Description:FIELD
The present disclosure relates to a process for removal of carbonyl impurities from a hydrocarbon stream.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Mixed C4 hydrocarbon stream: The term “mixed C4 hydrocarbon stream” refers to C4 hydrocarbon stream obtained from a naphtha cracker, a gas steam cracker or a gas-naphtha dual cracker, which consists of C4 hydrocarbons such as butadiene, along with the other hydrocarbons.
Condensate: The term “condensate” refers to the water available on-site, which is obtained by the conditions of high pressure steam and medium pressure steam. The condensate water is commonly used to make the processes economical.
Carbonyl washer column: The term “carbonyl washer column” also known as “a scrubber”, refers to a column that is commonly used for removing the carbonyl impurities from the mixed C4 stream.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Butadiene is an important industrial chemical, which is used in the manufacturing of synthetic rubber, latex paints, nylon, and the like. Butadiene is also a commonly used chemical in the Diels-Alder condensation for the synthesis of many diverse compounds. Butadiene is generally recovered from a mixture of C4 hydrocarbon streams obtained from naphtha or gas steam crackers. During recovery of the butadiene, small amounts of carbonyl-containing impurities (e.g., acetaldehyde, and acetone) are observed. These impurities have adverse effects on subsequent processes in which the butadiene is used as a raw material. So, it becomes important to remove these carbonyl impurities from the mixture of C4 hydrocarbon streams.
Conventionally, the organic carbonyl-containing compounds are removed from mixed C4 hydrocarbon stream with a "scrubbing solution” such as aqueous hydrazine wash. For this purpose, a carbonyl washer column is used in a butadiene (BD) plant to remove the carbonyl impurities. However, the aqueous hydrazine wash does not effectively remove all the carbonyl impurities present in the mixed C4 hydrocarbon stream and fails to meet the desired specification of less than 10 ppm of aldehyde in the mixed C4 hydrocarbon stream.
Further, mixed C4 hydrocarbon stream contains carbonyl impurities such as acetaldehyde, acetone, and other carbonyl compounds that can efficiently be removed by treating with alkali metal bisulfite. However, direct addition of the alkali metal bisulfite to the column may lead to corrosion due to acidic nature.
The composition of mixed C4 hydrocarbon stream varies with the process of plant operation i.e., from a gas cracker, a naphtha cracker, or a gas-naphtha dual cracker. The gas cracker product stream has a lesser percentage of C4 hydrocarbons as compared to the naphtha cracker product. So, the naphtha cracker product stream is preferably used for the butadiene production, which has high amount of C4 hydrocarbons in addition to compounds such as ethylene, propylene, and other hydrocarbon. Further, depending on the process optimization, a mix of the naphtha cracker product stream and the gas cracker product stream can be processed for producing the mixed C4 hydrocarbon streams.
The product stream from the gas cracker has high amount of carbonyl feed (> 350 ppm). Further, the product stream from the gas cracker is when mixed with the product stream of the gas-naphtha dual cracker, the mixed C4 hydrocarbon stream so obtained can have carbonyl content of more than 500 ppm. In such cases, the carbonyl removal efficiency from the mixed C4 hydrocarbon stream in the washer column does not meet the product specifications. The carbonyl impurities of <10 ppm in the product C4 hydrocarbon stream is desired for butadiene processes.
Furthermore, an increase in the amount of carbonyl impurities in the mixed C4 hydrocarbon stream conventionally increases the consumption of a fresh condensate in the carbonyl washer column. Further, increased consumption of the fresh condensate corrodes the processing units.
Therefore, there is felt a need for an efficient process for the removal of carbonyl impurities from a mixed C4 hydrocarbon stream that mitigate the drawbacks mentioned herein above or at least provide a useful alternative.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the background or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for the removal of carbonyl impurities from a mixed C4 hydrocarbon stream.
Still another object of the present disclosure is to provide a process for the removal of carbonyl impurities from a mixed C4 hydrocarbon stream that has high amounts of the carbonyl impurities.
Yet another object of the present disclosure is to provide an efficient process for removal of the carbonyl impurities from mixed C4 hydrocarbon stream.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a process for removal of carbonyl impurities from a mixed C4 hydrocarbon stream. The process comprising mixing the mixed C4 hydrocarbon stream comprising the carbonyl impurities, and a predetermined amount of an aqueous scrubbing solution having a pH in the range of 6.5 to 7.0, in a carbonyl washer column maintained at a predetermined temperature and at a predetermined pressure to obtain an aqueous phase comprising the carbonyl impurities in the form of water-soluble reaction products and an organic phase comprising a C4 hydrocarbon stream having reduced or no carbonyl impurities.
In accordance with the embodiments of the present disclosure, the carbonyl impurities comprise acetaldehyde and acetone.
In accordance with the embodiments of the present disclosure, the mixed C4 hydrocarbon stream is obtained from at least one of a naphtha cracking process, a gas stream cracking process and a gas-naphtha dual cracking process.
In accordance with the embodiments of the present disclosure, the aqueous scrubbing solution is prepared by using at least one selected from distilled water and condensate water.
In accordance with the embodiments of the present disclosure, the aqueous phase and the organic phase are colorless.
In accordance with the embodiments of the present disclosure, the aqueous scrubbing solution has a pH is in the range of 6.7 to 6.8.
In accordance with the embodiments of the present disclosure, the aqueous scrubbing solution comprises 1 mass% to 5 mass% of an alkali metal salt solution.
In accordance with the embodiments of the present disclosure, the alkali metal salt is at least one selected from the group consists of sodium bisulfite, potassium bisulfite, sodium hydroxide, and potassium hydroxide.
