AU2004203872B2 - Method for producing ferrous picrate - Google Patents

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention tide: Method for producing ferrous picrate The following statement is a full description of this invention, including the best method of performing it known to us: Method for producing ferrous picrate Field of the invention The present invention relates to the manufacture of ferrous picrate and the 5 preparation of fuel additives containing ferrous picrate. More particularly the present invention relates to a method of ferrous picrate production of improved efficiency and which produces fewer impurities as compared with known methods. Background of the invention 10 In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date: (i) part of common general knowledge; or 15 (ii) known to be relevant to an attempt to solve any problem with which this specification is concerned. The cost of diesel fuel is a major contributor to the operating cost of mining or manufacturing sites that operate diesel driven equipment. Ideally, diesel engines would operate at 100% efficiency with the fuel burning completely and 20 instantaneously when the piston is at the top of the power stroke. At this point the cylinder volume is at its minimum and a maximum amount of energy (as heat) would be extracted from the fuel and used to power the engine. However, in reality, no fuel combustion is 100% efficient and even modern diesel engines have a thermal efficiency of only 35-40%. In practice, the fuel energy is made available 25 more gradually (by slower burn), cylinder pressure rises and falls well short of the ideal. Much energy is lost as heat from the engine exhaust. The rest of the energy is lost by radiation or is lost to the cooling system as it removes excess heat from the engine. 30 It seems unlikely that on-going engine design improvements can offer any major improvements to thermal efficiency. Although there has been an increase in engine performance, the performance characteristics of modem diesel fuel have declined markedly over recent years. However, improvements in fuel technology still offer potential area savings and for the past 2 decades, attempts have been made to chemically improve fuels. 5 For example, attempts have been made to chemically improve the overall combustion reaction by the addition of trace amounts of a ferrous picrate catalyst. Over the past two decades of commercial use by the mining industry in Australia, ferrous picrate use has resulted in fuel savings of 6-8% for mine mobile equipment and 3-5%'for large medium speed engines in power generation service. 10 An intensive study involving approximately fifty large diesel power generation sets was conducted by Fuel Technology Pty Ltd, a company specialising in combustion and fuel technology. The study showed that when using catalyst treated fuel, exhaust temperatures were reduced an average 9.2*C, under static load conditions. This result is interpreted to mean that use of the catalyst, 15 provides more useable heat from the fuel, so less fuel is used and less heat is wasted via the exhaust. In light of its efficacy, efforts have been made to develop more commercially attractive methods for producing ferrous picrate. For some purposes, such as addition to carbonaceous fuel, it is highly desirable that ferrous 20 picrate be substantially free from ferric compounds and other undesirable impurities. However it has proved difficult to produce ferrous picrate free from such impurities by a commercially acceptable method. Furthermore, most of the processes for purification described in the patent literature involve several steps, resulting in low yields and rendering the product 25 expensive. Another problem associated with the processes of the prior art is that they use toxic or hazardous reactants, and ferrous picrate and picric acid which in the solid state may be explosive. Reactants of this type require special handling with due regard to appropriate safety precautions, which further increases the cost of 30 ferrous picrate manufacture. Accordingly, efforts have been made to find commercially acceptable processes for manufacturing comparatively pure ferrous picrate. For example, Australian patent no 621243 (63110/90) describes a process for preparing ferrous picrate comprising reacting picric acid in solution in a straight or branched chain aliphatic alcohol and an aromatic solvent with iron carbonyl at a temperature between 10 and 120"C. This process has a high yield of ferrous picrate and has relatively few steps. However, the major disadvantage is that it uses iron carbonyl which is highly toxic and requires special equipment and expertise to handle, 5 factors that contribute significantly to the manufacturing cost and limit use of the process to specialised factories. Another example of a process for preparation of ferrous picrate is described in Australian patent no 624964 (57904/90). This process includes the steps of (a) reacting an aqueous solution of a ferrous salt with an alkali hydroxide to produce 10 a ferrous hydroxide precipitate, (b) removing water and by-products from the ferrous hydroxide; (c) adding the ferrous hydroxide and a straight or branched chain aliphatic alcohol to a solution of picric acid in an aromatic solvent from which water has been removed, to produce a solution of ferrous picrate, and (d) removing any insoluble material from the solution, wherein the steps are 15 performed under an inert atmosphere. Another method for producing ferrous picrate comprises reacting under non-oxidising conditions, ferrous carbonate free from ferric compounds with a water-free solution of picric acid in a solvent medium selected from an aromatic hydrocarbon solvent, a mixture of aromatic hydrocarbon solvents, a straight-or a 20 branched-chain aliphatic alcohol, a mixture of straight-and/or branched-chain aliphatic alcohols, and