WO1997021781A1 - Desiccant compositions for removing moisture from fluids - Google Patents

Abstract

Described are biodegradable dessicant compositions with superior water adsorption capacity, the compositions comprising a biodegradable solid particulate substrate having starch affixed to the surface of substrate particles. The inventive compositions are useful in a wide variety of applications where conventional desiccants are utilized including, for example, systems for drying gases, such as air dryers. Also described are methods for making and using the inventive compositions.

Description

DESICCANT COMPOSITIONS FOR REMOVING MOISTURE FROM FLUIDS

REFERENCE TO RELATED APPLICATIONS This application claims priority upon U.S. Patent Application Serial No. 60/008,536 filed December 12, 1995, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to the removal of moisture from fluids to provide dried fluids. More specifically, the present invention relates in one aspect to synthetic starch-based compositions useful in providing dried gases useful, inter alia, in the pressurization of power and communication cables, paint spraying and ozone generation.

Discussion of Related Art

There are presently a wide variety of systems which utilize adsorbents to remove moisture from various fluids. For example, the presence of moisture in gases leads to difficulties in many industries and operations. For example, in processes for preparing a nitrogen-rich or oxygen-rich stream from air, if water and carbon dioxide are not first removed from the air, these components will freeze and block heat exchangers employed for cooling the gas prior to cryogenic distillation. Additionally, in a wide variety of systems, a slight drop in temperature can cause condensation to occur in pipelines and reservoirs which can lead to corrosion, scales, freeze-ups, and dirt, which may damage instruments and controls, cause blockages in air lines, produce excessive pressure drops, increase down-time and reduce the life of tools. Similarly in chemical, food and metal working industries, the presence of moisture in air and other gases produces undesired oxidation. It has also been found in the robotics field that extremely dry air is required for the efficient operation of pneumatic systems .

To produce relatively dry air, e.g. air having a dew point of less than about -60°C, it is often necessary to use an adsorptive drying system, such as a pressure-swing adsorption system having two desiccant beds and two three-way valves, operating according to the "Skarstro process" . In this process, moist compressed air is passed over one desiccant bed and the moisture is adsorbed onto the adsorbent, or desiccant, providing a dry air stream. A portion of this dry stream is routed for use, and another portion is diverted over the other, previously used, bed to regenerate the same. Since a large portion of the adsorbed water is contained at the bed entrance, during regeneration, the dry air is passed counter-current to the moist-air feed direction, so that the adsorbed water does not contaminate the rest of the bed. Removal of water occurs because the equilibrium favors transfer of moisture from the used desiccant to the dry air; and the bed is quickly depressurize , which stimulates a flash system. In a typical system, the valves are switched every 30 seconds or so, thus periodically using and regenerating each bed. The pressure swing adsorption system is thus a cyclic batch system where the desiccant beds are cycled from high pressure for loading to low pressure for regeneration. U.S. Patent No. 4,738,692 to Fresch at al. describes such a system and is hereby incorporated herein by reference in its entirety.

A number of theoretical guidelines, termed "Skarstrom's Rules", which may be followed for advantageous use of a pressure swing system, are described below. First, short cycle and low throughput per cycle are used to conserve the heat of adsorption, thereby maintaining an isothermal operation. By using short cycles, a hot bed during adsorption and a cold bed during regeneration are avoided, which would, if present, hinder the separation. Second, the purge volume/feed volume ratio is desirably about 1/1, the purge volume and feed volume being measured at their respective pressures, to ensure complete displacement. The purge/feed ratio is a key parameter in determining the product purity and is usually between 1.0 and 2.0 in practice. Third, for a pure product, the absolute pressure ratio between the high and low pressures should be greater than the reciprocal of the mole fraction of the product contained in the feed (assuming purge/feed=l) . Finally, the sizing of the beds should be 15 to 30 actual volume/volume (abbreviated v/v) of feed per bed per cycle when the purge/feed ratio is 1/1. One actual v/v of feed represents an amount of gas or vapor at the feed pressure in the empty bed. The feed throughput can be increased substantially if a high purge/feed ratio is employed.

Pressure swing adsorption uses mechanical energy to provide regeneration rather than heat, used by temperature swing adsorption. Because of the low and high pressure requirements, pressure swing adsorption can only be used with gaseous systems. Pressure swing adsorption is particularly useful in air drying, because the adsorption composition removes water, which can be removed from the air stream without considering recovery. Advantages of pressure swing adsorption include: (1) it works well when the weakly adsorbed species is the material needed in high purity; and (2) because of the rapid cycling, only a small volume of adsorbent is needed, thus limiting the size of the adsorption equipment, and therefore, also limiting the capital costs. Additionally, a pressure swing adsorbent has a longer useful life than an adsorbent used in temperature swing adsorbers, because temperature cycles to which the adsorbent is exposed are small, typically less than 5°C. Since heat in the form of thermal energy is not added, the Skarstrom cycle drier is sometimes referred to as a heatless drier. Applications of pressure swing adsorption include the heatless air drier, air separation processes, and hydrogen purification.

In many present pressure swing adsorption operations, zeolites and activated carbon are the adsorption compositions used. The oxidation of the surface of a normally hydrophobic activated carbon imparts polarity to the carbon surface inducing hydrophilicity and thereby improving its strength of water adsorption. In zeolites, the silica/alumina ratio can be adjusted to give higher affinity for water and other polar molecules .

However, the use of zeolites, activated carbon and other inorganic adsorbents is unsatisfactory in that these substances are not biodegradable. Thus when their adsorption capacity becomes deficient or when a strongly adsorbed fouling agent becomes attached to them, their disposal becomes necessary and, thus, biodegradability and environmental compatibility of these desiccants is of utmost importance. Especially in light of the current regulatory climate, there is a great need for an adsorbent composition which is biodegradable and, thus, readily disposed of after use.

Particulate cereal grain derivatives are known to be useful for moisture adsorption. The desiccant capacity of such materials, for instance corn grits, is thought to be primarily related to their major component, starch. Starch is a polysaccharide composed of glucose monosaccharides linked together by glycosidic bonds, typically containing 25% amylose and 75% amylopectin. Amylose is a linear amorphous polymer consisting of D-glucose units bound together by α-1, 4 O-glycosidic bonds. Amylopectin is similar to amylose but also has 1,6 O-glycosidic branches every 25- 30 monomer units.

