GB2163052A

GB2163052A - Method of manufacturing bordeaux powder

Info

Publication number: GB2163052A
Application number: GB08420796A
Authority: GB
Inventors: Alan Charles Hughes; Richard Charles Copeman; Amedee Escoubas
Original assignee: MCKECHNIE CHEM Ltd
Current assignee: MCKECHNIE CHEM Ltd
Priority date: 1984-08-16
Filing date: 1984-08-16
Publication date: 1986-02-19
Also published as: FR2569176A1; BE903031A; PT80960A; PT80960B; IT1184680B; ES546170A0; GB8420796D0; GB2163052B; ES8604069A1; IT8548405A0; NL8502263A; DE3526658A1

Abstract

The invention concerns the manufacture of the copper-based compound (tricalcium tetra copper hexahydroxide tetra sulphate (TTCHTS)) used as a fungicide and called "Bordeaux Powder" or "Bordeaux Mixture". The method comprises mixing together, in the dry state, a copper sulphate hydrate salt either with the oxide or hydroxide of calcium, and subjecting this dry mixture to milling for a reaction period wherein the compound TTCHTS is formed in the presence of free water liberated from the copper sulphate hydrate salt during the milling. Preferably, the mixture is comprised of copper sulphate pentahydrate and calcium oxide. The invented method presents advantages over the traditional wet process in which the compound TTCHTS is formed by admixture of aqueous solutions and precipitation.

Description

SPECIFICATION Method of Manufacturing Bordeaux Powder This invention concerns the manufacture of the copper-based compound called "Bordeaux Powder" or "Bordeaux Mixture" of which the chemical nomenclature is tricalcium tetra copper hexahydroxide tetra sulphate (hereinafter abbreviated to TTCHTS) and having the following chemical formula:- CuSO43Cu(OH)23CaS04 Bordeaux Powder is the dry powdrous compound TTCHTS which is widely used in agro-chemical applications as a copper-based fungicide which is applied in aqueous suspension by spraying or the like.

The dry powdrous compound TTCHTS is an important fungicide and has been manufactured industrially for many years by a traditional wet method of reacting copper sulphate solution with a suspension of a specific amount of calcium hydroxide. The compound TTCHTS is formed as suspended solids which are then separated from the liquor by suitable filtration. The resultant wet slurry containing the solids which has a water content of about 60%, is then subjected to drying. During the drying stage, the temperature has to be carefully controlled to prevent the undesirable formation of cupric oxide arising from the oxidation and decomposition of the TTCHTS.

The traditional wet industrial method as afore-mentioned is based on the older manual method carried out in the field in which lime was merely stirred into a solution of copper sulphate to produce the fungicidal liquor ready for application. It is from this old mixing method that the term "Bordeaux Mixture" has been derived.

The industrial wet method for producing the Bordeaux Powder involves substantial and expensive plant for mixing, subsequent filtration and drying stages to remove the water. The process is very expensive in terms of energy, particularly as all of the water added to complete the reaction in solution has to be removed after the reaction has been completed.

The object of this invention is to provide a new method of manufacturing the compound TTCHTS which is simpler and less expensive than the aforesaid industrial wet method involving substantial amounts of water for aqueous solution processing of the compound TTCHTS.

A further object of this invention is to provide a new method of manufacturing the compound TTCHTS by which the composition of the product may be varied to produce a range of Bordeux type mixtures not possible by the aforesaid industrial wet method.

According to this invention, we provide a method of manufacturing the compound TTCHTS characterised by mixing together in the dry state a copper sulphate hydrate salt either with the oxide or hydroxide of calcium, subjecting this dry mixture to milling for a reaction period wherein the reaction product of TTCHTS is formed in the presence of free water liberated from the copper sulphate hydrate salt during the milling.

