• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to a method for producing an aqueous solution of formaldehyde, wherein methanol is reacted with air to form a process gas having formaldehyde, and the process gas is fed to an absorber (6) in which formaldehyde is absorbed in water to form the aqueous solution of Formaldehyde to form, with a portion of the solution from the absorber (6) is branched off and cooled and then returned to the absorber (6). According to the invention, after cooling for a predetermined residence time, formation of polymethylene glycols is awaited to increase the absorbency of the branched portion of the solution of formaldehyde, after which the branched portion of the solution is heated and returned to the absorber (6). Furthermore, the invention relates to a device (1) for carrying out such a method.
    公开号:AT516530A1
    申请号:T50843/2014
    申请日:2014-11-20
    公开日:2016-06-15
    发明作者:Thomas Maria Josef Schmid
    申请人:Johnson Matthey Plc；
    IPC主号:
    专利说明:

    Process and apparatus for the preparation of an aqueous solution of formaldehyde
    The invention relates to a process for preparing an aqueous solution of formaldehyde, wherein methanol is reacted with air to form a process gas having formaldehyde, and the process gas is passed into an absorber in which formaldehyde is absorbed in water to add the aqueous solution of formaldehyde form, wherein a part of the solution is diverted from the absorber and cooled and then returned to the absorber. 10
    The invention further relates to an apparatus for producing an aqueous solution of formaldehyde by reacting methanol with air to form a process gas having formaldehyde, comprising a reactor for forming the process gas and an absorber downstream of the reactor for absorbing formaldehyde in water and forming the reactor aqueous solution of formaldehyde, wherein at least one circuit is provided, with which a part of the solution from the absorber branchable and coolable and after cooling in the absorber is traceable.
    Formaldehyde is produced industrially from methanol and air over silver or metal oxide catalysts and dissolved in water in an absorber or a wash column. Large-scale currently used methods are clearly presented in the chapter "Formaldehyde" in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition Vol. A11, page 624, Wiley-VCH Verlag, 2005. 25 In the reaction of methanol to formaldehyde not only undesirable side reactions occur, but other effects burden the purity and concentration of the aqueous solution of formaldehyde to be prepared. For example, formed in the reactor in the formation of formaldehyde from methanol and air inevitably also reaction water vapor. In a subsequent, relatively cool absorber, the product is diluted by condensation of this water of reaction, thus limiting the maximum possible product concentration. Typical maximum values of the concentration of formaldehyde which can be achieved without distillation and without wastewater fractions are about 56% by weight (% by weight). If processes are operated with water ballast, this dilution problem is even more pronounced.
    In addition, a portion of the methanol used is not converted in all processes and is found as "residual methanol" in the product again. This leads to a contamination of the product. On the other hand, this is accompanied by a loss of yield, which in turn is disadvantageous in terms of cost. 5
    Depending on the process, various techniques are used in the prior art in order to achieve the highest possible product concentrations and / or low residual methanol values. However, there are often compromises to be made, so that ultimately there is still potential for optimization. 10
    For example, in the silver catalyst process, the reaction conditions are adjusted so that the residual methanol content reaches a tolerable level. This is done for example by raising the catalyst temperature with the disadvantage of increased yield losses by more carbon dioxide producing 15 side reactions or shorter catalyst life due to higher temperatures and thus more rapid sintering of the catalyst silver.
    Alternatively, residual gas is recycled, resulting in addition to additional electricity costs and a higher design effort. As a further alternative, 20 "ballast water" can also be added to the reaction in order to be able to add more air at the same reaction temperature and thus to reduce the residual methanol content. Ballast water, however, dilutes the final product. In addition, the addition is also subject to the reaction leadership ago with severe limitations. 25 In the process with silver catalyst and incomplete methanol conversion (also called "methanol ballast process"), the residual methanol content is barely considered in the actual reaction. Rather, the entire product stream is distilled for quality improvement highly energy consuming, which is not very efficient. In addition to attempts to improve large-scale processes, other isolated approaches have also become known, but these have not yet been able to assert themselves significantly. For example, it has become known from US 2,943,701 to use alcohols such as cyclohexanol as a solvent to form hemiacetals with the formaldehyde from the gas stream, which are then thermally decomposed to give off very pure formaldehyde gas. This very expensive process is applicable, above all, to the production of ultrapure, anhydrous formaldehyde, but does not relate to the most economical mass production of aqueous solutions of formaldehyde. 5
    The use of urea solutions as absorbents also makes it possible to achieve selective absorption through the strong affinity of urea with formaldehyde. It is possible to operate the absorption of formaldehyde at relatively high temperatures, so that water vapor is not condensed out and thus higher product concentrations up to 10 85 wt .-% can be achieved with little residual methanol content (US 3,067,177 or US 4,065,421). However, it is disadvantageous that a urea-formaldehyde condensate is produced with limited applications, and not a much more universally usable aqueous formaldehyde solution. 15 object of the invention is to provide a method of the type mentioned, with the energy-saving manner higher levels of formaldehyde can be achieved with high yield without the residual methanol content increases.
