A process for producing formaldehyde

Abstract

The invention relates to a process for producing formaldehyde, the process comprising: - feeding methanol, air and steam into a reactor (13); - obtaining a crude formaldehyde containing gas stream by conversion of methanol in the reactor (13); - feeding the crude formaldehyde containing gas stream into an absorption column (21) in which formaldehyde is absorbed in water; wherein aqueous formaldehyde solution obtained in the absorption column is used at least partly as a heat source for producing steam in a heat pump.

Description

A process for producing formaldehydeSpecificationThe invention relates to a process for producing formaldehyde, the process comprising: feeding methanol, air and steam into a reactor; obtaining a crude formaldehyde containing gas stream by conversion of methanol in the reactor; feeding the crude formaldehyde containing gas stream into an absorption column in which formaldehyde is absorbed in water.Formaldehyde is an important reactant used in the production of resins, for example ureaformaldehyde, melamine resins or phenolic resins. Further formaldehyde is used as an intermediate for synthesizing other chemical compounds or may be directly used, for example as a corrosion inhibitor or as an aid in mirror finishing and electroplating.Formaldehyde generally is produced by conversion of methanol in the presence of a catalyst. Suitable processes for producing formaldehyde are described for example in A. W. Franz et aL, “Formaldehyde”, Ullmann’s Encyclopedia of Industrial Chemistry, 2016, DOI:10.1002 / 14356007. a11 _619.pub2.For complete conversion, methanol, air and steam are fed into a reactor, in which the methanol is converted into formaldehyde and hydrogen. The hydrogen reacts with the oxygen contained in the air, thereby forming water. The amounts of air and steam are selected such that the amount of hydrogen is kept below the lower explosive limit.The crude formaldehyde containing gas stream obtained by the conversion of methanol is cooled and then fed into an absorption column, in which the formaldehyde is absorbed in water. The absorption column generally comprises a plurality of stages, for example four stages. Presently the stages are cooled by withdrawing a part of the liquid phase from the column at a lower position of the stage, the liquid phase is cooled, generally by using air coolers, and then returned into the column at an upper position.Since cooling is carried out in air coolers, it is not possible to use the energy dissipated by cooling. Further, for evaporating the methanol additional heat must be supplied. The steam for supplying the heat generally is produced in a power station, so that carbon dioxide emissions are generated. Further, using air coolers has the disadvantage that cooling efficiency also depends on the ambient temperature.Therefore, it was an object of the present invention to provide a process for producing formaldehyde, which allows a cooling that is more stable than cooling by using air coolers and which further can be operated with reduced energy demand so that also the carbon dioxide emissions can be reduced.This object is achieved by a process for producing formaldehyde, the process comprising: feeding methanol, air and steam into a reactor; obtaining a crude formaldehyde containing gas stream by conversion of methanol in the reactor; feeding the crude formaldehyde containing gas stream into an absorption column in which formaldehyde is absorbed in water; wherein aqueous formaldehyde solution obtained in the absorption column is used at least partly as a heat source for producing steam in a heat pump.By using the aqueous formaldehyde solution obtained in the absorption column at least partly as a heat source for producing steam in a heat pump, a cooling independent from ambient conditions and hence a stable cooling can be achieved. Further, the steam generated in the heat pump may be used in the process for producing formaldehyde, for example for preheating feed streams being fed into the reactor. By using the steam in the process, the energy consumption of the whole process can be reduced. Further, as the external steam production for operating the process can be minimized, also the generation of carbon dioxide is reduced. However, as generally large amounts of steam are generated in a process for producing formaldehyde, it is particularly preferred to feed the steam into a steam grid and to replace steam produced in steam generation plants by using fossil energy sources. By the replacement of steam, emissions can be reduced, particularly carbon dioxide emissions, due to the reduced amount of steam produced on the basis of fossil energy sources.For producing the formaldehyde, in a first step methanol, air and steam are fed into a reactor, in which the methanol is converted into formaldehyde. Generally, the reaction is carried out in the presence of a catalyst, for example a silver catalyst.The methanol, steam and air may be mixed, thereby forming a feed stream and the feed stream containing the methanol, the steam and the air is fed into the reactor. The feed stream preferably has a temperature in a range from 67 to 88 °C, more preferred in a range from 70 to 85 °C and particularly in a range from 75 to 83 °C and a pressure in a range from 1 ,1 to 1 ,8 bar(abs), more preferred in a range from 1 ,3 to 1 ,7 bar(abs).To achieve the temperature with which the feed stream is fed into the reactor, it is possible to evaporate the methanol and to mix the evaporated methanol with steam and air and, if necessary, to further heat the feed stream in a heat exchanger upstream the reactor. Alternatively, it is also possible to feed water, methanol, air and recycled off-gas from the absorption column into an evaporator. The evaporator may be for example a circulation evaporator with an external heat exchanger. In this case, a liquid phase is withdrawn from an evaporator column, at least partly evaporated in a heat exchanger and then returned into the evaporator column. In the evaporator column, liquid phase and gaseous phase are separated and the gaseous phase is superheated in a further heat exchanger and fed into the reactor.The heat transfer medium used in the heat exchanger of the circulation evaporator for at least partly evaporating the liquid phase preferably is steam withdrawn from the absorption column to provide heat integration.The crude formaldehyde containing gas stream obtained in the reactor is cooled to a temperature in a range from 65 to 95 °C, more preferred to a temperature in a range from 70 to 90 °C and particularly to a temperature in a range from 75 to 85 °C and then fed into the absorption column.The absorption column preferably comprises at least two sections, preferably three to five sections and particularly four sections. Generally, water is fed into the absorption column at the top and a mixture of formaldehyde and water is withdrawn at the bottom of the absorption column. Further, in at least one section, the aqueous formaldehyde solution is withdrawn at the bottom of the at least one section, cooled and returned at the top