RU2152975C1 - Thermal decomposition of naphthenic acids - Google Patents

Abstract

FIELD: petroleum processing. SUBSTANCE: total acid number of crude oil is lowered when crude oil is heated at 204 C at pressure from 0.1 to 100 atm while simultaneously removing water vapors inhibiting total acid number lowering by blowing crude oil with gas at flow velocity from 0.178 to 356 cu. m/cu.m. EFFECT: facilitated crude oil neutralization. 19 cl, 1 dwg, 4 tbl, 4 ex

Description

 This application is a partial continuation of the application US 564202, registered October 20, 1995, which is a partial continuation of the application US 390729, registered February 17, 1995.

 The invention relates to the decomposition of naphthenic acids present in crude oil. In particular, the present invention relates to a thermal, non-catalytic treatment for the decomposition of these naphthenic acids.

 The presence of relatively large amounts of petroleum acids, for example naphthenic acids, in crude oil or its fractions is a big problem for refineries, and more recently for gas generating equipment. Essentially, these acids, which are present to a greater or lesser extent in virtually any crude oil, are corrosive, contribute to equipment failure, increase operating costs, shorten its operating cycle compared to conventional, degrade product quality and cause problems related to the environment.

A large number of publications, both patents and scientific articles, discuss the removal of naphthenic acid by conversion or absorption. For example, many water-based materials can be added to crude oil or crude fractions to convert naphthenic acids to some other substance, such as salts, which can be removed or be less corrosive. Other methods for the removal of naphthenic acids are also known, including absorption, for example, on zeolites. In addition, one of the generally accepted solutions to the problems of naphthenic acids is the use of materials based on expensive alloys in oil refining or gas generating equipment for processing raw materials with relatively high concentrations of naphthenic acids. Another common option is to mix crude oils with high total acid numbers (OKC) with crude oil having low OKC values, but the latter is significantly more expensive than the former. US Pat. No. 1953,353 discloses the decomposition of naphthenic acids contained in devoid of light fractions of crude oil or distillates, carried out at atmospheric pressure and at temperatures from 316 ^° C (600 ^° F) to 399 ^° C (750 ^° F). However, only CO _{2 is} considered as the only gaseous non-hydrocarbon decomposition product of naphthenic acids, and the reaction is not provided for in a continuous stream of inert gas to prevent the formation of reaction inhibitors.

 However, there remains a need to remove or at least substantially reduce the concentration of petroleum acids in crude oil or its fractions, carried out at low cost and preserve refining equipment, in particular in crude oil or its fractions with a total acid number (OKC) above about 2 mg KOH / g in accordance with ASTM D-664.

 In accordance with the present invention, the concentration of naphthenic acids in a feed containing such acids can be substantially reduced or at least reduced to a level at which the feed can be heat treated in flat carbon steel tanks to decompose these acids. Therefore, OKC can be markedly reduced. In the context of the present invention, heat treatment, in addition to its usual meaning, also means the absence of any catalyst to accelerate the conversion of naphthenic acids, the absence of any substance added for reaction or complexation with naphthenic acids, and the absence of naphthenic acid absorbents, t. e. the absence of any substance used to remove naphthenic acids.

The heat treatment is reduced to heating the feed to a temperature of at least about 204 ^° C (400 ^° F), preferably at least 316 ^° C (600 ^° F) for a period of time sufficient to substantially reduce the TAN in the feed, while at the same time removal of natural or degraded inhibitors. Inhibitors are primarily water vapor, the effect of which is enhanced by the presence of CO ₂ and / or CO.

The heat treatment process, of course, depends on time and temperature, provided that the temperature threshold level is reached. Thus, it is also possible to use higher temperatures with a corresponding reduction in processing time at these higher temperatures. However, given the nature of the processed raw materials, premature cracking of the bulk of hydrocarbons should be excluded or minimized, for example, less than about 0.5 wt. % gaseous hydrocarbons, preferably less than 0.2 wt. % gaseous hydrocarbons based on raw materials. The gases obtained from the decomposition of naphthenic acids are primarily water vapor, CO ₂ and CO. Other gases that can occur at very low cracking levels include light gaseous hydrocarbons, such as C ₁ -C ₄ alkyl or isoalkyls, as well as small amounts of hydrogen.

 The removal of water vapor and gaseous products can be accomplished by purging the feed with an inert gas stream, as well as by purging with natural gas, other gaseous hydrocarbons or other suitable gas, as well as by creating reduced pressure (evacuation), and the removal of water vapor, in addition, by absorption of water vapor absorbers or the interaction of water vapor with dehydrating agents.

 The proposed method preferably reduces OCC to levels less than about 1.5 mg KOH / g of oil, more preferably less than 1 mg KOH / g of oil, even more preferably less than 0.5 mg KOH / g of oil as measured by ASTM D- 664

 The drawing shows a decrease in OKC depending on water for example 4.

