FORM:0748877/IV(a)/1 A liquid non-ionic surface-active agent comprising a compound having, in the molecule, a chain of condensed ethylene oxide groups, is converted into solid form by mixing the liquid agent with an excess by weight of urea in the presence of a reaction diluent and, as a reaction activator, a compound having a solvent action on urea, maintaining the mixture until urea adduct formation has taken place, filtering or centrifuging to separate the solid product and utilizing the recovered liquid phase for the treatment of further quantities of liquid agent and urea, wherein the mixing takes place in a mixing zone and the maintenance of the mixture under reaction conditions takes place in a plurality of reaction zones separately fed with mixed reactants from the mixing zone, said reacton zones being supplied in a cyclic sequence from the mixing zone, at least part of the contents of each zone, in turn, after the required reaction period, being passed to a filtration or centrifuging zone for the separation of solid product from the liquid phase, the latter being recycled, at least in part, as reaction diluent and activator, to the mixing zone. The liquid agents and general conditions of adduct formation are as described in the parent Specification. A preferred class of liquid agent is that described in Specification 748,881. The reaction diluents and activators are the same as those described in Specification 748,878. In general, two to eight separate reaction zones are used. The preferred embodiment comprises treating the liquid agent with sulphur dioxide or an acid as described in Specifications 748,879 and 748,880 and then mixing the treated agent with solid urea and reaction diluent and activator in a mixer M, the resulting slurry being fed to reactor S1 via valved line V1. Further batches are prepared similarly and passed to the reactor until the latter is substantially filled by slurry, separated diluent having been displaced via an overflow line V111 and a ring main R to a storage tank T. The other reactors S2 to S6 are then likewise changed in sequence. The time cycle and relative sizes of the mixer and reactors are so arranged that when reactors S2 to S5 have been loaded, reaction is complete in reactor S1. The slurry layer in reactor S1 is then withdrawn and filtered to recover the solid product in a rotary filter (not shown) and the filtrate added to storage tank T which supplies mixer M with reaction diluent and activator. Reactor S6 is full when S1 has become empty and thereafter the cycle continues, S1 being charged while S2 is being emptied. Part of the diluent mixture is withdrawn from tank T continuously or batchwise and flash distilled, the distillate being returned to the tank and the residue comprising components of the liquid agent which form adducts with urea at a slow rate or do not form these adducts being withdrawn from the system. According to the Provisional Specification, liquid non-ionic surface-active agents generally may be so treated.
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