DE2404738A1 - Formaldehyde prodn by hydrocarbon oxidn - over a subgroup V, VI or VII oxide (contg) catalyst - Google Patents

Abstract

Vapor phase process for preparing HCHO comprises reacting lower mol. wt. hydrocarbon (contg. gases) and O2 (contg. gases) at elevated temp. over a catalyst consisting of, or contg., oxides of subgroups V, VI and/or VII elements esp. of V, Nb, Ta, Cr, Mo, W, Li, Mn, Tc or Re. Pref. oxidant is air and hydrocarbons have is not >4C (pure or in mixts.). HCHO is used to make resins and as reducing agent, disinfectant and preservative. HCHO is prepd. from inexpensive starting materials in high yield and with high selectivity. The gas and liquid streams are not corrosive and waste gases from the process may be used to generate heat.

Description

Process for producing formaldehyde The present invention relates to a process for the production of formaldehyde by oxidation of low molecular weight Hydrocarbons with oxygen or gases containing oxygen.

Various methods have already become known, according to which Formaldehyde can be produced by partial oxidation of methane. One This process starts from natural gas (98 ffi methane), which nnt air in the presence of nitrogen oxides as a catalyst at 60,000 (see F.I.A.T. Final Report No. 1085; Ullmann, Encyclopedia of Technical Chemistry, 3rd edition, 7th volume, pages 663 to 665 (1956)). In this experience a selectivity *) of 9.7% and Yields of formaldehyde of 130 g per Nm³ methane achieved. Occur as by-products Methanol, formic acid, carbon monoxide and carbon dioxide.

In a modification of this procedure are in addition to the nitrogen oxides solid catalysts used (see. Ullmann, 1. c.

*) Unless otherwise stated, here and below under Percent selectivity resistance number of moles of formaldehyde formed. 100 moles of converted methane Austrian patents 136 669, 156 o69, 158 644).

Selectivities of 1.7 to 21.3 ffi and yields are found here Formaldehyde obtained from 23 to 285 g per Nm3 methane. For the production of 1 kg of formaldehyde 13 to 3.5 kg of nitric oxide are consumed.

In another modification of this process (see German patent specification 1 o50 752), in addition to nitrogen monoxide, a catalyst located in a fluidized bed is used is used, which has good heat transfer properties. Those leaving the reaction space Gases are cooled by a second fluidized bed.

According to this process, formaldehyde can generally be obtained in selectivities can be obtained as they are achieved in the above-described methods. the The reaction temperature in this process is 47o0C, which is why only low space-time yields can be achieved that are not technically interesting. This procedure is because of the complicators; The nature of the equipment used is difficult from a procedural point of view to dominate.

A process has also been described in which methane is present of nitrogen oxides with oxygen in a so-called reverse flame with formation is converted by formaldehyde (see German Auslegeschrift 1 217 353). With this one 40 g of formaldehyde per Nm3 of methane used can be obtained. A Another method uses nitric acid vapor instead of nitrogen oxides as a catalyst (see German Auslegeschrift 1 159 421).

All of these processes have the disadvantage that the gaseous catalyst are continuously added to the starting products in sometimes quite considerable quantities got to. The resulting gas mixtures containing nitrogen oxides or nitric acid vapors are very corrosive, which means that all apparatus share the end must consist of high quality material. The formaldehyde formed by this process Always contains nitric acids as impurities that are very difficult to remove and are corrosive. In addition, the provision of ammonia requires nitrogen oxides or nitric acid additional effort.

Furthermore, methods are known in which enriched with ozone Oxygen, sulfur dioxide or sulfur trioxide as an oxidizing agent for the production of formaldehyde from methane can be used (see Ullmann, 1. c .; J. F. Walker Formaldehyde, 3rd Edition, New York (1964), pages 25-27, and U.S. Patents 2,532,930 and 2,590,124). As can be seen from the first two literature references, could However, these processes do not establish themselves in technology.

