Method for providing pellets suitable for incineration, pellets suitable for incineration and use thereof as fuel

Abstract

The invention relates to a method for providing pellets suitable for incineration from distillation residues of toluene diisocynate obtained by a gas-phase phosgenation process, pellets suitable for incineration obtainable according to the method of the invention, and pellets according to the invention for use as fuel in an incineration plant, particularly, the fuel can be used as alternative fuel of fossil fuel such as coal, petroleum or natural gas.

Description

[0001] This invention relates to a method for providing incineration-suitable pellets from the distillation residue of toluene diisocyanate obtained by gas-phase phosgenation, incineration-suitable pellets obtainable according to the method of the invention, and the use of the pellets according to the invention as fuel in incineration equipment, particularly as an alternative fuel to fossil fuels such as coal, oil or natural gas.

[0002] Industrial-scale isocyanate production generates distillation bottom streams that require further post-processing. These bottom streams contain not only distillation residues (also simply referred to as residues) consisting of compounds that are difficult to evaporate or cannot be evaporated without decomposition, but also a portion of the isocyanates to be produced. Isocyanates are intentionally not completely removed from the distillation bottoms during distillation, as this would cause a sharp increase in the viscosity of the bottom product, sometimes even solidification. This is particularly true for the production of toluene diisocyanate (TDI) via the phosgenation of toluene diamine (TDA). To maintain the fluidity of the distillation bottom streams, a certain minimum amount of TDI is intentionally retained. To improve yield, it is common practice in the prior art to further concentrate the distillation bottom streams after they are discharged from the distillation column, i.e., to recover as much TDI as possible from them again. This is done using a dryer, where the TDI (and optionally other evaporable components present) evaporates, and the remainder of the distillation bottom stream is concentrated into free-flowing solids, typically with the addition of additives such as pitch. For example, EP 0 626 368 A1 describes a post-treatment method for products of phosgenation in solution, wherein the residue obtained during distillation is continuously fed together with inert high-boiling hydrocarbons (preferably pitch) under distillation conditions into a heated product stirring vacuum dryer with a horizontal axis, wherein the portion of isocyanate remaining in the residue is continuously removed by distillation, and the remaining residue is continuously discharged as free-flowing, dust-free granules, optionally cooled, and optionally sent to incineration after grinding.

[0003] Similarly, EP 0 548 685 A2 describes a method for producing distilled pure isocyanate by reacting the corresponding amine with phosgene in a suitable solvent and followed by multi-stage distillation to obtain pure isocyanate, pure solvent, and a certain amount of residue, wherein the residue is post-treated, and more precisely, in such a manner as follows: the residue obtained from the distillation process is fed into a stirred and heated vessel partially containing a high-boiling-point hydrocarbon (preferably pitch) inert under distillation conditions; the remaining free isocyanate in the residue is removed by distillation, and the remaining residue is discharged as a free-flowing solid, cooled, and sent to incineration. It is also disclosed (but not experimentally verified) that the free-flowing solid can be ground before incineration.

[0004] EP 0 017 972 A1 describes a method for separating toluene diisocyanate and / or high-boiling solvents from a distillation residue obtained by reacting toluene diamine with phosgene in the liquid phase in the presence of a solvent and then distilling the reaction solution, wherein the distillation residue is treated in a fluidized bed at a temperature of 140°C to 280°C.

[0005] WO 2018 / 114846 A1 describes a method for efficiently recovering a portion of the isocyanate to be produced from the bottom stream of a distillation process generated during the post-treatment of a crude liquid process product containing the isocyanate to be produced, which is produced in an isocyanate production process (phosgenation of the corresponding amine). Phosgenation can be carried out in either the liquid or gas phase. A drying step is specifically described, in which the isocyanate to be produced is recovered to form a solid substantially to completely free of the isocyanate. This drying step is characterized by a minimum content of 15% by mass of the carbodiimide-containing compound based on the total mass of the distillation residue fed into the drying apparatus, wherein this minimum content can also be adjusted by in-situ carbodiimide oxidation. The drying step is preferably carried out in a drying apparatus selected from: a heated product-stirring vacuum dryer with a horizontal axis, a rotary tube dryer, a disc dryer, a belt dryer, and a granulating screw mill. Examples describe the use of a kneading dryer. The use of a so-called CFT (“combined fluidization technology”) dryer is not disclosed (see below). A release agent, preferably selected from bitumen, talc, chalk, inorganic pigments, and fully dried residue (from a previous drying process; according to the document, the returned portion may be finely ground beforehand, but no experimental verification is provided), is preferably added during the drying step to promote the formation of non-sticky dried residue granules. Bitumen is used in the examples. It is generally considered necessary to form a free-flowing solid (not just a paste-like product adhering to the drying apparatus). The drying step of the method produces a solid in which the isocyanate to be prepared is present in trace amounts, preferably up to 1.0% by mass, more preferably up to 0.1% by mass. Other possible uses of this residue (i.e., uses other than as a release agent) are not disclosed. This document discusses only the prior art in this regard, particularly EP 0 548 685 A2 and EP 0 626 368 A1 (see above), both of which involve liquid-phase phosgenation.

[0006] WO 2020 / 201277 A1 describes a drying apparatus for evaporating volatile components from a starting material to be dried (particularly a distillation bottom stream for isocyanate production, where isocyanate production can be achieved by phosgenation of the corresponding amine in the liquid or gas phase), a method for producing isocyanates using the drying apparatus, and the use of the drying apparatus for drying distillation bottom streams, oily waste, ink or paint waste, sewage sludge, mineral materials contaminated with organic compounds, and coal slurry. In drying the distillation bottom stream for isocyanate production, the method yields a solid in which the isocyanate to be produced is present at most, preferably, a maximum of 1.0% by mass, more preferably, a trace amount of 0.1% by mass. The potential applications of this residue are not disclosed. This document only discusses prior art in this respect, particularly application EP 0 626 368 A1 (see above), which relates to liquid-phase phosgenation.

[0007] In the drying apparatus described in WO 2020 / 201277 A1, the evaporated components (vapor) enter the condenser via a vapor dome and vapor conduits. This drying apparatus is characterized by intentionally allowing or facilitating partial condensation of the vapor within the vapor dome and / or vapor conduits during its operation, and discharging the condensed vapor components from the drying apparatus through means installed within the vapor dome and / or vapor conduits for this purpose. According to the teachings of this document, regardless of the application area and specific process mode, the drying apparatus is preferably selected from: product-stirring vacuum dryers with a horizontal axis (particularly kneading dryers, paddle dryers, and blade dryers, the latter of which can also be configured as CFT dryers—details on this type of dryer are provided below), rotary tube dryers, disc dryers, belt dryers, and granulation screw dryers.

[0008] CN 114 247 734 A describes a method for converting solid residues formed during the phosgenation of toluene diamine (especially in the gas phase) to produce toluene diisocyanate into a slurry, comprising: Transform solid residues into solid particles with an average diameter of ≤5 mm (particularly by grinding and / or pulverizing); Solid particles are separated into a first particle fraction with an average particle size >75μm and a second particle fraction with an average particle size ≤75μm; The first-stage solid particles and the second-stage solid particles were mixed at a weight ratio of 8:2 to 3:7, and... Solvents (especially water) are added to obtain a slurry.

[0009] The slurry can be sent to the incineration equipment.

