A process for the preparation of a carbon product

Abstract

The invention relates generally to a process for the preparation of a carbon product having a high degree of graphitization, comprising the steps of contacting a carbohydrate containing starting material with a molten salt wherein the molten salt comprises one or more hydrated salts selected from the group consisting of ZnCl2, MnCl2, FeCl3, AlCl3, MgCl2, CaCl2 and SbCl2 and carbonising the carbon containing starting material in mixture with the molten salt to form a carbon product by heating at temperatures between 100 and 300°C in a closed reactor system in an atmosphere free of oxygen (O2), forming the carbon product having a degree of graphitization DOG of at least 45% and separating the carbon product from the molten salt. The invention also relates to the carbon product obtainable by the process and to uses of the carbon product.

Description

A PROCESS FOR THE PREPARATION OF A CARBON PRODUCT BACKGROUND OF THE INVENTION

[0001] The invention relates generally to a process for the preparation of a carbon product by carbonising a carbon containing starting material. The invention also relates to the carbon product obtainable by the process and to the use of the carbon product according to the invention for the preparation of value-added materials. 2. Description of the Related Art

[0002] In recent times the carbonisation of biomass has received a lot of interest because it does not produce a lot of CO2or carbon containing volatiles compared to pyrolysis processes and in particular when compared to burning biomass. The carbon captured in the carbon product will not contribute to the global warming. The carbon efficiency of the process defines how much of the carbon in the carbon containing start material will be captured and not emitted to the atmosphere. Furthermore, the carbon product can have various different useful properties depending on the physico-chemical properties of the carbon product.

[0003] The carbon product can for example be used as soil improver or as absorbent in various processes. However, in recent times the interest has increased significantly in carbon for electronics purposes, such as conductive carbon in electrodes, in capacitors or in batteries.

[0004] Carbon materials produced from a biobased feedstock are sometimes also called biochar, even though the carbon material is not char. Biochar is the charcoal-like carbon product obtained when biomass, such as wood, manure or leaves, is heated in an oxygen deficient environment, i.e. pyrolysis. When biochar is chemically or physically activated, it is called activated or active carbon. Known physically activation processes include treatment with steam of carbon dioxide. Known chemical activation processes include treatment with phosphoric acid, zinc chloride, potassium or sodium hydroxide and potassium or sodium carbonate. Owing to the large surface area, high porosity and easy surface modification biochar and active carbon are widely applied as adsorbents.

[0005] Biochar is also well known for its agriculture amendment value for increasing crop yields, and as a form of activated carbon in water filtration and toxin remediation applications. It is also important as a carbon sequestration strategy as recognized by the UN Intergovernmental Panel on Climate Change (IPCC). The feedstock used, and quality produced of bio-chars can vary widely but it is possible through well-controlled pyrolysis technologies to create bio-chars that can be considered engineerable in their properties and serve as a new sustainable carbon platform. Such carbons would be suitable for more sophisticated applications like replacing the graphite and activated carbon electrode materials in high demand energy storage devices including Li-Ion batteries, and supercapacitors.

[0006] The summit of interest is to produce graphene, because it has high strength (200 times stronger than steel in perfect crystalline form) and super high electrical conductivity (5.8 times higher than copper compared on weight basis) and thermal conductivity. These properties promise application of graphene in many different applications such as anti-corrosion coatings and paints, efficient and precise sensors, faster and efficient electronics, energy storage (batteries), flexible displays, efficient solar panels, faster DNA sequencing, drug delivery, and more. Graphene has been described as potentially disruptive technology. However, graphene can be produced by methods that often are complex, expensive and have low production yields.

[0007] A process of particular interest starts from graphite (crystalline carbon) that occurs in nature Graphite comprises crystalline stacks of two-dimensional graphene or graphene oxide (go) layers but can also be produced by carbonisation of carbon containing (bio-)material. To obtain graphene as single layers the stack of layers in the graphite must be exfoliated. It is desired that the carbonisation results in a carbon product having a high content of graphite; i.e. a high degree of graphitisation. The degree of graphitisation during carbonisation is characterised by the ratio of sp2 and sp3 characteristic peaks as can be determined by Raman in a method as described below: in graphene or graphene oxide layers the carbon atoms have a sp2 orbital hybridisation, as opposed to other carbon atoms having sp3 orbital hybridisation.. A way of expressing the degree of graphitization (DOG) is Ig / (Id+Ig) wherein Ig and Id are respectively Raman adsorption intensities in band G at 1580 cm−1and Band D in the range of 1330–1340 cm−1which are representative of adsorption of sp2 carbon present in graphene layers and sp3 carbon present as defects in the graphene layers.

[0008] Ahmed A. MOOSA et. al. present (in Turk J Chem (2021) 45: 493-519) a review article on Graphene preparation and graphite exfoliation. Different graphene preparation methods include chemical vapor deposition on layers of transition metals, epitaxial growth on SiC, arc discharge, unzipping carbon nanotubes and oxidation of graphite to graphene-oxide (GO) with strong acids and strong oxidants to intercalate the graphite followed by exfoliation in water to single sheet GO and reduction of the GO to graphene. These methods are too intricate and complicated to be commercially relevant.

[0009] JP2022136860A describes an electric double layer capacitor (EDLC) as electricity storage device that comprises electrodes coated with activated carbon with a large surface area as collector, obtained by carbonisation of rice husk or coconut shell. Various different methods have been investigated to optimize the carbon properties to achieve optimum properties, which include capacity, long cycle life, durability. Such capacitors using activated carbon attempts are described in WO2018 / 092721, JP 2005-243933, JP 2014-165435, JP 2005-243933, JP 2007-67034 and JP 2016- 18808.

[0010] Sam et al in Synthesis of biomass-based carbon aerogels in energy and sustainability in Carbohydrate Research 491 (2020) describe carbon aerogel materials with very high surface area produced from biomass and their use i.a. as electrical conductor and supercapacitors. The fabricationprocedure of carbon aerogels generally comprises four main steps i.e., sol-gel polymerization, aging, drying and carbonization. Biomass is converted to carbon aerogels in a process comprising a gelation or hydrothermal step of cellulose in water in an autoclave placed in an oven at a relatively high temperature, followed by a solvent exchange step, where the water in the hydrogel is replaced with an organic solvent such as acetone, and a (freeze-)drying step, where the organic solvent is extracted without collapsing the structure to form the cellulose aerogel, followed by carbonisation of the cellulose aerogel to a carbon aerogel by high-temperature pyrolysis (usually between 600 °C and 1000 °C) under an inert gas (typically nitrogen). The process is complex, costly and has low productivity, so impractical at large industrial scale required for example for batteries.

[0011] WO2017 / 205960 discloses a method for production of activated carbon with high surface area without using strong acids or environmentally unfriendly ZnCl2. The process comprises synergistic activation using a first and a second salt, by mixing a carbon precursor with the first salt, preferably an alkali salt, and a second salt, preferably a salt comprising P and O, N and O or S and O, and activating the mixture by raising the temperature to a temperature preferably between about 150 °C to about 1000 °C, for example preheating at 200-700°C and activating at 800-1000°C.

[0012] WO2018 / 141911 (corresponding to EP3577064) discloses a process for converting hydrocarbons, preferably a lower hydrocarbon such as methane, to produce hydrogen by contacting the hydrocarbons with a molten salt (ZnCl2hydrate) at a temperature above 250°C, preferably above 500°C and wherein the hydrocarbons are cracked to produce hydrogen.

[0013] WO2016 / 087186 discloses a process for the conversion of cellulose biomass, comprising three steps: mixing a molten salt hydrate such as ZnCl2 hydrate with the biomass, at least partially hydrolysing the cellulose to monomer saccharides (such as glucose) and oligosaccharides, separating and converting the separated monomer- and oligosaccharides in a thermo-catalytic process, such as pyrolysis, catalytic pyrolysis, HTU or solvo-thermal conversion to make deoxygenated saccharides or pyrolysis oil.

[0014] WO2022 / 207757 discloses a process for converting waste material comprising a cellulose containing part and typically also a non-cellulosic material such as polymer material. The process involves contacting with a molten salt at low temperature below 125°C to dissolve cellulose in the molten salt and separating the solution from non-dissolved compounds. The cellulose is separated from the solution. The non-dissolved non-cellulosic material and optional cellulose degradation products are carbonised. Carbonisation of cellulose itself is not described.