By this invention, the TTCHTS compound is produced without firstly providing an aqueous solution of copper sulphate in which the reaction occurs and this invention is based upon the surprising and unexpected discovery that the compound TTCHTS can be obtained by dry milling the mixture of a copper sulphate hydrate salt and either calcium oxide or calcium hydroxide together. Thus, this invented method is much simpler than the wet method now used and is less expensive in terms of plant and overhead operating costs.

The invented method may inciude a finishing stage following the dry milling in which the TTCHTS reaction product is dried to reduce the moisture content to less than 4%.

The provision of this finishing stage of the invented method may not be essential and will depend on several factors including the water of crystallisation present in the selected copper sulphate hydrate salt and any heat generated during the reaction and by the dry milling.

According to a further feature of the invented method, the copper sulphate hydrate salt is mixed with a stoichiometric amount of either the oxide or hydroxide of calcium.

By selecting stoichiometric amounts of the dry ingredients for processing, the reaction product TTCHTS is formed without any free or excess copper sulphate or either calcium oxide or hydroxide. This feature is important where the TTCHTS compound is to be used admixed with water for fungicidal applications and wherein phytotoxicity arising from high levels of copper sulphate must be avoided. Similarly, in some applications, excess calcium in the form of lime must be avoided. Generally, a neutral TTCHTS compound is required to be produced for most standard agrochemical uses.

According to another feature of this invented method, the copper sulphate hydrate salt and either the oxide or hydroxide of calcium may be mixed together in amounts selected to provide the reaction product TTCHTS together with an excess of uncombined either copper sulphate or calcium oxide or calcium hydroxide.

By this feature, special formulations including the compound TTCHTS can be produced for Bordeaux type mixtures which may be required as sometimes referred to as acid or alkali having selected free quantities of copper sulphate or calcium oxide or calcium hydroxide. These special formulations are sometimes required, and in the industrial "wet" method it is not possible to produce the compound TTCHTS together with copper sulphate as the copper sulphate is soluble in the water which is removed by filtration. By this invented "dry" method, a complete range of Bordeaux type mixtures including TTCHTS can be produced by merely selecting the amounts of the dry ingredients to be mixed together and subject to the dry milling.Previously, such special formulations could only be made by making up the dry powdrous compound TTCHTS with water and, prior to spraying or the like, adding supplementary quantities of either lime or copper sulphate. Alternatively, such special formulations had to be made using the traditional manual technique as aforementioned.

Preferably, the copper sulphate salt is the pentahydrate (CuSO45H2O) and this is mixed with either hydroxide or oxide of calcium to complete the reactive formation of TTCHTS during the dry milling.

Preferably, the copper sulphate pentahydrate is mixed with of calcium oxide.

As will be appreciated, in the commercial manufacture of copper-based inorganic chemical compounds, there is no teaching from which the mere mixing of dry ingredients together and subjecting them to mechanical and attrition forces of milling would be expected to produce a chemical interaction resulting in a derived chemical compound. Various investigations and research into the chemical reactions which take place between calcium hydroxide and copper sulphate in solution have been published, and all of this known work is directed to the effects of the ions present in the water on the formation of the TTCHTS compound The traditional wet method of producing TTCHTS has survived for many years, and as far as we are aware, no steps have been taken previously to change the method other than by attempts at improving plant efficiency.

In order to understand the significant advance obtained by the invented method, it is useful here to refer to the traditional wet method as currently employed industrially. In this wet method, in order to obtain about 582 kilos of TTCHTS, a total quantity of water initially used for the process is 4700 litres which is added to the dry ingredients. 150 kilos of calcium hydroxide is suspended in 2000 litres of water and 675 kilos of copper sulphate pentahydrate is dissolved in 2700 litres of water. The reaction produces the yieid of TTCHTS and an additional 243 litres of water which is liberated from the copper sulphate pentahydrate. The weight to volume ratio of the suspended solids of the TTCHTS compound is only 11.8%, and these solids have to be recovered from the water and dried.In one method, there is a filtration stage using a rotary belt filter from which the solids in the form of a wet slurry with about 60% moisture are removed. The slurry is then dried by a continuous belt dryer. In another method, a spray drying technique is used in which the suspended solids and liquor are sprayed into a chamber with the water being flashed off and the solids being collected in a hopper or the like. In either case, in the drying stage, special control of temperature and atmosphere is required to prevent oxidation of the TTCHTS.

