A desiccant of this kind, which may for example be used as an energy storage material in heat pumps or as an absorption or adsorption agent in air conditioning plants, is for example known from Japanese patent applications Nos.

55039240 and 03009767.

The object of the present invention is to provide a desiccant which possesses improved absorption characteristics.

In order to accomplish that objective the desiccant according to the invention is characterized in that the carrier has a surface area of approx. 200-350 m2/g and/or a pore volume of approx. 0.8-1.5 cm3/g and/or a pore diameter of approx. 150-250 A.

Surprisingly it has become apparent that a desiccant comprising such a carrier has very good drying characteristics. The surface area and the pore volume provide a large moisture absorption capacity, whilst a relatively large pore diameter ensures that the moisture absorbed in the pores can be delivered relatively easily again, without any clogging of the pores and without capillary forces preventing the moisture exiting from the pores. The most favourable characteristics are obtained when all the above requirements are met, but favourable characteristics are also obtained when said requirements are met in part.

A very advantageous embodiment of the desiccant according to the invention is one wherein the hygroscopic material is provided on the carrier in a homogeneous distribution of at least one monomolecular layer.

Therefore, a highly preferred embodiment of the invention is met by a dessiccant as mentioned in the preamble, wherein the carrier has a surface area of approx.

200-350 m2/g, a pore volume of approx. 0.8-1.5 cm3/g, and a pore diameter of approx. 150-250 A, and wherein the hygroscopic material is provided on the carrier in a substantially homogeneous distribution of at least one monomolecular layer.

Because of the substantially complete coating of the carrier with a very thin homogeneous film of a hygroscopic material, the material of the carrier itself is not active in the drying process, so that the material of the carrier can be selected entirely on the basis of favourable carrier properties. Possible materials for the carrier comprise silica, alumina, carbon black, paper or the like. The carrier is preferably supplied in the form of particles, in particular spheres having a diameter of approx. 2.5-5 mm. Said spheres can be imparted relatively favourable mechanical characteristics, so that particles are obtained which are capable of withstanding a compressive force of 8 kg per particle in a crush test. Besides a porous material, also a material formed into a honeycomb structure or the like may be selected, or a porous material which has been formed into a honeycomb structure.

The invention will be explained in more detail hereafter by means of a number of examples.

EXAMPLE 1 Silica having a pore volume of approx. 1.2 cm3/g, a surface area of approx. 260 m2/g and an average pore diameter of approx. 200 A was selected as the carrier for the desiccant. 1 kg of silica was treated with a solution of 1200 ml of the following composition: 300 g of LiCl, 20 g of Ca (OH) 2,15 g of CaCl2 and 1635 ml of water. After treatment and drying, a desiccant having a bulk density of 0.47 g/cm3 was obtained.

A dynamic absorption test was carried out under the following circumstances. a. the initial weight of the desiccant was 20 g, b. an air flow was led through the desiccant at a flow rate of 1.48 m3/h, an air inlet temperature of Tinlet = 15 °C and a relative air humidity at the inlet of 80 %, c. the desiccant was regenerated at 100 °C with an air flow of 20 m3/h for 15 minutes.

From the test it became apparent that the desiccant absorbed 5.0 g of moisture during every cycle.

Also a dew point measurement produced favourable results. When using this desiccant and a regeneration temperature of 80 °C, exit air having a dew point of D. P. = -10 °C was obtained from air having a temperature of T = 17 °C and a dew point of D. P. = 11 °C at the inlet. When using this desiccant and a regeneration temperature of 70 °C, exit air having a dew point of D. P. =-3 °C was obtained from inlet air having a temperature of T = 22 °C and a dew point of D. P. = 12 °C.

The above desiccant was also tested in a much larger quantity.

A dynamic absorption test was carried out under the following conditions: a. the initial weight of the desiccant was 4 kg, b. an air flow was led through the desiccant at a flow rate of 137 m3/h and an adsorption time of 30 min., c. the desiccant was regenerated at 50 °C for a period of 30 min.