[0015] EP4206305 (corresponding to WO2023126410A1) describes a process to convert a carbon containing material, optionally containing a thermoplastic polymer material, in an anhydrous hydratable molten salt at temperatures between 200ºC to 500ºC and about ambient pressure in absence of oxygen and in presence of steam wherein the hydratable molten salt is rehydrated to phase separate the formed carbon phase and wherein the rehydrated molten salt is heated to formanhydrous molten and steam for use in the carbonisation step. US2012 / 108827 describes a process comprising hydrolysing cellulose to sugars and hydrogenating and dehydrating sugars in ZnCL molten salt to produce fuel additives.

[0016] US2013 / 245252 describes a process comprising hydrolysing cellulose to glucose, hydrogenating to form sorbitol and after dehydrating to isosorbide in ZnCL molten salt

[0017] Zhu Hongli et al describe in a publication with the title "Low temperature carbonization of cellulose nanocrystals for high performance carbon anode of sodium-ion batteries" (NANOENERGY, vol.33, 1 March 2017, pages 37-44) a process wherein cellulose is first hydrolised in 60% sulfuric acid, and then the nanocellulose is isolated, cast to a film and subsequently heated at 240 °C for 8 h in air and carbonised at 1000ºC (>2hrs) at which graphitisation occurred.

[0018] Matsagar Babasaheb et al describe in a publication with the title "Recent progress in the development of biomass-derived nitrogen-doped porous carbon" (Journal of Materials Chemistry A, vol.9, no.7, 1 January 2021, pages 3703-3728) several preparation methods of nitrogen doped porous carbon (NPC) from biomass, such as Hydrothermal carbonization (HTC), pyrolysis, template directed synthesis process using a biomass containing such as amino-acids or N-containing carbohydrate, i.e. glucosamine. Biomass-derived NPCs were also obtained using chemical activation methods using chemical activation agents, such as KOH, NaOH, ZnCl2, K2CO3, KHCO3, H3PO4, and AICl3 at temperature typically in the range of 400 to 900 °C.

[0019] Liu Wu-Jun et al describe in a publication with the title "High-Yield Harvest of Nanofibers / Mesoporous Carbon Composite by Pyrolysis of Waste Biomass and Its Application for High Durability Electrochemical Energy Storage", Environmental Science & Technology, vol.48, no. 23, 17 November 2014, pages 13951-13959) a process wherein sawdust was milled and preloaded with FeCl3 solution and dried. The obtained material was fast pyrolised at 873-1073 K (600 – 800C); volatiles were condensed in ethanol to produce bio-oil and solids M-NMCC were obtained (magnetic nanofiber / mesoporous carbon composites).

[0020] Xiaoxia Bai et al describe in a publication with the title "Hierarchical Porous Carbon with Interconnected Ordered Pores from Biowaste for High-Performance Supercapacitor Electrodes" ( NANOSCALE RESEARCH LETTERS, BIOMED CENTRAL LTD, LONDON, UK, vol.15, no.1, 21 April 2020 (2020-04-21), pages 1-10) a process using biowastes as precursors for the preparation of value-added nanomaterials; in particular using lignosulphonate as the precursor for preparation of capacitors. The process uses a silica template wherein lignosulphonate is loaded and carbonised at 900⁰C.

[0021] Sukamana et al described in “Effect of ZnCl2on properties of graphene produced from palm empty fruit bunch (Materials Science and Engineering 778 (2020) page 1 – 9) the production of graphene from waste from the production of palm oil by contacting empty fruit bunch with ZnCl2 and FeCl3, drying at 80 – 100⁰C and heating at 900°C.

[0022] Li Sun et al described in “From coconut shell to porous graphene-like nanosheets for high- power supercapacitors (J. Mater. Chem. A, 2013, 1,6462) the synthesis of porous graphene-like nanosheets (PGNSs) with a large surface area via an easy and cost-effective SAG (simultaneous activation–graphitization) route from renewable biomass waste coconut shell using graphitic catalyst (FeCl3) and activating agent (ZnCl2). The PGNSs possess good electrical conductivity due to the high graphitic degree. However, the carbon yields are low.

[0023] EP3985072 (corresponding to US11859089) describes a process for producing crystalline carbon black by injecting a water-in-oil micro-emulsion comprising carbon components, metal catalyst nanoparticles and water into the reaction zone which is at a temperature of above 600 °C, preferably even above 1100 °C and quenching.

[0024] Libin Tang et al describe (in Journal of Materials Chemistry, 2012, 22, 5676-5683) the bottom-up synthesis of large-scale graphene oxide nanosheets wherein graphene oxide nanosheets (GONs) were grown using a hydrothermal method starting from glucose, sugar and fructose in a 50 mL Teflon-lined autoclave at growth temperatures ranging from 160 to 220 °C in growth period of 70 to 660 min followed by thermal annealing under nitrogen atmosphere at temperatures ranging from 450 to 1300 °C.

[0025] Daniele Perondi et al describe (in Microporous and Mesoporous Materials 323 (2021) 111217) the preparation of graphene-like porous carbon nanosheets GPCNs involving simultaneous pyrolysis and activation of carbon precursors in molten salt to generate GPCNs. In the FeCl3 / ZnCl2system, the iron component facilitates the generation of GPCNs by forming a complanate carburized phase in the pyrolysis process, and ZnCl2 activates the formed carbon to produce a porous structure. Several types of metal-molten salts, such as LiCl / KCl, KCl / ZnCl2, and FeCl3 / ZnCl2 systems have been developed to synthesize nanosheets. Cellulose, FeCl3.H2O and ZnCl2are mixed, evaporated for 2 hours at 80°C, dried at 100°C and subsequently pyrolised in a pyrolytic reactor at a temperature from 700 - 1000°C.

[0026] S. Saqib Shams et al describe (in Materials Letters 161, (2015), 476–479) the synthesis of graphene from biomass using one-step pyrolysis wherein under flowing nitrogen atmosphere, camphor leaves were heated to 1200 °C at10°C / min and then cooled down to room temperature wherein the camphor leaves were reduced to graphene.

[0027] Deepti Krishnan et al describe (in ACS nano VOL.8, NO.1,449–457, 2014) Graphene Oxide Assisted Hydrothermal Carbonization of Carbon Hydrates. The process comprises hydrothermal carbonization (HTC) of glucose or cellulose in an autoclave at temperatures of about 200°C under autogenic pressure in the presence of Graphene oxide (GO) to alter the morphology of its HTC product, resulting in more conductive carbon materials with higher degree of carbonization. The carbon yield is about 10 wt %. The product is subsequently annealed in a microwave to increase graphitization and conductivity.

[0028] Muhammad Taqi provides (in BioResources 15(4), 9756-9785) a review on Biobased graphene derived from biomass wastes. The methods involve thermal treatment of the biomass, such as pyrolysis, carbonisation and graphitisation and are all involve high and even very high temperatures.

[0029] Dohyung Kang et al describe (in Applied Catalysis B: Environmental Volume 254, 5 October 2019, Pages 659-666) Catalytic methane pyrolysis in molten MnCl2-KCl wherein methane is decomposed to produce molecular hydrogen and solid carbon catalyzed by contact with molten KCl:MnCl2mixtures in a bubble column reactor from 700 to 1050 °C. The best carbon product obtained from the molten MnCl2(67)-KCl(33) comprises stacks of more than 30 layers of graphene having an I(D) / I(G) ratio of about 0.6 compared to carbon product obtained from KCl(100) having an I(D) / I(G) ratio of 1.37 corresponding to amorphous carbon.

[0030] The prior art processes generally have one or more problems of being complex and expensive, having low production yields or producing low quality carbon material. Thus, there is a particular need for an improved process that is less expensive, has a good yield, preferably is scalable to high production volumes and produces good quality carbon material that can be used for example for the manufacture of electronic materials, for example for electrodes and capacitors, for producing Graphene, Graphene Oxide and Carbon Fibers. SUMMARY DESCRIPTION OF THE INVENTION

[0031] The present invention addresses these problems by providing a process for the preparation of a carbon product having a high degree of graphitization, comprising the steps of a) contacting a carbon containing starting material with a molten salt i. wherein the carbon containing starting material is a carbohydrate containing starting material, ii. wherein the molten salt comprises one or more hydrated salts selected from the group consisting of ZnCl2,MnCl2, FeCl3, AlCl3,MgCl2,CaCl2and SbCl2,b) carbonising the carbon containing starting material in mixture with the molten salt to form a carbon product; i. by heating at temperatures between 100 and 300°C, preferably between 125 and 275°C, more preferably between 150 and 250°C, ii. in a closed reactor system, iii. in an atmosphere free of oxygen (O2), iv. forming the carbon product having a degree of graphitization DOG of at least 45% wherein degree of graphitization is defined as Ig / (Id+Ig) wherein Ig and Id are respectivelyRaman adsorption intensities in band G at 1580 cm−1and Band D in the range of 1330– 1340 cm−1, c) separating the carbon product from the molten salt, d) optionally washing the separated carbon product, e) optionally drying

[0032] It was surprisingly found that the process of the invention produces a carbon product having a high degree of graphitization (DOG) at a high yield. Due to the low temperatures for carbonisation in the molten salt hydrate, the conversion to carbon is complete with high carbon content and very low liquid hydrocarbons. Low amounts of liquid hydrocarbons could be achieved. A degree of graphitization of more than 45% and even no less than 55% or even 65% could be achieved at carbon yields CY over 70wt% and even higher than 80 wt%. A further advantage is that the energy consumption of the process is relatively low due to the relatively low temperatures. The carbon yield CY of the obtained carbon product is defined as the dry weight of the separated carbon product relative to the theoretical amount of carbon in the carbon containing starting material.

