Pellets, process for their production, and use thereof

Abstract

The present invention reveals a novel solid fuel in the form of pellets made from comminuted lignocellulosic energy crops materials: Spanish broom (Spartium junceum L.), giant miscanthus (Miscanthus x giganteus), Virginia mallow [Sida hermaphrodita (L.) Rusby], giant reed (Arundo donax L.), and / or waste materials from these plants, and concentrated black liquor or concentrated and dried black liquor obtained as a side-product from the production of lignocellulose fibers from said plants by the citric acid / hydrogen peroxide-based process, as well as the process for the production of said pellets. The pellets are characterized by ash content ≤7% w / w, sulfur content ≤0.08% w / w, and an intrinsic energy value of 16.00-19.50 MJ / kg. The pellets according to the present invention are used as an environmentally friendly and renewable solid fuel or starting material for manufacturing various renewable chemicals in biorefineries.

Description

[0001] PELLETS, PROCESS FOR THEIR PRODUCTION, AND USE THEREOF

[0002] DESCRIPTION

[0003] Field of Invention

[0004] The present invention relates to novel pellets as environmentally friendly and renewable solid fuel, the process of their production, and the use thereof.

[0005] Technical problem

[0006] The technical problem that is solved by the present invention includes :

[0007] (i) the production of environmentally friendly and renewable solid fuel in the form of pellets;

[0008] (ii) the production of thermal energy from solid fuels with reduced sulfur dioxide (SO2) emission; and production of residual ash; as well as

[0009] (iii) the use of two important waste materials from agriculture and related industries : waste small (<1 mm) cellulose fibers and fines; and the black liquor (BL) ; both side-products from the manufacturing processes of lignocellulose fibers from energy crops.

[0010] Thus the defined complex technical problem was solved by novel pellets as a solid fuel, which is based on Spanish broom (Spartium junceum L. ) , giant miscanthus (Miscanthus x giganteus) , Virginia mallow [Sida hermaphrodita (L. ) Rusby] , and giant reed Arundo donax L. ) , their waste small (<1 mm) cellulose fibers and fines (particles <0.2 mm) , as well as their specific BL obtained via citric acid-hydrogen peroxide ( H2O2 ) -mediated process for the production of lignocellulose fibers from energy crops. Prior Art

[0011] Biomass and its derivatives are a renewable energy source, which can, after processing, replace fossil fuels. Besides the use of biomass for energy production, it provides environmentally friendly waste management from agriculture and several related industries . Biomass can be converted to energy by different processes, depending on the quality of starting biomass, required energy type, use manner, environmental standards, economical possibilities, etc. One of the simplest solutions is the use of biomass is its conversion to pellets that can be directly employed as an environmentally sustainable and renewable solid fuel. The technology of biomass pelleting requires prior appropriate preparation of a mixture that would result in physical and chemical composition which would meet the corresponding technical standard. Briefly, typical pellets are of a cylindrical shape of diameter 6-8 mm, length 10-20 mm, density 1,000-1,200 kg / m3, and bulk density 550-700 kg / m3, see literature references 1 and 2:

[0012] 1) EN 14961-1:2020. Solid biofuels - Fuel specifications and classes - Part 1: General requirements; available at the link here: https : / / standards .iteh.ai / catalog / standards / cen / fcll2352-281a- 4465-9034-be81d919fab6 / en-14961-l-2010

[0013] 2) S. R. Chandrasekaran, P. K. Hopke, L. Rector, G. Allen, L. Lin: Chemical Composition of Wood Chips and Wood Pellets, Energy & Fuels 26 (2012) 4932-4937.

[0014] In the first instance, the pelletizing of energy crops biomass ensures a higher bulk density, which makes biomass more convenient for storage and transport, and facilitates its use in furnaces.

[0015] The pelletizing technology, including the biomass from energy crops is generally well-established and widely described in the technical, scientific, and patent literature. Briefly, the technology includes: the drying of starting material down to the moisture content of 13-15% w / w, biomass shredding down to 1-2 mm particle size, homogenization, pellet pressing (pelletizing) , and cooling the obtained pellets to avoid potential spontaneous ignition, see literature references 3-5 :

[0016] 3) A. Jasinskas, V. Kleiza, D. Streikus, R. Domeika, E.