It has been reported that the amylose found in corn starch has a degree of polyme ization between 930 and 990, while the amylopectin found in corn starch has a degree of polymerization between 4800 and 10200. Starch is considered a branched molecule because of the 1,6 O-glycosidic branches in amylopectin. Corn starch is approximately 40% crystalline, as has been shown by x-ray diffraction. Crystalline polymers have been shown to have extensive secondary intermolecular bonding. The crystallinity thus is believed to hinder the adsorption of water in the corn starch, because the hydroxyl groups on adjacent glucose units are complexed with each other and cannot adsorb water unless this secondary hydrogen bonding dissociates. The branched structure of amylopectin has overlapping hydroxyl groups which correspond to more hydroxyl groups per unit area of the starch surface. Thus an adsorption composition high in amylopectin has a greater adsorption capacity. As such, selectivity for water in corn starch is improved by maximizing the ratio of amylopectin to amylose. Although theoretically it would appear that starch itself would be an advantageous desiccant for use in drying systems such as a pressure swing dryer, starch particles themselves are typically only about 2 to 10 microns in diameter. As such, the use of starch in such a system is limited becuase it is difficult to move fluids through a bed packed with fine particles such as starch, there being a substantial pressure drop across such a bed. Therefore, there is a great need in the art for a mechanically stable, robust material having a larger average particle size than pure starch, yet exposing a sufficient amount of starch to through-flowing gases to provide good desiccant capacity.

In conventional methods of dehydrating materials which are liquids at room temperature, water is often separated from such materials using one or more of a wide variety of distillation techniques. For example, in the production of fuel-grade ethanol, the ethanol must be dried to 99.6% purity. Ethanol-containing mediums produced by fermentation have a very low ethanol concentration and, thus, downstream processing is required to remove water from the ethanol to obtain the 99.6%, fuel grade alcohol. In a conventional ethanol production process, 8-12% ethanol is produced by fermentation and run through a distillation column to yield an ethanol effluent having about 90% purity (i.e. containing about 10% by weight water). At atmospheric pressure, the maximum ethanol concentration which can be achieved by distillation is about 95.6% due to the formation of a water/ethanol azeotrope.

One approach which has been used to remove much of the remaining water from the water/ethanol azeotrope involves the use of a molecular sieve. This type of purification, however, requires a substantial input of energy. Another approach involves azeotropic distillation, but this too requires a substantial input of energy. A more energy-efficient approach that has been used to reduce energy requirements for removing the last 5% to 10% of water from ethanol is a fixed bed adsorption system that utilizes a desiccant composition and a heated inert gas stream for desiccant regeneration. One desiccant composition which has previously been advantageously used in this area is corn grits, this process being described in greater detail in U.S. Patent No. 4,345,973, to Ladisch et al. Adsorption on corn grits uses about 4 times less energy for achieving the same final ethanol composition, starting from a 90 weight percent feed, than does azeotropic distillation. This is because, for adsorption, the water-ethanol azeotrope does not have to be broken, the desiccant, i.e. corn grits, stores the heat of adsorption, and the heat helps to regenerate the bed at the end of each cycle.

Although the use of corn grits is an improvement in the dehydration of ethanol and other materials, there remain needs for improved, desiccant compositions having increased desiccant capacity, and for processes involving the manufacture and use of such compositions. Additionally, there is a need for a desiccant which has a defined composition, this feature being of increased importance in desiccants used in applications relating to food and pharmaceutical production and preparation, which are very closely regulated. The present invention addresses these needs.

SUMMARY OF THE INVENTION

Briefly describing one aspect of the present invention, there is provided a desiccating agent comprising a biodegradable, solid particulate substrate having starch affixed to the surface of the substrate particles. Preferred compositions are characterized by an increase in desiccant capacity as compared to, for example, corn grits. Other characteristics of preferred compositions of the invention include increased porosity, and increased external surface area.

According to another aspect of the present invention, there is provided a method for making an improved desiccant composition, comprising: (1) providing a mixture comprising a solid particulate substrate, starch and a liquid medium; and (2) heating the mixture to affix the starch to substrate particles, thus providing a desiccant composition. Once the desiccant composition has been thus prepared, it may be advantageously fragmented by grinding or milling to provide desiccant particles, these particles preferably then being separated into various size ranges, for example, using sieves.

In another aspect of the present invention, there is provided a method for drying a moisture-containing gas, comprising contacting the gas with a particulate composition including starch affixed onto substrate particles, so as to reduce the moisture content of the gas. According to another aspect of the present invention, there is provided a method for drying a moisture-containing starting liquid, comprising: (1) vaporizing the starting liquid to provide a moisture-containing vapor; (2) contacting the vapor with a particulate composition comprising starch affixed onto substrate particles, so as to remove moisture from the vapor; and (3) condensing the vapor to form a product liquid.

It is an object of the present invention to provide a desiccant composition which exhibits superior water adsorption characteristics, while exhibiting good mechanical strength.

It is another object of the present invention to provide an inexpensive, non-toxic composition having increased desiccant capacity for use in drying operations.

It is also an object of the present invention to provide superior methods for removing moisture from gases, for example, superior air drying methods.

Another object of the present invention is to provide superior methods for removing moisture from vaporized liquid starting streams, for example, superior ethanol purification methods .

Also, an object of the invention is to provide a synthetic desiccant having a defined composition.

Additional objects, advantages and features of the present invention will be apparent from the drawings and detailed description herein. BRIEF DESCRIPTION OF THE DRAWINGS

Although the characteristic features of this invention will be particularly pointed out in the claims, the invention itself, and the manner in which it may be made and used, may be better understood by referring to the following descriptions taken in connection with the accompanying FIGURES forming a part hereof.

FIG. 1 is a photomicrograph of corn starch powder.

FIG. 2 is a photomicrograph of a Lite-o'cobs 30 particle.

FIG. 3 is a photomicrograph of a Grit-o'cobs 60 particle.

FIG. 4 is a photomicrograph of the surface of the cobs 60 particle after being mixed with corn starch for 5 minutes.

FIG. 5 is a photomicrograph of the coating of starch on the cobs 60 after 60 minutes of mixing.

FIG. 6 is a photomicrograph of the top (smooth) side of an adsorbent sheet sample produced by the oven method of the present invention.

FIG. 7 is a photomicrograph of the bottom (rough) side of an adsorbent sheet sample produced by the oven method of the present invention.

FIG. 8 is a photomicrograph of the side view of a 0.4 ml water binder pellet made according to the present invention.

FIG. 9 is a photomicrograph of the cross section of a 0.4 ml water binder pellet made according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS For the purposes of promoting an understanding of the principles of the invention, reference will now be made to preferred embodiments thereof and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the invention, and such further applications of the principles of the invention as described therein being contemplated as would normally occur to one skilled in the art to which the invention relates .

