioxide by limiting available oxygen and thus promoting hydrocarbon formation.

[0004] The features herein are based in part on the observation that fossil fuel alternatives are attractive due to their renewable potential and reduced environmental impact. Unfortunately, conventional approaches to alternative fuels face drawbacks in cost and energy demand due to the production of alternatives, such as plant- and waste-based recycling, limiting yield and profitability. Therefore, the features herein substantially improve the production of organic products, such as bio-oil / biocrude and gas, by adding an oxidant to balance carbon dioxide production by adjusting the available oxygen added via the oxidant. The added oxidant limits the available oxygen that promotes carbon reaction with the organic waste, based on the stoichiometric scale of carbon and oxygen available for carbon dioxide production. Therefore, the oxidant, such as hydrogen peroxide, relies on the carbon present in the bulk organic waste.

[0005] These and other objects, features, and advantages of the present invention will become apparent from the following description of specific embodiments of the invention, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a context diagram of organic waste recycling as disclosed herein. [Figure 2] 1 is a graph of the improvement of the disclosed process over hydrothermal liquefaction (HTL). [Figure 3] 1 is a graph of an autothermal system herein using an oxidant on a waste stream of sewage sludge. [Figure 4] 1 is a graph of a self-heating system using plastic solid waste. [Figure 5] 5 is a graph of the reuse of green waste using the methods of FIGS. 1-4. [Figure 6] 6 is a graph of food waste reuse using the methods of FIGS. 1 to 5. [Figure 7] 1 shows a graph of oil yield for radical initiated hydrothermal liquefaction (RI-HTL). [Figure 8] 1 shows a use case of the disclosed method using sewage sludge. [Figure 9] 1 illustrates another use case of the disclosed method using food waste. [Figure 10] 1 is a graph of the effect of oxidation on bio-oil yield. [Figure 11] Catalyst wall test results are shown. [Figure 12A] The temperature profile of the experimental conditions for the effect of the oxidizing agent H2O2 is shown. [Figure 12B] The temperature profile of the experimental conditions for the effect of the oxidizing agent H2O2 is shown. DETAILED DESCRIPTION OF THE INVENTION

[0007] The following description presents an example of a method for autothermal hydrothermal liquefaction (AT-HTL) technology that greatly increases the yield of desirable products obtained from the thermal treatment of waste materials under pressure. The examples described herein apply the AT-HTL process to food waste, several different types of plastics, papermaking waste, and biorefinery (lignin), as well as sewage sludge. Much greater yields of energy-rich liquids, or sometimes solids, with favorable properties can be obtained using AT-HTL. Typical processes generally involve heating a wet organic stream to 280-400°C at pressures above 10 MPa for 1-120 minutes. Under these conditions, components in the waste stream break down into small organic molecules, which are then reconstituted into an energy-rich biocrude. The disclosed process improves product yields by adding an oxidant at substoichiometric levels, where "stoichiometry" refers to the amount of oxygen required for the complete conversion of carbon present in the feed stream to carbon dioxide. As used herein, the term "oxidant" refers to both oxidizing agents and radical initiators. Radical initiators that are not oxidizers, oxidizers that are not radical initiators, and materials that are both oxidizers and radical initiators have been tested and found to be effective. Hydrogen peroxide, which is both an oxidizer and a radical source and does not leave carbon by-products, may be preferred in some applications.

[0008] Instead of carbon dioxide production, the substoichiometric oxidant in the configuration herein allows for incomplete reaction with the organic waste, greatly increasing the reaction rate obtained from conventional methods, such as hydrothermal liquefaction (HTL). Part of the advantage over conventional methods is the rapid volumetric release of heat from the oxidant's reaction with the organic waste, thereby minimizing the time spent by the organic waste in the temperature range associated with solid char formation. This autothermal mechanism explains the char reduction observed with AT-HTL of food waste and sewage sludge. Interestingly, the reacted carbon could be considered sacrificial. However, the biocrude yield obtained from AT-HTL is superior to conventional methods, so sacrificing some of the carbon contained in the organic waste does not impair yield. In other examples, particularly for thermally stable plastics, AT-HTL increases reactivity to the point where complete plastic conversion can be obtained even at temperature conditions where conventional methods result in <1% conversion. Such examples, described further below, demonstrate that thermal effects alone cannot achieve such performance; reaction with the oxidant releases highly reactive radicals in the reaction mixture. These radicals then promote and propagate the reaction in which the polymer itself is otherwise stable.

