The present disclosure provides a process for treating spent filter earth containing oil obtained from a metal rolling process. In particular, the process relates to recovery of oil and filter earth which can be reused in the rolling process.

BACKGROUND

Lubrication is an essential part of all aluminium fabricating operations through the metal working processes. One of the most important ways of converting aluminium from cast slab/ingot into a usable industrial form is by hot, cold and foil rolling. These rolling processes make it possible to reduce an ingot of metal to plate gauges, sheet gauges and foil gauges.

During the cold and foil rolling process, lubricants lubricate the interface between the rolls and sheet metal, and they cool the metal as it passes between the rolls. After prolonged use, the lubricants get contaminated with finely divided metal particles, metal oxide particles, and other extraneous matter such as mill dirt. Due to such contamination, the usefulness of the lubricants is reduced as the contaminants act as an undesired abrasive. Therefore, it is necessary to remove the contaminants from the lubricant so that the same can be reused in the rolling process. In order to remove the contaminants from the lubricants, generally, filtration systems are used for reclamation of oils. These filtration systems employ a particulate filter medium using diatomaceous earth and/or activated fuller's earth. The used diatomaceous earth and/or activated fuller's earth (known as spent filter earth) is usually discarded as a waste after being used for filtration.

The discarded filter earth poses an environmental hazard due to the residual oil content (approx. 30-40%; mainly HNP i.e. Heavy Normal Paraffin). Additionally, disposal cost of hazardous waste is higher than that of non-hazardous waste. During disposal of the spent filter earth, a large amount of oil is lost along with the filter earth.

Further, due to disposal of the spent filter earth, fresh filter earth for filtration system is required which increases the overall cost involved in the rolling process. US Patent No. 6,059,976 teaches a process for reclaiming and recycling oil/water mixtures. This document provides a process for separating oil from contaminated oil water mixture (lubricant) using acid wash without filtration process. The oil recovered by the process disclosed in this document may not be suitable for reuse and the quality of the oil may be reduced. This document is silent on recovery of oil from spent filter earth and does not address situations when filter earth containing oil is obtained as a waste material. Therefore, there is a need for an efficient, cost effective process for separation and recovery of oil and filter earth from spent filter earth containing oil. Further, there is a need for a process which justifies the cost of recovery of oil and/or filter earth and provides reusable oil and reusable filter earth. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 indicates a graphical representation of the relationship between concentrations of sulphuric acid with percentage oil recovery on the basis of the experiment no. 1 to 8 in accordance with the present invention.

Figure 2 is an FTIR analysis (spectrum) of the recovered oil (in accordance with the present process) and fresh oil used in rolling process.

Figure 3 illustrates result of GC analysis conducted to analyze carbon chain distribution of the recovered oil (in accordance with the present process).

Figure 4 illustrates graphical representation of the experimental data of Table 5 in accordance with the present invention. Figure 5 and 6 illustrates SEM EDX analysis of fresh Hyflo Supercel and Fresh

Tonsil respectively.

Figure 7 illustrates comparison of clarity of the Waste HNP generated during the rolling process with the filtrate obtained by passing the waste HNP through a fresh filter earth and through recovered filter earth (in accordance with the present invention). Figure 8 illustrates comparison of clarity of the Waste HNP having carbon with the filtrate obtained by passing the waste HNP (having carbon) through a fresh filter earth and through recovered filter earth (in accordance with the present invention).

Figure 9 illustrates graphical representation of the experimental data of Table 8 in accordance with the present invention. Figure 10(a) to (e) illustrates SEM EDX analysis of recovered filter earth after 1 ^st , 2 ^nd , 3 ^rd , 4 ^th and 5 ^th recycle (in accordance with the present process) respectively.

SUMMARY A process for treating spent filter earth having oil is disclosed. The process comprising mixing the spent filter earth with water and an acid, such that the acid is in a range of 1-4% (w/v), heating the mixture obtained in the previous step, allowing the mixture to stand to facilitate formation of separate layers of filter earth, water and oil, recovering the filter earth, and recovering oil.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to embodiments 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 disclosed process, and such further applications of the principles of the invention therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to "one embodiment" "an embodiment" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase "in one embodiment", "in an embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The phrase "spent filter earth" used herein refers to waste diatomaceous earth, waste fuller's earth or combination thereof obtained from a rolling process.

