DE19822598A1 - Formaldehyde production by dehydrogenation of methanol - Google Patents

Abstract

In formaldehyde production by dehydrogenation of methanol at 650-1,050 deg C in the absence of oxygen, reaction is carried out in the presence of a gaseous compound (I) of an alkali(ne earth) element, copper, zinc or tin.

Description

The invention relates to a method for producing Formaldehyde by dehydration of methanol in the presence a gaseous catalyst.

Methods are primarily known from the prior art, which take place in the presence of solid heterogeneous catalysts. These include EP-B 0 405 486, in which silicate catalysts are described, and EP-B 0 405 348, according to which one Methanol in the presence of a solid catalyst Alkaline earth aluminate dehydrated with the exclusion of oxygen.

In the heterogeneously catalyzed reactions, the However, catalyst more or less over time deactivated quickly and must therefore be replaced. This is with production interruptions, forced attack spent catalyst or working up this Connected catalyst.

From the unpublished DE 196 44 188.9 is a Process known in which metallic sodium evaporated and the dehydration in the presence of the gaseous metal.

The object of the invention is a method for producing Formaldehyde, for which no solid catalyst or the Evaporation of elemental sodium with the each related problems, and still with high selectivity and high turnover.

The invention relates to a method for producing of formaldehyde by dehydration of methanol at a Temperature from 650 ° C to 1050 ° C below Exclusion of oxygen, which is characterized in that the reaction in the presence of a compound of alkali or alkaline earth elements, copper, zinc or tin in the Performs gas phase.  

The alkali and alkaline earth compounds are preferred in the form of methanolic solutions. Particularly preferred are alkali compounds.

As connections of the elements mentioned are in particular

• a) alcoholates, in particular methanolates or ethanolates, but also
• b) acetates, formates or oxalates,
• c) carbonates or in further embodiments
• d) hydroxides

used.

The solutions are preferably evaporated and diluted with an inert gas, especially nitrogen, into the Reaction zone passed. In a preferred one Embodiment is the sum of the amounts of used Compound and methanol at 1 to 30 mol% in the inert gas.

However, higher concentrations are also feasible.

The concentration is in the solutions used of the compounds mentioned to 0.03 to 25% by weight, in particular 0.03 to 15% by weight, preferably 0.03 to 3% by weight.

When increasing the molar fraction of methanol in the input stream the degree of conversion of methanol drops, while that actually converted amount (represented by the product Mole fraction and degree of turnover) increases.

A decisive influence on the degree of sales of Methanol also has the flow rate. The Reduction by 25% from 1.0 m / s to 0.75 m / s leads to Doubling of the degree of turnover with high selectivity. The Increasing the reactor temperature also leads to a higher degree of conversion of methanol.

Compared to the results with elemental sodium as The selectivity of formaldehyde in the catalyst  Dosage of, for example, sodium methylate comparable reaction conditions, especially at similar sales levels, higher. It lay during the measurements always made above 93%. While in Case of sodium as catalyst - due to the Experimental setup - a strong concentration gradient on site the mixing of sodium and methanol the catalyst according to the invention even before the reactor well mixed with the methanol. Because of the homogeneous Distribution, the side reactions are suppressed more, so that the selectivity of formaldehyde is further increased can be.

The reaction temperatures in the dehydrogenation of the Methanol generally range from 650 ° C to 1050 ° C, preferably 700 ° C to 920 ° C.

The pressure in the process is not critical. The only essential thing is that the reaction in the Gas phase expires.

The process according to the invention can be carried out batchwise, but preferably continuously.

It provides an anhydrous formaldehyde with good Selectivity and yield.

The results of the method according to the invention show that it succeeds in dosing compounds a better one Achieve result than when evaporating the elements like for example sodium.  

Test execution

One of the compounds mentioned as a catalyst is described in Dissolved methanol and into the heated via a capillary Reaction tube promoted. The reaction tube consists of a ceramic tube (alumina ceramic) with a Inner diameter of 8 mm. The reaction tube becomes vertical fixed in an electrically heated oven in which one 450 mm long zone isothermal on the given Reaction temperature can be kept. The capillary is introduced into the reaction tube from above so that the End of the capillary until the start of the isothermally heated Zone is enough.

When operating the experimental setup, make sure that the liquid flowing in the capillary when spraying into the zone heated to the reaction temperature is evaporated, as it evaporates inside the capillary Clogging of the capillary comes. Through a thermocouple, which is led through the capillary to the end of it control the temperature in the evaporation zone. Evaporation within the capillary can thereby be excluded.

A gas stream flows around the capillary from the outside the temperature in the capillary increases as low as possible hold.

The products obtained after the reaction zone are cooled to a temperature of 160 ° C. The composition of the product gas is determined using an on-line gas chromatograph. The conversion of methanol is calculated from the composition of the product gases using the following formula:

The selectivity to formaldehyde is calculated using the following formula:

example 1

Sodium methylate (Merck KGaA) is mixed with methanol on a Concentration of 0.3% w / w diluted. With the help of a Dosing pump is the dilute solution of sodium methylate atomized in the reaction zone. The capillary is included flows around a nitrogen stream. Results in the reaction zone one from the ratio of the two currents Methanol concentration of 13 mol%. The reaction zone is heated to a temperature of 700 ° C. At the end of the reactor after cooling the reaction gases a conversion of methanol from 44.6% measured. It does a formaldehyde selectivity reached by 98.9%.  

Examples 2 to 6

The results of experiments 2 to 6 are summarized in Table 1.

Claims (5)

1. A process for the preparation of formaldehyde by dehydrogenation of methanol at a temperature of 650 ° C to 1050 ° C with the exclusion of oxygen, characterized in that one carries out the reaction in the presence of a gaseous compound of the alkali or alkaline earth elements, copper, zinc or tin. 2. The method according to claim 1, characterized in that one of compounds of the elements mentioned

• a) alcoholates, in particular methanolates or ethanolates,
• b) acetates, formates or oxalates,
• c) carbonates or
• d) hydroxides

starts. 3. The method according to claims 1 and 2, characterized, that you use solutions that 0.03 to 30 wt .-% of mentioned compounds included. 4. The method according to claim 3, characterized, that the solutions 0.03 to 15 wt .-% of said Connections included. 5. The method according to claims 1 to 4, characterized, that one carries out the reaction at 700 ° C to 900 ° C.