    Another object of the invention is to provide a device of the type mentioned above, with the aqueous solution of formaldehyde with a high proportion of formaldehyde can be produced at a structurally low cost.
    The procedural object is achieved if, in a method of the type mentioned above, after cooling for a predetermined residence time, a formation of 25 polymethylene glycols in the diverted part of the solution is waited for
    To increase the absorption capacity of the branched portion of the solution of formaldehyde, after which the branched portion of the solution is heated and returned to the absorber. With a method according to the invention can be obtained in an energy-saving manner by the intended branching of a portion of the solution and its targeted temperature treatment, an increased proportion of formaldehyde in the produced aqueous solution of formaldehyde.
    The invention is based on the following considerations: Gaseous formaldehyde is not simply physically dissolved in water, but chemically absorbed. Depending on the temperature and concentration, methylene glycol further polycondensed to 5 polymethylene glycols with elimination of water according to equation 2. CH20 + H20 ^ H0 (CH20) H (1) H0 (CH20) H + H0 (CH20 ) H ^ H0 (CH20) 2H + H20 (2) 10 The polymethylene glycols according to Equation 2 can further polycondensate and form even longer molecules.
    The lower the temperature and the higher the formaldehyde concentration, the higher the proportion of longer chains of polymethylene glycols. From a chain length of eight 15 units, the water solubility is exceeded and therefore precipitates formaldehyde as a solid from the solution, which is why polymers from this length are not desirable.
    According to studies (eg BH Hasse, G. Maurer, Kinetics of the Poly (oxymethylene) Glycol Formation in Aqueous Formaldehyde Solutions, Ind. Eng. Chem. Res. 1991, 30, 20 2195), it takes depending on the pH, formaldehyde concentration and temperature for up to 90 minutes until longer polymethylene glycol chains are fully formed by cooling or absorbing additional formaldehyde. This water is split off. Therefore, it takes some time for the vapor pressure for formaldehyde to reach the low value (according to the respective temperature) mentioned in the literature. 25 The decay mechanism of these chains, which occurs, for example, when heated, is about three to four times slower.
    The slowness of the absorption of formaldehyde in water has hitherto been regarded as disadvantageous since corresponding residence times and, in turn, a corresponding design of an absorber are involved. Additionally or alternatively, therefore, accelerating catalysts such as sodium hydroxide are often added to accelerate the absorption, ie the complete formation of the polymethylene glycols.
    Formaldehyde absorption is highly exothermic, which is why in industrial formaldehyde absorbers the heat of absorption is often dissipated with circulation circuits via external coolers. In the absorber, for example, packed beds are used as mass transfer surfaces for absorption of formaldehyde. The formaldehyde solution reintroduced into the absorber after cooling has in the best case the formaldehyde vapor pressure, which corresponds to the literature value for this temperature. In practice, however, the actual vapor pressure is often undesirably higher because the residence time after the cooler is often too short and the polymethylene glycol chains could not fully develop. 10
    The invention now makes use of the slowness of the decay of longer polymethylene glycol chains. For this purpose, as it were "overheated", long-chain polymethylene produced for absorption, which absorbs little methanol and water vapor due to a higher temperature, but due to a previously generated 15 higher content of longer polymethylene glycols has very good formaldehyde absorption properties.
