CA1060876A - Malachite preparation - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Synthetic malachite of desirable particle size and distribution is coprecipitated with small amounts of uniformly dispersed bismuth. After nucleation, the crystals are grown at elevated temperatures. The malachite can be converted into a cuprous acetylide complex useful as an ethynylation catalyst.

Description

BACKGROIJND OF THE NVENTION
~his invention relates to a process for copre-cipitating malachite with bismuth, to a process of making a cuprous acetylide complex ethynylation catalyst starting with such coprecipitation, and to the complex produced.
In the production of 1,4-butynediol by the reaction of acetylene with formaldehyde in the presence of a cuprous acetylide complex catalyst, it is known to be desirable to inhibit the formation of cuprene, polymerized acetylene, by the use of inhibitors such as bismuth oxide.
U.S. Patent 2,300,969 - Reppe et al. (1942) discusses the use of several such inhibitors in the formation and use of such catalysts at elevated pressures such as about 20 atmospheres. U.S. Patent 3,650,985 - Kirchner (1972) mentions the utility of bismuth oxide as a cuprene inhibitor in cupric acetylide catalyst made and used at low partial pressures of acetylene, below 2 atmospheres. Neither of these patents indicates how the bismuth values can be incorporated uniformly into the catalyst itself.
It has been found that in the production of the low pressure catalysts according to U.S. Patent 3,650,985, if bismuth oxycarbonate is added separately to preformed malachite, it will separate in the catalyst which is eventually prepared, leading to unsatisfactory results.
Thus, it is desirable to have a satisfactory method of coprecipitating bismuth in the basic cupric carbonate or malachite which is the catalyst precursor.
Basic copper carbonate, known as malachite, Cu2(OH)2CO3, is normally prepared by either of two precipitation techniques. In the first, a solution of a

- 2 -copper salt such as copper nitrate or chloriae is neu-tralized to a pH of 7.0 with sodium or potassium carbonate or bicarbonate~ Initially, hydrated copper carbonate, amorphous CuC03 x(H2O), precipitates in the form of a thick gelatinous material which, on heating, slowly converts to malachite with the elimination of C02. Precipitates of crystals of malachite made by this technique generally comprise irregularly shaped particles ranging in size from less than 1 micron (~) to more than 25 ~ in average particle cross-sectional dimension~ If the gel has set up thoroughly, then the irregularity and broad aistribution of crystallite size on crystallization seem to be a result of tearing of the gel as it precipitates. The irregularly-shaped crystal-lites and wide distribution of particle size is rather un-desirable for use as a precursor in the production of cuprous acetylide ethynylation catalysts.
Another method for the precipitation of malachite involves feeding simultaneously the copper solution and the carbonate neutralization agent with agitation to maintain a pH in the range of 5 to 8. The hydrated copper carbonate so obtained is also subsequently converted to malachite at ambient temperature or more rapidly as the temperature is - increased. This technique produces a more regular crystal line product which consists of agglomerates of individual crystallites of about 2 to 3 ~ average cross-sectional dimension. The agglomerates range in size up to a maximum of about 30 ~. As with the first method of adding the carbonate neutralizer to the copper solution, so too with this method of simultaneously feeding them together, an amorphous hydrated copper carbonate is initially formed.

