SOLUTION

The invention relates to a process and apparatus for the preparation of open macropore individual crystals from solution by using a desalting agent in gas state.

The Hungarian patent application No. P 92 01070 discloses a process and apparatus for the preparation of open macropore individual crystals from solution by using a desalting agent in gas state. According to this specification the process is carried out by absorbing a homogeneously distributed desalting agent in gas state in the solution containing the crystals, which solution may contain also a surface-active agent. While continuously renewing the contact surfaces a crystallization occurs after reaching the limit of oversaturation.

The apparatus for implementation of the process comprises: a double-walled solution container provided with solution inlet; one or more series- and/or parallel-connected crystallizers(s) joining to the said solution container, fitted with gas inlet and supplementary gas inlet, outlets for gas, mother liquor and crystals as well as heat- exchanger; a recycling pipe leading therefrom to the solution container; a saturator joining to the gas inlet, having an inlet for the desalting liquid; optionally a container for the desalting liquid; and a gas heater. An embodiment of the apparatus comprises a pipe connecting the gas inlet of the crystallizer with the gas saturator.

A disadvantage of the known process referred to is that in addition to the open macropore individual crystals, poreless or mostly closed pore or less porous crystals with an unusual small size are formed in an amount of 20-30 %, wherein the volume proportion of the void part manifested by the pores is less than 1 20, furthermore loss of the desalting agent leaving with the solution as well as that of the substance forming the crystals occur The loss of desalting agent is high and makes the process expensive and uneconomic In addition, the discarded solution causes a considerable environmental pollution

A possibility exists for recycling the discarded solution to the container for dissolving the crystal-forming substance, however, the high content of desalting agent in the recycled solution prevents the dissolution of crystal-forming substance Thus, due to the operation incapacity of the process, the formation of crystals is stopped

The object of the invention is to develop a process and apparatus for the preparation of open macropore individual crystals from a solution by using a desalting agent, in gas state by eliminating or considerably reducing the disadvantages mentioned above

The invention is based on the recognition that, if the desalting agent to be absorbed in the solution of the crystal-forming substance is transformed into gas-form from a solution containing at least 1 % by weight of crystal-forming substance, no poreless or significantly less poreless or mostly closed pore or less porous crystals containing a void volume proportion of lower than 1 2 are obtained vis avis the known process, wherein the desalting agent is transformed into gas-form from a pure desalting agent or a solution

thereof, which is free from the crystal-forming substance. An other recognition of this invention is that is more easy to strip out the desalting agent from a solution containing the crystal-forming substance than from a solution free from these crystals.

Based on these recognitions the solution leaving the crystallizer containing the desalting agent and more than at least 1 % by weight, preferably more than 5 % by weight of crystal-forming substance is re-cycled for preparing the desalting agent in gas state, practically without employing fresh desalting agent; whereas the remaining solution, which contains crystal-forming substance and is practically free from desalting agent, is recycled for dissolution of the crystal-forming substance. Thus, a closed liquid circuit can be developped, the loss of desalting agent is reduced to a negligible amount, that of crystal-forming substance practically to zero. Thus, the environmental pollution can be eliminated and both the yield and quality of the open macropore crystals are unexpectedly improved.

Therefore the essence of the invention is that the desalting agent is transformed into gas-form from a solution containing more than at least 1 % by weight, preferably more than 5 % by weight of crystal-forming substance; furthermore, the solution separated from the crystals formed, containing crystal-forming substance and desalting agent is recycled to transform the desalting agent into gas- form and the solution leaving therefrom is recycled to dissolve the crystal-forming substances.

According to an embodiment of the process of invention, the desalting agent is transformed into gas-form by vaporization and/or evaporation by using a earner gas

For eliminating a loss of desalting agent and environmental pollution, a closed gas circuit is used namely, the gas leaving during crystallization is not emitted but, in form of a carrier gas, is led through the solution of the desalting agent

In an other embodiment of the process the gas leaving duπng crystallization is led as a earner gas through the solution of the desalting agent

The interface between the desalting agent in gas form and the solution of the crystal-forming substance should be renewed by constant stirnng, which may be performed by bubbling the gas mixture of the desalting agent and earner gas through the solution of crystal-forming substance and by continuous regeneration of the interface by means of gas bubbles