[0017] Vaiciukevicius , G. Gramauskas, M. T. Valentin: Assessment of Quality Indicators of Pressed Biofuel Produced from Coarse Herbaceous Plants and Determination of the Influence of Moisture on the Properties of Pellets, Sustainability 14 (2022) 1068;

[0018] 4) A. Lisowski, M. Dgbrowska-Salwin, E. Ostrowska-Ligpza, A. Mawrocka, M. Stasiak, A. Swiptochowski , J. Klonowski, M. Sypula, B. Lisowska: Effects of the biomass moisture content and pelleting temperature on the pressure-induced agglomeration process, Biomass Bioenergy 107 (2017) 376-383; and

[0019] 5) J. Styks, A. Knapczyk, B. Lapczyhska-Kordon : Effect of Compaction Pressure and Moisture Content on Post-Agglomeration Elastic Springback of Pellets, Materials 14 (2021) 879.

[0020] Besides wood-based biomass, the use of herbaceous energy plants as starting material is an especially important strategy for the sustainable production of pellets and renewable energy. In this strategy, many different energy crops have been studied with certain success. Among them, giant miscanthus (Miscanthus x giganteus) is probably the most studied energy crop, but Virginia mallow [Sida hermaphrodite (L. ) Rusby] , and giant reed Arundo donax L. ) , and cup plant (Silphium perfoliatum L. ) have also shown a great perspective due to lower heating values (LHV) around 16-18.5 MJ / kg, see literature references 2 and 6-11:

[0021] 6) Z. Kovacevic, V. Jurisic, M. Grubor, A. Matin, Tajana Kricka, S.

[0022] Bischof: Spanish broom (Spartium junceum L. ) Feedstock for bioplastic and bioenergy industry, Holistic Approach Environ . 9 (2019) 44-52;

[0023] 7) T. Kricka, A. Matin, N. Bilandzija, V. Jurisic, A. Antonovic, N. Voca, M. Grubor : Biomass valorisation of Arundo donax L., Miscanthus x giganteus and Sida hermaphrodite for biofuel production, Int. Agrophys. 31 (2017) 575-581;

[0024] 8) E. Jensen, P. Robson, K. Farrar, S. T. Jones, J. Clifton-Brown, R. Payne, I. Donnison: Towards Miscanthus combustion quality improvement: the role of flowering and senescence, GCB Bioenergy 9 (2017) 891-908;

[0025] 9) R. Molas, H. Borkowska, B. Sawicka: Long-term study on utilization of Virginia fanpetals - a valuable biomass, Agronomy Sci . 76 (2021) 97-116;

[0026] 10) J. Dahl, I. Obernberger: Evaluation of the combustion characteristics of four perennial energy crops (Arundo donax, Cynara cardunculus , Miscanthus x giganteus , and Panicum virgatum) , 2ndWorld Conference on Biomass for Energy, Industry and Climate Protection, 10-14 May 2004, Rome, Italy; available at the link here: https : / / www . researchgate . net / publication / 228722637 Evaluation of the combustion characteristics of four perennial energy crops A rundo donax Cynara cardunculus Miscanthus x giganteus and Panicu m virgatum and

[0027] 11) Pellets & Briquettes from Arundo; an article available on at the link here: https: / / arundobioenergy.com / pellets-and-briquettes /

[0028] Spanish broom (Spartium junceum L. ) has been studied as a source of highly valuable cellulose fibers for advanced composites with bioplastic, e.g., see literature reference 6. The manufacturing of lignocellulose or cellulose fibers from lignocellulose feedstock generally includes some type of delignification technology, where all or most of the lignin and hemicellulose present in the starting material are removed into the liquid fraction usually called the black liquor, yielding more or less pure cellulose fibers . This black liquor fraction typically contains water-soluble lignin- and hemicellulosedegradation products as well as chemicals employed or the delignification technology .

[0029] One very specific type of black liquor ( BL ) is manufactured by citric acid ( CA) -hydrogen peroxide ( H2O2 ) -mediated production of lignocellulose fibers from energy crops that has been recently developed for the processing of feedstock such as mentioned giant miscanthus and giant reed, or their mixtures .

[0030] CA

[0031] This specific BL, besides water-soluble lignin and hemicellulose degradation products , contains a certain amount of citric acid remaining from the delignification process , see literature reference 12 :

[0032] 12 ) HR patent application P20231398A; Process for manufacturing lignocell ulose fibers from energy crops, inventors : S . Bischof , Z . Kovacevic , T . Kricka , N . Bilandzij a ; applicant : Sveuciliste u Zagrebu Tekstilno-tehnoloski fakultet .

[0033] Apart from the black liquor, a side product of every delignification and accompanying process is also a waste of small ( <1 mm) cellulose fibers and fines ( <0 . 2 mm) that cannot be successfully used for the manufacturing of bioplastic composites . This small (<1 mm) cellulose fiber fraction and fines represent an important waste resource that needs to be converted to some valuable product or energy . The economic and environmentally friendly utilization of black liquor from different delignification technologies as well as a waste of small (<1 mm) cellulose fibers and fines (<0.2 mm) represent open technical problems for which no successful solutions have been found up to date.