It would be desirable to have a process for the production of basic copper carbonate crystalllne particles having ~ismuth incorporated therein with the particles being of a fairly uniform and relatively large particle size, The uniformity of dispersion ~f bismuth in the particles is de-sirable to permit the formation of ethynylation catalyst in which the bismuth values ~ill remain in place and continue to be e~fective in the prevention of cuprene ~ormation, SUMMARY OF THE INVENTION
The present invention, in certain of its embodi-ments, provides a process for the production of crystalline particles of basic copper cflrbonate having uniformly d~spersed therein bismuth in amount~ in the range of 2 to 5 percent by weight based on the amount of copper present, The process comprises three steps, First, hydrated copper carbonate particles are precipitated by the simultaneous addition to water of solutions of cupric salts and alkali metal carbonate or bicarbonate to f~rm a reaction mixture, The solutions are in such proportions as to maintaln the pH
about in the range of 5,0 to 8.o, Then the hydrated copper carbonate is converted to basic copper carbonate in the reaction mixture at a temperature of at least ~bout 60C, This conversion occurs through the nucleation of crystallites of malachite from the amorphous hydrated copper c~rbonateO
Subsequent additions of copper3 bismuth and carbonate pre-cipitate on these converted nuclei as more malachiteO The nucleated crystalline particles and agglomerates of such particles are grown while the bismuth is incorporated uni-formly into the particlesO The reaction mixture is kept at 1~W~6 temperatures of at least about 60C~ during the growth. The solutions of cupric salts, bismuth salts and sodium carbonate or bicarbonate are added in such proportions as to maintain the pH about in the range of 5.0 to 8.0 until the average cross-sectional dimension of the agglomerates of crystallites is at least about 10 microns.
The bismuth content herein is expressed in terms of percent by weight based on the amount of copper present.
Parts, percentages and proportions herein are by weight except where indicated otherwise.
Although it is necessary to have the bismuth present during the particle growth, it is also desirable and, as a practical matter may be necessary, to have it present also during the precipitation and nucleation steps.
The coprecipitated basic copper carbonate-bismuth particles can be used to make a cuprous acetylide complex useful as an ethynylation catalyst. The basic copper carbonate-bismuth particles are subjected as a slurry in aqueous medium at 50 to 120C., to the simultaneous action of formaldehyde and acetylene at a partial pressure of not more than 2 atmospheres. The aqueous medium has a pH of 3 to 10 at the initiation of the subjecting. Pref-erably, the reaction is continued until all of the cupric precursor is converted to the cuprous acetylide complex.
It is desirable for the medium in which the subjecting is done to have a pH in the range of 5 to 8 at least initially.
The resulting catalysts are a particulate cuprous acetylide complex which consists essentially of copper, carbon, hydrogen~ oxygen and bismuth in pr~portions corresponding to the general formula (CUC~)W(GH2o)x(c2H2~y(H2o)z wherein, when w = 4, x = 0.24 to 4,0, y = 0~24 to 2 40 and z = o.67 to 2.80, and in which the bismuth i~ present in an amount of 2 to 5%. The complex particles have a total sur-face area of at least 5 m~-/g, and the aver~ge particle cross-~ectiona~ dimension being at least 10 ~.
Preferably~ the particulate complex ha9 a total surface area of 15 to 75 m~/g, the average particle cross-sectional dimension being in the range of 10 to 40 ~, contain-ing 20 to 66% copper, 2 to 12.5 carbon atoms per copper atom, 0.2 to 2 hydrogen atoms per carbon atoms, 0.1 to 1 oxygen atom per carbon atom, and 2 to 4~ bismuth.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In contrast to the ~asic copper carbonate crystal production methods of the prior art~ the method of the pre-sent inv~ntion utlizes a rapid precipitatlon o~ ~ydrated copper carbonate followed by nu~leation and conversion of the hydrated copper carbonate to basic copper carbonate (malachite). The nucleation and conversion are encouraged by an elevated temperature, such a8 over 60C. The larger proportion of the reactants for forming the ba~ic copper car~
bonate, such as at least two-thirds of the copper, is not-added to the reaction mixture until a~ter the conversion to basic copper carbonate. At this time, the copper salts, neutralizing chemical~ and bismuth combine readily to produce a uniform dlspersion of bismuth in ba~ic copper carbonate crystalline particles of rather uniform and large partlcle size, This cry~tal grow~h avolds the initial formation of further gelatinous hydrated copper carbonate.