[0010] Fujian Jinhuang Environmental Protection Technology Co., Ltd for Wanhua Chemical Fujian Isocyanate Co., LtdThe environmental compatibility report for the supporting equipment established in June 2021 (see http: / / www.fuzhou.gov.cn / zgfzzt / shbj / zz / xxgk / spgs / 202106 / t20210628_4129694.htm; downloaded on June 2, 2023) discloses a method for handling so-called "TDI tar particles" in Chapter 3.6.8.2. These TDI tar particles have a diameter of approximately 1000 μm to 5000 μm. The tar particles are conveyed from the solids silo via a screw conveyor to a tar particle grinding and screening unit, where they are ground and screened. The ground and screened tar particles with a diameter <200 μm are then conveyed to the incineration unit, which is achieved by blowing the fine particles present after grinding from the top of the grinding unit via a conveyor fan. The conveying air loaded with tar particles is separated by a specific cyclone separator and dust collector and introduced into a tar powder buffer silo. Fine particles in the tar powder buffer silo are fed into the tar powder injection device via a conveying screw conveyor and rotary valve, where the tar powder is conveyed to the incineration equipment via a nitrogen gas stream. Unburned tar particles are collected and returned to the incineration equipment. This is achieved through a tar backwashing device installed near the ash silo to return unburned tar particles to the incineration equipment via a nitrogen gas stream. Wanhua is known to produce TDI via phosgenation of TDA in the liquid phase (see, for example, Wanhua Chemical (Fujian) Co., Ltd.'s September 2021 Environmental Compatibility Report on the Expansion of TDI Plant to 250,000 Tons / Year, Chapter 4.8.1.6, see https: / / www.fuzhou.gov.cn / zgfzzt / shbj / zz / xxgk / spgs / 202109 / P020210923330526893459.pdf; downloaded June 13, 2023). Therefore, this report does not address the specific characteristics of distillation residues obtained from gas-phase phosgenation.

[0011] As seen in the literature mentioned above, the solid residue obtained after liquid-phase phosgenation and subsequent drying is typically incinerated. To date, no effective material utilization method has been established for this dried residue. Previous attempts to use this solid residue as an asphalt admixture for road construction failed to achieve the desired results and thus its widespread application was not possible. Sending the solid residue to landfills ultimately results in the waste of potentially valuable raw materials. Incinerating the solid residue to utilize the heat released from combustion, particularly for generating high-pressure steam, which is then widely used in TDI equipment and can replace steam produced by other means (especially by burning natural gas, oil, or coal), is currently an effective method from both an economic and environmental perspective. Of course, applying this method to the post-processing of gas-phase phosgenation products is also desirable. However, the slurry preparation method described in CN 114 247 734 A is not without its drawbacks. On the one hand, the method described there is multi-stage, thus relatively expensive; on the other hand, the calorific value of the resulting slurry is lower than that of the pure solid.

[0012] In this regard, the objective is therefore to produce a solid residue that contains no TDI except for trace amounts of components, has a high calorific value, and possesses mechanical properties that facilitate its transport to incineration facilities. This solid residue should also, as far as possible, possess the property of being incinerated outside of the original TDI production facilities, such as in high-energy-consuming industrial facilities like cement or steel plants. To this end, the solid residue should also be easily transportable and can be transported, arbitrarily over long distances, outside of isocyanate production facilities, i.e., in public places. Finally, it is desirable that the solid residue be able to be incinerated as completely as possible in as many types of incineration facilities as possible, more specifically in incineration facilities actually configured for incinerating liquids (so-called LWIs – liquid waste incinerators), with as little ash and slag formation as possible, thereby achieving the widest possible range of applications.

[0013] Therefore, the present invention provides the following: In a first aspect, the present invention relates to a method for providing pellets suitable for incineration, wherein the method comprises the following steps: (A) Phosgenetically reacting p-toluenediamine in the gas phase to obtain toluene diisocyanate (especially m-toluenediamine to obtain m-toluene diisocyanate) to obtain a mixture of gaseous products, and cooling the mixture of gaseous products to obtain a crude liquid product; (B) Post-processing the liquid crude product to obtain (in particular) m-toluene diisocyanate, wherein the post-processing includes (at least one) distillation step, wherein a liquid distillation bottom stream containing (in particular) m-toluene diisocyanate and minor components with boiling points higher than (in particular) m-toluene diisocyanate is produced. (C) The liquid distillation bottom stream is introduced into a dryer through an inlet, and the liquid distillation bottom stream is dried in the dryer—preferably until the mass content of toluene diisocyanate (determined according to the method described in the specification [see below]) (based on the total mass of solid residue) is 0% to 0.100%, preferably 0% to 0.060%, more preferably 0% to 0.010%, particularly preferably 0% to 0.002%, extremely preferably 0% to 0.001%—to obtain solid residue, and the solid residue is discharged from the dryer through a discharge port, wherein the dryer is a paddle dryer having an internal space in which a rotor shaft rotatably driven about its axis is provided, which, during the drying process, uniformly distributes the distillation bottom stream onto the solid material agitated by rotor blades arranged on the rotor shaft and conveys it from the inlet toward the discharge port; and (D) The solid residue is ground into granules, and its volume-based particle size distribution (determined by wet dispersion method using Fraunhofer laser diffraction according to the method described in the instruction manual [see below]) is shown in d. 90 The size is 55μm to 500μm, preferably 60μm to 300μm, more preferably 100μm to 250μm, particularly preferably 100μm to 215μm, and extremely preferably 100μm to 180μm.

[0014] In a second aspect, the present invention relates to incinerated pellets that can be obtained (in particular) by the method according to the first aspect of the invention.

[0015] In a third aspect, the present invention relates to the use of the pellets according to the invention as fuel in incineration equipment, particularly as an alternative fuel to fossil fuels such as coal, oil or natural gas.

[0016] It has now been surprisingly discovered that solid residues that meet or at least approach the above requirements can be provided by phosgenation in the gas phase and drying in a specific dryer (so-called CFT dryer, details of which are described below) combined with grinding to a specific particle size.

[0017] Before providing a more detailed description of the invention below, it is necessary to clarify some terms: In the terminology of this invention, the term "distillation" refers both to "simple" distillation and to reflux distillation (rectification) with effective separation components. The same applies to derived terms such as "distillation step" or "distillation column." The bottom stream of distillation is understood to be the stream with the highest boiling point obtained during the distillation process. This type of stream is obtained from the so-called "bottom" (the lowest portion where high-boiling components are concentrated) of a distillation column or evaporator (the evaporator of a distillation column or, as described more specifically below, the evaporator of an optional pre-concentration unit).

[0018] All pressure data refer to absolute pressure.

[0019] The term "m-toluene diisocyanate" (m-TDI) refers to the position of the isocyanate groups relative to each other; these groups are interpositioned. Therefore, in this invention, m-TDI specifically refers to industrially relevant mixtures of the isomers 2,4-TDI and 2,6-TDI. However, the term also includes so-called T100, which consists almost entirely of 2,4-TDI.

[0020] In the context of this invention, the particle size distribution of the granules according to the invention is shown in percentiles, more precisely at least in d... 90 Percentile (which represents 90% by mass of particles smaller than this size based on the total mass of the aggregate), is also expressed as d in the preferred embodiment. 10 Percentile (which represents 10% by mass of particles smaller than this size based on the total mass of the aggregate).

[0021] The "start-up" of a dryer is understood as the period from when the dryer is in a stopped state until it reaches a stable state, during which the bottom feed of the liquid distillation continuously enters the dryer and solid residue is continuously removed from it. The "continuous operation" of the dryer refers to the drying period from the start of operation until the end of the drying process.

[0022] The following is a brief overview of various possible embodiments of the present invention: In a first embodiment of the method of the present invention (which can be combined with all other embodiments), step (A) includes the following: (AI) provides a gaseous (especially meta) toluene diamine stream; (A.II) Provides a gaseous phosgene stream; (A.III) In the mixing zone, the gaseous (especially meta) toluene diamine stream and the gaseous phosgene stream are mixed and converted into a gaseous product mixture in the reaction zone downstream of the mixing zone; (A.IV) Cooling a gaseous product mixture by contact with a quenching liquid within a quenching zone to obtain a mixture of reaction product mixture and quenching liquid; and (AV) The mixture of reaction product mixture and quench liquid mixture is fed into the collection zone for phase separation to obtain liquid crude product and gaseous crude process product, and both are taken out from the collection zone respectively.

