DE4126730A1 - Prepn. of calcium formate from calcium hydroxide and formaldehyde - uses calcium hydroxide with short solubility time, in presence of inhibitor for auto-condensation of formaldehyde - Google Patents

Abstract

In prepn. of Ca formate by reaction of Ca(OH)2 with HCHO in molar ratio of 1:4, in an aq. phase at 40-90 deg. C, in presence of a catalytic amt. of an inhibitor for the auto condensation of the HCHO, Ca(OH)2 with a solubility time of less than 200 secs. for 99% dissolution, determined by conductivity measurement at 20 deg. C after addn. of Ca(OH)2 as a 20 wt.% aq. suspension (milk of lime) to deionised water free from CO2 at a concn. of 0.8 g/l of Ca (OH)2 is used. After the reaction, the inhibitor is sepd. by pptn. and filtration or by ion-exchange, and at the same time, or later, HCHO still present is converted to formoses at pH above 7 by autocondensation, and Ca formate is recovered from the aq. soln. by crystallisation. USE/ADVANTAGE - Ca(OH)2 is quantitatively converted, the space/time yield is increased, and yields are high. The Ca formate is free from HCHO and inhibitors. Ca formate is used in tanning, to produce formic acid, as setting accelerator in cement, as silation aid, and as fodder additive in animal feeding

Description

The invention relates to a method for manufacturing of calcium formate in the aqueous phase by reaction of formaldehyde with calcium hydroxide in the presence of inhibiting the autocondensation of formaldehyde Fabrics.

Calcium formate, the calcium salt of formic acid practically exclusively as a by-product of Production of polyhydric alcohols (polyols) Pentaerythritol, trimethylolethane, trimethylolpropane and Neopentyl glycol won. It forms with the Implementation of those accessible through aldol condensation 3-hydroxyaldehydes with formaldehyde in the presence of Calcium hydroxide; Calcium formate is therefore the one Oxidation product of a mixed Cannizzaro reaction.

Calcium formate is used for a variety of purposes, such as aids in tannery, for the production of formic acid, as Setting accelerator in the cement industry, as Silage auxiliaries and increasingly as a nutritive effective feed additive in animal nutrition.

The latter area of application - calcium formate serves to improve feed conversion, to reduce of indigestion, avoiding microbial Feed spoilage (see Degussa AG brochure, "Calcium formate" - Ch 609-1-105-988 DD) - provides  special quality requirements so that Animal feed not containing calcium formate is denied.

Disadvantageous in the production of calcium formate By-product of polyol synthesis is that an increase formate production only together with an increase of the polyol production in question can; this sets corresponding sales opportunities for the Polyols ahead.

Methods for producing are also known Calcium formate by carbonylation of the Calcium hydroxide (see e.g. Gmelin manual, Volume Ca (B), pages 161-162 and Ullmanns Encyclopedia, 4th ed., Vol. A 12, pages 23-24). These procedures generally require technical complex systems, high pressures, high temperatures and mostly long reaction times.

The Cannizzaro reaction of formaldehyde with strong inorganic bases is represented by the following scheme reproduced:

Me (OH) _n + 2nCH₂O → Me (OOCH) _n + nCH₃OH
n = 1 for Me = K, Na, T1
n = 2 for Me = Ca, Ba, Pb (II), Sn (II)

The course of this reaction depends on the metal hydroxide used. Numerous studies have shown that certain metal hydroxides do not promote the Cannizzaro reaction, but rather an autocondensation of formaldehyde. Although the formaldehyde molecule does not have an αH atom and therefore no normal aldol condensation can occur, hydroxyaldehydes and ketones, especially pentoses and hexoses, the so-called formoses, are formed by a practically analogous reaction (T. Mizuno, A. Weiss, Adv. Carbohyd Chem. Biochem. 29: 173 (1974)). The formose-forming hydroxides include in particular Pb (OH) ₂ , Sn (OH) ₂ , TlOH and Ca (OH) ₂ .

It was therefore difficult to form calcium formate Calcium hydroxide and formaldehyde odorless and in high yield because of the autocatalytic formaldehyde condensation formaldehyde the desired formate formation is withdrawn.