~60~76 I~ the entire production of the basic copper car-bonate crystals i9 done at elevated temperatures such as over 60C, including precipitation~ nucleation and growth, the hydrated copper carbonate i8 not present for much time at all. Nucleation and conversion occur rapidly, and growth of the initial nuclei is the main phenomenon occurring.
Thus~ operating all steps of the productlon at elevated tem-perature leadg to the production of ~maller number of larger particlec. Actually~ each of the ~teps will take place at lower temperatures such as room temperature, about 23C.
Many nuclei would form and convert to malachlte before ery-stal growth depleted the concentration of reactants~ leading to the prevalence of smaller particle sizes, Al~o, with mala-chite production at lower temperatures, the bismuth values are not uniformly included in the ba~ic copper carbonate made this way but tend to segregate either auring ~ormation of the carbonat~ or later during use of the carbonate to ~orm cuprouæ acetylide complexes for use as e~hynylation cataly~t.
Thus, it is i~portant to use the procedure of the invention to Porm the basic copper carbonate-bismuth coprecipitates to be used in making the ethynylation catalysts, For the productlon o~ smaller sized crystallite~
and agglomerates, the nucleation can be conducted at a lower temperature followed by an increase in temperature to above 60C for relatively rapid converæion and growth and uniform dispersion of the bismuth. ~or the production of larger-slzed crystallltes and agglomerates, the nucleation al~o would be condueted at a h1gher temperature ~uch as àbove 60C, If the pH is raised at least 1.0 unit between the nucleation step and the growth step, this can lead to - even greater uniformity in particle size. Crystal growth occurs optimally in a band representing super-saturation on a plot of solubility versus temperature. The super-saturation band is wider for these products at higher pH
values. Therefore, higher pH within limits will lead to more deposition on existing nuclei and less formation of new small nuclei if the reaction continues to be conducted in the super-saturation band.
me conversion of the hydrated copper carbonate - to malachite as the malachite nucleates can be readily observed. Hydrated copper carbonate is blue and it tends to be a structureless gelatinous mixture. The malachite is green and crystalline.
If sodium carbonate is added to a copper nitrate solution having a pH of 3, as the pH rises to 4-1/2 the reaction product sets up as a thick gel. Further pH rise and agitation break up the gel, tearing as it converts to malachite to form very irregular particles related to the size of the torn gel. Above a pH of about 8.0, and at elevated temperatures the amorphous copper carbonate hydrate begins to convert to copper oxide which is undesirable.
Below a pH of 5.0, the gel formation becomes troublesome.
During the catalyst production, sodium iodide can be added separately. This produces some bismuth oxyiodide in the catalyst which acts as a further inhibitor for cuprene formation.
me catalyst is desirably about 15 to 20 ~
agglomerate size. Larger particles have advantages over smaller particles including more rapid filtration and drying, lack of dust formation and lack of band formation on settling. Fifty ~ agglomerate size is larger than desirable due to decreased activity of the catalyst.
Catalyst particles that are too small lead to filtering difficulties. The size of the agglomerates can be readily controlled by adjusting the temperature and pH of the steps of the production of the basic copper carbonate.
During the ethynylation reaction, acetylene inhibits the valence change of cuprous copper in the catalyst to elemental copper or cupric copper. This is desirable, because elemental copper is a catalyst for the polymerization of acetylene to cuprene. Cuprene is quite undesirable in these reactions because it tends to clog filters and cannot be readily removed. During some upset conditions in production operations, the flow of acetylene into the reactor is shut off due to emergency or sudden loss of supply. Bismuth, such as in the form of oxycarbonate uniformly incorporated in the catalyst, aids in protecting the catalyst from such degradation even while hot and in the absence of acetylene.
Above 4 or 5% bismuth, a second phase tends to separate from the catalyst after some weeks of operation in the ethynylation catalyst. This manifests itself in the formation of fine particles which cause filter difficulties. Also, such separation would tend to degrade the operation of the bismuth in the catalyst.