The present invention provides synthetic particulate compositions which have superior desiccant properties while also being biodegradable, and methods for preparing and using such compositions. Generally, such compositions can be obtained by affixing starch onto a solid particulate substrate, which may preferably be accomplished by mixing them together in an aqueous medium and then heating the mixture.

One starting material which is needed for advantageously practicing the present invention is starch, a substance which can be readily obtained commercially. Starch used in preferred aspects of the present invention has an average particle size of less than about 20 microns, more commonly ranging from about 2 to about 10 microns. Another starting material needed to practice the invention is a solid particulate substrate. In a preferred embodiment of the present invention, the solid particulate substrate is itself capable of adsorbing moisture, and also in a preferred embodiment, the substrate is a naturally derived biodegradable material such as a particulate fraction from a plant. Preferably, the substrate is a composition which comprises from about 40% to about 80% hemicellulose and from about 10% to about 50% cellulose by weight, more preferably from about 50% to about 70% hemicellulose and from about 20% to about 40% cellulose by weight. In a feature of the invention, the substrate is cob flour, which may also be readily obtained commercially. For example, three types of cob flour, namely, Grit-o'cobs 30, Grit-o'cobs 60 and Grit-o'cobs 1420, were used in the specific work described in the Examples below. Cob flour is derived from corncobs and typically has a compositions of about 60% hemicellulose, about 30% cellulose, about 8% lignin and about 2% ash. Cobs are resistant to attrition and both the xylan and cellulose contained in them have been shown to exhibit sorptive properties. Consequently, cob flour is used in a preferred embodiment of the invention to complement the moisture adsorbing properties of starch.

A further preferred starting material for use in the invention is a base, such as, for example, an aqueous alkali or alkaline earth metal hydroxide, suitably sodium hydroxide. Although it is not intended that the present invention be limited by theoretical mechanism, it is believed that the base acts to promote adhesion between the starch and the particulate substrate. In this regard, in a preferred aspect of the invention, the aqueous base, e.g. sodium hydroxide, has a concentration of from about 10 mM to about 70 mM, more preferably, the sodium hydroxide has a concentration of from about 20 mM to about 60 mM, and even more preferable, from about 30 mM to about 50 mM. Sodium hydroxide and a wide variety of other aqueous bases advantageously used in accordance with the present invention are readily available commercially.

To make a preferred desiccant composition according to the present invention, a mixture is provided which comprises a particulate substrate, starch and a liquid medium. Although almost any amount of liquid medium could be used in this regard, it is preferred that the liquid be present in an amount sufficient to simply wet the solids in the mixture, thereby promoting mixing and, in a preferred aspect of the invention, distributing a base throughout the mixture. It is preferred that the weight of solids in the mixture be at least equal to the weight of liquids.

This mixture is then heated to affix the starch to substrate particles, thus providing a layer of an agglomerate desiccant composition. In a preferred manner of making desiccant compositions according to the present invention, the wet mixture is spread to form a layer having a substantially even thickness before the mixture is heated. Preferably, the thickness of the layer is from about 1.0 mm to about 4.0 mm.

In one preferred embodiment of the present invention, the heating comprises providing substantially even heat to the top surface and to the bottom surface of the layer. As used herein, the term "providing substantially even heat" is intended to refer to providing heat at a temperature that does not vary by more than about 20°C in either direction, more preferably by no more than about 10°C in either direction. In this regard, heating the mixture according to this embodiment may be conveniently accomplished, for example, by placing the mixture in an oven. In this preferred embodiment, the resulting layer of agglomerate material is preferably from about 0.5 mm to about 3.0 mm thick.

In an alternate preferred embodiment of the invention, the heating comprises providing substantially even heat to only one surface of the layer. In this regard, heating the mixture according to this embodiment may be conveniently accomplished, for example, by placing the layer between an insulated surface and a heated metal surface, such as, for example, an iron or a similar heating device. In this preferred embodiment, the resulting bound complex is preferably from about 0.5 mm to about 3.0 mm thick. For purposes of the present invention, it is desired that the heating step extend for a sufficient amount of time and be a temperature sufficient to obtain the desired modification of the surface of the substrate particles. In this regard, the top surface and the bottom surface of the layer can be provided heat at a temperature of from about 130°C to about 190° for a period of time between about 10 minutes and about 20 minutes. Alternatively, heat is provided to one surface of the layer at a temperature of from about 150°C to about 210°C for a period of time between about 3 minutes and about 10 minutes. It will be readily understood by one of ordinary skill in the art that these temperatures and time periods may be varied to achieve the desired result.

After heating the mixture for a period of time and under conditions sufficient to achieve advantageous modification of the starting materials, the agglomerate layer is fragmented (e.g. milled or ground) into particles preferably having an average particle size of at least about 0.5 mm, typically falling in a range of about 0.5 mm to about 3.0 mm. As is known and commonly used in the relevant field, such sizes represent the average particle size of a particle distribution conventiently measured and/or selected using sieves of various mesh sizes.

Preferred desiccant compositions of the invention desirably have a speci .fi.c surface area of at least about 0.05 m2/gram, 2 typically in the range of about 0.05 to about 5 m /gram.

Surface area may be conveniently determined using the Brunauer,

Emmett, and Teller (BET) method, this method being well known in the relevant field.

According to the present invention, preferred desiccant compositions include from about 50% to about 85% starch and from about 15% to about 50% substrate by weight, more preferably from about 60% to about 75% starch and from about

25% to about 40% substrate. Inventive desiccant compositions can advantageously be made having increasing structural stablility by increasing the starch:cob ratio. Although it is not intended that the present invention be limited by theoretical mechanisms by which inventive compositions and methods achieve their advantageous results, it appears that the basis for adhesion of the substrate particles is a starch hydrate which forms a viscous gel. In this regard, the starch gel wets the surface of the substrate particles to be joined and when the water is removed, such as occurs when the material is heated in the oven, a solid noncrystalline film forms between the surfaces of substrate particles, holding them together. It has been previously determined that NaOH lowers the gelatinization temperature of starch by disrupting the hydrogen bonds in the granules, and, as such, heating results in the formation of a viscous gel, producing the glue to hold the mixture together. Although the gelled starch provides much

- li of the structural strength to the adsorbent, there is an optimum concentration for this form of the starch since it forms a coating on the surface and blocks the pores, thereby decreasing accessible surface area.