In accordance with the embodiments of the present disclosure, the carbonyl impurities in the mixed C4 hydrocarbon stream is in the range of 50 ppm to 700 ppm.
In accordance with the embodiments of the present disclosure, the mixed C4 hydrocarbon stream is fed to the carbonyl washer column at a feed rate in the range of 15 tons/hour to 20 tons/hour.
In accordance with the embodiments of the present disclosure, the aqueous scrubbing solution is fed to the carbonyl washer column at a feed rate in the range of 150 kg/hour to 300 kg/hour.
In accordance with another embodiment of the present disclosure, the aqueous scrubbing solution is fed to the carbonyl washer column at a feed rate in the range of 160 kg/hour to 250 kg/hour.
In accordance with an embodiment, a stoichiometric ratio of the carbonyl impurities to the aqueous scrubbing solution is in the range of 1:1 to 1:1.5.
In accordance with the embodiments of the present disclosure, the carbonyl washer column is maintained at a temperature in the range of 25 oC to 40 oC, and at a pressure in the range of 4 kg/cm2g to 8 kg/cm2g.
In accordance with the embodiments of the present disclosure, the C4 hydrocarbon stream from the carbonyl washer column comprises the reduced carbonyl impurities in the range of 0 to 10 ppm.
In accordance with the embodiments of the present disclosure, the mixed C4 hydrocarbon stream comprises impurities selected from para-tertiary butyl catechol (p-TBC) and soluble iron species, to provide the C4 hydrocarbon stream devoid of any colour and has reduced or no carbonyl impurities.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Fig. 1 illustrates an apparatus for the collection of mixed C4 stream, wherein (a) illustrates a stainless steel (SS) bomb, (b) illustrates a vessel containing aqueous scrubbing solution, and (c) illustrates a connector, in accordance with the present disclosure; and
Fig. 2 illustrates the testing results to observe the effect of condensate water from plant on a scrubbing solution and impurities components, wherein (a) illustrates a colorless solution when condensate water is mixed with para t-butyl catechol (p-TBC); (b) illustrates a colorless solution when condensate water is mixed with p-TBC solution and sodium bisulfite (SBS) solution; and (c) illustrates a dark red colour when condensate water is mixed with p-TBC solution and sodium hydroxide solution, the dark red colour matched with the plant observed colour in accordance with the present disclosure.
DETAILED DESCRIPTION
The present disclosure relates to a process for removal of carbonyl impurities from a mixed C4 hydrocarbon stream.
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, known processes or well-known apparatus or structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure are not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
Butadiene is an important industrial chemical, which is used in the manufacturing of synthetic rubber, latex paints, nylon, and the like. Butadiene is also a commonly used chemical in the Diels-Alder condensation for the synthesis of many diverse compounds. Butadiene is generally recovered from a mixture of C4 hydrocarbon streams obtained from naphtha or gas steam crackers. During recovery of the butadiene, small amounts of carbonyl-containing impurities (e.g., acetaldehyde, and acetone) are observed. These impurities have adverse effects on subsequent processes in which the butadiene is used as a raw material. So, it becomes important to remove these carbonyl impurities from the mixture of C4 hydrocarbon streams.
Conventionally, the organic carbonyl-containing compounds are removed from mixed C4 hydrocarbon stream with a "scrubbing solution” such as aqueous hydrazine wash. For this purpose, a carbonyl washer column is used in a butadiene (BD) plant to remove the carbonyl impurities. However, the aqueous hydrazine wash does not effectively remove all the carbonyl impurities present in the mixed C4 hydrocarbon stream and fails to meet the desired specification of less than 10 ppm of aldehyde in the mixed C4 hydrocarbon stream.
Further, mixed C4 hydrocarbon stream contains carbonyl impurities such as acetaldehyde, acetone, and other carbonyl compounds that can efficiently be removed by treating with alkali metal bisulfite. However, direct addition of the alkali metal bisulfite to the column may lead to corrosion due to acidic nature.
The composition of mixed C4 hydrocarbon stream varies with the process of plant operation i.e., from a gas cracker, a naphtha cracker, or a gas-naphtha dual cracker. The gas cracker product stream has a lesser percentage of C4 hydrocarbons as compared to the naphtha cracker product. So, the naphtha cracker product stream is preferably used for the butadiene production, which has high amount of C4 hydrocarbons in addition to compounds such as ethylene, propylene, and other hydrocarbon. Further, depending on the process optimization, a mix of the naphtha cracker product stream and the gas cracker product stream can be processed for producing the mixed C4 hydrocarbon streams.
The product stream from the gas cracker has high amount of carbonyl feed (> 350 ppm). Further, the product stream from the gas cracker is when mixed with the product stream of the gas-naphtha dual cracker, the mixed C4 hydrocarbon stream so obtained can have carbonyl content of more than 500 ppm. In such cases, the carbonyl removal efficiency from the mixed C4 hydrocarbon stream in the washer column does not meet the product specifications. The carbonyl impurities of <10 ppm in the product C4 hydrocarbon stream is desired for butadiene processes.
Furthermore, an increase in the amount of carbonyl impurities in the mixed C4 hydrocarbon stream conventionally increases the consumption of a fresh condensate in the carbonyl washer column. Further, increased consumption of the fresh condensate corrodes the processing units.
The present disclosure relates to a process for the removal of carbonyl impurities from a mixed C4 hydrocarbon stream.