With a solubility level in the ethynylation reaction media of about 0~5 ppm, bismuth can be digested out of the catalyst. This is more of a problem if the ~1~0876 bismuth content of the catalyst is over about 3%, but it is not a serious problem until above about 5% bismuth content.
In preferred techniques according to the inven-tion, bismuth nitrate in the desired concentration is dissolved in the copper nitrate solution which is then fed simultaneously with sodium carbonate to a crystallizer.
The pH is maintained between 6 and 7, and the temperature is in the 60-80C. range during crystal growth. For larger crystals, the temperature is also in that region initially ~or the precipitation and nucleation. In the resulting malachite, the bismuth is effectively coprecipi-tated and uniformly distributed. When such bismuth-containing malachite is utilized to form a cuprous acetylide complex ethynylation catalyst for butynediol synthesis, a substantial improvement in catalyst filterability and stability results.
Bismuth-containing malachite has been prepared according to the invention using early nucleation techniques with bismuth concentrations of 1%, 2%, 3%, 4%, 8%, 10%
and 15%. The resulting malachite was then used to prepare the ethynylation catalysts. Catalysts thus obtained were then sub~ected to extended life tests to determine the improved stability and operability as indicated by the absence of cuprene formation. For comparative purposes, catalysts were also made with a commercial grade of malachite. Life tests were run for a period of about 100 hours or more at which time the catalyst was removed and examined for the presence of cuprene. Cuprene is readily detected by its copper color, and it generally floats to the surface in the formaldehyde-water~solutlons used for the pro~uction o~ butynediol Excess bismuth salts can also digest out of the cataly~t and form residues of other colorsO
Li~e test results showed that cataly~ts produced from bismuth-free malachite precursoræ produced substantial amounts of cuprene during the 100-lhour life test Even more cuprene was produced when the catalyst was kept hot in the - absence of acetylene, simulating the sudden 109s of acetylene in a butynediol manu~actur~ng operation. Furthermore, when 5% bismuth in the form af bismuth subcarbonate wa~ mixed with bi~muth-free~malachite and the mixture was subsequently converted to catalyst, substantial cuprene formation wa~
still evident when the catalyst was evaluated A trace of cuprene was also noticed with the catalyst containing 1%
bismuth, but the catalyst~ made from malachite coprecipitated wlth high amounts of bismuth remained cuprene free. With 2% or more bismuth coprecipitated in the malachite, the re-sulting catalyst ~ould be held in an acetylene-free environ-ment ~or shor~ periods such as up to about 1/2 hour at ele-vated temperatures such as between 70 and 95C without de-gradation that cause~ excessive cuprene formation, which would end the use~ul li~e o~ the cat~l yst.
At bismuth loadlngs of 5% and higher~ some blsmuth separation from the catalyst results a~ter extended use Thus it appears that bismuth concentrations above 4% are less de~irable, and concentrations in the 2 to 4% range appear optimum for overall performance. One preferred catalyst with a 3~ bi~muth content wa3 usçd ~6~8'76 in the production of butynediol for 20 days without evidence of degradation or cuprene formation. Furthermore, i the relatively large and uniform particle sizes of catalysts obtained according to the present invention result in easier filtration. In butynediol preparation methods wherein the catalyst system operates as a slurry and the product is removed through a candle filter technique, the larger particle size is able to permit increased filtration rates.
EXAMP~E 1 Malachite - 4% Bi Starting Cold Crystalline particulate synthetic malachite con-taining 4% bismuth was prepared in accordance with the invention as follows:
Into a reaction vessel containing 300 cc. of water are simultaneously added two streams. One stream is a saturated solution of Na2CO3 in water and the other is a water solution containing 100 g. Cu(No3)2-3H2o, 2-32 g- Bi(No3)3-5H2o, 10 cc. HNO3 and 90 cc. of H2O.
The streams are added at rates such as to keep the pH in the precipitation vessel continuously at about 6.5, and heat is gradually applied from the beginning to commence the precipitation. The following table shows the rate of solution addition measured in terms of the copper nitrate solution still to be added, time since commencing addition and the temperature of the reaction mixture.