To the polyol production, such as pentaerythritol from acetaldehyde, formaldehyde and lime Discoloration of the reaction solution and loss of formaldehyde was reduced by formose formation variously suggested implementing in Perform presence of inhibitors. As Inhibitors are suitable according to US Pat. No. 2,186,272 oxalates of the elements Cr, Mn, Fe, Co, Ni and Cu, according to US-PS 23 29 514 elemental Ni, Cu, Pt and oxides or Hydroxides of Cu and Ag and according to US-PS 25 01 865 Boric acid and borates.

Technical patents 1 69 105 and 1 82 576 focus on the retardation of formaldehyde autocondensation using similar inhibitors. Finally, SU-PS 1 47 157 describes the preparation of calcium formate from formaldehyde and Ca (OH) ₂ in dilute aqueous solutions in the presence of selected metal salt inhibitors. In the aforementioned CS and SU documents, calcium hydroxide and formaldehyde are converted in a molar ratio of 1 to 3 to 1 to 4. If a high selectivity of the conversion of the formaldehyde in the sense of the Cannizzaro reaction is desired, long reaction times - around 5 hours - are necessary, whereby the space-time yield is considerably impaired. The SU patent also teaches that the best results can only be obtained using very dilute aqueous solutions - this measure again reduces the space-time yield and also requires the distillation of large amounts of water when calcium formate is obtained from the aqueous phase by crystallization should. The calcium formate obtained by this process still contains the inhibitors and is characterized by the pungent smell of the adhering residual formaldehyde. In SU-PS 1 47 157 no measures are taught how the residual formaldehyde and inhibitor are separated from the aqueous calcium formate solution in order to obtain an odor-free and inhibitor-free calcium formate which can thus be used as a feed additive.

The object of the present invention is a to show technical processes that allow Calcium formate in high yield and in terms of actual implementation of improved space-time yield to win. In addition, a way should be shown to formaldehyde-free and inhibitor-free Calcium formate.

This object is achieved by a process for the preparation of calcium formate by reacting calcium hydroxide with formaldehyde in a molar ratio of essentially 1 to 4 in the aqueous phase at 40 to 90 ° C in the presence of catalytic amounts of at least one inhibitor for inhibiting the autocondensation of formaldehyde, which thereby is characterized in that calcium hydroxide with a dissolution time of less than 200 seconds for 99% resolution, determined by means of conductivity measurement at 20 ° C after addition of the calcium hydroxide as a 20% by weight aqueous suspension (milk of lime) to CO ₂ -free deionized water a concentration of 0.8 g Ca (OH) ₂ per liter of water, after the reaction has ended, the inhibitors used are separated off by precipitation and filtration or by ion exchange treatment, at the same time or subsequently, at a pH of greater than 7, formaldehyde still present by autocondensation converted into formoses and known in itself Calcium formate is obtained from the aqueous solution by crystallization.

The subclaims are directed towards preferred Embodiments.

The method according to the invention leads previously known method not only to an almost quantitative yield, but also to a higher Space-time yield because of the special selected calcium hydroxide quality the reaction time could be significantly shortened. Normal building lime is not reactive enough; the implementation proceeds with this incomplete, so the resulting Calcium formate solution does not have a high content contains converted formaldehyde. While through the Use of lime with a dissolving time below 150 Seconds the yield of calcium formate usually is above 95%, this is reduced to about 65% if lime with a dissolving time of around 400 Seconds is used. Have proven their worth calcium hydroxide suspensions made from burned Lime by extinguishing with water in the presence of a  Intensive mixing device are manufactured; this The method is described in detail in DE-PS 27 14 858 described.

The determination of the dissolving time as a measure of the reactivity of the calcium hydroxide to be used is carried out under standardized conditions: 200 ml of CO ₂ -free, deionized water are placed in a double-walled vessel, which is heated with water from a thermostat to maintain a temperature of 20 ° C ; a conductivity probe, a stirrer and a thermometer are inserted through openings in the lid of the measuring vessel; the conductivity probe is connected to a conductivity meter and a recorder. With the help of a dispenser, a sufficient amount of a 20% by weight lime hydrate suspension / milk of lime is added so that the concentration in the measuring vessel is 0.8 g calcium hydroxide per liter. The writer records the increase in conductivity over time; the conductivity increases in proportion to the concentration and thus detects the amount of calcium hydroxide dissolved per unit of time.