[0034] The present invention solves the technical problem of the conversion of waste small (<1 mm) cellulose fiber and fines (<0.2 mm) into valuable, environmentally-f riendly, and fully renewable biofuel in the form of pellets with the use of the specific black liquor obtained by the delignification technology of giant miscanthus {Miscanthus x giganteus) and giant reed {Arundo donax L. ) by a specific citric acid / hydrogen peroxide-based production of lignocellulose fibers . The defined technical problem is solved in a new and inventive manner as will be disclosed in section Detailed description of the invention.

[0035] Summary of the Disclosure

[0036] The present invention discloses the pellets, for use as an environmentally friendly and renewable solid fuel, where said pellets are cylindrically shaped with a moisture content of less than 10% w / w, comprising :

[0037] (i) comminuted lignocellulosic materials selected from the group consisting of: Spanish broom {Spartium junceum L. ) , giant miscanthus Miscanthus x giganteus') , Virginia mallow [Sida hermaphrodite (L. ) Rusby] , giant reed {Arundo donax L. ) , and / or waste materials from these plants, or mixtures of these materials, in the amount of 50.0-99.5% w / w, and

[0038] (ii) concentrated black liquor, or concentrated and dried black liquor, obtained as a side-product from the processing of said plants by the citric acid (CA) / hydrogen peroxide (H2O2) -based process for the production of lignocellulose fibers, in the amount of 0.5-50.0% w / w,

[0039] CA where the said pellets have an ash content of less than 7.00% w / w, a sulphur content of less than 0.08% w / w, and an intrinsic energy value of 16.0 - 19.50 MJ / kg.

[0040] The concentrated black liquor used in the pellets according to the present invention is an aqueous solution that contains: (a) solubilized lignin and hemicellulose-degradation products in the amount of 5-50% w / w, and (b) citric acid (CA) in the amount of 10-20% w / w, with a residual water content of not more than 30% w / w.

[0041] Alternatively, concentrated and dried black liquor used for the preparation of the pellets according to the present invention, contains: (a) solubilized lignin and hemicellulose-degradation products in the amount of 50-90% w / w, and (b) citric acid (CA) in the amount of 10-50% w / w, with a residual water content of not more than 10% w / w.

[0042] The waste material from said plants that are employed as a starting lignocellulosic material is selected from the group consisting of waste fibers smaller than 1 mm, fine cellulosic particles able to pass through 200 mesh-screen or mixtures of these materials.

[0043] In a preferred embodiment of the present invention, the weight percentage of ingredient (i) is 75-99% w / w, preferably 90-98%, and ingredient (ii) is 1-25% w / w, preferably 2-10% w / w.

[0044] The pellets according to the present invention can be prepared by the process which includes the following preparation steps:

[0045] A. optional pre-drying of plant materials selected from the group consisting of: Spanish broom (Spartium junceum L. ) , giant miscanthus (Miscanthus x giganteus) , Virginia mallow [Sida hermaphrodita (L. ) Rusby] , giant reed (Arundo donax L. ) , or mixtures of these plants, and / or waste material from these plants, with a moisture content of less than 20% w / w, preferably of 16- 18% w / w,

[0046] B. comminution said plant materials down to the average particle size within the range of 3-5 mm which constitutes 70% w / w, where the rest of particles have size out of the said range,

[0047] C. mixing of one or more plant materials from step B with concentrated black liquor (CBL) , or concentrated and dried black liquor (DBL) , or a mixture thereof, at temperatures between 5- 100°C during 1-15 minutes,

[0048] D. conditioning of thus obtained mixture by standing at a temperature between 5-100°C during 5-30 minutes,

[0049] E. pelletizing of thus obtained mass in the pellet press to pellets at a temperature between 20-150°C and pressure 100-350 MPa, yielding the pellets,

[0050] F. optionally, spraying the hot pellets with an additional amount of CBL (ii) ,

[0051] G. optionally, drying the pellets down to not more than 10% w / w of residual moisture content, and

[0052] H. cooling the pellets down to a temperature between 20-30°C, yielding the pellets according to the present invention.

[0053] In a preferred embodiment of this invention, the mixture in step C is composed of concentrated black liquor (CBL) in the amount of not less than 80% w / w, and concentrated and dried black liquor (DBL) in the amount of not more than 20% w / w. In a further preferred embodiment of this invention, the process parameters in Step C are selected in a way that mixing is conducted at a temperature between 5-25 °C during 1-5 minutes, in Step D the conditioning is maintained at a temperature between 60-100°C during 5-20 minutes, and in Step E the pelleting is performed at a temperature between 60-100°C and a pressure of 120-300 MPa.