    It is preferred in the context of the invention that the diverted portion of the solution is diverted from the absorber at a temperature which is higher than a temperature at a return point in the absorber. In this regard, it can be provided in particular and with great advantage that the diverted part of the solution is heated after cooling and formation of Polymethylenglykolen by heat exchange with tracked diverted solution. This combines the benefits of higher formaldehyde concentration in the final product with the benefit of energy efficient process control. 25 On the one hand, the tracked solution must be cooled down anyway, on the other hand, the subsequently recirculated solution must be reheated, which can be carried out particularly energy-efficient by the proposed heat exchange. In between, the desired formation of polymethylene glycols takes place. Although it is not mandatory, but can also be provided with advantage that at several points of the absorber, a portion of the solution is diverted from the absorber and cooled to form polymethylene glycols, after which the part of the solution is heated and returned to the absorber. Along a height of an absorber can thus be provided a plurality of circuits with which an inventive
    Procedure is implemented. It is expedient to provide a corresponding circuit, at least on the head side, ie at the lowest temperatures. As a result, further corresponding circuits can be provided at the bottom, although the effectiveness decreases due to the increasing downward temperatures. Nevertheless, each additional cycle contributes to the improvement of the product. Usually, the methanol is reacted with the air in a reactor upstream of the absorber, in particular in order to be able to absorb the formaldehyde in it. In this case, in particular a multi-stage absorber can be provided. 10
    The further object of the invention is achieved if a residence time device is provided in a device of the type mentioned in the at least one circuit after a cooling device to increase an absorption capacity of the diverted portion of the solution of formaldehyde, and the residence time is followed by a 15 heating device, with which the diverted part of the solution can be heated before being returned to the absorber.
    With a device according to the invention several advantages are achieved: Firstly, due to the at least one intended circuit, a higher content of formaldehyde is achieved in the aqueous solution. On the other hand, impurities can be kept low by methanol.
    In order to achieve the highest possible concentration of formaldehyde in the aqueous solution, several cycles can be provided, with each of which part of the solution can be branched off from the absorber and cooled to form polymethylene glycols and heated after cooling and can be returned to the absorber. The more cycles that are provided, the higher the concentration of formaldehyde in the final solution. Preferably, the at least one circuit is designed such that the part of the solution can be branched off at a position of higher temperature of the absorber and can be returned to it at a cooler point.
    In particular, with regard to a high energy efficiency is advantageously provided that in the at least one circuit a plurality of heat exchangers are arranged and the diverted portion of the solution after cooling through a heat exchanger and formation of polymethylene glycols another heat exchanger for heating with tracked 5 diverted solution passes. Followed, anyway to be cooled solution is then cooled by again recycled, in particular high levels of polymethylene glycols having solution, the latter must be reheated anyway. Thus, a particularly efficient energy budget is given. Other features, advantages and effects of the invention will become apparent from the embodiments illustrated below. In the drawing, to which reference is made, Fig. 1 shows a device according to the invention.
    In Fig. 1, a device 1 according to the invention is shown. The device 1 has a device 4 with an evaporator and a gas mixer. About a first
    Feed line 2 is fed to methanol and air via a second feed line 3. Furthermore, 8 ballast water of the device 4 can be supplied via a ballast water stream. It is also possible, but this is not mandatory, to supply residual gas to the device 4 20 via a gas recirculation 9 in the process to be explained after absorption.
    The process gas created in the device 4 is fed to a reactor 5, which can be designed as in the prior art. For example, it may be a reactor 5, in which the process gas is catalytically supported by silver particles for the formation of formaldehyde. The gas discharged from the reactor 5 is fed to an absorber 6, which is connected downstream of the reactor 5. The absorber 6 can also be a unit, as in the case of the reactor 5, as used in the prior art. In the exemplary embodiment is a multi-stage absorber 6, on which a top condenser is mounted. However, the top condenser can also be separated from the actual absorber 6 in another variant embodiment. Incidentally, the absorber 6 may be formed arbitrarily, for. B. also with bubble trays, valve trays or sieve plates. For supplying process water, a corresponding process water line 7 is provided which opens into the top condenser. Via an exhaust pipe 10 residual gas is removed and a thermal
    Utilization supplied. As mentioned, at least part of the residual gas can be supplied via the gas recirculation 9 to the device 4 for producing the process gas.