The process comprising mixing the mixed C4 hydrocarbon stream comprising the carbonyl impurities, and a predetermined amount of an aqueous scrubbing solution having a pH in the range of 6.5 to 7.0 in a carbonyl washer column maintained at a predetermined temperature and at a predetermined pressure to obtain an aqueous phase comprising the carbonyl impurities in the form of water-soluble reaction products and an organic phase comprising C4 hydrocarbon stream having reduced or no carbonyl impurities.
In accordance with the embodiments of the present disclosure, the mixed C4 hydrocarbon stream is obtained from at least one of a naphtha cracking process, a gas stream cracking process and a gas-naphtha dual cracking process.
In accordance with the embodiments of the present disclosure, the process is a batch process or a continuous process.
In accordance with the embodiments of the present disclosure, the carbonyl impurities comprise acetaldehyde and acetone.
In accordance with the embodiments of the present disclosure, the aqueous scrubbing solution is prepared by using at least one selected from distilled water and condensate water. In an exemplary embodiment, the aqueous scrubbing solution is prepared by using distilled water. In another exemplary embodiment, the aqueous scrubbing solution is prepared by using condensate water.
In accordance with the embodiments of the present disclosure, the so obtained aqueous phase and the organic phase are colorless.
In accordance with the embodiments of the present disclosure, the amount of the carbonyl impurities in the mixed C4 hydrocarbon stream is in the range of 50 ppm to 700 ppm. In another embodiment, the amount of the carbonyl impurities in the mixed C4 hydrocarbon stream is in the range of 50 ppm to 550 ppm. In an exemplary embodiment, the amount of the carbonyl impurities in the mixed C4 hydrocarbon stream is 86 ppm. In another exemplary embodiment, the amount of the carbonyl impurities in the mixed C4 hydrocarbon stream is 104 ppm. In still another exemplary embodiment, the amount of the carbonyl impurities in the mixed C4 hydrocarbon stream is 115 ppm. In yet another embodiment, the amount of the carbonyl impurities in the mixed C4 hydrocarbon stream is 312 ppm. In yet another exemplary embodiment, the amount of the carbonyl impurities in the mixed C4 hydrocarbon stream is 600 ppm.
In accordance with the embodiments of the present disclosure, the aqueous scrubbing solution has a pH in the range of 6.7 to 6.8. In an exemplary embodiment, the aqueous scrubbing solution has a pH of 6.75.
In accordance with the embodiments of the present disclosure, the aqueous scrubbing solution comprises 1 mass% to 5 mass% of an alkali metal salt solution. In an exemplary embodiment, the aqueous scrubbing solution comprises 3 mass% of the alkali metal salt solution.
In accordance with the embodiments of the present disclosure, the alkali metal salt is at least one selected from the group consisting of sodium bisulfite, potassium bisulfite, sodium hydroxide, and potassium hydroxide. In an exemplary embodiment, the alkali metal salt is a combination of sodium bisulfite and sodium hydroxide.
In accordance with the embodiments of the present disclosure, the mixed C4 hydrocarbon is fed to the carbonyl washer column at a feed rate in the range of 15 tons /hour to 20 tons/hour. In an exemplary embodiment, the mixed C4 hydrocarbon is fed to the carbonyl washer column at the feed rate of 16 tons/hour.
In accordance with the embodiments of the present disclosure, the aqueous scrubbing solution is fed to the carbonyl washer column at a feed rate in the range of 150 kg/hour to 300 kg/hour. In accordance with another embodiment of the present disclosure, the aqueous scrubbing solution is fed to the carbonyl washer column at a feed rate in the range of 160 kg/hour to 250 kg/hour. In accordance with an exemplary embodiment, the aqueous scrubbing solution is fed to the carbonyl washer column at the feed rate of 250 kg/hour.
In accordance with the embodiments of the present disclosure, a stoichiometric ratio of the carbonyl impurities to the aqueous scrubbing solution is in the range of 1:1 to 1:1.5. In an exemplary embodiment, in the batch process, the stoichiometric ratio of the carbonyl impurities to the aqueous scrubbing solution is 1:1.1.
In accordance with the embodiments of the present disclosure, the carbonyl washer column is maintained at a temperature in the range of 25 oC to 40 oC, and at a pressure is in the range of 4 kg/cm2g to 8 kg/cm2g. In an exemplary embodiment, the temperature at the top of the column is 29 oC and at the bottom of the column is 29 oC. In the exemplary embodiment, the pressure at the top of the column is 5.6 kg/cm2g, and the pressure at the bottom of the column is 6.7 kg/cm2g.
In the batch operation, the time period of mixing the mixed C4 hydrocarbon stream and the aqueous scrubbing solution is in the range of 5 minutes to 30 minutes. In an exemplary embodiment, the time period of mixing of the mixed C4 hydrocarbon stream and the aqueous scrubbing solution is 20 minutes in a batch operation.
In the continuous flow operation, the mixed C4 hydrocarbon stream and the aqueous scrubbing solution combine and flow from the top to the bottom of the column, the time period of mixing of the mixed C4 hydrocarbon stream and the aqueous scrubbing solution is not more than 60 seconds.
In an embodiment, the time of mixing of the mixed C4 hydrocarbon stream and the aqueous scrubbing solution is in the range of 1 second to 60 seconds. In an exemplary embodiment, the time of mixing of the mixed C4 hydrocarbon stream and the aqueous scrubbing solution is 5 seconds. The reaction of the carbonyl compounds with the aqueous scrubbing solution involves an initial attack on the carbonyl carbon by the nucleophilic addition of bisulfite ion.