[0054] Yet in an additional preferred embodiment of this invention, the optional step F is executed if the overall amount of concentrated black liquor (CBL) is greater than 10% w / w, when 10% w / w of said CBL is added in step C, while the excess is applied in step F.

[0055] In an additional preferred embodiment of this invention, the optional step G is executed if the overall content of said ingredient (ii) is higher than 15% w / w in the final pellets - when then the drying of hot pellets has to be conducted.

[0056] Detailed Description of the Invention

[0057] The present invention reveals the pellets, for use as an environmentally friendly and renewable solid fuel, where said pellets are cylindrically shaped with a moisture content of less than 10% w / w, comprising :

[0058] (i) comminuted lignocellulosic materials selected from the group consisting of: Spanish broom (Spartium junceum L. ) , giant miscanthus (Miscanthus x giganteus) , Virginia mallow [Sida hermaphrodita (L. ) Rusby] , giant reed Arundo donax L. ) , and / or waste materials from these plants, or mixtures of these materials, in the amount of 50.0-99.5% w / w, and

[0059] (ii) concentrated black liquor (CBL) , or concentrated and dried black liquor (DBL) , obtained as a side-product from the processing of said plants by the citric acid (CA) / hydrogen peroxide (H2O2) -based process for the production of lignocellulose fibers, in the amount of 0.5-50.0% w / w,

[0060] CA where the said pellets have an ash content of less than 7.00% w / w, a sulfur content of less than 0.08% w / w, and an intrinsic energy value of 16.0 - 19.50 MJ / kg.

[0061] The concentrated black liquor (CBL) used in the pellets according to the present invention is an aqueous solution that contains:

[0062] (a) solubilized lignin and hemicellulose-degradation products in the amount of 5-50% w / w, and

[0063] (b) citric acid (CA) in the amount of 10-20% w / w, with a residual water content of not more than 30% w / w.

[0064] Alternatively, if concentrated and dried black liquor (DBL) is used for the preparation of the pellets according to the present invention, then it is characterized by:

[0065] (a) solubilized lignin and hemicellulose-degradation products in the amount of 50-90% w / w, and

[0066] (b) citric acid (CA) in the amount of 10-50% w / w, with a residual water content of not more than 10% w / w.

[0067] The waste material from said plants that are employed as a starting lignocellulosic material is selected from the group consisting of waste fibers smaller than 1 mm, fine cellulosic particles able to pass through 200 mesh-screen or mixtures of these materials.

[0068] In a preferred embodiment of the present invention, the weight percentage of ingredient (i) is 75-99% w / w, and ingredient (ii) is 1- 25% w / w. In a particularly preferred embodiment of the present invention, the weight percentage of ingredient (i) is 90-98% w / w, and ingredient (ii) is 2-10% w / w.

[0069] The pellets according to the present invention can be prepared by the process which includes the following preparation steps:

[0070] A. optional pre-drying of plant materials selected from the group consisting of: Spanish broom (Spartium junceum L. ) , giant miscanthus (Miscanthus x giganteus) , Virginia mallow [Sida hermaphrodita (L. ) Rusby] , giant reed Arundo donax L. ) , or mixtures of these plants, and / or waste material from these plants, with a moisture content of less than 20% w / w, preferably of 16- 18% w / w,

[0071] B. comminution said plant materials down to the average particle size within the range of 3-5 mm which constitutes 70% w / w, where the rest of particles have size out of the said range,

[0072] C. mixing of one or more plant materials from step B with concentrated black liquor (CBL) , or concentrated and dried black liquor (DBL) , or a mixture thereof, at temperatures between 5- 100°C during 1-15 minutes,

[0073] D. conditioning of thus obtained mixture by standing at a temperature between 5-100°C during 5-30 minutes,

[0074] E. pelletizing of thus obtained mass in the pellet press to pellets at a temperature between 20-150°C and pressure 100-350 MPa, yielding the pellets,

[0075] F. optionally, spraying the hot pellets with an additional amount of CBL (ii) , G. optionally, drying the pellets down to not more than 10% w / w of residual moisture content, and

[0076] H. cooling the pellets down to a temperature between 20-30°C, yielding the pellets according to the present invention.

[0077] In a preferred embodiment of this invention, the mixture in step C is composed of concentrated black liquor (CBL) in the amount of not less than 80% w / w, and concentrated and dried black liquor (DBL) in the amount of not more than 20% w / w.

[0078] In a further preferred embodiment of this invention, the process parameters in Step C are selected in a way that mixing is conducted at a temperature between 5-25 °C during 1-5 minutes, in Step D the conditioning is maintained at a temperature between 60-100°C during 5-20 minutes, and in Step E the pelleting is performed at a temperature between 60-100°C and a pressure of 120-300 MPa.

