Patented Nov. 14, 1944 2 1 3 6 2 1 9 0 0 UNITED STATES PATENT OFFICE 2,S.62,900 PRODUCT@ION OF CELLULOSE @ETHERS Walter Henry Groombridge @and John Downing,. Spondon, near Derby, En No Drawing. AI)pUcation September 16, 1942, Serial No. 458,56g.. In @Great Britain @September 11,1941 4 Claims. (Cl. 260-231) This inventiorl is concerhed with improve- agent employ!ad MRY vary, e. g. from 2 to 7 molecul6r)equivalents of each, per C6HioO5 unit of cellulose, according to the ether content,of the desired product. The production of the alk.ali-cellwose may be ' effected by various @methods. For example, cotton linters, wood Pulp or other ceuulosic raaterial may be mixed with a solution of sodium hydroxide of the required concentration, and excess @solution, if -any, niay then be removed by siibjecting the impregnated cel,lulose to Pressure. It is, hbwever, somewhat @diffidult to obtain thorough ancl uniform impregnation of cellulose *lth sodium hydroxide solutions of. the @ high @coiicentration@ process, and it has been found preferable to impregnate the cellulose with a rele@tively dilute solution of sodium hydroxide, for example a solution containing 15, 20 or 30% of sodium hydroxide, and then, after removal of an3@ excess solution, to concentrate the alkali ori the cellulose, particularly by azeotrople distihation. Pref erably, such an operation is carried out using an azeotroping liquid which is suitable @ for ii8e as. an inert medium in the @subsequ@nt (@th@rification. Aromatic hydrocarbons, for example bi@nzene, I xylene and particularly toluene, are 'vory suitable for this purpose. For example, the cellul6se may be steeped in an excess of a 20% aqueous s6lution of sodium hydroxide at gtmospheric temperature for about 10-20 minutes, after which the impregnated cellulose is pressed until it contains the required amount of alkali and is then introduced into a suitable vessel, together with toluene in an amount equal to about 10-20 tinies the weight of the original cellulose, and azeotropic distillation carried out until the required degree of concentration of the alkali has beeii effected. Altematively, the cellulose may be dispeised In toluene, a dilute aqueous solution of sodium hydroxide introduced into and 'well stirred:with the dispersion and azeotropic distillation then carri6d out. Usually the conditions emplo@ed for the pro-duction of the alkali-cellulose should. be such that an alkali-cellulose containing from 1 to 2 up to P-bout 2.5 mols of sodium hydroxide per C6HioO5 unit of cellulote is obtained and that the concentration of the sodium hydroxide, considered as a solution.in any water present, is at least 60% and is preferably considerablly higher, for example 80 or 90% or more. After the alkali-cellulose has been prepared the flrst stage (>f etherifteation is carried out, Possible and not consist of a mixture of cellulose 15, which should be @pre@ent duritig etherification if ethers of widely differing solubility properties. the best results are to, @ be obtained by, the present ments in the production of cellulos e derivatives and particularly in the @production of celluIGse ethers. In the developrnent of a ' satisfactory industrial 5 .process - for the production :of cellulose ethers, particulariy ethers which are soluble in organic solvents, there are a nurnber of considerations to be borne in mind. In the first place, if the Process is.to be economic the amount of alkali 10 and of et,heirifying agent required must not be excessive and a large proportion of by-products miii@t not be Produced. Again, the cellulose ether Produced by the process should be as uniform as It has been discovered that better,results are obtained from the above.points of view by incorporating the alkali and etherifying agent required in the etherifteation mixtur , e iri a number 20 of stages instead of having the total 4iiantities required present at the beginning of the:reaction, provided that certairi other conditions, which are discussed bL-@low, are observed. The alkali and etherifying agent may be in@troduced 9.5 continuously during the reaction or they may be introduced from time to tirne. 'Me amount of alkali present at any time should not exceed @about 2 to 2.5 mols for each C6HioO5 unit of cellulose and should be chi@mically equ ivalent to, or slightly 30 more thein chemically equivalent to, the amount of etherifying agent present. Moreover, It is important that the alkali present should be concentrated so that the etheriflcation mixture contain's a molecular ratio of alkali to water of at 35 least 2 to 3. Preferably the mixture i@ anhsrdrous or substantially so, particularly at the beginning of etherification. For example, when sodium hydroxide, which is the preferred alkali, is employed, a ratio of at least nine parts of sodium hydroxide 40 to one part of,water by weight is desirable. The invention will be describ@d with particular reference to the production of ethyl cellulose which