Accordingly, in this wet method, the dictating factor for the plant operation and efficiency is the initial water required-for the wet processing and the subsequent removal of both the initial water and the additional liberated water.

This invention has been derived from a radical new approach and discoveries made as a result of various experimental trials as will now be explained.

In the wet method, the chemical reaction to produce TTCHTS is:- 4CuSO45H2O+3Ca(OH)2=CuSO43Cu (OH)23CaSO4+20H20 The TTCHTS compound has no water of crystallisation, and the additional water liberated during the wet reaction is merely removed by filtration.

The molecular composition for TTCHTS can be derived by several other reaction routes based on theoretical reaction equations based on using copper sulphate salts and stoichiometric quantities of calcium oxide or calcium hydroxide. What was not known, and could not be predicted was whether any reaction would occur without the copper salt being in solution or whether water was required at all.

The trials were carried out by adding together stoichiometric quantities of a selected copper sulphate salt and either calcium oxide or calcium hydroxide to form a dry mixture which, after thorough mixing, was then subjected to a dry milling process in which the admixed ingredients were subjected to mechanical and attrition forces of milling with observations being made throughout the milling period to assess any reaction occurring. The observed milling period was limited to 48 hours as being the longest practical limit acceptable in an industrial process.

Each trial and the resuits thereof are now given with reference to the theoretical reaction equation and stoichiometric quantites.

Trial 1 Anhydrous copper sulphate and hydroxide of calcium.

4CuSO4 + 3Ca(OH)2 = CuSO43Cu(OH)23CaSO4 638.4 + 222.24 = 860.64 No reaction or change was noted after 48 hours of milling.

Trial 2 Monohydrate copper sulphate and hydroxide of calcium.

4CuS04 H2O + 3Ca(OH)2 = CuSO43Cu(OH)23CaSO4+4H20 710.4 + 222.24 = 860.64 +72 No reaction or change was noted after 48 hours of milling.

Trial 3 Monohydrate copper sulphate and oxide of calcium.

4CuS04 H20 + 3CaO = CuSO43Cu(OH)23CaS04 + H20 710.4 + 168.24 = 860.64 + 18 No reaction or change was noted after 48 hours of milling.

Trial 4 Pentahydrate copper sulphate and hydroxide of calcium.

4CuSO4 - 5H2O + 3Ca(OH)2 = CuSO43Cu(OH)23CaSO4 + 20H2O 998.40 + 222.24 = 860.64 + 360 A slow reaction was noted during milling and the green granular TTCHTS compound was formed during the 48 hours.

Trial 5 Pentahydrate copper sulphate and oxide of calcium.

4CuSO4. 5H2O + 3CaO = CuSO43Cu(OH)23CaSO4 + 17H2O 998.40 + 168.24 = 860.64 + 306 A reaction was noted during milling and this was faster than that of Trial 4. The green granular TTCHTS compound was formed during the 48 hours.

From the foregoing results of the Trials mentioned, it was surprising to find that there was a reaction to form TTCHTS in the mixtures as given for Trials 4 and 5 whilst no reaction was observed for the other mixtures of Trials 1, 2 and 3 which in theory should have been capable of producing TTCHTS if the reaction could be obtained in the "dry" state.

