Patent Application
20200224130
The present invention relates to processes for cleaning installation subjected to fouling by red oils deposits, such as basic wash units, caustic towers of steam crackers and all downstream units dealing with spent caustic. The invention relates to a curative process to be used in complement to known preventive processes that are directed to the inhibition or to the reduction of fouling deposits by red oils.
In cracking operations, such as the pyrolytic steam cracking of ethane, propane, and naphthas to form olefins, oxygenated compounds including carbonyl compounds, such as aldehydes and ketones, are formed. When the gas stream is passed through a basic wash (with pH>7) to remove acidic components such as hydrogen sulfides and carbon dioxide, oxygen-containing compounds such as acetaldehyde will undergo under polycondensation in presence of the basic wash or scrubbing conditions. The polymers formed are also called “red oils” due to their colour. The caustics towers are sometimes treated with additives to reduce the fouling. As aldehydes are not completely converted in the caustic tower, reactions are ongoing in spent caustic. This is why all downstream units and storages dealing with spent caustic are also prone to fouling.
An example of a preventive method for inhibiting fouling systems in caustic scrubber systems is disclosed in U.S. Pat. No. 5,194,143. The method disclosed consists in adding an effective amount for the purpose of an acetoacetate ester compound to the caustic wash system.
Another example of a preventive method is given by WO2011/138305 and relates to a method for reducing the formation of fouling deposits occurring in a caustic scrubber used to remove acid gases. The method disclosed uses a solvent such as a hydrocarbon aromatics selected from benzene, toluene and xylenes, introduced in the caustic scrubber and/or in the alkaline solution fed to the scrubber.
The acetaldehyde dissolved in spent caustic remains reactive and red oils formation in downstream units goes on. This induces severe fouling of the downstream installation. Spent caustic storage can contain high quantities of polymers, for instance a thickness of 50 cm of polymers is not a surprise. These deposits are gummy and sticking. The installation must be shut down for cleaning which is a costly operation. In addition, the time spent can be long so that the installation can be non-available for more than 10 days.
Red oils deposits can be removed manually, but this method is of low acceptance because of risks for health and safety in the workplace for the operators (i.e. HSE risks). High-pressure cleaning shows low efficiency due to the gummy and sticking properties of the red oils deposits. The use of additives has also been suggested, but they have a partial efficiency as there are used in emulsion, they generate waste hard to treat.
Thus there is still a need to find methods to clean the red oils deposits formed in installations such as basic wash units and downstream equipment.
Thus an object of the invention is to provide a cleaning process to remove red oils deposits formed in installations such as basic wash units and downstream equipment. It is also an object of the invention to provide a cleaning process that is simple to implement, that shows low HSE risks, that is cost efficient, that is time efficient and/or that generates waste simply to treat.
According to a first aspect, the invention provides a process for removing red oils deposits formed in an installation comprising:
It has been found by the inventors that surprisingly the fatty acid esters, and especially the fatty acid methyl esters have a great affinity for red oils. The fatty acid esters can be used to dissolve or reduce red oils viscosity creating a mixture that can be removed by a simple pump. The use of such a cleaning agent is particularly interesting as it does not require the operators to be exposed to harmful chemical substances and therefore does not increase the HSE risks. It allows the cleaning of the installation to be performed in one or less than one day in some cases, reducing the time wherein the installation is not available for maintenance reasons or partially stopped. Moreover, the waste generated (i.e. the mixture comprising the cleaning agent and the dissolved red oils) only contains hydrocarbons and can, therefore, be easily disposed of, for example by burning.
In an embodiment, the process comprises a step a) of washing the installation to remove a soda excess that is performed before the step b) of addition of the cleaning agent. With preference, in step a), washing is performed with water.
With preference, one or more of the following features can be used to further define the inventive process:
In an embodiment, the dissolution of the red oils deposit in the cleaning agent during step c) is monitored by measuring the density and/or the viscosity of the mixture and the step c) is ended when:
In another embodiment, the dissolution of the red oils deposit in the cleaning agent during step c) is monitored by attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy and the step c) is ended when the addition of fresh cleaning agent in the installation provides no further increase results in ATR-FTIR analysis, or by comparison of the Fourier transform of the interferogram of the mixture to the Fourier transform of the interferogram of a reference sample.