In accordance with the embodiments of the present disclosure, the C4 hydrocarbon stream from the carbonyl washer column has reduced carbonyl impurities in the range of 0 to 10 ppm. In an exemplary embodiment, the C4 hydrocarbon stream from the carbonyl washer column has no carbonyl impurities. In another exemplary embodiment, the C4 hydrocarbon stream from the carbonyl washer column has reduced carbonyl impurities of <5 ppm. In still another exemplary embodiment, the C4 hydrocarbon stream from the carbonyl washer column has reduced carbonyl impurities of 2 ppm. In yet another exemplary embodiment, the C4 hydrocarbon stream from the carbonyl washer column has reduced carbonyl impurities of 1 ppm. In still another exemplary embodiment, the C4 hydrocarbon stream from the carbonyl washer column has reduced carbonyl impurities of 3 ppm. In yet another exemplary embodiment, the C4 hydrocarbon stream from the carbonyl washer column has no carbonyl impurities.
In accordance with the embodiments of the present disclosure, the mixed C4 hydrocarbon stream comprises impurities from para-tertiary butyl catechol (p-TBC) and soluble iron species, to provide C4 hydrocarbon stream that is devoid of any colour and having reduced or no carbonyl impurities.
The para-tertiary butyl catechol (p-TBC) and soluble iron species are introduced during the process through the process equipment or are added to carry out the related processes.
The optimal feed rates of the aqueous scrubbing solution and the mixed C4 hydrocarbon stream, and the pH of their mixture during reaction efficiently removes the carbonyl impurities of the mixed C4 hydrocarbon stream even in the presence of soluble iron species and p-TBC to give a colorless hydrocarbon stream and colorless aqueous stream.
The process in accordance with the present disclosure is a commercially doable process for the removal of carbonyl impurities from mixed C4 hydrocarbon stream generated during naphtha/gas steam cracking.
The process in accordance with the present disclosure, removes carbonyl impurities from mixed C4 hydrocarbon entering the carbonyl washer column in butadiene (BD) dual cracker plant by treatment with the aqueous scrubbing solution.
The process of the present disclosure reduces the consumption of the fresh condensate that is used in the conventional processes for preparing the scrubbing solution. The process of the present disclosure also reduces the effluent load on the effluent treatment plant (ETP).
The present invention provides a cost effective and commercially feasible process comprises contacting the mixed C4 hydrocarbon stream (e.g., butadiene) with an aqueous scrubbing solution.
The process of the present disclosure is an environment-friendly process of removal of carbonyl impurities. The process of the present disclosure minimizes the loss of butadiene polymerization catalyst activity due to the absence of carbonyl impurities in the mixed C4 hydrocarbon stream. The mixed C4 hydrocarbon stream is a feed for butadiene polymerization process. The process of the present disclosure reduces the process challenges, while obtaining a quality butadiene product. Further, the process of the present disclosure impacts the effluent treatment as the effluent is free from coloration. The cost-benefit per annum is approximately Rs. 1.5 Crore.
The process of the present disclosure can be easily scaled up.
The developed process of the present disclosure can be commercialized at the carbonyl washer column, and can work efficiently for more than 365 days.
The process of the present disclosure reduces fresh condensate consumption and improves carbonyl washer efficiency.
The process of the present disclosure addresses the issue of coloration of condensate water from dark red to a faint colour, which could be due to the presence of para-tertiary butyl catechol (p-TBC) or soluble iron species in the mix C4 hydrocarbon stream. The mixed C4 hydrocarbon also contain p-TBC, which act as a stabilizer and polymerization inhibitor to butadiene, and other reactive monomer present in the streams.
p-TBC is a weak acid and dissociates in a basic medium and associates in acid medium (reversible upon pH adjustment). p-TBC is an anti-oxidant widely used in the industry and potent depigmenting agent. Dissociated form of p-TBC is highly soluble in water, while the associated form is not soluble. p-TBC can react with iron (Fe3+) in basic condition and formed red coloured complex. Generally, FeCl3 gives a green coloration with aqueous solution, while the alkaline solution rapidly changes to a green and finally to a black colour on exposure to the air. The association-dissociation of p-TBC is represented as:

Sodium bisulfite (SBS) can effectively be used for removal of carbonyl impurities by chemical treatment method from C4 column feed in carbonyl washer column. The concentration of sodium bisulfite requirement is based on the concentration of carbonyls present in the feed. However, to drive the equilibrium in favour of the desired reaction, the bisulfite needs to be in the stoichiometric amount or slightly more.
The reaction of carbonyl compounds specially aldehydes and ketones with sodium bisulfite proceeds in the aqueous solution which involves initial attack on the carbonyl carbon by the nucleophilic addition of bisulfite ion. SBS is an acidic salt formed by neutralization of strong acid and a weak base. It easily dissociates in water to form acidic solution. The bisulfite-carbonyl adduct is a non-volatile, thermally stable, and highly water-soluble material. The dissociation of bisulfite and its nucleophilic addition on the carbonyl group is illustrated as:

The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further illustrated herein below with the help of the following experiments. The experiments used herein are intended merely to facilitate an understanding of the ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the experiments should not be construed as limiting the scope of embodiments herein. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.

EXPERIMENTAL DETAILS:
Experiment 1: Process for removal of carbonyl impurities from a mixed C4 hydrocarbon stream (in lab scale) in accordance with the present disclosure
Samples of mixed C4 hydrocarbon streams and condensate water were collected from a plant for three consecutive days. The mixed C4 hydrocarbon stream was collected in a stainless steel (SS) vessel (bomb) as shown in Fig. 1.
An analysis for the determination of the carbonyl (aldehyde) content in the mixed C4 hydrocarbon streams and pH of the condensate water was performed and the results is tabulated in Table 1.