[0079] Yet in an additional preferred embodiment of this invention, the optional step F is executed if the overall amount of concentrated black liquor (CBL) is greater than 10% w / w, when 10% w / w of said CBL is added in step C, while the excess is applied in step F.

[0080] In an additional preferred embodiment of this invention, the optional step G is executed if the overall content of said ingredient (ii) is higher than 15% w / w in the final pellets - when then the drying of hot pellets has to be conducted.

[0081] To demonstrate an inventive step of this invention, the study of the preparation and key properties of the pellets according to the invention was performed. The model, control pellets were prepared from wheat (Triticum aestivum L. ) straw, see Example 1. These pellets are analyzed against fifteen (15) key parameters and the results are presented in Table 1. Table 1. Results of analysis of model (control) pellets made from wheat {Triticum aestivum L. ) straw, see Example 1. d.m. = expressed on a dry matter; HHV = higher heating value; LHV = lower heating value .

[0082] On the other hand, various options of comminuted plants selected from the group consisting of Spanish broom {Spartium junceum L. ) , giant miscanthus {Miscanthus x giganteus) , Virginia mallow [Sida hermaphrodita (L. ) Rusby] , and giant reed {Arundo donax L. ) and their corresponding fractions of waste small (<1 mm) cellulose fibers, as well as the corresponding concentrated black liquor fractions, have been used for the preparation of the pellets according to the present invention, see Examples 2-5. The products from these experiments were analyzed and the results are given in Table 2.

[0083] Table 2. Results of analysis of the pellets made from Spanish broom {Spartium junceum L. ) , giant miscanthus {Miscanthus x giganteus) , Virginia mallow [Sida hermaphrodita (L. ) Rusby] , and giant reed {Arundo donax L. ) according to the present invention, see Examples 2- 5.

[0084]

[0085] SBP = Spanish broom-based pellets; MGP = giant miscanthus-based pellets; VMP = Virginia mallow-based pellets; GRP = giant reed-based pellets; d.m. = expressed on a dry matter; HHV = higher heating value; LHV = lower heating value .

[0086] The results showed that pellets according to the present invention, in comparison to the control pellets made from wheat straw (Table 1) , exhibit :

[0087] (i) comparable or significantly higher HHV values, higher than 17.00-19.50 MJ / kg, and

[0088] (ii) significantly lower ash content, not less than 7.00% w / w,

[0089] (iii) with comparable low sulfur content, generally lower than 0.08% w / w.

[0090] Additionally, the pellets from the present invention showed drastically improved mechanical properties, e.g. , hardness parameter, which provides fewer fines during storage and transportation and thus reduces the risk of potential explosion hazard. Use of the pellets from the present invention

[0091] The pellets according to the present invention are used as an environmentally friendly and renewable solid fuel for the production of thermal energy.

[0092] Alternatively, according to the present invention are used as a starting material for the production of renewable chemicals in biorefineries .

[0093] Examples

[0094] General information

[0095] All quantitative pellet compositions are given as weight percentage (%) of the weight of a given ingredient to the total weight of the given pellet composition [% w / w] .

[0096] Room temperature (r.t. ) is referred to the temperature interval of 20-25 °C.

[0097] Pellets are prepared on a pilot pelletizing line consisting of a laboratory pellet press of type KHAL 14-175 of Amandus Kahl GmbH & Co. KG, Reinbek, Germany.

[0098] Analyses of the starting plant biomass and pellet samples are performed against the key parameter by the use of the standard analytical methods as follows: particles size distribution of starting plant biomass, EN ISO 17927-2; moisture, EN ISO 18134-2:2017; ash, EN ISO 18122:2015; coke, EN ISO 15148:2009; fixed carbon (Cfix) , by calculation; volatile matter, EN ISO 15148:2009; carbon (C) , hydrogen (H) , and nitrogen (N) contents, EN ISO 15104:2011; sulphur (S) content, EN ISO 15289:2011; oxygen (O) , by calculation; cellulose and hemicellulose content, NREL / TP-510-42623; lignin content, NREL / TP- 510-42618; as well as higher heating value (HHV) and lower heating value (LHV) , EN ISO 14918:2010; strength and hardness of pellets, EN ISO 16559:2022.