[0009] Figure 1 is a context diagram of the organic waste recycling disclosed herein. Referring to Figure 1, a process flow 100 of a method for obtaining useful organic products from a waste stream 101 is shown. An oxidant 103, such as H2O2 (see above), is added to the waste stream in a containment vessel 110 or similar sealed reactor adapted for pressure buildup. The waste stream is heated under pressure to obtain organic products including oil 122, gas 128, an aqueous mixture of oil and water 124, and char 126. Collecting the organic products (products) includes extracting the oil, filtering the char, and removing the aqueous mixture.

[0010] As shown in step 130, the aqueous phase is separated by sieving, filtration, or dehydration, resulting in a separated aqueous phase 120', which contains water along with various organic compounds. The solid char 126 can be easily separated from the oil by washing or dissolving in acetone, and the oil is separated from the char in step 140, and the recovered char 126' is either disposed of as waste or passed through a specific recycling channel. The collected oil 122' is similar to fossil fuel crude oil, but may have an oxygen content of up to 10% (approximately 5% to 10%). The recovered acetone 129 can be reused with successive iterations of passing through the containment vessel 110.

[0011] As discussed above, the oxidant 103, e.g., hydrogen peroxide, introduces a specific amount of oxygen to balance the production of useful hydrocarbons with carbon dioxide production. The oxidant is added to the containment vessel 110 in a sub-stoichiometric amount based on the stoichiometric ratio of oxygen in the oxidant and carbon in the waste stream, thereby limiting carbon dioxide production.

[0012] The amount of oxidant varies with the feedstock in the recycle stream and involves determining the stoichiometric amount of oxygen to form carbon dioxide with the carbon in the waste stream. Calculating an amount of oxygen less than the determined stoichiometric amount limits the oxygen available for carbon dioxide production. Oxidant is then added in the determined stoichiometric amount to achieve the calculated amount of oxygen.

[0013] A further consequence or enhancement from heating the waste stream is to cause or induce an autothermal reaction to result in a volumetric release of heat based on the reaction of the oxidant with the waste stream to increase the heat. In effect, the heat in the containment vessel 110 is seen as a rapid "burst" of temperature increase, not as a substitute for external heating, but as a chemically generated exothermic reaction occurring within the containment vessel.

[0014] The choice of oxidant can be optimized for economic or operational considerations. In the example use case shown below, hydrogen peroxide is used as an effective oxidant as it is environmentally safe, commonly available, and a safe and reliable source of oxidant. Preferably, oxygen directly from air would be a less expensive oxidant that retains the effectiveness of hydrogen peroxide. On the other hand, organic hydroperoxides (which have the formula of type ROOR (where R is organic), and are less stable and more expensive than hydrogen peroxide) may have reactivity advantages that make them preferable for some applications. Tert-butyl hydroperoxide is an example of this chemical family. Any suitable oxidant capable of achieving the desired sub-stoichiometric level may be used.

[0015] Figure 2 is a graph of the improvement of the disclosed process over hydrothermal liquefaction (HTL). While the basic HTL process alone can achieve advantageous results, the disclosed process offers significant advantages, particularly for bio-oil yields and certain waste dosages, such as carbon-rich sewage sludge (SS). Furthermore, basic HTL offers significant advantages over combustion and pyrolysis, thereby avoiding the need for energy-intensive drying. HTL is an effective method for processing high-moisture SS. By extension, the disclosed process has the ability to convert various types of waste into biocrude, comparable to fossil crude oil and capable of being upgraded in existing refinery configurations. Scaling this process to production levels is a capital-intensive process, and maximizing biocrude yield is a key aspect of economic viability.

