Background

Biomass conversion by hydrothermal processes is known in the art. Hydrothermal processes use water as reaction medium, and the biomass is subjected, in the presence of water, to high temperatures and pressures to yield valuable products. For example, partial wet oxidation (abbreviated PWO) of waste liquors sourced from lignocellulosic biomass has been used for producing carboxylic acids, whereas hydrogen has been obtained by supercritical water gasification (abbrevatied SCWG) from solid biomass. Hydrothermal liquefaction (abbreviated HTL) has been used for producing bio-oil as a main product and an aqueous phase, char and gas as side streams. In processing of lignocellulosic raw-materials it is also possible to recover lignin.

Due to the high temperature and pressures required by the process, conventional hydrothermal processing is energy consuming. Further, the products produced are typically impure and, depending on the raw-material, contain for example salts and in particular sulphurous compounds which are detrimental to further use, and require extensive purification of the products. Sulphurous compounds present in the raw-material may also hamper the

hydrothermal processing of the feedstock.

Summary of the Invention It is an aim of the present invention to eliminate at least a part of the problems relating to the art and to provide a novel process for hydrothermal treatment of biomass in order to obtain valuable products. The present invention is based on the concept of feeding biomass into a first hydrothermal unit operating at conditions of partial wet oxidation. The product obtained from the partial wet oxidation is then treated in a second hydrothermal unit operating at conditions of supercritical water gasification or hydrothermal liquefaction.

The method can be carried out

- subjecting the feedstock to partial wet oxidation in a unit of partial wet oxidation;

- recovering from the unit a downstream product; and

- feeding at least a part of the downstream product to a thermochemical conversion

reactor, where it is subjected to supercritical water gasification or hydrothermal liquefaction to produce biomass conversion products, which in particular are selected from bio-oil and syngas. Surprisingly, it has been found that by carrying out the process in at least the two indicated steps, in the indicated order, it is possible to convert biomass by hydrothermal processing while efficiently separating sulphurous compounds, innate in the raw-material, and salts from the product streams. Furthermore, less energy will be needed for heating the feed before a reactor operating at conditions of supercritical water gasification or hydrothermal liquefaction than conventionally as well as for maintaining the temperature of the reactor.

More specifically, the present process is mainly characterized by what is stated in the characterizing part of claim 1. Considerable advantages are obtained. Thus, the present process can be used for treating biomass, such as lignocellulosic biomass, from various fields of industry, as well as biomass from agriculture, such as manure, or waste from municipalities or industry, for example sewage, such as municipal wastewater or industrial wastewater. The proposed process provides a broad range of products. In fact, there is a wider spectrum than in conventional biomass processing plants. In view of this, and in consideration of the various feedstocks, profitability of the process can be further enhanced by flexible production planning based on the market need and prices. In other words, the input and output can be selected to provide processing of various raw-materials to yield a great number of products.

The process can be integrated into a pulp mill. The pulp mill can thereby be converted to the multi-product biorefinery plant. By such conversion the product spectrum of the mill would include lignin as a biomaterial, and bio-oil or syngas as bio-fuel or energy raw materials. Naturally, the mill will still produce pulps and paper.

Hydrogen-rich gas can be used as energy source to replace outsourced methane in the caustisizing section or sold as hydrogen gas. Carbon dioxide -rich gas can be used in acidification for lignin recovery or transferred to algae production area.

In addition to the conversion and separation of sulphurous compounds, it has been found that the introduction of a PWO unit before a SCWG or HTL reactor reduced tar and char formation will take place in that reactor.

As regards energy savings, PWO will promote conversion in the thermochemical conversion reactor, for example during SCWG. As a result of the enhancement of reactions in SCWG, the temperatures of that reaction step can be lowered and unwanted reactions mitigated.

The invention also provides for energy savings. PWO is an exothermic phenomenon. This reduces the amount of additional energy needed for reaching the temperature of the SCWG or HTL process in the thermochemical conversion reactor, compared to SCWG or HTL applied alone.

