It's from Proceed. Acad. May be. USSR, Chem. Ser. (1964), pp 641 to 643, known to use silver as a catalyst on pumice stone and aluminum as a support. It is found that only poor results are achieved with such catalysts. Therefore one uses silver spirals as Catalysts. The best result was with SüberSpiralen, a temperature of 600 ° C, a pressure of 544 to 816 mbar
and a yield of 69 percent. The end product Ί
is obtained in the form of a 25 percent by weight aqueous solution with
an additional 5 to 10 percent glycol. The data reported gives a
residence time of 0.037 seconds or a space-time yield of 4.46 grams of
glyoxal per hour and per volume of catalyst. Additional inert gas is not
used. The way of working with negative pressure is also unsatisfactory
with regard to the space-time yield.
K)
The Russian patent I36 352 describes the oxidation of glycol at 500 to JoO 0 C, silver on aluminum oxide (40 % A *?) Being used as a catalyst. The catalyst is calcined prior to use bsi 600 to 700 0 C for 2 hours. The flow speed is 2.1 meters per second. The starting mixture contains 40 percent glycol and 60 percent water. The yield is 61 percent, the Raura-Zelt-Äusbeute 12.8 grams of glyoxal per hour and gram of catalyst. The process has the disadvantage that the catalyst is difficult to prepare and a fairly dilute glycol solution has to be used. When the catalyst is used up, 2.B. from poisoning, it has to be worked up in numerous chemical operations.
In the German Auslegeschrift 1 032 732 it is stated that when using copper and silver as a catalyst, a promator, 2.B. TiOg and Mo 2 O 5 * are required and to increase the yield of inhibitors such as HCl, Cl 2 or ethylene dichloride must be added. The best result was followed by a space-time yield obtained from a 0 o43 grams per cm 5 per hour. One can improve the result according to the teachings of the Auslegeschrift, when applying the silver on pumice, & SiIie gel or aluminum oxide as support β The procedural
Ren Si is between 300 and 45O 0 C
'Air-nitrogen mixture with an oxygen content awi- Ί see 1.6 and 5 percent carried out. With a yield of 55 percent, a space-time yield of 0.10 2 l grams of glyoxal per enr catalyst space and hour is achieved. The space-time yield is unsatisfactory.
The German Offenlegungsschrift 1 923 048 describes the production of glyoxal and uses two components (a and b) as a catalyst
10
a) copper or silver and / or gold and also
b) germanium, tin, lead, nitrogen, phosphorus, arsenic, antimony and / or bismuth.
Preference is given to silver in combination with tin, phosphorus and / or arsenic and, overall, in particular copper over silver. A Reaktiönstemperatur of about I80 ° to 600 ° C, preferably from about 300 to 45O 0 C is indicated. Diluent gases with preferably a molar ratio of diluent gas to oxygen in the range from 5 to 200 to 1 can be used. Suitable residence times are between 0.1 and 20 seconds, with those of 1 to 5 seconds being preferred. The only comparatively numerous examples of copper catalysts example, with a copper-free silver catalyst (silver / phosphorous) is carried out at a temperature of about 430 to 45O 0 C. An unsatisfactory space-time yield is calculated from the information. Another disadvantage is the laborious preparation of the catalyst.
In the German Offenlegungsschrift 2,634,439, a catalyst is used used, which consists of phosphorus combined with Cu and / or Ag. The reaction becomes a bromine compound added, which is sufficient to increase the glyoxal yield, but which is not so great that the glycolaldehyde
education is noticeably increased or the conversion of ethylene glycol drops to less than about 90 percent. Inert gas is added. A copper / silver / phosphorus catalyst is always used in the examples. The space-time yield is only 1.5 grams of glyoxal per cnr catalyst and hour. Another disadvantage is that the catalyst can only be regenerated with great difficulty.
It is known from Annalen der Chemie, Volume 59 ^ (1955) 3 page 160, that n-hexane diol-2,5 heated by hydrogenation to about 150 0
C and so, with elimination of hydrogen to 70 percent hexanol (2) -on-
(5) j receives up to 80 percent acetonylacetone at higher temperatures.
15th
It is from Tetrahedron Letters, Volume 41 (1964), page 3074 known that 2,5-hexanediol with lead tetraacetate in Converting pyridine to 2,5-hexanedione at room temperature in 89 percent yield; the yield will be through Increasing the temperature does not improve. Acetic acid esters and unreacted alcohol occur as by-products. Reaction times of 10 to 20 hours are required; the by-products make work-up difficult.