[0023] In a second embodiment of the method of the invention (i.e., a specific configuration of the first embodiment), the quench liquid comprises an organic solvent, (in particular) m-toluene diisocyanate, or a mixture of an organic solvent and (in particular) m-toluene diisocyanate.

[0024] In a third embodiment of the method of the present invention (i.e., a specific configuration of the second and third embodiments), step (B) includes: (BI) Optionally, hydrogen chloride and phosgene are separated from the liquid crude product to obtain a liquid product depleted of hydrogen chloride and phosgene; (B.II) Optionally, the quench liquid is separated from the liquid crude product or the liquid product depleted of hydrogen chloride and phosgene to obtain a liquid product depleted of hydrogen chloride, phosgene and quench liquid; (B.III) A post-distillation treatment of a liquid crude product or a liquid product depleted of hydrogen chloride and phosgene or a liquid product depleted of hydrogen chloride, phosgene and quenched liquid, comprising (at least one) distillation step to obtain a liquid distillation bottom stream containing (particularly) m-toluene diisocyanate and minor components with boiling points higher than (particularly) m-toluene diisocyanate.

[0025] In a fourth embodiment of the method of the invention (i.e., an alternative to the fifth embodiment described below, but which may be combined with all other embodiments), the distillation step (at least one) for obtaining a liquid distillation bottom stream containing (particularly) m-toluene diisocyanate and a minor component with a boiling point higher than (particularly) m-toluene diisocyanate is distillation in a partitioned column, wherein a top stream, a side stream, and a bottom stream are obtained, wherein the side stream contains (particularly) m-toluene diisocyanate, and the bottom stream is a liquid distillation bottom stream containing (particularly) m-toluene diisocyanate and a minor component with a boiling point higher than (particularly) m-toluene diisocyanate.

[0026] In a fifth embodiment of the method of the present invention (i.e., an alternative to the fourth embodiment described above, but which may be combined with all other embodiments), the distillation step (at least one) for obtaining a liquid distillation bottom stream containing (particularly) m-toluene diisocyanate and minor components with boiling points higher than (particularly) m-toluene diisocyanate is distillation in a partitioned column, wherein a top stream, a side stream, and a bottom stream are obtained, wherein the side stream contains (particularly) m-toluene diisocyanate, and the bottom stream is pre-concentrated in an evaporator downstream of the partitioned column to obtain a liquid distillation bottom stream containing (particularly) m-toluene diisocyanate and minor components with boiling points higher than (particularly) m-toluene diisocyanate.

[0027] In a sixth embodiment of the method of the present invention (i.e., a specific configuration of the fifth embodiment), pre-concentration is carried out at a temperature of 120°C to 180°C and a pressure of 10 mbar to 60 mbar, preferably at a temperature of 130°C to 175°C and a pressure of 25 mbar to 45 mbar.

[0028] In a seventh embodiment of the method of the present invention (i.e., a specific configuration of the fourth to sixth embodiments), distillation in the partition column is carried out at a temperature of 160°C to 200°C and a pressure of 50 mbar to 100 mbar (wherein these two data are based on the bottom of the partition column).

[0029] In an eighth embodiment of the method of the present invention (which can be combined with all other embodiments), step (C) uses solid residue from a previous drying operation, granules from a previous drying and grinding operation, and / or (otherwise provided) inert solids (e.g., particularly alumina) as the solid material for starting operation of the dryer. "Starting operation" is understood to refer to the initial drying operation period from when the dryer is in a stopped state until it reaches a stable state, during which the bottom stream of liquid distillation continuously enters the dryer and solid residue is continuously removed from the dryer.

[0030] In a ninth embodiment of the method of the invention (which can be combined with all other embodiments), the solid material in the continuously operating dryer includes, and in particular constitutes, a portion of, the solid residue formed during continuous operation. "Continuous operation" of the dryer is understood to refer to the drying period from the start of operation until the end of the drying operation.

[0031] In a tenth embodiment of the method of the present invention (which can be combined with all other embodiments), the drying of the bottom distillate stream in step (C) is carried out at a temperature of 150°C to 500°C and a pressure of 20 mbar to 200 mbar, preferably at a temperature of 185°C to 320°C and a pressure of 50 mbar to 180 mbar, and particularly preferably at a temperature of 250°C to 310°C and a pressure of 80 bar to 150 bar.

[0032] In the eleventh embodiment of the method of the present invention (which can be combined with all other embodiments), a rotor mill is used for grinding in step (D).

[0033] In the twelfth embodiment of the method of the present invention (which can be combined with all other embodiments), for the particle size distribution of the granules obtained in step (D): d 10 The thickness is from 2.5 μm to 30 μm, preferably from 2.5 μm to 20 μm. 90 and d 10 In principle, the various preferred levels within the value range can be arbitrarily combined with each other.

[0034] In the thirteenth embodiment of the method of the present invention (which can be combined with all other embodiments), fractions with a diameter greater than 500 μm, preferably greater than 300 μm, particularly preferably greater than 250 μm, especially preferably greater than 215 μm, and extremely preferably greater than 180 μm are removed from the granules by sieving.

[0035] In a first embodiment of the pellets of the present invention, the pellets have a toluene diisocyanate mass content (total of all isomers) of 0% to 0.100%, preferably 0% to 0.060%, more preferably 0% to 0.010%, particularly preferably 0% to 0.002%, and extremely preferably 0% to 0.001% based on their total mass (determined by the method described in the specification [see below]).

[0036] In a first embodiment of the invention, the incineration equipment is used to provide heat for cement production, steel production, steel processing in casting equipment, or chemical production.

[0037] In a second embodiment of the invention, the incineration equipment is a component of the isocyanate production equipment and is used to provide the heat required for isocyanate production.

[0038] In a third embodiment of the application of the invention (which may be combined with all other embodiments), the fuel is burned at an incineration temperature of 900°C or higher, preferably 1000°C or higher, particularly preferably 1100°C or higher, wherein the incineration temperature in each case does not exceed preferably 2000°C, particularly 1500°C.

[0039] In a fourth embodiment of the invention (i.e., a specific configuration of the third embodiment), the fuel is subjected to a residence time of 2 seconds or more at the combustion temperature, preferably 2 to 10 seconds, and particularly preferably 2 to 5 seconds.

[0040] In a fifth embodiment of the application of the invention (which may be combined with all other embodiments), the application includes features of one or more embodiments of the method of the invention described above.

[0041] The embodiments briefly described above, as well as other possible configurations of the invention, are described in more detail below. Unless the contrary becomes obvious to those skilled in the art from the context, or unless the invention explicitly states otherwise, all the embodiments described above, as well as other configurations of the invention described below, can be arbitrarily combined with and with each other.

[0042] In a first aspect, the present invention relates to a method for providing pellets suitable for incineration, as described above, comprising steps (A) to (D) as described above. Detailed aspects of the method of the invention will now be described. It goes without saying that all these detailed aspects also apply mutatis mutandis to the other two aspects of the invention—the pellets suitable for incineration and their use as fuel in incineration equipment—so it need not be mentioned repeatedly.

[0043] Step (A) of the method of the present invention, namely, the phosgenation of toluene diamine in the gas phase to obtain toluene diisocyanate, is known in the prior art. In a preferred configuration, step (A) is performed as follows: In step (AI), a gaseous TDA feed stream is provided. Suitable methods for this are known in principle to those skilled in the art. Preferred embodiments are described below.