Acccording to a further embodiment of the process, the solution of crystal-forming substance is stined and the interface between the desalting agent in gas form and the solution is continuously renewed by utilizing the bubbles of the introduced gas mixture of the desalting agent and earner gas

The apparatus according to the invention is specified referring to Fig 1

The apparatus shown on Figure 1 which can be operated continuously or periodically consists of a single- or double-walled solution container 1 provided with a stiner, heat-exchanger a temperature-sensing unit and a -regulating device, a concentration-

measuring and -regulating device which are not illustrated on the drawing. The solution container 1 is connected with one or more series- and/or parallel-connected crystallizer(s) 3 by means of one or more solution-outlet pipe 21, which is (are) equipped with a pump 7 and/or a mechanically or automatically operated liquid closing unit 17. The solution container 1 is provided with a stirrer, a solution inlet 29 and/or a feeder for the crystal-forming solid substance and liquid. The single- or double-walled crystallizer 3 have a heat- exchanger and an organ controlling and regulating the oversaturation. A connecting pipe 37, which may be regulated by closing unit 13, leads from crystallizer 3 to crystal separator 4 optionally including a crystal-outlet 28 equipped with a closing unit. Optionally, the crystal separator 4 is connected through the mother liquor outlet pipe 22 to a device 5 adjusting concentration of the desalting agent. The adjusting device 5 is provided with a feeder 19 for the desalting agent, with a pipe 27 recycling the crystal-forming solid substance into the solution container 1; and with a device measuring and regulating the concentration of the desalting agent. The crystal separator 4 or optionally the device 5 adjusting the concentration of the desalting agent is connected through the pipe 23 provided with a pump 6 and closing unit 14 with a single- or double- walled evaporator 2 of the desalting agent. This evaporator 2 is equipped with heat-exchanger, a device for measuring and regulating the liquid level as well as a device for measuring and regulating the temperature. The evaporator 2 is connected with the solution container 1 through pipe 24 recycling the solution, which pipe has a closing unit 12. The evaporator 2 is further connected

with crystallizer 3 through gas outlet 25 wherefrom gas pipe 26, equipped with splash head 9 and 11, liquid seal 10, pump 8 and gas inlet 10, recycling to the evaporator 2 of the desalting agent The liquid pipe 20 leads from the splash heads 9 and 10 to the feeder 19 of the desalting agent

An embodiment of the apparatus according to the invention compnses in crystallizer 3 an organ controlling and regulating the oversaturation, said organ switching on in an adjusted sequence and intervals at an adjustable value of oversaturation and switching off at an other adjustable value thereof the individual operation of the solution inlet 29 and/or feeder of the solid, crystal-forming substance and liquid and/or the individual operation of stock pumps and/or the individual operation of gas inlet and/or closing units and/or the individual operation of devices for measuring and regulating the concentration and temperature, and/or organs regulating heat- exchangers

A preferred embodiment of the apparatus of invention consists of controlling a regulating organ for oversaturation, adjusted according to the difference between two time points of oversaturation, regulating the individual operation of solution inlet 29 and/or feeder of the solid, crystal-forming substance and liquid, individual operation of stock and/or gas inlet and/or individual operation of closing units and/or the individual operation of devices measunng and regulating the temperature and concentration of the crystallizer solution and/or individual operation of the heat- exchangers

Another embodiment of the apparatus according to the invention is provided with an organ controlling and regulating the oversaturation on the basis of measurement of density and/or refractive index or measurement of the differences between densities and/or refractive indices.

Another embodiment of the apparatus according to the invention includes a controlling organ regulating the oversaturation on the basis of optical measurement.

A still further possible embodiment of the apparatus according to the invention contains both a crystallizer 3 and/or an evaporator 2 for the desalting agent with a foam-layer.

Another embodiment of the apparatus according to the invention includes in crystallizer 3 and/or evaporator 2 of the desalting agent one or more cylindrical insert(s) and/or statical stirring element(s) with a diameter smaller than the half thereof for regulation of stirring.