No explanation for the difference has been proved, but as a result of the trials an hypothesis is advanced which relates to the presence of water of crystallisation of the copper sulphate salt and the release of this from the salt when the dry mixture is subjected to the milling and the energy thereby imparted to the mixture. No water of crystallisation is present in the anhydrous copper sulphate of Trial 1 in which no reaction was noted. In both of the successful Trials 4 and 5 using the pentahydrate copper sulphate it is possible that the milling causes the pentahydrate to commence losing the water, that is firstly the weakest bonded molecule of water and this reacts with the oxide or hydroxide of calcium with a consequential exothermic effect increasing the temperature so that the next weakest bonded molecule of water is then released for further reaction and exothermic effect.This loss of the water of crystallisation of the pentahydrate copper sulphate can continue until all five water molecules have been liberated to complete the reaction with the calcium oxide or hydroxide to form TTCHTS.

Although in the mixtures of Trials 2 and 3 there is water of crystallisation present, it is likely that the initial energy levels obtained by our milling experiment were not sufficient to release the bond of the water molecule, and for this reason no reaction commenced. For these reasons, it appears that for a "dry" method to work to obtain the reaction required for TTCHTS to form, then the copper sulphate salt must be a hydrate and the milling be sufficient to cause liberation of water from the copper sulphate salt.

Further experimental trials based on the mixture of Trial 5 have been carried out, and it has been found that the reaction during energetic dry milling can be completed in about 30 minutes.

The TTCHTS compound as produced by the invented "dry" method of the foregoing Trials and for use as a fungicide is of the neutral type not containing any free copper sulphate which has not been converted by the reaction. For this it is important that the admixture of the two ingredients be in the stoichiometric quantities to complete the reaction. The reason for this is that when the TTCHTS compound is used as a fungicide and added to water, the copper level in the water must be controlled to avoid phytotoxicity in the crop to be sprayed or treated. In the "wet" method, this careful control of the quantities of the copper sulphate and lime was not essential and the control exercised was only one required to avoid copper sulphate in the liquor removed during filtration of the solids.

Nevertheless, by the invented "dry" method, it is possible to mix the dry ingredients in selected amounts other than the stoichiometric amounts in order to produce the TTCHTS compound with a deliberate excess of copper sulphate or calcium hydroxide or calcium oxide. By this means, a range of Bordeaux type mixtures to provide specific properties for the eventual application in suspension/solution in water can be achieved by a single simple method of manufacture.

The moisture content of the TTCHTS product must also be controlled, and although the compound is produced in the "dry" state, there is the water released during the reaction as explained above. As can be seen from the formulae given under Trials 4 and 5, a quantity of water is released which can be calculated as being equivalent respectively to 29.5% and 26.3% by weight of the compound. This moisture can be removed to reduce the moisture content to less than 4% by drying in any suitable manner, and such drying could be done by completing the reaction in the mill and after completion removing the product to a belt dryer. It is envisaged that the mill may incorporate extraction means for removing moisture either during or after the reaction caused by the milling.

From the foregoing, it will be appreciated that by using the invented "dry" method of manufacture, all of the problems associated with the traditional industrial "wet" method and the significant costs thereof are avoided.

Claims

1. A method of manufacturing tricalcium tetra copper hexahydroxide tetra sulphate (herein abbreviated to TTCHTS and otherwise known as Bordeaux Powder) characterised by mixing together in the dry state a copper sulphate hydrate salt either with the oxide or hydroxide of calcium, subjecting this dry mixture to milling for a reaction period wherein the reaction product of TTCHTS is formed in the presence of free water liberated from the copper sulphate hydrate salt during the milling.

2. The method according to claim 1 further characterised by a further finishing stage following the dry milling in which the TTCHTS reaction product is dried to reducethe moisturecontentto less than 4%.

3. The method according to claim 1 or Claim 2 wherein the copper sulphate hydrate salt is pentahydrate.

4. The method according to claim 3 wherein the copper sulphate pentahydrate is mixed with calcium hydroxide.

5. The method according to claim 3 wherein the copper sulphate pentahydrate is mixed with calcium oxide.

6. The method according to any one of the preceding claims wherein the copper sulphate hydrate salt is mixed with a stoichiometric amount of either oxide or hydroxide of calcium.

7. The method of manufacturing TTCHTS by dry millling substantially as hereinbefore described.