[0044] The conversion of TDA to the gas phase can be carried out in all evaporation devices known in the art, especially falling film evaporators. Evaporation devices that guide a small flow of working material through the falling film evaporator with high circulation power are preferred. To minimize the thermal stress of TDA, regardless of the specific configuration of the evaporation device, the evaporation operation is preferably assisted by introducing vapors of an inert gas (such as N2, He, Ar (especially N2)) or an inert solvent, preferably selected from aliphatic hydrocarbons (preferably decahydronaphthalene), non-halogenated aromatic hydrocarbons (preferably toluene or xylene, especially toluene), halogenated aromatic hydrocarbons (preferably chlorobenzene, p-dichlorobenzene, o-dichlorobenzene, chlorotoluene or chloronaphthalene, especially o-dichlorobenzene), or mixtures of the above organic solvents. Furthermore, the evaporation of TDA—if necessary, superheating—(especially to 200°C to 430°C, preferably 250°C to 420°C, more preferably 250°C to 400°C) is preferably carried out in a multi-stage operation to avoid the formation of unevaporated droplets in the gaseous amine stream. Particularly preferred are multi-stage evaporation and superheating steps, wherein a droplet separator is installed between the evaporation system and the superheating system, and / or the evaporation device itself also functions as a droplet separator. Suitable droplet separators are known to those skilled in the art.

[0045] In step (A.II), a gaseous phosgene stream is provided. Preferably, the molar ratio of phosgene to primary amine groups is set to 1.1:1 to 20:1, more preferably 1.2:1 to 5.0:1. As described above for TDA, the phosgene is also preferably heated to a temperature of 200°C to 430°C, preferably 250°C to 420°C, more preferably 250°C to 400°C, and optionally diluted with the vapor of an inert gas (such as N2, He, Ar (especially N2)) or an inert solvent, preferably selected from aliphatic hydrocarbons (preferably decahydronaphthalene), non-halogenated aromatic hydrocarbons (preferably toluene or xylene, especially toluene), and halogenated aromatic hydrocarbons (preferably chlorobenzene, p-dichlorobenzene, o-dichlorobenzene, chlorotoluene, or chloronaphthalene, especially o-dichlorobenzene) or mixtures of the above organic solvents.

[0046] In step (A.III), the co-reactants TDA and phosgene are mixed in a mixing zone and reacted in a downstream reaction zone. Preferably, the separately heated co-reactants TDA and phosgene are supplied to the mixing and reaction zone via a nozzle device. Possible configurations of such nozzle devices are known to those skilled in the art.

[0047] In addition to the previously mentioned methods for diluting the TDA gaseous stream and the phosgene gaseous stream, a separate dilution gas stream (an inert gas, such as N2, He, Ar (especially N2), or a vapor of an inert solvent, preferably selected from aliphatic hydrocarbons [preferably decahydronaphthalene], non-halogenated aromatic hydrocarbons [preferably toluene or xylene, especially toluene], halogenated aromatic hydrocarbons [preferably chlorobenzene, p-dichlorobenzene, o-dichlorobenzene, chlorotoluene or chloronaphthalene, especially o-dichlorobenzene], or a mixture of the above organic solvents) can be directly introduced into the mixture in step (A.III). In this case, the dilution gas stream is preferably heated to a temperature of 100°C to 500°C, preferably 150°C to 450°C, and more preferably 150°C to 400°C.

[0048] The further reaction of the co-reactants TDA and phosgene mixed in the mixing zone in the reaction zone is preferably carried out adiabatically. An adiabatic reaction means that the generated heat of reaction does not require targeted removal via a heat transfer medium. Therefore, apart from unavoidable heat loss, the enthalpy of the reaction is quantitatively reflected in the temperature difference between the product gas stream and the reactant gas stream. The invention also relates to a method in which step (A.III) is carried out adiabatically, and wherein the composition and temperature of the TDA gaseous stream in step (A.I) and the phosgene stream in step (A.II) are selected such that the temperature in the mixing zone and the reaction zone in step (A.III) is set to 250°C to 450°C, preferably 270°C to 425°C, more preferably 280°C to 420°C. This means that the temperature at each point in the mixing zone and the reaction zone is within this range.

[0049] The mixing zone and the reaction zone are preferably located within a common technical device—a reactor—for carrying out the chemical reaction. In this arrangement, the mixing zone and the reaction zone typically transition smoothly into each other, rather than being strictly separated as with a separate mixing device (which is also feasible in principle). The reaction zone, after the reactants are mixed, serves to provide residence time to ensure the most complete possible conversion. The structural details of suitable phosgenation reactors are known to those skilled in the art.

[0050] In the reaction zone, TDA and phosgene are rapidly converted to TDI, preferably in an adiabatic manner as described. The reaction is preferably carried out in such a manner that the TDA is completely converted before entering the quenching zone, which is described in more detail below.

[0051] In step (A.IV), the resulting TDI-containing gaseous product mixture is rapidly cooled and liquefied (except for trace components remaining in the gas phase) in a quenching zone by contact with a quenching liquid (“quenching”). Suitable quenching liquids include (organic) solvents, TDI, and mixtures of TDI and (organic) solvents, especially solvents and mixtures of TDI and (organic) solvents. The solvent used for quenching is preferably selected from chlorobenzene, o-dichlorobenzene, p-dichlorobenzene, trichlorobenzene isomers, toluene, xylene isomers, and mixtures of the above solvents. Particularly preferred solvents are chlorobenzene and dichlorobenzene, with o-dichlorobenzene being extremely preferred. Contact is preferably achieved by injecting the quenching liquid into the gaseous product mixture stream.

[0052] The possible construction and operation of the quenching zone are known in principle in the prior art. Existing apparatus and methods can also be applied to this invention. For example, EP 1 403 248 A1 and EP 1 935 875 A1 disclose possible configurations of the quenching zone.

[0053] The temperature of the quenching liquid used in step (A.IV) is preferably selected such that, on the one hand, it is high enough to reverse-crack TDI carbamoyl chloride into TDI and hydrogen chloride. (Although it is not certain whether the carbamoyl chloride intermediate known in liquid-phase phosgenation will also be generated in gas-phase phosgenation, the temperature of the quenching liquid should be high enough to suppress this reaction, since it is conceivable independently that liquid TDI will partially react with the present hydrogen chloride gas to generate TDI carbamoyl chloride during quenching.) On the other hand, the TDI and the solvent optionally used as a diluent in the gaseous TDA stream and / or gaseous phosgene stream should be substantially condensed or substantially dissolved in the solvent, while excess phosgene, hydrogen chloride, and the inert gas optionally used as a diluent should pass through the quenching zone in a substantially uncondensed or undissolved state; therefore, the temperature of the quenching liquid should not be selected to be too high. Quenching liquids maintained at temperatures between 50°C and 200°C, preferably between 80°C and 180°C, are particularly suitable for selectively obtaining TDI from the gaseous reaction mixture.

[0054] Given a temperature, pressure, and composition, those skilled in the art can easily predict, based on physical data, what mass content of TDI will condense during quenching or be quenched in an uncondensed state. Similarly, it is easy to predict what mass content of excess phosgene, hydrogen chloride, optional solvent, and optional inert gas used as a diluent will be quenched in an uncondensed state or dissolved in the quenching liquid. Therefore, the mixture of reaction products and the quenching liquid obtained in the quenching zone comprises both gaseous and liquid components, i.e., it is a two-phase mixture.

[0055] In step (AV), the two-phase mixture of the reaction product mixture obtained in step (A.IV) and the quench liquid is sent to a collection zone for phase separation.

[0056] In a preferred embodiment, the mixing zone, reaction zone, quenching zone, and collection zone are arranged from top to bottom in the order described above in an upright, particularly conical, cylindrical, or conocyl-cylindrical reactor. In this embodiment, the mixture of reaction products and the mixture of quenching liquid obtained in step (A.IV) flows into the collection zone under gravity (i.e., "automatically"). In another collection zone arrangement, in some cases it is necessary to pump the mixture of reaction products and quenching liquid into the collection zone.