into the at least one section. Particularly, aqueous formaldehyde solution is withdrawn at the bottom of each section, cooled returned at the top into the respective section. At the bottom section, a part of the aqueous formaldehyde solution is withdrawn as crude product and the remainder is cooled and returned. At the top section, besides the aqueous formaldehyde solution, additionally water is added. The amount of water preferably corresponds to the amount of water in the aqueous formaldehyde solution withdrawn at the lowest section to enable a continuous process. The water may be added as a separate stream or may be mixed with the aqueous formaldehyde solution withdrawn below the top section. Preferably, the water is mixed with the aqueous formaldehyde solution. Depending on the temperature of the water, additional cooling of the aqueous formaldehyde solution withdrawn at the bottom of the top section and fed back at the top of the top section may not be necessary.In each section, formaldehyde is absorbed in the aqueous formaldehyde solution so that the concentration of the aqueous formaldehyde solution increases from the top section to the bottom section. By absorption of formaldehyde, the concentration of formaldehyde in the crude formaldehyde containing gas stream decreases from bottom to top of the absorption column. For an intense contact of the liquid phase and the gas phase, it is preferred that each section comprises internals, for example trays or packings, preferably packings. Suitable packings may be structured packings or random packings. The aqueous formaldehyde solution is withdrawn below the internals of the respective section and returned above the internals of the respective section.If the absorption column comprises at least two sections, it is preferred that in at least one section the aqueous formaldehyde solution is used as a heat source for producing steam in a heat pump. For this purpose, the aqueous formaldehyde solution is withdrawn at the bottom of the at least one section, being used as a heat source in the heat pump and, after being used as heat source in the heat pump, is recycled at the top into the at least one section.In a preferred embodiment, the absorption column comprises a bottom section, a top section and at least one intermediate section, wherein the aqueous formaldehyde solution is withdrawnat the bottom of at least one of the intermediate sections and, after being used as heat source in the heat pump, is recycled into the absorption column at the top the respective intermediate section. If the absorption column comprises more than one intermediate section, it is particularly preferred, that the aqueous formaldehyde solution withdrawn at the bottom of each intermediate section is used as heat source in a heat pump.A heat pump in the context of the present invention is any apparatus in which a process stream is evaporated and optionally heated. Subsequently the process stream compressed in a pump or compressor to a higher pressure and temperature level. The heat pump used for generating steam may be of any type, for example an open loop heat pump or a closed loop heat pump.In a preferred embodiment, the heat pump is an open loop heat pump comprising a heat exchanger, in which a water stream is heated by heat transfer from the aqueous formaldehyde solution, a flash apparatus, in which a part of the heated water stream evaporates to form steam, and at least one compressor, in which the steam is compressed to generate process steam.For heating the water stream by heat transfer from the aqueous formaldehyde solution, a heat exchanger is used. The heat exchanger may be of any type suitable for cooling an aqueous formaldehyde solution known to a skilled person. Suitable heat exchangers for example are shell-and-tube heat exchangers.In the flash apparatus, a part of the water stream evaporates due to expansion. By partly evaporating water, saturated steam and a liquid phase are obtained. The saturated steam is separated from the liquid phase, withdrawn from the flash apparatus and compressed in the at least one compressor to generate process steam.The water not being evaporated in the flash apparatus and forming the liquid phase may be withdrawn and used as heated water or, preferably, the water not being evaporated in the flash apparatus is recycled into the heat exchanger.The flash apparatus may be any apparatus suitable for flash evaporation and subsequent phase separation. Preferably, the flash apparatus is a flash tank, in which the saturated steam forms an upper phase and the water not being evaporated a lower liquid phase. The pressure in the flash tank may be set by using a vacuum pump or, preferably, by the at least one compressor for compressing the steam. The water withdrawn from the flash apparatus and recycled into the heat exchanger is compressed before being fed into the heat exchanger. As some of the water is withdrawn as steam, it is necessary that also fresh water is fed into the heat exchanger. Preferably, the fresh water and the recycled water are mixed and then fed into the heat exchanger. The fresh water and the recycled water may be mixed before being compressed in the pump or, if the pressure of the fresh water already corresponds to the pressure with which the water is to be fed into the heat exchanger, downstream the pump for compressing and feeding the recycled water into the heat exchanger. The fresh water fed into the heat exchanger preferably is degassed and demineralized water.The water stream being fed into the heat exchanger preferably has a pressure in a range from 1 to 4 bar(abs), more preferred in a range from 1.5 to 2.5 bar(abs) and particularly in a range from 1 .8 to 2.2 bar(abs). The temperature of the water being fed into the heat exchanger preferably is in a range from 30 to 75 °C, more preferred in a range from 40 to 70 °C and particularly in a range from 55 to 65 °C.In the heat exchanger, the water preferably is heated to a temperature in a range from 45 to 95 °C, more preferred to a temperature in a range from 55 to 85 °C and particularly to a temperature in a range from 65 to 75 °C.For evaporating a part of the water, the water stream is expanded in the flash apparatus to a pressure in a range from 0.01 to 1 .0 bar(abs), more preferred to a pressure in a range from 0.1 to 0.8 bar(abs) and particularly to a pressure in a range from 0.15 to 0.4 bar(abs).Besides an open loop heat pump with a flash evaporator, it is also possible that the heat pump is an open loop heat pump comprising a heat exchanger, in which a water stream is evaporated by heat transfer from the aqueous formaldehyde solution, and a compressor, in which the evaporated water is compressed to generate process steam. If no flash evaporator is used, it is necessary that the water being heated in the heat exchanger has a pressure being low enough that at least a part of the water evaporates in the heat exchanger by heat transfer from the aqueous formaldehyde solution. Preferably, the water being fed into the heat exchanger has a pressure in a range from 0,05 to 0,85 bar(abs), more preferred in a range from 0,15 