Table 1: Analysis of total aldehydes in the mixed C4 hydrocarbon samples and the condensate water pH at different days of test
Day 1 Day 2 Day 3
Total carbonyls (ppm) 92 Total carbonyls (ppm) 108 Total carbonyls (ppm) 118
Condensate water pH 9.1 Condensate water pH 8.7 Condensate water pH 9.3

It can be observed from Table 1 that the carbonyl content in the mixed C4 hydrocarbon streams was in the range of 92 ppm to 118 ppm. The condensate water was basic in nature, with pH in the range of 8.7 to 9.3 due to the presence of dissolved hydrazine-type compounds.
Initially, preliminary lab experiments were performed to find a source of plant observed colour from the carbonyl washer column. Separate solutions each for NaOH, sodium bisulfite, p-TBC, and iron species (FeCl3) were prepared. A colourless solution was observed by mixing condensate water and p-TBC (refer Fig. 2(a)). Another colourless solution was observed when condensate water, p-TBC solution and SBS solution were mixed (refer Fig. 2(b)). However, a dark red colour was observed when the condensate water, p-TBC solution and NaOH solution were mixed together (refer Fig. 2(c)). The dark red colour was very much matching with a plant observed colour.
In another set of experiments, the plant observed colour of the carbonyl washer discharge was slightly different than the colour of the solution obtained by mixing iron to a solution of NaOH and p-TBC. However, the plant observed colour was exactly matching with a solution obtained by mixing a solution of iron species (FeCl3) and SBS with the solution of NaOH and p-TBC.
The carbonyl removal efficiency in the conventional process was also observed to decline with time and pH, and finally, the SBS dosing in the plant was required to be stopped. It was observed that the dark red colour was due the presence of NaOH and Fe ions with para-Tert-Butyl Catechol (p-TBC) in the reaction mixture. The presence of iron impurities in plant carbonyl washer outlet was confirmed by Inductively Coupled Plasma (ICP) analysis and the SBS was detected by X-ray diffraction (XRD) analysis. This was confirmed by the observation that, in the absence of base (NaOH), the solution of all reacting mixtures did not give any colour.
The collected mixed C4 hydrocarbon stream comprising carbonyl impurities mainly acetaldehyde and acetone in the range of 92 ppm to 118 ppm were treated with reducing agent such as sodium bisulfite (SBS) in an aqueous medium, or pH adjusted sodium bisulfite with NaOH solution at an ambient condition to remove the carbonyl impurities. The gas samples from a scrubber outlet were collected for the carbonyl analysis. The carbonyl content of the mixed C4 hydrocarbon stream was analysed in LowPX GC at QC-HMD by using the ASTM D7423 method.
Example 1- Removal of the carbonyl impurities by excess SBS at an acidic pH
Carbonyl removal from mixed C4 hydrocarbon was carried out by scrubbing the fixed amount (~25 g) of mixed C4 hydrocarbon gas from a commercial plant into the SBS solution. 200 g of 3 wt% SBS prepared in distilled water (DI) was taken into the scrubber. The pH of the SBS solution was 4.1. The mixed C4 hydrocarbon contained a total carbonyl impurity of 86 ppm. After passing 25 g of mixed C4 hydrocarbon samples, the pH of the aqueous phase was 4.4. The carbonyls in the outlet C4 hydrocarbon sample (organic phase) after the reaction were 1 ppm.
Example 2- Removal of the carbonyl impurities by excess SBS at a neutral pH
Carbonyl removal from mixed C4 hydrocarbon was carried out by scrubbing the fixed amount (~25 g) of mixed C4 hydrocarbon gas into a SBS solution. 200 g of 3 wt.% SBS prepared in DI water was taken into the scrubber. The pH of the SBS solution was adjusted to 7 by addition of NaOH solution. The mixed C4 hydrocarbon contained a total carbonyl impurity of 86 ppm. After passing 25 g of mixed C4 hydrocarbon samples, the pH of the aqueous phase was 6.9. The carbonyls in the outlet of the C4 hydrocarbon sample (organic phase) after the reaction were 2 ppm.
Example 3- Removal of the carbonyl impurities by excess SBS at a basic pH
Carbonyl removal from mixed C4 hydrocarbon was carried out by scrubbing the fixed amount (~25 g) of mixed C4 hydrocarbon gas into a SBS solution. 200 g of 3 wt.% SBS prepared in distilled (DI) water was taken into the scrubber. The pH of the SBS solution was adjusted at 9 by addition of NaOH solution. The mixed C4 hydrocarbon contained a total carbonyl impurity of 86 ppm. After passing 25 g of mixed C4 hydrocarbon samples, the pH of the aqueous phase was 9. The carbonyls in the outlet C4 hydrocarbon sample (organic phase) after the reaction were 2 ppm.
Example 4- Removal of the carbonyl impurities by excess SBS at an acidic pH
Carbonyl removal from mixed C4 hydrocarbon was carried out by scrubbing the fixed amount (~25 g) of the mixed C4 hydrocarbon gas into a SBS solution. 200 g of 3 wt.% SBS prepared in condensate water was taken into the scrubber. The pH of the SBS solution was 5.3. The mixed C4 hydrocarbon contained a total carbonyl impurity of 104 ppm. After passing 25 g of the mixed C4 hydrocarbon samples, the pH of the aqueous phase was 5. The carbonyls in the outlet C4 hydrocarbon sample (organic phase) after the reaction were 6 ppm.