a mixture of straight-and/or branched-chain aliphatic alcohols with aromatic hydrocarbon solvents to produce a solution of ferrous picrate. Producers of industrial chemicals such as ferrous picrate continually 25 attempt to improve their processes and obtain commercial savings in terms of production costs and the input of time and energy to their processes. Some commercial savings can be derived from minimising the use or handling of hazardous materials, reducing energy input to the process and producing products of good purity so that the need for further the purification is minimised 30 or eliminated. Thus, an ongoing need exists for improvement to ferrous picrate production processes in terms of commercial efficiency, product purity and product storage stability. In particular a need exists for a process for producing ferrous picrate that is comparatively simple and commercially viable, yet produces comparatively few ferric compounds and other impurities by comparison with the ferrous picrate production methods of the prior art. A need also exists for the ferrous picrate product to exhibit storage stability when incorporated into carbonaceous fuels. Summary of the invention The present invention therefore provides in one embodiment a process for producing a ferrous picrate comprising the steps of (a) dissolving picric acid in a mixture of an aromatic hydrocarbon and an aliphatic alcohol in the presence of a trace amount of water and a source of 10 metallic iron to form a ferrous picrate solution, and (b) blending the ferrous picrate solution obtained from step (a) with an organic solvent to form a ferrous picrate having a water content not exceeding about 0.25% by volume. The product of the above process is useful as an additive to fuels. 15 The present invention provides in another embodiment a process for preparing a ferrous picrate additive for fuels, or a concentrate suitable for use in the preparation of a fuel additive, comprising the steps of (a) reacting metallic iron, picric acid and water together in a solvent containing a mixture of one of more aliphatic alcohols and another component selected from 20 aromatic hydrocarbons, aromatic paraffins and naphthenes or mixtures of one or more thereof to form a ferrous picrate solution, and (b) blending the ferrous picrate solution formed in step (a) with an organic solvent to form a fuel additive, or a concentrate suitable for use in the preparation of a fuel additive, having a water content not exceeding about 0.25% by volume. 25 The reaction may be carried out at a temperature in the range of from about 5 to 60'C. The reaction may suitably be carried out at ambient temperature. One of the advantages of the process of the present invention is that the reaction between metallic iron and picric acid can occur at room temperature so that it is unnecessary to add energy in the form of heat. This provides savings in 30 installation and running costs over the ferrous picrate processes of the prior art such as the carbonyl process. The reaction may be carried out under an inert atmosphere, using an inert gas that inhibits undesirable oxidation reactions and avoids fire risk. Any inert gas such as nitrogen or argon would provide a suitable inert atmosphere, although nitrogen is preferable to argon and other gases because it is comparatively less expensive. As used herein, the proportion of water in the reaction is expressed as the 5 % volume of water in the total volume of liquid. Without wishing to be bound by theory, it is believed that the trace amount of water catalyses the reaction between picric acid dissolved in the solvent and metallic iron. The trace amount of water present in step (a) may be between about 0.25 and 0.5 % by volume. 10 However, it is undesirable that the amount of water in the product of step (b) exceeds about 0.25% by volume because the ferrous picrate produced may exhibit storage instability. Preferably the proportion of water present in the product of step (b) is between about 0.01 and 0.12 % by volume. The picric acid used in the process of the present invention may be in the 15 form of a slurry of picric acid in water. Although dry picric acid is commercially available, it is explosive and therefore requires specialised handling techniques. One of the advantages of the process of the present invention is that the aqueous slurry of picric acid may be used instead of dry picric acid, minimising the need for specialised handling. 20 If an aqueous slurry of picric acid is used, the processes disclosed herein may include an initial step of extracting the picric acid into an aromatic hydrocarbon phase and separating the hydrocarbon phase from the aqueous phase. The separation may be carried out by any convenient method such as decantation, or by use of a separating funnel. 25 The metallic iron may be in any convenient form such as iron filings, mild steel sheet and/or steel wool. In a preferred embodiment, steel wool provides an inexpensive source of metallic iron and provides a large surface area to speed reaction with the picric acid. Suitable aromatic hydrocarbons that may be used in the processes of the 30 present invention may be chosen from the group comprising alkyl benzenes or benzene. In a preferred embodiment the aromatic hydrocarbon solvent is an alkyl benzene, such as toluene, xylene or solvents marketed under the trade name Solvesso (a trade name of Exxon Corporation) or equivalent products which include a mixture of commercial aromatic hydrocarbon fractions, or a combination of any thereof. The aromatic hydrocarbon solvent may additionally include other hydrocarbon species such as paraffins and naphthenes, or both. Suitable aliphatic alcohols may be chosen from the group including straight- or branched-chain aliphatic alcohols or mixtures thereof. Typically the 5 straight or branched chain aliphatic alcohols are from about C 2