All of these processes are simple catalyst preparation in terms of simple and economical operation and good space-time yield unsatisfactory.
It has now been found that diketones of the formula '
example 1
One uses a plant rait evaporator and a vertical one Tubular reactor. The top of the reactor contains the feed for the vaporous starting mixture and the Reactor hood. The catalyst layer is below the top of the reactor, with a cooling zone below. The reactor is connected to an absorption column.
A catalyst made of silver crystals (2δ parts) of the following composition is introduced into the reactor (layer height 20 mm);
(Wt. %
)
(mm)
A mixture of 254 parts of n-hexanediol-2.5 and 247 parts of air is fed to the evaporator per hour and evaporated. The vaporous starting mixture is passed through the catalyst and reacted at 650 ° C. and 1.4 bar. The load is 0.8 t / m · h. The dwell time, based on the empty tube, is 0.1 second. The gaseous reaction mixture is now cooled to 20 ° C. and then washed with water. In the form of a 49.6 percent by weight solution, 210.3 parts per hour of n-hexanedione-2.5 with a boiling point of 191 ° C., corresponding to a yield of 84.2 % of theory, no proportion of unreacted n-hexanediol-2 , 5 and 6.8 parts of hexanol-2-one-5. The space-time yield is 31> Λ g / enr · h. The life of the catalyst is 125 days, the conversion is 100 percent.
Description
translated from German
The present invention relates to a phosphorus-doped silver fixed catalyst bed, available by
I. Silver crystals obtained by electrodeposition of silver obtained
from an aqueous silver salt solution arranges a fixed bed of silver
catalyst,
II. An activated from the starting
silver catalyst fixed bed Silver catalyst fixed bed by going through
this (the starting silver catalyst fixed bed) at one Temperature of 150
to 800 ° C a gas mixture containing Me thanol and oxygen (gas mixture
M), conducts, and
III. the activated fixed silver
catalyst bed with 1 to 20,000 ppm by weight of phosphorus, based on the
silver, in the form a finely divided phosphorus compound with a melting
or decomposition temperature of more than 500 ° C (phosphorus
connection P).
The invention further relates to a method for the
production thereof position and a process for the production of
formaldehyde using a phosphorus-doped according to the invention Silver
catalyst fixed bed.
Silver catalysts used for the oxidation of
methanol to form aldehyde are suitable, are generally known (see
Ullmann's Encyclopedia of Technical Chemistry, 3rd Edition, Urban and
Schwarzenberg, Munich-Berlin, 1956, 7th volume, pp. 660 to 663).
According to this process, silver is made in an electrolytic cell
oxidized anodically to silver ions and cathodically oxidized again to
silver reduced. The coarsely crystalline silver formed on the cathode
is suitable as a catalyst for formaldehyde synthesis from methanol.
Advantageous
effects when using phosphorus compounds as promoters for the oxidation
of methanol Formaldehyde occur in the presence of a silver catalyst,
are also from CN-A-85100530, EP-A-0467169 and JP-A-38227/83 known.
EP-A-0467169
describes the preparation of a catalyst Fixed bed made up of layers of
silver crystals which ent a powdery phosphorus-containing salt as a
promoter hold. The phosphorus-containing salt on the silver
catalyze applied before the silver catalyst with a hot Gas mixture
containing oxygen and methanol in contact brought.
However, the
fixed catalyst beds described there are immediately after the
application of the phosphorus-containing salt in a modification of low
activity and just change relatively slowly into a modification of high
activity with which formaldehyde is produced in high yield and with
high conversion len leaves. This has the following problems:
A
fixed catalyst bed described in EP-A-0467169, the in a generally
customary continuously operated system is used for the industrial
production of formaldehyde, loses activity over time, so that the yield
decreases. Around The system must therefore be able to operate
economically exchange the used for a certain operating time a fresh
fixed catalyst bed can be made, for which the Synthesis process must be
interrupted. To the synthesis process then restart, it is necessary to
Preheat the fixed bed to at least 360 ° C, so that for the
Implementation required activation energy is available. Because the
heat due to the high surface area of the catalyst is delivered quickly,
it is not technically easy, however well to reach high temperatures. In
practice this is done Heating the fixed catalyst bed, for example, by a
hot stream of inert gas (e.g. nitrogen or Carbon dioxide) through the
fixed catalyst bed and, if the Catalyst has reached the required
temperature, the gas stream adds the gaseous reactants. Is the reaction
first? once started and the catalyst is fully active reached, the
heating of the fixed catalyst bed is not more necessary because the
oxidation of methanol to formaldehyde is exothermic and the reaction
zone, i.e. H. the catalyst Fixed bed, heated to 500 to 700 ° C and thus
the Akti vation of the reaction has the required minimum temperature.