Example 5- Removal of the carbonyl impurities by excess SBS at a neutral pH
Carbonyl removal from mixed C4 hydrocarbon was carried out by scrubbing the fixed amount (~25 g) of the mixed C4 hydrocarbon gas into a SBS solution. 200 g of 3 wt.% SBS prepared in condensate water was taken into the scrubber. The pH of the SBS solution was 7.1 adjusted by addition of NaOH solution. The mixed C4 hydrocarbon contained a total carbonyl impurity of 104 ppm. After passing 25 g of the mixed C4 hydrocarbon samples, the pH of the aqueous phase was 7.1. The carbonyls in the outlet C4 hydrocarbon sample (organic phase) after the reaction were 3 ppm.
Example 6- Removal of the carbonyl impurities by excess SBS at a basic pH
Carbonyl removal from mixed C4 hydrocarbon was carried out by scrubbing the fixed amount (~25 g) of the mixed C4 hydrocarbon gas into the SBS solution. 200 g of 3 wt.% SBS prepared in condensate water was taken into the scrubber. The pH of the SBS solution was adjusted to 9.1 by addition of NaOH solution. The mixed C4 hydrocarbon contained a total carbonyl impurity of 104 ppm. After passing 25 g of mixed C4 hydrocarbon samples, the pH of the aqueous phase was 9.1. The carbonyls in the outlet C4 hydrocarbon sample (organic phase) after the reaction were 2 ppm.
Example 7- Removal of the carbonyl impurities by stoichiometric SBS at near neutral pH
Carbonyl removal from mixed C4 hydrocarbon was carried out by scrubbing the fixed amount (~75 g) of the mixed C4 hydrocarbon gas into the SBS solution. Stoichiometric amount of SBS (0.009 g) with respect to 75 g mixed C4 hydrocarbon having 100 ppm carbonyls was taken in 200 g condensate water. The pH of the SBS solution was 6.5. The mixed C4 hydrocarbon contained a total carbonyl impurity of 115 ppm. After passing 75 g of mixed C4 hydrocarbon samples, the pH of the aqueous phase was 7.1. The carbonyls in the outlet mixed C4 hydrocarbon sample (organic phase) after the reaction were 4 ppm.
Example 7A- Removal of the carbonyl impurities by stoichiometric SBS at a basic pH
Carbonyl removal from mixed C4 hydrocarbon stream was carried out by scrubbing the fixed amount (~75 g) of mixed C4 hydrocarbon gas into the SBS solution. Stoichiometric amount of SBS (0.009 g) with respect to 75 g mixed C4 hydrocarbon having 100 ppm carbonyls was taken in 200 g condensate water. The pH of the SBS solution was adjusted to 7.1 by addition of NaOH solution. The mixed C4 hydrocarbons contain total carbonyls of 115 ppm. After passing 75 g of mixed C4 hydrocarbon samples, the pH of the aqueous phase was 8.1. The carbonyls in the outlet mixed C4 hydrocarbon sample (organic phase) after the reaction were 7 ppm.
Example 8- Removal of the carbonyl impurities by stoichiometric SBS at a basic pH
Carbonyl removal from mixed C4 hydrocarbon stream was carried out by scrubbing the fixed amount (~75 g) of mixed C4 hydrocarbon gas into the SBS solution. Stoichiometric amount of SBS (0.009 g) with respect to 75 g mixed C4 hydrocarbon having 100 ppm carbonyls was taken in 200 g condensate water. The pH of the SBS solution was adjusted to 8.1 by adding NaOH solution. The mixed C4 hydrocarbon contains total carbonyls of 115 ppm. After passing 75 g of mixed C4 hydrocarbon C4 samples, the pH of the aqueous phase was 8.6. The carbonyls in the outlet mixed C4 hydrocarbon sample (organic phase) after the reaction were 14 ppm.

Example 9- Removal of the carbonyl impurities by stoichiometric SBS at a basic pH
Carbonyl removal from mixed C4 hydrocarbon was carried out by scrubbing the fixed amount (~25 g) of mixed C4 hydrocarbon gas into the SBS solution. Stoichiometric amount of SBS (0.009 g) with respect to 25 g mixed C4 hydrocarbon having 100 ppm carbonyls was taken in 200 g condensate. The pH of the SBS solution was adjusted to 10.9 by adding NaOH solution. The mixed C4 hydrocarbon contained total carbonyls of 115 ppm. After passing 25 g of mixed C4 hydrocarbon samples, the pH of the aqueous phase was 11. The carbonyls in the outlet mixed C4 hydrocarbon sample (organic phase) after the reaction were 15 ppm.
Table 2: Removal of carbonyls from the mixed C4 hydrocarbon stream by applying various scrubbing solution from different water streams
Example no Composition Before Reaction After Reaction
H2O SBS
(3 wt.%) NaOH
(3 wt.%) Mixed C4 hydrocarbon (g) Colour of mixed C4 hydrocarbon pH of the
SBS solution Carbonyl in mixed C4 hydrocarbon (ppm) Colour of aqueous /organic phase pH of
aqueous phase (SBS solution) Carbonyl in organic phase (ppm)
1 DI H2O 200 g - ~25 g Colourless 4.1 86 Colourless 4.4 1
2 DI H2O 200 g As required ~25 g Colourless 7.0 86 Colourless 6.9 2
3 DI H2O 200 g As required ~25 g Colourless 9.0 86 Colourless 9.0 2
4 Condensate water 200 g - ~25 g Light yellowish 5.3 104 Colourless 5.0 6
5 Condensate water 200 g As required ~25 g Light yellowish 7.1 104 Light yellowish 7.1 3
6 Condensate water 200 g As required ~25 g Colourless 9.1 104 Colourless 9.1 2
7 Condensate water (200 g) ~0.009 g - ~75 g Colourless 6.5 115 Colourless 7.1 4
7A Condensate water (200 g) ~0.009 g As required ~75 g Colourless 7.1 115 Colourless 8.1 7
8 Condensate water (200 g) ~0.009 g As required ~75 g Colourless 8.1 115 Colourless 8.6 14
9 Condensate water (200 g) ~0.009 g As required ~25 g Colourless 10.9 115 Colourless 11.0 15
*DI - Distilled water
As observed from Table 2, the carbonyl removal efficiency was found to be very significant in each case, although some of the solutions had neutral or basic pH before the reaction. The neutral or basic SBS solutions were prepared by adding NaOH. With stoichiometric amount of SBS addition and maintaining near to neutral pH (Example 7, 7A), and effective removal of aldehyde impurities was achieved. When similar study was done under basic condition pH above 8 the aldehyde removal efficiency was comparatively less (example 8).