[0033] A further advantage of the process is that the carbon product can relatively easily be recovered by washing out the molten salt, which is easy compared to prior art carbonisation or pyrolysis processes as the carbonisation product of the invention has a low liquid hydrocarbons residue and there is no need to for additional separation or cleaning steps for side product.

[0034] In the carbonisation process a bio-based material can advantageously be used that has a high oxygen content, which is normally a disadvantage as the oxygen needs to be removed for most purposes (like bio-oil) in the form of CO2, but for the present envisaged use as precursor for carbon, functionalized carbon and graphene materials it is actually not a problem but an advantage. The carbonisation process of the invention thus converts biomass to useful carbon product and water while producing very low amounts of carbon-dioxide or low hydrocarbons residues (like char, pitch or Hydrocarbon liquids) and using low amount of energy, which is all very beneficial for the environment.

[0035] An advantage of the process of the invention is that it allows to produce a carbon product with properties that can vary between wide ranges and can easily be tailored to meet the requirements in a wide range of different applications as will be described below. Typically, the carbon product can have a high oxygen content OC (i.e. bound oxygen atoms for example in hydroxyl, ether or carboxylic groups), wherein high is considered above 20 wt%. High oxygen content is achieved in particular when the starting material is carbohydrate and when carbonisation is done in hydrated molten salt at relatively low temperature. The high oxygen content in the carbon product provides for hydrophilic and reactive properties. Such carbon material was found to be a good precursor material for several applications. It can easily be dispersed in water, can adsorb and form film on polar surface, can bind ions, such as metal ions, and thus can be modified and functionalized relatively easily. A relatively high oxygen content is also desired for adhesion on polar surfaces, for example for use inmetal electrodes or capacitors. The process of the invention typically produces a carbon product having oxygen content in the range between 20 and 40 wt%.

[0036] On the other hand, in some applications where high conductivity is desired the oxygen content OC should be relatively low; typically, below 20 wt%, below 10 wt% or even below 5 wt%. Such relatively low OC, high DOG and high conductivity is achieved in particular when the carbon product obtained according to the invention is subjected to a further post treatment step. A preferred post-treatment to further reduce the oxygen content of the carbon product is post-heating the separated and optionally washed carbon product preferably to a temperature above 200°C, preferably above 250°C, more preferably above 300°C in oxygen free atmosphere, in an oven or with microwave heating. Post heating does not need to be in a closed reactor and can be done in an open reactor but in an atmosphere free of oxygen. When using microwave heating in the post-heating step, there is no need to add conductive carbon into the carbon product because the carbon product obtained by the process of the invention is microwave absorbing.

[0037] The inventors have found that the carbon product obtained by the process of the invention having an oxygen content in the range between 20 and 40 wt% and a very high degree of graphitization of at least 45% is a suitable starting material for production of graphene because the carbon product has very little defects in the graphene oxide sheets and can be exfoliated without the need of an oxidation step as in the prior art. It is believed that the low defects are due to the mild conditions of the process in the molten salt hydrate. A mild post-treatment of the carbon product for further de-oxygenation will result in a high yield of graphene like carbon having high porosity, a high capacitance and a high conductivity.

[0038] Accordingly, the invention also relates to a carbon product obtainable by the process according to the invention; in particular the carbon product having a DOG of at least 45%, preferably at least 55%, more preferably at least 60% and even more preferably at least 65%.

[0039] Accordingly, the invention also relates to the use of the carbon product according to the invention for the manufacture of electrode materials or electrodes, wherein optionally residual molten salt used in the carbonisation step is used as electrolyte.

[0040] Accordingly, the invention also relates to the use of the carbon product according to the invention as a precursor for the manufacture of Carbon Fibers, Graphene and Graphene Oxide. DETAILED DESCRIPTION OF THE INVENTION

[0041] The process of the invention for the preparation of a carbon product having a high degree of graphitization, comprises the steps of a. contacting a carbon containing starting material with a molten salt i. Wherein the carbon containing starting material is a carbohydrate containing starting material,ii. Wherein the molten salt preferably comprises one or more hydrated salts selected from the group consisting of ZnCl2,MnCl2, FeCl3, AlCl3,MgCl2, CaCl2and SbCl2b. carbonising the carbon containing starting material in mixture with the molten salt to form a carbon product; i.by heating at temperatures between 100 and 300°C, preferably between 125 and 275°C, more preferably between 150 and 250°C, preferably by heating in an oven or by heating with microwaves, ii.in an atmosphere free of oxygen (O2), iii.forming the carbon product having a degree of graphitization DOG of at least 45%, preferably at least 55%, more preferably at least 60% and even more preferably at least 65%; wherein degree of graphitization is defined as Ig / (Id+Ig) wherein Ig and Id are respectively Raman adsorption intensities in band G at 1580 cm− 1and Band D in the range of 1330–1340 cm−1c. separating the carbon product from the molten salt, d. optionally washing the separated carbon product, e. optionally drying.

[0042] The term molten salt is used to indicate that the salt is used at an elevated temperature where it is in the liquid state and can act as a ionic solvent, which implies that the temperature is above the melting temperature in case of a pure salt or above a eutectic melting point in case of a mixture of salts and, in case of a hydrated salt, the temperature where the salt dissolves in its hydrated water. In all cases reference is made to a molten salt

[0043] In the process of the invention the salt is a metal halide salt in hydrated form, wherein the metal is Zinc, Aluminum, Antimony, Manganese, Iron, Calcium or Magnesium or combinations thereof and the halide is chloride; ZnCl2, MnCl2, FeCl3, AlCl2, MgCl3, CaCl2, SbCl2. These molten salts are hydratable and have appropriate low melting temperature in the hydrated state. The molten salts, in particular ZnCl2, has catalytic properties for the carbonisation process. It was found that the molten salts, in particular ZnCl2, creates high surface areas in the carbon product, which is beneficial for adsorption properties and as collector for electrode materials. Therefore, the most preferred salt is ZnCl2. Preferably the molten salt comprises at least 50 wt.%, more preferably at least 70 wt%, even more preferably at least 80 wt% and most preferably at least 90 or even 95 wt% ZnCl2relative to the total amount of salts, with the remainder of the molten salt being one or more other metal halide salts, preferably AlCl3, MnCl2, SbCl3, MgCl2, CaCl2 or FeCl3 and most preferably FeCl3. Preferably only ZnCl2 hydrate is used as the molten salt. Extra acid (preferably HCl, in case of Zinc-chloride) may be added to promote carbonisation.

[0044] In the process according to the invention, the hydrated salt comprises water; preferably in an amount below 30 wt%, preferably below 25wt% relative to the weight of the hydrated salt. Above30 wt% the mixture starts foaming during carbonisation step b) and the yield and the DOG is lower. The amount of water is preferably above 1 wt%, preferably above 5 wt%, more preferably above 10 wt% and even more preferably above 15 wt%. A higher amount of water lowers the melting temperature of the hydrated molten salt and allows the process to be carried out at the specified very low temperatures. In the closed reactor system, the water that initially is in the hydrated molten salt and the water formed by carbonisation of the carbohydrate does not leave the reactor.

[0045] The carbon containing starting material is a carbohydrate containing starting material. Carbohydrates have shown to be a very good starting material as carbohydrates because in molten hydrated salt, in particular in ZnCl2, carbohydrates carbonize easily by splitting off water at the low carbonisation temperatures and surprisingly form a carbon product with a well-developed graphite structure as exemplified by the high degree of graphitization (DOG) with a high oxygen content and a good porosity.