The present disclosure provides a process for treating spent filter earth containing oil. The process comprising mixing the spent filter earth with water and an acid, such that the acid is in a range of 1-4% (w/v), heating the mixture and allowing the mixture to stand which facilitates formation of separate layers of filter earth, water and oil. The process further comprising recovering the filter earth and recovering oil.

In accordance with an embodiment, firstly the acid is mixed with water at room temperature to obtain an acid solution, such that the pH of the acid solution is in the range of 0.5 to 2.5. Spent filter earth containing oil is added to the acid solution at room temperature and the pH of thus obtained mixture is in the range of 0.5 to 2.5.

In accordance with an embodiment, the acid is selected from a group comprising hydrochloric acid, sulphuric acid and phosphoric acid. In accordance with an embodiment, the heating of the mixture of spent filter earth, water and acid is carried out at a temperature in a range of 70-90 °C for a time period in a range of 30 - 120 minutes. Such heating of the mixture is carried out under constant stirring.

In accordance with an embodiment, the recovery of the filter earth is carried out by filtration and the filtrate comprising oil and water is further processed to separate oil for reuse (recycle or regeneration). By way of an example, the filtrate is kept in a separating funnel and the upper layer of oil is collected to obtain recovered oil.

In accordance with an embodiment, the process further comprising washing of the recovered oil with water to remove inorganic acidity followed by alkali treatment of the washed oil to remove organic acidity. By way of an example, alkali treatment is carried out using potassium hydroxide. After the alkali treatment, the recovered oil is subjected to distillation (removal of moisture and purification) to obtain oil which can be reused in the rolling process.

In accordance with an embodiment, the process further comprising washing and drying of the recovered filter earth followed by heating at a temperature in a range of 750- 800 °C to obtain activated filter earth which can be reused in a filter for the removal of contaminants from the oil used in rolling process.

The disclosed process has an efficiency of approximately 40 - 80% for oil recovery. The quality of the recovered oil is comparable to the fresh oil used in a rolling process. While calculating the percentage of oil recovery from the disclosed process, firstly total quantity of oil present in the spent filter earth is calculated by solvent extraction method. The obtained quantity of oil is considered as 100%. Therefore, in view of such quantity percent oil recovery obtained from the disclosed process is calculated. For example, if 35 gm. of oil is recovered from 100 gm. of spent filter earth by solvent extraction method, then this 35 gm. of oil will be considered as 100% oil present in the spent filter earth. Subsequently, by using the present process if 29 gm. of oil is recovered then the percent oil recovery is 82.85% with respect to the quantity of oil calculated by solvent extraction method. The activated filter earth is optimum for reuse in the rolling process. Further, the acid treatment of the spent filter earth in accordance with the disclosed process facilitates opening of the pores of the filter earth and the same attributes to increase in porosity and life of the recovered filter earth. Porosity of filter earth and oil flow rate through the same are linked. Higher the porosity better will be the oil flow rate. The activated filter earth can be reused multiple times after treating it in accordance with the disclosed process subsequent to each use. In accordance with an embodiment, the activated filter earth can be reused upto 5 times after treating it in accordance with the disclosed process subsequent to each use.

The following example(s) are exemplary and should not be understood to be in any way limiting. The following examples are conducted using fuller earth as a filter media and the phrase "filter earth" used in the following examples refers to "fuller's earth".

Example 1:

The following experiments (Table 1) were conducted to establish relationship between percent oil recovery and concentration of sulphuric acid used in the present process: Table 1

Further, it has been noted that with the increase in the concentration of the sulphuric acid, the colour of the recovered oil and the recovered filter earth improves. Figure 1 indicates a graphical representation of the relationship between concentrations of sulphuric acid with percentage oil recovery on the basis of the above listed experiment no. 1 to 8.