Further advantages are features include the following:

- side or waste streams and residues becoming valuable raw materials;

- fossil-based resources are replaced with renewables;

- from the supply chain network viewpoint, bio-oil can be upgraded to liquid biofuel or can be intermediate as the energy carrier;

- the feed supply can be secured due to feedstocks from various sectors; - the formation of waste is minimized through the utilization in the proposed hydrothermal process;

- atom economy is increased;

- formation of ash and particulate matter is reduced or even prevented since biomass has negligible ash content compared to fossil resources; and

- water is used as reaction medium which gives a safe solvent for biomass processing.

It should be noted that sulphur bound to lignin is a particularly problematic form of sulphur which may not be possible to remove completely in the sulphate form as salts. Alternatively, it stays as salts in the liquid/aqueous phase. Thus, one advantage of removing lignin is also to get lower sulphur content in the inlet stream to the thermochemical conversion reactor and hence in the product of this reactor as well.

Sectorial integration provides a more enhanced supply chain network than distributed- centralized approaches: utilizing both solid and wet biomass from various sectors (e.g. black liquor, sawdust, straw and other residues from agriculture and forestry), producing multiple products and flexible operation to adapt changes in market demand.

The sectorial integration enabled has great impacts as well:

- the energy production concept can be changed from central massive production to distributed small scale production in agroforestry places;

- rural areas and distinct self-dependent regions in terms energy can be developed;

- massive imports of fossil fuel or nuclear raw materials for energy are eliminated;

- population distribution is made mor e even, and hence easier management of social services; and

- industrial employment in rural areas

Further features and advantages will be discussed in the following in connection with preferred embodiments. Brief Description of the Drawings

Figure 1 shows a process diagram of a hydrothermal conversion process according to one embodiment, and

Figure 2 shows sectorial integration for supply chain network.

Description of Embodiments

Abbreviations:

"PWO" stands for partial wet oxidation, which also is referred to as oxidative hydrothermal treatment, e.g. by adding oxygen gas to be dissolved or electrolysis of some part of water in the feedstock. "SCWG" stands for supercritical water gasification.

"HTL" stands for hydrothermal liquefaction or "subcritical liquefaction".

In the present technology, PWO and SCWG or HTL are combined: PWO is an intermediate step serving for some energy, dissolution of suspended solid organics (if there is any) and starting to breakdown the biomass structure. Then, less energy will be needed for heating prior to SCWG or HTL and heating the reactor to maintain the temperature. In addition, any inorganic salt content can be recovered in the vertical reactor. There is lignin recovery section and the remaining liquid can be recycled since dilution of the biomass (e.g. weak black liquor) is needed anyways for the reaction process. Furthermore, the reactor can serve for both HTL or SCWG as well by adjusting pressure and temperature. This enables switching the product between syngas and bio-oil in accordance with the market demand. Further flexibility can be provided by flow rates: the proportion of liquid going through lignin recovery section. In case of integration to a pulp mill, the aqueous discharge and solid brine can be recycled to the chemical recovery section of the mill. As discussed above, in one embodiment, the present technology provides a method of hydrothermally converting a biomass feedstock. The method comprises the steps of subjecting the feedstock to partial wet oxidation in a partial wet oxidation unit, recovering from the unit a downstream product, and feeding at least a part of the downstream product to a thermochemical conversion reactor. In the conversion reactor, the product of the partial wet oxidation is subjected to supercritical water gasification or hydrothermal liquefaction to produce conversion products of the biomass. The conversion products are, in particular, selected from the group of bio-oil and syngas. It should be noted that, although only one thermochemical conversion reactor is being considered in the below examples, it is possible to operate the process with two or more reactors. The reactors can be placed in serial or parallel arrangement or combinations thereof. It is also possible to operate one reactor under conditions of SCWG and another under conditions of HTL.

The feedstock of the process involves lignocellulosic biomasses from various sectors. Thus, the feedstock spectrum covers, for example, biomasses from the forest product industry, black liquor, sawdust and woodchips being the main feedstocks; and from agricultural sector, the residues being, e.g., rice straw, wheat straw, non-wood black liquor and leaves, suitable for the proposed process.

The above listed feedstocks are similar regarding the modelling and process design: lignin, cellulose and hemicellulose as the main components with varying ratios. Therefore, a general process model and design tool can be developed for the hydrothermal conversion of the mentioned feedstocks.