to 0,6 bar(abs) and particularly in a range from 0,2 to 0,4 bar(abs).The temperature, with which the water is fed into the heat exchanger of the open loop heat pump preferably corresponds to the temperature of the water fed into the heat exchanger of the heat pump with flash evaporator.As an alternative, the heat pump is a closed loop heat pump comprising a closed loop in which a heat transfer medium flows and which comprises a first heat exchanger, a second heat exchanger, a compressor and an expansion unit, and generating steam comprises:(i) evaporating a heat transfer medium in the first heat exchanger by heat transfer from the aqueous formaldehyde solution;(ii) compressing the evaporated heat transfer medium in the compressor, wherein the temperature of the evaporated heat transfer medium increases;(iii) heating and at least partly evaporating water in the second heat exchanger by heat transfer from the evaporated heat transfer medium, wherein the heat transfer medium is cooled;(iv) expanding the cooled heat transfer medium in the expansion unit;(v) returning the expanded heat transfer medium into the first heat exchanger;(vi) repeating steps (i) to (v), wherein the at least partly evaporated water obtained in step (iii) is compressed to generate process steam.The heat transfer medium may be for example glycol-water mixtures or heat transmission liquids like ethyleneoxide, cyclobutene, 1 -butyne, cis-butene, trans-butene, 1 ,3-butadiene, 1- butene, propyne, butane, isobutene, dimethylether, cyclopropane, ammonia, propadiene, neopentane, isobutane, R441A, R1233ZDE, R1234ZEZ, R1224YDZ, R40, R436B, R510A, R435A, R429A, R436A, RE235CB2, R152A and R440A.If the heat pump is a closed loop heat pump, the water to be evaporated in the second heat exchanger preferably has a pressure in a range from 0.9 to 4 bar(abs), more preferred in a range from 1 to 2 bar(abs) and particularly in a range from 1.2 to 1 .5 bar(abs) and a temperature in a range from 10 to 99 °C, more preferred in a range from 40 to 80 °C and particularly in a range from 50 to 70 °C. The steam obtained in the second heat exchanger preferably has a temperature in a range from 96 to 160 °C, more preferred in a range from 99 to 140 °C and particularly in a range from 104 to 120 °C.The aqueous formaldehyde solution being withdrawn below any of the sections in the absorption column and used as heat source for producing steam in the heat pump preferably has a temperature in a range from 50 to 95 °C and particularly in a range from 70 to 85 °C.Particularly if the absorption column comprises at least three sections, it is preferred that the part of the aqueous formaldehyde solution withdrawn below the bottom section and recycled into the absorption column at the top of the bottom section is cooled in a heat exchanger by heat transfer to the feed stream. In this case it is particularly preferred that the heat exchanger is the heat exchanger of the circulation evaporator.The steam produced in the heat pump may have any pressure. Depending on the pressure of the steam produced in the heat pump, it is possible to further compress the steam to obtain low pressure steam, medium pressure steam or high pressure steam. Further, it is possible to divide the steam produced in the heat pump into separate streams which can be compressed to different pressures. This allows for example to produce medium pressure steam and high pressure steam, low pressure steam and medium pressure steam, low pressure steam and high pressure steam or even low pressure steam, medium pressure steam and high pressure steam.In the context of the present invention, the term “low pressure steam” means steam having a pressure in a range from 0.9 to 4 bar(abs), more preferred in a range from 1 to 2 bar(abs) and particularly in a range from 1 .2 to 1.5 bar(abs) and a temperature in a range from 96 to 160 °C, more preferred in a range from 99 to 140 °C and particularly in a range from 104 to 120 °C.The term “medium pressure steam” means steam having a pressure in a range from 4 to 8 bar(abs), more preferred in a range from 4.5 to 7 bar(abs) and particularly in a range from 5 to 6 bar(abs) and a temperature in a range from 143 to 220 °C, more preferred in a range from 147 to 210 °C and particularly in a range from 151 to 200 °C.The term “high pressure steam” means steam having a pressure in a range from 8 to40 bar(abs), more preferred in a range from 10 to 30 bar(abs) and particularly in a range from 16 to 20 bar(abs) and a temperature in a range from 170 to 280 °C, more preferred in a range from 180 to 260 °C and particularly in a range from 201 to 240 °C.Besides producing low pressure steam, medium pressure steam or high pressure steam, it is also possible to use the steam produced in the heat pump without any further compression. This is for example suitable, if the steam directly is used in a specific process, for example for heating a stream or an apparatus.Particularly preferably, the process steam generated in the heat pump is low pressure steam having a pressure of up to 4 bar(g). The low pressure steam produced in the heat pump may be fed for example into a low pressure steam grid and / or directly to a steam consumer for low pressure steam.If it is intended to produce medium pressure steam, it is possible that at least a part of the process steam produced in the heat pump is compressed to a pressure in a range from 4 to 8 bar(g). The thus produced medium pressure steam then may be fed for example into a medium pressure steam grid and / or directly to a steam consumer for mid pressure steam.Besides producing the medium pressure steam by compressing the process steam generated in the heat pump, it is also possible to obtain medium pressure steam by mixing low pressure steam generated in the heat pump with high pressure steam.Besides producing low pressure steam or medium pressure steam, it is also possible produce high pressure steam. In this case, at least a part of the steam is compressed to a pressure of more than 8 bar(g). The high pressure steam then may be fed into a high pressure steam grid and / or directly to a steam consumer for high pressure steam.For compressing the steam, only one compressor may be used or a cascade of at least two compressors. If only one compressor is used, the compressor preferably comprises at least two compressor stages. The number of compressors or of compressor stages depends on the pressure of the steam to be produced.For setting the properties of the steam, particularly the temperature, it is possible to inject water after at least one compressor or compressor stage. Preferably, water is injected after each compressor or compressor stage.To obtain pure steam and to reduce or avoid formation of deposits, particularly lime scale deposits or deposits of other salts that may be contained in water, it is particularly preferred that the water used for producing the steam is demineralized and degassed water.The present invention further relates to a target product that can be obtained or achieved by a method according to the present invention.The publication Prior Art Disclosure; Issue 684; paragraphs