Desiccant compositions of the present invention are useful in a wide variety of applications in which it is desired to remove water from a fluid. In one aspect of the invention, the inventive desiccant compositions are utilized to adsorb water from moist air, thus providing dry air. For instance, using methods of the invention, air can be dried to a dew point of about -60°C to about -80°C, for example starting with air at a dewpoint of about 0°C to about -10°C.

A preferred use of an inventive composition is in a pressure swing adsorption system. There presently exist a wide variety of processes which require as a first step the generation of a stream of dry air such as that produced by a pressure swing dryer. Examples of these applications include pressurization of power and communication cables, paint spraying and ozone generation. The desiccant capacity of inventive desiccant compositions is comparable or superior to many conventional desiccants presently used in these types of systems. As used herein, the term "desiccant capacity" is intended to refer to the efficiency with which the desiccant composition adsorbs water vapor, for example, as compared to alternative desiccant compositions. For example, superior desiccant capacity can be observed as the ability of the desiccant composition under similar conditions to remove a greater amount of moisture from a fluid than a corresponding desiccant. Advantageously, inventive desiccant compositions are biodegradable and thus readily disposed of and the primary starting materials, starch and cob flour, are readily available and relatively inexpensive. Additionally, inventive desiccant compositions are extremely robust, capable of withstanding at least tens of thousands of pressure cycles in a pressure swing adsorption system.

In another advantageous aspect of the present invention, the inventive desiccant compositions are utilized as water adsorption compositions in the purification of an organic compound which is liquid at room temperature (e.g. about 25°C) . The organic compound may be, for example, an aliphatic or aromatic compound, including e.g. alcohols, ethers, ketones, alkanes, acids, and the like. Preferably, the organic compound will be relatively volatile, for instance having a boiling point of less than about 120°C.

The organic compound may also be one which forms an azeotrope with water. In this case, processes of the invention can be used as a convenient alternative or supplement to splitting the azeotrope by specialized distillation or other processes. For instance, inventive compositions can be used in an ethanol purification system to remove the final 5-10% water from a wet ethanol stream resulting from the distillation of a crude fermentation broth. In a preferred mode, the wet ethanol or other organic liquid is vaporized to provide a moisture-containing vapor, which is then contacted with the inventive desiccant compositions to remove water. Then, the vapor is condensed and the resulting product liquid has a lower moisture content than prior to contact with the desiccant. In such processes the inventive desiccant compositions are preferably used in a fixed bed adsorption system and, more preferably, the liquid is dried from an initial water content of about 2% to about 30% by weight, to a product liquid which has a water content of less than about 1% by weight, more preferably less than about 0.5% by weight, by contact with the inventive desiccant compositions. The use of an inventive biodegradable desiccant is particularly advantageous because when the desiccants become deficient due to fouling or other means, they can be readily disposed of without fear of adverse environmental effects.

The inventive desiccant compositions may also be utilized in an evaporative air cooling system to replace conventional air conditioners that cool and dehumidify homes and cars. There is a growing interest in developing alternative systems to standard air conditioners, and many manufacturers are developing evaporative cooler systems using, for example, zeolites as desiccators. The present invention provides an adsorption composition which can be utilized in such a system as an advantageous alternative to zeolites.

Since air conditioning involves both reducing the humidity and lowering the temperature of the air, conventional air conditioning units must cool atmospheric air to its dew point before any moisture is removed. Thus, the air is cooled to a low temperature to reach the desired humidity and, to correct the uncomfortably cold but drier air, the air often has to be reheated to the desired final temperature. In an improved air conditioner which utilizes a desiccator such as that provided by the present invention (a "latent air conditioner"), removing moisture from the air to provide a lower humidity level is accomplished by passing the air through desiccant wheels which dry air using desiccant compositions. During the drying process, the air temperature is increased, so a final sensible cooling step over a thermal wheel and an evaporative cooler is used to cool the air to the desired temperature.

More specifically, in this system, desiccants are contained in a large rotating wheel. Atmospheric air enters and passes through one half of the wheel (top or bottom), which contains dry desiccants, so moisture is removed from the product air. Water is sprayed into the product air, and because the air is dry, some of the water will be evaporated. By using an energy balance, it can be readily seen that as the water is evaporated by the air, the temperature of the air must decrease. The resulting air will be cool and at a comfortable relative humidity. On the other side of the wheel, air will be heated and sent through. This action will regenerate the desiccant for drying the ambient air by the time the wheel revolves another half turn.

A comparison of energy requirements shows that the latent mode of air conditioning consumes much less power, only about one fifth, of that consumed by conventional methods. The lower power requirement of this desiccant-type air conditioner results from the splitting of the sensible and the latent loads. Drier air being easier to cool than moist air, the capacity of the mechanical cooling system is decreased. Also, the need for expensive reheating is eliminated.

In another advantageous use of inventive desiccant compositions, the compositions are simply placed in locations for which dryness is desired. One example of such a location is within packaging for storing or shipping products such as, for example, computers, tissue papers, chemicals, granular salts, sugars and the like, wherein it is of utmost importance to keep the product free from moisture. In many uses such as these, the inventive desiccant may be advantageously encapsulated in a gas-permeable membrane, thus forming a desiccant packet. Alternatively, the desiccants can simply be scattered among packaging material, depending upon the specific use desired. The invention will be further described with reference to the following specific Examples. It will be understood that these Examples are illustrative and not restrictive in nature.

EXAMPLE ONE

MAKING A DESICCANT COMPOSITION FROM COB FLOUR AND STARCH

Starch and Cob Materials.

The corn starch (Lot 46F-312, No. S-4126) was obtained from the Sigma Chemical Co. and was found by Scanning Electron Microscopy ("SEM") to be almost spherical with an average diameter of 10 microns. Corn grits used for control studies were obtained from Short Milling Co. (Kankakee, IL) . The average particle size used for this study were 0.71, 0.9, 1.75, 2.3 and 5.2 mm. These materials were screened before use. The small amount of fines which passed a 25 mesh screen were discarded.

Three types of cob flour (Grit-o'cobs 30, Grit-o'cobs 60 and Grit-o'cobs 1420) were obtained from Andersons' Corncob Products, Inc., Delphi, IN. Cob flour is derived from corncobs and typically has a compositions of about 60% hemicellulose, about 30% cellulose, about 8% lignin and about 2% ash. All particle and pore sizes were estimated from SEM examination.