Raw materials that can be effectively processed by the proposed method of heat treatment include raw materials containing naphthenic acids, for example, non-benzene oil or crude fractions. The crude fractions that can be processed are stripped oils (since light distillate with a boiling point of 204 ^o C contains little naphthenic acids), atmospheric oil distillates and vacuum gas oils, for example gas oils with boiling ranges of 343-566 ^o C (650- 1050 ^o C). Preferably, the feedstock includes unbranched and topped oil and vacuum gas oils, in particular unbranched and topped oil.

The feed can be processed at a pressure greater than, equal to or less than atmospheric, for example in the range from 0.01 to 10 MPa (0.1 to 100 atmospheres), preferably less than 1.5 MPa (15 atmospheres), more preferably 0.1-1 MPa (1-10 atmospheres) and preferably in an inert atmosphere, such as nitrogen or other non-oxidizing gases. Since heat treatment leads to acid decomposition, measures should be taken to remove gaseous decomposition products, i.e. water vapor, CO ₂ and CO, as well as products of minimal cracking. It is especially necessary to constantly remove the water vapor obtained by the decomposition of acids or supplied with raw materials in order to minimize the inhibition of the process of acid decomposition. Any light fractions or light hydrocarbon cracking products can be isolated by condensation and, if necessary, reconnected with the processed feed. In practice, reaction chambers with ventilation equipment can be used to conduct the heat treatment process. In a preferred embodiment, CO ₂ and CO are also blown away. The gas used for purging may be natural gas or other gaseous hydrocarbons commonly found in refineries or gas generating units. Gas purge rates are in the range 0.1781 - 356.2 m ³ / m ^{3 of} feed (1-2000 standard cubic feet per barrel of feed). Preferably, the gaseous products are removed from the reaction zone so that the partial pressure of CO + CO _{2 is} below 0.0035 MPa (0.5 psi) and the partial pressure of H ₂ O is below about 1.4 kPa (0.2 psi abs.)

Since processing depends on time and temperature, a preferred temperature range is 316-482 ^° C (600-900 ^° F), more preferably 371-427 ^° C (700-800 ^° F). The processing time (holding time at temperature) can vary over a wide range and is inversely proportional to temperature, for example from 30 seconds to 10 hours, preferably 1-90 minutes, more preferably 30-90 minutes. Of course, at any given temperature, longer processing times will usually lead to lower OKC values, and care must be taken not to exceed the cracking levels indicated above.

 As mentioned, reaction chambers can be used to carry out the process both periodically and continuously. Specialists in this field will easily imagine tubular reactors for the implementation of the process.

 The invention is further illustrated by way of non-limiting examples.

EXAMPLE 1
All experiments (unless specifically noted) were performed in an open reactor, including distillation equipment similar to that described in ASTM D-2892 or ASTM D-5236. About 300 grams of a sample of the crude oil fraction boiling above 343 ^° C (650 ^° F) was placed in a distillation flask. (Unbended oil was not used, despite its easy availability, to avoid physical loss of the sample fraction boiling below 343 ^o C (650 ^o F)). The sample was quickly heated to the desired temperature and kept at this temperature for up to six hours in an inert atmosphere, for example, nitrogen. Stirring was carried out either by bubbling nitrogen through the sample, or, preferably, using a rod of a magnetic stirrer. Aliquots were taken periodically to measure OKC.

In a series of experiments, a fraction of African crude oil (Bolobo), boiling above 343 ^o C (650 ^o F), was subjected to six-hour aging in the reaction zone at temperatures ranging from 204 ^o C to 343 ^o C (400 to 650 ^o F) followed by cooling to room temperature overnight. These experiments were carried out at atmospheric pressure in a nitrogen atmosphere. Temperature heating was carried out in a certain sequence: the first hour at 204 ^o C (400 ^o F), the second hour at 232 ^o C (450 ^o F), the third hour at 260 ^o C (500 ^o F), the fourth hour at 288 ^o C ( 550 ^o F), the fifth hour at 316 ^o C (600 ^o F), the sixth hour at 343 ^o C (650 ^o F). The sample was cooled to room temperature and left overnight until an aliquot was taken. The content of naphthenic acids was monitored by measuring OKC at the beginning of the experiment and at the end of each day. The results are presented in table 1.

 The value of OKC decreases almost linearly during these experiments.

EXAMPLE 2
In a series of experiments, the decomposition of naphthenic acids by heat treatment was carried out in open and closed reactors. In an open reactor, the produced gas could slowly exit, while in a closed reactor, the resulting gases were held. The decrease in OKC and the yield of gas obtained were determined, the results are shown in table 2.

The closed reactor consisted of tubular cylinders (25 g of oil in a 65 cm ³ reactor) or miniballs (5 g of oil in a 12 cm ³ reactor).