There the fixed catalyst bed immediately after the Re action is not yet
fully active, initially only small amounts of the reactants through the
fixed catalyst bed are managed, since the implementation is otherwise
not very selective or even there is a risk that the fixed catalyst bed
a Assumes modification in which it is inactive. Only after about 30
hours the fixed catalyst bed has reached its full activity and can be
loaded with the maximum amount of reactants per unit of time be
steady.
Because during the activation phase that is
required to get out the fixed catalyst bed described in EP-A-467 169
with a modification of high activity that Time yield is relatively low,
there is a need for Fixed catalyst beds that have a shorter activation
phase need until they have their final highly active modification
achieved. In addition, the activation energy required for the
implementation on the freshly prepared fixed catalyst bed required
(i.e. the minimum temperature that the catalyzer must have a fixed bed
for the reaction to start), be as low as possible.
The present
invention was therefore based on the object easy to manufacture fixed
catalyst bed that the production of formaldehyde by oxidative
dehydrogenation of Enables methanol in high yield and with high sales
and does not have the deficiencies described. In particular, the
Activation step, which is generally in the production plant for the
production of formaldehyde, be as short as possible. Furthermore, the
economic Production of formaldehyde be possible so that by the Change
of the fixed catalyst bed caused production loss is as small as
possible.
Accordingly, the phosphorus-doped described above were Silver catalyst fixed bed found.
The
preparation of the silver crystals described in step I is generally
known (cf. Ullmann’s encyclopedia of technical Chemistry, 3rd edition,
Urban and Schwarzenberg, Munich-Berlin, 1956, 7th volume, pp. 660 to
663). Let particularly good results deal with the starting catalyst
described in DE-A-23 22 757 sator fixed beds.
Suitable silver
crystals are obtained in particular when one the electrolysis according
to that in German patent specification 11 66 171 described procedures
performed.
An aqueous silver nitrate solution is preferred as
the electrolyte used. This silver nitrate solution generally has one pH
of 1 to 4 and contains 1 to 5 wt .-% silver. Of the The pH is
conveniently adjusted with nitric acid.
The electrodes usually
used in the electrolysis of Silver electrodes used. Suitable anodes are
bags, in which the silver to be oxidized in general as granules
or has been filled in as powder. As cathodes come into special
silver sheets into consideration.
Electrolysis is conveniently
carried out at current densities of 80 to 500 A / m² cathode area and
electrolyte temperatures from 10 to 30 ° C carried out.
To achieve these current densities, most are electrical lysis cell voltages from 1 to 15 volts required.
It
is recommended to use the silver crystals formed on the cathode to be
continually removed from the cathode. It will be in space common silver
crystals with a grain size of 0.2 to 5 mm receive.
Usually, a single electrolysis is sufficient to make usable Obtain silver crystals.
Such
fixed beds, also referred to as "short layers" are generally known and
for example in Ullmanns Encyclopedia of Technical Chemistry, 4th
edition, Verlag Chemie- Weinheim-New York, Volume 13, pp. 539 to 541.
In
general, one arranges the silver crystals to an initial Fixed silver
catalyst bed consisting of 1 to 9 layers of Silver crystals exist and a
total layer thickness of 1 to 10 cm. Such fixed silver catalyst beds
are known for example from DE-C-23 22 757, which hereby fully are
constantly involved.
Step II leads to activation of the starting
silver fixed catalyst bed at a temperature of 100 to 800, preferably
200 to 700 ° C, preferably continuously a gas mixture (M) which
contains methanol and oxygen. The gas mixture generally contains 0.25
to 0.60, preferably 0.35 to 0.50 mol of oxygen per mol of methanol and
0.2 to 3.0, preferred 0.67 to 1.75 moles of water per mole of methanol
and 0.9 to 2.3 before adds 1.3 to 1.8 moles of nitrogen per mole of
methanol. To the defini tional temperature, it is advisable to use the
gas mix to these temperatures at the start of the passage heat up. In
general, there is no need to preheat the gas mix (M) after a certain
time, because the fixed bed the heat of reaction released to the
required temperature heats up.
The activation of the
starting catalyst is expediently taken sator fixed bed in a fixed bed
reactor as usual usually for the production of formaldehyde by
oxidative Dehydrogenation of methanol is used and passed through it
continuously the gas mixture (M). The reak preferably stands gate
vertically and the gas mixture (M) is from top to bottom passed through
the bottom of the reactor. Such reactors or processes are for example
in EP-A-467 169, DE-A-24 44 586 and EP-A-0 150 436, to which reference
is made here in full is taken.