Cobs are resistant to attrition and both the xylan and cellulose contained in them have been shown to exhibit sorptive properties. Consequently, cob flour is used in a preferred embodiment of the invention to complement the moisture adsorbing properties of starch. The cob 1420 material, with an average size of 1.05 mm, was used to confirm the intrinsic capability of cobs to act as a sorbent sieve. It had a particle size close to the 0.9 mm corn grits which were used as a control in this work.

Coating Procedure

The coating of starch on cob particles was studied using a 2:1 weight ratio of starch to cobs mixed together at ambient temperature in various tests for 5, 10, 20, 30, 40, 50, 60 minutes and 2 days. Mixing was done in a glass jar that was placed on rollers. The starch and the cob were introduced into the jar and the rolling action of the jar mixed the cob and the starch. Examination of the resulting particles showed 5 minutes of mixing was too short while the best distribution and coating of the starch in the cob particle occurred at 60 minutes. An extended mixing time of 2 days did not result in further improvements.

The mixing method was also tested in a moist atmosphere, since it was thought that the moisture adsorbed by the powders in the humid atmosphere could create a binder, and therefore increase the number of starch granules attached to the cob surface. The powders were stored for 16 hours in a closed oven at 60°C with a pan of water to create a humid atmosphere. Following mixing of the humidified particles, SEM examination suggested that the starch coating on the cob flour particle had not increased signi icantly. Therefore, it was concluded that moisture did not cause additional binding of the starch granules to the surface of the cob, and the dry method was used in subsequent runs. The preferred method ultimately involved addition of 40 mM NaOH to the starch/cob mixture at a liquid to solid ratio of 1 to 1.5. The blended mixture consisted of the proportions of 1 gm starch, 0.5 gm cobs 60 and 1 ml of 0.04 M NaOH. The resulting adsorbent agglomerates were subjected to heat treatment to fix the starch onto the cob matrix.

Heat Treatment (Fixing/Aggregation) Procedure.

The adsorbent agglomerates were fixed from this mixture by two methods: the surface heat source method and the oven method. In the former, the blended mixture was folded in an aluminum foil sheet and placed between an insulated ceramic surface and a heated metal surface at 180°C for 5 minutes. The heat source was removed. After cooling, the foil was pealed back and a 1 mm thick sheet of agglomerated starch and cob particle was obtained.

In the oven method, an agglomerated mixture of 4 gm starch, 2 gm cobs 60 and 4 ml 0.04 M NaOH was spread in a 10 cm diameter petri dish with another petri dish pressing down on it. This was then placed in a Blue M single wall gravity convection laboratory oven and baked for 15 minutes at 160°C. A sheet, of material having a thickness of 1.5 mm was obtained. Particle Formation.

Sheets for either method were broken into smaller pieces and ground using mortar and pestle. The agglomerates were examined under the SEM. The average particle size of the adsorbent particles (1.15 mm) was measured by sieve analysis using 14, 16, 18, 20 and 25 mesh sieves whose openings corresponded to 1.40, 1.18, 1.00, 0.85 and 0.71 mm, respectively. The synthesized adsorbents were characterized with respect to surface area, crystallinity and resistance to attrition (described more fully in the following Examples) .

Selection of Heat Treatment Method.

The adsorbents synthesized in the two methods of heat treatment were nearly the same structurally and functionally. However, the oven method was preferred because more adsorbents could be produced in a shorter time. For both methods, the side away from the heat source became more smooth compared to the side closest to the heat source which remained rough. FIGS. 6 and 7 illustrate this effect for adsorbent prepared using the oven method. It was hypothesized that heat forced the water vapor to the other side, where it condensed with starch to form a smooth film (FIG. 6). The film is a likely contributor to the structural integrity of the starch cob matrix while the rough side contributed surface area through a dense and uniform coating of immobilized starch (FIG. 7) . EXAMPLE TWO

ANALYSIS OF MATERIALS Scanning Electron Microscopy.

The basic material, cob flour and corn starch, from which the adsorbent was to be synthesized, as well as the particles derived from the synthesis procedure, described above in Example 1, were examined using a scanning electron microscope (SEM). The JEOL T300 SEM was used at an opening voltage of 5kV. Samples were conductor-coated an Anatech LTD Hummer 6.2 sputter coater or an Edwards vacuum, E306A. SEM photomicrographs were used to select the size of the cob flour and also as an aid for developing methods for fixing starch on the surface of the cobs.

Surface Properties of Starch and Cobs.

Corn starch is nearly spherical with an average diameter of 10 microns (FIG. 1) while the cobs 30 and cobs 60 materials were 300 and 150 microns, respectively (FIGS. 2 and 3) . The cobs 30 material has elongated pores of 50 x 20 microns (FIG. 2) while cobs 60 particles had round pores with a size on the order of 10 microns (FIG. 3). The cobs 60 particle was chosen based on the SEM photomicrographs, since the pores were thought to be most likely to retain a high surface density of starch particles which could lodge into the holes. Mixing of Starch with Cobs

Photomicrographs also showed that the greatest amount of starch adhered to the cob after a mixing time of 60 minutes, when dry conditions were used. Extended periods of mixing did not result in an increase in the starch coating. The photomicrographs of the cob surface after 5 and 60 minutes of mixing are shown in FIGS. 4 an 5, respectively. FIG. 5 shows how the starch particles assembled in the macropores of the cobs during the mixing process.

Moisture Determination.

Moisture content was determined by drying the samples in a convection oven for 16 hours at 103°C. The loss in weight was used to calculate the percent moisture. At ambient conditions, both corn grits and the inventive desiccant composition were determined to have 5.0 percent moisture.

Elemental Analysis.

Selected samples of corn grits, corn starch, cob, and synthesized adsorbent were analyzed for carbon, hydrogen, nitrogen, oxygen and sodium with Perkin-Elmer 240 C Elemental Analyzer (Norwalk, CT) using acetanilide as a standard. The results with respect to the synthesized adsorbent and the corn grits were as follows: Elemental Analysis (%)

Synthesized Corn

Adsorbent Grits

Carbon 45.0 46.0

Hydrogen 6.0 7.0

Nitrogen 0.5 3.0

Sodium 1.0 N/A

Oxygen 45.5 42.0

Ash 2.0 2.0

Crystallinity (X-Ray Diffraction) .

The percent crystallinity of the starch granule plays a role in the adsorption properties of the material. In a starch granule, the crystalline regions are held together by hydrogen bonds which can not be utilized as adsorption sites. Therefore, changing the crystallinity of the starch adsorbents would alter the adsorption properties. X-ray diffraction was used to determine if crystallinity of the materials was modified during processing and drying.