-C

13 in length. In one embodiment, the alcohol is chosen from the group consisting of iso-propanol, n.butanol, iso-octanol, tri-decanol, and mixtures of any thereof. The process of the present invention may further include the removal of any unreacted metallic iron, such as any unreacted steel wool provided to the 1) process as a source of metallic iron, and the removal of any other insoluble matter. For example, steel wool can include traces of silicon, carbon and metals other than iron. These traces of silicon, carbon and metals other than iron may be present as a fine black precipitate in the reaction which may be removed by filtration, decantation or other convenient method. 15 The organic solvent may be chosen from the group including aromatic hydrocarbons, mixtures of aromatic paraffins and naphthenes, one or more aliphatic alcohols, or mixtures thereof. For example, the solvent may be toluene, xylene or a commercial product comprising a mixture of aromatic hydrocarbons and paraffins and naphthenes or distillate or a straight- or branched-chain aliphatic 20 alcohol or a solution of picric acid in an organic solvent, or any mixture thereof. The present invention provides in one particularly preferred embodiment a process for preparing a ferrous picrate additive comprising the steps of (a) reacting metallic iron in the form of steel wool, picric acid and water together in a solvent containing a mixture of one of more aliphatic alcohols and 25 another component selected from aromatic hydrocarbons, aromatic paraffins and naphthenes or mixtures of one or more thereof to form a solution of ferrous picrate, (b) removing any unreacted steel wool and other insoluble matter from the ferrous picrate solution formed in step (a), and 30 (c) adding the ferrous picrate solution from step (b) to a component selected from a sufficient quantity of an aromatic hydrocarbon, a quantity of a mixture of a solvent containing aromatic hydrocarbons, aromatic paraffins and naphthenes, a solution of picric acid in an aromatic hydrocarbon or in a solvent containing aromatic hydrocarbons, aromatic paraffins and naphthenes, and a quantity of an aliphatic alcohol, or any mixture of the foregoing, to form a fuel additive, or a concentrate suitable for use as a fuel additive, having a water content not exceeding about 0.25% by volume. The present invention also provides a product produced by the above 5 process. Description of Preferred Embodiment The present invention will now be further described with reference to the following non-limiting examples: 10 EXAMPLE 1 Step 1. Preparation of picric acid solution Wet picric acid consisting of 15g of dry picric acid and 15g of water were added to 500mL of Solvesso 100 and the mixture stirred gently until the picric acid was in solution. The mixture was poured into a glass separating funnel and 15 allowed to stand until the aqueous phase had settled to the bottom and the supernatant organic phase was clear. The aqueous phase was then run off into another container for disposal. Approximately 0.1 % by volume of water remained in the organic phase. Step 2. Manufacture of Fuel Additive Concentrate. 20 To a one litre glass bottle fitted with a solvent resistant screw cap 400ml of the above picric acid solution, 100ml of butanol HFP, 2ml of water and 2.5g of steel wool were added. The temperature of the liquid was about 22 0 C. The atmosphere above the liquid was replaced with nitrogen by means of a rubber tube attached to a steel bottle of nitrogen, the rubber tube removed and the glass 25 bottle capped. The bottle and contents were then placed in a horizontal position on a laboratory roller and rotated at a speed of approximately 30 revolutions per minute. Within one minute, the liquid had assumed a definite green colour indicating that a reaction between steel wool and the picric acid had commenced 30 with the formation of ferrous picrate which is green in colour. Rolling was continued for two hours and another sample of the liquid was withdrawn. The ferrous iron content of the liquid was determined by the 1.10 phenanthroline procedure. The result was 1080 mg of ferrous iron per litre.