[0046] The carbohydrate containing starting material can in principle be any biomass source. Suitable carbohydrates can be selected from the group consisting of monosaccharides, oligosaccharides, poly-saccharides or mixtures thereof. Most preferred are cellulose and glucose. In a special embodiment, further described below, the carbon containing starting material is the carbon product obtained by the process of the invention to further increase the DOG and decrease the oxygen content. A suitable source of carbohydrate containing starting material is wood, saw-dust, paper, cotton or empty fruit bunch that preferably is finely comminuted. Wood is suitable as it comprises mainly cellulose and lignin which can also be carbonized. Preferably, in view of obtaining a high DOG and CY, the carbohydrate containing starting material is relatively pure; preferably the carbohydrate containing starting material comprises carbohydrates in an amount of at least 50, 70, 80 or even at least 90 wt% relative to the total weight of the carbohydrates containing starting material. The amount of the carbohydrate containing starting material relative to the total weight of the carbohydrate containing starting material and the hydrated molten salt is preferably between 1 and 30 wt.%, preferably between 2 and 20 wt%, more preferably between 5 and 15 wt%.

[0047] Optionally (and preferably) a carbon seed material, more preferably graphene-oxide or carbon black, is added to the carbon containing start material. Graphene-oxide works well but is too expensive, so carbon black is preferred. More preferred is that the carbon seed material is the carbon product obtained by the process of the invention preferably having high degree of graphitization or DOG>50%, that is in part recycled to the process step a) or b), preferably in a catalytic amount in case of GO because it is so expensive. Good results were obtained with amounts between 0.001 and 0.5 gr / 100gr of the salt in case of GO. In case carbon black or carbon product obtained by process of the invention is used as seed, the upper limit is not critical because it is the same as the envisaged end carbon product but is preferably low in view of efficiency.

[0048] In step b), the carbon containing starting material is carbonized to form the carbon product in mixture with the molten salt by heating at carbonisation temperatures between 100 and 300°C,preferably between 125 and 250°C, more preferably between 150 and 200°C. The heating can be done in two or more stages at increasing temperature levels within the mentioned temperature ranges. The temperatures are very low compared to prior art pyrolysis and carbonisation processes, which range from 350 – 1000⁰C. Low temperatures generally result in slow conversion, but in the process of the invention good results are obtained because the metal salt (in particular ZnCl2) acts as catalyst even at low temperatures when using carbohydrates as the carbon containing starting material. Low temperature increases the carbon yield CY (less CO2formation), increases the DOG and results in higher oxygen contents. A high temperature increases conversion speed but decreases CY. However, the carbonisation of carbohydrates in the hydrated molten salt proceeds much faster than carbonisation processes described in the prior art, which is surprising considering the very low temperatures.

[0049] The carbonisation can be done by heating in an oven or by heating with microwaves / induction radiation in an atmosphere free of oxygen (oxygen here means molecular oxygen or O2). The carbonisation is done in anaerobic conditions to avoid combustion of the carbon. The carbonisation is done in the presence of water, and the closed system prevents that water evaporates and leaves the reactor. A further advantage of carrying out step b) in a closed reactor system is to avoid air coming in, which has the risk of combustion, or in a system which is open to atmosphere, but pressurised above atmospheric pressure to avoid air from leaking into the system. A closed system can be an autoclave but also a reactor provided with means, for example a condenser to cool, condense and collect gasses formed.

[0050] An advantage of using a molten salt hydrate compared to anhydrous molten salt is that it reduces the risk of combustion because the carbonisation temperature is lower and because the water in the salt hydrate creates steam at higher temperatures that is inert and can be used to expel oxygen from the reactor. This is preferably done before starting the carbonisation in the closed reactor system. A closed reactor system can be provided with a condenser to cool, condense and collect gasses formed or can be an autoclave. The reactor can be a pressurized continuous reactor, a continuous reactor wherein besides a stream of solid products also a separate stream of gas and / or liquid products is separated whereby water condensed in step is returned to the reactor.

[0051] In a first embodiment, in carbonisation step b) the carbohydrate containing start material is heated in the molten salt hydrate in the closed reactor system at the specified carbonisation temperature using external heating, preferably in an oven or autoclave, wherein the molten salt is a hydrated molten salt.

[0052] The amount of carbon containing starting material relative to the total weight of carbon containing starting material and the molten salt is preferably between 1 and 30 wt.%, preferably between 2 and 20 wt, more preferably between 5 and 15 wt%. The carbonisation time is typically less than 4 hours, preferably even less than 3 hours more preferably even less than 2 hours and possibly less than 1 hour.

[0053] In second embodiment, in carbonisation step b) the carbon containing start material is heated in the molten salt hydrate using microwave heating. In this process the heating is caused by the energy absorption of the microwaves (also referred to as internal heating as opposed to external heating in for example an oven). Water contained in the mixture of the carbon containing material and molten hydrated salt is an adsorbent of the microwave energy. In a preferred embodiment, in step a) a microwave absorbing material, preferably conductive carbon material, more preferably carbon black, is mixed with the carbon containing start material as a seed and in carbonisation step b) the mixture is heated using microwave heating. The microwave heating is very fast and high ratio of carbon containing start material to the molten salt can be used. Preferably, the weight ratio of carbon containing starting material to the total weight of the carbon containing starting material and the hydrated salt is 0.2 – 2, preferably 0.5 – 1.5, more preferably 0.7 – 1.3.

[0054] The amount of microwave absorbing material is chosen to have an effective transfer of heat in the carbon product. The microwave absorbing material is preferably mixed and as homogeneously dispersed as possible. However, the amount is not very critical in a preferred case wherein the microwave absorbing material is the carbon product obtained by the process of the invention that is in part recycled to the process step b). Good results are obtained when the weight ratio of microwave absorbing material and hydrated salt solvent is between 0.05 and 0.5, preferably between 0.18 and 0.3 and more preferably between 0.15 and 0.25. In this embodiment the heating is very efficient, and carbonisation time can be less than 1 hour, preferably even less than 0.5 hours. Very low oxygen contents and very high conductivity can be obtained when using longer microwave times and higher microwave energy. A microwave energy between 50 and 500 W per 22 gr mixture can suitably be used to mildly heat the mixture for carbonisation in a time frame between 5 and 30 minutes. The microwave power scales with the amount of material to be heated. A realistic power range is 50 – 500W per 100 gr of the mixture.

[0055] The process is very fast even though the carbonisation temperatures are very low. Evidently the carbonisation time depends on the temperature. The carbonisation time can be as short as 60 minutes or less even less than 30 minutes to convert the carbon containing starting material to the carbon product to a degree of graphitization DOG of at least 45%, preferably at least 55%, more preferably at least 60% and even more preferably at least 65%.

[0056] After the carbonisation step b) the formed carbon product is separated from the molten salt in step c). The separation is preferably done by addition of water to precipitate carbon product that is still dissolved in the molten salt and to extract the salt from the carbon product by dissolving it in the water. Water is also preferred to separate the salt from the carbon product because it can more easily be removed to recover and recycle the molten salt to step a). Cold water is preferred in the first addition of water as it also quickly cools the molten salt.

[0057] Preferably, the salt is further separated from the carbon product by washing with water, preferably at a temperature between 50 and 90 ºC. Washing is preferably done in multiple stepsdepending on the required purity of the carbon material. Preferably, one or more solid separation steps are performed either by centrifugation and / or by filtration after each washing step. Typically, a washing cycle comprises washing the carbon product by stirring in water at a temperature between 50 and 90 ºC for a time preferably between 1 and 60 minutes, filtering, and washing the separated carbon product on the filter; this washing cycle is preferably repeated one or more times until the Zinc concentration is below 0.5wt%, preferably below 0.2 wt% and more preferably below 0.1 wt%. Another suitable method is washing by refluxing in water in a Soxhlet type of extraction.

[0058] More preferably, the carbon product is separated from the one or more salts by washing with acidified water, preferably having a pH below 4, preferably below 3, more preferably below 2 and most preferably below 1. It was found advantageous to wash with acidic washing water to improve the efficiency of the washing step and to prevent precipitation of metal salts, for example ZnOHCl, after dilution with water. Any liquid carbons that may be formed will mainly be carboxylic acids that remain in the salt and wash water. It was observed that the washing water was clear which is indicative that the carbonisation is proceeding without producing organic products and char as occurs in pyrolysis process. Reversely, when brownish discoloration of the wash water is observed it is indicative that the carbonisation did not go well and that the product yield and carbon yield is low.

[0059] The separation and washing can optionally be done by addition of an organic anti-solvent that causes the carbon- product to separate from the molten salt followed by separating the precipitated or coagulated carbon product for example by filtration. Suitable organic anti-solvents are C1 to C8 alcohols and ketones, in particular the alcohols of the group of straight chain and branched chain C1 to C4 alcohols, such as methanol, ethanol, propanol, and iso-propanol. Particularly suitable ketones include the C3 to C5 ketones such as acetone and methylethylketone (MEK). Preferred organic anti-solvents agents are acetone, ethanol and t-butyl alcohol. Such organic anti-solvents can be used after cooling, preferably after the first addition of water to more completely separate carbon product from the salt and enhance extraction of liquid hydrocarbons from the carbon product. Optionally, the organic anti-solvent is used in a mixture with water for washing the carbon product and / or is used alternating with water washing steps.