The apparatus is operated in the following manner:

The solution of crystal-forming substance or the solid crystal- forming substance and solvent are introduced through solution inlet 29 or through the feeder of crystal-forming solid substance and liquid to the container 1. Here the temperature of solution is adjusted by using a device measuring and regulating the temperature, as well as a heat-exchanger. The concentration of the solution is adjusted by using a device measuring and regulating the concentration. Optionally the dissolution of an occasional solid substance and the homogenity of the solution is promoted by stirring. The solution

prepared is introduced through pφe(s) 21 by pump 7 into one or more crystalhzer(s) 3 Preferably, at least two senes-connected crystallizers 3 are used In the crystallizer 3 the solution of the crystal-forming substance is constantly stirred in a bubble- or foam- layer by the mixture of desalting gas and earner gas, whilst the desalting agent is absorbed and the crystals are separated The solution containing the crystals is led to the crystal separator 4 through the conncecting pipe 37, which is regulated by a closing unit 13 In the crystallizer 3 the size and porosity of the separated crystals are influenced by a device measunng and regulating the oversaturation, if desired, the temperature is also regulated by a heat- exchanger In the crystal separator 4, which may be a peπodically or continuously operating pressure filter or a sedimentator, the crystals are separated from the solution containing the desalting agent and the crystal-forming substance being in equihbnum therewith The crystals are separated through the crystal-outlet 28, the residual solution is led through solution-outlet 22, optionally into vessel 5 for adjusting the desalting agent concentration or directly into the evaporator 2 of the desalting agent In the adjuster 5 of the desalting agent concentration, which is measured by a device 31 measunng and regulating the concentration, is adjusted (corrected) by using the feeder 29 of salting out agent The solid crystals separated in some cases are recycled into the solution container 1 through the recycling pipe 27 for the solid substance From the crystal separator 4 or adjuster 5 of desalting agent concentration the solution is conducted through pipe 23 equipped with a closing unit 14 into the desalting

agent evaporator 2, to which the desalting agent in gas form containing a small amount of carrier gas leaving crystallizer 3 is recycled through the gas pipe 26, into which carrier gas may be supplemented through the gas inlet 18. The desalting agent solution is mixed with this gas in a foam- or bubble-layer in the evaporator 2 of desalting agent. The level and temperature of the evaporator are adjusted by using a heat-exchanger, by means of the device 33 measuring and regulatingt the liquid level as well as device 32 measuring and regulating the temperature. From evaporator 2 of the desalting agent the solution which became poor in desalting agent is recycled to the solution container 1 through the recycling pipe 24 equipped with closing unit 12; and a new solution of the crystal- forming substance is prepared by utilizing is. In such a manner, the solution of crystal-forming substance and the desalting agent dissolved therein circulate in a closed circuit in the apparatus and the possible losses should only be supplemented in a known manner through the solution inlet 29 or feeder for crystal-forming solid substance and liquid or through feeder 19 of the desalting agent.

The gas mixture of the desalting agent and the carrier gas is led from evaporator 2 of the desalting agent through the gas-outlet 25 into crystallizer 3, wherein the major part of the desalting agent is absorbed; whereas the desalting agent in gas form containing a small amount of earner gas is recycled into the evaporator 2 of desalting agent through the splash heads 9 and 11, pump 8 and pipe 26. Thus, both the desalting agent and the carrier gas also flow in a closed circle and the possible losses of canier gas in gas form should only

be completed in a known manner through the gas inlet 18 leading to the connecting gas-transfernng pipe 26

The process of the invention is detailed by the following non- hmiting Example

In the apparatus of a penodically run plant two, senes- connected crystallizers are equipped and 400 ml of sodium chlonde solution saturated at 25 °C, which still contained 0 01 g of nitnlo- tnacetylamide (NTAA), was treated at a gas flow rate of 0 1 m/sec in such a manner that the gaseous nitrogen, circulated in a closed circuit vapounzed 38 g of alcohol at 35 °C dunng 50 minutes from an aqueous solution of 200 ml volume containing 9 % by weight of sodium chlonde and 50 % by weight of ethanol as desalting agent The vapounzed alcohol was absorbed in the crystallizers without any loss A total amount of product 15 g with an average gam size of 200 μm was formed in homogeneous grain size distnbution The crystal charactenstic pore size was 5-10 μm and 20-30 μm pore size was in the centre of crystals About 90 % of the product were porous

By evaporating 118 5 g of salt-free concentrated ethanol in an open gas circuit at 35 c during the same time (50 minutes) then not more than 55 3 g of ethanol remained in absorbed state in the crystallizers, which resulted 17 g of product The crystals had an average grain size of 150 μm The product contained 10 % of agglomerate, the porous crystal content amounted only about to 70 % A loss of about 50 % of the alcohol occured