Rolling was continued for a further 22 hours and another sample was withdrawn. The ferrous iron content of the liquid was found by chemical analysis to be 2010 mg per litre. Step 3. Filtration of the Concentrate. 5 The- contents of the glass bottle were then filtered through a stainless steel screen on 10 micron mesh size, thus removing the unreacted material including the excess steel wool and the unreacted non-iron components of the steel wool such as carbon, silicon and metallic carbides. As this filtration step is rapid the nitrogen blanket was dispensed with. The yield was 490 ml. 10 Step 4. Blending The liquid obtained in Step 3 was suitable for use as an additive to carbonaceous fuel. However as the water content was in excess of that deemed to be desirable for stability in storage it was blended with a mixture of 100ml of butanol HFP and 100ml of the picric acid solution from Step 1. 15 The water content of the final product was approximately 0.25 % by volume. EXAMPLE 2 A concentrate was prepared in substantial accordance with Steps 1, 2 and 3 above with the exceptions that the period of reaction was 3 hours and the water 20 was replaced with the same quantity of the aqueous phase retained from Step 1. The ferrous iron content of the resulting liquid was found to be 1200 mg/l. In the chemical reaction in Step 2, picric acid combined with iron extracted from the steel wool to form ferrous picrate, thus reducing the free picric acid level of the liquid. One part by weight of iron combines with approximately 9 parts by 25 weight of picric acid. It has been established that water content not exceeding about 0.25 %by volume, free picric acid level of at least about 1.5% w/v and butanol content of at least about 12% by volume is necessary for product stability. A product with a ferrous iron content of 560 mg/l, suitable for use as an 30 additive to carbonaceous fuel, and which was stable in storage was prepared in the following manner. Fuel Additive Concentrate (1200mg/L ferrous iron) 234ml Picric acid solution from Step 1 100ml Butanol HFP 16ml Solvesso 100 150ml Total 500ml EXAMPLE 3 5 Step 1 - Preparation of picric acid solution 1000 litres of Solvesso 100 or equivalent aromatic solvent was pumped into a 1000 litre capacity reactor tank fitted with an air operated motor driving twin mixing paddles. Wet picric acid consisting of 30 kgs dry weight was carefully added to the 10 solvent via the manhole on the tank top with the mixing paddles rotating at 205 rpm and operating at an air pressure 140 kPa. After addition of the picric acid, the top manhole was closed and a nitrogen blanket injected into the air space above the solvent liquid. The mixture was stirred for 2 hours and then allowed to settle for 15 approximately one hour before the water was drained from the conical bottom of the tank via a valve. The water was drained through a glass chamber to enable the partition between water and solvent to be observed. When the water had been partitioned a representative sample was drawn from the tank sample point and submitted to the laboratory for a titration test to 20 determine the free picric content of the mixture which is theoretically 3% wt/v. The picric acid solution was then drained and stored in a bulk container. Step 2 - Manufacture of Fuel Additive Concentrate 750 litres of picric acid solution was pumped into a reactor tank followed by 250 litres of n-Butanol. Metallic iron in the form of steel wool was placed into 25 a stainless steel carrier assembly and inserted into the tank via the top manhole. The carrier assembly was held in a Vee formed block with the steel wool suspended in the solvent mixture. Water which had been drained from the tank in step 1 upon completion of picric acid solution manufacture was added to the reactor tank at the rate of 0.1% 30 (that is, for each 1000 litres of solvent one litre of water was added), dependent upon the moisture content of the picric acid solution. Had the reaction stalled a further 500 mls to 1 litre of water could have been added.

Following addition of all components, the manhole cover was closed and a nitrogen blanket introduced. The mixing paddles were activated at a rotation speed of 160 rpm by the air motor operating on an air pressure of 80 kPa. After approximately one hour stirring, drawing of samples commenced. 5 Drawing was continued until the samples were observed to be very dark green colour at which time a sample was submitted for analysis of ferrous iron content by spectrophotometry. Once the ferrous iron level reached 1200 - 1500 mg/I the system was shut down. The time taken to reach this concentration of ferrous iron was 10 approximately 24 hours. Step 3 - Blending The storage stability of the raw concentrate produced in Step 2 is low and it was imperative to blend away to a range of finished products or to lower ferrous iron level concentrate in the range 470 - 600 mg/. 15 The volume of concentrate required for the desired blend was calculated and pumped from the reactor tank via a 10-micron filter into a blend tank. Additional picric acid solution was added together with n-butanol and Solvesso 150 or equivalent aromatic solvent. The volume and relative proportions of components added can be varied according to the concentration of ferrous picrate 20 being produced. The blended products were subjected to quality control checks to precisely confirm the -ferrous -iron level before being pumped into appropriate containers for storage and/or despatch for sale. The word 'comprising' and forms of the word 'comprising' as used in this 25 description does not limit the invention claimed to exclude any variants or additions. Modifications and improvements to the invention will be readily apparent to those skilled .in the art. Such modifications and improvements are intended to be within the scope of this invention.