[0060] After separation and optional washing the carbon product is dried by heating, preferably at a temperature between 80 and 150 ºC, more preferably between 80 and 120ºC, to obtain the carbon product. This product is preferably milled to a fine powder.

[0061] In yet another embodiment, the resulting carbon product contains salts that can function as electrolyte. This can be conveniently achieved in the process of the invention, wherein the washing is stopped before completely removing the salt to intentionally leave a residual amount of the salt in the formed carbon product to act as electrolyte, wherein preferably the residual metal-halide salt is converted to it’s metal-oxide and / or metal hydroxide, preferably by addition of a strong base, which preferably is KOH or NaOH, wherein the amount of residual salt is preferably between 0.01 – 20 wt%, preferably 0.02 – 15 wt%, more preferably 0.5 – 10 wt% of the total weight, and wherein mostpreferably the residual salt is ZnCl2and / or ZnCl2converted to ZnO and / or Zn(OH)2by addition of a strong base, preferably KOH or NaOH.

[0062] After separation step c) and washing step d) the carbon product is either not dried to obtain a wet carbon gel product or dried by freeze drying to obtain a dry carbon gel product, or dried by heating, preferably at a temperature between 80 and 150 ºC, preferably 80 – 120ºC, to obtain a carbon powder product. It has been observed that the washed carbon product has a gel-like consistency, which can be advantageous to use in some applications to avoid reducing porosity resulting from drying. In another embodiment this gel-like carbon product is freeze dried to produce a highly porous aerogel type of carbon product. However, in most cases, it is preferred that after the separation and optional washing step, the carbon product is dried by heating.

[0063] The carbon yield CY of the obtained carbon product (dried), defined as the dry weight of the separated carbon product relative to the theoretical amount of carbon in the carbon containing starting material, is preferably at least 40 wt%, preferably at least 45 wt%, more preferably at least 50 wt%, but CY of at least 60, 70 or even 80 wt% is achievable. The relative graphitization yield, defined as the wt.% percentage of carbon in the starting carbon material that is converted to graphite (DOG x CY) is at least 20%, preferably at least 25%, more preferably at least 30% and most preferably at least 40%.

[0064] The process according to the invention results in a carbon product comprising an oxygen atom content between 20 and 40 wt% and a DOG of at least 45%, preferably at least 55%, more preferably at least 60% and even more preferably at least 65%. The inventors have found that the carbon product obtained by the process of the invention having an oxygen content in the range between 20 and 40 wt% and a very high degree of graphitization of at least 45% is a very suitable starting material for different uses. The high oxygen content allows the carbon product to be functionalized, and the combination of a high DOG and OC makes the product suitable for production of conductive carbon, in particular graphenes, which have very interesting uses.

[0065] Thus, in a preferred embodiment, the carbon product obtained is functionalized in one of the further steps; 1) a functionalization step wherein the carbon product is modified to contain one or more heteroatoms, preferably sulfur, nitrogen or metals, and / or 2) a step to reduce the oxygen content, preferably by heating, optionally with reducing agent wherein the surface area and / or oxygen content can be reduced for example for enhancing electrical conductivity. These embodiments will be described in more detail below.

[0066] The separated and optionally washed and dried carbon product is optionally heated in a further heating step e) to a temperature above 200°C, preferably above 250°C, more preferably above 300°C preferably in oxygen free atmosphere. This can further lower the OC. Optionally, the washed and preferably dried carbon product is subjected to post heat treatment using microwave energy.

[0067] In a special embodiment of the invention, the carbon containing starting material is the carbon product obtained by the process of the invention which is further carbonized in a secondcarbonisation according to the invention to further increase the conductivity and decrease the oxygen content. Preferably, the carbon starting material in the second carbonisation is the carbon product obtained by the process according to the first embodiment described above which is carbonized according to the second embodiment described above; i.e first heated in salt hydrate in a closed reactor in the presence of water according to the invention and then heated with microwave radiation.

[0068] Alternatively, the carbohydrate containing start material is first carbonized using a molten salt hydrate in an oven and further carbonized using microwave heating, preferably without addition of a microwave energy adsorber when the carbon product from the first carbonisation step is sufficiently carbonized to act as a microwave energy adsorber. One advantage of this two-step carbonisation process is the flexible production of a carbon product having a relatively high OC of typically above 20 or above 25 wt% in a first carbonisation step which can be done in bulk followed by a relatively easy smaller scale carbonisation step for production of a carbon product having a relatively low OC of typically below 25 or 20 wt%.

[0069] Reduction of the oxygen content of graphene oxides is known in the art. In some prior art processes graphene is prepared by the redox method wherein the interlayer distance in graphite is increased by first oxidizing the graphite to insert oxygen-containing groups in order to be able to exfoliate to obtain single-layer structure (of GO) and then remove these oxygen groups by reductants to recover the original carbon plane with purely in-plane sp2 orbitals (reduced GO). This method is known as Hummers method, Staudenmaier’s method or Brodie’s method. The oxidation method introduces defects in the graphite sheet, which will also deteriorate properties. The advantage of the carbon product of the invention is that it already has a high degree of graphitization and relatively high oxygen content, so the oxidation step is not necessary for exfoliation and less defects are created in the layer structure, which has the potential to create a reduced graphene-oxide with properties that are closer to pure graphene.

[0070] The optionally exfoliated carbon product has to be further subjected to a posttreatment to reduce the oxygen content and convert the graphene-oxide GO to graphene (G). This is also called the deoxygenation step.

[0071] The inventors have found that the prior art process using heating at high temperatures results in loss of carbon and creation of defects. The carbon product of the invention has low number of defects and is a good starting point for making graphenes by applying a mild posttreatment to deoxygenate the GO. The invention thus also relates to a process wherein a carbon product obtainable by the process of the invention comprising an oxygen atom content between 20 and 40 wt% and a DOG of at least 45%, preferably at least 55%, more preferably at least 60% and even more preferably at least 65% is optionally exfoliated and further subjected to a mild treatment to reduce oxygen content to an oxygen atom content below 20 wt%, preferably below 15 wt%, more preferably below 10 wt% and most preferably below 5 wt%.

[0072] Exfoliation can be done in several known ways. A preferred way is Liquid phase exfoliation wherein the carbon product is dispersed in a suitable chemical environment (e.g., in an organic solvent or in a mixture of water and surfactant). A surfactant or dispersing agent is used to match the surface tension of the solvent to the carbon product. Suitable surfactants are N-methyl-2-pyrrolidone (NMP), ortho-dichlorobenzene and dimethylformamide. The exfoliation is generally driven by mechanical force provided by, e.g., ultrasound or a blender. Examples of methods for liquid phase exfoliation can be found in Nature Materials 13 p.624-630 (2014) and Nature Nanotechnology 3, p. 563 - 568 (2008). Exfoliation can also be done by electrochemical cathodic treatment. Examples of methods for electrochemical expansion can be found in WO2012120264 A1

[0073] Known mild deoxygenation post-treatments are chemical reduction, thermal reduction, hydrothermal / solvothermal reduction, electrochemical reduction or photocatalytic reduction. In a preferred embodiment the deoxygenation is done by heating the separated, washed and dried carbon product to a temperature above 200°C, preferably above 250°C, more preferably above 300°C, in oxygen free atmosphere, in an oven or preferably by microwave heating. This process will result in a high yield of graphene like carbon having high porosity, a high capacitance and a high conductivity that can meet industry standards of conductive carbon.

[0074] A suitable deoxygenation post-treatment is Chemical reduction because it is relatively easy to set a mild deoxygenation condition by choice of an appropriate concentration and reducing power. In this process reducing agents are added to a suspension of the (preferably exfoliated) carbon product. Suitable reductants are hydrazine / hydrazine hydrate, ammonia, sodium borohydride (NaBH4), hydroiodic acid (HI), sodium dithionite, metal salts (e.g., SnCl2), organic reducing agents such as gallic acid, Ethylenediamine, Sodium citrate, L-cysteine and L-ascorbic acid (vitamin C).

[0075] The invention also relates to a carbon product obtainable by the process according to any of the embodiments of the process of the invention described above; in particular to a carbon product formed in the carbonisation step has a DOG of at least 45%, preferably at least 55%, more preferably at least 60% and even more preferably at least 65%, having an oxygen atom content between 20 and 40 wt%, and preferably at least 55 wt% carbon atoms and between 3.0 and 6.0 wt% Hydrogen atoms. Typically, the carbon product has an I-number between 100 and 700, preferably between 200 and 500 and an MB-number between 150 – 500 preferably between 200 and 400.