According to a second aspect, the invention relates to the use of one or more fatty acid esters as cleaning agent in a process for removing red oils deposit from an installation, wherein the use comprises dissolving the red oils deposit in the fatty acid esters.
The process is the process according to the first aspect, thus preferably the one or more fatty acid esters are selected from fatty acid methyl esters, fatty acid ethyl esters and any mixture thereof. More preferably the one or more fatty acid esters are selected from one or more fatty acid methyl esters.
In a preferred embodiment, the one or more fatty acid esters are selected to have:
In an embodiment, the one or more fatty acid esters are a biodiesel.
In an embodiment, the use comprises:
For the purpose of the invention the following definitions are given:
“Red oils” is a term that describes an organic contaminant frequently encountered in caustic towers. The “red oils” are formed from an organic polymer that forms from the aldol condensation of acetaldehyde in sodium hydroxide solution. Initially, the acetaldehyde forms a light floating yellow oil that continues to polymerize into a more familiar orangish/red colour—hence the term “red oil”. These red oils form more sticky heavy oils that are difficult to separate. This causes fouling and plugging issues in the caustic tower and downstream spent caustic handling systems.
Fatty acid esters are a type of ester that results from the combination of a fatty acid with an alcohol. When the alcohol component is glycerol, the fatty acid esters produced can be monoglycerides, diglycerides, or triglycerides.
Biodiesels are typically fatty acid esters produced by the transesterification of vegetable fats and oils which results in the replacement of the glycerol component with a different alcohol.
Fatty Acid Methyl Esters (FAME) are esters of fatty acids. The physical characteristics of fatty acid esters are closer to those of fossil diesel fuels than pure vegetable oils, but properties depend on the type of vegetable oil. A mixture of different fatty acid methyl esters is commonly referred to as biodiesel, which is a renewable alternative fuel. FAME has physical properties similar to those of conventional diesel. It is also non-toxic and biodegradable.
The process of the invention is a process for removing red oils deposits formed in a basic wash unit and/or in its downstream equipment. According to the invention, preferably the basic wash unit is using caustic soda and is selected from a caustic tower, a caustic scrubber, a caustic wash downstream an amine gas scrubber, wherein the basic wash unit preferably includes all related equipment selected from pumps, piping and settlers; and preferably the downstream equipment of a basic wash unit is selected from a spent caustic settler, a spent caustic washer, a spent caustic mixer, a spent caustic storage, a spent caustic oxidizer, a spent caustic neutralizing drum, a spent caustic stripper. This process is a curative process that differs from a preventive process in that the basic wash unit is not or partially not in use during the maintenance operation.
The process comprises the following steps:
The inventive process uses a cleaning agent comprising a solvent to dissolve the red oils wherein said solvent comprises one or more fatty acid esters. Among the solvents that could be used, fatty acid esters have been found to be preferred because of their good affinity with the red oils and also because they are bio-sourced. Moreover, their use does not increase the risk for health and safety in the workplace for the operators during the cleaning. This is of importance because the basic wash units may contain caustic soda, sulphides, benzene products, etc. Another advantage of the use of fatty acid esters is that they do not lead to corrosion problems.
In a preferred embodiment of the invention, the process comprises an optional step a) of washing the installation to remove at least partially a soda excess. Step a) is performed before the step b) of addition of the cleaning agent. This step enhances the efficiency of the cleaning process by protecting the one or more fatty acid esters against too much hydrolysis. This washing is preferably performed with water.
In a preferred embodiment of the invention, the process also includes an optional step of determination of the quantity of the red oils deposit to be removed, preferably from the volume and/or of the weight of the red oils deposit to be removed. This step can be performed before the washing step a) or after said washing step a) when a washing step a) is conducted. The determination step is performed by defining the volume of the red oils deposit within the installation. Said volume is determined by measuring or evaluating the thickness of the layer of the red oils deposit. The evaluation can also be done using historical data. This determination does not need to be accurate, and allows to provide an assistance to a first determination of the quantity of fatty acid esters that will be needed to clean the installation in step b). The other criteria to determine the needed quantity of fatty acid esters is to use the minimum volume required to allow a circulation in the installation.