The instrument used was a Siemens X-ray diffractometer (Kahrlsruhe, Germany) and the software package used was Diffractometer At, v.3.2 (Siemens Co., 1993). The HT voltage was set at 40kV an the x-ray tube current at 20mA. A copper wire source was used to give K radiation. The detector slits used were 1°, 1°, 1°, and 0.15°. An aluminum sample holder with a quartz bottom was used to hold the powder samples during examination. X-ray diffraction patterns of corn starch, a 2:1 mixture of corn starch and cob flour, adsorbent particles before use in the dryer, and adsorbent particles after 86,400 cycles were obtained as described. The initial materials show some crystalline peaks in the amorphous hump. These spikes were no longer present in the synthesized particles showing that crystallinity had been reduced because of the adsorbent synthesis method. This behavior is consistent with the dissociation of the crystalline structure of starch and desirable since water adsorption in starch is believed to be due to its amorphous regions. Comparison of the x-ray diffraction patterns shows that there is no change in crystallinity after extended use in the dryer.

EXAMPLE THREE

ANALYZING SPECIFIC SURFACE AREA OF AN INVENTIVE DESICCANT COMPOSITION TO DETERMINE POROSITY

Materials and MethodsSpecific Surface Area (Porosity) by

Mercury Porosimeter.

The specific surface area of the adsorbent material was found by mercury intrusion using a mercury porosimeter. A powder sample was placed in the porosimeter container and the chamber was evacuated to remove gases and vapors. The chamber was then filled with mercury. Mercury first filled the pores between particles. As the pressure in the chamber was increased, mercury entered the pores in the particles. The volume of mercury forced into the chamber was recorded as a function of pressure. The specific surface area of the material was directly proportional to the unit area work, defined as the pressure applied over an incremental penetration volume, a relationship that is well-known in the relevant art.

Porosity of Synthesized Adsorbent

Mercury intrusion results showed that the porosity of the adsorbents (5.21 m /gm) was nearly 10 times greater than the corn grits (0.51 m_/gm) of the same size. Density estimates showed that while the solid density was nearly the same as the starting material (1.4 gm/cm_), the bulk density of the synthesized adsorbents (0.63 gra/crti- ) was less than half of that of the corn grits. This difference is also reflected by the packing densities of the corn grits and synthesized adsorbent which were 0.74 and 0.30 g/mL bed volume, respectively. The lower bulk density reflects the higher internal porosity of the synthesized adsorbent.

EXAMPLE FOUR

MAKING PELLETS FROM INVENTIVE DESICCANT COMPOSITIONS

Agglomerated Adsorbent Production

Many Commercial dryer units are designed to use desiccant pellets of 5 mm by 1 mm dimensions. To make the synthesized adsorbents easily adaptable to existing equipment using molecular sieves, the particles may advantageously be agglomerated to a similar size. A larger adsorbent implies a reduction of surface area, but ideally the air flow would be able to move through connected power within the material, or the pore diffusion of the sorbed compounds would be sufficiently rapid to make effective use of the material's internal porosity. The average particle size of the cylindrical molecular sieve pieces that originally accompanied the Puregas pressure-swing dryer used in this research was approximately 0.5 cm in length and 1 mm in diameter. By agglomerating the adsorbent particles into pellets, a similar size for the adsorbent material could be achieved.

Pellet Production

Pellet production was done by compaction and extrusion of the synthesized adsorbent particles and a binder. A syringe was used as an extrusion tube to form the cylindrical pellets. A 1.00 cc Monoject Tuberculling syringe was modified by cutting of the tip to create a cylinder with an approximate diameter of 4mm. The rubber end of the plunger was removed to leave only the plastic, enabling the plunger to move easily down the tube.

Two methods for compaction were used. In the first method, the syringe was filled with loose particles, with the open end of the syringe held to a flat hard surface for compaction. The material was compacted together with the plunger, and the process repeated until the entire syringe was filled with compressed material. The adsorbent rod was then extruded and allowed to air dry. This resulted in a rod of material approximately 40 mm in length and 4 mm in diameter. To form the required 0.5 cm length pellet, the 40 mm rod was cut with a razor blade. Cutting the rods caused undesirable dust formation and loss of material. Further, the adsorbent rod would frequently become stuck in the tube, so that the plastic syringe wall had to be cut away from the rod with a razor blade to extrude the material. This necessitated modification of the production procedure.

In the second method, the syringe was half-filled with loose particles, which were compressed to form a pellet with the required length of 0.5 cm, the pellets were then extruded and air dried. This procedure was much faster and did not produce the waste from the cutting of the dry rod to size.

A multi-pellet producer was designed to decrease the time required to make the large quantities of pellets needed for testing in the dryer. This apparatus consisted of ten syringes fixed by epoxy to a plastic bar, with the plungers similarly ecured to another plastic bar. Ten syringes could thus be filled at one time which decreased pellet production time.

By selecting an appropriate binding agent and compacting the adsorbent particles together, a pellet of similar size and shape to the molecular sieves was formed from the starch/cob agglomerate. Two types of binders were investigated. The first was the wood chemical lignosulfonate. Two different concentrations of lignin in water were employed, 0.25 g and 0.5 g in 3 ml of deionized water (0.08 g/ml and 0.17 g/ml). Three ml of deionized water were heated on a hot plate on setting #4. The lignin powder was added and stirred. 0.1 ml of this solution was added to one gram of adsorbent particles and stirred with a spatula until the mixture appeared homogeneous (approximately 2 minutes). The particles clotted together in groups of two or three. Another 0.1 ml of liquid was added and the mixture was stirred. These mixtures were placed into the syringe, compacted and extruded.

Pellets made with 0.25 g lignin and 3 ml water had the same color as the initial adsorbent particles. They were crumbly in some places and strong in others. It was assumed that this was due to that materials not being thoroughly mixed. The 0.5 g lignin/3 ml water treated pellets had dark brown patches from the lignin liquid, and were sticky to the touch.