[1000] to

[8005] ; ISSN: 2198-4786; published: February 12, 2024 will be regarded as Reference RF1 , which is incorporated herein by reference in its entirety. Preferably, the target product is a product as described in Reference RF1 ; paragraphs

[1000] to

[8005] ,Preferably, the process described herein is further a process for the production of a product, preferably a target product. The converting step to obtain the target product preferably comprises one or more step(s) as described below and can be performed by conventional methods well known to a person skilled in the art. The converting step preferably comprises one or more step(s) selected from: recycling, preferably depolymerizing, gasifying, pyrolyzing, and / or steam cracking; and / or purifying, preferably crystallizing, (solvent) extracting, distilling, evaporating, hydrotreating, absorbing, adsorbing and / or subjecting to ion exchanger; and / or assembling, preferably foaming, synthesizing, chemical conversion, chemically transforming, polymerizing and / or compounding; and / or forming, preferably foaming, extruding and / or molding; and / or finishing, preferably coating and / or smoothing. In addition, the one or more step(s) are described in detail in Reference RF1 ; paragraphs

[1000] to

[8005] ,The term “building block”, as used herein, comprises compounds, which are in a gaseous or liquid state under standard conditions of 0°C and 0.1 MPa. Building blocks are typically used in chemical industry to form secondary products, which provide a higher structural complexity and / or higher molecular weight than the building block on which the secondary product is based. The building block is preferably selected from the group consisting of hydrogen, carbon monoxide, carbon dioxide, ethylene oxide, ethylene glycols, syngas comprising a mixture of hydrogen and carbon monoxide, alkanes, alkenes, alkynes and aromatic compounds. The alkanes, alkenes, alkynes and aromatic compounds comprise in particular 1 to 12 carbon atoms, respectively.The term “monomer”, as used herein, comprises molecules, which can react with each other to form polymer chains by polymerization. The monomer is preferably selected from the group consisting of (meth)acrylic acid, salts of (meth)acrylic acid; in particular sodium, potassium and zinc salts; (meth)acrolein and (meth)acrylates. (Meth)acrylates comprising 1 to 22 carbon atoms are preferred, in particular comprising 1 to 8 carbon atoms.The terms (meth)acrylic acid, (meth)acrolein or (meth)acrylate relate to acrylic acid, acrolein or acrylate and also to methacrylic acid, methacrolein or methacrylate, where applicable. Further, the monomer can be selected from hexamethylenediamine (HMD) and adipic acid. The building block can further be an intermediate compound.The term “intermediate compound”, as used herein, comprises organic reagents, which are applied for formation of compounds with higher molecular complexity. The intermediate compound can be selected for example from the group consisting of phosgene, polyisocyanates and propylene oxide. The polyisocyanates are in particular aromatic di- and polyisocyanates, preferably toluene diisocyanate (TDI) and / or diphenylmethane diisocyanate (MDI). The buildingblock and the monomer and typical converting step(s) to obtain the building block or monomer are described in more detail in paragraphs

[1000] to

[1012] of Reference RF1.The term “polymer A”, as used herein, comprises thermoplastic, e.g., polyamide or thermoplastic polyurethane, thermoset, e.g., polyurethane, elastomer, e.g., polybutadiene, or a copolymer or a mixture thereof and is defined in more detail in paragraphs

[2001] to

[2007] of Reference RF1.The term “polymer composition A”, as used herein, comprises all compositions comprising a polymer as described above and one or more additive(s), e.g. reinforcement, colorant, modifier and / or flame retardant, and is defined in more detail in paragraph

[2008] of Reference RF1.The term “polymer product A”, as used herein, comprises any product comprising the polymer A and / or polymer composition A as described above and is defined in more detail in paragraphs

[2009] and

[2010] of Reference RF1. The step(s) to obtain the polymer, preferably polymer A, polymer composition, preferably polymer composition A or polymer product, preferably polymer product A is / are described in more detail in paragraph

[2011] of Reference RF1.The term “industrial use polymer”, as used herein, comprises rheological polymers, polycarboxylate, alkoxylated polyalkylenamine, alkoxylated polyalkylenimine, polyether-based, dye inhibition polymers and soil release cleaning polymers defined in more detail in paragraphs

[3035] to

[3044] of Reference RF1.The term “industrial use surfactant”, as used herein, comprises non-ionic, anionic and amphoteric industrial use surfactants defined in more detail in paragraphs

[3008] to

[3034] of Reference RF1.The term “industrial use descaling compound”, as used herein, comprises nonphosphate based builders (NPB) and phosphonates (CoP) described in more detail in paragraphs

[3001] to

[3005] of Reference RF1.The term “industrial use biocide”, as used herein, refers to a chemical compound that kills microorganisms or inhibits their growth or reproduction defined in more detail in paragraphs

[3006] to

[3007] of Reference RF1.The term “industrial use solvent”, as used herein, comprises alkyl amides, alkyllactamides, alkyl esters, lactate esters, alkyl diester, cyclic alkyl diester, cyclic carbonates, aromatic aldehydes and aromatic esters defined in more detail in paragraphs

[3045] to

[3055] of Reference RF1.The term “industrial use dispersant”, as used herein, comprises anionic and non-ionic industrial use dispersants defined in more detail in paragraphs

[3056] to

[3058] of Reference RF1.The term “composition and / or formulation thereof’ with reference to the industrial use polymers, industrial use surfactants, descaling compounds and / or industrial use biocides refers toindustrial use compositions and / or institutional use products and / or fabric and home care products and / or personal care products defined in more detail in paragraph

[3059] of Reference RF1 . The converting step(s) to obtain the industrial use polymer, industrial use surfactant, descaling compound and / or industrial use biocide are defined in more detail in paragraph

[3060] of Reference RF1. The converting steps to obtain the industrial use composition or formulation of the industrial use polymer, industrial use surfactant, descaling compound and / or industrial use biocide are defined in more detail in paragraph

[3061] of Reference RF1.The term “agrochemical composition”, as used herein, typically relates to a composition comprising an agrochemically active ingredient and at least one agrochemical formulation auxiliary. Examples of agrochemical compositions, active ingredients and auxiliaries are described in more detail in Reference RF1 , paragraph

[4001] , The agrochemical composition may take the form of any customary formulation. The agrochemical compositions are prepared in a known manner, e.g. described by Mollet and Grubemann, Formulation technology, Wiley VCH, Weinheim, 2001 ; or Knowles, New developments in crop protection product formulation, Agrow Reports DS243, T&F Informa, London, 2005. The converting step(s) to obtain the agrochemically active ingredients and auxiliaries may be conducted in analogy to the production step(s) of their analogues that are based on petrochemicals or other precursors that are not gained by recycling processes. In addition, conversion to compounds mentioned in sections “Polymer” and “Cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter, further cosmetic ingredient or compositions or formulations thereof’ may be performed as described in these sections as well as the respective paragraphs in Reference RF1.The term active pharmaceutical ingredients and / or intermediates thereof, as used herein, comprises substances that provide pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body. Intermediates thereof are isolated products that are generated during a multi-step route of synthesis of an active pharmaceutical ingredient.The term pharmaceutical excipients, as used herein, comprises compounds or compound mixtures used in compositions for various pharmaceutical applications, which are not substantially pharmaceutically active on itself. Active pharmaceutical ingredients and / or intermediates thereof and pharmaceutical excipients are defined in more detail in paragraph