is soluble in organid solvents from alkalicellulose using diethyl sulphate as etherifying 45 agent and sodium hydroxide as the alkali, since this is the process with which the present application is particularly concerned. The invention is not, hdwever, limited to such a process but - is applicable generally to the production of cel50 lulose ethers using appropriate etherifying agents in -the presence of alkali. For example, methyl cellulose rnay be produced using dimethyl sulphate and potassium hydroxide. The total amounts of alkali and etherifying 55 2 2,362,900 preferably in the presence of an inert diluent, by introducing an amount of diethyl sulphate chemically equivalent, or slightly less than cheniically equivalent, to the sodium hydroxide present and heating the etherification mixture at a suitable 5 temperature, for example 100-120' C. As indicated above, toluene is very 8uitable, both as an , azeotroping agent and as an inert diluent, and it is therefore very convenient to carry out the azeotroping operation with toluene and then to 10 effect etherification by incorporating diethyl sulphate with the alkali-cellulose, together with further toluene if necessary, and refluxing the reaction mixture until substantially all of the iliethyl sulphate has been exhausted, which usually 15 takes about 1-2 hours. A further quantity of sodium hydroxide amounting e. g. to I to 2 mols , per C6HloO5 unit of cellulose is then introduced. Preferably, it is introduced in the form of a. relatively dilute aqueous solution and concentrated 20 by azeotropic distillation, for example until the concentration is 80 or 90% or more. When this stage is reached a further amount of diethyl sulphate, chemically equivalent or slightly less than chemically equivalent to the sodium hydroxide, 'S 25 introduced and etherification continued as inthe first stage of the process. The operations described above may then be repeated one or more times until an ether having the required ethoxy content, e. g. 35, 40 or 45% ethoxy, is obtained. 30 If It is desired to produce an ether having as high a viscosity as possible it is desirable to carry out the production'of the alkali-cellulose and the etherification stages in an inert atmosphert" for example in an atmosphere of nitrogen. 35 The following examples are given to illustrate the invention: Example I 162 parts (I mol) of wood pulp are steeped In 40 a bath of 20% aqueous sodium hydroxide for about 10 minutes at atmospheric temperature and the Impregnated material is then pressed until itcontains about 200 parts of the sodium hydroxide solution, which corresponds with about 45 one mol of sodiUM hydroxide based on the eellulose. Th6 impregnated cellulose Is then Introduced into a reaction vessel provided with a stirrer, ana- a reflux condenser and abo'ut 3000 piirts by weight of toiuene is added. Th6 sodium '5 0 hydroxide Present is concentrated by azeotropic distillation at the boiling point until an anhydrous alka ..,I,i,::C@llulose is obtained, the toluene which is distilled over being separated from the water and fed back to the vessel. 77 parts (0.5 55 mol) of diethyl sulphate are then added and heating at the boiling point is continued for about two hours. 200 parts of 20% sodium hydroxide are then added and concentration of the hydroxide until it is anhydrous again effected by f)O azeotropic distillation as described above, after which another 77 parts of diethyl sulphate are introduced and the reaction continued for about 2 hours at the boiling Point. These operations are repeated until about 4 mols of sodium hy- 65 droxide and 2 mols of diethyl sulphate have been reacted. The ethyl cellulose is then separated froni the other constituents of the reaction mixture, purified and dried. Example 11 70 The Production of ethyl cellulose is carried out as described In Example I with the exception that the wood pulp is dispersed in the toluene and the first amount of sodiurn @ydroxide sqlution is iA, 75 troduced into the toluene and concentrated bY azeotropic distillation prior to the Introduction of the diethyl sulphate. Example III The production of ethyl cellulose is carried out as described in Example I or II, with the exception tha@t the amounts of sodium hydroxide and diethyl sulphate intr(>duced in the flrst stage are increased to two mols and one mol respectively and the process is completed in two further stages using one mol of alkali and 0.5 mol of diethyl sulphate at each stage. Having described our invention what we desire to secure by Letters Patent Is: 1. Process for the production of cellulose ethers, which comprises treating cellulose with an aqueous solution of alkali containing an amount of alkali greater than that which is molecularly equivalent to the cellulose, removing the alkali in excess of a substantially 1: 1 molecular ratio relative to the cellulose, adding an azeotroping inert liquid to the mixture and azeotropically distilling off the