[0076] The invention also relates to a carbon product obtainable by the process according to the invention that also includes a post treatment step to reduce the oxygen content to an oxygen (atom) content below 20 wt%, preferably below 10 wt%, more preferably below 5 wt% and most preferably below 3 wt%.

[0077] As explained, the process allows very flexible adjustment of process conditions to achieve a wide range of different properties useful for different applications. The carbon product preferably has one or more of the features a) to d): a) an oxygen content between 1 and 40 wt%, wherein the OC ispreferably above 10 wt% for capacitance, adhesion and adsorption and preferably below 20 wt% in view of conductivity; b) a surface area SA between 100 and 3000 m2 / g, preferably between 200 and 2000 m2 / gr, c) comprising a fraction of the metal halide salt or it’s converted metal oxide or metal hydroxides preferably ZnCl2, ZnO and / or Zn(OH)2 d) a pore volume between 0.3 and 3.0 ml / g, preferably between 0.5 and 2.0 ml / g e). A wide conductivity range from 0 to 73 S / m was achieved as shown in the examples even without further upgrading the obtained carbon product, for example by exfoliation methods, which makes it a promising start material for electrical applications.

[0078] The carbon product of the invention, especially the carbon product with higher OC (higher than about 15 or 20 wt%), can be functionalized relatively easily in view of different uses of the carbon product; for example to improve the amount or specificity of absorption of target molecules. This can be done in further steps comprising; - a functionalization step wherein the carbon product is modified to contain one or more heteroatoms, preferably sulfur, nitrogen or metals, wherein preferably a functional compound comprising such heteroatoms is added after the carbonisation step to absorb in the carbon product and bind or react with oxygen in the carbon product, for example by impregnation of a solution of such functional compound and optionally drying, optionally followed by a treatment, preferably a heat treatment at temperature above 350°C, to bind the functional compound in the carbon, and / or - an oxygen reduction step, preferably by heating or with reducing agent wherein the surface area and / or oxygen content can be reduced for example for enhancing electrical conductivity.

[0079] Alternatively, the functionalization step can be done by adding a functional compound before the carbonisation step b); these functional compounds are preferably sulfur and / or nitrogen containing organic compounds that also carbonize during the carbonisation step. Metal containing functional compounds are preferably added to the carbon product after carbonisation.

[0080] The invention also relates to functionalized carbon product obtainable by the process described above.

[0081] The carbon product obtained by the process is a powder having granular carbon particles. The carbon product can be shaped in ways known in the art (granulating, extruding, compacting etc). In a special embodiment the shaping is done before carbonisation by shaping the mixture of the carbon containing start material and molten salt into a shape and then carbonising. For example, a mixture of cellulose and molten salt can be spun to a fiber and subsequently carbonized followed by (optionally partly) removing the salt.

[0082] Alternatively, and more easily, the shaping is done after carbonisation. Carbon fibers can be made by spinning the mixture of the carbonized carbon product in the molten salt after carbonisation step b), optionally after mixing with a binder, into a water bath wherein the molten salt is removed to obtain a fiber comprising the carbon product of the invention, which then can be subjected to further treatments as described above, for example functionalization and heating.

[0083] Alternatively, and more easily, the shaping is done after carbonisation and separating step c) and optionally after washing step d). For example, the carbon product obtained after step c) or d) (optionally dried and further heated or functionalized) comprises a low amount of water forming a paste like mixture that can readily be shaped and subsequently dried or heated at high temperature for example as defined in step e) to increase the hardness of the shaped carbon product and increase conductivity. Optionally the carbon product is mixed with a binder material before shaping.

[0084] Another advantage of the carbon product of the invention having such high degree of graphitization (DOG) is that it is a good precursor for producing graphene or graphene-oxide. The invention also relates to the use of the carbon material of the invention as a precursor for the manufacture of Carbon Fibers, Graphene and Graphene Oxide.

[0085] The invention also relates to the use of the carbon material obtainable by the above- described processes for the manufacture of electrode materials or electrodes, wherein optionally residual salt is used as electrolyte.

[0086] Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

[0087] Further modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention. The invention is further illustrated by the following examples.

[0088] The invention is illustrated by the experiments described below. DESCRIPTION OF EXPERIMENTS Degree of graphitisation by Raman spectroscopy

[0089] Analyses were performed in a Horiba-Jobin Yvon iHR320 system with a Symphony detector coupled with an Olympus microscope. The laser used was HeNe (632.8 nm), with approximately 10 mW of power. Raman spectroscopy analysis was conducted to evaluate the degree of graphitization of materials produced. From Raman spectra the ratio of ID / IG bands were determined. Band D is usually found in the range of 1330–1340 cm− 1 and is linked to sp3 carbon that is not present in graphene layers whereas band G in 1580 cm− 1 is linked to sp2 carbon that is present in graphene layers. A lower ID / IG ratio implies a carbon product having high graphitization, having higher amount of graphene (or graphene oxide) and a more orderly graphite structure. Measurement of oxygen content

[0090] The oxygen content is defined as the weight percentage of oxygen atoms in the obtained carbon product divided by the weight of the carbon product, wherein the weight of the oxygen atoms iscalculated from the mole percentage Oxygen atoms. The oxygen content is measured by elemental analysis. A Flash 2000 (Interscience) instrument was employed to analyze the elemental composition (C, H, and O mass fraction) of solid carbon samples. In this analysis, the samples were completely oxidized in O2 and the [C], [H] mass fraction were calculated directly based on the amount of CO2 and H2O formed, and the [O] mass fraction was obtained by difference Measurement of methylene blue (MB) number

[0091] A standard MB curve is measured as follows: Weigh 0, 2, 4, 6, 8, 10 g of a methylene blue solution (1mg / g) in a 15 ml vial and fill it up with D-water to a total weight of 10g and homogenize it; measure the transmission on a photometer (520nm) in a cuvette and plot the transmission against the methylene blue concentration to get the standard curve.

[0092] A carbon product is measured as follows: Weigh 10 mg (d.b.) of carbon material into a 10 ml glass tube; add 10 g of methylene blue solution and a mini magnetic stirrer; Stir for 24 hrs. Weigh 200 mg of sample solution in a cuvette through a Syringe filter (0.45 micron); add Demi water until the content of cuvette is 4.0 gram and homogenize the content of cuvette; measure the % Transmission on Photometer (520nm) against demi water as blank(100%T). The amount of MB remaining (g / g) is read on the X-axis of the standard curve. The methylene blue (MB) number is calculated as MB number (mg / g) = m(1000-C) / (A*B / 100) wherein A = g Carbon sample B = wt% solids Carbon sample (120ºC / 2 hrs) and C = Amount of MB remaining in solution read from the standard curve(mg). Measurement of Iodine number

[0093] The Iodine number is measured according to ASTM D 4607.

[0094] The methylene blue number and the iodine number determination are simple measurements that can be used for estimation of surface area and pore volume of activated carbons. The methylene blue molecule is relatively big and is mainly adsorbed in mesopores. However, a small portion is also found in larger micropores. The smaller iodine molecule makes penetration in micropores possible. A high methylene blue number implies a high volume and surface area in mesopores. A high iodine number implies a high volume and surface area in micropores. The surface area, the micropore volume and the total pore volume of activated carbons can be estimated by iodine and methylene blue numbers using multiple regression as demonstrated by Cleiton A. Nunes e Mário C. Guerreiro in Quim. Nova, Vol.34, No.3, 472-476, 2011 with the title: “ESTIMATION OF SURFACE AREA AND PORE VOLUME OF ACTIVATED CARBONS BY METHYLENE BLUE AND IODINE NUMBERS”. Measurement of yield

[0095] The carbon yield CY is defined as the measured weight of dried carbon product divided by the calculated weight of carbon in the carbon containing start material from which the carbon product is obtained. Measurement of the concentration of zinc in the filtrate

[0096] The concentration of zinc in the filtrate was measured with a titration with EDTA 0.1N with Eriochrome black-T as indicator. Procedure: Transfer zinc solution to Erlenmeyer flask. Dilute to about 100 mL with distilled water, add 1 g of NH4Cl, and bring the pH to 9.5-10.0 with Amonia 5% Add a pinch of Eriochrome Black T ground with sodium chloride (100 mg of indicator plus 20 g of analytical grade NaCl). Titrate with EDTA solution till the color changes to blue and calculate the moles of Zinc ions. Measurement of Conductivity

[0097] 1-2 gram of Carbon sample is placed into the vertical PVC tube with a steel plate as bottom. Then the bolt is screwed through the nut compacting the carbon sample between the steel plate bottom and the bolt. The bolt is tightened by hand until hand locked. Then the electrical resistance, length and diameter of the Carbon bed is measured. The Conductivity in S / m is calculated with the formula below. Conductivity(S / m) = L / ((R1-R0)*3.14*(d / 0.5)2) L= length of compressed carbon bed d= diameter of compressed carbon bed R1= Electrical resistance of compressed carbon bed R0=Electrical resistance of nut and bolt without carbon bed Materials used

[0098] ZnCl2 (from Sigma, 31650-M); Cellulose (from Sigma C6288); graphene oxide (from Merck 763705); graphite flakes (from Sigma, 332461). Preparation of ZnCl2hydrate molten salt solvent.