Finally, in German Offenlegungsschrift 2 201 429, the Gas phase oxidation of methane with air in a reaction zone designed as a flame described. The mean residence time in the flame zone is within narrow limits to be observed, which is very difficult to control from a procedural point of view. With this one Process can use formaldehyde in amounts up to about 300 g per Nm3 methane used can be obtained.

In addition, considerable amounts of methanol are produced.

It is also known that hydrocarbons such as ethane, ethylene, Propane, propylene, butane, butylene, in a similar way to formaldehyde from methane to manufacture. Here, aluminum phosphate activated with metal oxides is used as a catalyst used (see Ullmann, 1. c.).

There has now been a process for the production of formaldehyde in the Gas phase from low molecular weight hydrocarbons or containing these Gases and oxygen or oxygen-containing gases found that characterized is that you carry out the reaction at an elevated temperature in the presence of catalysts performs, which consist of oxides of the elements of the V., VI. and / or VII. subgroup des Consist of the periodic table or contain these oxides.

The catalysts to be used according to the invention can consist of pure Oxides of the elements vanadium, niobium, tantalum, chromium, uranium, molybdenum, tungsten, manganese, Technetium and rhenium exist.

However, mixtures of these oxides with one another, as well as Mixtures of these oxides with other oxides, e.g. B. with oxides of silicon, aluminum, Iron, calcium, magnesium, sodium and / or potassium can be used. Such mixtures for example between 10 and 100% by weight / q of one or more oxides of V., VI. and or VII. Subgroup of the periodic table included. The proportions of other oxides can for example: Up to 90% by weight SiO2, A1203, CaO and / or MgO, each up to to 5 wt .-% Na20, K20. and iron oxides. Under the term "mixtures of oxides" both homogeneous and heterogeneous mixtures are understood here. Several Catalysts containing oxides can, for example, from solutions of salts corresponding elements are produced. So you can z. B. from aqueous solutions mixed oxides produced from ammonium vanadate, ammonium molybdate and ammonium tungstate use as catalysts in the process according to the invention.

The catalysts to be used according to the invention can also have Be applied to carriers. If a carrier is used, the content of metal oxides in the catalyst, for example, about 0.1 to 50 wt.%, preferably 0.1 to 10 wt. be.

Suitable carrier materials are, for example, natural silica and artificial silicates, aluminum oxide, spinels, Pumice stone, titanium dioxide. One can also use that on which the metal oxides to be used according to the invention are based Use metal as a carrier.

The pure oxides of vanadium, molybdenum or tungsten are preferred, in particular V205, MoO3 or W03 are used in the process according to the invention, where these oxides can also be applied to the carrier materials mentioned.

The catalyst can be in various forms, for example as a powder, in coarse-grained form or in the form of balls, sausages, pills or Cylinders, and in a fixed bed, or for better heat dissipation in a fluidized bed or another moving catalyst bed can be used. When working in a fluidized bed are for example spherical catalyst particles with a diameter of o, ol suitable up to 2 mm.

In the fixed bed, any shaped catalyst particles with a Particle size of generally about 0.2 to 20 mm can be used. For example are sausages with a length of 4-18 mm or balls with a diameter from 0.4 to 10 mm suitable.

Should the catalyst in its activity by carbon deposition decrease, can be done by burning off in the presence of air at elevated temperature, for example at 400 to 75oC, easily restore the original activity.

The process according to the invention is carried out in the gas phase. Within the range for working in the gas phase, pressure, temperature, Composition of the starting products and flow rates within wide limits can be varied.

The process according to the invention can be reduced at normal pressure Pressure or increased pressure. Suitable pressures are, for example 1 to 100 atm. It is preferred to operate at pressures from normal pressure to 30 atm. In general, the reaction temperatures are between about 350 and 750 ° C. For example can work at temperatures of 400 to 7000C, preferably 450 to 6700C will.