Room temperatures deionized water was also investigated as a binder. Two different ratios of water to adsorbent particles, 0.2 ml/g and 0.4 ml/g, were investigated. The production method for the addition of the binder to the particles was the same as for the lignin method. These mixtures were placed into the syringe, compacted and extruded. Pellets made with the addition of 0.4 ml/g water exhibited the best physical qualities of all the pellets produced. The 0.2 ml/g water pellets were crumbly, while the 0.4 ml/g water pellets were much stronger. Using water decreased the number of steps in the binding step, and did not result in sticky pellets. FIGS 8 and 9 show photomicrographs of the side and cross section of one of the 0.4 ml/g water binder pellets, respectively. From the side view of the pellet (FIG. 8), it was noted that some of the gelled starch had coated the side of the pellet. This was seen in patches on the pellets examined in the SEM. This gel film blocked the pores on the surface of the pellet, which implied that the adsorption capabilities would be lower for the agglomerated material than for the adsorbent particles, since the surface area of the material was reduced by this film, lowering the volume density of adsorption sites. The air flow through the pellet via the connected pores would also be reduced due to the filled pores, preventing the moist air from reaching additional adsorption sites inside the pellet.

To test the adsorbent pellets in the arid dryer, 270 ml of material were needed. Deionized water was chosen as the binder and required minimal preparation. The production method of using 0.4 ml of water per gram of adsorbent was chosen because the pellets were more stable than the material produced using 0.2 ml/g water. The multi-pellet device was used to compact and extrude ten pellets at a time. The average length of a pellet was 5mm, with a diameter of 4 mm (compared to molecular sieve size 5 mm x 1 mm).

Approximately 135 ml of pellets were put into each chamber, with masses of 43.340 g and 46.367 g. The initial pressure was set to 30 psi and a controlled air flow rate set to 1.9 SLPM. The adsorbent pellets achieved a dew point of -22°C. The pressure drop access the dryer was approximately zero.

Increasing the air flow through the chambers of the dryer at 30 psi resulted in a dew point of -17°C. The average product flow rate was calculated to be 6.1 SLPM, and the average purge rate was 9.8 SLPM.

Decreasing the system pressure to 10 psi produced a dew point value of approximately -12°C. The average product flow was calculated to be 3.3 SLPM, and average purge was 4.1 SLPM.

The adsorption chambers containing the adsorbent pellets increased in temperature during the run, and were warm to the touch. A cooling fan was used circulate room temperature air over the chambers. At a system pressure of 30 psi and an increased flow rate, the reduction of the dew point by fan cooling the chambers was 2°C. At a system pressure of 10 psi and an increased flow rate, the result fan cooling was to decrease the dew point from -12°C to -14°C. The cooling fan was turned off and the dew point returned to a steady state value of -12°C after ten minutes. Final particle size measurements were taken after the pellets had experienced a total of 30,000 cycles. The pellets were removed from the drier chambers and sieved through a #8 sieve (2.36mm opening) . Any material that was not part of a pellet was considered a fine. The average mass of the two chambers were 43.1034 g and 42.6690 g, and the average mass of the fines for the two chambers was 0.5247 g (1.2% fines). The final volumes for the chambers were 134 ml and 132 ml (from 135 ml) .

EXAMPLE FIVE

ATTRITION TESTS OF INVENTIVE DESICCANT COMPOSITIONS

Particle Attrition Test.

An experimental procedure using a Cresent Wig-L-Bug (Lyons, Illinois) electric motor (#3110B) was created to test the mechanical stability of the adsorbent particles and pellets relative to corn grits. These results could be used to anticipate the attrition of the materials over extended periods in the pressure-swing dryer. This device rapidly shook a container holding the adsorbent, and was used as an accelerated test to predict the attrition of the materials over many cycles in the pressure-swing dryer. The procedure consisted of placing 1.4 g of corn grits (which had previously been sieved through a 25 mesh screen to remove fines initially present) into the Wig-L-Bug holder and then shaking for 5 seconds. A small amount of dust was formed on the inside of the holder, but mass of the grits was not significantly depleted and approximately 0.15% fines were formed. The extent of attrition was consistent with the attrition of corn grits, previously tested in the dryer for 88 days (254,000 cycles) which had produced about 0.15% fines (particles under 0.7 mm). When the grits were shaken for 10 seconds 0.6% fines were formed.

The starting adsorbent particles were sieved and any fines less than #25 mesh were discarded. 0.5 g of the particles were placed in the Wig-L-Bug holder for 5 second of agitation. The adsorbents were resieved and 0.02 g of fines were collected (4% fines). Adsorbent pellets (0.5 g) 5 mm in length were tested in the Wig-L-Bug machine (6 pellets) . After 5 seconds, one pellet had broken in half and 0.02g of fines were produced (4% fines); and this probably represented material that had abraded from the broken pellet.

EXAMPLE SIX REMOVING MOISTURE FROM A GAS

The operational sorption capacity of the corn grits and the synthesized adsorbents was tested in a commercially available pressure-swing dryer. The dryer was a PUREGAS dryer (Model HF 2000A106-A130, General Cable Co., Westminster, Co.) with two 152 mm desiccant chambers. Each chamber held 135 ml of desiccant which corresponded to 40 g of synthesized adsorbent, or 100 g of corn grits. The actual bed height in both cases was 125 mm. The dryer was fitted with other external components to provide a system in which inlet air flow rate an inlet and outlet moisture contents could be controlled and/or monitored. The chambers were loaded by placing the air tubes that had an aeration metal disk and sponge filter on it into a hole at the bottom of the chamber. In the respective runs, the grits, cob flour and the synthesized adsorbent composition were loaded on top of this in the chamber and then another sponge filter and disk were placed on top of the grits. A spring, another metal disk, and a retaining ring were placed on top of this. The retaining ring was compressed to fit into the chamber and then released into a groove on the inside of the desiccant chamber. This apparatus held the adsorbent bed stationary during pressure changes. The beds were screwed into the pressure swing adsorption system, which could then be run.

Hu idification of Inlet Air

Air at approximately 320kPa and 298K was humidified to -5°C dew point by bubbling it through 1 L of distilled water. Trace amounts of oil were removed by oil traps along the air line. The flow of air at the outlet was maintained at 1.8 L/min (STP, 273K, 101.3kPa) by a flow controller (Matheson, Model 8240). The dry air flow was used for the regeneration cycle was 11.5 L/min (STP), with each of the two sorbent beds cycling between sorption and regeneration every 30 seconds. The low outlet/purge ratio was used in order to promote rapid equilibration of the bed to steady state outlet moisture conditions .

Measurement of Dew Point

The dew point of the dry air was measured by a System 580 Hygrometer (Panametrics Inc. , Waltham, MA) which has a range of -80° to 10°C dew point. The moisture sensor relates the amount of water adsorbed (through the electrical impedance) to the vapor pressure of water in the atmosphere around the gold coated, anodized aluminum oxide element. The detector was insensitive to temperature and flow rate at these system conditions. Dew point temperature was chosen to report the data since it provides a sensitive measure of low moisture levels .