~6087~;

TABLE I
MALACHITE PRODUCTION

Solu-tion TimeTemperature to be Added Minutes _ (C.)(cc. CuNO3) 10 (nucleation) 70 125 The reaction product was allowed to digest until it reached a pH of 8.0 and then was filtered and dried.
me particles had an average cross-sectional dimension of 15-20 ~. The product contained 4% bismuth uniformly dispersed through the crystalline particles.
It is desirable to add only about 1/4 to l/3 of the reactants until nucleation and conversion occurr which may happen simultaneously, and then to add the remaining reactants after nucleation to grow the bismuth-containing-malachite crystals.

Malachite - 3% Bi Starting Cold Crystalline particulate synthetic malachite containing 3% bismuth was prepared in accordance with - Example 1, but using 1.74 g. Bi(No3)3-5H2o. The following table shows data analogous to that o~ Example 1, and also gives the pH at several times during the reaction.

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The crystallizing was finished at a pH of 6.8 to insolu-blize all the malachite. The product was then digested to a pH of 8.0, washed, filtered and dried. The resulting product had particles of 15 to 25 microns cross-sectional dimension with good dispersion of bismuth at the 3% level.

Catalyst Preparation In a typical catalyst preparation 45 g. of malachite containing 3% bismuth and 25 g. Cu is charged to a glass vessel with jacket heating along with 600 g.
of 37% formaldehyde and 2 g. of CaC03 for neutralizing the formic acid generated. A N2-diluted C2H2 stream is passed through the vessel using a sintered glass frit for gas distribution. Temperature is controlled between 70 and 80C. and pressure at 4 to 5 psig. As the malachite is converted to copper acetylide, C02 is eliminated and the system is thus provided with a vent to effect CO2 removal. The system is also e~uipped with a small recycle gas pump so that unreacted C2H2 is recycled, and makeup C2H2 and N2 are added to maintain the pressure. The C2H2 concentration, as measured by gas chromatography in the off gas, is generally maintained in the 2 to 5% by volume range to achieve the most active catalyst. After all C02 is eliminated the reactor is cooled, the contents are re-moved and the catalyst is washed with water to eliminate product butynediol and unreacted formaldehyde. The catalyst thus obtained is stored under water until it is subjected to evaluation with respect to stability and long term activity.

-:~L06~1~76 Catalyst Evaluation Life Test For evaluation, the catalyst derived from a 45 g. malachite charge is charged to a jacketted vessel with 600 cc. of 15% formaldehyde solution. Acetylene gas is passed through a sintered glass frit to achieve the necessary distribution and mass transfer. Reactor tempera-ture is increased to 90C. and after 8 hours to 95C.
Acetylene is fed continuously as is a 37% formaldehyde ~o solution to maintain a steady state 10% formaldehyde con-centration. Product is continuously withdrawn through a sintered glass filter so that catalyst remains in the reactor. Sodium bicarbonate solution is added continuously to maintain pH in the 6.0 to 6.2 region as measured by -~ an in-reactor pH probe. Total reactor pressure is main-tained at 5 psig. Activity is measured as weight units of C2H2 consumed/hour/weight unit of copper in the reactor and is calculated continuously from the rate of formalde-hyde consumption. A life test runs for approximately 100 hours or longer after which the system is cooled, the catalyst withdrawn, filtered and washed free from reactants and product and examined for cuprene content. Cuprene is readily detected by its characteristic copper color and tends to float on the surface of the water layer under which the evaluated catalyst is stored.
Table III below summarizes the results of life tests with cuprous acetylide catalysts of the invention.
When more than 5% bismuth was used, various colored materials were deposited on the catalyst. Bismuth salts separate as a result of bismuth digesting out of the catalyst.

Above 1% bismuth, cuprene was not detected except in the cases in which the bismuth was not coprecipitated with the malachite, tests 11 and 12. Catalysts containing 2, 5 and 15% bismuth were exposed to elevated temperatures in the absence of acetylene without deleterious subsequent formation of cuprene.

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It has now been found that in the proce~ de3cribed hereinbefore the hydrated copper carbonate particles may be prcciplt~ted by admixlng aqueou~ sc)lutions o~ cupric salts and of alkal~ metal carbonate or bicarbonate, The solution~
may, for e~ample, be admixed dlrectly or admixed by separately or slmultaneously admixing ~he solutions wlth ~ater. The solution~ are admi~ed in proportions 90 as to maintain the p~ of the resultant reaction mixture in the range of about 5.0 to 8.o~ The reactlon mixture is subsequently treated a~
described herelnbe~ore.
The pre~ent invention is ~urther illustrated by the i:~ollowing example.

.
Qne hundred grams of NaHC ~ are slurried in 400 cc of water. Into this slurry, ~lowly ~nd over a two hour period, i3 fed a solution of CU(No3)2 3H2 188 gm Bi(N3~3~5H2 3.48 gm HN03- concentrated 20 cc in 200 cc o~ water, The pH of the slurry is initially about 7,8, but fall~ slowly to about 7.2 as addition oP the solution progres~es and formation of ~alachlte commences, The temper~
ature of the slurry is maintained at about 65C until mala-chite formation 19 complete, and the malachite is then fll-tered from the reaction mas~ and dried.
The application is a division of copending application serlal NoO 220 936, filed February 24, 1975.