[5001] of Reference RF1. The converting step(s) to obtain the active pharmaceutical ingredients and / or intermediates thereof and pharmaceutical excipients may comprise one or more synthesis steps and can be performed by conventional synthesis and techniques well known to a person skilled in the art.The terms animal feed additives, human food additives, dietary supplements, as used herein, comprises Vitamins, Pro-Vitamins and active metabolites thereof including intermediates and precursors, especially Vitamin A, B, E, D, K and esters thereof, like acetate, propionate, palmitate esters or alcohols thereof like retinol or salts thereof and any combinations thereof; Tetraterpenes, especially isoprenoids like carotenoids and xanthophylls including their intermediates and precursors as well as mixtures and derivates thereof, especially betacarotene, Canthaxanthin, Citranaxanthin, Astaxanthin, Zeaxanthin, Lutein, Lycopene, Apocarotenoids, and any combinations thereof; organic acids, especially formic acid, propionic acid and salts thereof, such as sodium, calcium or ammonium salts, and any combinations thereof, such as but not limited to mixtures of formic acid and sodium formiate, propionic acid and ammonium propionate, formic acid and propionic acid, formic acid and sodium formiate and propionic acid, propionic acid and sodium propionate and formic acid and sodium formiate; glycerides of carboxylic acids and short and medium chain fatty acids, conjugated linoleic acids, such as omega-6 fatty acid (C18:2) methyl ester and 1 ,2-propandiol and beverage stabilizers, such as polyvinylpyrrolidone-polymer or polyvinylimidazole / polyvinylpyrrolidone-copolymer. Animal feed additives, human food additives and dietary supplements are defined in more detail in paragraph

[5002] of Reference RF1 . The converting step(s) to obtain the animal feed additives, human food additives, dietary supplements may comprise one or more synthesis steps and can be performed by conventional synthesis and techniques well known to a person skilled in the art.The terms aroma chemical and aroma composition as used herein, comprise a volatile organic substance with a molecular weight between 70-250 g / mol comprising a functional group with a carbon skeleton of C5-C16 carbon atoms comprising linear, branched, cyclic, for example with a ring size of C5-C18, bicyclic or tricyclic aliphatic chains and but not necessarily one or more unsaturated structural elements like double bonds, triple bonds, aromatics or heteroaromatics and preferably the one or more additional functional groups are selected from alcohol, ether, ester, ketone, aldehyde, acetal, carboxylic acid, nitrile, thiol, amine. In one aspect, the aroma chemical is a terpene-based aroma chemical, for example selected from monoterpenes and monoterpenoids, sesquiterpenes and sesquiterpenoids, diterpenes, triterpenes or tetraterpenes. Aroma chemicals can be combined with further aroma chemicals to give an aroma composition. Aroma chemicals and aroma compositions are defined in more detail in paragraph

[5003] of Reference RF1. The converting step(s) to obtain the aroma chemical and aroma composition may comprise one or more synthesis steps and can be performed by conventional synthesis and techniques well known to a person skilled in the art.The term “aqueous polymer dispersion”, as used herein, comprises aqueous composition(s) comprising dispersed polymer(s) and is defined in more detail in the section

[6001] entitled “aqueous polymer dispersion” of Reference RF1 . The dispersed polymer(s) may be selected from acrylic emulsion polymer(s), styrene acrylic emulsion polymer(s), styrene butadiene dispersion(s), aqueous dispersion(s) comprising composite particles, acrylate alkyd hybrid dispersion(s), polyurethane(s) (including UV-curable polyurethanes) and polyurethane - poly(meth)acrylate hybrid polymer(s).The term “emulsion polymer”, as used herein, comprises polymer(s) made by free-radical emulsion polymerization. Aqueous polyurethane dispersion(s) are defined in more detail in the section

[6002] entitled “Polyurethane dispersions” of Reference RF1. UV-curable polyurethane(s) is / are defined in more detail in the section

[6017] of Reference RF1 . Polyurethane - poly(meth)acrylate hybrid polymer(s) is / are defined in more detail in the section

[6016] of Reference RF1.The term “polymeric dispersant”, as used herein, comprises preferably polymer(s) comprising polyether side chain, in particular polycarboxylate ether polymer(s) and polycondensation product(s) defined in more detail in paragraph

[6020] entitled “Polymeric dispersant” of Reference RF1 . The converting (polymerization) step(s) to obtain the aqueous polymer dispersion(s) comprising emulsion polymer(s) is / are defined in more detail in the section

[6003] entitled “Emulsion polymerization” of Reference RF1 . The converting (polymerization) step(s) to obtain the aqueous polyurethane dispersion(s) is / are defined in more detail in the section

[6014] entitled “Process for the preparation of aqueous polyurethane dispersions” and section

[6017] entitled “Aqueous UV-curable polyurethane dispersions, their preparation and use and compositions containing them” of Reference RF1. Composition(s) and uses of aqueous polymer dispersion(s) and of polymeric dispersant(s) are defined in more detail in the following sections of Reference RF1 : section

[6004] entitled “Uses of aqueous polymer dispersions”, section

[6005] entitled “Binders for architectural and construction coatings” section

[6006] entitled “Binders for paper coating” section

[6007] entitled “Binders for fiber bonding” section

[6008] entitled “Adhesive polymers and adhesive compositions” section

[6015] entitled “Aqueous polyurethane dispersions suitable for use in coating compositions” section

[6016] entitled “Aqueous polyurethane - poly(meth)acrylate hybrid polymer dispersions suitable for use in coating compositions” section

[6017] entitled “Aqueous UV-curable polyurethane dispersions, their preparation and use and compositions containing them section

[6018] entitled “Inorganic binder compositions comprising polymeric dispersants and their use”