The cross-sectional area of the
reactor is advantageously chosen and the starting silver catalyst fixed
bed equal and orders so in the reactor that the layers of silver
crystals perpendicular to the direction of flow of the gas mixture (M).
In
general, it is sufficient to produce the activated silver fixed
catalyst bed if you go through the starting silver fixed catalyst bed
at a temperature of 100 to 500 before drawn from 200 to 700 ° C, per
cm² cross-sectional area of the initial Silver catalyst fixed bed
0.0001 to 0.5, preferably 0.01 to 0.5 kg of methanol in the form of the
gas mixture (M), through this (the Output silver catalyst fixed bed)
conducts. Passing the specified amounts of the gas mixtures (M) is
advantageously carried out at a speed that is generally chosen that the
passage 0.01 to 500, preferably 0.1 to 100, particularly preferably
requires 1 to 50 h.
During the activation phase, the methanol
that is in the gas mixture (M) is contained, almost quantitative to
form implemented aldehyde. That means that you already have step II for
the production of formaldehyde, even if the Space-time yield is not
quite as high as that phosphorus-doped silver catalyst fixed bed
according to the invention.
In step III, the activated silver
catalyst fixed bed with 1 to 20,000, preferably 5 to 5000 ppm by weight
of phosphorus, based on the silver, in the form of a finely divided
phosphorus compound a melting or decomposition temperature of more than
500 ° C (Phosphorus compound P).
The phosphorus compounds (P)
used are phosphorus salts dress. Examples of these are those mentioned
in DE-A-40 22 603 phosphorus-containing salts, e.g. B. inorganic
phosphates of alkali, Alkaline earth metals, and heavy metals such as
Ag, Zn and Fe or of boron and Ammonium.
Phosphates or pyrophosphates of alkali or earth are preferred alkali metals, e.g. B. Na₄P₂O₇, Li₃PO₄, Mg₃ (PO₄) ₂, Ca₃ (PO₄) ₂.
In
general, one proceeds in such a way that one finely divided Powder of
the phosphorus compound (P) on the activated silver catalyst fixed bed
or sprinkle it with a solution of Impregnated phosphorus compound (P)
and the solvent ver leaves to steam.
The grain size of the phosphorus compound (P) used as powder is not critical, in general it is approximately 1 mm to 1 µm.
The
solutions of the phosphorus compounds (P) are in general to aqueous
solutions containing 0.01 to 50 wt .-% of Contain phosphorus compound
(P). To impregnate the activated The silver catalyst fixed bed is one
of these solutions soaked or particularly advantageous the solutions to
the acti fourth silver catalyst fixed bed sprayed on and the solution
medium then evaporates.
The amount of phosphorus compound
sprayed or sprinkled on (P) is preferably chosen so that the amount of
phosphorus is 0.01 to 100, preferably 0.05 to 10 mg per cm² of the
phosphorus-doped Silver catalyst fixed bed cross-sectional area is.
It
is convenient during the application of the phosphorus compound (P) on
the activated fixed silver catalyst bed gas flow line (M) not to be
interrupted.
This procedure has the advantage that, provided
that Production of the phosphorus-doped silver catalyst fixed bed is
carried out in a fixed bed reactor, which is also for the oxidative
dehydrogenation of methanol to formaldehyde suitable is the production
of formaldehyde from the gas mixture (M) using the phosphorus-doped
silver according to the invention fixed catalyst bed directly on its
production can close. Usually the gas mixture (M), which one to
activate the output silver catalyst fixed bed and for the production of
formaldehyde from the gas mixture (M) under Use of the phosphorus-doped
silver catalyst fixed bed used the same composition. That way it is
possible to manufacture the phosphorus-doped silver catalyst Fixed bed
where formaldehyde is already being produced can and the production of
formaldehyde using the fixed catalyst bed according to the invention
particularly efficient combine.
It is also possible to
use a phosphorus-doped silver catalyst sator fixed bed with maximum
activity in an iterative ver drive to manufacture by initially only one
in step III Part, advantageously 0.01 to 2 mg, preferably 0.05 to 1 mg
Phosphorus, per cm² of the cross-sectional area of the activated silver
fixed catalyst bed in the form of the phosphorus compound (P) apply
this and step the amount of phosphorus compound (P) wise, for example
in steps of 1 to 100%, based on the amount initially applied increases
and at the same time the out prey on formaldehyde controlled. The
applied The amount of phosphorus compound (P) increased gradually until
no increase in yield by further application of the phosphorus
connection (P) can be achieved more.