Example 2:

The following experiments (Table 2) were conducted to establish relationship between quality of recovered oil and concentration of sulphuric acid used in the present process: Table 2

Example 3:

FTIR analysis is provided in Figure 2 which illustrates that the quality of the recovered oil is comparable to the fresh oil used in metal rolling process. The only difference in the peaks generated during the analysis is that in case of the recovered oil a peak has been observed at a wavenumber of 1715, which is due to the conversion of fatty alcohol to fatty acid due to acid treatment.

Further GC analysis was conducted to analyse carbon chain distribution of the recovered oil (in accordance with the present process). Result of GC analysis is illustrated in Figure 3. Comparative results of carbon chain distribution in fresh oil and in the recovered oil are summarized below in Table 3: Table 3

HNP carbon chain

GC Analysis (in recovered

Carbon Chain Distribution distribution Specs (in fresh

oil)

HNP)

<C-13 1 % Max Nil

C-13 15 % Max Nil

C-14 55 % Min 68.75

>C-14 30 % Max 31.24

Fresh Heavy Normal Paraffin (HNP) is nothing but paraffinic oil with hydrocarbons of different chain length e.g. C-13, C-14, C-16 etc. In the fresh HNP there is C-13 up to 15% maximum but during rolling operation, lot of C-13 will get evaporated due to its lower boiling point and if we check the composition of HNP which is continuously used in rolling we will find that C-13 concentration is almost nil. Hence the oil recovered from spent filter earth having composition of C- 14=68.75% & > C- 14=31.24 can be used again without any problem. Example 4:

Following experiments (Table 4) were conducted to calculate the gross calorific value of the recovered filter earth obtained from the present process and the spent filter earth generated as such from the rolling process:

Table 4

A Spent filter earth as such 2793

1 400 1.1 100 40.34% 598

2 400 2.3 100 43.21% 1230**

3 400 3 100 65.63% 389

4 400 4.2 100 78.39% 435

5 400 5 100 80.32% 436

6 400 10 100 80.97% 415

7 400 15.3 100 81.55% 385

8 400 20.1 100 81.89% 1069**

** To be rechecked

It can be noted that spent filter earth generated from the rolling process has a calorific value of 2793 cal/gm and after the treatment of the spent filter earth in accordance with the present process the calorific value get reduced to about 400 cal/gm. From the above listed examples (including Example 1 to 4), it is clear that the experiment Nos. 5 and 6 are optimum in which percent oil recovery is about 80.97% and the recovered filter earth has a calorific value of about 436 cal/gm.

Example 5: Treatment of recovered filter earth:

After separation of the spent filter earth from the layers of oil and water by filtration, the obtained spent filter earth is subjected to washing with water under vacuum in a funnel followed by filtration. After filtration, spent filter earth is dried under vacuum and subjected to heating at a temperature in a range of 750 to 800 °C. Thus obtained spent filter earth is then allowed to cool at room temperature and then the same can be reused in the purification of oil of rolling process. Example 6:

Activity and porosity of recovered filter earth have been checked by the following methods:

1. Porosity of recovered filter earth by measuring oil flow rate through filter beds at constant pressure;

2. Activity of recovered filter earth is measured by comparing the reduction of acidity and colour of the oil passed through said recovered filter earth.

Results of Method 1:

Following table 5 provides comparative analysis of flow rate and filtration time for recovered filter earth vis-a-vis fresh filter earth.

Table 5

100 1932 0.0518 3826 0.0261

Average Flow

0.052 0.027 Rate

Figure 4 illustrates graphical representation of the above experimental data (Table 5). It is observed that oil flow rate for recovered filter earth is higher i.e. 0.052 ml/sec as compared to oil flow rate through fresh filter earth i.e. 0.027 ml/sec, which indicates that acid treatment of the spent filter earth opened the pores of the filter earth and the same attributes to increase in porosity of the spent filter earth and an increase in life of the filter earth.

Figure 5, 6 and 10(a) illustrates SEM EDX analysis (Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy) of fresh Hyflo Supercel (commercially available filter earth), Fresh Tonsil (commercially available filter earth) and recovered filter earth (in accordance with the present process) respectively.

Further, the following table 6 provides elemental composition obtained by SEM EDX analysis of fresh Hyflo Supercel (commercially available filter earth), Fresh Tonsil (commercially available filter earth) and recovered filter earth (in accordance with the present process).