    It is essential in the context of the invention that at least one circuit K1, K2 5 is provided. The first circuit K1 is located in an upper part of the absorber 6 or connects to it there and in turn flows into it in the said area. The first circuit K1 has a branch point 11, at which part of the solution present in the absorber 6 is branched off. Furthermore, the first circuit K1 has a first heat exchanger 13 and a second heat exchanger 14. Between these heat exchangers 13,14 a first residence time container 15 is provided, from which the removed part of the solution via the first heat exchanger 13 and thus returned to the absorber 6 under heating, for which a return point 12 is provided in the absorber 6. When using a method according to the invention, a portion of the solution is taken at the branch point 11 with, for example, 65 ° C and cooled after passing through the first heat exchanger 13 in the second heat exchanger 14, which acts as a cooling device to a temperature of about 28 ° C. Thereafter, the diverted portion of the solution flows through the residence time tank 15, which is designed so that 20 after cooling in the second heat exchanger 14, the desired
    Be able to form polymethylene glycol chains. Subsequently, the branched off part of the solution passes through the first heat exchanger 13, in which the solution is heated to a temperature of about 50 ° C in heat exchange with nachgeführter solution that comes later to the dwell time 15. Subsequently, the branched-off part of the solution at the return point 12 is again introduced into the absorber 6; the place of
    Due to the low rate of disintegration of the polymethylene glycol chains formed, the solution recycled at a temperature of 50 ° C. with respect to formaldehyde behaves like a solution at a significantly lower temperature and therefore has a particularly good absorption capacity for formaldehyde. At the same time, the recirculated solution due to the heating to 50 ° C, only a slight tendency to absorb water or methanol. Similarly, a second circuit K2 may be provided, which acts below the first circuit K1. This second circuit K2 is structurally analogous in structure to the first circuit K1 and has a third heat exchanger 16, a fourth heat exchanger 17 and a second residence time container 18. In principle, further circuits can also be provided, although the temperature rises in the absorber 6 at the bottom and thus also the efficiency of further circuits is lower than in the first circuit K1. Finally, at the lower end of the absorber 6, an aqueous solution of formaldehyde can be removed via a product removal 19. The invention is described below with reference to two concrete exemplary embodiments with different process control (data in% by weight).
    Example 1:
    An ordinary multi-stage absorber of a formaldehyde process with 15 silver catalyst, water ballast and residual gas recirculation is with a
    Absorber head temperature of 50 ° C operated. 6% of the formaldehyde produced, 55% of the unconverted methanol and 25% of the ballast and water of reaction escape. This stream is completely recycled to the process, but about 11% of the formaldehyde and methanol are lost through side reactions. There is obtained 55% formaldehyde with 0.5% methanol.
    With the same process control and the same absorber head temperature, but with dynamically selective absorption by a circuit K1 escape only 1.5% of the produced formaldehyde, continue to 55% of unconverted methanol and 25% 25 of the ballast and water of reaction. The yield improves by 0.5%, the product concentration increases to 58% formaldehyde with further 0.5% methanol.
    Example 2:
    In a typical pressureless absorber of a formaldehyde process with metal oxide catalyst, 55% formaldehyde with 0.5% methanol is prepared at an absorber head temperature of 25 ° C.
    In the same process, however, with dynamically selective absorber with a cycle K1 is obtained with an absorber head temperature of 40 ° C and the elimination of the feed water 60% formaldehyde with 0.4% methanol.
    权利要求:
    Claims (10)
    [1]
    claims
    A process for preparing an aqueous solution of formaldehyde, wherein methanol is reacted with air to form a process gas 5 having formaldehyde, and the process gas is fed to an absorber (6) in which formaldehyde is absorbed in water to form the aqueous solution of formaldehyde to form, wherein a part of the solution from the absorber (6) is branched off and cooled and then returned to the absorber (6), characterized in that after cooling for a predetermined residence time to wait for a formation of polymethylene glycols in the branched part of the solution to increase an absorbency of the branched portion of the solution of formaldehyde, after which the branched portion of the solution is heated and returned to the absorber (6).
    [2]
    2. The method according to claim 1, characterized in that the branched portion 15 of the solution from the absorber (6) is branched off at a temperature which is higher than a temperature at a return point (12) in the absorber (6).
    [3]
    3. The method according to claim 2, characterized in that the diverted portion of the solution is heated after cooling and formation of Polmethylenglykolen by heat exchange with 20 tracked diverted solution.
    [4]
    4. The method according to any one of claims 1 to 3, characterized in that at several points of the absorber (6) part of the solution from the absorber (6) is branched off and cooled to form polymethylene glycols, after which the part of the solution 25 is heated and is returned to the absorber (6).
    [5]
    5. The method according to any one of claims 1 to 4, characterized in that the methanol is reacted with the air in a the absorber (6) upstream reactor (5). 30
    [6]
    6. The method according to any one of claims 1 to 5, characterized in that the process gas is fed into a multi-stage absorber (6).