[0099] Abbreviations

[0100] CBL - concentrated black liquor; from the citric acid-H2O2-mediated process for the production of lignocellulose fibers from energy crops; see literature reference 12; contains NLT 70% dry matter and NMT 30% residual water

[0101] DBL - essentially dehydrated black liquor; from the citric acid- H2O2-mediated process for the production of lignocellulose fibers from energy crops; see literature reference 12; contains NLT 90% dry matter and NMT 10% residual water d.m. - a dry matter (expressed on a dry matter) GRP - giant reed-based pellets

[0102] HHV - higher heating value; represents the upper limit of the available thermal energy produced by the complete combustion of fuel; it is measured as a unit of energy per unit mass or volume of substance or fuel; expressed in [MJ / kg]

[0103] LHV - lower heating value; is another measure of available thermal energy produced by the combustion of fuel, however, in contrast to HHV, it considers energy losses such as the energy used to vaporize water; it is also measured as a unit of energy per unit mass or volume of substance or fuel; expressed in MJ / kg

[0104] MGP - giant miscanthus-based pellets

[0105] NMT - not more than

[0106] NLT - not less than

[0107] SBP - Spanish broom-based pellets

[0108] VMP - Virginia mallow-based pellets

[0109] % w / w - weight percentage [of a given ingredient (within the pellets) expressed on the total weight of the pellets]

[0110] Example 1. Control-1: Preparation of pellets made from wheat (Triticum aestivum L. ) straw Wheat straw (30.00 kg) of moisture content 12.00% w / w was milled in a laboratory hammer mill yielding a comminuted feedstock of particle size : average 3.15-5 mm, not less than 70% w / w, and

[0111] <3.15 mm and / or >5 mm, not more than 30% w / w.

[0112] Thus obtained feedstock was subjected to pelletized in a pilot pelletizing press at a temperature of 100-120 °C, a pressure of 150- 200 MPa, with a speed of 12-13 mm / min, and a hold time of around 10 seconds, to pellets of the following size: diameter 6 ± 1.0 mm and length (L) , 3.15 40 mm. The obtained pellets were left to cool to room temperature. The product was in the form of pale brown pellets.

[0113] The results of the analysis of these pellets are presented in Table

[0114] 1.

[0115] Example 2. Preparation of pellets made from Spanish broom (Spartium junceum L. ) according to the present invention

[0116] Spanish broom (Spartium junceum L. ; 28.50 kg; 95.00% w / w) of moisture content 11.00% w / w was milled in a laboratory hammer mill yielding a comminuted feedstock of particle size: average 3.15-5 mm, not less than 70% w / w, and

[0117] <3.15 mm and / or >5 mm, not more than 30% w / w.

[0118] To this comminuted feedstock, concentrated black liquor (CBL; 1.50 kg; 5.00% w / w) from the delignification of giant miscanthus (Miscanthus x giganteus) via the citric acid-H2O2-mediated process for production of lignocellulose fibers described in literature reference 12, with NMT 30% w / w water was added, and the resulting mixture was stirred for 20-30 o / min during 10 minutes. The mixture was left to stand at r.t. for 30 minutes.

[0119] Thus obtained feedstock was subjected to pressing in a pilot pelletizing press at a temperature of 100-120 °C, a pressure of 150- 250 MPa, with a speed of 12-13 mm / min, and a hold time of around 10 seconds, to pellets of the following size: diameter 6 ± 1.0 mm and length (L) , 3.15 40 mm. The obtained pellets were left to cool to room temperature. The product (about 30.00 kg) was in the form of pale brown pellets.

[0120] The results of the analysis of these pellets are presented in Table 2.

[0121] Example 3. Preparation of pellets made from giant miscanthus (Miscanthus x giganteus) according to the present invention

[0122] Giant miscanthus (Miscanthus x giganteus; 27.00 kg; 90.00% w / w) of moisture content 12.30% w / w was milled in a laboratory hammer mill yielding a comminuted feedstock of particle size: average 3.15-5 mm, not less than 70% w / w, and <3.15 mm and / or >5 mm, not more than 30% w / w.

[0123] To this comminuted feedstock, concentrated black liquor (CBL; 1.50 kg; 5.00% w / w) from the delignification of giant miscanthus via the citric acid-H2O2-mediated process for the production of lignocellulose fibers described in literature reference 12, with NMT 30% w / w water was added, and the resulting mixture was stirred for 20-30 o / min during 10 minutes. The mixture was left to stand at r.t. for 30 minutes .

[0124] Thus obtained feedstock was subjected to pressing in a pilot pelletizing press at a temperature of 100-120 °C, a pressure of 150- 250 MPa, with a speed of 12-13 mm / min, and a hold time of around 10 seconds, to pellets of the following size: diameter 6 ± 1.0 mm and length (L) , 3.15 40 mm.

[0125] Hot pellets were sprayed with an additional amount of the same type of CBL (1.50 kg; 5.00% w / w) , and the resulting moistened pellets were dried at 100-110 °C until the residual moisture content of NMT 10% w / w. The obtained pellets were left to cool to room temperature. The product (about 30.00 kg) was in the form of pale brown pellets. The results of the analysis of these pellets (MGP) are presented in

[0126] Table 2.