Table 6

Results of Method 2;

Contaminated oil (Waste HNP) generated during the rolling process is passed through a fresh filter earth and through recovered filter earth (in accordance with the present invention) and the following with regard to the acidity of the oil is observed:

Table 7

It has been observed that the acidity of the contaminated oil is reduced by same amount and the clarity of the filtered oil in both the cases is comparable (as illustrated in Figure 7). Furthermore, an experiment was conducted in which 1 gm of activated carbon

(mesh size 12 by 40) is mixed with 100 ml of fresh oil (fresh HNP) and the same is filtered through fresh filter earth and recovered filter earth (in accordance with the present process) separately. 5 gm of filter earth in both the cases is taken to form a pre bed and filtration area is 3.14 sq.cm. Clarity wise no difference is observed in the filtrates from recovered filter earth and fresh filter earth (as illustrated in figure 8).

Example 7:

The porosity level of filter earth after l ^st reuse then after 2 ^nd , 3 ^rd 4 ^th and 5 ^th reuse were analyzed (Table 8 below). The 2 ^nd ,3 ^rd , 4 ^th and 5 ^th reuse (or regeneration cycle) was carried out after treatment of the spent filter earth in accordance with the disclosed process subsequent to each use. Changes in the rate of filtration were observed after each reuse. Rate of filtration was decreased significantly after 3 ^rd regeneration cycle of filter earth. Depending upon the required filtration rate, one may choose number of regeneration cycles for the recovered filter earth. Figure 9 illustrates graphical representation of the experimental data (Table 8). Table 8

Decrease in filtration rate might be due to porous structure breakage during the processing of fuller earth. The same can be observed by the SEM analysis of samples i.e. fresh Hyflo Supercel (Figure 5), Fresh Tonsil (Figure 6) and recovered filter earth after 1 ^st , 2 ^nd , 3 ^rd , 4 ^th and 5 ^th recycle (Figure 10(a) to (e)) respectively. Further, on the basis of said SEM analysis the composition of the recovered filter earth (after 1 ^st , 2 ^nd , 3 ^rd , 4 ^th and 5 ^th recycle), fresh Hyflo Supercel and fresh Tonsil is provided below in Table 9: Table 9

SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW

A process for treating spent filter earth having oil, comprising mixing the spent filter earth with water and an acid, such that the acid is in a range of 1-4% (w/v), heating the mixture obtained in the previous step, allowing the mixture to stand to facilitate formation of separate layers of filter earth, water and oil, recovering the filter earth, and recovering oil.

Such process(s), wherein the spent filter earth is obtained from a metal rolling process.

Such process(s), further comprising distilling the recovered oil for reuse. Such process(s), wherein prior to the distillation, washing of the recovered oil is carried out with water to remove inorganic acidity followed by alkali treatment of the washed oil to facilitate removal of organic acidity.

Such process(s), wherein the distilled recovered oil is reused in metal rolling process.

Such process(s), further comprising washing and drying of the recovered filter earth followed by heating at a temperature in a range of 750-800 °C to obtain activated filter earth for reuse.

Such process(s), wherein the spent filter earth has been reused at least twice after treating and activating subsequent to each use in a metal rolling process.

Such process(s), wherein acid is selected from a group comprising hydrochloric acid, sulphuric acid and phosphoric acid.

Such process(s), wherein heating of the mixture of spent filter earth, water and acid is carried out at a temperature in a range of 70-90 °C. Such process(s), wherein heating of the mixture of spent filter earth, water and acid is carried out for a period in a range of 30-120 minutes.

INDUSTRIAL APPLICABILITY

The present process provides a recovery of high quality oil which can be reused as a lubricating oil in the rolling mill processes. Further, the present process also provides recovery of a high quality, highly porous spent filter earth material which can be reused as a filter material in the rolling process for purification of lubricating oils. In particular, the amount of 1-4% (w/v) of suphuric acid provides an optimum and cost-efficient process wherein the cost of recovery of oil and filter earth is justified on account of obtaining reusable material. Utilization of the present process reduces the overall expenses involved in the rolling process. The process disclosed is highly efficient and the percent recovery of oil is approximately 80%.