Patent GB-755018-A (GB)
Title: Improvements in or relating to the continuous hydrolysis of esters in homogeneous phase and apparatus therefor
IPC: C08B17/02
Filed: 1953-08-05
Abstract: <PICT:0755018/IV(a)/1> Cellulose triacetate is continuously hydrolysed in a solvent medium by mixing a hydrolysing agent with a solution of the acetate and continuously passing the resulting mixture through a reactor consisting of at least one cylindrical chamber, a rotatable shaft passing through the longitudinal axis of the chamber and circular disc - shaped elements rigidly mounted on the shaft and dividing the chamber into compartments, each of the elements having at least one opening in an offset relation from one element to the next and the clearance between the edge of each element and the chamber wall being only small; the shaft is slowly rotated so as to cause the mixture to pass through the reactor evenly, the average time of passage of the mixture through the reactor being 3-10 hours and the temperature of the mixture in the reactor being maintained at 40-80 DEG  C.  The viscosity of the solution of the triacetate is preferably adjusted to be 20-80 poises, especially 30-70 poises at 40-80 DEG  C.  The hydrolysing agent is preferably added in two stages to the triacetate solution.  In the first stage a portion, e.g. 70-90 per cent, of the hydrolysing agent is added to the solution at ordinary temperature or below.  In the second stage the remainder of the hydrolysing agent, which has been heated and may even be vaporized, is injected into the mixture resulting from the first stage operation.  Both these stages take place before the introduction of the mixture into the reactor and may be effected in any appropriate kind of known mixing apparatus.  In the example, a solution of cellulose triacetate in acetic acid is led continuously into a mixer at a rate of 120 litres per hour, and 42 litres per hour of a mixture of 60, 40 and 1 parts by weight of acetic acid, water and sodium acetate respectively are also continuously introduced into the mixer at 15 DEG  C., whereafter 6 to 7 litres per hour of a vaporized mixture of 60 parts of acetic acid and 40 parts of water is continuously injected into the resulting solution.  The temperature of the whole mixture is thus brought to 75 DEG  C. and its viscosity is then between 30 and 70 poises.  The solution is then passed through three vertical cylindrical chambers 1 in series, entering each chamber through one or more of the inlet tubes 5 and leaving each chamber through the outlet tube 6.  The temperature of the reaction mixture is kept at 75 DEG  C. by the circulation of hot water through the jacket 2 surrounding each chamber.  A rotatable shaft 3 passing through the chamber has mounted on it, rigidly and at right angles to its axis, circular flat discs 4 nearly touching the wall of the chamber and each having a sectorshaped opening 7, each opening being, for example, offset 90 degrees from one disc to the next. The time of passage of the reaction mixture through the chamber is regulated by external valves and metering pumps (not shown) and by the areas of the openings 7 in the discs 4.  Stationary scraper blades 8 lead back towards the axis of the chamber those portions of the reaction mixture which would otherwise remain near the chamber wall.  There may be more than one opening in each disc, and the offset relationship between openings from one disc to the next may be other than 90 degrees.  The included angle of the sector may be 6 degrees, and the shaft 3 may rotate at 15 revolutions per hour.  The lower portion of the shaft 3 may be hollow and the resulting duct may communicate with a number of short tubes, e.g. four, radiating out from the shaft.  The reaction mixture may enter the base of the chamber 1 through such a duct in the shaft 3 and the radial tubes instead of through the inlet tubes 5.  The apparatus may be used for the hydrolysis of other carboxylic acid esters of cellulose.ALSO:<PICT:0755018/III/1> A continuous reactor which may be used for the continuous hydrolysis of cellulose triacetate (see Group IV(a)) comprises a vertical cylindrical chamber 1, having inlet tubes 5 and an outlet tube 6.  The temperature of the reaction mixture in the chamber is maintained at the required level by the circulation of a heating medium through the jacket 2.  A rotatable shaft 3 passing through the chamber 1 has mounted on it rigidly and at right angles to its axis circular flat discs 4 nearly touching the wall of the chamber and each having a sector-shaped opening 7, each opening being for example offset 90 degrees from one disc to the next. The time of passage of the reaction mixture through the chamber is regulated by external valves and metering pumps (not shown) and by the areas of the openings 7 in the discs 4.  Stationary scraper blades 8 lead back towards the axis of the chamber those portions of the reaction mixture which would otherwise remain near the chamber wall.  There may be more than one opening in each disc and the offset relationship between openings from one disc to the next may be other than 90 degrees.  The included angle of the sector may be 6 degrees, and the shaft 3 may rotate at 15 revolutions per hour.  The lower portion of the shaft 3 may be hollow and the resulting duct may communicate with a number of short tubes, e.g. four, radiating out from the shaft.  The reaction mixture may enter the base of the chamber 1 through such a duct in the shaft 3 and the radial tubes instead of through the inlet tubes 5.  The apparatus may be used for the hydrolysis of other carboxylic acid esters of cellulose, the saponification of polyvinyl acetate, the acetylation of polyvinyl alcohol and the treatment with a strong acid of the residual acetic acid from the manufacture of cellulose acetate.