The feedstock spectrum also covers lignocellulosic biomass from various other sectors, such as manure of various livestocks, is also possible. Further, waste from municipalities or industry, for example sewage, such as municipal wastewater or industrial wastewater, can also be used as a feedstock. As a feed, wet biomass can be used as such or, in some embodiments, wet biomass blended with solid biomass or even solid biomass dispersed in aqueous phase. By feeding aqueous biomass, costs of pretreatment can be reduced. The use of different raw-material sources provides for a multi-feed process.

The products of the process include bio-oil and syngas. "Bio-oil" refers to aliphatic hydrocarbons (such as alkanes) and aromatic hydrocarbons and combinations thereof which are liquid at ambient temperature and pressure (typically 25 °C and 1 bar). The hydrocarbons are typically fully or partially saturated, but they can also contain unsaturation in the form of, for example, double bonds between carbon atoms. Further, the hydrocarbons may contain functional groups, such as carboxylic groups, anhydride and ester groups. The liquid hydrocarbons typically have 4 to 38 carbon atoms, for example 4 to 24 carbon atoms.

"Syngas" refers to synthetic gas produced through decomposition of organic feedstock, in gas phase at the ambient temperature and pressure: containing mainly hydrogen, methane, carbon dioxide and carbon monoxide as well as lower amounts of hydrocarbons with 2 and 3 carbons (i.e. "light hydrocarbons"). There can be some water vapor or oxygen included in the syngas.

In one embodiment, the syngas contains, for example at least two of the following

components: hydrogen, carbon monoxide and methane.

The products of the process can also contain mixtures of bio-oils and syngas.

One embodiment comprises producing a bio-oil formed by aliphatic, aromatic hydrocarbons or mixtures of aliphatic and aromatic hydrocarbons, which are liquid at ambient temperature and pressure; and/or syngas composed mainly of hydrogen, methane, carbon dioxide and carbon monoxide as well as lower amounts of light hydrocarbons with 2 and 3 carbons, which are gas at ambient temperature and pressure., Turning now to Figure 1 , it can be noted that one embodiment of the process includes partial wet oxidation (PWO) and supercritical water gasification (SCWG) or hydrothermal liquefaction (HTL). As can be seen from the drawing, the process starts with a unit of PWO for liquid feedstocks or simultaneous dissolution and PWO for solid feedstocks. In this way, the process can utilize both liquid and solid feedstocks from various sectors of agriculture and forestry.

In one embodiment, the PWO unit operates under oxygen partial pressure of 0.5-1.5 MPa and at a temperature in the range of 180-240 °C.

Then, some portion of the downstream goes to lignin recovery through acidification. For alkaline biomass, lignin precipitates when pH reduces to 9-10. After that, washing and filtering steps are typically required to get lignin as a product.

The other portion and residual liquid from the lignin recovery section are transferred to the thermochemical conversion reactor.

In a first embodiment, the thermochemical conversion reactor produces bio-oil through sub- critical liquefaction for example at a pressure of 4 to 22 MPa and at a temperature in the range of 250 to 350 °C. In a second embodiment, in the reactor syngas is produced through SCWG (supercritical water conditions. Supercritical water gasification can be carried out at a temperature of 375 to 740 °C, for example 600 to 700 °C, and at a pressure of 25 MPa or more, for example 25 to 30 MPa. Typically, supercritical water gasification is carried out for an aqueous feed containing less than 10 % of dissolved organic matter. The duration of the supercritical water gasification is for example 1 to 5 minutes.

By selection of reactor embodiment, the energy balance of the whole process can be optimized as can the product yields. The separation of the products and aqueous effluent can be performed by two -stage syngas separation or by using a drum. Based on the product demand, this conversion process can be operated in a flexible way by adjusting the flow rates and conditions in the units. In the separation section, syngas is cooled and separated into carbon dioxide-rich and hydrogen-rich products in two stages of high- pressure and low-pressure separators. In case of bio-oil production, the cooled product can go to low pressure separator which would function as drum in that case. Finally, the aqueous effluent can also be recycled for dilution purposes as SCWG is usually implemented with less than 10 % dissolved organic content.