water present from the alkalitreated cellulose, separating the azeotroping liquid from the water and returning the azeotroping liquid to the treated cellulose, introducing an etherifying agent therein in a chemicglly equivalent proportion to the alkali present, heating the reaction mixture until substantially all the etherifying agent bas reacted adding additional aqueous alkali to the reacti@@ mixture in a substantially 1:1 molecular ratio relative to the cellulose, azeotropically distilling off the water, separating theazeotroping liquid from the water and returning the azeotroping liquid to the reaction mixture, adding a further chemically equivaient proportion of etherifying agent thereto relative to the alkali present, heating the reaction mixture until substantially all of said etherifying "ent has reacted, and repeating said sequence of ag operations for at least two more reaction stages. 2. Process for the production of cellulose ethers, which comprises treating cellulose with an aqueous solution of sodium hydroxide containing an amount of sodium hydroxide greater than that which is molecularly equivalent to the cellulose, removing the sodium hydroxide in excess of a substantially 1: I molecular ratio relative to the cellulose, adding an azeotroping inert liquid to the mixture and azeotropically distilling off the water present from the alkali-treated cellulose, separating the azeotroping liquid from the water and returning the azeotroping liquid to the treated cellulose, introducing an etherifying agent therein in a chemically equivalent proportion to the sodium hydroxide present, heating the reaction miiiture until substantially all the etherifying agent has reacted, adding additional aqueous sodium hydroxide to the reaction mixture in a substantially 1:1 molecular ratio relative to the cellulose, azeotropically,distiuing off the water, separating the azeotroping liquid from the water and retuming the azeotroping liquid to the reaction mixture, adding a further chemically equivalent proportion of etherifying agent thereto relative to the sodium hydroxide present, heating the reaction mixture until substantially all of said etherifying agent has reacted, and rel>eat., ing said sequence of operations for at least two more reaction stages' 3. Process for the production of cellulose ethers, which comprises treating cellulose with an aqueous solution of sodium hydroidde containing All amount of sodium hydroxide at least molecu- 2,302,900 3 le,rly equivalent to the cellulose, reznoving &nY ,odium hydroxide in excess of a substantiiLIly ,:I molecular ratio relative to the cellulose, adding toluene to the rnixture and heating the latter to azeotropically distill off the water present from the 9,lkali-treated cellulose, separating the toluene frorn the water and returning it to the reaction mixture, intrc>ducing diethyl sulfate therein in a chemically ecluivalent proportion to the sodium hydroxide pres@nt, heating the reaction mixture until substantially all the diethyl gulfate has reacted, adding additional aqueous sodium hydroxide to the reaction mixture in a substantially 1: 1 molecular ratio relative to the cellulose, azeotropically distilling off the water present, I separating the toluen6 from the water and returning the toluene to the reaction mixture, adding a further chemically equivalent proportion of diethyl sulfate thereto relative to the sodium hydroxide present, heating the reaction mixture '20 until substantially all of said die.thyl sulfate ha4 reacted, and repeating saict sequence of operations for at least two more reaction stages. 4. Process for the production of cellulose ethers, comprising treating celluiose with an 25 aqueous solution of sodiuni hydroxide containing Rn amount of isodiurn hydroxide at least rnoleoularly equivalont to. the cellulose for about 10 rninutes at atmospheric ternperature, removing any sodium hydroxide in excess of substantially 1: I rnolecular ratio relative to the cellulose, addino toluene to the rnixture and heating the latter to azeotropically distill off the water present from the alkali-treated cellulose, separating the toluene from the water and returning it to the reaction mixture, introducing diethyl sulfate therein in a chemically equivalent proportion to the sodium hydroxide present, heating the reaction mixture at the boiling point for about 2 hours, adding additional aqueous sodium hydroxide to the.reaction mixture in a substantially 1: 1 1 rnolecular ratio relative to the cellulose, azeotropically distilling off the water present, separating the toluene from the water and returning the toiuene to the reaction mixture, @idding a further chemically equivalent proportion of diethyl sulfate thereto relative to the sodium hydroxide present, heating the reaction mixture at the boiling point for about 2 hours, and repeating said sequence of operations for at least two more reaction stages. WALTER HENRY GROOMBRIDGE. JOHN DOVINING.