Claims (20)

1. A process for producing a ferrous picrate, comprising the steps of: (a) dissolving picric acid in a mixture of an aromatic hydrocarbon and an aliphatic alcohol in the presence of a trace amount of water and a source of 5 metallic iron to form a ferrous picrate solution; and (b) blending the ferrous picrate solution obtained from step (a) with an organic solvent to form a ferrous picrate having a water content not exceeding about 0.25% by volume.

2. A process according to claim 1, wherein the process is performed in an 13 inert atmosphere.

3. A process according to claim 2, wherein said inert atmosphere comprises nitrogen or argon.

4. A process according to any one of claims 1 to 3, wherein said mixture of an aromatic hydrocarbon and an aliphatic alcohol is a solvent comprising a mixture of 15 one or more aliphatic alcohols and other components selected from the group consisting of aromatic hydrocarbons, aromatic paraffins and naphthenes, and mixtures of any thereof.

5. A process according to claim 4, wherein the aromatic hydrocarbon is an alkyl benzene. 2n

6. A process according to claim 5, wherein the alkyl benzene is selected from the group consisting of toluene, xylene or a solvent identified by the trade name Solvesso or equivalent products containing a mixture of commercial aromatic hydrocarbon fractions, or a combination of any thereof.

7. A process according to any one of claims 1 to 6, wherein the aliphatic 25 alcohol is a C 2 -C, 3 straight- or branched- chain aliphatic alcohol.

8. A process according to claim 7, wherein the aliphatic alcohol is selected from the group consisting of iso-propanol, n. butanol, iso-octanol, tri-decanol, and mixtures of any thereof.

9. A process according to any one of claims 1 to 8, wherein the trace amount of water in step (b) is present in the range of from 0.01 to 0.12% by volume of water in the total volume of liquid.

10. A process according to any one of claims 1 to 9, wherein the source of metallic iron is steel wool.

11. A process according to any one of the preceding claims, wherein the process is carried out at a temperature in the range of from 5 to 60"C.

12. A process according to any one of the preceding claims, further comprising the step of removing any unreacted metallic iron and other insoluble matter from 10 the ferrous picrate solution.

13. Ferrous picrate produced by a process according to any preceding claim.

14. A process for producing an additive for fuels, or a concentrate suitable for use in the preparation of a fuel additive, comprising the steps of: (a) reacting metallic iron, picric acid and water together in a solvent 15 containing a mixture of one of more aliphatic alcohols and another component selected from aromatic hydrocarbons, aromatic paraffins and naphthenes or mixtures of any thereof, to form a ferrous picrate solution, and (b) blending the ferrous picrate solution formed in step (a) with an organic solvent to form a fuel additive, or a concentrate suitable for use in the 20 preparation of a fuel additive, having a water content not exceeding about 0.25% by volume.

15. A process for producing an additive for fuels, or a concentrate suitable for use in the preparation of a fuel additive, comprising the steps of: (a) reacting metallic iron in the form of steel wool, picric acid and water 25 together in a solvent containing a mixture of one of more aliphatic alcohols and another component selected from aromatic hydrocarbons, aromatic paraffins and naphthenes or mixtures of any thereof, to form a ferrous picrate solution, (b) removing any unreacted steel wool and other insoluble matter from the ferrous picrate solution, and 30 (c) adding the liquid produced from step (b) to a component selected from a sufficient quantity of an aromatic hydrocarbon, a quantity of a mixture of a solvent containing aromatic hydrocarbons, aromatic paraffins and naphthenes, a solution of picric acid in an aromatic hydrocarbon or in a solvent containing aromatic hydrocarbons, aromatic paraffins and naphthenes, and a quantity of an aliphatic alcohol, or any mixture of the foregoing, to form a fuel additive, or a concentrate suitable for use in the preparation of a fuel additive, having a water 5 content not exceeding about 0.25% by volume.

16. A liquid additive, or a concentrate suitable for use in the preparation of a fuel additive, produced in accordance with the process of claim 14 or 15.

17. A process for producing a ferrous picrate, substantially as hereinbefore described and with reference to any one of the Examples. 10

18. Ferrous picrate produced by a process which is substantially as hereinbefore described and with reference to any one of the Examples.

19. A process for producing an additive for fuels, or a concentrate suitable for use in the preparation of a fuel additive, substantially as hereinbefore described and with reference to any one of the Examples. 15

20. A liquid additive, or a concentrate suitable for use in the preparation of a fuel additive, substantially as hereinbefore described and with reference to any one of the Examples. Fuel Technology Pty Ltd 12/08/2004