Claims (6)

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

1. A process for the production of a particulate cuprous acetylide complex having uniformly dispersed therein bismuth in the amount of 2 to 5 percent by weight based on the amount of copper present, said process comprising the following steps:
precipitating hydrated copper carbonate particles by the simultaneous addition to water of aqueous solutions of cupric salts and alkali metal carbonate or bicarbonate to form a reaction mixture, said aqueous solution being in such proportions as to maintain the pH about in the range of 5.0 to 8.0, nucleating and converting the hydrated copper car-bonate to basic copper carbonate in the reaction mixture by holding the reaction mixture at a temperature of at least about 60°C., and growing agglomerates of the nucleated crystalline particles by precipitating basic copper carbonate con-taining bismuth by the addition to the reaction mixture of aqueous solutions of cupric salts, bismuth salts and alkali metal carbonate or bicarbonate in such proportions as to maintain the pH about in the range of 5.0 to 8.0 with the reaction mixture at a temperature of at least about 60°C, until the average cross-sectional dimension of the agglomerates of crystallites is at least about 10 microns, and then subjecting the agglomerated basic copper carbonate as a slurry in aqueous medium at 50 to 120°C., to the simultaneous action of formaldehyde and acetylene at a partial pressure of not more than 2 atmospheres, said aqueous medium having a pH of 3 to 10 at the initiation of said subjecting, and continuing the reaction until a particulate cuprous acetylide complex consisting essentially of copper, carbon, hydrogen, oxygen and bismuth in proportions corresponding to the general formula (CuC2)w(CH2O)x(C2H2)y(H2O)z-Bi wherein, when w = 4, x = 0.24 to 4.0, y = 0.24 to 2.40 and z = 0.67 to 2,80, and in which the bismuth is present in an amount of 2 to 5 percent by weight based on the amount of copper present, the complex particles having a total surface area of at least 5 m2/g, the average particle cross-sectional dimension being at least 10 microns, is obtained.

2. The process of Claim 1 in which said aqueous medium has a pH of 5 to 8 at the initiation of said subjecting.

3. The process of Claim 1 in which said temperature, formaldehyde concentration and acetylene pressure are maintained until substantially all of the cupric precursor is converted to cuprous acetylide complex.

4. A particulate cuprous acetylide complex which consists essentially of copper, carbon, hydrogen, oxygen and bismuth in proportions corresponding to the general formula (CuC2)w(CH2O)x(C2H2)y(H2O)z-Bi wherein, when w = 4, x = 0.24 to 4.0, y = 0.24 to 2.40 and z = 0.67 to 2.80, and in which the bismuth is present in an amount of 2 to 5 percent by weight based on the amount of copper present, the complex particles having a total surface area of at least 5 m2/g, the average particle cross-sectional dimension being at least 10 microns, when produced by the process of claim 1.

5. A particulate cuprous acetylide complex which consists essentially of copper, carbon, hydrogen, oxygen and bismuth in proportions corresponding to the general formula (CuC2)w(CH2O)x(C2H2)y(H2O)z-Bi wherein, when w = 4, x = 0.24 to 4,0, y = 0.24 to 2.40 and z = 0.67 to 2.80, and in which the bismuth is present in an amount of 2 to 5 percent by weight based on the amount of copper present, the complex particles having a total surface area of 15 to 75 m2/g, an average particle cross-sectional dimensions in the range of 10 to 40 µ, and which contains 20 to 66 percent by weight copper, 2 to 12.5 carbon atoms per copper atom, 0.2 to 2 hydrogen atoms per carbon atoms, 0.1 to 1 oxygen atom per carbon atom, and 2 to 4 percent bismuth by weight based on the amount of copper present, when prepared by the process of claim 1.

6. In the production of 1,4-butynediol by reaction of acetylene and formaldehyde in the presence of a cuprous acetylide catalyst, the improvement comprising use of the cuprous acetylide complex of claim 4 or claim 5 as the catalyst.