[0127] Example 4. Preparation of pellets made from Virginia mallow [Sida hermaphrodita (L. ) Rusby] according to the present invention

[0128] Virginia mallow [Sida hermaphrodita (L. ) Rusby; 28.50 kg; 95.00% w / w) of moisture content 11.20% w / w was milled in a laboratory hammer mill yielding a comminuted feedstock of particle size: average 3.15-5 mm, not less than 70% w / w, and <3.15 mm and / or >5 mm, not more than 30% w / w.

[0129] To this comminuted feedstock, concentrated black liquor (CBL; 1.50 kg; 5.00% w / w) from the delignification of giant reed (Arundo donax L. ) via the citric acid-LRCh-mediated process for the production of lignocellulose fibers described in literature reference 12, with NMT 30% w / w water was added, and the resulting mixture was stirred for 20-30 o / min during 10 minutes. The mixture was left to stand at r.t. for 30 minutes.

[0130] Thus obtained feedstock was subjected to pressing in a pilot pelletizing press at a temperature of 100-180 °C, a pressure of 180- 300 MPa, with a speed of 12-13 mm / min, and a hold time of around 10 seconds, to pellets of the following size: diameter 6 ± 1.0 mm and length (L) , 3.15 d L d 40 mm. The obtained pellets were left to cool to room temperature. The product (about 30.00 kg) was in the form of pale brown pellets.

[0131] The results of the analysis of these pellets (VMP) are presented in

[0132] Table 2.

[0133] Example 5. Preparation of pellets made from giant reed (Arundo donax L. ) according to the present invention Giant reed (Arundo donax L. ; 29.10 kg; 97.00% w / w) with moisture content of 13.72% w / w was milled in a laboratory hammer mill yielding a comminuted feedstock of particle size: average 3.15-5 mm, not less than 70% w / w, and

[0134] <3.15 mm and / or >5 mm, not more than 30% w / w.

[0135] To this comminuted feedstock, concentrated black liquor (CBL; 0.90 kg; 3.00% w / w) from the delignification of giant reed via the citric acid-H2O2-mediated process for the production of lignocellulose fibers described in literature reference 12, with NMT 30% w / w water was added, and the resulting mixture was stirred for 20-30 o / min during 10 minutes. The mixture was left to stand at r.t. for 30 minutes.

[0136] Thus obtained feedstock was subjected to pressing in a pilot pelletizing press at a temperature of 120-180 °C, a pressure of 150- 250 MPa, with a speed of 12-13 mm / min, and a hold time of around 10 seconds, to pellets of the following size: diameter 6 ± 1.0 mm and length (L) , 3.15 d L d 40 mm. The obtained pellets were left to cool to room temperature. The product (about 30.00 kg) was in the form of pale brown pellets.

[0137] The results of the analysis of these pellets (GRP) are presented in

[0138] Table 2.

[0139] Example 6. Preparation of pellets made from giant miscanthus and giant reed according to the present invention

[0140] Giant miscanthus (Miscanthus x giganteus; 25.50 kg; 85.00% w / w) of moisture content 11.32% w / w, was milled in a laboratory hammer mill yielding a comminuted feedstock of particle size: average 3.15-5 mm, not less than 70% w / w, and

[0141] <3.15 mm and / or >5 mm, not more than 30% w / w.

[0142] To this comminuted feedstock, waste small (<1 mm) cellulose fibers from giant reed (3.00 kg; 10.00% w / w; contained 9.50% w / w residual moisture) , and dehydrated black liquor (DBL; 1.50 kg; 5.00% w / w) from the delignification of giant miscanthus via the citric acid-H2O2~ mediated process for the production of lignocellulose fibers described in literature reference 12, with NMT 10% w / w water was added, and the resulting mixture was stirred for 20-30 o / min during 10 minutes. The mixture was left to stand at r.t. for 30 minutes.

[0143] Thus obtained feedstock was subjected to pressing in a pilot pelletizing press at a temperature of 120-180 °C, a pressure of 200- 250 MPa, with a speed of 12-13 mm / min, and a hold time of around 10 seconds, to pellets of the following size: diameter 6 ± 1.0 mm and length (L) , 3.15 40 mm. The obtained pellets were left to cool to room temperature. The product (about 30.00 kg) was in the form of pale brown pellets.

[0144] The results of the analysis of these pellets were closely similar to those for MGP whose preparation is described in Example 3.

[0145] Industrial Applicability

[0146] The present invention discloses a new type of pellets as an environmentally friendly solid fuel based on one specific waste material. Therefore, the industrial applicability of the invention is obvious .

