An integrated hydrotreating and steam pyrolysis process for the direct processing of a crude oil to produce olefinic and aromatic petrochemicals, the process comprising: a. separating the crude oil at a cut point in the range of from 150°C to 260°C into light components and heavy components; b. charging the heavy components and hydrogen to a hydroprocessing zone operating under conditions effective to produce a hydroprocessed effluent having a reduced content of contaminants, an increased paraffinicity, reduced Bureau of Mines Correlation Index, and an increased American Petroleum Institute gravity; c. charging the hydroprocessed effluent and steam to a convection section of a steam pyrolysis zone; d. heating the mixture from step (c) and passing it to a vapor-liquid separation section for separating into a light fraction and a heavy fraction with a vapor-liquid separation device based on physical and mechanical separation, the vapor-liquid separation section includes a pre-rotational element for conversion of the linear velocity of the incoming mixture into a rotational velocity, the pre-rotational element comprising an entry portion and a transition portion, the entry portion having an inlet for receiving the flowing fluid mixture and a curvilinear conduit, a controlled cyclonic section having an inlet adjoined to the pre-rotational element through convergence of the curvilinear conduit and the cyclonic section and a riser section at an upper end of the cyclonic member through which the light fraction passes; and a liquid collector/settling section through which the heavy fraction passes; e. charging light components from step (a), the light fraction from the vapor-liquid separation section, and steam to a pyrolysis section of the same steam pyrolysis zone for thermal cracking; f. recovering a mixed product stream from the steam pyrolysis zone; g. separating the thermally cracked mixed product stream; h. purifying hydrogen recovered in step (g) and recycling it to step (b); i. recovering olefins and aromatics from the separated mixed product stream; and j. recovering pyrolysis fuel oil from the separated mixed product stream. a. separating the crude oil at a cut point in the range of from 150°C to 260°C into light components and heavy components; b. charging the heavy components and hydrogen to a hydroprocessing zone operating under conditions effective to produce a hydroprocessed effluent having a reduced content of contaminants, an increased paraffinicity, reduced Bureau of Mines Correlation Index, and an increased American Petroleum Institute gravity; c. charging the hydroprocessed effluent and steam to a convection section of a steam pyrolysis zone; d. heating the mixture from step (c) and passing it to a vapor-liquid separation section for separating into a light fraction and a heavy fraction with a vapor-liquid separation device based on physical and mechanical separation, the vapor-liquid separation section includes a pre-rotational element for conversion of the linear velocity of the incoming mixture into a rotational velocity, the pre-rotational element comprising an entry portion and a transition portion, the entry portion having an inlet for receiving the flowing fluid mixture and a curvilinear conduit, a controlled cyclonic section having an inlet adjoined to the pre-rotational element through convergence of the curvilinear conduit and the cyclonic section and a riser section at an upper end of the cyclonic member through which the light fraction passes; and a liquid collector/settling section through which the heavy fraction passes; a pre-rotational element for conversion of the linear velocity of the incoming mixture into a rotational velocity, the pre-rotational element comprising an entry portion and a transition portion, the entry portion having an inlet for receiving the flowing fluid mixture and a curvilinear conduit, a controlled cyclonic section having an inlet adjoined to the pre-rotational element through convergence of the curvilinear conduit and the cyclonic section and a riser section at an upper end of the cyclonic member through which the light fraction passes; and a liquid collector/settling section through which the heavy fraction passes; e. charging light components from step (a), the light fraction from the vapor-liquid separation section, and steam to a pyrolysis section of the same steam pyrolysis zone for thermal cracking; f. recovering a mixed product stream from the steam pyrolysis zone; g. separating the thermally cracked mixed product stream; h. purifying hydrogen recovered in step (g) and recycling it to step (b); i. recovering olefins and aromatics from the separated mixed product stream; and j. recovering pyrolysis fuel oil from the separated mixed product stream.