The molar ratio of Ca (OH) ₂ to H ₂ CO mentioned for the reaction of "essentially" 1 to 4 means that one of the two reactants can be used in a slight excess; The excess should expediently be less than 10%, in particular less than 5% of theory, but the stoichiometric molar ratio of 1 to 4 is particularly preferred.

In the process according to the invention, the total amount of water is kept as low as possible that the formate solution obtained is as highly concentrated as possible and the energy expenditure for isolating the formate is low. Formaldehyde is generally used as a commercially available aqueous solution, in particular with a content of 37% by weight; in principle, formaldehyde oligomers of the formula HO (CH ₂ O) _n H with n = 10 to 30 can also be used, provided that depolymerization takes place before the actual reaction.

The implementation of calcium hydroxide with formaldehyde can be done in different ways For example, it is possible to use aqueous formaldehyde, a lime suspension and the inhibitor together in a reactor, for example in a loop reactor, to implement, the desired reaction temperature, preferably 50 to 70 ° C, by cooling is maintained. According to a preferred, very Safe procedure is in the form of calcium hydroxide an aqueous suspension to a submitted and Temperature-controlled formaldehyde / inhibitor solution pumped in: because there is always little calcium hydroxide in the reactor , the exothermic reaction in the case of Malfunctions due to the addition of formic acid be stopped at any time. Also the addition of one aqueous formaldehyde solution to a heated, Calcium hydroxide presented containing inhibitor Suspension is workable. The implementation formed methanol can, if desired, during or after the implementation of The reaction mixture is distilled off. If the Obtaining crystalline calcium formate Concentration step includes methanol be distilled off next to part of the water.

To inhibit the autocondensation of formaldehyde during the implementation they come in the beginning metals and Metal connections in question. But it has been shown that many heavy metal salts Prevent formaldehyde auto-condensation that Do not promote or even encourage the Cannizzaro reaction inhibit so that the reaction after a certain turnover comes to a standstill. This different Behavior follows from the selected examples following table.  

table

Formaldehyde content depending on the reaction time in the presence of various inhibitors

(Batch: 76 g Ca (OH) ₂ 97% in 600 ml water; 324 g H₂CO 37% by weight; 50 ° C)

It was found that Mn (II) salts, in particular Mn (II) acetate, boric acid and borates of the alkali and alkaline earth metals, molybdates and tungstates, such as Me _n WO ₄ and Me _n MoO ₄ with n = 2 for Me = Alkali metal and n = 1 for Me = alkaline earth metal, also Zr (IV) and Hf (IV) compounds, in particular ZrCl ₄ , Zr (OAlkyl) ₄ and zirconyl salts - such also arise when using z. B. ZrCl ₄ in the reaction mixture gallium III compounds and boranates for the process according to the invention are outstandingly effective inhibitors. With such inhibitors, the reaction from calcium hydroxide with formaldehyde generally proceeds to a residual formaldehyde content in the reaction mixture of less than 1% by weight. The inhibitors are usually used in amounts of 0.2 to 20 mmol per mole of calcium hydroxide.

The aqueous obtained after the actual reaction Calcium formate solution contains the inhibitors as well as the Residual formaldehyde and undissolved components from the used lime. While the unresolved Components, if necessary after discontinuation of a pH value of 7 by adding formic acid, in Can be removed in the usual way, for example by filtration prepared the removal of the residual formaldehyde Problems. A distillative separation of the Formaldehyde, such as by pressure distillation complex and little with the low concentration economically; an oxidative elimination by Addition of hydrogen peroxide was not successful satisfactorily. It has now been found that after Removal of the inhibitors, preferably by ion exchange treatment can be accomplished may, the residual formaldehyde at a pH above 7 quickly and completely through auto-condensation saccharified. The pungent smell disappears  of formaldehyde and the solution turns yellow until brown. If this is desired, it can be added lightened the color with little hydrogen peroxide be, so that practically from such a solution colorless calcium formate can be obtained. Also without the mentioned measure to decolorize the calcium formate solution free of inhibitor and formaldehyde can be known as Calcium formate suitable for feed additives in crystalline form by crystallization, for example vacuum crystallization with subsequent Solids separation and drying, win.