[0057] In the collection zone, the mixture of reaction products and quench liquid obtained in step (A.IV) is separated into a liquid crude process product and a gaseous crude process product. The liquid crude process product contains at least TDI and minor components with boiling points higher than TDI (and optionally a solvent used as the quench liquid, optional byproducts with boiling points lower than TDI or unreacted impurities introduced by co-reactants, optional dissolved excess phosgene, and optional dissolved hydrogen chloride). The gaseous crude process product contains at least the reaction byproduct hydrogen chloride (and optionally excess phosgene, optional evaporated solvent, optional inert gas, and optional unliquefied TDI). Preferably, the liquid and gas phases are continuously removed from the collection zone. In this embodiment, the resulting liquid phase is the starting material for post-processing in step (B), i.e., this liquid phase is the liquid crude product.

[0058] The liquid crude product obtained in step (A) is fed into the post-processing in step (B) to obtain the generated toluene diisocyanate. This post-processing method is itself known in the prior art.

[0059] In principle, the post-treatment of crude isocyanate can be carried out according to methods known in the art. Optionally, dissolved phosgene and dissolved hydrogen chloride are first separated from the liquid crude product obtained in step (A) in a separate step (BI). Step (BI) can, in principle, be carried out in various manners and methods known to those skilled in the art, particularly by distillation, absorption, or a combination of both.

[0060] Following or preferably immediately after step (A), the solvent can then be separated in a separate step (B.II). Step (B.II) can be carried out using various methods and techniques known to those skilled in the art, particularly by distillation.

[0061] In step (B.III), TDI is separated by distillation. In principle, this can be achieved by various means and methods known to those skilled in the art.

[0062] Various implementations are feasible regarding the configuration details of the post-processing according to step (B). Preferred variations are described below: Variant 1 Variant 1 is described in principle in Chem System's PEP report on TDI / MDI (Chem Systems, Process Evaluation Research Planning TDI / MDI 98 / 99 p8, Tarrytown, NY, USA: Chem Systems 1999, pp. 27-32). It is preferably used when the liquid reaction mixture, after distillation to separate hydrogen chloride and phosgene (corresponding to step (BI) in the terminology of this invention), still contains >50% by mass, preferably 51% to 85% by mass, more preferably 55% to 65% by mass, based on its total mass. This mixture is then sent to solvent separation (corresponding to step (B.II) in the terminology of this invention), where the solvent-TDI mixture is first distilled off in a pre-evaporator in a solvent distillation column. In the solvent distillation column, the solvent is distilled off and sent back to the process. Based on its total mass, the bottom stream of the solvent distillation contains not only TDI but also, particularly, preferably 15% to 25% by mass of solvent. The feed stream is introduced into a so-called intermediate column, where further solvent is distilled off, and the solvent-free bottom product is sent to a final distillation column for TDI purification. This is operated under negative pressure and yields purified, marketable isocyanate TDI as the distillate stream (corresponding to step (B.III) in the terminology of this invention). A portion of the TDI remains in the bottom stream of the final distillation column. The tasks of the intermediate column and the TDI purification distillation column can also be combined in a baffle column, where a vapor stream of low-boiling components and solvent is obtained, a pure TDI fraction is obtained as the distillate stream taken from the baffle region, and a product stream containing TDI and high-boiling components (distillation residue) is obtained as the bottom stream of the distillation. The bottom stream of the distillation from the TDI purification distillation column or the baffle column combining the intermediate column and the TDI purification column is post-processed to recover TDI. For this purpose, the stream can be fed into a pre-evaporator for solvent distillation, as shown in Figure II.A.5 of the above-described PEP system report. The bottom product of the pre-evaporator is then sent to post-processing to recover the TDI contained therein. Alternatively, instead of feeding the distillation bottom stream from step (B.III) into the pre-evaporator, the distillation bottom stream can be directly fed to the post-processing stage to recover the TDI contained therein.

[0063] Variant 2 Compared to variant 1, in this embodiment, the liquid reaction mixture after distillation to separate hydrogen chloride and phosgene still has a solvent content of only ≤50.0% by mass based on its total mass. This mixture is fed to a pre-evaporator, from which the solvent-TDI mixture is distilled off to a distillation column. In this embodiment, the TDI has already been desolventized in the subsequent distillation column, so the bottom stream of that column can be directly fed into the TDI purification column, thus reducing the number of columns in this variant compared to variant 1. The TDI purification column operates under negative pressure and yields marketable purified isocyanate TDI as the distillate stream. The tasks of the TDI purification column and its upstream distillation column can also be combined in a baffle column, where a vapor stream of low-boiling components and solvent is obtained, a pure TDI fraction is obtained as the distillate stream taken from the baffle region, and a product stream containing TDI and high-boiling components (distillation residue) is obtained as the bottom stream of the distillation. The distillation bottom stream from the TDI purification column or the distillation bottom stream from a baffle column combining the TDI purification column and its upstream distillation column is post-processed to recover TDI. For this purpose, the stream can be fed into the aforementioned pre-evaporator. The bottom product from this pre-evaporator is then sent to post-processing to recover the TDI it contains. Alternatively, the distillation bottom stream from step (B.III) can be sent directly to post-processing to recover the TDI it contains, without necessarily feeding it into the pre-evaporator.

[0064] Variant 3 Variant 3 includes the distillation sequence described in Variant 2 and Variant 1, but without the pre-evaporator mentioned in each. In this case, the portion of the distillation residue from the distillation sequence is carried together to its respective final TDI purification column by liquid flow. This method is also known in principle (EP 1 717 223 A2). In this case, the distillation residue is completely discharged through the bottom feed stream from the last distillation column (referred to as step (B.III) in the terminology of this invention).

[0065] Variant 4 This variant is preferred. Since step (A) of the method of the present invention is carried out in the gas phase and gas-phase phosgenation typically yields a crude liquid product (containing at most a relatively small amount of dissolved phosgene and dissolved hydrogen chloride compared to liquid-phase phosgenation), it is not necessary to separately separate hydrogen chloride and phosgene in step (BI) in this variant. The crude liquid product is directly fed to solvent separation (corresponding to step (B.II)) (wherein the solvent, optionally dissolved hydrogen chloride, and optionally dissolved phosgene are separated from the top by distillation); or, if the solvent content is sufficiently low (possible implementations for this are described in EP 3 634 947 B1), directly to a TDI purification column. In both cases, the TDI purification column is preferably configured as a baffled column. Low-boiling-point substances (i.e., byproducts with boiling points below TDI, optionally still present hydrogen chloride, optionally still present phosgene, optionally solvent, and optionally inert gases) are discharged from the top as vapor. The purified TDI is discharged as a distillate stream in the baffled region. The resulting distillation bottom stream contains distillation residue and a certain amount of TDI (which is not distilled out to maintain the processability of the distillation bottom stream) and optionally trace amounts of solvent. Instead of a partitioned column, two partitionless distillation columns connected in series can also be used.

[0066] In this variant, the solvent separation according to step (B.II), if carried out, is preferably conducted at a temperature of 160°C to 200°C and a pressure of 160 mbar to 220 mbar (both figures refer to the bottom of the distillation column used). The resulting bottom stream contains, based on its total mass, preferably 9% to 20% solvent, 79% to 90% TDI, and 1% to 5% compounds with a boiling point higher than TDI.

[0067] Especially when carried out in a partitioned column, the TDI purification according to step (B.III) is preferably carried out at a temperature of 160°C to 200°C and a pressure of 50 mbar to 100 mbar, where both figures refer to the bottom of the distillation column used. The resulting distillate bottom stream contains, based on its total mass, preferably 0.00% to 1.00% by mass of solvent, 80.0% to 95.0% by mass of TDI, and 4.00% to 20.0% by mass of compounds with boiling points higher than TDI.