The dryer system was set up prior to each run. The water reservoir was emptied of any remaining water by slowly pressurizing the system with the feed line open. The system was then vented and the reservoir was refilled with 600 ml of deionized water. Finally, the feed valve was closed, the system pressure turned on, and vent closed (in that order). The computer program used to record the dew point data from the hygrometer was Lablog2 v. 3.52 (Quinn-Curtis, Computer Boards, Inc., Mansfield, MA) Air flow rates for both the product air and the purge air were measured by recording the time required for a 2 L graduated cylinder to fill with product or purge air. The 2 L cylinder was completely filled with water and inverted into a bucket of water (the small amount of water lost during the inversion was estimated). Output air was transported into the cylinder by a tube. The time to fill the cylinder was recorded three times for each run and the average value was taken as the flow rate. The ideal gas law was then used to calculate the volume displaced at standard conditions of 293K and atmospheric pressure. Results and Discussion

Cob 1420 material was evaluated in the air dryer to examine the adsorption capabilities of the cob flour alone, without the addition of starch granules. The large particle size of cob (1.05 mm) was selected as the control because it was comparable in size to the synthesized adsorbent particles. This material also had a surface area of 5.88 m„/g. At a pressure of 308 kPa and a controlled air flow rate of 1.9 SLPM, a steady state dew point of -63°C was achieved after 40 hours, as compared to a steady state dew point of -20°C for regular corn grits. This dew point was maintained through 25,000 cycles, after which the run was discontinued, and the material was removed from the chambers. Even though the final average particle size was found to be 1.04 mm after this run, there was about 5% increase in the particle which were 0.85 mm or smaller, and several percent fines were present. This was significantly higher than the fines observed for corn grits after 254,000 cycles. While the outlet dew point is comparable to that of the smallest grits, the tendency for these cobs to form dust was undesirable. Nonetheless, the results showed that the cobs would, themselves, adsorb water to the same degree as starch. Hence, they provided a useful scaffold upon which the starch particles could be immobilized.

Synthesized adsorbents, made according to Example 1, were also tested in this pressure swing system. The inventive desiccant compositions also achieved a steady state dew point of -63°C.

Claims

What is claimed is:

01. A desiccant composition, comprising: a solid particulate substrate, said substrate comprising a biodegradable composition; and starch, said starch being affixed to the surface of substrate particles.

02. The desiccant composition of claim 01, wherein said solid particulate substrate comprises a particulate corn fraction.

03. The desiccant composition of claim 01, wherein said solid particulate substrate comprises corn cob flour.

04. The desiccant composition of claim 01, said substrate comprising from about 40% to about 80% hemicellulose; and from about 10% to about 50% cellulose, by weight.

05. The desiccant composition of claim 01, said substrate comprising from about 50% to about 70% hemicellulose; and about 20% to about 40% cellulose, by weight.

06. The desiccant composition of claim 01, wherein said desiccant composition comprises from about 50% to about 85% starch, and from about 15% to about 50% substrate, by weight. 07. The desiccant composition of claim 01, wherein said desiccant composition comprises from about 60% to about 75% starch, and from about 25% to about 40% substrate, by weight.

08. The desiccant composition of claim 01, wherein said starch is affixed to said substrate by heating a mixture comprising said starch and said substrate.

09. A method for making a desiccant composition, comprising: providing a mixture comprising a solid particulate substrate, starch, and an aqueous medium; and heating the mixture to affix the starch to substrate particles, thus providing an agglomerate.

10. The method according to claim 09, wherein the aqueous medium is a basic aqueous medium.

11. The method according to claim 10, wherein the basic aqueous medium comprises sodium hydroxide.

12. The method according to claim 11, wherein the basic aqueous medium comprises sodium hydroxide having a concentration of from about 10 mM to about 70 mM. 13. The method according to claim 11, wherein the basic aqueous medium comprises sodium hydroxide having a concentration of from about 20 mM to about 60 mM.

14. The method according to claim 11, wherein the basic aqueous medium comprises sodium hydroxide having a concentration of from about 30 mM to about 50 mM.

15. The method according to claim 09, wherein the particulate substrate comprises cob flour.

16. The method according to claim 09, further comprising: fragmenting the agglomerate into particles having an average particle size of from about 0.5 mm to about 3.0 mm.

17. The method according to claim 09, wherein the particulate substrate is biodegradable.

18. The method according to claim 09, further comprising, before said heating, spreading the mixture to form a layer having a top surface and a bottom surface; the layer having a substantially even thickness of from about 1.0 mm to about 4.0 mm. 19. The method according to claim 18, said heating comprising providing substantially even heat to the top surface and to the bottom surface of the layer.

20. The method according to claim 19, said heating comprising heating in an oven.

21. The method according to claim 19, said heating comprising providing heat at a temperature of from about 130°C to about 190°C.

22. The method according to claim 19, wherein the agglomerate is from about 1.0 to about 2.0 mm thick.

23. The method according to claim 18, said heating comprising providing substantially even heat to only one surface of the layer .

24. The method according to claim 23, said heating comprising placing the layer between an insulated surface and a heated metal surface.

25. The method according to claim 24, wherein the heated metal surface has a temperature of from about 150°C to about 210°C. 26. The method according to claim 23, wherein the agglomerate is from about 0.5 to about 1.5 mm thick.

27. A product obtainable by the method of claim 09.

28. A method for drying a moisture-containing gas, comprising contacting the gas with a desiccant composition comprising starch affixed onto substrate particles.

29. The method according to claim 28, wherein the gas comprises air .

30. The method according to claim 29, wherein the air is dried to a dew point of lower than about -60°C.

31. The method according to claim 28, wherein said contacting step comprises contacting in a pressure-swing adsorption system.

32. A method for drying a moisture-containing starting liquid, comprising : vaporizing the starting liquid to provide a moisture-containing vapor; contacting the vapor with a dessicant composition comprising starch affixed onto substrate particles, so as to remove moisture from the vapor; and condensing the vapor to provide a product liquid.

33. The method according to claim 32, wherein said starting liquid comprises an organic compound which forms an azeotrope with water.

34. The method according to claim 32, wherein said starting liquid comprises an organic compound having a boiling point of less than about 120°C.

35. The method according to claim 34, wherein the organic compound is an alcohol.

36. The method according to claim 34, wherein the organic compound is ethanol.

37. The method according to claim 36, wherein the product liquid contains less than about 1% by weight water.

38. The method according to claim 32, wherein said contacting step comprises contacting in a fixed bed adsorption system.