[0016] In Figure 2, three tests 210, 220, and 230 demonstrate the benefits of the disclosed method. The basic HTL method 210, heating to 300 °C for 10 minutes under high pressure (10-35 MPa), has a biocrude yield 211 of 59.4% and a char yield of approximately 14%. However, liquefaction was improved by adding an oxidant (HO) to the reactor to initiate the depolymerization and liquefaction of complex organic waste into useful fuel and chemical precursors, maximizing conversion and minimizing the co-production of low-value solids. This method increased the biocrude yield and minimized the char yield. When the oxidant was added at a substoichiometric O:C ratio of 0.3 (220), the bio-oil yield 221 increased to 75.8%, while the char yield decreased to 4%. An even greater improvement is shown at an O:C ratio of 0.05 (230) for the corresponding bio-oil 231 and char 233 yields. Other differences for aqueous / water and gas yields are also shown.

[0017] Once extracted and / or produced, bio-oil / biocrude can be upgraded by hydrodeoxygenation, which is a hydrocracking process to remove oxygen from oxygen-containing compounds. The primary difference between bio-oil and fossil fuels is the oxygen content, which can be as high as 10%, and therefore, removing the oxygen makes bio-oil more consistent with fossil fuel crude oil.

[0018] In general, the disclosed method converts organic wet waste as biocrude into fuel precursors. This conversion is compatible with wet waste without drying and can be applied to food waste, sewage sludge, biomass waste, and many other forms of waste. A typical iteration involves heating the containment vessel to 250°C-400°C and maintaining a pressure of 10-35 MPa. This is a more rapid process than anaerobic digestion, which produces a more valuable liquid product compared to biogas generation.

[0019] Table I shows the chemical composition of the expected feedstock. Typical waste streams include biowaste (meaning non-edible plant matter), sewage sludge, plastics, vegetable waste, and food waste, all of which have abundant sources for the production of bio-oil and other organic products.

[0020] [Table 1]

[0021] The disclosed AT-HTL process can be optimized by adjusting the reaction temperature, reaction time, solids loading, and amount and, optionally, type of oxidant for the organic waste. A general strategy is to tailor the stringency of conditions, including the amount of oxidant, to the reactivity of the organic waste. For example, food waste is generally considered highly reactive under HTL conditions. We have found complete conversion and optimal biocrude yields for food waste at 300°C. Polyethylene, generally considered unreactive under HTL conditions, requires 400°C for complete reaction under AT-HTL conditions. Food waste and polystyrene, which have reactive intermediates to polyethylene, require intermediate reaction conditions to convert these two waste streams. Finally, it should be noted that AT-HTL compresses the reaction windows of different feedstreams, with the potential benefit of coprocessing mixed waste streams. Coprocessing mixed feedstreams has the advantage of eliminating the need for pre-reaction separation, thereby reducing overall processing costs.

[0022] FIG. 3 is a graph of the autothermal process herein using an oxidizer with a waste stream of solids (SS) for tests 310, 320, and 330 at 300°C for 10, 50, and 90 minutes, respectively. SS is a by-product of wastewater treatment. It is typically a mix of organic matter from human waste, food waste particles, microorganisms, trace chemicals, and inorganic solids from consumer products and pharmaceuticals, along with water bound to these materials. In an example configuration, the waste stream includes sewage sludge, which is derived from municipal waste by-products with over 50% carbon. SS is a significant problem due to its environmental risks and high treatment / disposal costs.

[0023] [Table 2]

[0024] In each of the time frames 310, 320, and 330, the first test (leftmost) uses no oxidant. The second (center) test has an oxidant (O:C) ratio of 0.3, and the third (rightmost) test has an O:C ratio of 0.05. This shows the effect of oxidant on biocrude yield, demonstrating consistently higher biocrude yields because the substoichiometric oxidant ratio provides less oxygen, effectively "starving" CO2 production in favor of bio-oil production. Oxidant ratios of 0.3 and 0.05 effectively limit oxygen to approximately 30% and 5%, respectively, of the oxygen required for complete CO2 conversion. The figure shows that approximately 80% of the carbon can be converted to biocrude using the modified HTL. The arrows highlight the benefit of H2O2 (oxidant) addition. Other oxidants based on similar stoichiometry yield similar results. Table II shows the percentage breakdown of the results.