 The results showed that in closed systems a decrease in OCC is not achieved, and this leads to the conclusion that an increase in gas pressure prevents the decomposition of acids. A direct comparison of the open and closed systems in experiments 4 and 5 showed a more than 50% increase in the decrease in TCC for an open system compared to a closed system.

EXAMPLE 3
In another series of experiments, the decomposition of naphthenic acids by heat treatment was carried out in an autoclave to demonstrate the benefits of removing gaseous products from the reaction zone. In experiment 1, the resulting gases were constantly removed using helium supplied at a rate of 227.1 m ³ / m ³ (1275 cubic feet / barrel), while in experiment 2, gaseous products were retained, so that the maximum pressure increased to 0.803 MPa (100 psi ² h.). OCC was determined, the results are presented in table 3.

 The results confirm that the removal of gases from the reaction zone leads to a noticeable improvement in the reduction of OCC by 82% with respect to the initial value of OCC 5.3. On the contrary, in the absence of gas removal, a decrease in TCC by only 45.5% was achieved.

EXAMPLE 4
In the next series of experiments in an autoclave, the effect of inhibiting the reaction with water vapor in the presence or absence of CO ₂ and / or CO with respect to a decrease in TAN during heat treatment was studied. The results are presented in table 4. In each experiment, the estimated partial pressure of water vapor (H ₂ O, kPa) obtained from the conversion of OKC was less than 1.41 (as can be seen from the data for the added water).

In experiment 1, without the addition of water vapor and in the presence of carbon oxides, obtained only upon decomposition of naphthenic acids, for this series of experiments, the greatest decrease in OKC was obtained by 86.2%. In experiments 2, 3 and 4, the addition of increasing amounts of water vapor to the purge gas led to an ever smaller decrease in TOC compared to the base experiment. In runs 5, 6, and 7, close amounts of water were added along with CO ₂ , CO, and CO ₂ + CO, respectively. All three experiments showed lower levels of reduction in OCC compared with experiment 2.

These effects are clearly visible in FIG. 1, which shows the decrease in OKC in% depending on the added amount of H ₂ O in g / min in accordance with the data in table 4.

Claims (19)

1. A method of reducing the total acid number (OKC) of a raw material in the form of unbased crude oil or crude fractions, comprising heat treating the raw material in a treatment zone at a temperature of at least about 204 ^{° C.} (400 ^° F.) and a pressure of from 0.1 to 100 atmospheres characterized in that the treatment is carried out for a time sufficient to substantially reduce the OKC, while at the same time during the heat treatment they remove water vapor that inhibit the decrease in the OKC by blowing the raw material with gas at the gas velocity used for purging, in shaft from 0.1781 to 356 m ³ / m ³ (1 to 2,000 standard cu. ft per barrel of feedstock). 2. The method according to claim 1, characterized in that the gaseous reaction products formed in the specified method - water, CO and CO ₂ - are simultaneously removed from the treatment zone. 3. A method according to claim 2, characterized in that said gaseous reaction products are removed such that the partial pressure of CO + CO ₂ amounts to less than 3.5 kPa (0.5 pound / inch ² absolute) and the partial pressure of water vapor is less than 1.4 kPa (0.2 lb / in ² abs).  4. The method according to claim 2, characterized in that additionally light hydrocarbons are removed from the treatment zone.  5. The method according to claim 2, characterized in that essentially all gaseous reaction products are removed from the treatment zone.  6. The method according to claim 1, characterized in that the feed is a dehydrated crude oil.  7. The method according to claim 2, characterized in that the raw material has an OKC in excess of 2 mg KOH / g of raw material.  8. The method according to claim 7, characterized in that the heat-treated raw material has an OCC less than about 1.5 mg KOH / g of raw material. 9. The method according to claim 7, characterized in that the heat treatment is carried out at a temperature of at least 316 ^o C (600 ^o F). 10. The method according to claim 7, characterized in that the temperature range of the heat treatment is approximately 316 - 482 ^o C (600 - 900 ^o F).  11. The method according to p. 9, characterized in that the processing time is in the range from about 1 minute to about 10 hours  12. The method according to claim 9, characterized in that the heat-treated raw material has an OCC less than about 1.0 mg KOH / g of raw material.  13. The method according to claim 9, characterized in that the feed is unbroken crude oil.  14. The method according to claim 9, characterized in that the raw material is stripped crude oil.  15. The method according to claim 9, characterized in that the feedstock is atmospheric oil distillation fuel oil. 16. The method according to claim 9, characterized in that the feed is a vacuum gas oil with boiling ranges of 343 - 566 ^o C (650 - 1050 ^o F).  17. The method according to claim 9, characterized in that, depending on the feed, the gas phase contains less than 0.5 wt.% Of the obtained gaseous hydrocarbon products.  18. The method according to claim 9, characterized in that the treatment is carried out at a pressure of about 1 to 10 atm. 19. The method according to claim 4, characterized in that the light hydrocarbons are C ₁ - C ₄ hydrocarbons.

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