[0099] The ZnCl2 hydrate molten salt solvent was prepared by adding 80g of anhydrous ZnCl2 to 20 g of demineralized water. Obviously the ZnCl2hydrate salt becomes a molten salt only after heating to a temperature above the melting temperature. The ZnCl2hydrate salt can be mixed with the carbon containing material before heating above the melting temperature or the ZnCl2 hydrate salt is heated to form the molten salt solvent and then mixed with the carbon containing material. Comparative Examples CA - CB

[0100] Comparative example CA and CB are Raman measurements on commercially available samples: CA: crystalline layered carbon (Pure Graphite from Sigma, 332461) and CB: amorphous carbon (from Kuraray) was measured with as described above.

[0101] Comparative examples CA and CB show the boundaries of a very high and very low degree of graphitization (DOG) of commercial “pure” graphite having DOG = 0.88 and “amorphous” active carbon having DOG = 0.33. The DOG value is expected to range between that of the “pure” graphite and amorphous carbon, so the higher the DOG the more it looks like pure graphite. It is a qualitative value of the amount of graphite formed in the carbon product but is not to be taken quantitative.Comparative Examples CD – CE

[0102] Comparative examples CD – CE represent data taken from literature described above: Ref 1 is Dohyung Kang, Ref 2 is Perondi, Ref.3 is Deepti Krishan. These prior art references also describe graphitisation processes and report Raman measurements from which the DOG can be derived (wherein DOG is 1 / (1+Id / Ig)). Prior art Ref 1 describes carbonisation of methane in eutectic salts at extremely high temperatures and very long times resulting in low CY and low DOG. Prior art Ref 2 describes carbonisation of cellulose in eutectic salts in an oven. Despite the high temperatures and very long time the carbon yield CY is low and the DOG is not very high. Prior art Ref 3 describes Graphene Oxide Assisted carbonisation of cellulose by microwave heating without use of a salt. The graphene oxide is too expensive to be practically feasible and nevertheless the CY was only 10 wt% which is very low compared to the present invention and the conductivity is low compared to obtained values of the measured carbon products of the invention. Example Ex1

[0103] A reaction mixture was prepared by mixing 8 g of Glucose was mixed with 100g of ZnCl2- hydrate (80% ZnCl2), in an autoclave reactor of 200 ml, under a nitrogen blanket. The reactor was heated to 175ºC in 30 min and kept on that temperature for 30 min. Then it was cooled down to a temperature below 70ºC in 30 min. The reaction product was washed and filtered with excess of demi water acidified (pH<4) with HCl until the concentration of zinc detected in the filtrate was below 1 mg / l.

[0104] The carbon products obtained in the (comparative) examples were measured using the above-described measurement methods for ID / IG to determine the degree of graphitization (DOG), the oxygen content OC and the carbon yield CY. In all examples, demi water was used. The results are summarized in Table 1. Example Ex2

[0105] A reaction mixture was prepared as in Ex1 except that also 10 mg of Graphene oxide was added to the mixture. The mixture was carbonized, cooled and washed as in Ex1, except that the reactor was heated to 190ºC in 30 min and kept on that Temperature for 300 min. Example Ex3

[0106] Reaction mixture was prepared as in Ex1 except that 8 g cellulose was used as the carbohydrate starting material. Examples Ex4 - 9

[0107] Reaction mixtures were prepared as in Ex1 with different carbon containing starting materials and variations in temperatures and times as indicated in table 1. Cellulose –C in examples 5 and 11 is highly crystalline cellulose which is cellulose form which the amorphous phase has been selectively removed. Ex5 compared to Ex6 shows that higher crystallinity provides higher DOG. Ex7compared to Ex6 shows that 175ºC instead of 150ºC provides higher DOG, but higher temperatures do not necessarily result in higher DOG. Examples Ex10 - 12

[0108] Reaction mixtures were prepared as in Ex1 using hydrated ZnCl2 salt except that the mixture was heated at the indicated temperature by heating in a microwave as indicated in table 1. Example Ex13

[0109] A reaction mixture was prepared from 3,2 g sawdust as the carbohydrate containing starting material, 32 g ZnCl2salt and 8g water. The mixture was put in an autoclave and heated up to 250ºC in 30 minutes and after that heated for an additional 120 minutes. The carbon product was separated by adding demi water (acidified to pH<2 with HCl) and washed in a soxthlet extraction apparatus until the concentration of zinc detected in the filtrate was below 1 mg / l and then dried. The carbon yield was no less than 70 wt% and the DOG was 0.69. The I number and MB number were 395 and 264 respectively indicating a good porosity. Example Ex14

[0110] A reaction mixture was prepared from 8 g cotton linter as the carbohydrate containing starting material, 55 g ZnCl2salt, 15g FeCl3salt and 22g water. The mixture was put in an autoclave and heated up to 170ºC in 60 minutes and after that heated for an additional 60 minutes and separated, washed and dried as described in Ex13. The carbon yield was no less than 68.6 wt%. The I number and MB number were 450 and 328 respectively indicating a good porosity. Example Ex15

[0111] A reaction mixture was prepared from 8 g cotton linter as the carbohydrate containing starting material, 80 g ZnCl2salt and 20g water. The mixture was put in a microwave autoclave and heated up to 170ºC in 10 minutes and after that heated for an additional 30 minutes and separated, washed and dried as described in Ex13. The carbon yield was no less than 80.0 wt%. The I number and MB number were 330 and 276 respectively indicating a reasonable good porosity. Comparative Example CEx16

[0112] A reaction mixture was prepared from 8 g cotton linter as the carbohydrate containing starting material, 60 g ZnCl2 salt and 40g water acidified to a pH below 2. The mixture was put in a microwave autoclave and heated up to 170ºC in 10 minutes and after that heated for an additional 30 minutes and separated, washed and dried as described in Ex13. The product was tar-like substance that was difficult to filter and the filtrate was brownish. The carbon yield was 79.4 wt%. The I number and MB number were 130 and 74 respectively indicating a very low porosity.Table 1 EXP sample carbonisation method DOG OC CY(%) (wt%) CA Pure Graphite Commercial product 0.88 CB Active Carbon Commercial product 0.33 CC CH4 (Ref.1)* MnCl / KCl @ 1050C 5 hr 0.42 30 CD1 cellulose (ref.2) pyrolytic / 700- 900C / 1hr 9.6-24 CD2 cellulose (ref.2)1FeCl / 6ZnCl / 700C / 1 hr0.49 33.4CD3 cellulose (ref.2)1FeCl / 6ZnCl / 800C / 1hr0.46 7.3CE Cellulose / GO (ref.3) 350C / MW 4 10 Ex1 Glucose ZnCl hydr / 175C / 30m 0.53 30 45-50 Ex2 Glucose / GO ZnCl hydr / 175C / 30m 0.63 28 Ex3 cellulose ZnCl hydr / 175C / 30m 0.69 30 45-50 Ex4 cellulose ZnCl hydr / 175C / 60m 0.68 60 Ex5Cellulose - CZnCl hydr / 170C / 60m 0.74 60Ex6 glucose ZnCl hydr / 150C / 30m 0.63 71 Ex7 glucose ZnCl hydr / 175C / 30m 0.78 Ex8 glucose ZnCl hydr / 200C / 30m 0.64 Ex9 glucose ZnCl hydr / 250C / 30m 0.65 45 Ex10 cellulose ZnCl hydr / 175C / 30m / MW 0.61 31 Ex11 Cellulose-C ZnCl hydr / 170C / 30m / MW 0.59 Ex12 Glucose ZnCl hydr / 175C / 30m / MW 0.65 Ex13 sawdust ZnCl hydr / 250C / 120m 0.69 70 Ex14 Cotton linter Zn / Fe-Cl hydr / 170C / 60m 0.69 68.6 Ex15 Cotton linter ZnCl hydr / 170C / 30m 80.0 CEx16** Cotton linter ZnCl hydr / 170C / 30m 79.4 *ref 1 is Dohyung Kang, ref 2 is Perondi, ref.3 is Deepti Krishan publications described above **: 40% water used: the product was tar-like substance that was difficult to filter and the filtrate was brownish.