[0025] The general trend is an increase in bio-oil yield based on substoichiometric levels of oxidant. Under the pressure and temperature in the reactor, the results show that heating results in at least one of oxidation and radical initiation, with radical initiation being based on free radicals formed from the heat and pressure in the containment vessel surrounding the waste stream. Therefore, the effect of the oxidant is to form free radicals resulting from the heat and pressure applied to the containment vessel for the waste stream for radical initiation. In this way, the oxidant contributes oxygen to the reaction, resulting in a hydrocarbon chain. One effect of the oxidant is to create weak positions in the hydrocarbon chain and add or introduce free radicals to form short-chain oxygenated molecules. While hydrogen peroxide is used as an example of an oxidant, the oxidant may include at least one selected from hydrogen peroxide, perchloric acid, sodium perchlorate, and organic hydroperoxides.

[0026] By way of background, radicals, or free radicals, are unstable molecules with an unpaired valence electron. A notable example of a free radical is the hydroxyl radical (HO), a molecule with one bond "dangling" from oxygen, due to the loss of one hydrogen atom from a water molecule. Two other examples are the carbene molecule (CH2), which has two dangling bonds, and the superoxide anion (·O-2), which is an oxygen molecule, O2, with one dangling bond and one extra electron. In contrast, the bonds that appear to be dangling are actually broken by the addition or removal of electrons, resulting in the hydroxyl anion (HO-), oxide anion (O 2- ) and carbenium cations (CH +3 ) is not a radical. The autothermal effect (AT) described above is due to such radical initiation (RI).

[0027] Figure 4 shows a graph of the autothermal radical initiation method using plastic solid waste. Plastic solid waste (PSW) is a collection of plastic materials in the global environment that adversely affects wildlife, wildlife habitats, and humans. Tests with PSW were conducted at different temperatures of 325°C and 350°C for 20 minutes, with and without an oxidizer. An oxidizer (O:C) ratio of 0.3 was selected to study the effect of the novel method on biocrude yield. Moderate biocrude (bio-oil) yield in the absence of an oxidizer was observed in test 410, with a slight improvement at a temperature of 350°C in test 430. An O:C oxidizer ratio of 0.3 showed substantial improvement only at 325°C (420), and even more so at 350°C in test 440. In general, increasing the temperature to 350°C and 400°C is particularly advantageous for plastics with high carbon content. Char reduction is also achieved with greater bio-oil yields. In a typical scenario, the waste stream includes polyethylene, polystyrene and polypropylene.

[0028] Figure 5 is a graph of green waste reuse using the methods in Figures 1-4. Green waste (GW) is generally defined as biodegradable waste resulting from yard waste, such as grass clippings, clippings, old stumps, tree branches, twigs, leaves, flowers, weeds, and unwanted indoor plants, but not from food consumables. Experimental tests using GW were conducted with and without oxidizer at different temperatures of 275°C, 300°C, and 325°C for 20 minutes. An oxidizer:C ratio of 0.15 was selected to study the effect of the novel method on biocrude yield.

[0029] 5, oxidant-based tests 520, 540, and 560 show roughly a 35% reduction in char with minimal decomposition to oil production at various temperatures. Non-oxidant tests 510, 530, and 550 all have substantially higher char production.