Example 10
Another lab trial was performed when the amount of the aldehyde impurity in the mixed C4 hydrocarbon stream was 600 ppm. Further, the efficiency of the process was tested in the presence of other impurities such as p-TBC and iron. The iron impurity may be introduced in the carbonyl column because of the leaching from carbon-steel alloy. The details and results of this lab trial are given in the Table 3.
Table 3: Lab trial
Composition Total volume Colour Final
pH
H2O SBS (3 wt%) NaOH (3 wt%) TBC (1000 ppm) FeCl3 (200 ppm) Mixed C4 hydrocarbon with aldehyde content of 600 ppm Extra H2O
25 ml 5 ml 5 ml 5 ml 5 ml 5 ml 0 ml 50 ml Colorless 7.1

It was observed that a colourless aqueous phase was obtained with a pH of 7.1 when the mixed C4 hydrocarbon stream was treated with 5 ml of 3 wt% of SBS solution at a pH of 6.5 in the presence of other impurities such as iron and p-TBC. The amount of aldehyde impurities in the product stream of mixed C4 hydrocarbon was 8.
At lab scale, a little excess of SBS than the stoichiometric amount was beneficial to keep the reaction in a forward direction for effective removal of carbonyls. Carbonyl: SBS = 1:1.1 ratio was maintained.
For the lab analysis, the mixed C4 hydrocarbon was mixed with the aqueous scrubbing solution (SBS solution) for 10, 15 and 20 minutes, better results were observed with 20 minutes of the mixed C4 hydrocarbon flown in the SBS solution.
Planned and established set-up demonstrated an efficient process for removal of carbonyl impurities from mixed C4 hydrocarbon stream through chemical route.
Experiment 2: Commercial Process Operation data for Carbonyl Impurity Removal
Table 4 illustrates a composition of mixed C4 hydrocarbon stream to the carbonyl washer column collected from a naphtha cracker plant indicating the presence of 312 ppm of carbonyl impurities.
Table 4: An example of feed composition of the mixed C4 hydrocarbon stream to the carbonyl washer column
Feed composition Value Unit
C3s and lighter compounds 0.04 wt.%
Isobutane 1.16 wt.%
Propadiene <0.01 wt.%
n-butane 5.8 wt.%
t-2-butene 4.78 wt.%
Butene-1 14.85 wt.%
Iso butylene 17.61 wt.%
Cis-2-butadiene 3.35 wt.%
1,2 butadiene 0.19 wt.%
Methyl acetylene 0.01 wt.%
1,3 BD 51.03 wt.%
Vinyl acetylene 0.93 wt.%
Ethyl acetylene 0.16 wt.%
Iso-pentane 0.01 wt.%
n-pentane <0.01 wt.%
C5 plus unknowns 0.01 wt.%
Retarder 23 wt. ppm
Acetonitrile <5 wt. ppm
Dimer 145 wt. ppm
Carbonyls 312 wt. ppm
Unknown 0.03 wt.%

The plant and the process operation conditions of the mixed C4 hydrocarbon entering the carbonyl washer column in the naphtha cracker plant is as given in Table 5.
Table 5: Operation conditions of C4 carbonyl washer column
Feed flow 16.5±0.5 tons/hour
Carbonyl content in the mixed C4 hydrocarbon 80 to 312 ppm
Column Top Temperature 28.7 oC
Column Bottom Temperature 28.6 oC
Column Top pressure 5.6 kg/cm2 g
Column Bottom pressure 6.7 kg/cm2 g
SBS concentration 3.5 %
SBS flow 125±5 kg/hour
Time of contacting the mixed C4 hydrocarbon and SBS solution 5 seconds

Examples 11-15
In a commercial operation of the C4 carbonyl washer column at a commercial plant, the C4 feed entering carbonyl washer column at 16.5±0.5 tons/ hour (TPH). The sodium bisulfite solution was adjusted to desired pH by addition of an alkali solution (3 wt% NaOH).
The pH adjusted SBS solution was added to the C4 carbonyl washer column at different dosing rates. The carbonyl impurities removal results are summarized in Table 6.
Table 6: Effect of SBS addition rate on carbonyl impurities removal in the C4 carbonyl washer column in the plant
Example no. SBS dosing rate (kg/hour) Inlet pH of the SBS solution Outlet aldehyde (ppm) Aldehyde removal efficiency (%) Outlet pH
of the SBS containing aqueous stream Colour of treated
outlet stream
11 45±5 7 >20 80 9.8 Dark red
12 125±5 7 >10 85 9 Dark red
13 170±10 7 < 10 90 7 Light coloration
14 170±10 6.7-6.8 < 5 >98 7 No colour
15 250 6.7-6.8 Nil > 98 7 No colour

Observations:
During trial of example 11, pH of the carbonyl washer bottom was observed 9.8/9.9, which was surprisingly high as compared to SBS dosing solution having pH ~7. Fe content (soluble iron) was reported to be 4 ppm to 4.1 ppm and the carbonyl washer bottom solution was deep red colour.