The inhibitors can be removed in a manner which is coordinated with the particular inhibitor. After the reaction, some inhibitors are at least partially in undissolved form or can be precipitated as poorly soluble compounds and can be separated from the still alkaline calcium formate solution by filtration, the formation of formose already starting during the filtration. When using, for example, manganese (II) salts as inhibitors, a large part of the manganese can be separated off by filtration alone. As previously emphasized, it is generally desirable to quantitatively separate the inhibitors, which is accomplished by ion exchange treatment of the undissolved calcium formate solution. Cationic inhibitors can be obtained using weakly acidic, macroporous cation exchangers with chelating anchor groups with amino and carboxyl groups, in particular iminodiacetate anchor groups, or amino and phosphonic acid groups, such as, for example, -N (CH ₂ -PO ₃ H) ₂ anchor groups, the acid groups usefully in the Ca form, separate from the aqueous calcium formate solution. It was not foreseeable that, despite the high concentration of Ca ²⁺ ions, the inhibitors used could be quantitatively fixed to the exchange resin and recovered by elution with an acid. Anionic inhibitors, such as in particular MoO ₄ ^2- and WO ₄ ^2- , can be separated off in the formate form by passing the reaction mixture over basic ion exchangers. If the ion exchange treatment is carried out with a previously neutralized calcium formate solution, the pH value must then be adjusted back to above 7 in order to allow the quantitative saccharification of the residual formaldehyde.

Despite the essentially stoichiometric and therefore particularly economical molar ratio of Reaction partner surprisingly becomes one practically quantitative conversion of calcium hydroxide achieved. In addition, the input materials cannot be only in low, but also in high Implement concentrations without resulting in yield and Loss of quality comes; the resulting Calcium formate solution can thus be saturated or even be oversaturated, which makes the effort for the Isolation of crystalline calcium formate from solution is low. Further advantages of the invention Process are the improved space-time yield as well as the simple removal of the inhibitors and the Residual formaldehyde. The quality of the won Crystalline calcium formate is sufficient for all known ones Applications.

Example 1a

230 g (3 mol) calcium hydroxide (97% content) with a 99% solution time of 140 sec are suspended in 1800 g water and heated to 50 ° C., 0.6 g (0.0025 mol) ZrCl ₄ and 972 g 37 wt .-% Ger formaldehyde (50 ° C warm) added. The heating bath is set at 50 to 52 ° C. The internal flask temperature rises to 57 to 59 ° C due to the exothermic reaction. After a reaction time of 120 minutes, the mixture is neutralized with 9 g of formic acid. The clear, colorless solution formed after the filtration contains 380 g of calcium formate (content determination by separating the Ca ions using a strongly acidic ion exchanger and titration of the acid released), which corresponds to a yield of 97% (product from the formic acid addition was subtracted). The residual formaldehyde content is 0.6 g / 100 g solution, the filtration residue approx. 5 g.

Example 1b

1 l of a calcium formate solution, prepared and filtered according to Example 1a, but not yet neutralized, with a CH ₂ O content of 0.8% is passed at 60 ° C. over the Lewatit® TP-207 ion exchanger (Bayer AG). The running solution is kept at 60 ° C. After a few minutes, the color changes to light yellow and then slowly turns brownish. The mixture is neutralized with formic acid and 3 ml of 30% by weight H ₂ O _{2 are} added. The resulting weakly colored solution no longer contains free formaldehyde and is free of zircon (atomic absorption analysis). When this solution is evaporated under reduced pressure, calcium formate crystallizes out as a practically colorless and odorless product.

Example 2

Approach analogous to Example 1; instead of the Zr inhibitor, 1500 mg (0.01 mol) of NaBO ₂ .4H ₂ O were used as the inhibitor. The reaction was stopped after 120 min by neutralization with 10 g of formic acid. The solution (3000 g) contains 377 g calcium formate (96.7% of theory) and a residual formaldehyde content of 0.8 g / 100 g solution.

Example 3a

Approach analogous to Example 1; instead of the Zr inhibitor, 1.0 g (0.004 mol) of manganese II acetate. 4H ₂ O is used as the inhibitor. The bath temperature is initially set at 55 to 57 ° C. Due to the exothermic nature of the Cannizzaro reaction, the internal temperature in the reaction vessel rises to about 70 ° C. The bath temperature is kept at approx. 70 ° C. After 80 minutes the mixture is neutralized by adding 8 g of formic acid. The residual formaldehyde content of the solution is 0.5 g / 100 g solution.