[6019] 100% curable coating compositions UV-crosslinkable poly(meth)acrylate(s) and its / their uses are defined in more detail in section

[6009] entitled “UV-crosslinkable poly(meth)acrylates for use in UV- curable solvent-free hotmelt adhesives and their use for making pressure-sensitive self- adhesive articles” of Reference RF1. Polyisocyanate(s), composition(s) comprising them and their uses are defined in more detail in section

[6010] entitled “Polyisocyanates” of Reference RF1. Hyperbranched polyester polyol(s) and its / their uses are defined in more detail in section

[6011] entitled “Organic solvent based hyperbranched polyester polyols suitable for use in coating compositions” of Reference RF1. The converting step(s) to obtain the hyperbranched polyester polyols is / are defined in more detail in the section

[6012] entitled “Preparation of organic solvent based hyperbranched polyester polyols” of Reference RF1. Coating composition(s) comprising hyperbranched polyester polyol(s), polyisocyanate(s) and additive(s) and substrate(s) coated therewith are defined in more detail in section

[6013] entitled “Organic solvent based two component coating compositions comprising hyperbranched polyester polyols and polyisocyanates” of Reference RF1 . Unsaturated polyester polyol(s), solvent-based coating composition(s) comprising said unsaturated polyester polyol(s) and substrate(s) for coating with said coating composition(s) are defined in more detail in section

[6018] entitled “Organic solvent based coating composition comprising unsaturated polyester polyols” of Reference RF1. 100% curable coating composition(s) is / are defined in more detail in section

[6019] of Reference RF1. Polymeric dispersant(s) for inorganic binder compositions is / are defined in more detail in section

[6020] of Reference RF1. The inorganic binder composition(s) comprising the polymeric dispersants and their use are defined in more detail in section

[6021] of Reference RF1 . The converting step(s) to obtain the polymeric dispersant(s) are defined in more detail in section

[6020] of Reference RF1.The term “inorganic binder composition” comprising the polymeric dispersant(s), as used herein, comprises preferably in particular hydraulically setting compositions and compositions comprising calcium sulfate and is defined in more detail in section

[6021] of Reference RF1 entitled “Inorganic binder compositions comprising the polymeric dispersant and their use”. Specific building material formulation(s) comprising polymeric dispersant(s) or building product(s) produced by a building material formulation comprising a polymeric dispersant are disclosed in more detail in section

[6021] of Reference RF1.The term “cosmetic surfactant”, as used herein, comprises non-ionic, anionic, cationic, and amphoteric surfactants and is defined in more detail in paragraph

[7002] of Reference RF1.The term “emollient”, as used herein, refers to a chemical compound used for protecting, moisturizing, and / or lubricating the skin and is defined in more detail in paragraph

[7003] of Reference RF1.The term “wax”, as used herein, comprises pearlizers and opacifiers and is defined in more detail in paragraph

[7004] of Reference RF1.The term “cosmetic polymer”, as used herein, comprises any polymer that can be used as an ingredient in a cosmetic formulation and is defined in more detail in paragraph

[7005] of Reference RF1.The term “UV filter”, as used herein, refers to a chemical compound that blocks or absorbs ultraviolet light and is defined in more detail in paragraph

[7006] of Reference RF1.The term “further cosmetic ingredient”, as used herein, comprises any ingredient suitable for making a cosmetic formulation. Several sources disclose cosmetically acceptable ingredients.E. g. the database Cosing on the internet pages of the European Commission discloses cosmetic ingredients and the International Cosmetic Ingredient Dictionary and Handbook, edited by the Personal Care Products Council (PCPC), discloses cosmetic ingredients.The term “composition and / or formulation thereof’ with reference to the cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter and / or further cosmetic ingredient refers to personal care and / or cosmetic compositions or formulations defined in more detail in paragraph

[7007] of Reference RF1 . The converting step(s) to obtain the cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter or further cosmetic ingredient is / are defined in more detail in paragraph

[7008] of Reference RF1.The terms “polymer B”, “polymer composition B”, “coating composition”, “other functional composition”, “foil”, “molded body”, “coating” and “coated substrate” are well known to the person skilled in the art and are defined in more detail from paragraph