The phosphorus-doped silver
catalyst fixed beds lose how other known silver catalysts too, when
used for the production of formaldehyde steadily in activity, what in
falling sales and yields of formaldehyde is noticeable.
This
loss of activity of the catalysts of the invention leaves avoid
yourself partially if you per kg of methanol in the form of Gas mixture
(M), which, based on 1 cm² of the cross-sectional area of the
phosphorus-doped silver catalyst fixed bed, through this conducts,
additionally either continuously or discontinuously (in one portion
after introduction of a defined amount on gas mixture (M)) 0.01 to 100
ppm by weight of phosphorus, based on the phosphorus-doped silver
catalyst fixed bed, in the form of Applies phosphorus compound (P) to
this without the introduction to interrupt the gas mixture (M). With
continuous opening The loss of activity can slow down the step have
discontinuous application partially reversed ge be made.
The
subsequent application of the phosphorus compound (P) can in done in
the same way as in step II during production of the phosphorus-doped
silver catalyst fixed bed is.
If the subsequent application of
the phosphorus compound (P) made intermittently, so the intervals
between the subsequent application of the phosphorus compound (P) on
the Phosphorus-doped fixed silver catalyst bed usually as long chosen
that during this time not more than 500, preferably 1 to 5 kg of
methanol in the form of the gas mixture (M), based on 1 cm²
Cross-sectional area of the phosphorus-doped silver catalyst
solid betts, be guided through this, otherwise otherwise in the
meantime the yield would drop too much.
The manufacturing
process of formaldehyde by oxidative dehy drugging of methanol using
the invention Fixed catalyst bed is otherwise in a conventional manner
carried out by the gas mixture (M) at temperatures of about 500 to 750
° C, especially 600 to 710 ° C by the phosphorus doped silver catalyst
fixed bed conducts. The procedure is in generally at a pressure of 0.5
to 2 bar, preferably of 0.8 to 1.8 bar carried out continuously. It is
before partly, the reaction gases leaving the catalyst zone cool down
within a short time, e.g. B. at temperatures of 50 to 350 ° C. The
cooled gas mixture is then more appropriate as an absorption tower, in
which the formaldehyde is washed with water from the gas mixture.
Special, special ders advantageous variants of the generally known
method for the production of formaldehyde, which also in the invention
Methods can be used are described in DE-A-24 44 586, DE-A-24 51 990,
EP-A-0 083 427 and EP-A-0 150 436, whose subject is included here,
recommended.
By using the fixed catalyst bed according to the
invention can be particularly economical formaldehyde by oxidative
Establish dehydrogenation of methanol.
In particular, the gas
containing methanol and oxygen is needed mixture that you add to your
synthesis process Activation by the fixed bed leads only to a
comparative wise low temperature to be preheated. Furthermore, the Time
required for activation is relatively short, so that overall the
space-time yield of the process for the preparation of formaldehyde is
higher.
example 1
In
a vertical test reactor with an inside diameter of 15 cm was a
three-layer starting silver fixed catalyst bed of the same diameter
with a total layer thickness of 2 cm attached. The bottom layer
consisted of 1000 g silver crystals of grain size 1 to 2.5 mm, the
middle one Layer of 65 g silver crystals with a grain size of 0.75 to 1
mm and the top layer of 185 g of grain size silver crystals 0.2 to 0.75
mm.
Through
an output silver catalyst fixed bed that is at 340 ° C had been heated,
a gas mixture consisting of Methanol, water and air passed. The crowd
was growing during the 23-hour activation period to 32 kg of methanol
per hour, 21.4 kg water and 54 kg air increased (final load). At the
end of Activation period, the temperature in the fixed bed was 700 ° C.
This flow rate was during the entire test period kept constant. Then
0.42 mg of phosphorus per cm² the cross-sectional area of the activated
silver catalyst solid beds in the form of a 3% by weight aqueous
solution of Na₄P₂O₇ sprayed on its surface, the supply of gas mixing
was continued.
The
reactor was operated continuously and after one Certain operating hours
of the reactor were further amounts of phosphorus applied to the
phosphorus-doped silver catalyst fixed bed. The respective quantities
(in the table are the accumulated quantities indicated), the yields of
formaldehyde and the time obtained point of the subsequent phosphorus
application, calculated from Time at which the phosphorus-doped silver
catalyst solid bed was produced by phosphorus on the acti fourth fixed
silver catalyst bed are applied Take the table.