    [7]
    7. Apparatus (1) for producing an aqueous solution of formaldehyde by reacting methanol with air to form a process gas having formaldehyde, comprising a reactor (5) for forming the process gas and an absorber (6) downstream of the reactor (5) for absorption Formaldehyde in 5 water and forming the aqueous solution of formaldehyde, wherein at least one circuit (K1, K2) is provided, with the part of the solution from the absorber (6) branched off and cooled and after cooling in the absorber (6) traceable characterized in that in a at least one circuit (K1, K2) after a cooling means a residence time means is provided to increase an absorption capacity 10 of the branched portion of the solution of formaldehyde, and the residence time means is followed by a heating device, with which the branched part the solution before heating in the absorber (6) is heated.
    [8]
    8. Device (1) according to claim 7, characterized in that a plurality of 15 circuits (K1, K2) are provided, with which each part of the solution from the absorber (6) branched off and to the formation of polymethylene glycols cooled and heated after cooling and in the absorber (6) is traceable.
    [9]
    9. Device (1) according to claim 7 or 8, characterized in that the at least one circuit (K1, K2) is formed so that the part of the solution at a position higher temperature of the absorber (6) can be branched off and on a cooler Place in these is traceable.
    [10]
    10. Device (1) according to one of claims 7 to 10, characterized in that in the at least one circuit (K1, K2) a plurality of heat exchangers (13,14, 16,17) are arranged and the diverted part of the solution after cooling through a heat exchanger (13,16) and formation of polymethylene glycols, a further heat exchanger (14,17) passes through for heating with tracked diverted solution.
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    同族专利:
    公开号 | 公开日
    AT516530B1|2018-02-15|
    WO2016079544A1|2016-05-26|
    CN107108423A|2017-08-29|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    DE2308409A1|1973-02-21|1974-08-29|Basf Ag|Process for the preparation of concentrated, aqueous solutions of formaldehyde|
    EP0748786A1|1995-05-16|1996-12-18|Patentes Y Novedades S.L.|A process for the continuous preparation of aqueous formaldehyde solutions|
    US2943701A|1960-07-05|Effect of chso oonoenteation in the chhf|
    GB697906A|1949-01-05|1953-09-30|Celanese Corp|Process for the production of formaldehyde|
    CH398530A|1957-10-30|1966-03-15|Montedison Spa|Continuous process for the production of durable, concentrated aqueous solutions containing urea, formaldehyde and urea-formaldehyde condensation products|
    US3277179A|1962-01-02|1966-10-04|Lummus Co|Manufacture of aqueous formaldehyde solution and paraformaldehyde|
    DE1183896B|1963-03-22|1964-12-23|Bayer Ag|Process for the purification of gaseous formaldehyde|
    US4065421A|1976-03-17|1977-12-27|Reichhold Chemicals, Inc.|Continuous process for the production of aqueous urea-formaldehyde solutions|
    US4348540A|1981-06-29|1982-09-07|Monsanto Company|Manufacture of aqueous formaldehyde|
    JPH0662478B2|1984-04-12|1994-08-17|三菱瓦斯化学株式会社|Formaldehyde solution manufacturing method|
    US4990685A|1988-07-19|1991-02-05|Bayer Aktiengesellschaft|Process for the preparation of aqueous formaldehyde solutions|CN109701293B|2019-02-28|2021-08-27|潍坊惠丰化工有限公司|Solvent displacement condensation tower and method for producing anhydrous formaldehyde|
    WO2021220150A2|2020-04-28|2021-11-04|University of Maribor|The process of removing formaldehyde and volatile organic compounds from waste industrial gases|
    法律状态:
    2021-07-15| MM01| Lapse because of not paying annual fees|Effective date: 20201120 |
    优先权:
    申请号 | 申请日 | 专利标题
    ATA50843/2014A|AT516530B1|2014-11-20|2014-11-20|Process and apparatus for the preparation of an aqueous solution of formaldehyde|ATA50843/2014A| AT516530B1|2014-11-20|2014-11-20|Process and apparatus for the preparation of an aqueous solution of formaldehyde|
    PCT/GB2015/053555| WO2016079544A1|2014-11-20|2015-11-20|Process and apparatus for preparing an aqueous solution of formaldehyde|
    CN201580071195.1A| CN107108423A|2014-11-20|2015-11-20|For the method and apparatus for the aqueous solution for preparing formaldehyde|
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