Higher SBS dosing rate (125±5 kg/hour) in the carbonyl washer column showed better result in terms of carbonyl removal. The carbonyl removal efficiency increased from 80% to greater than 98%, when pH of the inlet SBS solution was 6.7 to 6.8. As the rate of addition of scrubbing solution was increased, the pH of the outlet stream changed from basic to neutral. The outlet stream of the treated mixed C4 hydrocarbon stream was also observed to have dark red coloration when the pH of the outlet stream was basic. At the optimized pH 7 condition, when there was an increase in the SBS dosing rate to 170±10 kg/hour, there was 90% efficiency and less than 10 ppm aldehyde was present in the outlet stream of the treated stream. Further, the issue of coloration was also addressed from dark red to faint colour with the optimal pH of the scrubbing solution and the optimal feed rate of the scrubbing solution. Furthermore, upon adjusting the pH to 6.7-6.8 and keeping the SBS dosing rate at 170±10 kg/hour, the carbonyl removal efficiency of greater than 98% was achieved and the outlet feed contained < 5ppm of carbonyl impurities.
When the SBS dosing rate was increased to 250 kg/hr and the pH was 6.7 – 6.8, the throughput of the C4 carbonyl washer column was further increased and there were no aldehyde impurities observed in the outlet treated mixed C4 hydrocarbon sample.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of: the process for removal of carbonyl impurities from a mixed C4 hydrocarbon stream that:
• is simple, economical, and environment friendly;
• is efficient in the removal of higher amounts of carbonyl impurities;
• can be easily scaled up for commercial purpose;
• reduces the effluent load on effluent treatment plant (ETP);
• reduces fresh condensate consumption and improves carbonyl washer efficiency;
• addresses the issue of coloration of the outlet stream (organic phase) and aqueous phase; and
• can run for longer time period.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation. , C , Claims:WE CLAIM:
1. A process for removal of carbonyl impurities from a mixed C4 hydrocarbon stream, said process comprising mixing
• said mixed C4 hydrocarbon stream comprising said carbonyl impurities, and
• a predetermined amount of an aqueous scrubbing solution having a pH in the range of 6.5 to 7.0,
in a carbonyl washer column maintained at a predetermined temperature and at a predetermined pressure to obtain an aqueous phase comprising said carbonyl impurities in the form of water-soluble reaction products and an organic phase comprising a C4 hydrocarbon stream having reduced carbonyl impurities.
2. The process as claimed in claim 1, wherein said carbonyl impurities comprise acetaldehyde and acetone.
3. The process as claimed in claim 1, wherein said mixed C4 hydrocarbon stream is obtained from at least one of a naphtha cracking process, a gas stream cracking process and a gas-naphtha dual cracking process.
4. The process as claimed in claim 1, wherein said aqueous scrubbing solution is prepared by using at least one selected from distilled water and condensate water.
5. The process as claimed in claim 1, wherein said aqueous phase and said organic phase are colorless.
6. The process as claimed in claim 1, wherein said aqueous scrubbing solution has a pH in the range of 6.7 to 6.8.
7. The process as claimed in claim 1, wherein said aqueous scrubbing solution comprises 1 mass% to 5 mass% of an alkali metal salt solution.
8. The process as claimed in claim 7, wherein said alkali metal salt is at least one selected from the group consisting of sodium bisulfite, potassium bisulfite, sodium hydroxide, and potassium hydroxide.
9. The process as claimed in claim 1, wherein the carbonyl impurities in said mixed C4 hydrocarbon stream is in the range of 50 ppm to 700 ppm.
10. The process as claimed in claim 1, wherein said mixed C4 hydrocarbon stream is fed to said carbonyl washer column at a feed rate in the range of 15 tons/hour to 20 tons/hour.
11. The process as claimed in claim 1, wherein said aqueous scrubbing solution is fed to said carbonyl washer column at a feed rate in the range of 150 kg/hour to 300 kg/hour.
12. The process as claimed in claim 1, wherein said aqueous scrubbing solution is fed to said carbonyl washer column at a feed rate in the range of 160 kg/hour to 250 kg/hour.
13. The process as claimed in claim 1, wherein a stoichiometric ratio of said carbonyl impurities to said aqueous scrubbing solution is in the range of 1:1 to 1:1.5.
14. The process as claimed in claim 1, wherein said carbonyl washer column is maintained at a temperature in the range of 25 o C to 40 o C, and at a pressure in the range of 4 kg/cm2 g to 8 kg/cm2 g.
15. The process as claimed in claim 1, wherein said C4 hydrocarbon stream from said carbonyl washer column comprises the reduced carbonyl impurities in the range of 0 to 10 ppm.
16. The process as claimed in claim 1, wherein said mixed C4 hydrocarbon stream comprises impurities selected from para-tertiary butyl catechol (p-TBC) and soluble iron species.
17. The process as claimed in claim 16, wherein said process provides C4 hydrocarbon stream devoid of any colour and has reduced or no carbonyl impurities.

Dated this 21st day of February, 2024

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
OF R.K.DEWAN & CO.
AUTHORIZED AGENT OF APPLICANT

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI