An insoluble basic calcium lignosulfonate salt has been produced heretofore by treating the waste liquor from the calcium-base acid sulfite process of wood pulping with an excess of lime. Before precipitating the basic calcium lignosulfonate, the liquor is largely freed of compounds, such as sulfurous acid and sulfites, by giving it a mild treatment with calcium hydroxide.
While this process effectively separates high molecular weight lignosulfonates from the low molecular weight lignosulfonates and from the carbohydrates contained in the liquor, the resulting basic calcium lignosulfonate product is insoluble and a further costly treatment with chemicals, such as sulfuric acid or other means, has been necessary to split on an excess of lime and convert the product into a solu- “ice ble form. The latter treatment with sulfuric acid, however, introduces undesirable contaminants in the soluble product since the calcium lignosulfonate solution contains a considerable amount of calcium sulfate. The retained calcium sulfate in the solution is a deleterious scale-forming contaminant and is otherwise undesirable.
A soluble calcium lignosulfonate with less calcium sulfate content can be prepared by using sodium bicarbonate instead of sulfuric acid to precipitate the calcium. This introduces sodium into the product which is also undesirable. In effect, such a final, sugar-free product is a mixed calcium and sodium lignosulfonate, rather than the desired calcium lignosulfonate itself.
Another process of removing’the excess of calcium from basic calcium lignosulfonate in order to result in a soluble product is to treat a slurry of the insoluble salt with carbon dioxide to a point where a calcium carbonate precipitate’is formed and removed. This process is also costly in that it requires the use of costly apparatus to clean flue gas of ash, carbon and other constituents and operating labor, thereby resulting in considerable cost for pure, clean carbon dioxide.In consequence, there has long been a need for satisfactory and economical processes of isolating lignosulfonates from solutions in which they are associated with carbohydrates, and in particular for an improved method of converting a precipitate of basic calcium lignosulfonate into soluble calcium lignosulfonate.We have now discovered a novel process for converting a precipitate of insoluble basic calcium lignosulfonate, substantially free from sugars, into Water soluble calcium lignosulfonate.
This conversion involves the use of a special type of ion exchange material or resin which has been found to adsorb the excess calcium of the insoluble basic calcium lignosulfonate from a slurry of the salt in water. The resin is then removed from the solution and the calcium adsorbed on the resin is finally removed therefrom by the action of sulfurous acid, thereby producing regeneration of the resin and a solution of calcium bisulfite and sulfurous acid which may be used directly for numerous purposes, such as the preparation of sulfite pulping liquor.As another product of the system, calcium bisulfite suitable for use in making pulping liquor or other purposes is also obtained from the alkaline supernatant liquor of pH value 8 to 10 resulting from the original precipitation of insoluble basic calcium lignosulfonate by the action of calcium hydroxide.
This supernatant solution is contacted with the carboxylic-acid type ion exchange material in acid form and the calcium is adsorbed thereon. Then the resulting calcium-containing ion exchange material is separated from the solution and finally the resin is treated with a water solution of sulfurous acid for regenerating the ion exchange material and producing the acid calcium bisulfite.It is, therefore, among the objects of this invention to provide in isolated form a water-soluble lignosulfonate which has a high molecular weight.
Another object is to provide a novel ion exchange process in which a slurry of basic calcium lignosulfonates is contacted with an ion exchange resin to produce a solution of the normal calcium salt.Another object is to provide a novel process for the production of such a product which does not involve the addition of extraneous or contaminating chemicals.Another object is to provide a novel process of the kind which involves the use of lime and in which lime may be recovered as calcium bisulfite in a form’suitable for use in making calcium-base sulfite liquor or for other purposes.
Another object is to provide-such a novel process in which the calcium removed from the basic calcium lignosulfonate is produced directly in the form of a soluinorganic compounds and which is suitable for use as a deflocculating agent, such as those used in the preparation of lime-base drilling muds, and as a relatively pure organic compound for other uses, such as a base material for the preparation of other salts of high molecular weight lignosulfonic acid and for the preparation of organic compounds from the lignosulfonate radical by derivativeforming or cleavage reactions.