The starting products can be used in pure form or mixed with others Gases are used. For example, as low molecular weight hydrocarbons those with up to 4 carbon atoms can be used. Generally one uses methane, Ethane, propane, butane, ethylene, propylene, butylene as pure compounds or in the form of mixtures. The low molecular weight hydrocarbons can also be mixed can be used with higher hydrocarbons. Such mixtures can, for example contain up to about 3% by volume of higher hydrocarbons. In addition, the low molecular weight Hydrocarbons mixed with other gases such as nitrogen, carbon dioxide, carbon monoxide, Noble gases and water vapor can be used.

If low molecular weight hydrocarbons are used as the feedstock 2 - 4 carbon atoms are used, catalysts can also be used which consist of pure silicon dioxide or silicon dioxide to 90-100% by weight and aside Oxides of, for example, aluminum, iron, vanadium, molybdenum, tungsten, calcium, Contains magnesium, sodium and / or potassium. In addition, such catalysts Contains traces of sodium chloride.

Catalysts that contain more than 90 (JD silicon dioxide, for example have an inner surface of 30 - 500 m2 / g.

The oxygen can be used in pure form or in a mixture with other gases, such as nitrogen, carbon monoxide, carbon dioxide, noble gases, water vapor and / or hydrocarbons can be entered into the method according to the invention. Air is preferred as oxygen containing gas is used.

The amount of oxygen or oxygen-containing gases released after the Process according to the invention for the oxidation of low molecular weight hydrocarbons used to formaldehyde can be varied within wide limits. For example one can per mole of low molecular weight hydrocarbon o, o1 to 1 & o moles of oxygen, calculated as pure oxygen.

The explosion limits are of course within this range to consider. Preference is given to per mole of low molecular weight hydrocarbon 0.05 to 20 moles of oxygen are used. Of course, the reactants in the Mixture with inert gases can be used. There can be mixtures of oxygen, low molecular weight Hydrocarbons and inert gases with a content up to 98 vol .-%, for example up to 80% by volume of inert gases can be used. So you can, for example, the invention Process in the presence of inert gases such as nitrogen, carbon dioxide, noble gases and / or Perform water vapor.

According to the different options for arranging the Catalyst, the reactor can be designed differently. Comes with a plague bed catalyst worked, the catalyst can, for example, in one or more reaction tubes be firmly arranged (tubular reactor). The reaction tubes can be made of metal, one ceramic mass or quartz. Metal pipes are preferably used, which are lined with a ceramic mass.

Fluid catalyst applied in the form of a fluidized bed, so is a fluidized bed reactor of conventional design is expediently used.

The feeding of the feedstock to the reactor and their heating can be done in several ways. For example, you can use low molecular weight Hydrocarbons or gases containing them and oxygen or oxygen containing Mix gases in a pressure chamber or a mixing nozzle and the feed mixture thus obtained in a heat exchanger initially to, for example, 300 to 600 µm preheat and then feed to the reactor, where it can be further down to the Reaction temperature is heated.

However, the reactants can also be heated separately and feed them separately to the reactor.

The flow rate of the gas mixture in the reactor can be wide Limits can be varied. For example, the flow rate is regulated in such a way that that contact times in the reaction space of o, o1 to 50 seconds, preferably of o, o5 to 5 seconds, calculated for the catalyst bed at a given reaction temperature, result.

The gases leaving the reactor contain unreacted starting products, including any inert gases added, and as reaction products Formaldehyde and water.

The reaction mixture leaving the reactor is generally the Workup fed. Working up can be carried out as usual. For example can be worked up in a washer, by indirect cooling or by fractional cooling can be carried out. The laundry can be done with water, for example be carried out, it being possible to use multi-stage scrubbers. You get such an aqueous formaldehyde solution. From this solution can by distillation Formaldehyde solutions are produced, many of which are instant technical Re-use are suitable. If the work-up is carried out by cooling, can one z. B. Use ice water as a coolant. In this way of working, the educated Formaldehyde condenses out of the reaction gas with the water formed.