In step b) of the process, the cleaning agent is added and put into contact with the red oils deposit. According to the invention, the cleaning agent is one or more fatty acid esters and is preferably selected from fatty acid methyl esters, fatty acid ethyl esters and any mixture thereof. Preferably, in step b), the one or more fatty acid esters are one or more fatty acid methyl esters (FAME). In a preferred embodiment, the cleaning agent is a biodiesel. Preferably the cleaning agent is used pure, i.e. without being dissolved in water.
In a preferred embodiment of the invention, the one or more fatty acid esters added are selected to have a carbon chain length ranging from 4 to 36 carbon atoms, preferably from 8 to 24 carbon atoms, more preferably from 10 to 22 carbon atoms and even more preferably from 14 to 20 carbon atoms. In a preferred embodiment, the one or more fatty acid esters added have a carbon chain length of 18 carbon atoms. It has been found by the inventors that long-chain fatty acid esters are more efficient than the shortest ones, as the red oils also show long carbon chains.
Fatty acid esters with high flash point have been found to be more efficient to dissolve the red oils. Thus preferably, the one or more fatty acid esters are selected to have a flash point above 50° C., preferably above 80° C., more preferably above 100° C., even more preferably above 120° C., and most preferably above 160° C. The flash point is the lowest temperature at which vapours of the material will ignite when given an ignition source.
The volume or the weight of the one or more fatty acid esters to be added in step b) is to be selected according to the solubility of the red oils deposit within the fatty acid ester. As the process may comprise one or more sequence of steps b) to d), it is also possible to add a fixed volume and/or weight of fatty acid esters to the basic washing unit and to repeat the sequence of steps b) to d) until the red oils deposit has been entirely dissolved and removed by pumping.
In an embodiment of the invention, the content of the one or more fatty acid esters to be added in step b) is at least the content of the red oils deposit to be removed. For instance, if the weight content of red oils deposit to be removed is determined to be about 30 tons, then the weight content of fatty acid esters to be added is 30 tons or more, such as 40 tons for instance. The ratio can be forced by the design of the equipment to be able to ensure recirculation and the number of batches that are planned by the operator. Thus preferably, the one or more fatty acid esters are added to the red oils at a weight ratio in the range of 0.2:1 to 10:1, preferably at a weight ratio fatty acid esters to red oils in the range of 0.2:1 to 10:1, more preferably in the range of 0.5:1 to 5:1, even more preferably of 1:1.
Once the one or more fatty acid esters have been introduced within the installation, they are circulated within the installation in step c) of the process. This circulation of the fatty acid esters can be done by recirculation pumps or by high-pressure injectors and/or gas bubbling. The gas used for gas bubbling includes nitrogen, steam, process gas, etc. The cleaning operation can be performed during installation shutdown or operation. When it is performed during installation operation; the process gas is used to create the bubbling and turbulence of the fatty acid esters. The circulation of the fatty acid esters facilitates the dissolution of the red oils deposit by creating turbulence. Any agitating means can also be used to achieve an agitation of the fatty acid esters in the installation. Turbulence plays a role in cleaning operation, decreasing the time needed to achieve the result.
In an embodiment of the invention, the step c) of circulating the one or more fatty acid esters in the installation is performed at a temperature ranging from 0° C. to 150° C., preferably from 20° C. to 130° C. more preferably from 50° C. to 110° C. For instance the step c) of circulating the fatty acid esters in the installation is performed at 80° C. The installation can be provided with heating means for this purpose.
In an embodiment, step c) of circulating the one or more fatty acid esters in the installation is monitored in order to follow the saturation of the cleaning agent. When the cleaning agent is saturated, the red oils deposit does not dissolve anymore and the mixture is to be removed. If the quantity of cleaning agent was not sufficient to dissolve entirely the red oils deposits, then the steps b) to d) can be performed again. The monitoring of the dissolution of the red oils deposit in the cleaning agent can be performed by different methods.
In an embodiment, the monitoring is performed by monitoring the density of the mixture of the cleaning agent and the dissolved red oils. Indeed, it has been found that during dissolution, the density is increased until a defined level where it becomes constant. According to the invention the step c) of dissolving the red oils in the cleaning agent is ended when monitoring the density of the mixture and the step c) is ended when the density is stabilized showing that there is no further Red Oils dissolution or reached the target density determined by laboratory testing.