[0068] Therefore, all four variants described above provide a distillation bottom stream that contains not only distillation residue but also a significant amount of TDI, which is then post-processed to obtain the TDI. For this purpose, the distillation bottom stream is optionally pre-concentrated in an evaporator before being fed to the drying step (C), which will be described in detail below. Pre-concentration may be advantageous if the distillation bottom stream obtained as described above can be further concentrated in the evaporator without solidification. In embodiments of the invention, the distillation bottom stream fed to step (C) is therefore the bottom stream of a pre-concentrated evaporator. In principle, this pre-concentration by distilling off TDI (and optionally other distillable components) can be carried out in any evaporator known to those skilled in the art. Pre-concentration is particularly preferred in an evaporator selected from thin-film evaporators, rising-film evaporators, falling-film evaporators, long-tube evaporators, spiral-tube evaporators, forced-circulation flash evaporators, or combinations thereof. Falling-film evaporators are particularly preferred here. Multiple evaporators can also be connected in series. Pre-concentration is preferably carried out at a temperature of 120°C to 180°C and a pressure of 10 mbar to 60 mbar, more preferably at a temperature of 130°C to 175°C and a pressure of 25 mbar to 45 mbar. Pre-concentration can be carried out continuously or discontinuously. A continuous process mode is preferred.

[0069] In step (C) of the method of the present invention, the distillation bottom stream obtained in step (B) is dried, the distillation bottom stream containing toluene diisocyanate and minor components with boiling points higher than toluene diisocyanate. According to the invention, a special paddle dryer is used for this purpose. In the paddle dryer, the solid material is in motion by a particularly rapidly rotating paddle system, which is at least close to a fluidized bed (or ideally, and preferably, a fluidized bed). The starting material to be dried, i.e., the distillation bottom stream from step (B) in this case, is conveyed to this quasi-fluidized bed (or actual fluidized bed). Thus, the starting material to be dried is applied to a bed that is at least substantially (ideally, and preferably actually) fluidized. Such dryers, particularly suitable for drying viscous products, are known by the term: Combined Fluidization Technology (CFT) dryer. Unlike convection fluidized bed dryers, this fluidization is purely mechanical. CFT dryers are described, for example, in WO 2012 / 159736 A1 and EP 2 540 702 A2. These dryers are characterized by a rotor shaft rotatably driven about its axis within the internal space of the dryer. This rotor shaft is configured to distribute the starting material onto a solid material agitated by rotor blades arranged on the rotor shaft during the drying process and convey it from the inlet to the outlet. During the operation of the dryer, a fluidized bed of material is already present when the starting material to be dried first enters the dryer (i.e., when a dryer that has never been operated begins operation). For this purpose, (1) the dried material, i.e., in this case, the solid residue from a previous drying operation (i.e., obtained through steps (A) to (C) of the invention), or (less preferably) the granules from a previous drying and grinding operation (i.e., obtained through steps (A) to (D) of the invention), or (2) an inert solid under the current conditions (preferably inorganic spherical particles, such as, in particular, alumina spheres), is introduced into the dryer and moves with the rotor shaft. After the start-up phase, a stable operating state is entered, in which the starting material solidifies through drying and is discharged partly in solid form and partly in the form of a fluidized bed of solid particles for subsequent drying operations. At this point, there is naturally no need to add any more dried material or inert solids; this is therefore only done when the dryer starts running.

[0070] Preferably, the solid residue from the previous drying operation or the granules from the previous drying and grinding operations are used as solid materials during the initial operation, as this avoids diluting the combustible granules obtained in step (D) with non-combustible inert materials. For this purpose, a portion of the solid residue obtained in step (C) or a portion of the granules obtained in step (D) is simply retained instead of being sent for incineration. Such solid residue or granules are naturally unavailable during the initial start-up of the dryer. Inert solids are used in this case if solid residue / granules cannot be obtained from other dryers / grinding units (e.g., from other production lines that also carry out the method of the invention, optionally also from other isocyanate production sites). It should be noted that during the limited time following such initial start-up, the resulting solid residue diluted with inert solids may sometimes need to be mixed with subsequently generated solid residues (or, in extreme cases, discarded) to prevent an excessive decrease in the calorific value of the granules obtained in step (D) or to avoid interfering with the operation of the grinding unit. Therefore, according to the method of the invention, it is preferable to use solid residue from previous drying operations or solid residue from previous drying and grinding operations as solid material, and at most, inert solids provided by other means, such as, in particular, alumina (see above), are used when the dryer is first started to run.

[0071] The drying of the bottom stream of distillation is preferably carried out at a temperature of 150°C to 500°C and a pressure of 20 mbar to 200 mbar, particularly preferably at a temperature of 185°C to 320°C and a pressure of 50 mbar to 180 mbar, and especially preferably at a temperature of 250°C to 310°C and a pressure of 80 mbar to 150 mbar.

[0072] During the drying process, TDI evaporates, is discharged, and liquefies in a condenser, thereby essentially recovering all the TDI originally present in the stream to be dried. The remaining solid residue consists almost entirely of distillation residue, and isomers of TDI are present at most in insignificant trace amounts. This solid residue is typically macroscopically granular, with a particle size in the range of a few millimeters, and especially up to 5.0 millimeters.

[0073] In step (D), the solid residue obtained in step (C) is ground into granules, the volume-based particle size distribution of which is determined by wet dispersion method using Fraunhofer laser diffraction as described in more detail below. 90 The particle size is 40 μm to 500 μm, preferably 40 μm to 300 μm, more preferably 40 μm to 250 μm, particularly preferably 45 μm to 215 μm, and extremely preferably 50 μm to 200 μm. Excessively fine particles can adversely affect transport, and it cannot be ruled out that excessively fine particles tend to re-agglomerate into larger particles. Therefore, in a preferred embodiment, d 10 The thickness is from 2.5 μm to 30 μm, preferably from 2.5 μm to 20 μm.90 and d 10 In principle, the various preferred levels within the value range can be arbitrarily combined with each other.

[0074] Method for determining particle size distribution using laser diffraction Measurements were performed using the Fraunhofer method. The portion of light deflection caused solely by diffraction is considered here. The measured particle size corresponds to the equivalent diameter of iso-diffractive spheres. Measurements were performed using a wet dispersion method, with water used as the dispersion medium. To stabilize the dispersion, the surfactant "TWEEN® 80" (polyoxyethylene (20) dehydrated sorbitan monooleate) was used as a dispersant, and ultrasonication (60 seconds) was applied. Quality requirements of DIN ISO 13320:2022-12 must be followed. For the purposes of this invention, results are expressed in d... 90 Percentiles are shown, and any option is also indicated by d. 10 Percentiles are shown, representing 90% by mass (d) of the total mass of the particles, respectively. 90 ) or 10% of mass (d) 10 The particles are smaller than the equivalent diameter.

[0075] The grinding can be performed using grinding methods known in the prior art that are suitable for fine grinding of solids.

[0076] The initial results were validated in Retsch's ZM200 ultracentrifugal mill. In this mill, the introduced solid feed stream is set to rotational motion and conveyed by centrifugal force to a rotating screen, where the particles to be ground are sheared and discharged through the screen. Examples of suitable rotational speeds (expressed in revolutions per minute – Upm) range from 6000 Upm to 18000 Upm. Examples of suitable screen mesh sizes are 120 µm or 250 µm.

[0077] Centrifugal mills are a special case, also known as rotor mills, in which the material to be ground is pulverized by impact, shearing, and / or impingement forces using a rotor. This grinding principle is also applied to so-called basket mills, which are particularly suitable for industrial-scale applications. These mills are equipped with high-speed rotating screens (usually rotating in the opposite direction).

[0078] Preferred are rotor mills with high rotational speeds of up to 100 m / s or higher. The material to be ground is accelerated to these speeds during rotation, subjected to shearing between the rotor arms and the mill's inner wall (preferably designed with grooves), and pulverized into fine particles. Discharge is carried out, for example, by conveying air, using a rapidly rotating turbine impeller screen to remove only the sufficiently pulverized particles from the mill.