HTL process produces bio-oil as the main product and aqueous phase, char and gas as the side streams. After HTL, upgrading process is still required for bio-oil usage as fuel. Nevertheless, HTL provides bio-oil with less oxygen content compared to fast pyrolysis, thus requiring less hydrogen when upgrading. As such HTL of wood biomass is not fully competitive with petroleum-based gasoline in terms of techno-economic analysis. However, in the present combination, HTL becomes quite an interesting alternative.

The dry matter (solids) content of the aqueous phase subjected to HTL can be up to 40 wt-%.

Typically, the dry matter content is 5 to 30 wt-%. The proper dry matter content can be selected depending on the feedstock.

Alkali such as sodium hydroxide can be added before the PWO or HTL unit. The amount can be up to 60 % of feed dry matter content, typically less (10-30 wt) % of feed dry matter content. The duration of the HTL is for example 1 to 12 minutes.

Table 1 shows examples of the range of operation conditions and the products. Table 1. Process conditions of the hydrothermal conversion process in Figure 1

In Figure 1 , some main streams are identified by numerals. Stream 1 is the flow of biomass feedstock, optionally liquid biomass feedstock, into the partial wet oxidation reactor 11.

Stream 2 is the inlet stream of oxygen and/or cooking chemicals into unit 1 1. Stream 3 is the outlet (downstream product) of the partial wet oxidation reactor 11. Stream 4 is the inlet feed of the SCWG or HTL reactor 18 Stream 5 contains the products - i.e. syngas and/or bio-oil - and water at high temperature and pressure (in practice, at the pressure and temperature of the reactor 18). Stream 5 goes to heat exchange and separation.

Stream 6 is the aqueous effluent remained from the separation operation of Stream 5. The stream "Effluent water" is heated and recycled to the reactor as Stream 6.

There can be various options for heat exchange network as a process design aspect. For example, in Figure 1, Stream 5 has heat exchange first with the mixture of PWO and filtration downstreams (unit 15) and then the effluent water (unit 20). Alternatively, Stream 5 can have heat exchange first with the effluent water and then with the PWO and filtration downstreams mixture. Stream 7 is the lignin stream. This stream is further washed to remove the remaining inorganic solids in the lignin precipitate. The washing step is not shown in Figure 1.

Table 2 below shows the composition of the various streams as an example of Kraft black liquor processing in case of SCWG operation in reactor 18. The calculation is based on 1 kg dry-ash-free (daf) biomass in stream 1, assuming a 20 % split to lignin recovery. The yields, compositions and conditions can slightly vary within these ranges in case of other feedstocks.

Table 2. Composition of streams 1 to 7

Table 2 also shows the elemental sulphur amounts. Stream 1 contains inorganic sulphur as sulphate and sulphide, and organic sulphur bound to lignin molecules.

PWO oxidizes the sulphur into sulphates at least partially or even completely. Assuming complete oxidation, the same amount of sulphur as in stream 1 exists in streams 3 and 4 but in sulphate form. Inorganic sulphur is completely oxidized but organic sulphur may remain bound to lignin molecules. In case of partial oxidation sulphur, syngas with a sulphur content of less than 5 ppm can be achieved, thus still eliminating the gas-cleaning need for further usage of the gas product.

Then, in case of SCWG, the whole sulphur content will leave the reactor as sulphate salts in "Brine and char" streams at the bottom of the reactor and the cyclone. These "brine and char" streams will contain 0.12 kg/kg daf of Na and O.055 kg/kg daf of S.

Stream 5 contains no sulphur (or less than 5 ppm), i.e. the gases are sulphur-free after separation.

In case of HTL, sulphur entering the reactor in stream 4 in sulphate form will remain in stream 5 in sulphate form as well. In the separation stage, it will remain in the "Effluent water" stream, i.e. sulphur-free bio-oil.

A biomass feedstock having a lignin content can be fed into the partial wet oxidization and the organics partially decomposed, e.g. lignin of low molecular weight (about 100 to 5000 g/mol). This reduces the tar and char formation in the thermochemical reactor 18 compared to SCWG or HTL applied alone without PWO.

In one embodiment, the plant is built as a regional biomass conversion plant for the supply chain network shown in Figure 2.

The conversion process is the heart of biomass supply chain networks.