In an embodiment, the step c) is ended when the graph displaying the results of the monitoring of the density of the mixture shows an asymptote. In another embodiment, the step c) is ended when the density increase of the mixture is above 0.30 g/cm3 as determined at 30° C. as determined using density meter DMA35N from Antoon Parr.
In another embodiment, the monitoring of the dissolution of the red oils deposit in the cleaning agent during step c) is performed by monitoring the mixture by attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy and the step c) is ended by comparison of the Fourier transform of the interferogram of the mixture to the Fourier transform of the interferogram of a reference sample.
In another embodiment, the monitoring of the dissolution of the red oils deposit in the cleaning agent during step c) is performed by monitoring the viscosity of the mixture and the step c) is ended when the viscosity is stabilized showing that there is no further Red Oils dissolution.
Tests Methods
The flash point is measured according to ISO3679.
The density of the mixture of fatty acid esters and dissolved red oils was determined using density meter DMA35N from Antoon Parr. The DMA 35N portable density meter measures the density of liquids in g/cm3 or kg/cm3 according to the U-tube principle.
The absorbance of the mixture of fatty acid esters and dissolved red oils was determined using ATR-FTIR.
The capability of the FTIR (Fourier Transform Infra Red) is to identify functional groups. FTIR relies on the fact that the most molecules absorb light in the infra-red region of the electromagnetic spectrum. This absorption corresponds specifically to the bonds present in the molecule. The frequency range is measured as wave numbers typically over the range 4000-600 cm-1. Attenuated total reflection (ATR) is a sampling technique used in conjunction with infrared spectroscopy which enables samples to be examined directly in the solid or liquid state without further preparation.
The viscosity of the mixture of fatty acid esters and dissolved red oils was determined using ANTON PAAR's viscosimeter SVM 3000. It is a rational viscometer with a cylinder geometry. It is based on a modified Couette principle.
Different cleaning agents have been tested:
The tests were performed under the following test protocol. The tests were carried out on a block of red oils of 50-70 cm3. The volume of cleaning agent added was 250 mL. The mixture was stirred at moderate magnetic stirring and the reaction temperature was maintained at 80° C. The loss of mass was followed up during the tests. The results have been reported in table 1. The loss of mass percentage is based on the initial mass of the red oils.
CA5 shows very good results but is harmful to the environment. From the results, it can be seen that the kinetics of the reaction cannot be raised by raising the concentration of the cleaning agent. Surprisingly, CA1 shows very good results for dissolution of the red oils.
The mixture of fatty acid methyl esters (FAME) of CA5 with a detergent has been tested diluted in water 10 vol %. Different detergents were tested such as basic detergent and acid detergent. The tests were performed according to the same test protocol as in example 1. The results were not conclusive as no loss of mass was observed.
Tests with a mixture of FAME comprising 60 wt % of methyl ester of rapeseed and 40 wt % of methyl palm ester were performed under the same test protocol except for the temperature that was selected to be 20° C. or 80° C. The mixture was used pure, i.e. not diluted. The results of the tests show an influence of the temperature on the kinetics of the reaction. Indeed, the similar loss of mass was achieved after 24 hours at 20° C. and after 1.5 hours at 80° C.
Tests have been performed to determine the suitable content of FAME (80 wt % of methyl ester of rapeseed; 20 wt % of methyl palm ester) to be added to a predetermined content of red oil. The results have been reported in
The test was performed at an industrial scale on a column of 8 m3 containing about 1 m3 of red oils. 2 m3 of FAME was added, the temperature was 80° C., and the duration of the test was over 14 hours. To follow the evolution of the reaction density measurements were performed. The density has been measured at 70° C. and at 30° C. The results are reported in
FTIR tests have been performed on fatty acid esters and on the mixture of fatty acid esters with dissolved red oils. The results are presented in
Tests have been performed on fatty acid esters and on the mixture of fatty acid esters with dissolved red oils. The viscosity is measured after filtration over 5 μm filter. The results have been reported in table 2.
It can be seen that the dissolution of red oils in the FAME results in an increase in the viscosity. This change of density can be used to assess the success of the cleaning operation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17193049.8 | Sep 2017 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/076029 | 9/25/2018 | WO | 00 |