Example 3b

1 l of the filtered calcium formate solution from Example 3 with a pH of 7.1 and a residual content of 45 mg Mn ²⁺ is at 20 ° C over 100 ml of the ion exchanger TP-207 (Bayer AG) (Ca ²⁺ form ) headed. The continuous solution contains only 0.1 mg / l manganese. After alkalization to pH 8, the solution turns yellow-brown and after 10 minutes at 50 ° C., no more formaldehyde can be detected in the solution.

Example 4

Example 3a was repeated, but was followed completed implementation not neutralized, but only filtered. It already colored during the filtration the solution yellow-brown; within 10 minutes The formaldehyde content in the solution dropped to 60 ° C less than 0.1%.

Example 5 (not according to the invention)

Approach analogous to example 1. 230 g (3rd Mole) calcium hydroxide (97%) with a 99% solution time of 400 sec. After 120 min with 10 ml of formic acid neutralized (pH 6.8). The solution contains 252 g Calcium formate (65% of theory), the Residual formaldehyde content is 4 g / 100 ml, the dried filter residue is 84 g.

Example 6a

377.5 g of a 20% lime milk suspension, which was produced in accordance with DE-PS 27 14 858 and has a 99% dissolution time of 40 seconds, is mixed with 1.3 g (0.004 mol) of Na ₂ WO ₄ .2H ₂ O and 200 g H ₂ O added. The heating bath is set to 55 ° C; 325 g / 4.0 mol) 37% formaldehyde are added dropwise within 1 h. The maximum temperature is limited to 65 ° C by cooling. The mixture is stirred for a further 30 minutes, neutralized and, after the filtration, a clear colorless solution (900 g) of calcium formate with a content of 14.2% and about 0.6 g of residual formaldehyde is obtained.

Example 6b

1 l of the filtered calcium formate solution from Example 5 with a pH of 6.9 and a remaining one Tungsten content of 39 mg W-VI / l becomes over 100 at RT ml of a commercially available one loaded with formate ions strongly basic ion exchanger. The continuous solution still contains 1.0 mg / l W-VI. To Alkalizing sets the autocondensation of the Residual formaldehyde, and from the formaldehyde-free Calcium formate solution is made in a known manner crystalline calcium formate by evaporation of the Water and methanol.

Claims (6)

1. A process for the preparation of calcium formate by reacting calcium hydroxide with formaldehyde in a molar ratio of essentially 1 to 4 in the aqueous phase at 40 to 90 ° C in the presence of catalytic amounts of at least one inhibitor for inhibiting the autocondensation of formaldehyde, characterized in that calcium hydroxide with a dissolving time of less than 200 seconds for 99% dissolution, determined by means of conductivity measurement at 20 ° C. after addition of the calcium hydroxide as a 20 wt.% aqueous suspension (milk of lime) to CO ₂ -free deionized water at a concentration of 0.8 g Ca (OH) ₂ per l of water, after the reaction has ended, the inhibitors used are separated off by precipitation and filtration or by ion exchange treatment, at the same time or subsequently, formaldehyde still present at a pH of greater than 7 is converted into formoses by autocondensation and in known form calcium formate from the water solution by crystallization. 2. The method according to claim 1, characterized, that calcium hydroxide and formaldehyde in Molar ratio of 1 to 4 uses and preferably the calcium hydroxide used has a dissolving time of less than 150 seconds.   3. The method according to claim 1 or 2, characterized, that calcium hydroxide and formaldehyde at 50 to 70 ° C implemented. 4. The method according to one or more of claims 1 to 3, characterized, that as an inhibitor at least one compound from the series Manganese (II) salts, tungstates and Molybdate, zircon (IV) compounds, Gallium III salts, boric acid, borates and boranates starts. 5. The method according to one or more of claims 1 to 4, characterized, that the inhibitor in an amount of 0.5 to 20 mmol per mole of calcium hydroxide. 6. The method according to one or more of claims 1 until 5, characterized, that one for the separation of cationic inhibitors weakly acidic, macroporous cation exchanger with chelating anchor groups in the Ca form and for Removal of basic anionic inhibitors Ion exchanger used in the formate form.