To achieve a high selectivity, it can be useful to use the To conduct the reaction so that with a single pass through the reactor only a partial Sales takes place.

For example, pressure, temperature, composition of the starting gas mixture, Amount of catalyst and / or flow rate can be varied accordingly. The residual gas remaining after the formaldehyde formed has been separated off can be returned to the reactor as cycle gas.

It is expedient to add the consumed portions to this gas low molecular weight hydrocarbons and oxygen as fresh gas. Consequently a closed circuit is obtained. In the circulatory system accumulate the inert gases and the by-products in the cycle gas. One can go through continuous or discontinuous side stream withdrawal an excessively high increase in these gases in the Prevent cycle gas.

The amount of exhaust gas discharged is also expediently replaced by fresh gas.

In a preferred embodiment of the method according to the invention it works as follows: low molecular weight hydrocarbons and air as fresh gas are in a volume ratio of about 2: 1 in a blower with formaldehyde freed circulating gas mixed. The fresh gas replaces the consumed parts of low molecular weight hydrocarbons and oxygen, as well as the amount of discharged Exhaust gas. The gas mixture thus obtained is first in a heat exchanger, the is heated by the gases leaving the reactor, preheated to about 300 to 600 ° C and fed into the reactor. In the reactor, the gas mixture is brought to a reaction temperature heated further from about 450 to 670 ° C. The reactor contains a fixed Catalyst made from oxides of vanadium, molybdenum or tungsten on silicon dioxide exists as a carrier and has the shape of balls with a diameter of 0.4 to 4 mm. The reaction is carried out at a pressure between 1 and 30 atm. The flow rate is regulated so that contact times in the range of 0.05 to 5 seconds result. The gas mixture leaving the reactor is first via the heat exchanger and then passed into a scrubber, in which the formaldehyde formed is washed out with water will. The aqueous formaldehyde solution is worked up by distillation. the end that of Formaldehyde-free gas mixture is called a substream Exhaust gas discharged and the remainder fed back into the cycle.

The method according to the invention is distinguished from the known Process characterized in that formaldehyde in large amounts in a simple manner continuously from cheap and easily accessible raw materials with high selectivity and yield can be produced. The implementation of the method according to the invention is relative simple, since all reaction parameters are variable within wide limits. All in the process The gas and liquid flows that occur are not aggressive, which is why there are no material problems occur for pipes and containers. The exhaust gas from the process according to the invention can be used to preheat the feedstock and to heat the reactor to the reaction temperature be used.

Formaldehyde is an important raw material for the chemical industry. Large amounts of formaldehyde are used in the production of resins, for example phenol-formaldehyde resins, used. In the form of aqueous solutions, formaldehyde can also be used as a reducing agent, Disinfectants or preservatives may be used. Regarding further Possible uses of formaldehyde are referred to Ullmann, 1. c. Page 670, noted.

Example 1 In an electrically heated reaction tube 70 cm in length and 1.78 cm in diameter, which consists of quartz, becomes 40 cm3 of a catalyst Filled, which consists of 15 wt .- MoO3 on SiO2 as a carrier in the form of grains. The specific surface is 110 m2 / g. The grains have a spherical shape with abrasion-resistant surface. The grain size distribution is in the range from 0.4 to 2 mm in diameter. The catalyst was made as follows: Si2 spheres as a carrier were soaked in (NH4) 2MoO4 solution and the mixture under Stir evaporated. Subsequently, the catalyst particles became several at 6ovo00 Annealed for hours in a stream of air. The length of the catalytic converter section is 16 cm. This stretch has a homogeneous temperature that is kept at 61oOC. In The reaction takes place in this temperature zone.

