FIELD OF THE INVENTION:

The present invention relates to the technical field of crude oil distillation. Specifically, the present invention relates to the technical field of vacuum distillation of crude oils. More specifically, the present invention relates to the anti-cracking additive composition and use thereof in reducing the cracking in a reduced crude oil vacuum heater.

BACKGROUND OF THE INVENTION:

Reduced crude oil (RCO) from atmospheric distillation tower bottom is heated up in a vacuum heater to around 390-410 °C before it is introduced into the vacuum distillation column. During the heating process, RCO is prone to cracking which can lead to issues such as generation of high hot well off gases (HWOG) and thus creating poor vacuum. The poor vacuum reduces distillate yield and leads to high SR yield & poor bitumen quality.

In a vacuum heater, cracking is majorly influenced by sulphur species present in the RCO. These sulphur species lead to H2S generation, and in turn leading to high hot well off gases. Many a times, refinery HWOG analysis shows H2S content above the acceptable amine absorber inlet limit (10 vol%). In addition, the free radicals formed during cracking can further induce chain reactions increasing lighter components. This results in lower vacuum (-740 mm Hg to -720 mm Hg) resulting in slippage of vacuum gas oil (VGO) into SR, and thus affecting bitumen quality.

To mitigate these issues, furnace coil output temperature (COT) is sometimes lowered by a couple of degrees or a turbulizing steam is adjusted which affects plant performance. Further, prior solutions also include addition of additive compositions to enhance distillate yield.

CN102071047A discloses a residual oil modifier for a coking delaying device and use thereof. The residual oil modifier has high practicality for raw material residual oil and can effectively improve the properties of residual oil, delay coking, effectively reduce coking amount and consequently improve the yield of middle-grade distillate. The said modifier is prepared from 1 to 25 percent of antioxygen, 1 to 20 percent of oxidation and corrosion inhibitor, 1 to 25 percent of metal deactivator, 1 to 20 percent of dispersant and the balance of solvent, and by heating, uniformly stirring and cooling.

CN102888241A discloses an aid for improving the yield of liquid oil in an oil delayed coking device and a preparation method for the aid. The aid is prepared from N,N-bis(salicylidene) propylenediamine, p-tert-butylcatechol, tetrapentaerythritol ester, octylphenol polyoxyethylene (30) ether, N,N-di-n-butyl ammonia methylbenzotriazole and a solvent. The aid is directly added into raw material residual oil, so that a phenomenon that a coking device is coked when heating a furnace pipe and the on-stream period is prolonged can be avoided, the generation amount of coke and dry gas is reduced, and the liquid oil yield is improved.

CN101899327A discloses an anti-coking agent for high-temperature equipment and preparation and application thereof. The anti-coking agent is synthesized, by the conventional method, from the following components by weight ratio: 55%-95% of polyalkenyl succinimide esters, 3%-25% of antioxidants and 2%-20% of metal deactivators, wherein an organic solvent accounts for 50% of the total materials by weight; the antioxidant is particularly one or more of 2,6-di-tert-phenol, alkyldiphenylamine, N,N'-di-sec-butyl-p-phenylenediamine, p,p'-di-iso-octyldiphenylamine, N- phenyl-alpha naphthylamine and pentaerythrite tetra[beta(3,5-di-tert-butyl-4- hydroxyphenyl)propionate] ; the metal deactivator is particularly one or more of N,N'- disalicylidene propanediamine, triazole derivatives and thiadiazole derivatives; the organic solvent is particularly aromatic solvent, diesel or solvent oil; and the polyalkenyl succinimide esters are prepared from polyalkenyl succinimide, aldehydes and polyesters. The anti-coking agent of the invention has the advantages of good anti-coking effect, high thermostability, wide applicable temperature range and corrosion resistance.

However, as earlier stated that the cracking is majorly influenced by sulphur species present in the RCO which leads to H2S generation, and in turn leading to high hot well off gases. Accordingly, it is also important to effectively reduce the H2S generation so that effective vacuum can be maintained in the vacuum heater. Accordingly, there is a need for a solution which when applied in a vacuum heater can reduce cracking/improve vacuum, increase distillate yields and quality, mitigate corrosion and also contribute in reducing amine consumption in amine absorber for HWOG.

SUMMARY OF THE PRESENT INVENTION:

The present invention provides an anti-cracking additive composition, wherein, the additive composition includes a H2S scavenger, an antioxidant, and a solvent. Wherein, the H2S scavenger is selected from carboxylates of Fe, carboxylates of Ni, carboxylates of Co, carboxylates of Zn or a combination thereof. The antioxidant is selected from di-tert-butyl phenols, di-tert-butyl cresols, hydroquinone, pyrogallol, propylgallate, butylated hydroxylanisole or a combination thereof. The solvent is selected from an aromatic solvent.