[0113] The Examples Ex1 – Ex12 done at our laboratory show that the process of the invention compared to the prior art can operate at lower temperatures with higher carbon yield, without necessarily having to use expensive graphene oxide seeding. Furthermore, the obtained carbon according to the invention contains a high oxygen content, which is perceived as beneficial adsorption properties and because it is considered more easy to exfoliate. The MB and I numbers shows considerable porosity in mesopores and in micropores. The carbon yield in the above-mentioned examples according to the invention is 45wt% or much higher, which is much higher than the prior art processes (ref 2). The high carbon yield implies a low carbon loss, so it means low emission of CO2, which is desirable in view of global warming. The carbon products of the invention have a higher DOG than the prior art (ref 2) even though the carbonisation temperatures are much lower. Ex13 to Ex15 shows that natural carbohydrate sources saw-dust and cotton can be used.

Claims

WHAT IS CLAIMED IS:

1. A process for the preparation of a carbon product having a high degree of graphitization, comprising the steps of a. contacting a carbon containing starting material with a molten salt i. wherein the carbon containing starting material is a carbohydrate containing starting material, ii. wherein the molten salt comprises one or more hydrated salts selected from the group consisting of ZnCl2, MnCl2, FeCl3, AlCl3, MgCl2, CaCl2 and SbCl2, b. carbonising the carbon containing starting material in mixture with the molten salt to form a carbon product; i. by heating at temperatures between 100 and 300°C, preferably between 125 and 275°C, more preferably between 150 and 250°C, ii. in a closed reactor system, iii. in an atmosphere free of oxygen (O2), forming the carbon product having a degree of graphitization DOG of at least 45% wherein degree of graphitization is defined as Ig / (Id+Ig) wherein Ig and Id are respectively Raman adsorption intensities in band G at 1580 cm− 1and Band D in the range of 1330–1340 cm−1, c. separating the carbon product from the molten salt, d. optionally washing the separated carbon product, e. optionally drying.

2. The process according to claim 1, wherein the one or more hydrated salts comprise at least 50 wt.%, preferably at least 70 wt% more preferably at least 90 wt% and most preferably at least 95 wt% ZnCl2relative to the total amount of salts in the hydrated salt, with the remainder of the salts preferably being AlCl3, MnCl2, SbCl3, MgCl2, CaCl2 or FeCl3, most preferably FeCl3.

3. The process according to claim 1 or 2, wherein the hydrated salt comprises water in an amount up to 30 wt% relative to the weight of the hydrated salt.

4. The process according to anyone of claims 1 - 3, wherein in carbonisation step b) the carbohydrate containing start material is heated in the molten hydrated salt in the closed reactor system using external heating, preferably in a closed reactor provided with a condenser to cool, condense and collect gasses formed or in an autoclave.

5. The process according to anyone of claims 1 - 4, wherein the amount of the carbohydrate containing starting material relative to the total weight of the carbohydrate containing starting material and the hydrated molten salt is between 1 and 30 wt.%, preferably between 2 and 20 wt%, more preferably between 5 and 15 wt%.

6. The process according to anyone of claims 1 - 5, wherein a carbon seed material, preferably graphene-oxide or carbon black, is added to the carbon containing start material as a seed for carbonisation, wherein preferably the carbon seed material is the carbon product obtained by the process of claim 1 that is in part recycled to the process step a) or b).

7. The process according to anyone of claims 1 - 6, wherein the heating in step b) is done by microwave or inductive heating and wherein preferably in step a) a microwave absorbing material, preferably a conductive carbon material, more preferably carbon black, is provided and in step b) the heating is done using microwave heating, a. wherein preferably the weight ratio of microwave absorbing material and molten hydrated salt is between 0.05 and 0.5, preferably between 0.18 and 0.3 and more preferably between 0.15 and 0.25, b. wherein preferably the microwave absorbing material is the carbon product obtained by the process of claim 1 that is in part recycled to the process step b).

8. The process according to anyone of claims 1 to 7, wherein the carbohydrates containing starting material is wood, saw-dust, paper, cotton or empty fruit bunch, preferably finely comminuted.

9. The process according to anyone of claims 1 to 8, wherein the carbon containing starting material comprises one or more carbohydrates selected from the group consisting of monosaccharides, oligosaccharides and poly-saccharides, preferably cellulose or glucose or mixtures thereof and preferably in an amount of at least 50, 70, 80 or even at least 90 wt% relative to the total weight of the carbon containing starting material.

10. The process according to anyone of claims 1 - 9 wherein in step c) the carbon product is separated from the molten hydrated salt by addition of a coagulant selected from the group consisting of water, ketones or alcohols or combinations thereof, preferably water.

11. The process according to anyone of claim 10, wherein the coagulant is water and the separated carbon product is washed with water to wash out the salt, wherein preferably the separating and washing is done in one step by refluxing in water in a Soxhlet type of extraction, optionally followed by drying.

12. The process according to claim 11, wherein the washing is stopped before completely removing the salt to intentionally leave a residual amount of the salt in the formed carbon product, wherein optionally the residual salt is converted to it’s metaloxide and / or metal hydroxide, preferably by addition of a strong base, which preferably is KOH or NaOH, wherein the amount of residual salt is between 0.01 – 20 wt%, preferably 0.02 – 15 wt%, more preferably 0.5 – 10 wt% of the total weight, and wherein more preferably the residual salt is ZnCl2and / or ZnCl2converted to ZnO and / or Zn(OH)2.

13. The process according to anyone of claims 1 - 12, wherein after separation step c) and washing step d) the carbon product is either a. not dried to obtain a wet carbon gel product, or b. dried by freeze drying to obtain a dry carbon gel product, or c. dried by heating, preferably at a temperature between 80 and 120 ºC, to obtain a carbon powder product.

14. The process according to anyone of claims 1 – 13, wherein the obtained carbon product comprises an oxygen atom content between 20 and 40 wt% and a DOG of at least 45%, preferably at least 55%, more preferably at least 60% and even more preferably at least 65%.

15. The process of anyone of claims 1 - 14 wherein the carbon product obtained is functionalized in further steps; - a functionalization step wherein the carbon product is modified to contain one or more heteroatoms, preferably sulfur, nitrogen or metals, and / or - a step to reduce the oxygen content, preferably by heating, optionally with reducing agent wherein the surface area and / or oxygen content can be reduced for example for enhancing electrical conductivity.

16. The process according to claim 15, wherein the carbon product comprising an oxygen atom content between 20 and 40 wt% and a DOG of at least 45%, preferably at least 55%, more preferably at least 60% and even more preferably at least 65%, is optionally exfoliated, and is further subjected to a mild treatment to reduce the oxygen content to an oxygen content below 20 wt%, preferably below 15 wt%, more preferably below 10 wt% and most preferably below 5 wt%.

17. The process according to claim 16, wherein the mild treatment to reduce oxygen content is chemical reduction, thermal reduction, hydrothermal / solvothermal reduction, electrochemical reduction or photocatalytic reduction.

18. The process according to claim 17, comprising heating the separated, washed and dried carbon product to a temperature above 200°C, preferably above 250°C, more preferably above 300°C, in oxygen free atmosphere in an oven or by microwave heating.

19. The process according to anyone of claims 1 - 18, wherein the carbon yield CY of the obtained carbon product, defined as the dry weight of the carbon product relative to the theoretical amount of carbon in the carbon containing starting material, is at least 40 wt%, preferably at least 50 wt% more preferably least 60, or even at least 70 wt%.

20. A carbon product obtainable by the process according to anyone of claims 1 – 14 having a DOG of at least 55%, more preferably at least 60% and even more preferably at least 65% and having an oxygen atom content between 20 and 40 wt%, and preferably having at least 55 wt% carbon atoms and between 3.0 and 6.0 wt% Hydrogen atoms.

21. The carbon product of claim 20 having an I-number between 100 and 700, preferably between 200 and 500 and an MB-number between 150 – 500 preferably between 200 and 400.

22. A carbon product obtainable by the process according to anyone of claims 15 – 19 having an oxygen atom content below 20 wt%, preferably below 10 wt%, more preferably below 5 wt% and most preferably below 3 wt%.

23. Use of the carbon product according to anyone of claims 10 – 22 as a precursor for the manufacture of Carbon Fibers, Graphene and Graphene Oxide, for the manufacture of electrode materials or electrodes or for the manufacture of absorbents.