[8000] to

[8005] of Reference RF1 .In a preferred embodiment, the target product is selected from: i) building block or monomer; or ii) polymer, preferably polymer A, polymer composition, preferably polymer composition A, or polymer product, preferably polymer product A; or iii) cleaning polymer, cleaning surfactant, descaling compound, cleaning biocide or composition or formulation thereof; or iv) agrochemical composition, agrochemical formulation auxiliary or agrochemically active ingredient; or v) active pharmaceutical ingredient or intermediate thereof, pharmaceutical excipient, animal feed additive, human food additive, dietary supplements, aroma chemical or aroma composition; or vi) aqueous polymer dispersion, preferably polyurethane or polyurethane - poly(meth)acrylate hybrid polymer dispersion, emulsion, binder for paper and fiber coatings, UV-curable acrylic polymer for hot melts and coatings polyisocyanates, hyper branched polyester polyol, polymeric dispersant for inorganic binder compositions, unsaturated polyester polyol or 100% curable composition; or vii) cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter, further cosmetic ingredient or composition or formulation thereof; or viii) polymer B, polymer composition B, coating composition, other functional composition, foil, molded body, coating or coated substrate.In a preferred embodiment, the content of the formaldehyde in the target product is 1 weight- % or more, preferably 2 weight-% or more, more preferably 5 weight-% or more, more preferably 15 weight- % or more, more preferably 30 weight-% or more, more preferably 40 weight-% or more, more preferably 60 weight-% or more, more preferably 80 weight-% or more, more preferably 90 weight-% or more, more preferably 95 weight-% or more; and / or the content of the formaldehyde in target product is 100 weight-% or less, preferably 95 weight- % or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less; and preferably the content is determined based on identity preservation and / or segregation and / or mass balance and / or book and claim chain of custody models, preferably based on mass balance, preferably the International Sustainability and Carbon Certification (ISCC) standard.In a preferred embodiment, preferably according to the above-mentioned embodiments of the process, the method comprises the step of converting the product of the process, namely formaldehyde, which can be achieved or obtained by one of the above-mentioned embodiments, to obtain the target product.An embodiment of the invention is shown in the figure.The only figure shows schematically a process for producing formaldehyde with using aqueous formaldehyde solution as heat source in a heat pump.For producing formaldehyde, a mixture of methanol and water is fed into a circulation evaporator 1 via a first feed line 3 and air is fed into the circulation evaporator 1 via a second feed line 5.In the circulation evaporator, the methanol and the water are evaporated. For this purpose, liquid water and methanol are withdrawn from an evaporation apparatus 7 and fed into a heat exchanger 9 for heat integration, in which the water and methanol are heated. If the heat supplied to the water and methanol in the heat exchanger 9 for heat integration is not sufficient for at least partly evaporate the water and methanol, an additional heat exchanger 11 may be provided. In the heat exchanger 9 for heat integration and, optionally, the additional heat exchanger, the water and methanol are at least partly evaporated and the thus obtained two phase stream, containing steam and gaseous methanol as gas phase and liquid water and liquid methanol as liquid phase is returned into the evaporation apparatus.In the evaporation apparatus, the liquid phase and the gas phase are separated and the gas phase is fed into a reactor 13 via a feed line 15. In the feed line 15, a superheater 17 may be provided, in which the gas phase, containing air, methanol and steam is heated to a temperature in a range from 80 to 100 °C.In the reactor 13, the methanol is converted into formaldehyde, thereby obtaining a crude formaldehyde containing gas stream. To reduce conversion of the formaldehyde into undesired by-products, the crude formaldehyde containing gas stream is cooled in a cooler 19 immediately after leaving the reactor 13.The cooling medium used for cooling the crude formaldehyde containing gas stream preferably is water. Due to the reaction heat, the water is evaporated in the cooler 19, thereby obtaining steam, which may be further used.If cooling in the cooler 19 is not sufficient, an additional cooler 20 may be provided for further cooling the crude formaldehyde containing gas stream. Preferably, the crude formaldehyde containing gas stream is cooled to a temperature in a range from 70 to below 100 °C, particularly in a range from 75 to 90 °C before feeding it into an absorption column 21 . The absorption column 21 usually comprises at least two sections, more preferred at least three sections and particularly four sections. For illustration purposes, the absorption column shown here comprises three sections, a bottom section 23, an intermediate section 25 and a top section 27.The crude formaldehyde containing gas stream is fed into the absorption column 21 below the bottom section 23 and water is fed into the absorption column 21 above the top section 27 via a water feed 29. In the absorption column 21 , the crude formaldehyde containing gas stream rises and flows in countercurrent to a water stream, which absorbs formaldehyde from the crude formaldehyde containing gas stream. By absorption, an aqueous formaldehyde solution is obtained, wherein the formaldehyde content in the aqueous formaldehyde solution increasesfrom top to bottom of the absorption column 21 and the formaldehyde content in the crude formaldehyde containing gas stream decreases from bottom to top.At the top of the absorption column 21 an off-gas stream 31 is withdrawn. The off-gas stream 31 may be cooled in an off-gas cooler 33. If the off-gas stream 31 is cooled, the cooling medium used for cooling the off-gas stream 31 preferably is water. The water generally at least partially evaporates in the off-gas cooler 33, thereby obtaining steam. The steam obtained in the off-gas cooler 33 by cooling the off-gas and the steam obtained in the cooler 19 by cooling the crude formaldehyde containing gas stream may be mixed, withdrawn from the process via a steam line 35 and supplied to further use. For this purpose, the steam for example may be fed into a steam grid. If the pressure of the steam grid is higher than the pressure of the steam obtained in the cooler 19 and the off-gas cooler 33, the steam obtained in the cooler 19 and the off-gas cooler 33 can be compressed to obtain the required pressure for supplying it to the steam grid.At the bottom of the absorption column 21 , a concentrated aqueous formaldehyde solution is obtained. The concentrated aqueous formaldehyde solution preferably is used as a heating medium in the heat exchanger 9 for heat integration. By heat transfer from the concentrated aqueous formaldehyde solution to the liquid methanol and water, the liquid methanol and water are heated and, optionally, at least partly evaporated and the concentrated aqueous formaldehyde solution is cooled. A part of the concentrated aqueous formaldehyde solution is withdrawn via a product line 37 and the remainder of the cooled concentrated aqueous formaldehyde solution is recycled into the absorption column 21 above the bottom section 23 via a recycle line 39.According to the invention, aqueous formaldehyde solution obtained by absorption in the absorption column 21 is used as a heat source in a heat pump.In the embodiment shown here, the aqueous formaldehyde solution is withdrawn below the intermediate section 25.If the absorption column comprises more than one intermediate section 25, it is necessary to withdraw aqueous formaldehyde solution below each intermediate section, to cool the aqueous formaldehyde solution and to recycle the cooled aqueous formaldehyde solution above the respective section. In this case, the aqueous formaldehyde solution withdrawn below any section can be used as a heat source in a heat pump. It is for example possible, to use the aqueous formaldehyde solution withdrawn below each intermediate section as heat source in a heat pump. If the absorption column comprises more than one intermediate section 25, it is particularly preferred to use the aqueous formaldehyde solution withdrawn below the lowest intermediate section 25, i.e. the intermediate section directly above the bottom section as heat source in a heat pump.If the absorption column comprises only two sections, it is preferred to use a part of the aqueous formaldehyde solution withdrawn below the bottom section 23 as heat source in the heat pump. However, it is preferred that the absorption column comprises at least oneintermediate section 25 so that the aqueous formaldehyde solution withdrawn below at least one of the intermediate sections is used as heat source in a heat pump.In the heat pump, steam is generated. For this purpose, a recycle line 41 with at least one heat exchanger 43 is provided. The aqueous formaldehyde solution used as heat source in the heat pump flows through the recycle line 41 and the at least one heat exchanger 43. In the at least one heat exchanger 43, water is heated by heat transfer from the aqueous formaldehyde solution.The number of heat exchangers 43 depends on the heat transfer surface and the possible size of the heat exchangers needed for sufficient heating of the water and cooling of the aqueous formaldehyde solution. The water and the aqueous formaldehyde solution preferably flow in countercurrent through the at least one heat exchanger 43. Suitable heat exchangers 43 for example are shell-and-tube heat exchangers.The aqueous formaldehyde solution fed into the at least one heat exchanger 43 preferably has a temperature in a range from 50 to 95 °C and the water is heated to a temperature in a range from 40 to 95 °C. The pressure of the water heated in the at least one heat exchanger is in a range from 1 to 4 bar(abs) and the temperature of the water fed into the at least one heat exchanger is in a range from 30 to 75°C.After heating, the water is fed into a flash apparatus 45, for example a flash vessel. In the flash vessel, the water is expanded to a pressure in a range from 0.01 to 1 bar(abs). By expansion a part of the water evaporates. Thus, in the flash apparatus 45 a liquid phase containing liquid water and a gas phase, containing saturated steam are obtained.The liquid phase is withdrawn from the flash apparatus 45, compressed in a pump 47 and fed into the at least one heat exchanger 43 for heating. The saturated steam is withdrawn via a steam line 49 and fed into at least one compressor 51 , in which the saturated steam is compressed and, thereby superheated to obtain process steam. For setting the properties, a water injection 53 may be provided.To keep the amount of water in the flash apparatus constant, fresh water, particularly demineralized and degassed water is added via a water feed 55.If the absorption process is operated but no steam is to be produced or the heat supplied to the water for steam production is not sufficient to cool the aqueous formaldehyde solution to a required temperature for recycling it into the absorption column, an additional heat exchanger 57 may be provided. The additional heat exchanger 57 preferably is an air cooler.If it is further intended to use only a part of the aqueous formaldehyde solution as a heat source in the heat pump for generating steam, a bypass line 59, which bypasses the at least one heat exchanger 43, may be provided.Besides the heat pump using a flash apparatus 45, alternatively, an open loop heat pump without flash apparatus may be used, if the water is completely evaporated in the at least one heat exchanger 43, or a closed loop heat pump comprising an additional closed circuit for a working fluid may be used.