The dew point of the exit air was 11 °C.

EXAMPLE 2 100 g of silica having a surface area of approx.

260 m2/g, a pore volume of approx. 1.2 cm3/g, and an average pore diameter of approx. 200 A was treated with 120 ml of an aqueous solution of Na2SiO3 9H2O (250 g in 2000 ml of water), and subsequently dried. The dried material was then treated

with an aqueous solution of LiCl (330 g of LiCl in 1635 ml of water) and regenerated. The desiccant appeared to possess a high absorption capacity, whilst the active constituent could not be removed under mild conditions (temperature 20-100 °C and a relative humidity of up to 100%). The results were comparable with those of the first example.

EXAMPLE 3 Silica (100 g) having a surface area of approx. 260 m2/g, a pore volume of approx. 1.2 cm3/g, and an average pore diameter of approx. 200 A was treated with 120 ml of a lithium chloride solution (230 g of LiCl in 1635 ml of water). The material was then regenerated again an impregnated with 120 ml of LiCl (100 g) in 1635 ml of water.

With this desiccant the dynamic absorption test described in example 1 resulted in an absorption of approx.

5.5 g of moisture during each cycle. A dew point measurement showed that when this desiccant and a regeneration temperature of 80 °C were used, exit air having a dew point of D. P. =-12 °C was obtained from inlet air of T = 17 °C and D.P. = 11 °C.

EXAMPLE 4 Alumina having a pore volume of approx. 1.0 cm3/g, a surface area of approx. 260 m2/g and an average pore diameter of approx. 154 A was selected as the carrier for the desiccant. 1 kg of alumina was treated with a solution of 1000 ml of the following composition: 300 g of LiCl, 20 g of CaCl2 and 1635 ml of water. After treatment and drying a desiccant having a bulk density of 0.49 g/cm3 was obtained.

A static adsorption test showed that the desi-ccant had a high adsorption capacity, unlike untreated alumina, whose adsorption capacity is only very small.

A dynamic absorption test was carried out under the following circumstances. a. the initial weight of the desiccant was 20 g,

b. an air flow was led through the desiccant at a flow rate of 1.48 m3/h, an air inlet temperature of Tinlet = 15 °C and a relative air humidity at the inlet of 80%, c. the desiccant was regenerated at 100 °C with an air flow of 20 m3/h for 15 minutes.

From the test it became apparent that the desiccant absorbed 4.8 g of moisture during every cycle.

Also a dew point measurement produced favourable results. When using this desiccant and a regeneration temperature of 80°C, exit air having a dew point of D. P. = -9 °C was obtained from air having a temperature of T = 17 °C and a dew point of D. P. = 11 °C at the inlet. When using this desiccant and a regeneration temperature of 70 °C, exit air having a dew point of D. P. =-2 °C was obtained from inlet air having a temperature of T = 22 °C and a dew point of D. P.

= 12 °C.

Summarising the above, the desiccant can be said to exhibit the following advantageous characteristics: A. a high static and dynamic adsorption capacity of up to 1.3 g of moisture per 1 g of desiccant; B. a low regeneration temperature (up to 35-40 °C) combined with a high adsorption capacity; C. the capacity to produce an air flow having any relative humidity (20-95%) during a regeneration process; D. a small bulk density; E. a good resistance against washing out of the active components.

In view of the characteristics of the desiccant according to the invention, said desiccant could be used in the following devices: airconditioning plants for utilising waste energy (supermarkets, offices and the like), airconditioning plants for passenger cars, caravans and the like, as a desiccant for the atmospheric treatment and pressure treatment of air, as an agent for producing air having a specified relative

humidity, as a material in a heat pump, and as an energy storage material.

The invention is not limited to the above-described embodiments, which can be varied in various ways within the scope of the invention.