Claims

CLAIMS1. Pellets, for use as an environmentally friendly and renewable solid fuel, where said pellets are cylindrically shaped with a moisture content of less than 10% w / w, comprising:(i) comminuted lignocellulosic materials selected from the group consisting of: Spanish broom <Spartium junceum L>, giant miscanthus <Miscanthus x giganteus> , Virginia mallow {Sida hermaphrodita <L> Rusby}, giant reed <Arundo donax L>, and / or waste materials from these plants, or mixtures of these materials, in the amount of 50.0-99.5% w / w, and(ii) concentrated black liquor <CBL>, or concentrated and dried black liquor <DBL>, obtained as a side-product from the processing of said plants by the citric acid (CA) / hydrogen peroxide (H2O2) -based process for the production of lignocellulose fibers, in the amount of 0.5-50.0% w / w, where the said pellets have the ash content of less than 7.00% w / w, the sulfur content of less than 0.08% w / w, and the intrinsic energy value of 16.0 - 19.50 MJ / kg.

2. Pellets according to claim 1, wherein the concentrated black liquor <CBL> is an aqueous solution that contains (a) solubilized lignin and hemicellulose-degradation products in the amount of 5- 50% w / w, and (b) citric acid in the amount of 10-20% w / w, with the residual water content of not more than 30% w / w.

3. Pellets according to claim 1, wherein the concentrated and dried black liquor <DBL> is an aqueous solution that contains (a) solubilized lignin and hemicellulose-degradation products in the amount of 50-90% w / w, and (b) citric acid in the amount of 10-50% w / w, with the residual water content of not more than 10% w / w.

4. Pellets according to any of previous claims, wherein the waste material from said plants is selected from the group consisting of waste fibers smaller than 1 mm, fine cellulosic particles able to pass through 200 mesh-screen, and mixtures of these materials.

5. Pellets according to any of previous claims, wherein, the weight percentage of ingredient (i) is 75-99% w / w and ingredient (ii) is 1-25% w / w, preferably 90-98% w / w, and 2-10% w / w.

6. A process for the preparation of pellets according to any of claims 1-5, wherein, the preparation steps are:A. optional pre-drying of plant materials selected from the group consisting of: Spanish broom <Spartium junceum L>, giant miscanthus <Miscanthus x giganteus> , Virginia mallow {Sida hermaphrodita <L> Rusby} , giant reed <Arundo donax L>, or mixtures of these plants, and / or waste material from these plants, with the moisture content of less than 20% w / w, preferably of 16-18% w / w,B. comminution said plant materials down to the average particle size within the range of 3-5 mm which constitutes 70% w / w, where the rest of particles have size out of the said range,C. mixing of one or more plant materials from step B with concentrated black liquor <CBL>, or concentrated and dried black liquor <DBL>, or a mixture thereof, at temperatures between 5-100°C during 1-15 minutes,D. conditioning of thus obtained mixture by standing at a temperature between 5-100°C during 5-30 minutes,E. pelletizing of thus obtained mass in the pellet press to pellets at a temperature between 20-150°C and pressure 100- 350 MPa, yielding the pellets,F. optionally, spraying the hot pellets with an additional amount of CBL (ii) ,G. optionally, drying the pellets down to not more than 10% w / w of residual moisture content, andH. cooling the pellets down to a temperature between 20-30°C, yielding the pellets according to the present invention.

7. The process for the preparation of pellets according to claim 6, wherein the mixture in step C is composed of concentrated black liquor <CBL> in the amount of not less than 80% w / w, andconcentrated and dried black liquor <DBL> in the amount of not more than 20% w / w .8 . The process for the preparation of pellets according to claims 6 and 7 , wherein, the process parameters in Step C are selected in a way that mixing is conducted at a temperature between 5-25 ° C during 1-5 minutes , in Step D the conditioning is maintained at a temperature between 60-100 ° C during 5-20 minutes , and in Step E the pelleting is performed at a temperature between 60-100 ° C and a pressure of 120-300 MPa .9 . The process for the preparation of pellets according to claims 6- 8 , wherein the optional step F is executed if the overall amount of concentrated black liquor <CBL> is greater than 10% w / w, when 10% w / w of said CBL is added in step C , while the excess is applied in step F .10 . The process for the preparation of pellets according to claims 6- 8 , wherein the optional step G is executed if the overall content of said ingredient ( ii ) is higher than 15% w / w in the final pellets - when then the drying of hot pellets has to be conducted .11 . A use of pellets according to claims 1-5 as an environmentally friendly and renewable solid fuel for the production of thermal energy, or , starting material for the production of renewable chemicals in biorefineries .

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