The sectorial integration concept in Figure 2 requires multi-feedstock-multi-product processes as regional conversion of biomass, i.e. the ability to process different feedstocks from both forestry and agriculture, and multi-functional process units for flexible production. In addition, the regional conversion processes can produce energy for their dedicated regions as well: for instance, syngas can be used directly for the energy need of a region. Even though hydrothermal processes are suitable for biomass, no process option alone is proven as sufficient for industrial application in terms of techno-economic performance. This invention can be a solution. For a region including a pulp mill, the proposed process can be integrated with the mill and receive feedstocks from the other biomass sectors in the region as well. This will combine the benefits reduced infrastructure cost and multi-feedstock-multi-product biorefinery. The sectorial integration network provides regional development as well regarding the social aspect. The biomass source sites (rural areas) can provide valuable feedstock for the regional conversion processes.

Therefore, regional processes provide industrial employment in rural areas: local farming people, engineers, scientists and other associated business management people. Consequently, the concept will provide distributed population over the rural and urban areas as well as mixing people with urban and rural backgrounds, thus facilitating the social services reaching everybody and everywhere. In addition, supporting this concept also with local wind turbines and solar panels, this concept has potential to switch the energy policy from central power plants distributing electricity to very large areas to energy-independent smaller areas, thus saving energy distribution losses. From the resources viewpoint, the countries can use their own biomass resources to produce energy and biofuels.

For instance, black liquor and wood can be used in countries with a developed paper and pulp industry based on wood raw-materials, whereas an agricultural country can use agricultural and livestock residues (such as manure and straw). In addition, non-wood pulp mills in agricultural places can have solution for black liquor treatment through the proposed process since the commercial recovery boiler treatment is unfeasible for non-wood mills. The impact of silica on viscosity disables to concentrate the non-wood black liquor more than 50 % solid content, which results in inefficient energy production in recovery boiler. Nevertheless, non-wood black liquor can be utilized in the proposed hyrothermal process. To sum up, the proposed process enables multi-feedstock-multi-product and flexible operation, producing lignin and syngas or bio-oil. The process uses the benefits of hydrothermal conversion methods and potentially provides energy efficient production. This process concept can also overcome the concerns of the availability of feedstock since it utilizes biomass from various sectors. The economy potential calculation determines that the process has potential for industrial implementation.

In summary, embodiments of the present technology will provide for:

• A hydrothermal process for both liquid and solid feedstocks

· Combination of PWO, lignin recovery and SCWG or HTL

• Multi-feed-multi-product process utilizing black liquor, saw dust, wood chips, bark, agricultural residues and possibly various manure feedstocks to produce lignin, syngas and bio-oil

• The same plant equipment for production of bio-oil and syngas, operating flexibly · Flexible operation through adjusting the proportion of black liquor to lignin recovery, and temperature and pressure in the reactor in accordance with the desired products and feedstock

• Oxidizing the sulphur content by PWO to avoid H ₂ S gas outlet from the reactor and, optionally, avoiding or reducing sulphur content in bio-oil.

· Reduced tar and char formation in the SCWG or HTL reactor via PWO as a pre- treatment

• Improving yield of the SCWG or HTL operation by incorporating a PWO step prior to either operation.

• Reduced energy need to heat the feedstock to SCWG or HTL temperature by

incorporating a PWO step prior to either operation.

Thus, embodiments comprise for example the following: 1. Method of hydrothermally converting a biomass feedstock selected from liquid and solid lignocellulosic feedstocks and combinations thereof, comprising subjecting the feedstock to partial wet oxidation, lignin recovery and supercritical water gasification or hydrothermal liquefaction.

2. The method according to embodiment 1, wherein supercritical water gasification or hydrothermal liquefaction is carried out in the same plant equipment for producing bio-oil or syngas, respectively.

Reference Numerals

1-7 flows

11 partial wet oxidation or cooking

12, 15, 20, 21 heat exchanger

13 , 24 high pressure pump

14 acidification reactor

16 filter

17 cyclone

18 reactor (SCWG or HTL)

19 furnace

22 high pressure separator (gas/liquid)

23 low pressure separator (gas/liquid) or drum

25 3-way plug valve

26 expansion valve