[0030] Figure 6 is a graph of food waste reuse using the methods in Figures 1–5. Food waste (FW) consists primarily of organic waste from various sources, including field waste, processing plants, kitchens, and restaurants. Available studies predict that the amount of food discarded annually will increase by one-third by 2030. Experiments were conducted on food waste with and without an oxidant at different temperatures: 300°C, 325°C, and 350°C, for different reaction times (20 and 60 minutes). An oxidant (O:C) ratio of 0.2 was selected to study the effect of the novel method on biocrude yield. Referring to Figure 6, the biocrude yields obtained from runs 610–660 indicate that the use of an oxidant can convert approximately 45% of the carbon to biocrude. A particularly large yield is demonstrated by the 20-minute reaction temperature of 325°C (640) using an O:C oxidant ratio of 0.2 (20%).

[0031] The above experiments demonstrate that the enhanced hydrothermal liquefaction method maximizes biocrude yield and minimizes the co-production of low-value solids. This method was applied to different waste sources, including sewage sludge, plastic solid waste, vegetable waste, and food waste. Different operating conditions were applied to the various configurations shown, and correspondingly different enhancements in biocrude yield and reductions in char yield were observed. Adjustment of the oxidant amount to achieve a sub-stoichiometric ratio varied based on the carbon content of the input feedstock. In the particularly notable case of sewage sludge, the configuration described herein resulted in an approximately 40% increase in biocrude yield, while solids yield decreased by roughly 70%.

[0032] Figure 7 shows a graph 700 of oil yields from radical-initiated hydrothermal liquefaction (RI-HTL). In Figure 7, each reaction shows a 20 minute reaction time with a 3:1 peroxide charge. A particularly noteworthy comparison occurs in 701, where at 350°C, RI-HTL conditions increase oil yield from <1% to >85%. Other tests illustrate that the AT / RI method generates substantially greater oil yields even at lower temperatures.

[0033] Figure 8 shows a use case 800 of the disclosed method with sewage sludge. The addition of H2O2 shows approximately a 50% increase in biocrude and approximately a 50% decrease in char. The oil 801 yield steadily increases toward 0.05 with temperature and sub-stoichiometric depletion of oxygen. The aqueous fraction 802 varies, while the char 803 is minimized with certain combinations of time and temperature. Gas 804 production is rather consistent, while losses 805 tend to decrease with increasing oil 801 yield.

[0034] 9 shows another use case of the disclosed method using food waste. Food waste test 900: T=325℃ t=20 minutes C:O ratio=2, 4, 5, 7, 10, 20, 33 Solid input = 15% The reactor conditions were maintained at 100°C.

[0035] Biocrude 901 yield increased from 43% to 62% at optimal conditions with a C:O ratio of 5, while solids 902 generally decreased with increasing oil yield. Aqueous solution 903 and gas 904 yields varied, while losses 905 were generally the opposite of oil production, similar to sewage sludge in Figure 8.

[0036] The general trend of increased oil production with the RI / AT substoichiometric method is attributed to several mechanisms: 1) oxidation—the availability of H2O2 compared to equimolar amounts of oxygen; 2) heat—the temperature increase caused by H2O2; and 3) quantification of the radical-radical pathway.

[0037] Figure 10 is a graph of the effect of oxidation on bio-oil yield. In Figure 10, the reactor was charged with stoichiometric O2, and the overall increase in carbon yield across oil 1001, aqueous phase 1002, char 1003, and gas 1004 suggests that oxygen alone cannot explain the favorable yield. HO must affect yield through other means.

[0038] In the case of sewage sludge, for example, ·H2O2 can decompose in an exothermic reaction.

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[0039] A glass liner test was conducted by adding a glass liner to a Parr reactor, which inhibited hydrogen peroxide interaction with the reactor walls and resulted in an increased rate of oxygen generation. Figure 11 shows the results of the catalyzed wall test. The conclusion is that the use of a liner inhibits wall-catalyzed reactions and promotes oxygen generation. This suggests that the potential for radical-initiated reactions is catalyzed by the wall surface.