There are in a mixing chamber with a volume of looo cm3 at 250C hourly 35.8 1 air and 85.7 1 CH4 metered in and mixed. That has methane a degree of purity of 99.95% by volume.

This gives a starting gas composition of 29.5% by volume of air and 70.5% by volume methane or 6.18% by volume oxygen, 23.32% by volume nitrogen and 70.5 % By volume methane. The gas mixture thus obtained is heated to 450 ° C. in a preheater and passed over the catalyst at 610 ° C. and 30 cm WS overpressure.

A throughput speed is calculated from the specified numerical values of 121.5 l / h, a flow rate of 42.4 cm / sec and a contact time of 0.38 sec. The outflowing reaction gas was passed through three, 100 cm3 of water containing gas washer bottles passed to the amount of formaldehyde formed to determine. The quantitative analysis of the solution was carried out both by gas chromatography as well as titrimetric. A Porapak-N column was used for gas chromatographic analysis used. The titrimetric determination of the formaldehyde was carried out using the sulfite method. After a reaction time of 6 hours, 6.9 g of formaldehyde were obtained.

The gas mixture freed from formaldehyde was also used for determination the yield was again analyzed by gas chromatography.

A Porapak Q and a molecular sieve 13 X column were used for this. The calculated selectivity is 29.4%, based on O2 or 33.3%, based on on CH4, i.e. that is, 33.3% of the methane converted has been oxidized to formaldehyde are.

This corresponds to a yield of 445 g HCHO per Nm3 methane.

Example 2 The procedure was as in Example 1, but the Reaction temperature adjusted to 558 ° C and a gas mixture of the following composition used: 28.8 vol .-% air, 62.8 vol .-% methane, 1.8 vol .-% ethane, 2.9 vol .-% higher Hydrocarbons (mainly propane), 2.8% by volume water vapor and 0.9% by volume Carbon dioxide. The flow rate was 196.8 l / h. The catalyst passed of 5 wt. V205 on SiO2 as a carrier and was in an amount of 25 cm3 in the Reaction tube filled. The specific surface, the external shape and the grain size distribution of the catalyst was as in Example 1. The catalyst was as in Example 1, however made using NH4VO3 solution.

After a reaction time of 5 hours, 4.02 g of formaldehyde were obtained.

Example 3 The procedure is as in Example 1, but the Reaction temperature adjusted to 508 ° C. and a gas mixture of 34.7% by volume of air and 65.3 vol% ethane (purity 99.95) with a throughput rate of 172.2 l / h used.

The catalyst consisted of 10% by weight of WO3aif A1203 as a carrier and was filled into the reaction tube in an amount of 20 cm3. In the aqueous solution 2.89 g of formaldehyde were found after a reaction time of 5 hours.

Example 4 The procedure was as in Example 1, but pure Silica in spherical shape (0.4-2 mm in diameter) with 2 an inner surface of 170 m / g used as a catalyst. A gas mixture was passed over this catalyst consisting of 76.2 vol.% isobutylene and 23.8 vol.% air at a reaction temperature of 41,000 passed at a flow rate of 125.6 l / h. Bs became 1.7 every hour g formaldehyde obtained.

Claims (4)

Claims 1. Process for the production of formaldehyde in the Gas phase from low molecular weight hydrocarbons or gases containing them and oxygen or oxygen-containing gases, characterized in that one the reaction is carried out at an elevated temperature and in the presence of catalysts, those from oxides of the elements of the V., VI. and / or VII. subgroup of the periodic table exist or these Contains oxides. 2. The method according to claim 1, characterized in that as Catalysts Oxides of vanadium, ITiobium, tantalum, chromium, molybdenum, tungsten, uranium, Manganese, technetium, rhenium used. 3. The method according to claim 1 and 2, characterized in that one Low molecular weight hydrocarbons with up to 4 carbon atoms as pure compounds or in the form of mixtures. 4. The method according to claim 1 to 3, characterized in that one Air is used as the gas containing oxygen.