Wherein, the H2S scavenger is carboxylates of Zn such as but not limited to Zinc Oleate. The antioxidant is di-tert-butyl cresols such as but not limited to 2,6-Di-tert-butyl-p-cresol. The solvent is an aromatic solvent selected from xylene, toluene, superior kerosene oil (SKO), light diesel oil (LDO), naphtha or a combination thereof.

Specifically, in the said anti-cracking additive composition, the Zinc Oleate is 2-4 % by weight, 2,6-Di-tert-butyl-p-cresol is 50-70% by weight, and the aromatic solvent is 30-50% by weight. The weight percent is based on the total weight of the additive composition

The present invention also provides a method for preparation of the said anti-cracking additive composition, wherein, the method includes mixing the Zinc Oleate and 2,6-Di-tert-butyl-p-cresol in a solvent. The solvent is an aromatic solvent selected from xylene, toluene, superior kerosene oil (SKO), light diesel oil (LDO), naphtha or a combination thereof. Specifically, 2-4 % by weight of the Zinc Oleate, and 50-70% by weight of 2,6-Di-tert-butyl-p-cresol are mixed in 30-50% by weight of the said aromatic solvent.

Further, the present invention also provides a process for mitigating cracking of the reduced crude oil in a vacuum heater, wherein, the process comprises adding the said anti-cracking additive composition along with reduced crude oil into the vacuum heater. Wherein, the said anti-cracking additive composition is added in a dosage range of 5 to 500 ppm. OBJECTIVES OF THE PRESENT INVENTION:

It is the primary objective of the present invention to mitigate the cracking in a Reduced Crude Oil (RCO) vacuum heater and thus to improve the vacuum during vacuum distillation of RCO.

It is the main objective of the present invention to provide an anti-cracking additive composition which dosed along with RCO to mitigate the cracking.

It is further objective of the present invention to maintain the vacuum in the vacuum heater and to increase the distillate yield.

It is further objective of the present invention to lower the cracking of sulphur compounds and to reduce the H2S production.

It is further objective of the present invention to significantly decrease the production of hot well off gases (HWOG) in a Reduced Crude Oil (RCO) vacuum heater.

DESCRIPTION OF THE INVENTION:

For better understanding of the present invention, cracking of RCO is explained hereinafter. The cracking of RCO is a three-stage process including primary cracking, secondary cracking, and condensation of products of cracking. Primary Cracking is unavoidable as this is due to the cleavage of weakest bonds (carbon and hetero atoms) in the least volatile fraction. This will trim the heavier molecules of their non-core heterogeneous parts resulting in decrease of the heaviest fraction. However, as the core of these heavy molecules is intact, the asphaltenes content does not reduce or even increases fraction wise. This also contributes to higher boiling (SIMDIS) profile of the SR. However, the middle and lighter fractions are not affected much during this step. But their volume percentage increases due to generation of similar molecules from the cracking of heavier fraction.

Further, the secondary cracking is dominant of the two cracking processes, as the secondary cracking is not only driven by higher heats of enthalpy, but also acidic sulphur moieties generated in situ during the primary process. This would aggravate the cracking of core part of the heavier molecules, and thus leads to the formation of gases or highly volatile distillates. Accordingly, it is necessary to control this step, by the formation of the middle distillates and limiting the formation of gases/ highly volatile distillates.

Accordingly, the present disclosure provides a novel anti-cracking additive composition which when dosed along with RCO, will reduce cracking, and improve vacuum. Thus, this increases distillate yields and quality, mitigate corrosion, and also contribute to reducing amine consumption in amine absorber for HWOG.

The additive composition as disclosed herein is specifically developed to target and to control the secondary cracking step. The said additive composition leads to the formation of the middle distillates and limits the formation of gases or highly volatile distillates.

Accordingly, the present invention provides an anti-cracking additive composition, wherein, the additive composition includes an H2S scavenger, an antioxidant, and a solvent. Wherein, the H2S scavenger is selected from carboxylates of Fe, carboxylates of Ni, carboxylates of Co, carboxylates of Zn or a combination thereof. The antioxidant is selected from di-tert-butyl phenols, di-tert-butyl cresols, hydroquinone, pyrogallol, propylgallate, butylated hydroxylanisole or a combination thereof. The solvent is selected from an aromatic solvent.

Wherein, the H2S scavenger is carboxylates of Zn such as but not limited to Zinc Oleate. The antioxidant is di-tert-butyl cresols such as but not limited to 2,6-Di-tert-butyl-p-cresol. The solvent is the aromatic solvent selected from xylene, toluene, superior kerosene oil (SKO), light diesel oil (LDO), naphtha or a combination thereof. Further, in an exemplary embodiment, the solvent is xylene.