[0079] Also suitable are so-called coal mills, such as those used for grinding coal in coal-fired power plants. Suitable examples include so-called tube mills (mills with a length-to-diameter ratio greater than 5, in which the grinding media used are spheres, cylinders or rods) or vertical mills (mills consisting of rotating grinding discs, in which the grinding media are pressed against the grinding discs by their own weight and additional force usually from hydraulic cylinders, wherein the grinding media that can be used include spheres, cylindrical, conical or convex spherical rollers).

[0080] Alternatively, other commercially available mills that generate high mechanical stress and prevent excessive product heating can be used (e.g., by using cold conveying air that can absorb dissipated grinding energy).

[0081] The grinding of the solid residue proceeded smoothly, which was completely unexpected and even more surprising to those skilled in the art, because the polymeric compounds in the residue could become rubbery during the grinding process, making it impossible to pulverize them according to the methods and procedures described. This, in turn, would hinder the complete incineration of the residue.

[0082] To reliably avoid the presence of excessively large particles, it may be advantageous to remove any optional residual particles from the milled granules by sieving. Preferably, particles with a diameter greater than 500 μm are separated, more preferably greater than 300 μm, more preferably greater than 250 μm, extremely preferably greater than 215 μm, and very preferably greater than 180 μm. In the terminology of this invention, for non-perfectly spherical particles, the term "diameter" as used herein should be understood as its maximum size and, in practical applications, corresponds to the mesh size of the sieve used; that is, to separate portions with a diameter greater than 500 μm, a sieve with a mesh size of 500 μm is used, etc.

[0083] In a second aspect, the present invention relates, as described above, to pellets suitable for incineration that can be obtained, particularly, by the method of the present invention. The volume-based particle size distribution of these pellets (determined as described above by laser diffraction) includes d... 90 The micrometer size is 40 μm to 500 μm, preferably 40 μm to 300 μm, more preferably 40 μm to 250 μm, particularly preferably 45 μm to 215 μm, and extremely preferably 50 μm to 200 μm. As already mentioned in the description of the method of the present invention, d 10 Preferably, the micrometer diameter is from 2.5 μm to 30 μm, more preferably from 2.5 μm to 20 μm. 90 and d 10 In principle, the various preferred levels within the value range can be arbitrarily combined with each other.

[0084] To avoid being constrained by theory and assumptions, the pellets are almost entirely composed of oligomers formed by the interaction of TDI isomers and / or byproducts. Apart from trace amounts of free TDI (the sum of all isomers; particularly, a maximum of 0.100% by mass of TDI, preferably a maximum of 0.060% by mass, more preferably a maximum of 0.010% by mass, particularly preferably a maximum of 0.002% by mass, extremely preferably a maximum of 0.001% by mass, based on the total mass of the pellets), the pellets also contain at most small amounts of chlorinated byproducts. The TDI content data refers to extractable TDI determined by the following method: Methods for determining the residual content of (extractable, i.e., non-"chemically bound") TDI Gas chromatography was used for analysis using cumene as an internal standard. The gas chromatograph was equipped with a flame ionization detector (FID) and operated with hydrogen as the carrier gas. 5.0 g of granules and 10 mL of a 0.1% cumeneacetonitrile solution (purity ≥99.0%; water content <100 ppm) were mixed in an ultrasonic bath at room temperature (20°C) for 10 min, followed by standing for another 10 min. To quantify the TDI content, the area of ​​TDI and optionally present aminotolyl isocyanate (generated from TDI and trace amounts of water) was used. Aminotolyl isocyanate was calculated as TDI.

[0085] In a third aspect, the present invention relates, as described above, to the use of the pellets of the invention as fuel in an incineration plant, or in other words, to a method of incinerating the pellets provided by the method of the present invention in the first aspect in an incineration plant. The pellets of the present invention are characterized in that they can be used in conventional incineration plants and replace fossil fuels (coal, oil, or natural gas) there. This protects these valuable raw materials and enables more sustainable material use possibilities.

[0086] If the incineration equipment is actually designed for incinerating liquids (i.e., a so-called LWI – liquid waste incinerator), it typically requires structural modifications to adapt it for incinerating the pellets of this invention. However, such modifications usually only involve the fuel supply. In LWI equipment, the liquid to be incinerated is typically fed into the combustion chamber via spray nozzles. These nozzles need to be optionally replaced with devices for supplying solids with the same particle size as the pellets of this invention. The same applies, correspondingly, to incineration equipment designed only for incinerating gases.

[0087] Such solids supply devices may in particular include suction via venturi nozzles, pneumatic conveying, and / or screw conveyors. These devices are known in the prior art and therefore need not be described further here.

[0088] The incineration is preferably carried out at a temperature of 900°C or higher, more preferably 1000°C or higher, and particularly preferably 1100°C or higher. Preferably, the incineration temperature does not exceed 2000°C, especially 1500°C. The pellets are preferably subjected to the above-mentioned incineration temperature for a period of 2 seconds or longer, preferably 2 to 10 seconds, and more preferably 2 to 5 seconds, to ensure as complete incineration as possible. Very particularly preferably, the residence time of the pellets at the incineration temperature of 1000°C to 1500°C is 2 to 5 seconds.

[0089] To initiate combustion, it is preferable to preheat the combustion chamber to the stated temperature using auxiliary fuel (e.g., natural gas or diesel). Once combustion of the pellets of the present invention begins, combustion of the auxiliary fuel is stopped. The ratio of auxiliary fuel to pellets is preferably gradually (i.e., not abruptly) reduced to zero.

[0090] Since the granules of this invention contain nitrogen, it is recommended to take measures to avoid the formation of nitrogen oxides (NOx). Such measures are known in the prior art. Of particular note is the so-called staged combustion, which is used, for example, in the cement industry. In this staged combustion, the fuel is processed in separate zones with insufficient oxygen (λ<1; the so-called reduction zone) and excessive oxygen (λ>1; the so-called burnout zone). Here, λ refers to the so-called combustion air ratio (also known as air ratio or air index), which is the ratio of the actual air volumetric flow rate to the minimum air volumetric flow rate (the minimum amount of air required for complete fuel conversion).

[0091] The incineration equipment does not necessarily need to be located near the TDI production site. The pellets of this invention can also be used in incineration equipment to provide heat for various applications, such as cement production, steel production, steel processing in casting equipment, or the production of various chemicals. However, it is particularly preferred that the incineration equipment is an integral part of an isocyanate production facility and is used to provide the heat required for isocyanate production. Nowadays, isocyanate production facilities are typically integrated facilities, which not only involve the phosgenation of a specific amine to produce a specific isocyanate, but may also include sub-equipment for producing different isocyanates and their precursors (aromatic amines and corresponding aromatic nitro compounds). In this case, the energy utilization of the combustion heat is preferably carried out in such a way that steam (especially water vapor) is first generated and fed into a steam integration network that can heat multiple sub-equipment units (especially all sub-units) of the integrated facility, more precisely, regardless of whether these sub-equipment units are classified as being used for the phosgenation of TDA to produce TDI, the phosgenation of another amine to produce another isocyanate, or for the production of one or more precursors of TDI or other isocyanates. All of these are included in the term "for providing the heat required for isocyanate production."

[0092] Example: Example 1: Grinding Experiment In a Retsch ZM200 ultra-high-speed centrifugal mill, the solid residue provided in steps (A) to (C) of the method according to the present invention is ground at a rotational speed of 6000 rpm using a sieve with a nominal mesh size of 250 µm (step (D)). The particle size distribution is studied by wet dispersion method using laser diffraction, wherein the measured value d 10 = 17.30 µm and d 90 =212.00 µm. The pellets obtained by this method are suitable for incineration without any problems.

