Technical Field The invention concerns a process for manufacturing an environmentally safe, quickly acting snow and ice dissolving liquid chief) y composed of amide and nitrate compounds in aqueous medium by reactions in liquid state.

The freeing from snow and ice of public roads, sidewalks, railway switches and other objects to be protected from slipperiness hazard and operating u'oubies in winter is an important requirement in view of the transport and facilities safety and, first of all, on account of the life danger. On the other hand, it is a fact of experi- ence, that the complete removal of the slipperiness producing frozen moisture by mechanic means (shoveling, sweeping or"plowing") cannot in most cases be at- tained satisfactorily, since the slipperiness takes its origin first of all in the thin ice film adhering to the surface of e. g. asphalt and concrete. The sleet and the poorly visible ice film stemming from the hoar-frost on the road surface is particularly dangerous the prevention, removal and hindering in regeneration of which can be attained reasonably such as without the expensive and circumstantial heating of the road surface only by use of ice dissolving compounds according to the present state of the art.

Background Art As snow and ice melting compound rock salt is predominantly used first of all by economic reasons. Because of its limited solubility in water (slightly above 300

g/liter), it is generally strewn out in solid state that, in turn, leads to deceleration in ice melting and to troubles in uniform spreading. At the same time the economy as such becomes contestable due to the fact that to the uniform spreading of the rock salt, all the more to enable the speed-controlled dosage by the salt-strewing vehicle complicated and expensive equipment are needed, whilst the uniform strewing out of the liquid can be attained (in given cases with some transformation) by the sum- mcr street-sprinklers that are idle in winter. The use of the solid rock salt becomes even more expensive by its wetting in order to prevent it from being whirled away by the wind that results, besides additional expenses, in further cumbersome opera- tions. If, however, the salt-for roughening the road surface-is mixed with sand as well, in addition to the expenses linked with the said mixing, the expenses will ther be augmented by the spring clearing away of the sand.

Accordingly, it is obvious that to the technical-economic comparison of the so) id and liquid compositions a complex evaluation is needed, the mere contrasting of the chemicals'prices isn't satisfactory. On this account the liquid anti-skid agents have also come to the fore recently, all the more so because the corrosive effect of the rock salt is particularly deleterious to the metallic elements of vehicles, bridges, overpasses and subsoil objects. Another objection is that the vegetation is also suf- fering damage by the salting of the soil.

As anti-skid liquid, ethylene-glycol containing compositions have also been used first of all for airdrome runways'deicing in order to decrease in corrosion activating effect of the salt. This method, however, has increasingly been restricted recently on account of the heavily toxic effect of the glycol, especially if it can get as far as the subsoil water before being biologically decomposed to a satisfactory degree.

An anti-skid liquid chiefly composed of nitrogen chemical fertilizer components (urea [K] and ammonium-nitrate [A]) can be learnt in the description of the Hun- garian patent No. 216865 and European patent No. 0824575 offering detailed

grounds for the prescribed mass ratio of the main components (i. e water, K and A) in view of the manner of action and of other, e. g. environment protection aspects, without giving instructions for the way of manufacture. On this account the only inference can be drawn even by the specialist that the said three main components are to be mixed with one another in the given ratio in order to produce the ice melting target-liquid in a direct or indirect way. The indirect way consists in pro- viding the prescribed nitrogen compounds in part as liquid nitrogen chemical fcrtil- izcr, in part, however, as solid A to the manufacturing of the target-product.

Grounds for the Tari ! et When producing Hquid makes, it is always advantageous from operationat point of view ifatso the main raw materials are In liquid state available and if thc Icasl pos- siblc solid components'quantity using up or transitional formation occurs, In adds- tion, the explosion hazard of the A must also be taken into account in the given case allowing for a number of accidents having taken place so far. The operations with solid A become troublesome also because of its hygroscopic nature that makes the calculated quantity of the raw material uncertain and the wet granules'sticking makes circumstantial the operations too. This latter hardship, albeit in a less degree, arises in case of the K as well.

In the course of the A manufacture, to the still warm, from the bottom of the sprin- kler conveyed granules, fine limestone, dolomite or bentonite dust suitable for coating their surface is fed in the air circulating rotary cooler, in order to decrease in explosion hazard and to prevent the granules from sticking. On this account, the original 35% nitrogen content of the pure A will be decreased to 34%, this is usu- ally marked with inscription"34 N"on the sacked shipment. Since the mass of the additive makes in round figure 3% referred to the compound A, the ice combating liquid will be strongly turbid owing to the insoluble suspended impurities therein.

Although this is not disadvantageous for the ice combating (the roughening additive is even advantageous), in order to prevent the spraying nozzles from getting clogged, however, the sedimentation and/or filtration of the turbid liquid is indis- pensable. When starting from nitrogen chemical fertilizers widely used in agricul- ture consisting of A and limestone mixture, that can in given eases constitute a"'6 N"quality according to the previous treatment, the problems stemming from the solid A feeding become still more conspicuous.

The Inventive Steps From the said data the inference can be drawn that the target-make described in me Hungarian patent No. 216865 and European patent No. 0824575 is, as far as possi- blc, to be got avoiding the use of the solid main component prime materials. Since the A and K arc, as a mattcr of fact, manufactured (albeit in several variations as far as the details are concerned) according to the present state of the art by dehydration of the concentrates having come into being after the neutralization of the nitric acid and the thermal decomposition of the carbamate respectively and the said dchydra- tion is connected with graining and powdering in different constructional and op- crational ways in multi-step evaporators, the main components of the target-make are to be mixed in prescribed ratio in the phase of dehydration that the anti- explosion and anti-adhesion additives haven't yet been fed to the concentrate in. If the complete concentrating of the prime components is eliminated, both the explo- sion and sticking hazard can obviously be avoided.

A further inference leading to the invention was that the liquid described in the pat- ents treated characteristic for the present state of the art cannot be theoretically re- garded as simple mixture of the components (as e. g. the ethanol-water or ethanol- glycol mixture), since the properties of the liquid, upon getting to the prescribed mass ratio (5 parts water + 4 parts K + 7 parts A) undergo an abrupt change in

quality due to a compound-formation. The 4: 7 K: A ratio at 8 parts of mass water represents the eutectic composition with-28 °C (=-18, 4 °F) freezing point ensuring at the same time the greatest possible decrease in freezing point, i. e. the lowest freezing point whatever the other than 8 water mass ratio. The presence of water mediates a special type of interaction between the acceptor nitrogen of the amide substituents of the K and NH4 + cations of the A on the one hand and the donor ni- trogen of the N03 anions on the other leading among others to a drastic increase in solubility both for A and K (in fact, the A and the K react with one another too in the presence of water). This peculiar effect can be elucidated by the following data.

At ambient tcmperaturc ncarly onc wcight fraction of K and A respectively can be dissolved in one weight fraction of water (it is of primary concern in view of the concrete technology that the water-solubility of both compounds rapidly increases on increase in temperature). If, however, both K and A are together in a mass ratio of 4: 7 at ambient temperature, 2 weight fractions of K and 3,5 weight fractions of A pass into the liquid state beside one weight fraction of water resulting in a 2: 4: 7 water-K-A mass ratio. Since in this liquid beside one weight fraction water there are 5,5 weight fractions of A + K, albeit in case of pure A or K only one weight fraction of either of them could be in dissolved state, it is obvious that the A and K have rc- acted with one another i. e. they have dissolved one another mutually by the media- tion of water. This interaction, or, from another aspect, compound formation evi- dences itself in the change of several macroscopic properties, such as decrease in propensity to corrosion and explosion, biodegradation accelerated by the organic components in the soil as well as the significant change in the original properties of the A and K compounds (masking by A and K linkage in chemical bond).

The compound producing manifests itself also by one of its fundamental criteria: the 2: 4: 7 mass ratio corresponds to a 5: 3: 4 molar ratio (allowing for the nearly complete suppression of the A dissociation). Accordingly, the law of constant pro- portions is also fulfilled.

The recognition of the compound formation contributed to the realization of the process in compliance with the invention (direct liquid synthesis), because the K- A interaction and the availability of the extreme concentration ratios taking their origin therein enables the combination of the K and A manufacturing steps in an advantageous phase as well as the elimination of their preparation in solid state to- gether with the use and thereafter the filtration of additives hindering from cxplo- sion-and sticking along with the additional expenses of the evaporation and the technical-economic advantages thereof.

Disclosure of the Invention Although the equipment and operations of the K and A manufacturing technology are different as far as the details are concerned, they functionally fit in with one all- other to such an extent that the operational phase needed to the carrying out of the process according to the invention is generally within reach.

When manufacturing the K, ammonium-carbamate is produced in the first step by having liquid ammonia and carbon-dioxide gas reacted, then water will be split off therefrom by thermal decomposition that results in molten K formation containing about 20% water at 180-200 °C (-360-390 °F). The granular final product is usually attained by its (mostly two-step) evaporation. When manufacturing A, the present day processes start from a 45-65% nitric acid solution and ammonia gas, having them reacted at atmospheric pressure or at slight overpressure, then the aqueous A concentrate originated in metathesis is evaporated in part by the heat of reaction, in part by external heating in (mostly multi-step) vacuum-evaporators, combined with graining, sizing and powdering.

Applying the process according to the invention, the K and A containing concen- trates are mixed in the 4 K and 7 A content ratio in the phase of the evaporative op- erations that has the water quantity corresponding to the prescribed 5 weight ratios got into the produced mixture. This ensures, at the same time, due to the compound formation treated, that the produced liquid keeps the nitrogen-compounds in liquid state at any temperature, containing even excess water in such an extent, that en- ables the quick dissolution of the anti-corrosion inhibitors at the temperature of the formation in spite of the endothermic process of the 4K-7A compound buildup.

The heat needed to it is, however, ensured by the heat capacity of the liquid itse) f.

This leads to the decrease in the temperature of the hot concentrates'mixture by about 20 °C (36 °F) but it remains even then at about 100 °C (-210"F) or in a re- ion thereabove. This ensures the quick dissolution of the solid inhibitors fed into the hot liquid during agitation.. Since the dissolution rate of the solid additives is a productivity determining factor in the given case and, on the other hand, since this rate increases exponentially on increase in temperature, the treated combination of the K and A manufacturing operations is more advantageous even in view of the productivity than the blending the A, the K and the inhibitor compounds with water at ambient temperature, as it would be done basic to the patents treated.

When combining the A and K manufacturing steps, beside ensuring the 4: 7 K: A ratio in the make as treated, the specific quantity of the water is also to be set corre- sponding to the prescribed weight fraction 5, i. e. 31, 25 % (regardless of the slight change due to the inhibitors). The weight fraction of the water can reliably be con- trolled in continuous way of operation both by choosing the rate (degree) of the multi-step evaporation and by prescription of the nitric acid concentration used to the A manufacture inside the generally applied 45-65 % range.

Best Mode for Carrvins out of the Invention Although the implementation of the process according to the invention represents the knowledge of the trade, the following examples can serve as further elucidation to the technical solution, remarking that the data therein can be changed adjusting themselves to the A and K manufacturing technology according to the sense.

EXAMPLE I Manufacture connected with the Hobbler's nitric acid neutralization In this ammonium-nitrate manufacturing variety the produced ammonium-nitrate solution is partiat) y rc-circutated into the upper part of the atmospheric ncutraliza- tion tower and saturated with ammonia again, then this alkaline solulioll is rellcu- tralizcd with nitric acid solution fed at the bottom of the bent-tube, while in the lower part of the column the neutral ammonium-nitrate solution is evaporated, i. e. concentrated by means of air blowing in. This technology enables all kinds of am- monium-nitrate concentrate side-draw that ensures its concentrating needed to the urea-melt (stemming from the carbamate-splitting unit generally in a concentration of about 80 %) in order to maintain continuously the main components'5 : 4: 7 weight-fractions in the target-make as prescribed in the foregoing. In case of the example, to manufacture (without inhibitors) a 3200 kg make batch, 2200 kg am- monium-nitrate concentrate of 63,6 % is introduced into the target-make producing blending reactor from the Hobbler neutralizer section before the vacuum evaporator and 1000 kg urea melt of 80% is fed thereto, then, during continuous agitation, the inhibitors (among others the benzoate compounds) are fed into the liquid still of 100 °C (~ 210 °F) in spite of its cooling by about 20 °C (36 °F) during the instantaneous reaction. Under such circumstances the complete dissolution of the inhibitors pro- ceeds during short time (not more than five minutes).

EXAMPLE 2 Manufacture connected with ITN-type nitric acid neutralization Since the carbamate decomposer, whatever the degree of the carbamate re- circulation, generally provides a urea-melt concentration of about 80'/,) and the oc- casional fluctuation thereof doesn't constitute any hardship in the regulation of the ammonium-nitrate concentrate feeding either and since nor the construction and way of operation of the target-make reactor depend on the raw-material main com- ponents'producing conditions, it is in this example only the side-draw carrying out of the ammonium-nitrate concentrate in the prescribed quality and concentration that departs from the solution according to the previous or other examples.

In the ITN reactor relatively thin (~ 48 °S,) nitric acid is neutralized at moderate overpressure that enables a continuous Nl14NO3 concentration selling prescribed and regulated between 60-70 % by the vapor-withdrawal rate in the liquid sepa- rator after the neutralizing reactor and before the mu ! ti-step evaporator. ! n this way the NH4NO3 concentration of 63,6 °X) according to the previous example can be maintained and in the following the feeding and operational prescriptions detailed therein are to be observed.

Accordingly, the advantages of the process according to the invention, contrary to the solutions representing the current state of the art, i. e. blending the main compo- nents of the target-make directly, lie in enabling the elimination and saving of the nitrogen-fertilizer main components'complete concentrating, evaporating, graining, powdering, then that of the target-make sedimentation and/or filtration as well as in the exclusion of the explosion hazard along with the drawbacks due to the grains' sticking, in making use of the operational advantages inherent in the homogeneous reactions ensured by the liquid reactants, in intensification of the manufacturing, in accomplishment of the perfectly interdependent chemical combine system by dis- connecting the shipment of the nitrogen fertilizer intermediates.