Further, the present invention provides a method for preparation of the said anti-cracking additive composition, wherein, the method includes mixing an H2S scavenger, an antioxidant, and a solvent. Wherein, the H2S scavenger is selected from carboxylates of Fe, carboxylates of Ni, carboxylates of Co, carboxylates of Zn or a combination thereof. The antioxidant is selected from di-tert-butyl phenols, di-tert-butyl cresols, hydroquinone, pyrogallol, propylgallate, butylated hydroxylanisole or a combination thereof. The solvent is selected from an aromatic solvent.

Wherein, the H2S scavenger is carboxylates of Zn such as but not limited to Zinc Oleate. The antioxidant is di-tert-butyl cresols such as but not limited to 2,6-Di-tert-butyl-p-cresol. The solvent is aromatic solvent selected from xylene, toluene, superior kerosene oil (SKO), light diesel oil (LDO), naphtha or a combination thereof. Further, in an exemplary embodiment, the solvent is xylene.

Specifically, 2-4 % by weight of the Zinc Oleate, and 50-70% by weight of 2,6-Di-tert-butyl-p- cresol are mixed in 30-50% by weight of the said solvent and wherein the solvent is xylene.

Specifically, the present invention provides an anti-cracking additive composition containing (i) 2-4 % by weight Zinc Oleate (ii) 50-70% by weight 2,6-Di-tert-butyl-p-cresol (iii) 30-50% by weight Xylene. The weight percent is based on the total weight of the additive composition. The said anti-cracking additive composition acts as an anti-cracking additive to mitigate cracking in a reduced crude oil vacuum heater and improve vacuum during vacuum distillation operations.

Experimental Methodology:

The cracking experiments were conducted in a Mini Pot Still equipment using Reduced Crude oils of high sulphur crudes. The cracking experiments were conducted using the following protocol:

1. RCO was allowed to crack by heating to a temperature of 400 °C, at atmospheric pressure (as the experiments were carried out at atmospheric pressure) for 1-2 minutes, till head temperature drop is observed.

2. The cracked RCO was distilled under a vacuum of 1 torr till 450 deg °C and 0.2 torr thereafter till 540 °C.

3. The above steps were repeated with adding the said additive at a dosage of 300 ppm. Further, the parameters which were considered as indicative of the chemical performance include density, H2S, bromine number, asphaltene content, Sulphur speciation, mercaptans, and distillation profile. The results of the experiments are provided below in Table 1.

Table 1: Performance evaluation of the additive

Further, the below table 2 provides outcome of mass balance of distillation of RCO cracked with said anti-cracking additive composition (RCO+ ACA- 1 ) and RCO cracked without said anticracking additive composition.

Table 2: Mass balance of distillation as for H2S and for the anti-cracking additive composition.

Table 3: Hot well oil analysis results The technical outcome of the cracking experiments as conducted, and the results as provided hereinabove is discussed hereinafter.

It is observed from the above experiments that the density of hot well oil has decreased after adding the additive. This indicates presence of lighter components in the hot well oil which would have otherwise got cracked and ended up in off-gases. Accordingly, when the RCO is dosed with the said anti-cracking additive composition there is significant decrease in hot well off gases (HWOG) and thus the vacuum in the vacuum heater does not get effected which results in higher distillate yield.

Further, the Bromine number of the condensable(s) collected during distillation shows a significant decrease which is a direct indication of reduction in olefins.

From the asphaltenes analysis, it can be concluded that cracking has reduced as the asphaltenes weight % in 540+ cut has increased with additive.

Further, the Sulphur speciation results indicate increase in Polyalkyl BT and polyalkyl DBT/NBT which further indicates reduced cracking of sulphur compounds.

Further, the Mercaptans in the condensable(s) are higher with additive as compared to the one collected without additive. This indicates that mercaptans have not cracked to H2S when the RCO is dosed with the said anti-cracking additive composition.

From the distillation data it can be inferred that the lower boiling range components have decreased in the condensable(s) when the RCO is dosed with the said anti-cracking additive composition, thus, indicating that cracking has been inhibited.

From the mass balance it is observed that yield of 540+ has decreased during the distillation carried out with RCO dosed and cracked with the said anti-cracking additive composition. Further, H2S detected during the cracking experiments without the additive was around 8 ppm. With the additive, H2S detected was in the range of 2 ppm. This indicates that cracking of Sulphur compound has decreased to a significant extent. Accordingly, the present invention also provides a process for mitigating secondary cracking of the reduced crude oil in a vacuum heater, wherein, the process comprises adding the said anticracking additive along with reduced crude oil into the vacuum heater.

Accordingly, it is concluded that the anti-cracking additive composition as disclosed herein mitigates cracking in Reduced Crude Oil (RCO) vacuum heater and improves vacuum during vacuum distillation of RCO. Further, the said additive composition shows excellent cracking mitigation properties through a synergistic effect of the individual components.