Reissued Nov. 18, 1952 Re. 23,584 UNITED STATES PATENT oFFICE 28,584 MANUFACTURE OF PENTAERYTER OL Harry Jackson, Stevenston, and Griffith Glyn Jones, Annan, Scotland, assignors to imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Original No. 2,562,102, dated July 24, 1951. Serial No. 695,050, September 5, 1946. Application for reissue December 3, 1951, Serial No. 259,698. In Great Britain September 1, 1945 2 Claims. (CL 260-635) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue. 1. 2 The present invention is concerned with a new and calcium formate if there are present 4 moles and improved process for the manufacture of formaldehyde and 0.5 mole calcium hydroxide pentaerythritol by means of the well known re per mole acetaldehyde. When the theoretical action that occurs between acetaldehyde and quantities of the reagents are present, the fact formaldehyde in aqueous solution in presence of that the formaldehyde and the lime are partly a strong base such as calcium hydroxide. consumed in the formation of the aforesaid by In the earlier preparations of pentaerythritol products implies that there will be insufficient to described in the literature the tWO aldehydes Were react with the whole of the acetaldehyde to form caused to react in presence of the base at very pentaerythritol. With the object of minimising high dilutions over long periods of time, so that O the loss occasioned by formation of these by they were not well adapted for commercial pro products, it is usual to employ somewhat more duction. In the processes that have been en than the theoretical proportions of formaldehyde ployed commercially for the production of penta and lime, for instance 4.5 moles formaldehyde per erythrito, the aldehydes are used in considerably mole acetaldehyde, and at least sufficient calcium higher concentrations, the acetaldehyde concen 5 hydroxide to leave some undissolved lime after tration usually exceeding one mole for every 80 the reaction is over. moles water, and the temperatures are such that When a reaction mixture, in which acetalde the alkaline condensation is completed in the hyde is gradually added to a mixture of lime and course of an hour or two or even less. The alkali formaldehyde Solution in excess as aforesaid, has most commonly used is line; and after the 20 been allowed to warm up during the early stages alkaline condensation is over a precipitant for of the reaction and is maintained at a suitable the calcium formate and other soluble calcium. temperature during the addition of the acetalde compounds present in the resulting Solution is hyde, there is a tendency for a further rise in the introduced, and the clear liquor is evaporated temperature to take place spontaneously after the down under reduced pressure until crude penta 25 acetaldehyde has all been added. It has hitherto erythritol can be crystallised from it. The pre been the practice, in order to ensure the comple cipitation of the calcium compounds is commonly tion of the desired reaction after the ingredients carried out by acidifying the solution with sul Of the reaction mixture have all been introduced phuric acid in amount sufficient to convert them to permit the temperature to rise to a point just into calcium sulphate, most of which settles out, short of the point at which a dark yellow or brown the clear liquor being further treated for the 30 colour develops, and to keep the reaction mixture conversion of the calcium Sulphate remaining in stirred until the falling aldehyde concentration the solution into insoluble compounds or partly of the Solution shows no further tendency to di into insoluble compounds and partly into soluble minish. This temperature may be anything from compounds that will not deposit during the about 45 C. to 63 C. according to the manner evaporation. in which the reaction is carried out. Figures It is well known that troublesome by-products have been published by Friedrich and Braun are formed in the reaction mixture. These troublesome by-products include Syrupy products (Berichte 1930, LXIII, page 2687) indicating that resulting from self-condensation of formaldehyde when one half mole of lime is used per mole in presence of the base, and also dipentaerythritol. 40 acetaldehyde and the reaction mixture is heated It has also been stated that tripentaerythritol at the end to 45° C., the ratio of pentaerythritol which, like dipentaerythritol, is a polyhydroxy to other compounds in the crude pentaerythrito compound but contains two ether groups instead is at a maximum when five moles formaldehyde of one, is formed. Both the syrupy self-conden are used per mole acetaldehyde. sation products of formaldehyde and the poly It is an object of the present invention to in pentaerythritols interfere with the recovery of the prove the ratio of the amount of pentaerythritol pentaerythritol. The syrupy products, however, to the amount of other products formed in the are easily soluble in alcohol and can be removed reaction, and especially to improve the ratio of from the crude pentaerythritol much more easily pentaerythritol to poly-pentaerythritols in the than can the crystalline poly-pentaerythritols, crude crystallised pentaerythritol so that penta from which it is especially difficult to separate the erythritol of improved purity may be obtained. pure pentaerythritol, even by recrystallisation. A further object is to provide a process suitable It should theoretically be possible to achieve for commercial application wherein an improved the complete conversion of the reagents in the yield of pentaerythritol of high quality is ob alkaline reaction mixture into pentaerythritol 55 tained, . . . .

88,584 3 4. The present invention is based in part on the maining in solution into barium sulphate and observation that, when the condensation is calcium formate, further filtration and evapora carried out in presence of an excess over the tion under reduced pressure, theoretical amount of the alkaline material sun In putting the invention into effect, the amount client to leave an excess on the disappearance of of formaldehyde employed in the reaction mix the acetaldehyde, the employment of increasingly ture per mole acetaldehyde may range from 5 to large excesses of formaldehyde over the theoreti about 10 moles, or even more, and is preferably cal quantity reckoned on the acetaldehyde, at least 7 moles. The amount of the line should ranging from about 5 to 10 or even more moles preferably be sufficient to leave an undissolved per mole acetaldehyde results in a progressive 0 excess at the end of the reaction. Preferably the reduction in the amount of the dipentaerythritol formaldehyde solution and the calcium hydroxide or other by-products formed in the reaction that are mixed together and the acetaldehyde, desira crystallises from the concentrated liquors with bly in aqueous solution, is gradually added to the the pentaerythritol and that in part on the ob mixture with agitation. Except that during the servation that if the customary heating at the 5 admixture of the reagents and during the sub end of the reaction is omitted and the tempera sequent period while the mixture is kept agitated ture of the alkaline reaction mixture is never al until the acetaldehyde is consumed the tempera lowed to exceed 33 C., and the reaction is inter ture must be rigorously controlled so that it never rupted whenever the acetaldehyde has been con exceeds 33 C. and apart from the preferably high sumed, any such amounts of formaldehyde may 20 proportion of formaldehyde used the conduct of be employed without giving rise to any extensive the condensation reaction according to the pres formation of syrupy formaldehyde alkaline con ent invention need present no special feature. An densation products and can be easily removed incidental advantage of the lower maximum tem and largely recovered so that pentaerythritol of peratures to which the reaction mixture is sub high quality may be obtained in improved yield. 25 jected lies in the fact that they tend to minimise According to the present invention, a process the losses occasioned by volatilisation of the acet for the manufacture of pentaerythritol by the aldehyde, and this can only be advantageous to interaction of formaldehyde and acetaldehyde in the yield of pentaerythritol-obtained. If desired the presence of a strongly basic hydroxide con the cooled alkaline reaction mixture may be prises the employment of a considerable excess 30 filtered or decanted away from the undissolved of formaldehyde Over the theoretical reckoned on portion of the excess of lime before the liquor is the acetaldehyde and a quantity of said hydroxide treated with acid used to convert the free lime exceeding the theoretical amount sufficient to present in it or calcium salt, for instance sul leave an excess on the disappearance of the acet phuric acid, sufficient of the acid being employed aldehyde, maintaining the alkaline reaction mix to confer a faint permanent formic acid acidity ture at a temperature not exceeding 33 until the on the liquor. Methyl Red may be used at this disappearance of the acetaldehyde and thereupon, stage to indicate by a change in colour from still at a temperature not exceeding 33 C., re yellow to red when sufficient acid has been added. moving its free alkalinity. When Sulphuric acid is used the precipitated After the free alkalinity of the reaction mixture 40 calcium sulphate is preferably removed, for in has been removed by adding sufficient of an acid stance by filtration. Acids yielding easily soluble to render the solution only slightly acid to an in calcium salts may however be used instead of sul dicator changing colour at about the same acidity phuric acid, for instance formic acid, and in this fas Methyl Red the unreacted excess of formal case the whole of the free line dissolves up and dehyde may be stripped from the reaction mix filtration is rendered unnecessary at this stage. ture, preferably by steam distillation at Ordinary Pentaerythritol mother liquors rich informic acid or increased pressure. Temperatures in the re may be used for this purpose. - gion of 100° C. are incapable of converting the The formaldehyde is next stripped from the formaldehyde present in the no longer alkaline liquid by distillation, preferably in a current of medium into syrupy by-products. High tempera steam, and is recovered in the aqueous distillate. tures are indeed beneficial at this stage since they The distillation is preferably carried out at ordi tend to decompose powdery or crystalline poly nary atmospheric pressure or even at an increased mers of formaldehyde which might otherwise pressure, since under the prevailing non-alkaline tend to contaminate the subsequently crystallised conditions high temperatures no longer can result crude pentaerythritol and render any further 55 in the formation of syrupy products from the purification thereof more difficult. In order to formaldehyde. It is frequently convenient to facilitate the recovery of the formaldehyde in the conduct the distillation so as to effect a diminu distillate obtained, it is preferred that when re tion in the volume of the liquor being distilled. moving the free alkalinity of the liquor contain The formaldehyde-containing aqueous distillate ing the pentaerythritol and the formate of the OU obtained is practically free from formic acid and base formed in the reaction, the amount of acid can be used, after concentration by fractional used should be insufficient to liberate any sub distillation, if necessary, in a subsequent prepara stantial proportion of the formic acid present in tion. It is accordingly economical to employ the said formate, as will be the case if the mix quite substantial excesses of formaldehyde over ture is made only slightly acid to Methyl Red. 65 the theoretical in the reaction mixture, for in The distillate will thus be practically free from stance from 7 to 10 moles per mole acetaldehyde formic acid. The pentaerythritol may then be and thereby obtain the benefits in yield and free recovered from the stripped liquor substantially don from di-pentaerythritol that accrue from in known manner, for instance in the case where the use of high molar ratios of formaldehyde to calcium hydroxide has been used as the strongly 70 acetaldehyde. basic hydroxide, as is preferable, by addition of The stripped liquor containing the pentaeryth sufficient sulphuric acid to liberate the formic ritol and calcium formate in solution may next acid from the calcium formate in the solution be treated with sufficient sulphuric acid to liber filtration from calcium sulphate, treatment with ate the formic acid from the calcium formate witherite so as to convert calcium sulphate re 5 and the resulting mixture may be worked up

ass8. 6 substantially in known manner, the production to only about 15 grams per litre of. the decalci of the pentaerythritol in the final stages being fed liquor. facilitated by the relative freedom of the final Another aliquot portion of the solution acid concentrate from syrupy products and, more par fied to redness with Methyl Red but still con ticularly when a large excess of formaldehyde taining calcium formate, was rendered alkaline over the theoretical amount has been used, its by the addition of the amount of hydrated lime reduced di-pentaerythritol content. equivalent to the amount of sulphuric acid that The invention is further illustrated in the fol had been used, namely 0.3 mole per mole acetal lowing examples: dehyde, and was warmed with stirring to 50 C. O On being kept at 50° C. for some time its tem Example I perature commenced to rise without external This example illustrates the advantage in re heating. The rise in temperature was checked spect of high quality product of the process ac so that it did not amount to more than a few cording to the invention over a process in which degrees. the alkaline liquor is finally heated, the formalde 15 The liquor was then treated with sufficient sul hyde present in the reaction mixture at the start phuric acid to convert the whole of the calcium in each case amounting to 5.8 moles per mole formate into calcium sulphate, and was settled aldehyde. and filtered and treated with witherite and again 12.5 lbs. acetaldehyde (in the form of 29.6 lbs. filtered. The clear filtrate was then evaporated of 42.33% aqueous solution) (1 mole). 20 under reduced pressure as before until crystal 49.4 lbs. formaldehyde (in the form of 135.8 lbs. lisation commenced. Two crops of crystals of 36.4% formalin) (5.8 moles). were obtained, further evaporation yielding a 16.8 lbs. hydrated lime (0.8 mole). syrupy residue which did not crystallise and 250 lbs, water, which on careful evaporation to dryness weighed The hydrated lime and the water were stirred 25 38 grams per litre of decalcified solution. This to form a slurry and the addition of formaide residue was of dark amber colour and treacly hyde was commenced at 25° C. Five minutes consistency, and had a strong odour of caramel. later the addition of the acetaldehyde Solution The quality of the crude pentaerythritol ob-. was started. The whole of the formaldehyde tained was substantially the same as that of was added at a constant rate to the stirred 30 the crude product obtained according to the slurry over 20 minutes, and the rate of addition method of our invention but the yield of pure of the acetaldehyde solution was regulated So pentaerythritol estimated by the nitration meth that the reaction mixture remained at or below od was only 67.5% calculated on the acetalde 300 C. with the cooling water circulating around hyde. the reaction vessel. Under these conditions 35 Example II about 45 minutes was required for the addition The condensation was carried out as described of the acetaldehyde. The mixture was stirred in Example I up to the stage of the first addi for a further 60 minutes with the water in the tion of sulphuric acid, except that the amount jacket stationary. The temperature falling to of formaldehyde used was 192 lbs. of a 35.6% 28° C. by this time the liquor was free from the 40 formalin solution, corresponding to a molar odour of acetaldehyde. It was then cooled to formaldehyde acetaldehyde ratio of 8 to 1. The 20° C. 16.8 lbs. of 50% sulphuric acid (0.3 mole) whole of the product was then worked up as were then added, this amount sufficing to render described for the first aliquot portion of the so the liquor acid to Methyl Red. The liquor was lution in Example . The yield of pure penta allowed to settle and the calcium sulphate de 45 erythritol by the nitration method in the crude posited was filtered off and washed, the filtrate pentaerythritol amounted to 82% of the theo and washings being bulked in a calibrated vessel retical based on the acetaldehyde used, the crude for measurement. An aliquot portion of the pentaerythrito (in three crops) containing about liquor was passed down a packed distillation 94-96% pentaerythritol and about 0.1% di column in counter-current to a current of steam 50 pentaerythritol. The first crop amounted to at atmospheric pressure until the formaldehyde about 34 of the whole melted at 253-254 C. and concentration in the stripped liquor had fallen was 98-99% pure pentaerythritol. to 0.1% free formaldehyde. The calcium formate We claim: in the stripped liquor was then converted into ... In the process for the production of penta calcium sulphate by the addition of the calcul 55 erythritol by the interaction of formaldehyde lated quantity of sulphuric acid (0.5 mole per and acetaldehyde in the presence of a strongly mole acetaldehyde) and the liquid was allowed basic metallic hydroxide, the increasing of the to settle. It was then filtered, treated with Sufi ratio of pentaerythritol to poly-pentaerythritol cient witherite to convert the remaining Soluble in the reaction mass which comprises employ sulphate in the liquor into barium sulphate and 60 ing between five and ten moles formaldehyde and again filtered. The filtered liquor was treated in excess of one-half mole of said hydroxide per with a small amount of ammonia Sufficient to mole of acetaldehyde in the reaction mixture, convert any residual formaldehyde into hexa maintaining the alkaline reaction mixture at a methylene tetramine, and the solution was evap temperature not exceeding 33 C. until the dis orated down under reduced pressure until the 65 appearance of the acetaldehyde and thereupon, pentaerythritol began to crystallise. The solu still at a temperature not exceeding 33 C., re tion was cooled and the crystal crops were bulked nowing the free alkalinity of the reaction mix and analysed by a nitration method in order to ture by addition of sufficient acid to impart an determine their pure pentaerythritol content, acidity to the Solution equivalent to the acidity which was 75.6% of the theoretical calculated which will just change the color of Methyl Red, on the amount of acetaldehyde employed. The distilling formaldehyde from the reaction mix crude pentaerythritol had a pure pentaerythritol ture until not to exceed 0.1% free formaldehyde content of approximately 90% and a dipenta remains therein, then converting water-soluble erythritol content of about 3-4% as estimated by metallic salts in the remaining reaction mixture nitration. The uncrystallisable residue amounted to water-insoluble metallic salts to precipitate

28,084 7 - - the latter, and faltering out the insoluble metal- thereas removing metalo salts from the reaction f lic salts. nature, and thereafter recovering pertaerythr } 2. In the process for the production of penta- to from the reactions mattatre. . erythrito by the interaction of formaldehyde and acetaldehyde in the presence of a strongly basic 5 ARRY JACKSON. pentaerythritoli it, to poly-perstaerythritol E. 2. in theE. reof C, C, ONS. action mass which comprises employing between REFERENCEs CTED fe and ten moles formaldehyde and fr eaccess The following references are of record in the acetaldehydeof Elti. in the reacgiri nature, per notara E. . 10 file of this patent or the original patent: ing the alkaline reaction macture at a tempera- UNITED STATES PATENTS ture not ecceeding 33 C. until the disappearance Number Name . Date of the acetaldehyde and thereupon, still at a 2,152,371 Wyler ------Mar, 28, 1939 temperature not ecceeding 33 C., removing the 15 224034 Wyler ------May 6, 1941 free alkalinity of the reaction mature by addi- 2,292,926 Brubaker et al. ------Aug. 11, 1942 tion of sufficient acid to impart an acidity to 2325,589 Bried ------Aug. 3, 1943 the solution equivalent to the acidity aphich Dill 2,360,186 Wyler ------Oct. 10, 1944 ust change the color of methyl red, distilling 2,369,083 Spurlin ------Feb. 8, 1945 formaldehyde from the reaction micture until 20 2.372,602 Owens ------Mar, 2, 1945 not to eacceed 0.1% free formaldehyde remains 2,401,749 Burghardt ------June 11, 1948