[0040] The exothermic effect follows the hypothesis that the hot injection of H2O2 results in an increase in temperature from the occurrence of an exothermic reaction. Under the following reactor conditions: Pressurize with N2 P0=200PSI P rxn =1250PSI T=300 Reactor contents: Sewage sludge H2O2, injected at 295℃

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[0041] Figures 12A and 12B show the temperature profiles of experimental conditions for the effect of the oxidant HO. Figure 12A shows a mild test with the introduction of HO, while Figure 12B shows the theoretical increase. The temperature increase indicates that HO acts as an exotherm and that this effect alone is insufficient to explain the increase in oil yield.

[0042] While the systems and methods defined herein have been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the scope of the invention as encompassed by the appended claims.

Claims

1. 1. A method for obtaining useful organic products from a waste stream, comprising: adding an oxidant to said waste stream; heating the waste stream under pressure to obtain at least two of oil, gas, an aqueous mixture of oil and water, and char; extracting the oil, filtering the char, and removing the aqueous mixture, thereby obtaining useful organic products; A method comprising:

2. The method of claim 1 , wherein adding the oxidizing agent further comprises adding the oxidizing agent in a sub-stoichiometric amount.

3. 3. The method of claim 2, wherein a sub-stoichiometric ratio is based on a stoichiometric ratio of oxygen in the oxidant and carbon in the waste stream, thereby limiting the production of carbon dioxide.

4. determining a stoichiometry of carbon and oxygen to form carbon dioxide in the waste stream; calculating the determined substoichiometric amount of oxygen to limit the oxygen available for carbon dioxide production; adding said oxidizer in an amount to achieve said calculated amount of oxygen; The method of claim 2 further comprising:

5. 3. The method of claim 2, wherein the sub-stoichiometric amount is based on limiting the available oxygen for carbon dioxide production.

6. 10. The method of claim 1, further comprising heating the waste stream to cause an autothermal reaction, the autothermal reaction resulting in the volumetric release of heat based on a reaction of the oxidant with the waste stream to increase heat.

7. 10. The method of claim 1, further comprising dissolving the oil in acetone to separate the oil from the char.

8. 10. The method of claim 1, further comprising forming free radicals resulting from heat and pressure applied to the waste stream containment vessel for radical initiation.

9. 10. The method of claim 1, further comprising heating the containment vessel to 250°C to 400°C and maintaining the pressure at 10 to 35 MPa.

10. The method of claim 1 , wherein the waste stream comprises biowaste, the biowaste comprising non-edible plant matter.

11. 10. The method of claim 1, wherein the waste stream comprises sewage sludge derived from municipal waste by-products having greater than 50% carbon on a dry ash-free basis.

12. 10. The method of claim 1, wherein the waste stream comprises polyethylene, polystyrene, and polypropylene.

13. 10. The method of claim 1, wherein heating causes at least one of oxidation and radical initiation, the radical initiation being due to free radicals formed around the waste stream from the heat and pressure in a containment vessel.

14. The method of claim 1 , wherein the oxidizing agent contributes oxygen to the reaction, resulting in a hydrocarbon chain.

15. 10. The method of claim 1, further comprising adding or introducing free radicals to create weak positions in the hydrocarbon chain and to form short-chain oxygenated molecules.

16. 2. The method of claim 1, wherein the oxidizing agent is at least one selected from hydrogen peroxide, perchloric acid, sodium perchlorate, and organic hydroperoxides.

17. 17. The method of claim 16, wherein the organic hydroperoxide is of the formula R-O-O-R.

18. The method of claim 1 , wherein the oil has at least 5% oxygen.

19. 10. The method of claim 1, further comprising upgrading the oil by hydrodeoxygenation.

20. 1. A method for obtaining bio-oil from a waste stream comprising sewage sludge, comprising: adding hydrogen peroxide to said waste stream in a sub-stoichiometric amount of 0.05 to 0.3 for complete conversion of available oxygen in said waste stream to carbon dioxide; heating the waste stream in a containment vessel to 300°C to 325°C under a pressure of 10 to 35 MPa to obtain an oil yield of at least 50% of the carbon in the waste stream; extracting the oil and filtering the residual char and aqueous mixture, thereby obtaining bio-oil; A method comprising:

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