[0093] Example 2 (Comparative) and Example 3: Observations on the incineration of residues of different particle sizes In both embodiments, the solid residue provided in steps (A) to (C) of the method according to the invention is ground using a super rotor air vortex mill and sieved through a sieve with a nominal mesh size of 180 µm (step (D)). This residue is derived from the "start-up product" of a CFT dryer and therefore contains a low content of alumina (approximately 0.1% by mass). The following d values ​​are determined by wet dispersion using laser diffraction. 10 and d 90 value:

[0094] Two samples were incinerated: A basic cylindrical incineration chamber with a vertical arrangement was employed. At the start of each experiment, the incineration chamber was heated by burning natural gas. The natural gas was then gradually replaced by ground residue. The ground residue was agitated in a hot air stream via a metering screw conveyor with a rotary valve and fed into the incineration chamber from above (target mass flow rate gradually increasing to 9.0 kg / h). A second hot air stream was supplied from the side to the inlet. The resulting flue gas was extracted from the lower region of the incineration chamber, drawn out by a blower, cooled, and passed through a bag filter to separate entrained fly ash. The particles collected here were subjected to incineration temperatures of approximately 900°C to 1000°C for only a very short period (approximately 0.9 s). This short residence time is attributed to the experimental design and is beneficial for assessing the effect of particle size on incineration. A portion of the flue gas, thus desolvated, was recycled by merging with the side-supplyed air stream. During the test, the exhaust gas was monitored for O2, CO2, CO, and NO. x The components of this aspect were analyzed.

[0095] The following observations were made: In Example 2 (Comparative), fuel supply issues arose. After completely replacing natural gas with ground residue, the highest temperature reached 982°C. Unstable flame appearance was observed, associated with fluctuating flue gas composition (O2, CO, and NO) and incomplete combustion (45% to 50% unburned carbon in the fly ash collected by the bag filter). The lower region of the incineration chamber contained predominantly inorganic (attributable to alumina content) solid incineration residue with 2.2% to 5.2% by mass of unburned carbon.

[0096] Fuel supply was not an issue in Example 3. The highest temperature reached was 1046°C after completely replacing natural gas with the ground residue. A stable flame appearance and uniform flue gas composition were observed. Combustion was almost complete. The fly ash collected in the bag filter contained 25% to 30% unburned carbon. The lower region of the incineration chamber contained predominantly inorganic (attributable to alumina content) solid incineration residue with 0.9% to 1.1% by mass of unburned carbon.

Claims

1. A method for providing pellets suitable for incineration, comprising the following steps: (A) P-toluenediamine is phosgenated in the gas phase to obtain toluene diisocyanate, thereby obtaining a mixture of gaseous products, and the mixture of gaseous products is cooled to obtain a crude liquid product; (B) The liquid crude product is post-processed to obtain toluene diisocyanate, wherein the post-processing includes a distillation step, wherein a liquid distillation bottom stream containing toluene diisocyanate and minor components with boiling points higher than toluene diisocyanate is generated. (C) The liquid distillation bottom stream is introduced into the dryer through the feed port, the liquid distillation bottom stream is dried in the dryer to obtain solid residue, and the solid residue is discharged from the dryer through the discharge port, wherein the dryer is a paddle dryer having an internal space in which a rotor shaft that can be rotated about its axis is provided. During the drying process, the rotor shaft distributes the distillation bottom stream onto the solid material agitated by rotor blades arranged on the rotor shaft and conveys it from the feed port toward the discharge port. and (D) Grinding solid residue into granules, the volume-based particle size distribution of which d 90 The range is from 55μm to 500μm.

2. The method of claim 1, wherein step (A) comprises: (AI) provides a gaseous toluene diamine feed stream; (A.II) Provides a gaseous phosgene stream; (A.III) The gaseous toluene diamine stream and the gaseous phosgene stream are mixed in the mixing zone and converted into a gaseous product mixture in the reaction zone downstream of the mixing zone; (A.IV) Cooling the gaseous product mixture by contact with the quenching liquid in the quenching zone to obtain a mixture of the reaction product mixture and the quenching liquid; (AV) The mixture of reaction product mixture and quench liquid mixture is fed into the collection zone for phase separation to obtain liquid crude product and gaseous crude process product, and both are taken out from the collection zone respectively.

3. The method of claim 2, wherein step (B) comprises: (BI) Optionally, hydrogen chloride and phosgene are separated from the liquid crude product to obtain a liquid product depleted of hydrogen chloride and phosgene; (B.II) Optionally, the quench liquid is separated from the liquid crude product or the liquid product depleted of hydrogen chloride and phosgene to obtain a liquid product depleted of hydrogen chloride, phosgene and quench liquid; (B.III) Distillation posttreatment of liquid crude product or liquid product depleted of hydrogen chloride and phosgene or liquid product depleted of hydrogen chloride, phosgene and quenched liquid, comprising a distillation step to obtain a liquid distillation bottom stream containing toluene diisocyanate and minor components with boiling points higher than toluene diisocyanate.

4. The method of any one of claims 1 to 3, wherein the distillation step for obtaining a liquid distillation bottom stream containing toluene diisocyanate and a minor component with a boiling point higher than toluene diisocyanate is distillation in a partition column, wherein a top stream, a side stream, and a bottom stream are obtained, wherein the side stream contains toluene diisocyanate, and the bottom stream is a liquid distillation bottom stream containing toluene diisocyanate and a minor component with a boiling point higher than toluene diisocyanate.

5. The method of any one of claims 1 to 3, wherein the distillation step for obtaining a liquid distillation bottom stream containing toluene diisocyanate and a minor component with a boiling point higher than toluene diisocyanate is distillation in a partitioned column, wherein a top stream, a side stream, and a bottom stream are obtained, wherein the side stream contains toluene diisocyanate, and the bottom stream is pre-concentrated in an evaporator downstream of the partitioned column to obtain a liquid distillation bottom stream containing toluene diisocyanate and a minor component with a boiling point higher than toluene diisocyanate.

6. The method of claim 5, wherein the pre-concentration is carried out at a temperature of 120°C to 180°C and a pressure of 10 mbar to 60 mbar.

7. The method according to any one of claims 4 to 6, wherein the distillation in the partition column is carried out at a temperature of 160°C to 200°C and a pressure of 50 mbar to 100 mbar.

8. The method as claimed in any of the preceding claims, wherein step (C) uses solid residue from a previous drying operation, granules from a previous drying and grinding operation, and / or inert solids as the solid material for starting the dryer operation.

9. The method as claimed in any of the preceding claims, wherein the solid material during continuous operation of the dryer comprises a portion of the solid residue formed during continuous operation.

10. The method as claimed in any of the preceding claims, wherein the drying of the bottom distillate stream in step (C) is carried out at a temperature of 150°C to 500°C and a pressure of 20 mbar to 200 mbar.

11. The method as described in any of the preceding claims, wherein for the particle size distribution of the granules obtained in step (D), d 10 The range is from 2.5 μm to 30 μm.

12. The method as described in any of the preceding claims, wherein fractions with a diameter of 500 μm or larger in the granules are removed by sieving.

13. Granular material suitable for incineration that can be obtained by any of the preceding claims.

14. The pellets of claim 13, having a toluene diisocyanate content of 0% to 0.100% based on their total mass.

15. Use of the pellets as fuel in an incineration plant as described in any one of claims 13 or 14.

16. The use as described in claim 15, wherein the fuel is burned at an incineration temperature of 900°C or higher.

17. The use as described in claim 16, wherein the fuel is subjected to a residence time of 2 seconds or more at the combustion temperature.

18. The use as described in any one of claims 15 to 17, wherein the incineration equipment is used to provide heat for cement production, steel production, steel processing in casting equipment, or chemical production. or The incineration equipment is a component of the isocyanate production equipment and is used to provide the heat required for isocyanate production.

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