Claims

Claims1 . A process for producing formaldehyde, the process comprising: feeding methanol, air and steam into a reactor (13); obtaining a crude formaldehyde containing gas stream by conversion of methanol in the reactor (13); feeding the crude formaldehyde containing gas stream into an absorption column (21) in which formaldehyde is absorbed in water; wherein aqueous formaldehyde solution obtained in the absorption column is used at least partly as a heat source for producing steam in a heat pump.

2. The process according to claim 1 , wherein the absorption column (21) comprises at least two sections (23, 25, 27), wherein in at least one section (23, 25, 27) the aqueous formaldehyde solution is withdrawn at the bottom of the at least one section (23, 25, 27) and, after being used as heat source in the heat pump, is recycled at the top into the at least one section (25).

3. The process according to claim 1 , wherein the absorption column (21) comprises a bottom section (23), a top section (27) and at least one intermediate section (25), wherein the aqueous formaldehyde solution is withdrawn at the bottom of at least one of the intermediate sections (25) and, after being used as heat source in the heat pump, is recycled into the absorption column (21) at the top the respective intermediate section (25).

4. The process according to any of claims 1 to 3, wherein the heat pump comprises a heat exchanger (43), in which a water stream is heated by heat transfer from the aqueous formaldehyde solution, a flash apparatus (45), in which a part of the heated water stream evaporates to form steam, and at least one compressor (51), in which the steam is compressed to generate process steam, wherein preferably the water not being evaporated in the flash apparatus (45) is recycled into the heat exchanger (43).

5. The process according to claim 4, wherein the water is expanded in the flash apparatus (45) to a pressure in a range from 0.01 to 1.0 bar(abs).

6. The process according to any of claims 1 to 3, wherein the heat pump is an open loop heat pump comprising a heat exchanger, in which a water stream is evaporated by heat transfer from the aqueous formaldehyde solution, and a compressor, in which the evaporated water is compressed to generate process steam.

7. The process according to any of claims 1 to 3, wherein the heat pump is a closed loop heat pump comprising a closed loop in which a heat transfer medium flows and which comprises a first heat exchanger, a second heat exchanger, a compressor and an expansion unit, and generating steam comprises:(i) evaporating a heat transfer medium in the first heat exchanger by heat transfer from the aqueous formaldehyde solution;(ii) compressing the evaporated heat transfer medium in the compressor, wherein the temperature of the evaporated heat transfer medium increases;(iii) heating and at least partly evaporating water in the second heat exchanger by heat transfer from the evaporated heat transfer medium, wherein the heat transfer medium is cooled;(iv) expanding the cooled heat transfer medium in the expansion unit;(v) returning the expanded heat transfer medium into the first heat exchanger;(vi) repeating steps (i) to (v), wherein the at least partly evaporated water obtained in step (iii) is compressed to generate process steam.

8. The process according to any of claims 1 to 7, wherein the aqueous formaldehyde solution being used as heat source in the heat pump has a temperature in a range from 50 to 95 °C.

9. The process according to any of claims 1 to 8, wherein the water being fed into the heat exchanger (43) has a pressure in a range from 1 to 4 bar(abs) and a temperature in a range from 30 to 75 °C.

10. The process according to any of claims 1 to 9, wherein the water is heated in the heat exchanger (43) to a temperature in a range from 45 to 95 °C.11 . The process according to any of claims 1 to 10, wherein the process steam has a pressure of up to 4 bar(g) and is fed into a low pressure steam grid and / or directly to a steam consumer for low pressure steam.

12. The process according to any of claims 1 to 11 , wherein at least a part of the steam is compressed to a pressure in a range from 4 to 8 bar(g) and fed into a mid pressure steam grid and / or directly to a steam consumer for mid pressure steam.

13. The process according to any of claims 1 to 12, wherein at least a part of the steam is compressed to a pressure of more than 8 bar(g) and fed into a high pressure steam grid and / or directly to a steam consumer for high pressure steam.

14. The process according to any of claims 1 to 13, wherein the water used for producing the steam is demineralized and degassed water.

15. A method for producing a target product by converting the formaldehyde, which can be obtained or has been obtained by the process according to any one of claims 1 to 14.

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